Browse Treatment Technologies by:

• Technology Name
• Treated Constituents
• Site Name

All Treatment Technologies, Sorted by Technology Name

• Adsorption To Peanut Shells
  

  Innovative technology using carbonized peanut shells to physically adsorb selenium.

  • Treated Constituent: selenium
  • Scale: Lab-scale
  • Example Site: None Known
  • Operations: Before treatment, peanut shells are treated with strong sulfuric acid to carbonize the shells while partially oxidizing the cellulose and hemicelluloses and fragmenting the lignin. The sulfuric acid treatment results in a carbonaceous material with functional groups for both the sorption and reduction of selenium.
  • Long-term Maintenance: Unknown
  • System Limitations: Sorption was found to be temperature dependent.
  • Costs: This process has only recently been developed and is not well characterized. Peanut shells are readily available at low cost.
  • Effectiveness: Removals as high as 63 percent were observed for 25 mg/L selenide solutions. Selenite sorbed to the material at an optimal pH of 1.5. As pH increased, sorption capacity decreased.
• Algal-Bacterial Selenium Removal
  

  Algal treatment occurs via enhanced cyanobacterial and algal growth through nutrient addition. These additional nutrients increase algal biomass, thereby increasing selenium volatilization rates. In addition to treatment by volatilization, the algal biomass generated also serves as a carbon source to support microbial selenium reduction processes.

  • Treated Constituent: selenium
  • Scale: Pilot-scale
  • Example Site: Panoche Drainage District on the west side of the San Joaquin Valley, California
  • Operations: This system uses a combination of ponds containing algae and bacteria in which selenate is reduced to selenite and elemental selenium.
  • Long-term Maintenance: Unknown
  • System Limitations: Seasonally limited with treatment affected by duration of solar light and ambient temperatures. Difficulty of generating sufficient biomass to promote biological reduction and the inability to treat selenium to regulatory levels. Although much of the total selenium may be removed using the ABSR system, it is essential that the remaining selenium is in a form that is not readily bioavailable to aquatic organisms. In the ABSR system, if the selenium that remains has been transformed into a more bioavailable form, then the system could possibly be increasing the concentrations of selenium absorbed by aquatic life.
  • Costs: Potentially low-cost treatment, but can require large land area as well as the need for separation of the high-rate and reduction ponds. The preliminary total cost estimate for a 10-acre-foot per day ABSR facility is less than $291 (2013 USD) per acre-foot of treated drainage water. The ABSR system is one of the most economical and therefore easily adopted selenium removal systems.
  • Effectiveness: Preliminary results have shown that the method may be able to reduce the total selenium in the drainage water up to 80 percent. During 1997 and 1998, the best-performing ABSR plant configuration reduced nitrate by more than 95 percent and reduced total soluble selenium mass by 80 percent. The results of this studysuggest that the ABSR system may not be successfully reducing the bioavailability of selenium to aquatic organisms. Although microcosm data was limited, results lead to the conclusion that certain steps of the system may be increasing bioavailability.
• Alkalinity-Producing Systems
  

  Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

  • Treated Constituents:
    • acidity
    • copper
    • ferrous iron
    • lead
    • manganese
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Copper Basin Mining site, southeastern Tennessee
    • Douglas Highwall site, Tucker County, West Virginia
  • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
  • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
  • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
  • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
  • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
• Aluminator® Passive Treatment System
  

  The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

  • Treated Constituents:
    • acidity
    • aluminum
    • iron
  • Scale: Pilot-scale
  • Example Sites:
    • Buckeye Reclamation Landfill site, Belmont County, Ohio
    • Casselman River Watershed, Somerset County, Pennsylvania
    • Little Mill Creek site, Jefferson County, Pennsylvania
    • Metro site, Pennsylvania
    • Greendale site, Clay County, West Virginia
  • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
  • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
  • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
  • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
  • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Anoxic Limestone Drains (ALD)
  

  ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

  • Treated Constituent: acidity
  • Scale: Full-scale
  • Example Sites:
    • Fabius Coal Preparation Plant, Alabama
    • Tennessee Valley Authority site, Alabama
    • Tecumseh - AML site 262, Indiana
    • Ohio Abandoned Bituminous Coal, southeast Ohio
    • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
    • Copper Basin Mining site, southeastern Tennessee
    • Valzinco Mine, Virginia
  • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
  • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
  • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
  • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
  • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• Aquafix
  

  The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

  • Treated Constituents:
    • aluminum
    • copper
    • iron
    • manganese
    • zinc
  • Scale: Pilot-scale
  • Example Sites:
    • Dinero Tunnel, Colorado
    • Summitville Mine, Colorado
    • Jennings Randolph Lake, Maryland
    • Crystal underground copper mine, Butte, Montana
    • Almeda Mine, near Grants Pass, Oregon
  • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
  • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
  • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
  • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
  • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
• Bauxsol™
  

  A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

  • Treated Constituents:
    • acidity
    • aluminum
    • arsenic
    • cadmium
    • copper
    • cyanide
    • iron
    • lead
    • nickel
    • phosphates
    • zinc
  • Scale: Full-scale
  • Example Site: Gilt Edge Mine, South Dakota
  • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
  • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
  • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
  • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
  • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
• Biochemical Reactors (Bioreactors)
  

  Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

  • Treated Constituents:
    • arsenic
    • cadmium
    • chromium
    • copper
    • lead
    • nickel
    • selenium
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Golinsky Mine, Shasta Lake City, California
    • Leviathan Mine, California
    • Stowell Mine, Shasta Lake City, California
    • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
    • West Fork Mine, Missouri
    • Copper Basin Mining site, southeastern Tennessee
  • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
  • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
  • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
  • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
  • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
• Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
  

  This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

  • Treated Constituents:
    • mercury
    • metals
    • nitrate
    • selenium
  • Scale: Full-scale
  • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
  • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
  • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
  • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
  • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
  • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
• Catalyzed Cementation Of Selenium
  

  Catalyzed cementation removes heavy metals from solution by cementation on an iron surface. The process is optimized by adding catalysts that increase selenium removal efficiency.

  • Treated Constituent: selenium
  • Scale: Pilot-scale
  • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
  • Operations: Feed water is fed through a series of static mixers where pH is lowered before entering the elemental iron reactor. The reactor is a specialized tank designed to fluidize iron particles. The iron particles carried out are trapped in a small, cone-bottom tank and pumped back to the reactor for reuse. The processed feed water exiting the small, cone-bottom tank is routed to an 80-gallon reactor where the pH is raised again with a lime slurry and an oxidizer is added that completes the required reaction.
  • Long-term Maintenance: Solids that accumulated in the bottom of the thickener were periodically removed by a diaphragm pump. This sludge slurry was then processed by a filter press. The sludge liquid separated from the solids was returned to the thickener. The filter cake solids removed from the filter press were prepared for analysis or disposal by placing them in appropriate containers. Both filter cake samples were analyzed and found to be below the TCLP threshold value for selenium of 1 mg/L.
  • System Limitations: High chemical costs and solid waste disposal required. No long-term studies of the stability of the cementation waste have been undertaken.
  • Costs: Capital: $1,428,860 (2013 USD for all monetary values) Annual O&M Cost: $1,537,114 Net Present Value of Annual O&M Costs: $12,529,666 Total Net Present Value: $2,248,485 Net Present Value of $/1000 gallons treated: $10.78 Generic cost estimate: Based on 300 gpm plant, 2 mg/L selenium influent, Capital: $1.6 million, O&M: $1.6 million, Net Present Value: $12.5 million, $/1000 gal.: $10.78, $/kg selenium: $1,423.
  • Effectiveness: Garfield Wetlands-Kessler Springs water: water with total selenium concentrationsof 1,950 μg/L (primarily as selenate) was tested at a flow rateof 1 gpm. Even after extensive optimization in the field, the lowest effluent concentration achieved was 26 μg/L. Continued optimization in the laboratory achieved a mean effluent selenium concentration of 3 μg/L.
• Ceramic Microfiltration
  

  This treatment system is designed for the removal of heavy metals from an acid mine drainage system. It uses ceramic microfiltration to remove the precipitated solids.

  • Treated Constituent: metals
  • Scale: Pilot-scale
  • Example Sites:
    • Black Hawk and Central City, Colorado
    • Upper Blackfoot Mining Complex, near Lincoln, Montana
    • Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
  • Operations: Wastewater proceeds through a hydroxide precipitation step, which consists of adding sodium hydroxide. The pH will be adjusted to between 8.5 and 9.5 in a two-stage pH adjust system. The wastewater is then transferred to the concentration tank. At this point, the wastewater will be pumped through the cross-flow ceramic membrane. The absolute pore size of the membrane is 0.2 microns. Therefore, the only metals that will remain in the filtered water will be dissolved metals.
  • Long-term Maintenance: Ceramic membranes should be backwashed periodically and chemical cleaning is required at weekly to three-month intervals, depending on water quality. Backwash waste requires disposal or recycling. Chemical waste is generated during periodic cleanings.
  • System Limitations: High capital and O&M costs. Requirement of osmotic pressure. Fouling of membranes and scale production. Reliance on external power. Potential difficulty of concentrate disposal. Feed solution regarding quality predictability.
  • Costs: Pressure-driven membrane separation processes may involve higher capital and O&M costs than other water treatment technologies, depending on the size of the treatment unit, the volume of feed solution to be addressed, and the cleanup goals. The system at the Upper Blackfoot Mining Complex cost $666,192 (2013 USD).
  • Effectiveness: Ceramic microfiltration removes 99.5 percent ofthe heavy metals from wastewater streams with a system that meets the new proposedstandards. Upper Blackfoot Mining Complex: the system has been operating and meeting standards since January 2009.
• Colloid Polishing Filter Method (CPFM)
  

  CPFM technology uses a proprietary compound (Filter Flow [FF] 1000) that consists of inorganic, oxide based granules. FF 1000 is formulated to remove heavy metals and radionuclides from water through a combination of sorption, chemical complexing and filtration. The technology developer, Filter Flow Technology, Inc., states that sorption on the FF 1000 accounts for the majority of the removal action.

  • Treated Constituents:
    • colloidal radionuclides
    • complex non-tritium radionuclides
    • heavy metals
    • ionic radionuclides
  • Scale: Pilot-scale
  • Example Sites:
    • Rocky Flats Environmental Technology site near Golden, Colorado
    • K-Basin at DOE's Hanford Facility, Hanford, Washington
    • N-Spring at DOE's Hanford Facility, Hanford, Washington
  • Operations: Pre-treated water is pumped from the bag filters to the colloid filter press units where heavy metals and radionuclides are removed and discharged.
  • Long-term Maintenance: The only major system components that require regular maintenance are the filter packs in the colloid filter press unit. They require periodic replacement or regeneration.
  • System Limitations: A CPFM system is not designed to operate at temperatures near or below freezing. If such temperatures are anticipated, the CPFM system and associated storage tanks should be kept in a heated shelter, such as a building or shed. In addition, piping to the system must be protected from freezing. A CPFM system requires potable water, electricity and compressed air for operation.
  • Costs: Ground water remediation costs for an l00-gpm CPFM system could range from about $3.23 to $11.32 (2013 USD) per 1,000 gallons, depending on contaminated ground water characteristics and duration of the remedial action. The cost of building a system is estimated to be about $121,244 to $161,658 (2013 USD). A skid-mounted system that treats water at flow rates up to 100 gpm could be built for about $242,487 to $323,316 (2013 USD).
  • Effectiveness: Filter Flow Technology, Inc. reports that its CPFM system has effectively removed trace ionic heavy metals and non-tritium radionuclides from water that has been pre-treated to reduce suspended solids.
• Constructed Wetlands
  

  Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

  • Treated Constituents:
    • Iron
    • arsenic
    • cadmium
    • copper
    • dissolved aluminum
    • lead
    • manganese
    • nickel
    • selenium
    • sulfate
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Keystone site, California
    • Burleigh Tunnel wetland, Colorado
    • Asarco’s West Fork site, Missouri
    • Commerce/Mayer site, Oklahoma
    • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
    • Friendship Hill wetland, Fayette County, Pennsylvania
    • Latrobe wetland, Westmoreland County, Pennsylvania
    • Somerset wetland, Somerset County, Pennsylvania
    • Copper Basin Mining site, southeastern Tennessee
  • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
  • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
  • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
  • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
  • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• EcoBond
  

  EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

  • Treated Constituents:
    • aluminum
    • arsenic
    • cadmium
    • chromium
    • lead
    • mercury
    • radionuclides
    • selenium
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Clear Creek (Gregory Gulch OU), Colorado
    • Golden Sunlight Mines, Inc., near Whitehall, Montana
    • Gilt Edge Mine, South Dakota
    • Frontier Hard Chrome, Vancouver, Washington
  • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
  • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
  • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
  • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
  • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
• Electrocoagulation
  

  In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

  • Treated Constituents:
    • arsenic
    • copper
    • heavy metals
    • lead
    • phosphates
    • total suspended solids
    • zinc
  • Scale: Lab-scale
  • Example Site: None Known
  • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
  • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
  • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
  • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
  • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
• Electrocoriolysis ELCORTM
  

  Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

  • Treated Constituents:
    • cadmium
    • colloidal solids
    • ionizable metals
    • iron
    • manganese
    • particles and inorganic pollutants – besides copper
    • zinc
  • Scale: Lab-scale
  • Example Site: None Known
  • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
  • Long-term Maintenance: Unknown
  • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
  • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
  • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
• Electrodialysis Reversal (EDR)
  

  Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

  • Treated Constituents:
    • arsenic
    • dissolved solids
    • nitrate
    • radium
  • Scale: Full-scale
  • Example Site: Unspecified mine, South Africa
  • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
  • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
  • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
  • Costs: Unknown
  • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
• Evaporation
  

  Evaporation is the vaporization of pure water to concentrate contaminants as a solid or in a brine stream.

  • Treated Constituent: selenium
  • Scale: Pilot-scale
  • Example Site: San Joaquin, California
  • Operations: Solar evaporation ponds and enhanced evaporation systems have been examined for selenium treatment. Enhanced evaporation system accelerates evaporation rates by spraying water in the air. The use of mechanical evaporators can produce concentrated brine followed by crystallization, drying and solid waste disposal. Requires minimal energy and no pre-treatment. Mechanical evaporation machines can rapidly increase the evaporation process, with up to 14 times more efficiency than space taken by the same area of pond.
  • Long-term Maintenance: Sediments accumulated during evaporation require disposal. Land-based mechanical evaporation machines require more attention if wind direction varies greatly and if the site is sensitive to spray droplet drift. A pond-based unit requires less operator attention.
  • System Limitations: Solar evaporation is likely unsuitable for metals removal from MIW due to the prevailing cold climate where operations are typically located. Enhanced evaporation system has not been applied to MIW treatment. Risk of infiltration to ground water (depending on liner type) could occur. May pose a risk to wildlife. An ecological risk assessment should be performed prior to implementation.
  • Costs: The cost of constructing additional storage ponds and the added cost of cleanup and revegetation are often prohibitive. Lower costs because the technology relies on solar radiation for evaporation. Evaporation pond treatment in the San Joaquin valley cost $754 USD per acre-foot of treated water, with $3.3 million/year (2013 USD) for O&M.
  • Effectiveness: Evaporation ponds reduced selenium concentrations by only 25 percent in the San Joaquin Valley.
• Ferrihydrite Adsorption (Iron Co-Precipitation)
  

  Ferrihydrite adsorption is a two-step physical adsorption process in which a ferric salt is added to the water source at proper conditions such that a ferric hydroxide and ferrihydrite precipitate results in concurrent adsorption of selenium on the surface. Also known as iron co-precipitation.

  • Treated Constituents:
    • arsenic
    • selenium
  • Scale: Full-scale
  • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
  • Operations: Oxidation of ferrous iron to ferric iron and formation of ferric hydroxide is a common reaction in water that causes iron staining because the ferric hydroxide is insoluble and readily precipitates from water. Oxidation of water soluble ferrous iron to ferric iron is the most common method of removing iron from water. This process is relatively fast at pH values above 6.5 and very rapid at a pH of 8.5 or above. Pretreatment to optimize pH might be required. Flow equalization required as part of the treatment train.
  • Long-term Maintenance: Iron residuals with adsorbed selenium will require thickening and dewatering for disposal as solid waste. Will require toxicity characteristic leaching procedure (TCLP) testing to determine whether or not the sludge should be disposed of as hazardous waste.
  • System Limitations: Consistent removal to regulatory levels of selenium has not been proven. Potential release of selenium from ferrihydrite residuals. Gravity sedimentation may be required to separate iron solids and adsorbed metals from the water matrix. High operational costs typical of chemical treatment. Ion exchange capacity for selenium can be greatly reduced by competing ions (e.g., sulfates, nitrates).
  • Costs: Cost of a 1 MGD treatment system is estimated at $11.8 million (2013 USD), with an estimated annual O&M cost of about $4.3 million (2013 USD).
  • Effectiveness: At the Garfield Wetlands-Kessler Springs site, water contained 1,950 μg/L selenium, primarily as selenite. Using an iron concentration of 4,800 mg/L, the mean effluentselenium concentration was 90 μg/L. The minimum reported selenium concentration was 35 μg/L. Selenium removal is not proven to less than 5 μg/L.
• Fluidized Bed Reactor (FBR)
  

  In a fluidized, or pulsed, bed reactor, contaminated water is passed through a granular solid media at high enough velocities to suspend or fluidize the media, creating a completely mixed reactor configuration for attached biological growth or biofilm.

  • Treated Constituents:
    • nitrate
    • perchlorate
    • selenium
  • Scale: Pilot-scale
  • Example Site: San Joaquin, California
  • Operations: In this type of reactor, a fluid is passed through a granular solid material at velocities sufficient to suspend or fluidize the solid media. Media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. FBRs allow for shorter residence times for treatment and a smaller overall footprint due to the vertical orientation of the vessels and the efficiency of treatment.
  • Long-term Maintenance: Requires daily cleaning of the influent strainer, tank walls, recycle tank and piping due to biological growth. Envirogen FBR systems are designed to be operated continuously – they do not require cyclical backwash operations.
  • System Limitations: Presence of excess nitrates necessitates sufficient carbon or energy source, leading to additional biomass. External carbon source may be required. Waste biomass may be hazardous waste.
  • Costs: Total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). The annual O&M cost for the same system is estimated at $3.2 million (2013 USD). A recent third-party analysis performed for the North American Mining Council showed that initial capital costs for an FBR system can be one-third or less the cost of a packed bed reactor system designed for similar treatment requirements.
  • Effectiveness: At a pilot test with a flow rate of 1 gpm, total selenium decreased from 520 μg/L to 380 μg/L. Envirogen FBR technology demonstrated the abilityto achieve <5 ppb selenium over a 10-month period in treatingmining leachate at a U.S.-based coal mining site.
• Ion Exchange
  

  Ion exchange is the reversible exchange of contaminant ions from a process stream with more desirable ions of a similar charge adsorbed to solid surfaces known as ion exchange resins. This process provides hardness removal, desalination, alkalinity removal, radioactive waste removal, ammonia removal and metals removal.

  • Treated Constituents:
    • hardness
    • metals
  • Scale: Pilot-scale
  • Example Site: Soudan Park, Minnesota
  • Operations: Ion exchange is generally used as a polishing step to remove low-concentration contaminants, and often requires pre-treatment prior to application. Important considerations include type of resin, the volume and type of regenerant, the backwash water source, backwash quantities, the need for pre-filtration of solids, the column configuration, the need for pH adjustment before and after ion exchange, and the cycle length. Flow equalization/diversion is required as part of the overall system.
  • Long-term Maintenance: Once ion exchange sites on the resin are completely full, the resin must be regenerated in order to be used again. Scale removal may be required to prevent resin fouling. The higher the concentration of TDS in the water, the more frequently the resin will need to be regenerated with caustic soda and rinsed with backwash water.
  • System Limitations: Pre-filtration may be needed to remove suspended solids that would plug the resin bed. Organics, strong oxidants and high temperatures can degrade the resin. Resins may need to be disposed of if they cannot be regenerated, meaning high disposal costs. High sulfate can result in exhaustion of the resin.
  • Costs: Estimated annual costs for one site, the Soudan Mine discharge (average flow of 86,400 gpd), are about $168,993 (2013 USD).
  • Effectiveness: Generally greater than 90 percent recovery rates, given resin specificity for target constituent and regenerant and back wash requirements. A lab test was performed using process solutions fromKennecott Mining Company containing 0.93 mg/L selenium and 80 mg/L sulfate atpH 4. The resin removed selenium to less than 1 μg/L.
• Limestone Pond
  

  Limestone ponds are a passive treatment idea in which a pond is constructed on the upwelling of MIW seep or underground water discharge point. Limestone is placed in the bottom of the pond and the water flows upward through the limestone.

  • Treated Constituents:
    • acidity
    • aluminum
    • iron
  • Scale: Pilot-scale
  • Example Site: None Known
  • Operations: Similar to ALDs, this system is recommended for low dissolved oxygen water containing no Fe3+ and Al3+. The advantage of this system is that the operator can observe if limestone coating is occurring because the system is not buried. If coating occurs, the limestone in the pond can be periodically disturbed with a backhoe to uncover the limestone from precipitates or to knock or scrape off the precipitates. If the limestone is exhausted by dissolution and acid neutralization, then more limestone can be added to the pond over the seep.
  • Long-term Maintenance: Replacement of exhausted limestone.
  • System Limitations: Unknown
  • Costs: Unknown
  • Effectiveness: Unknown
• Nanofiltration Membrane Technology
  

  Nanofiltration is a form of filtration that uses a semi-permeable membrane. The pores are typically much larger than those used in reverse osmosis - close to one nanometer diameter - thus it is not as fine a filtration process as reverse osmosis.

  • Treated Constituents:
    • metals
    • sulfate
  • Scale: Pilot-scale
  • Example Site: Kennecott South, Utah
  • Operations: Similar to reverse osmosis, but operates at one-third the pressure requirement. However, due to larger pore size, it is generally less effective. Requires small space and allows for modular construction. Can offer improved recoveries by rejecting a smaller portion of the salts including selenium, thereby reducing scale potential. Concentrates selenium, reducing the volume for ultimate reduction treatment.
  • Long-term Maintenance: Requires frequent membrane monitoring and maintenance. Membrane life expectancies vary from less than six months to over five years, depending on the quality of the feed solution. Requires treatment and disposal of the residuals.
  • System Limitations: There are pressure, temperature and pH requirements to meet membrane tolerances.
  • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million. Annual O&M costs are estimated at $3.2 million (2013 USD). Capital costs for a single-stage filtration unit are quoted at USD $2,392/gpm feed: a plant treating 500 gpm would cost $1.2 million (2013 USD). Additional pre-treatment may be 50 percent of the treatment plant cost, ranging from $359 to $1,196 (2013 USD) per gpm feed. Operating costs are quoted at about $0.60-0.72/1,000 gallons for a nanofiltration unit, with an additional $0.12-0.18/1,000 gallons for additional pretreatment (2013 USD).
  • Effectiveness: Rejection rates: 60 percent for sodium chloride, 80 percent for calcium carbonate, and 98 percent for magnesium sulfate.
• Open Limestone Channels (OLCs)
  

  Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

  • Treated Constituents:
    • acidity
    • aluminum
    • copper
    • iron
    • lead
    • manganese
    • selenium
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Lick Creek in southwestern Indiana
    • Brandy Camp site in Pennsylvania
    • Many sites in northwest Virginia
    • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
    • Brownton, Dola, Florence, Webster and Airport sites
    • McCarty Highwall site in Preston County, West Virginia
  • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
  • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
  • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
  • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
  • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Permeable Reactive Barriers
  

  A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

  • Treated Constituents:
    • aromatics
    • arsenic
    • cadmium
    • chromium
    • cobalt
    • copper
    • ethane
    • ethene
    • iron
    • lead
    • manganese
    • methane
    • nickel
    • nitrate
    • phosphate
    • propane
    • radionuclides
    • selenium
    • sulfate
    • technetium
    • uranium
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Durango site, Colorado
    • Tenmile Creek, Montana
    • Nickel Rim, Ontario
    • Monticello Mill Tailings, Utah
  • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
  • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
  • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
  • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
  • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Photoreduction
  

  During photoreduction, ultraviolet light is used to generate electron-hole pairs on the surface of a photocatalyst. Contaminants absorbed to the surface of the photocatalyst undergo redox reactions induced by the electrons and holes created by the exposure to ultraviolet light. The treated species are then desorbed and the surface of the photocatalyst is regenerated.

  • Treated Constituent: selenium
  • Scale: Lab-scale
  • Example Site: None Known
  • Operations: TiO2 has been found to be an effective photocatalyst for the reduction of both selenate and selenite in solution. Using ultraviolet light at wavelengths less than 380 nanometers at a pH of 3.5 in the presence of TiO2 and formic acid will reduce Se(VI) and Se(IV) to Se(0).
  • Long-term Maintenance: Unknown
  • System Limitations: Unknown
  • Costs: Unknown
  • Effectiveness: Concentrations of 20 μg/L to 40 μg/L of selenate and selenite were tested, with ultraviolet exposure times ranging between two and eight hours producing final effluentconcentrations between1 μg/L and 31 μg/L total selenium.
• Reverse Osmosis
  

  Reverse osmosis is the pressure-driven separation through a semi-permeable membrane that allows water to pass through while rejecting contaminants.

  • Treated Constituents:
    • metals
    • sulfate
  • Scale: Full-scale
  • Example Site: Kennecott South, Utah
  • Operations: Reverse osmosis is being used at the Kennecott South site as the primary technology for addressing the TDS and sulfate-impacted ground water extracted from the Zone A Sulfate Plume. At the Kennecott South site, reverse osmosis is used with nanofiltration for pre-treatment to avoid reverse osmosis membrane clogging, fouling or damage.
  • Long-term Maintenance: Kennecott site: the manufacturer of the membranes recommended a lifespan of three years, with periodic cleaning cycles. Kennecott’s planning and designing of the treatment system and optimizing operational activities around the quality of the feed water has allowed Kennecott to realize about six years of operational life on the membranes.
  • System Limitations: Requires high operating pressure. Not practical above 10,000 mg/L TDS. Requirements for pre-treatment and chemical addition to reduce scaling/fouling. Reverse osmosis permeate steam will require treatment prior to discharge to receiving waters to meet aquatic toxicity test. Frequent membrane monitoring and maintenance. May require temperature control at low and high temperatures to minimize viscosity effects.
  • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million (2013 USD). Annual O&M costs are estimated at $3.2 million (2013 USD). Total capital costs for the Bingham Canyon Water Treatment Plant: about $16.1 million (2013 USD). Total yearly O&M costs (40 percent of these costs are labor and 24-hour maintenance expenses) for the Bingham Canyon Water Treatment Plant: about $1.3 million (2013 USD).
  • Effectiveness: Kennecott site BinghamCanyon Water Treatment Plant: has consistently seen permeate production efficiencies in the range of 71 to 72 percent. Demonstrated at full scale to remove selenium to <5 μg/L. Can remove 90 to 98 percent of TDS. A TDS removal efficiency of 98.5 percent was observed during pilot-testing of the membranes tested.
• Silica Micro Encapsulation (SME)
  

  SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

  • Treated Constituents:
    • aluminum
    • arsenic
    • chromium
    • copper
    • iron
    • lead
    • mercury
    • radionuclides
    • zinc
  • Scale: Pilot-scale
  • Example Site: Gilt Edge Mine, South Dakota
  • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
  • Long-term Maintenance: Unknown
  • System Limitations: Expensive reagents
  • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
  • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Successive Alkalinity Producing System (SAPS)
  

  Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

  • Treated Constituents:
    • acidity
    • aluminum
    • copper
    • iron
    • manganese
    • zinc
  • Scale: Full-scale
  • Example Sites:
    • Summitville Mine, Colorado
    • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
  • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
  • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
  • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
  • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
  • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
• Zero Valent Iron (ZVI)
  

  Zero valent iron (ZVI) can be used to reduce selenium oxyanions to elemental selenium. Ferrous cations can also reduce selenate to selenite and subsequently remove selenite by adsorption to iron hydroxides.

  • Treated Constituents:
    • arsenic
    • selenium
  • Scale: Pilot-scale
  • Example Sites:
    • Dry Valley Mine, Idaho
    • Richmond Hill Mine, South Dakota
  • Operations: ZVI acts as a reducing agent in the redox reaction. The iron acts as both a catalyst and an electron donor for the reaction. Systems have typically applied the media in tanks or filter vessels that hold elemental iron. Pre-treatment in the form of pH adjustment may be required. Flow equalization/diversion is required as part of the treatment train.
  • Long-term Maintenance: ZVI media is finite and will require removal, disposal and replacement. Residuals will require TCLP testing to determine whether sludge should be disposed of as hazardous waste.
  • System Limitations: Requires long contact time. Forms iron oxides and sludge. Passivation and exhaustion of the iron. ZVI treatment is pH and temperature dependent. Due to iron content and reducing environment, aeration followed by clarification is recommended.
  • Costs: For column-based system (using steel wool): total installed cost for a 1 MGD system is estimated at $13.9 million (2013 USD). For stirred-tank based system (using granular ZVI): total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). Annual O&M cost is estimated at $3.2 million (2013 USD).
  • Effectiveness: At Richmond Hill Mine, the process is able to remove selenium to concentrations of 12 μg/L to 22 μg/L. Catenary Post pilot: 5 μg/L to 14 μg/L selenium was treated to> 5 μg/L.
• Electro-biochemical Reactor
  

  The Electro-Biochemical Reactor (EBR) is a biological water treatment system based on redox reactions that directly supplies electrons to the microbes and reactor environment.

  • Treated Constituent: metals
  • Scale: Pilot-Scale
  • Example Sites:
    • Unnamed Metal Mine in the Yukon Territory, Canada
    • Landusky Mine, Montana
  • Operations: Electrons needed for microbial contaminant transformations are directly supplied using an applied voltage potential of 1 to 3 volts and very low current. These electrons represent a “free” energy source that is available independent of microbial nutrient metabolism.
  • Long-term Maintenance: Not Reported
  • System Limitations: Electrode configurations and materials are being examined with respect to electron transfer, charge density, lifespan, and observed impacts on nutrient utilization and biotransformation kinetics.
  • Costs: Not reported, but described as 40 percent lower capital costs of current biotreatment facilities.
  • Effectiveness: Average of 99 percent Se removal to ≤2.0 µg/L
    
    
    
    Average co-contaminant removals of 93.5 percent to 99.7 percent
• Alkaline Flush
  

  Alkaline Flush Technology introduces an alkali reagent to adjust groundwater and sediment pH and the surface chemistry of sediments to provide in situ remediation of acidic‐metals impacted alluvial aquifers.

  • Treated Constituent: metals
  • Scale: Lab-Scale
  • Example Site: None Known
  • Operations: The alkaline flush causes mobile metals to sorb or precipitate, strengthens metal sorption and works against desorption. The alkaline flush creates the unsatisfied demand for metal sorption that will continue to remove metal contaminants from groundwater passing through the formation.
  • Long-term Maintenance: Not Reported
  • System Limitations: Not Reported
  • Costs: Not Reported
  • Effectiveness: Not Reported
• ChitoRem®
  

  ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

  • Treated Constituents:
    • aluminum
    • cadmium
    • copper
    • iron
    • zinc
  • Scale: Pilot-Scale
  • Example Sites:
    • Barker-Hughesville Mining District, Montana
    • Kittanning Run, Altoona, Pennsylvania
  • Operations: Applied as carbon substrate in BCR setup.
  • Long-term Maintenance: Not reported
  • System Limitations: Possible flow limitations.
  • Costs: Not reported
  • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
• MicroDesal™
  

  MicroDesalTM is a mechanical evaporation system that removes contaminants with a turbulent highly dynamic tornado flow, causing a rapid-evaporation process by increasing the air speed and surface area of the micro-water droplets.

  • Treated Constituents:
    • metals
    • nitrate
    • phosphorous
  • Scale: Lab-Scale
  • Example Site: None Known
  • Operations: Treatment is accomplished without using filters, membranes, or chemicals.
  • Long-term Maintenance: Not reported
  • System Limitations: Not yet proven at higher through-puts.
  • Costs: Not reported
  • Effectiveness: Lab-scale removal rates:
    
    
    
    Fe – 99.8 percent
    
    Se – 89.3 percent
• Metal- Removing Units (MRUs)
  

  MRU’s provide surface area for the growth of microbial biofilm which oxidizes manganese at much lower pH than a purely abiotic system.

  • Treated Constituents:
    • aluminum
    • iron
    • manganese
  • Scale: Pilot-Scale
  • Example Site: Eagle Mine, Pennsylvania
  • Operations: Each MRU Unit treats flows of 10-20 gpm of impacted water (average 15gpm) with light to heavy loads of dissolved and/or precipitating metals. MRU’s can be installed at end-of-pipe situations.
  • Long-term Maintenance: Metal holding capacity for 6 to 12 months between clean-outs, depending on loading. Operational parameters:
    
    
    
    • Total Iron concentration of <0.35mg/L.
    
    • pH 6.8 and greater
    
    • Total N and Total P below 0.3mg/L
  • System Limitations: Operational parameters:
    
    
    
    • Total Iron concentration of <0.35mg/L.
    
    • pH 6.8 and greater
    
    • Total N and Total P below 0.3mg/L
  • Costs: Install, including site specific material, equipment, and labor, cost is $9,500 per unit.
    
    
    
    Annual costs per MRU is $800-$1,000 per unit
  • Effectiveness: Average rates of manganese removal is >200 grams/m3/day.
    
    
    
    Manganese effluent of
    
    <1.0mg/L, and as low as
    
    0.1 mg/L are possible when MRU’s are kept within operational parameters.
• Aeration Treatment Systems
  

  Aeration involves the mechanical introduction of oxygen to enhance the oxidation and decrease the solubility of metals in MIW.

  • Treated Constituents:
    • dissolved metals
    • pH
  • Scale: Full-Scale
  • Example Site: Leviathan Mine, California
  • Operations: Aeration is often applied in conjunction with acid-neutralizing agents (e.g., lime or caustic soda), chemical oxidants, flocculants, filtration, and settling basins.
  • Long-term Maintenance: Not reported
  • System Limitations: Not effective at sites where MIW has relatively high oxygen content.
  • Costs: Not reported
  • Effectiveness: Aeration has use as a sole remediation technology in limited situations, but is much more commonly applied in conjunction with other technologies.

All Treatment Technologies, Sorted by Treated Constituents

• Acidity
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Limestone Pond
    

    Limestone ponds are a passive treatment idea in which a pond is constructed on the upwelling of MIW seep or underground water discharge point. Limestone is placed in the bottom of the pond and the water flows upward through the limestone.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Site: None Known
    • Operations: Similar to ALDs, this system is recommended for low dissolved oxygen water containing no Fe3+ and Al3+. The advantage of this system is that the operator can observe if limestone coating is occurring because the system is not buried. If coating occurs, the limestone in the pond can be periodically disturbed with a backhoe to uncover the limestone from precipitates or to knock or scrape off the precipitates. If the limestone is exhausted by dissolution and acid neutralization, then more limestone can be added to the pond over the seep.
    • Long-term Maintenance: Replacement of exhausted limestone.
    • System Limitations: Unknown
    • Costs: Unknown
    • Effectiveness: Unknown
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
• Aluminum
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Limestone Pond
    

    Limestone ponds are a passive treatment idea in which a pond is constructed on the upwelling of MIW seep or underground water discharge point. Limestone is placed in the bottom of the pond and the water flows upward through the limestone.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Site: None Known
    • Operations: Similar to ALDs, this system is recommended for low dissolved oxygen water containing no Fe3+ and Al3+. The advantage of this system is that the operator can observe if limestone coating is occurring because the system is not buried. If coating occurs, the limestone in the pond can be periodically disturbed with a backhoe to uncover the limestone from precipitates or to knock or scrape off the precipitates. If the limestone is exhausted by dissolution and acid neutralization, then more limestone can be added to the pond over the seep.
    • Long-term Maintenance: Replacement of exhausted limestone.
    • System Limitations: Unknown
    • Costs: Unknown
    • Effectiveness: Unknown
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
  • Metal- Removing Units (MRUs)
    

    MRU’s provide surface area for the growth of microbial biofilm which oxidizes manganese at much lower pH than a purely abiotic system.

    • Treated Constituents:
      • aluminum
      • iron
      • manganese
    • Scale: Pilot-Scale
    • Example Site: Eagle Mine, Pennsylvania
    • Operations: Each MRU Unit treats flows of 10-20 gpm of impacted water (average 15gpm) with light to heavy loads of dissolved and/or precipitating metals. MRU’s can be installed at end-of-pipe situations.
    • Long-term Maintenance: Metal holding capacity for 6 to 12 months between clean-outs, depending on loading. Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • System Limitations: Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • Costs: Install, including site specific material, equipment, and labor, cost is $9,500 per unit.
      
      
      
      Annual costs per MRU is $800-$1,000 per unit
    • Effectiveness: Average rates of manganese removal is >200 grams/m3/day.
      
      
      
      Manganese effluent of
      
      <1.0mg/L, and as low as
      
      0.1 mg/L are possible when MRU’s are kept within operational parameters.
• Aromatics
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Arsenic
  
  

  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
  • Electrodialysis Reversal (EDR)
    

    Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

    • Treated Constituents:
      • arsenic
      • dissolved solids
      • nitrate
      • radium
    • Scale: Full-scale
    • Example Site: Unspecified mine, South Africa
    • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
    • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
    • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
    • Costs: Unknown
    • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
  • Ferrihydrite Adsorption (Iron Co-Precipitation)
    

    Ferrihydrite adsorption is a two-step physical adsorption process in which a ferric salt is added to the water source at proper conditions such that a ferric hydroxide and ferrihydrite precipitate results in concurrent adsorption of selenium on the surface. Also known as iron co-precipitation.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: Oxidation of ferrous iron to ferric iron and formation of ferric hydroxide is a common reaction in water that causes iron staining because the ferric hydroxide is insoluble and readily precipitates from water. Oxidation of water soluble ferrous iron to ferric iron is the most common method of removing iron from water. This process is relatively fast at pH values above 6.5 and very rapid at a pH of 8.5 or above. Pretreatment to optimize pH might be required. Flow equalization required as part of the treatment train.
    • Long-term Maintenance: Iron residuals with adsorbed selenium will require thickening and dewatering for disposal as solid waste. Will require toxicity characteristic leaching procedure (TCLP) testing to determine whether or not the sludge should be disposed of as hazardous waste.
    • System Limitations: Consistent removal to regulatory levels of selenium has not been proven. Potential release of selenium from ferrihydrite residuals. Gravity sedimentation may be required to separate iron solids and adsorbed metals from the water matrix. High operational costs typical of chemical treatment. Ion exchange capacity for selenium can be greatly reduced by competing ions (e.g., sulfates, nitrates).
    • Costs: Cost of a 1 MGD treatment system is estimated at $11.8 million (2013 USD), with an estimated annual O&M cost of about $4.3 million (2013 USD).
    • Effectiveness: At the Garfield Wetlands-Kessler Springs site, water contained 1,950 μg/L selenium, primarily as selenite. Using an iron concentration of 4,800 mg/L, the mean effluentselenium concentration was 90 μg/L. The minimum reported selenium concentration was 35 μg/L. Selenium removal is not proven to less than 5 μg/L.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
  • Zero Valent Iron (ZVI)
    

    Zero valent iron (ZVI) can be used to reduce selenium oxyanions to elemental selenium. Ferrous cations can also reduce selenate to selenite and subsequently remove selenite by adsorption to iron hydroxides.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Pilot-scale
    • Example Sites:
      • Dry Valley Mine, Idaho
      • Richmond Hill Mine, South Dakota
    • Operations: ZVI acts as a reducing agent in the redox reaction. The iron acts as both a catalyst and an electron donor for the reaction. Systems have typically applied the media in tanks or filter vessels that hold elemental iron. Pre-treatment in the form of pH adjustment may be required. Flow equalization/diversion is required as part of the treatment train.
    • Long-term Maintenance: ZVI media is finite and will require removal, disposal and replacement. Residuals will require TCLP testing to determine whether sludge should be disposed of as hazardous waste.
    • System Limitations: Requires long contact time. Forms iron oxides and sludge. Passivation and exhaustion of the iron. ZVI treatment is pH and temperature dependent. Due to iron content and reducing environment, aeration followed by clarification is recommended.
    • Costs: For column-based system (using steel wool): total installed cost for a 1 MGD system is estimated at $13.9 million (2013 USD). For stirred-tank based system (using granular ZVI): total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). Annual O&M cost is estimated at $3.2 million (2013 USD).
    • Effectiveness: At Richmond Hill Mine, the process is able to remove selenium to concentrations of 12 μg/L to 22 μg/L. Catenary Post pilot: 5 μg/L to 14 μg/L selenium was treated to> 5 μg/L.
• Cadmium
  
  

  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
• Chromium
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Cobalt
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Colloidal Solids
  
  

  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
• Copper
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
• Cyanide
  
  

  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
• Dissolved Aluminum
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Dissolved Solids
  
  

  • Electrodialysis Reversal (EDR)
    

    Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

    • Treated Constituents:
      • arsenic
      • dissolved solids
      • nitrate
      • radium
    • Scale: Full-scale
    • Example Site: Unspecified mine, South Africa
    • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
    • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
    • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
    • Costs: Unknown
    • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
• Ethane
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Ferrous Iron
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
• Hardness
  
  

  • Ion Exchange
    

    Ion exchange is the reversible exchange of contaminant ions from a process stream with more desirable ions of a similar charge adsorbed to solid surfaces known as ion exchange resins. This process provides hardness removal, desalination, alkalinity removal, radioactive waste removal, ammonia removal and metals removal.

    • Treated Constituents:
      • hardness
      • metals
    • Scale: Pilot-scale
    • Example Site: Soudan Park, Minnesota
    • Operations: Ion exchange is generally used as a polishing step to remove low-concentration contaminants, and often requires pre-treatment prior to application. Important considerations include type of resin, the volume and type of regenerant, the backwash water source, backwash quantities, the need for pre-filtration of solids, the column configuration, the need for pH adjustment before and after ion exchange, and the cycle length. Flow equalization/diversion is required as part of the overall system.
    • Long-term Maintenance: Once ion exchange sites on the resin are completely full, the resin must be regenerated in order to be used again. Scale removal may be required to prevent resin fouling. The higher the concentration of TDS in the water, the more frequently the resin will need to be regenerated with caustic soda and rinsed with backwash water.
    • System Limitations: Pre-filtration may be needed to remove suspended solids that would plug the resin bed. Organics, strong oxidants and high temperatures can degrade the resin. Resins may need to be disposed of if they cannot be regenerated, meaning high disposal costs. High sulfate can result in exhaustion of the resin.
    • Costs: Estimated annual costs for one site, the Soudan Mine discharge (average flow of 86,400 gpd), are about $168,993 (2013 USD).
    • Effectiveness: Generally greater than 90 percent recovery rates, given resin specificity for target constituent and regenerant and back wash requirements. A lab test was performed using process solutions fromKennecott Mining Company containing 0.93 mg/L selenium and 80 mg/L sulfate atpH 4. The resin removed selenium to less than 1 μg/L.
• Heavy Metals
  
  

  • Colloid Polishing Filter Method (CPFM)
    

    CPFM technology uses a proprietary compound (Filter Flow [FF] 1000) that consists of inorganic, oxide based granules. FF 1000 is formulated to remove heavy metals and radionuclides from water through a combination of sorption, chemical complexing and filtration. The technology developer, Filter Flow Technology, Inc., states that sorption on the FF 1000 accounts for the majority of the removal action.

    • Treated Constituents:
      • colloidal radionuclides
      • complex non-tritium radionuclides
      • heavy metals
      • ionic radionuclides
    • Scale: Pilot-scale
    • Example Sites:
      • Rocky Flats Environmental Technology site near Golden, Colorado
      • K-Basin at DOE's Hanford Facility, Hanford, Washington
      • N-Spring at DOE's Hanford Facility, Hanford, Washington
    • Operations: Pre-treated water is pumped from the bag filters to the colloid filter press units where heavy metals and radionuclides are removed and discharged.
    • Long-term Maintenance: The only major system components that require regular maintenance are the filter packs in the colloid filter press unit. They require periodic replacement or regeneration.
    • System Limitations: A CPFM system is not designed to operate at temperatures near or below freezing. If such temperatures are anticipated, the CPFM system and associated storage tanks should be kept in a heated shelter, such as a building or shed. In addition, piping to the system must be protected from freezing. A CPFM system requires potable water, electricity and compressed air for operation.
    • Costs: Ground water remediation costs for an l00-gpm CPFM system could range from about $3.23 to $11.32 (2013 USD) per 1,000 gallons, depending on contaminated ground water characteristics and duration of the remedial action. The cost of building a system is estimated to be about $121,244 to $161,658 (2013 USD). A skid-mounted system that treats water at flow rates up to 100 gpm could be built for about $242,487 to $323,316 (2013 USD).
    • Effectiveness: Filter Flow Technology, Inc. reports that its CPFM system has effectively removed trace ionic heavy metals and non-tritium radionuclides from water that has been pre-treated to reduce suspended solids.
  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
• Ionizable Metals
  
  

  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
• Iron
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
  • Limestone Pond
    

    Limestone ponds are a passive treatment idea in which a pond is constructed on the upwelling of MIW seep or underground water discharge point. Limestone is placed in the bottom of the pond and the water flows upward through the limestone.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Site: None Known
    • Operations: Similar to ALDs, this system is recommended for low dissolved oxygen water containing no Fe3+ and Al3+. The advantage of this system is that the operator can observe if limestone coating is occurring because the system is not buried. If coating occurs, the limestone in the pond can be periodically disturbed with a backhoe to uncover the limestone from precipitates or to knock or scrape off the precipitates. If the limestone is exhausted by dissolution and acid neutralization, then more limestone can be added to the pond over the seep.
    • Long-term Maintenance: Replacement of exhausted limestone.
    • System Limitations: Unknown
    • Costs: Unknown
    • Effectiveness: Unknown
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
  • Metal- Removing Units (MRUs)
    

    MRU’s provide surface area for the growth of microbial biofilm which oxidizes manganese at much lower pH than a purely abiotic system.

    • Treated Constituents:
      • aluminum
      • iron
      • manganese
    • Scale: Pilot-Scale
    • Example Site: Eagle Mine, Pennsylvania
    • Operations: Each MRU Unit treats flows of 10-20 gpm of impacted water (average 15gpm) with light to heavy loads of dissolved and/or precipitating metals. MRU’s can be installed at end-of-pipe situations.
    • Long-term Maintenance: Metal holding capacity for 6 to 12 months between clean-outs, depending on loading. Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • System Limitations: Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • Costs: Install, including site specific material, equipment, and labor, cost is $9,500 per unit.
      
      
      
      Annual costs per MRU is $800-$1,000 per unit
    • Effectiveness: Average rates of manganese removal is >200 grams/m3/day.
      
      
      
      Manganese effluent of
      
      <1.0mg/L, and as low as
      
      0.1 mg/L are possible when MRU’s are kept within operational parameters.
• Lead
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Manganese
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
  • Metal- Removing Units (MRUs)
    

    MRU’s provide surface area for the growth of microbial biofilm which oxidizes manganese at much lower pH than a purely abiotic system.

    • Treated Constituents:
      • aluminum
      • iron
      • manganese
    • Scale: Pilot-Scale
    • Example Site: Eagle Mine, Pennsylvania
    • Operations: Each MRU Unit treats flows of 10-20 gpm of impacted water (average 15gpm) with light to heavy loads of dissolved and/or precipitating metals. MRU’s can be installed at end-of-pipe situations.
    • Long-term Maintenance: Metal holding capacity for 6 to 12 months between clean-outs, depending on loading. Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • System Limitations: Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • Costs: Install, including site specific material, equipment, and labor, cost is $9,500 per unit.
      
      
      
      Annual costs per MRU is $800-$1,000 per unit
    • Effectiveness: Average rates of manganese removal is >200 grams/m3/day.
      
      
      
      Manganese effluent of
      
      <1.0mg/L, and as low as
      
      0.1 mg/L are possible when MRU’s are kept within operational parameters.
• Mercury
  
  

  • Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
    

    This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

    • Treated Constituents:
      • mercury
      • metals
      • nitrate
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
    • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
    • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
    • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
    • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Metals
  
  

  • Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
    

    This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

    • Treated Constituents:
      • mercury
      • metals
      • nitrate
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
    • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
    • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
    • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
    • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
  • Ceramic Microfiltration
    

    This treatment system is designed for the removal of heavy metals from an acid mine drainage system. It uses ceramic microfiltration to remove the precipitated solids.

    • Treated Constituent: metals
    • Scale: Pilot-scale
    • Example Sites:
      • Black Hawk and Central City, Colorado
      • Upper Blackfoot Mining Complex, near Lincoln, Montana
      • Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
    • Operations: Wastewater proceeds through a hydroxide precipitation step, which consists of adding sodium hydroxide. The pH will be adjusted to between 8.5 and 9.5 in a two-stage pH adjust system. The wastewater is then transferred to the concentration tank. At this point, the wastewater will be pumped through the cross-flow ceramic membrane. The absolute pore size of the membrane is 0.2 microns. Therefore, the only metals that will remain in the filtered water will be dissolved metals.
    • Long-term Maintenance: Ceramic membranes should be backwashed periodically and chemical cleaning is required at weekly to three-month intervals, depending on water quality. Backwash waste requires disposal or recycling. Chemical waste is generated during periodic cleanings.
    • System Limitations: High capital and O&M costs. Requirement of osmotic pressure. Fouling of membranes and scale production. Reliance on external power. Potential difficulty of concentrate disposal. Feed solution regarding quality predictability.
    • Costs: Pressure-driven membrane separation processes may involve higher capital and O&M costs than other water treatment technologies, depending on the size of the treatment unit, the volume of feed solution to be addressed, and the cleanup goals. The system at the Upper Blackfoot Mining Complex cost $666,192 (2013 USD).
    • Effectiveness: Ceramic microfiltration removes 99.5 percent ofthe heavy metals from wastewater streams with a system that meets the new proposedstandards. Upper Blackfoot Mining Complex: the system has been operating and meeting standards since January 2009.
  • Ion Exchange
    

    Ion exchange is the reversible exchange of contaminant ions from a process stream with more desirable ions of a similar charge adsorbed to solid surfaces known as ion exchange resins. This process provides hardness removal, desalination, alkalinity removal, radioactive waste removal, ammonia removal and metals removal.

    • Treated Constituents:
      • hardness
      • metals
    • Scale: Pilot-scale
    • Example Site: Soudan Park, Minnesota
    • Operations: Ion exchange is generally used as a polishing step to remove low-concentration contaminants, and often requires pre-treatment prior to application. Important considerations include type of resin, the volume and type of regenerant, the backwash water source, backwash quantities, the need for pre-filtration of solids, the column configuration, the need for pH adjustment before and after ion exchange, and the cycle length. Flow equalization/diversion is required as part of the overall system.
    • Long-term Maintenance: Once ion exchange sites on the resin are completely full, the resin must be regenerated in order to be used again. Scale removal may be required to prevent resin fouling. The higher the concentration of TDS in the water, the more frequently the resin will need to be regenerated with caustic soda and rinsed with backwash water.
    • System Limitations: Pre-filtration may be needed to remove suspended solids that would plug the resin bed. Organics, strong oxidants and high temperatures can degrade the resin. Resins may need to be disposed of if they cannot be regenerated, meaning high disposal costs. High sulfate can result in exhaustion of the resin.
    • Costs: Estimated annual costs for one site, the Soudan Mine discharge (average flow of 86,400 gpd), are about $168,993 (2013 USD).
    • Effectiveness: Generally greater than 90 percent recovery rates, given resin specificity for target constituent and regenerant and back wash requirements. A lab test was performed using process solutions fromKennecott Mining Company containing 0.93 mg/L selenium and 80 mg/L sulfate atpH 4. The resin removed selenium to less than 1 μg/L.
  • Nanofiltration Membrane Technology
    

    Nanofiltration is a form of filtration that uses a semi-permeable membrane. The pores are typically much larger than those used in reverse osmosis - close to one nanometer diameter - thus it is not as fine a filtration process as reverse osmosis.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Pilot-scale
    • Example Site: Kennecott South, Utah
    • Operations: Similar to reverse osmosis, but operates at one-third the pressure requirement. However, due to larger pore size, it is generally less effective. Requires small space and allows for modular construction. Can offer improved recoveries by rejecting a smaller portion of the salts including selenium, thereby reducing scale potential. Concentrates selenium, reducing the volume for ultimate reduction treatment.
    • Long-term Maintenance: Requires frequent membrane monitoring and maintenance. Membrane life expectancies vary from less than six months to over five years, depending on the quality of the feed solution. Requires treatment and disposal of the residuals.
    • System Limitations: There are pressure, temperature and pH requirements to meet membrane tolerances.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million. Annual O&M costs are estimated at $3.2 million (2013 USD). Capital costs for a single-stage filtration unit are quoted at USD $2,392/gpm feed: a plant treating 500 gpm would cost $1.2 million (2013 USD). Additional pre-treatment may be 50 percent of the treatment plant cost, ranging from $359 to $1,196 (2013 USD) per gpm feed. Operating costs are quoted at about $0.60-0.72/1,000 gallons for a nanofiltration unit, with an additional $0.12-0.18/1,000 gallons for additional pretreatment (2013 USD).
    • Effectiveness: Rejection rates: 60 percent for sodium chloride, 80 percent for calcium carbonate, and 98 percent for magnesium sulfate.
  • Reverse Osmosis
    

    Reverse osmosis is the pressure-driven separation through a semi-permeable membrane that allows water to pass through while rejecting contaminants.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Full-scale
    • Example Site: Kennecott South, Utah
    • Operations: Reverse osmosis is being used at the Kennecott South site as the primary technology for addressing the TDS and sulfate-impacted ground water extracted from the Zone A Sulfate Plume. At the Kennecott South site, reverse osmosis is used with nanofiltration for pre-treatment to avoid reverse osmosis membrane clogging, fouling or damage.
    • Long-term Maintenance: Kennecott site: the manufacturer of the membranes recommended a lifespan of three years, with periodic cleaning cycles. Kennecott’s planning and designing of the treatment system and optimizing operational activities around the quality of the feed water has allowed Kennecott to realize about six years of operational life on the membranes.
    • System Limitations: Requires high operating pressure. Not practical above 10,000 mg/L TDS. Requirements for pre-treatment and chemical addition to reduce scaling/fouling. Reverse osmosis permeate steam will require treatment prior to discharge to receiving waters to meet aquatic toxicity test. Frequent membrane monitoring and maintenance. May require temperature control at low and high temperatures to minimize viscosity effects.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million (2013 USD). Annual O&M costs are estimated at $3.2 million (2013 USD). Total capital costs for the Bingham Canyon Water Treatment Plant: about $16.1 million (2013 USD). Total yearly O&M costs (40 percent of these costs are labor and 24-hour maintenance expenses) for the Bingham Canyon Water Treatment Plant: about $1.3 million (2013 USD).
    • Effectiveness: Kennecott site BinghamCanyon Water Treatment Plant: has consistently seen permeate production efficiencies in the range of 71 to 72 percent. Demonstrated at full scale to remove selenium to <5 μg/L. Can remove 90 to 98 percent of TDS. A TDS removal efficiency of 98.5 percent was observed during pilot-testing of the membranes tested.
  • Electro-biochemical Reactor
    

    The Electro-Biochemical Reactor (EBR) is a biological water treatment system based on redox reactions that directly supplies electrons to the microbes and reactor environment.

    • Treated Constituent: metals
    • Scale: Pilot-Scale
    • Example Sites:
      • Unnamed Metal Mine in the Yukon Territory, Canada
      • Landusky Mine, Montana
    • Operations: Electrons needed for microbial contaminant transformations are directly supplied using an applied voltage potential of 1 to 3 volts and very low current. These electrons represent a “free” energy source that is available independent of microbial nutrient metabolism.
    • Long-term Maintenance: Not Reported
    • System Limitations: Electrode configurations and materials are being examined with respect to electron transfer, charge density, lifespan, and observed impacts on nutrient utilization and biotransformation kinetics.
    • Costs: Not reported, but described as 40 percent lower capital costs of current biotreatment facilities.
    • Effectiveness: Average of 99 percent Se removal to ≤2.0 µg/L
      
      
      
      Average co-contaminant removals of 93.5 percent to 99.7 percent
  • Alkaline Flush
    

    Alkaline Flush Technology introduces an alkali reagent to adjust groundwater and sediment pH and the surface chemistry of sediments to provide in situ remediation of acidic‐metals impacted alluvial aquifers.

    • Treated Constituent: metals
    • Scale: Lab-Scale
    • Example Site: None Known
    • Operations: The alkaline flush causes mobile metals to sorb or precipitate, strengthens metal sorption and works against desorption. The alkaline flush creates the unsatisfied demand for metal sorption that will continue to remove metal contaminants from groundwater passing through the formation.
    • Long-term Maintenance: Not Reported
    • System Limitations: Not Reported
    • Costs: Not Reported
    • Effectiveness: Not Reported
  • MicroDesal™
    

    MicroDesalTM is a mechanical evaporation system that removes contaminants with a turbulent highly dynamic tornado flow, causing a rapid-evaporation process by increasing the air speed and surface area of the micro-water droplets.

    • Treated Constituents:
      • metals
      • nitrate
      • phosphorous
    • Scale: Lab-Scale
    • Example Site: None Known
    • Operations: Treatment is accomplished without using filters, membranes, or chemicals.
    • Long-term Maintenance: Not reported
    • System Limitations: Not yet proven at higher through-puts.
    • Costs: Not reported
    • Effectiveness: Lab-scale removal rates:
      
      
      
      Fe – 99.8 percent
      
      Se – 89.3 percent
• Methane
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Nickel
  
  

  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Nitrate
  
  

  • Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
    

    This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

    • Treated Constituents:
      • mercury
      • metals
      • nitrate
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
    • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
    • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
    • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
    • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
  • Electrodialysis Reversal (EDR)
    

    Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

    • Treated Constituents:
      • arsenic
      • dissolved solids
      • nitrate
      • radium
    • Scale: Full-scale
    • Example Site: Unspecified mine, South Africa
    • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
    • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
    • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
    • Costs: Unknown
    • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
  • Fluidized Bed Reactor (FBR)
    

    In a fluidized, or pulsed, bed reactor, contaminated water is passed through a granular solid media at high enough velocities to suspend or fluidize the media, creating a completely mixed reactor configuration for attached biological growth or biofilm.

    • Treated Constituents:
      • nitrate
      • perchlorate
      • selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: In this type of reactor, a fluid is passed through a granular solid material at velocities sufficient to suspend or fluidize the solid media. Media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. FBRs allow for shorter residence times for treatment and a smaller overall footprint due to the vertical orientation of the vessels and the efficiency of treatment.
    • Long-term Maintenance: Requires daily cleaning of the influent strainer, tank walls, recycle tank and piping due to biological growth. Envirogen FBR systems are designed to be operated continuously – they do not require cyclical backwash operations.
    • System Limitations: Presence of excess nitrates necessitates sufficient carbon or energy source, leading to additional biomass. External carbon source may be required. Waste biomass may be hazardous waste.
    • Costs: Total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). The annual O&M cost for the same system is estimated at $3.2 million (2013 USD). A recent third-party analysis performed for the North American Mining Council showed that initial capital costs for an FBR system can be one-third or less the cost of a packed bed reactor system designed for similar treatment requirements.
    • Effectiveness: At a pilot test with a flow rate of 1 gpm, total selenium decreased from 520 μg/L to 380 μg/L. Envirogen FBR technology demonstrated the abilityto achieve <5 ppb selenium over a 10-month period in treatingmining leachate at a U.S.-based coal mining site.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • MicroDesal™
    

    MicroDesalTM is a mechanical evaporation system that removes contaminants with a turbulent highly dynamic tornado flow, causing a rapid-evaporation process by increasing the air speed and surface area of the micro-water droplets.

    • Treated Constituents:
      • metals
      • nitrate
      • phosphorous
    • Scale: Lab-Scale
    • Example Site: None Known
    • Operations: Treatment is accomplished without using filters, membranes, or chemicals.
    • Long-term Maintenance: Not reported
    • System Limitations: Not yet proven at higher through-puts.
    • Costs: Not reported
    • Effectiveness: Lab-scale removal rates:
      
      
      
      Fe – 99.8 percent
      
      Se – 89.3 percent
• Perchlorate
  
  

  • Fluidized Bed Reactor (FBR)
    

    In a fluidized, or pulsed, bed reactor, contaminated water is passed through a granular solid media at high enough velocities to suspend or fluidize the media, creating a completely mixed reactor configuration for attached biological growth or biofilm.

    • Treated Constituents:
      • nitrate
      • perchlorate
      • selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: In this type of reactor, a fluid is passed through a granular solid material at velocities sufficient to suspend or fluidize the solid media. Media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. FBRs allow for shorter residence times for treatment and a smaller overall footprint due to the vertical orientation of the vessels and the efficiency of treatment.
    • Long-term Maintenance: Requires daily cleaning of the influent strainer, tank walls, recycle tank and piping due to biological growth. Envirogen FBR systems are designed to be operated continuously – they do not require cyclical backwash operations.
    • System Limitations: Presence of excess nitrates necessitates sufficient carbon or energy source, leading to additional biomass. External carbon source may be required. Waste biomass may be hazardous waste.
    • Costs: Total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). The annual O&M cost for the same system is estimated at $3.2 million (2013 USD). A recent third-party analysis performed for the North American Mining Council showed that initial capital costs for an FBR system can be one-third or less the cost of a packed bed reactor system designed for similar treatment requirements.
    • Effectiveness: At a pilot test with a flow rate of 1 gpm, total selenium decreased from 520 μg/L to 380 μg/L. Envirogen FBR technology demonstrated the abilityto achieve <5 ppb selenium over a 10-month period in treatingmining leachate at a U.S.-based coal mining site.
• Phosphate
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Propane
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Radionuclides
  
  

  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Radium
  
  

  • Electrodialysis Reversal (EDR)
    

    Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

    • Treated Constituents:
      • arsenic
      • dissolved solids
      • nitrate
      • radium
    • Scale: Full-scale
    • Example Site: Unspecified mine, South Africa
    • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
    • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
    • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
    • Costs: Unknown
    • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
• Selenium
  
  

  • Adsorption To Peanut Shells
    

    Innovative technology using carbonized peanut shells to physically adsorb selenium.

    • Treated Constituent: selenium
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: Before treatment, peanut shells are treated with strong sulfuric acid to carbonize the shells while partially oxidizing the cellulose and hemicelluloses and fragmenting the lignin. The sulfuric acid treatment results in a carbonaceous material with functional groups for both the sorption and reduction of selenium.
    • Long-term Maintenance: Unknown
    • System Limitations: Sorption was found to be temperature dependent.
    • Costs: This process has only recently been developed and is not well characterized. Peanut shells are readily available at low cost.
    • Effectiveness: Removals as high as 63 percent were observed for 25 mg/L selenide solutions. Selenite sorbed to the material at an optimal pH of 1.5. As pH increased, sorption capacity decreased.
  • Algal-Bacterial Selenium Removal
    

    Algal treatment occurs via enhanced cyanobacterial and algal growth through nutrient addition. These additional nutrients increase algal biomass, thereby increasing selenium volatilization rates. In addition to treatment by volatilization, the algal biomass generated also serves as a carbon source to support microbial selenium reduction processes.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: Panoche Drainage District on the west side of the San Joaquin Valley, California
    • Operations: This system uses a combination of ponds containing algae and bacteria in which selenate is reduced to selenite and elemental selenium.
    • Long-term Maintenance: Unknown
    • System Limitations: Seasonally limited with treatment affected by duration of solar light and ambient temperatures. Difficulty of generating sufficient biomass to promote biological reduction and the inability to treat selenium to regulatory levels. Although much of the total selenium may be removed using the ABSR system, it is essential that the remaining selenium is in a form that is not readily bioavailable to aquatic organisms. In the ABSR system, if the selenium that remains has been transformed into a more bioavailable form, then the system could possibly be increasing the concentrations of selenium absorbed by aquatic life.
    • Costs: Potentially low-cost treatment, but can require large land area as well as the need for separation of the high-rate and reduction ponds. The preliminary total cost estimate for a 10-acre-foot per day ABSR facility is less than $291 (2013 USD) per acre-foot of treated drainage water. The ABSR system is one of the most economical and therefore easily adopted selenium removal systems.
    • Effectiveness: Preliminary results have shown that the method may be able to reduce the total selenium in the drainage water up to 80 percent. During 1997 and 1998, the best-performing ABSR plant configuration reduced nitrate by more than 95 percent and reduced total soluble selenium mass by 80 percent. The results of this studysuggest that the ABSR system may not be successfully reducing the bioavailability of selenium to aquatic organisms. Although microcosm data was limited, results lead to the conclusion that certain steps of the system may be increasing bioavailability.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
    

    This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

    • Treated Constituents:
      • mercury
      • metals
      • nitrate
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
    • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
    • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
    • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
    • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
  • Catalyzed Cementation Of Selenium
    

    Catalyzed cementation removes heavy metals from solution by cementation on an iron surface. The process is optimized by adding catalysts that increase selenium removal efficiency.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: Feed water is fed through a series of static mixers where pH is lowered before entering the elemental iron reactor. The reactor is a specialized tank designed to fluidize iron particles. The iron particles carried out are trapped in a small, cone-bottom tank and pumped back to the reactor for reuse. The processed feed water exiting the small, cone-bottom tank is routed to an 80-gallon reactor where the pH is raised again with a lime slurry and an oxidizer is added that completes the required reaction.
    • Long-term Maintenance: Solids that accumulated in the bottom of the thickener were periodically removed by a diaphragm pump. This sludge slurry was then processed by a filter press. The sludge liquid separated from the solids was returned to the thickener. The filter cake solids removed from the filter press were prepared for analysis or disposal by placing them in appropriate containers. Both filter cake samples were analyzed and found to be below the TCLP threshold value for selenium of 1 mg/L.
    • System Limitations: High chemical costs and solid waste disposal required. No long-term studies of the stability of the cementation waste have been undertaken.
    • Costs: Capital: $1,428,860 (2013 USD for all monetary values) Annual O&M Cost: $1,537,114 Net Present Value of Annual O&M Costs: $12,529,666 Total Net Present Value: $2,248,485 Net Present Value of $/1000 gallons treated: $10.78 Generic cost estimate: Based on 300 gpm plant, 2 mg/L selenium influent, Capital: $1.6 million, O&M: $1.6 million, Net Present Value: $12.5 million, $/1000 gal.: $10.78, $/kg selenium: $1,423.
    • Effectiveness: Garfield Wetlands-Kessler Springs water: water with total selenium concentrationsof 1,950 μg/L (primarily as selenate) was tested at a flow rateof 1 gpm. Even after extensive optimization in the field, the lowest effluent concentration achieved was 26 μg/L. Continued optimization in the laboratory achieved a mean effluent selenium concentration of 3 μg/L.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Evaporation
    

    Evaporation is the vaporization of pure water to concentrate contaminants as a solid or in a brine stream.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: Solar evaporation ponds and enhanced evaporation systems have been examined for selenium treatment. Enhanced evaporation system accelerates evaporation rates by spraying water in the air. The use of mechanical evaporators can produce concentrated brine followed by crystallization, drying and solid waste disposal. Requires minimal energy and no pre-treatment. Mechanical evaporation machines can rapidly increase the evaporation process, with up to 14 times more efficiency than space taken by the same area of pond.
    • Long-term Maintenance: Sediments accumulated during evaporation require disposal. Land-based mechanical evaporation machines require more attention if wind direction varies greatly and if the site is sensitive to spray droplet drift. A pond-based unit requires less operator attention.
    • System Limitations: Solar evaporation is likely unsuitable for metals removal from MIW due to the prevailing cold climate where operations are typically located. Enhanced evaporation system has not been applied to MIW treatment. Risk of infiltration to ground water (depending on liner type) could occur. May pose a risk to wildlife. An ecological risk assessment should be performed prior to implementation.
    • Costs: The cost of constructing additional storage ponds and the added cost of cleanup and revegetation are often prohibitive. Lower costs because the technology relies on solar radiation for evaporation. Evaporation pond treatment in the San Joaquin valley cost $754 USD per acre-foot of treated water, with $3.3 million/year (2013 USD) for O&M.
    • Effectiveness: Evaporation ponds reduced selenium concentrations by only 25 percent in the San Joaquin Valley.
  • Ferrihydrite Adsorption (Iron Co-Precipitation)
    

    Ferrihydrite adsorption is a two-step physical adsorption process in which a ferric salt is added to the water source at proper conditions such that a ferric hydroxide and ferrihydrite precipitate results in concurrent adsorption of selenium on the surface. Also known as iron co-precipitation.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: Oxidation of ferrous iron to ferric iron and formation of ferric hydroxide is a common reaction in water that causes iron staining because the ferric hydroxide is insoluble and readily precipitates from water. Oxidation of water soluble ferrous iron to ferric iron is the most common method of removing iron from water. This process is relatively fast at pH values above 6.5 and very rapid at a pH of 8.5 or above. Pretreatment to optimize pH might be required. Flow equalization required as part of the treatment train.
    • Long-term Maintenance: Iron residuals with adsorbed selenium will require thickening and dewatering for disposal as solid waste. Will require toxicity characteristic leaching procedure (TCLP) testing to determine whether or not the sludge should be disposed of as hazardous waste.
    • System Limitations: Consistent removal to regulatory levels of selenium has not been proven. Potential release of selenium from ferrihydrite residuals. Gravity sedimentation may be required to separate iron solids and adsorbed metals from the water matrix. High operational costs typical of chemical treatment. Ion exchange capacity for selenium can be greatly reduced by competing ions (e.g., sulfates, nitrates).
    • Costs: Cost of a 1 MGD treatment system is estimated at $11.8 million (2013 USD), with an estimated annual O&M cost of about $4.3 million (2013 USD).
    • Effectiveness: At the Garfield Wetlands-Kessler Springs site, water contained 1,950 μg/L selenium, primarily as selenite. Using an iron concentration of 4,800 mg/L, the mean effluentselenium concentration was 90 μg/L. The minimum reported selenium concentration was 35 μg/L. Selenium removal is not proven to less than 5 μg/L.
  • Fluidized Bed Reactor (FBR)
    

    In a fluidized, or pulsed, bed reactor, contaminated water is passed through a granular solid media at high enough velocities to suspend or fluidize the media, creating a completely mixed reactor configuration for attached biological growth or biofilm.

    • Treated Constituents:
      • nitrate
      • perchlorate
      • selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: In this type of reactor, a fluid is passed through a granular solid material at velocities sufficient to suspend or fluidize the solid media. Media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. FBRs allow for shorter residence times for treatment and a smaller overall footprint due to the vertical orientation of the vessels and the efficiency of treatment.
    • Long-term Maintenance: Requires daily cleaning of the influent strainer, tank walls, recycle tank and piping due to biological growth. Envirogen FBR systems are designed to be operated continuously – they do not require cyclical backwash operations.
    • System Limitations: Presence of excess nitrates necessitates sufficient carbon or energy source, leading to additional biomass. External carbon source may be required. Waste biomass may be hazardous waste.
    • Costs: Total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). The annual O&M cost for the same system is estimated at $3.2 million (2013 USD). A recent third-party analysis performed for the North American Mining Council showed that initial capital costs for an FBR system can be one-third or less the cost of a packed bed reactor system designed for similar treatment requirements.
    • Effectiveness: At a pilot test with a flow rate of 1 gpm, total selenium decreased from 520 μg/L to 380 μg/L. Envirogen FBR technology demonstrated the abilityto achieve <5 ppb selenium over a 10-month period in treatingmining leachate at a U.S.-based coal mining site.
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Photoreduction
    

    During photoreduction, ultraviolet light is used to generate electron-hole pairs on the surface of a photocatalyst. Contaminants absorbed to the surface of the photocatalyst undergo redox reactions induced by the electrons and holes created by the exposure to ultraviolet light. The treated species are then desorbed and the surface of the photocatalyst is regenerated.

    • Treated Constituent: selenium
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: TiO2 has been found to be an effective photocatalyst for the reduction of both selenate and selenite in solution. Using ultraviolet light at wavelengths less than 380 nanometers at a pH of 3.5 in the presence of TiO2 and formic acid will reduce Se(VI) and Se(IV) to Se(0).
    • Long-term Maintenance: Unknown
    • System Limitations: Unknown
    • Costs: Unknown
    • Effectiveness: Concentrations of 20 μg/L to 40 μg/L of selenate and selenite were tested, with ultraviolet exposure times ranging between two and eight hours producing final effluentconcentrations between1 μg/L and 31 μg/L total selenium.
  • Zero Valent Iron (ZVI)
    

    Zero valent iron (ZVI) can be used to reduce selenium oxyanions to elemental selenium. Ferrous cations can also reduce selenate to selenite and subsequently remove selenite by adsorption to iron hydroxides.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Pilot-scale
    • Example Sites:
      • Dry Valley Mine, Idaho
      • Richmond Hill Mine, South Dakota
    • Operations: ZVI acts as a reducing agent in the redox reaction. The iron acts as both a catalyst and an electron donor for the reaction. Systems have typically applied the media in tanks or filter vessels that hold elemental iron. Pre-treatment in the form of pH adjustment may be required. Flow equalization/diversion is required as part of the treatment train.
    • Long-term Maintenance: ZVI media is finite and will require removal, disposal and replacement. Residuals will require TCLP testing to determine whether sludge should be disposed of as hazardous waste.
    • System Limitations: Requires long contact time. Forms iron oxides and sludge. Passivation and exhaustion of the iron. ZVI treatment is pH and temperature dependent. Due to iron content and reducing environment, aeration followed by clarification is recommended.
    • Costs: For column-based system (using steel wool): total installed cost for a 1 MGD system is estimated at $13.9 million (2013 USD). For stirred-tank based system (using granular ZVI): total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). Annual O&M cost is estimated at $3.2 million (2013 USD).
    • Effectiveness: At Richmond Hill Mine, the process is able to remove selenium to concentrations of 12 μg/L to 22 μg/L. Catenary Post pilot: 5 μg/L to 14 μg/L selenium was treated to> 5 μg/L.
• Sulfate
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • Nanofiltration Membrane Technology
    

    Nanofiltration is a form of filtration that uses a semi-permeable membrane. The pores are typically much larger than those used in reverse osmosis - close to one nanometer diameter - thus it is not as fine a filtration process as reverse osmosis.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Pilot-scale
    • Example Site: Kennecott South, Utah
    • Operations: Similar to reverse osmosis, but operates at one-third the pressure requirement. However, due to larger pore size, it is generally less effective. Requires small space and allows for modular construction. Can offer improved recoveries by rejecting a smaller portion of the salts including selenium, thereby reducing scale potential. Concentrates selenium, reducing the volume for ultimate reduction treatment.
    • Long-term Maintenance: Requires frequent membrane monitoring and maintenance. Membrane life expectancies vary from less than six months to over five years, depending on the quality of the feed solution. Requires treatment and disposal of the residuals.
    • System Limitations: There are pressure, temperature and pH requirements to meet membrane tolerances.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million. Annual O&M costs are estimated at $3.2 million (2013 USD). Capital costs for a single-stage filtration unit are quoted at USD $2,392/gpm feed: a plant treating 500 gpm would cost $1.2 million (2013 USD). Additional pre-treatment may be 50 percent of the treatment plant cost, ranging from $359 to $1,196 (2013 USD) per gpm feed. Operating costs are quoted at about $0.60-0.72/1,000 gallons for a nanofiltration unit, with an additional $0.12-0.18/1,000 gallons for additional pretreatment (2013 USD).
    • Effectiveness: Rejection rates: 60 percent for sodium chloride, 80 percent for calcium carbonate, and 98 percent for magnesium sulfate.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Reverse Osmosis
    

    Reverse osmosis is the pressure-driven separation through a semi-permeable membrane that allows water to pass through while rejecting contaminants.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Full-scale
    • Example Site: Kennecott South, Utah
    • Operations: Reverse osmosis is being used at the Kennecott South site as the primary technology for addressing the TDS and sulfate-impacted ground water extracted from the Zone A Sulfate Plume. At the Kennecott South site, reverse osmosis is used with nanofiltration for pre-treatment to avoid reverse osmosis membrane clogging, fouling or damage.
    • Long-term Maintenance: Kennecott site: the manufacturer of the membranes recommended a lifespan of three years, with periodic cleaning cycles. Kennecott’s planning and designing of the treatment system and optimizing operational activities around the quality of the feed water has allowed Kennecott to realize about six years of operational life on the membranes.
    • System Limitations: Requires high operating pressure. Not practical above 10,000 mg/L TDS. Requirements for pre-treatment and chemical addition to reduce scaling/fouling. Reverse osmosis permeate steam will require treatment prior to discharge to receiving waters to meet aquatic toxicity test. Frequent membrane monitoring and maintenance. May require temperature control at low and high temperatures to minimize viscosity effects.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million (2013 USD). Annual O&M costs are estimated at $3.2 million (2013 USD). Total capital costs for the Bingham Canyon Water Treatment Plant: about $16.1 million (2013 USD). Total yearly O&M costs (40 percent of these costs are labor and 24-hour maintenance expenses) for the Bingham Canyon Water Treatment Plant: about $1.3 million (2013 USD).
    • Effectiveness: Kennecott site BinghamCanyon Water Treatment Plant: has consistently seen permeate production efficiencies in the range of 71 to 72 percent. Demonstrated at full scale to remove selenium to <5 μg/L. Can remove 90 to 98 percent of TDS. A TDS removal efficiency of 98.5 percent was observed during pilot-testing of the membranes tested.
• Technetium
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Total Suspended Solids
  
  

  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
• Uranium
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Zinc
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Electrocoagulation
    

    In electrocoagulation, water is treated using electrolysis with graphite or stainless steel cathodes in conjunction with a metal anode. When a voltage is applied across the electrodes, insoluble precipitates are formed from ions of the metal electrode and selenium, arsenic or other metals present in the water.

    • Treated Constituents:
      • arsenic
      • copper
      • heavy metals
      • lead
      • phosphates
      • total suspended solids
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: A hybrid electrocoagulation-microfiltration process was tested in the laboratory using industrial wastewater from copper production to remove selenium, arsenic, copper, lead, zinc and cadmium. Water was pre-treated using lime neutralization and sedimentation followed by electrocoagulation. After electrocoagulation, water was filtered using a microfiltration flat sheet ceramic membrane. It then underwent a final lime neutralization step. Anode material selection is dependent on wastewater composition. Electrocoagulation can reduce sludge production significantly compared to other chemical processes such as iron reduction.
    • Long-term Maintenance: Systems are expected to require low maintenance and minimal operator attention. Regular replacement of electrodes is necessary.
    • System Limitations: High energy consumption. Raises the temperature of the water stream, rendering the direct discharge of the water difficult. The conductivity of the contaminated water must be high. Demonstrated to work more efficiently when lower concentrations of pollutants are present and pH is between 4 and 8.
    • Costs: For some applications, operating costs, including electric power, replacement of electrodes, pump maintenance and labor, can be less than $1.53 (2013 USD) per thousand gallons. Capital cost is significantly less than alternative technologies. A potential cost advantage of the electrocoagulation process is the generation of a lesser amount of sludge. The sludge is generally easier to dewater and may be beneficially recovered.
    • Effectiveness: Not proven for full-scale treatment of mining wastes. Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel and zinc aregenerally reduced by 95to 99 percent.
  • Electrocoriolysis ELCORTM
    

    Electrocoriolysis is a patented apparatus for separating and removing ionizable components dissolved in water by separating ionizable substances into fractions by the action of electric current and of Coriolis force. Liquid containing ionizable components is continuously fed in the apparatus, and the purified solvent and the solute in a concentrated solution are continuously removed while the liquid is rotated.

    • Treated Constituents:
      • cadmium
      • colloidal solids
      • ionizable metals
      • iron
      • manganese
      • particles and inorganic pollutants – besides copper
      • zinc
    • Scale: Lab-scale
    • Example Site: None Known
    • Operations: The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species.
    • Long-term Maintenance: Unknown
    • System Limitations: A system capable of being incorporated into fixed or mobile units for ex-situ surface wastewater treatment.
    • Costs: The technology is a continuous process, as opposed to a batch process to achieve cost-effective operation. The energy used is only the energy used in the electrolytic process. For commercial ELCOR™ devices, all sources of energy consumption must be included.
    • Effectiveness: One of the objects of the invention for the dynamic mode is a capacity of water treatment of up to, but not limited to 1.5 million gallons per day (MGD) for a single mobile or transportable unit. Recovery of water of adequate purity for reuse (e.g., irrigation).
  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.

All Treatment Technologies, Sorted by Site

• Almeda Mine, near Grants Pass, Oregon
  
  

  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
• Asarco’s West Fork site, Missouri
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Barker-Hughesville Mining District, Montana
  
  

  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
• Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Black Hawk and Central City, Colorado
  
  

  • Ceramic Microfiltration
    

    This treatment system is designed for the removal of heavy metals from an acid mine drainage system. It uses ceramic microfiltration to remove the precipitated solids.

    • Treated Constituent: metals
    • Scale: Pilot-scale
    • Example Sites:
      • Black Hawk and Central City, Colorado
      • Upper Blackfoot Mining Complex, near Lincoln, Montana
      • Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
    • Operations: Wastewater proceeds through a hydroxide precipitation step, which consists of adding sodium hydroxide. The pH will be adjusted to between 8.5 and 9.5 in a two-stage pH adjust system. The wastewater is then transferred to the concentration tank. At this point, the wastewater will be pumped through the cross-flow ceramic membrane. The absolute pore size of the membrane is 0.2 microns. Therefore, the only metals that will remain in the filtered water will be dissolved metals.
    • Long-term Maintenance: Ceramic membranes should be backwashed periodically and chemical cleaning is required at weekly to three-month intervals, depending on water quality. Backwash waste requires disposal or recycling. Chemical waste is generated during periodic cleanings.
    • System Limitations: High capital and O&M costs. Requirement of osmotic pressure. Fouling of membranes and scale production. Reliance on external power. Potential difficulty of concentrate disposal. Feed solution regarding quality predictability.
    • Costs: Pressure-driven membrane separation processes may involve higher capital and O&M costs than other water treatment technologies, depending on the size of the treatment unit, the volume of feed solution to be addressed, and the cleanup goals. The system at the Upper Blackfoot Mining Complex cost $666,192 (2013 USD).
    • Effectiveness: Ceramic microfiltration removes 99.5 percent ofthe heavy metals from wastewater streams with a system that meets the new proposedstandards. Upper Blackfoot Mining Complex: the system has been operating and meeting standards since January 2009.
• Brandy Camp site in Pennsylvania
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Brownton, Dola, Florence, Webster and Airport sites
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Buckeye Reclamation Landfill site, Belmont County, Ohio
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Burleigh Tunnel wetland, Colorado
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Casselman River Watershed, Somerset County, Pennsylvania
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
• Clear Creek (Gregory Gulch OU), Colorado
  
  

  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
• Commerce/Mayer site, Oklahoma
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Copper Basin Mining site, southeastern Tennessee
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Crystal underground copper mine, Butte, Montana
  
  

  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
• Dinero Tunnel, Colorado
  
  

  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
• Douglas Highwall site, Tucker County, West Virginia
  
  

  • Alkalinity-Producing Systems
    

    Alkalinity-Producing Systems (APS) combine the use of an anoxic limestone drain (ALD) and anaerobic compost wetlands. Ponded water overlies an 18-inch layer of organic material, usually compost, which is over an 18- to 24-inch layer of limestone. Acid water is ponded over the materials and the head created by the column of water forces the water through the organic material to filter out or precipitate ferric iron and to consume oxygen through organic matter decomposition.

    • Treated Constituents:
      • acidity
      • copper
      • ferrous iron
      • lead
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Copper Basin Mining site, southeastern Tennessee
      • Douglas Highwall site, Tucker County, West Virginia
    • Operations: Under current designs, ponded water about 3 to 6 feet in depth overlies an 18-inch layer of compost, which is over an 18- to 24-inch layer of limestone. Douglas Highwall site: The treatment system was constructed by digging a large trench along the old railroad grade. The first cell of the system was 1,225 feet long by 8 feet wide and 6 feet deep. About 2 feet of gravel-sized limestone were placed on the bottom with 4 feet of organic material (a peat, hay and soil mixture, 50:40:10) over the top. Cell I was filled with about 880 tons of limestone and about 1,450 cubic yards of organic material.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Flushing the wetlands may be a solution to increasing the treatment success and may aid in the prevention of clogging.
    • System Limitations: In situations where dissolved oxygen concentrations are >1 mg/L, the oxygen must be removed from the water before introduction into an anoxic limestone bed. For waters with high sulfate (>1,500 mg/L), gypsum may also precipitate. Noxious odors (hydrogen sulfide) are sometimes produced near the system.
    • Costs: The entire project cost at the Douglas Highwall site, including all reclamation activities and water treatment systems, was $2.2 million (2013 USD). The wetland-drain system costs were about $630,489 (2013 USD). The cost to treat the acid mine drainage with this wetland system is estimated to be $1,305 (2013 USD) per ton of acid neutralized. This cost per ton is almost equivalent to sodium hydroxide chemical treatment cost, which is estimated at $1,349 (2013 USD) per ton.
    • Effectiveness: The alkaline-producing systems are predicted toremove about 15 to 20 gallons per square meter per day of acid. This value represents the commonly accepted target that most wetlandbuilders expect.
• Dry Valley Mine, Idaho
  
  

  • Zero Valent Iron (ZVI)
    

    Zero valent iron (ZVI) can be used to reduce selenium oxyanions to elemental selenium. Ferrous cations can also reduce selenate to selenite and subsequently remove selenite by adsorption to iron hydroxides.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Pilot-scale
    • Example Sites:
      • Dry Valley Mine, Idaho
      • Richmond Hill Mine, South Dakota
    • Operations: ZVI acts as a reducing agent in the redox reaction. The iron acts as both a catalyst and an electron donor for the reaction. Systems have typically applied the media in tanks or filter vessels that hold elemental iron. Pre-treatment in the form of pH adjustment may be required. Flow equalization/diversion is required as part of the treatment train.
    • Long-term Maintenance: ZVI media is finite and will require removal, disposal and replacement. Residuals will require TCLP testing to determine whether sludge should be disposed of as hazardous waste.
    • System Limitations: Requires long contact time. Forms iron oxides and sludge. Passivation and exhaustion of the iron. ZVI treatment is pH and temperature dependent. Due to iron content and reducing environment, aeration followed by clarification is recommended.
    • Costs: For column-based system (using steel wool): total installed cost for a 1 MGD system is estimated at $13.9 million (2013 USD). For stirred-tank based system (using granular ZVI): total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). Annual O&M cost is estimated at $3.2 million (2013 USD).
    • Effectiveness: At Richmond Hill Mine, the process is able to remove selenium to concentrations of 12 μg/L to 22 μg/L. Catenary Post pilot: 5 μg/L to 14 μg/L selenium was treated to> 5 μg/L.
• Durango site, Colorado
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Eagle Mine, Pennsylvania
  
  

  • Metal- Removing Units (MRUs)
    

    MRU’s provide surface area for the growth of microbial biofilm which oxidizes manganese at much lower pH than a purely abiotic system.

    • Treated Constituents:
      • aluminum
      • iron
      • manganese
    • Scale: Pilot-Scale
    • Example Site: Eagle Mine, Pennsylvania
    • Operations: Each MRU Unit treats flows of 10-20 gpm of impacted water (average 15gpm) with light to heavy loads of dissolved and/or precipitating metals. MRU’s can be installed at end-of-pipe situations.
    • Long-term Maintenance: Metal holding capacity for 6 to 12 months between clean-outs, depending on loading. Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • System Limitations: Operational parameters:
      
      
      
      • Total Iron concentration of <0.35mg/L.
      
      • pH 6.8 and greater
      
      • Total N and Total P below 0.3mg/L
    • Costs: Install, including site specific material, equipment, and labor, cost is $9,500 per unit.
      
      
      
      Annual costs per MRU is $800-$1,000 per unit
    • Effectiveness: Average rates of manganese removal is >200 grams/m3/day.
      
      
      
      Manganese effluent of
      
      <1.0mg/L, and as low as
      
      0.1 mg/L are possible when MRU’s are kept within operational parameters.
• Fabius Coal Preparation Plant, Alabama
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• Friendship Hill wetland, Fayette County, Pennsylvania
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Frontier Hard Chrome, Vancouver, Washington
  
  

  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
• Gilt Edge Mine, South Dakota
  
  

  • Bauxsol™
    

    A material based on mud residues generated during alumina production has the capacity to neutralize acid and trap trace metals, with application to the treatment of acid rock drainage and mine tailings. BauxsolTM is prepared by chemical and physical modification of the caustic red mud residue generated by the Bayer process for extracting alumina from bauxite prior to electrolytic reduction. Pure BauxsolTM has a high acid-neutralizing capacity due to the abundance of amorphous and finely crystalline mineral phases that form weak bases. Pure BauxsolTM also has a very high trace metal trapping capacity. It also has a high capacity to trap and bind phosphate and some other chemical species. Reagents precipitate and settle within 48 hours to form a thin layer of sediment.

    • Treated Constituents:
      • acidity
      • aluminum
      • arsenic
      • cadmium
      • copper
      • cyanide
      • iron
      • lead
      • nickel
      • phosphates
      • zinc
    • Scale: Full-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: The treatment involves directly adding product(s) to the dammed water. The products can be dispersed into the dam using any conventional means and usually by existing infrastructure on site. The duration of the treatment, the selection of the product or products to be used, the intervals between applications of the various products will be determined by the degree of contamination and the size of the dam. After treatment, suspended particles in the water in the dam quickly settle to form a thin layer of sediment typically less than 5 millimeters thick. The extracted metals remain locked in the exhausted BauxsolTM sediment covering the tailings.
    • Long-term Maintenance: The technology allows for treated water to be safely discharged into the environment, obviating the need for indefinite storage of contaminated water. The sediment remaining after the treated water is discharged is able to be easily revegetated and will support healthy plant growth. Therefore, it is expected that there is no added requirement to treat or dispose of this sediment.
    • System Limitations: For effective treatment, the arsenic should be present as arsenate. If arsenite is present, it should be oxidized before treatment with Bauxsol™. For ponded water, a good solution is to use additives, such as ferrous sulfate, ferric chloride, aluminum sulfate or jarosite minerals to create more positive charges on the surfaces of mineral particles in the Bauxsol™. Bauxsol™ does remove arsenite, but the efficiency is only about 10 percent of that for the removal of arsenate. Arsenic uptake by Bauxsol™ is interfered with by anions such as phosphate and sulfate, but the interference is not serious.
    • Costs: BauxsolTM is relatively inexpensive and can occur in situ. There is no requirement to invest significant amounts of capital in treatment and process plants. BauxsolTM technology can be cost effective because it uses one waste technology to treat another and is not capital-intensive. The overall cost associated with using the process for any site is affected by the quantity of each product required for the treatment, which depends on the level of contaminants and the quantity of water, and the location of the site relative to the production facility. It is expected that most water bodies can be treated in the price range of $1,298 to $2,597 (2013 USD) per 1 million liters. However, specific costing is required on a job-by-job basis.
    • Effectiveness: BauxsolTM is designed to sequester over 99.99 percent of all heavy metals from soils and water, including acid, arsenic, cyanide and toxic metal combinations. Its acid neutralization capacity is also high, due to the abundance ofamorphous and finely crystalline mineral phases that form weak bases. Neutralizes 3.5 to 7.5 moles of acid/kg BauxsolTM (14 moles/kg if the pH is < 5). The ability of the minerals to trap trace metals is also strongly time-dependent. Although most of the initial metal trapping is complete within 24 hours, metal trapping will continue, albeit more slowly, for many months and the longer the material is left, the more tightly the metals are bound.
  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
  • Silica Micro Encapsulation (SME)
    

    SME encapsulates metals in an impervious microscopic silica matrix that prevents the metals from migrating or otherwise adversely affecting human health or the environment. Its physical and chemical components include an initial exothermic reaction and pH adjustment followed by an electrokinetic reaction and metal hydroxyl formation that leads to silica encapsulation.

    • Treated Constituents:
      • aluminum
      • arsenic
      • chromium
      • copper
      • iron
      • lead
      • mercury
      • radionuclides
      • zinc
    • Scale: Pilot-scale
    • Example Site: Gilt Edge Mine, South Dakota
    • Operations: At an evaluation project at the Gilt Edge Mine, waste rock was treated by building a portable enclosed structure next to the pit. Waste rock was treated in batches before it was loaded into the pit. The treatment facility included the enclosed structure, concrete mixing corral, slurry delivery unit, reagent delivery silos and a water storage tank. SME usually achieves control of contaminants in a single step, without the need for pre-treatment with chemicals or post-treatment flocculation or filtration.
    • Long-term Maintenance: Unknown
    • System Limitations: Expensive reagents
    • Costs: Total cost of Gilt Edge evaluation was $16.5 million (2013 USD). More than $13 million (2013 USD) of the total cost was spent on reagent.
    • Effectiveness: Gilt Edge Mine waste rock results: Mean iron reduction: 94.82 percent. Mean sulfate reduction mean: 33.18 percent. Mean aluminum reduction: 88.14 percent. Contrary to conventional treatment processes that typically degrade over time, the SME silica matrix continues to strengthen and tighten, further isolating contaminants from the environment.
• Golden Sunlight Mines, Inc., near Whitehall, Montana
  
  

  • EcoBond
    

    EcoBond forms a chemical chain that binds with metal ions forming insoluble metal complexes, reducing bioavailability. It produces a reaction that proceeds at ambient temperatures and does not produce secondary waste streams or gases.

    • Treated Constituents:
      • aluminum
      • arsenic
      • cadmium
      • chromium
      • lead
      • mercury
      • radionuclides
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Clear Creek (Gregory Gulch OU), Colorado
      • Golden Sunlight Mines, Inc., near Whitehall, Montana
      • Gilt Edge Mine, South Dakota
      • Frontier Hard Chrome, Vancouver, Washington
    • Operations: EcoBond can be deployed as a solid and tilled into acid-generating mine waste, or it can be applied as a liquid and sprayed from a hydroseed cannon to apply the compound to mine pit walls, high angle mine slopes and waste piles, and environmentally sensitive areas, such as riparian zones along streambeds. EcoBond is designed to react with the pyrite within 24 to 48 hours. The pH stabilizes at an environmentally safe level and, as a result, the available Fe+3 in the system decreases.
    • Long-term Maintenance: EcoBond has a 1,000-year simulated durability that has been verified by TCLP leaching parameters.
    • System Limitations: The EcoBond was not effective at reducing zinc and copper. Since the chemicals are applied with water, the reactions and subsequent effectiveness are limited to the surfaces that can be contacted. This makes treatment at depth or in large stockpiles difficult, since the flow paths in mine waste are complex.
    • Costs: Compared to similar technologies, EcoBond is relatively expensive. The total cost of the implemented technology at the Golden Mines demonstration was $33,934 (2013 USD). The per unit cost for this technology was $10.06 (2013 USD). That figure is based on a unit equaling 2,500 square feet.
    • Effectiveness: Reduced Al by 7 percent, Fe by 26 percent, Mn by 55 percent, Ni by 64 percent, and sulfate by 31 percent. Limited inhibition of copper andzinc. The maximum percent reduction of total metals from the EcoBond treated plot was less than 50 percent.
• Golinsky Mine, Shasta Lake City, California
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
• Greendale site, Clay County, West Virginia
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
  
  

  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
• Jennings Randolph Lake, Maryland
  
  

  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
• K-Basin at DOE's Hanford Facility, Hanford, Washington
  
  

  • Colloid Polishing Filter Method (CPFM)
    

    CPFM technology uses a proprietary compound (Filter Flow [FF] 1000) that consists of inorganic, oxide based granules. FF 1000 is formulated to remove heavy metals and radionuclides from water through a combination of sorption, chemical complexing and filtration. The technology developer, Filter Flow Technology, Inc., states that sorption on the FF 1000 accounts for the majority of the removal action.

    • Treated Constituents:
      • colloidal radionuclides
      • complex non-tritium radionuclides
      • heavy metals
      • ionic radionuclides
    • Scale: Pilot-scale
    • Example Sites:
      • Rocky Flats Environmental Technology site near Golden, Colorado
      • K-Basin at DOE's Hanford Facility, Hanford, Washington
      • N-Spring at DOE's Hanford Facility, Hanford, Washington
    • Operations: Pre-treated water is pumped from the bag filters to the colloid filter press units where heavy metals and radionuclides are removed and discharged.
    • Long-term Maintenance: The only major system components that require regular maintenance are the filter packs in the colloid filter press unit. They require periodic replacement or regeneration.
    • System Limitations: A CPFM system is not designed to operate at temperatures near or below freezing. If such temperatures are anticipated, the CPFM system and associated storage tanks should be kept in a heated shelter, such as a building or shed. In addition, piping to the system must be protected from freezing. A CPFM system requires potable water, electricity and compressed air for operation.
    • Costs: Ground water remediation costs for an l00-gpm CPFM system could range from about $3.23 to $11.32 (2013 USD) per 1,000 gallons, depending on contaminated ground water characteristics and duration of the remedial action. The cost of building a system is estimated to be about $121,244 to $161,658 (2013 USD). A skid-mounted system that treats water at flow rates up to 100 gpm could be built for about $242,487 to $323,316 (2013 USD).
    • Effectiveness: Filter Flow Technology, Inc. reports that its CPFM system has effectively removed trace ionic heavy metals and non-tritium radionuclides from water that has been pre-treated to reduce suspended solids.
• Kennecott South, Utah
  
  

  • Nanofiltration Membrane Technology
    

    Nanofiltration is a form of filtration that uses a semi-permeable membrane. The pores are typically much larger than those used in reverse osmosis - close to one nanometer diameter - thus it is not as fine a filtration process as reverse osmosis.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Pilot-scale
    • Example Site: Kennecott South, Utah
    • Operations: Similar to reverse osmosis, but operates at one-third the pressure requirement. However, due to larger pore size, it is generally less effective. Requires small space and allows for modular construction. Can offer improved recoveries by rejecting a smaller portion of the salts including selenium, thereby reducing scale potential. Concentrates selenium, reducing the volume for ultimate reduction treatment.
    • Long-term Maintenance: Requires frequent membrane monitoring and maintenance. Membrane life expectancies vary from less than six months to over five years, depending on the quality of the feed solution. Requires treatment and disposal of the residuals.
    • System Limitations: There are pressure, temperature and pH requirements to meet membrane tolerances.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million. Annual O&M costs are estimated at $3.2 million (2013 USD). Capital costs for a single-stage filtration unit are quoted at USD $2,392/gpm feed: a plant treating 500 gpm would cost $1.2 million (2013 USD). Additional pre-treatment may be 50 percent of the treatment plant cost, ranging from $359 to $1,196 (2013 USD) per gpm feed. Operating costs are quoted at about $0.60-0.72/1,000 gallons for a nanofiltration unit, with an additional $0.12-0.18/1,000 gallons for additional pretreatment (2013 USD).
    • Effectiveness: Rejection rates: 60 percent for sodium chloride, 80 percent for calcium carbonate, and 98 percent for magnesium sulfate.
  • Reverse Osmosis
    

    Reverse osmosis is the pressure-driven separation through a semi-permeable membrane that allows water to pass through while rejecting contaminants.

    • Treated Constituents:
      • metals
      • sulfate
    • Scale: Full-scale
    • Example Site: Kennecott South, Utah
    • Operations: Reverse osmosis is being used at the Kennecott South site as the primary technology for addressing the TDS and sulfate-impacted ground water extracted from the Zone A Sulfate Plume. At the Kennecott South site, reverse osmosis is used with nanofiltration for pre-treatment to avoid reverse osmosis membrane clogging, fouling or damage.
    • Long-term Maintenance: Kennecott site: the manufacturer of the membranes recommended a lifespan of three years, with periodic cleaning cycles. Kennecott’s planning and designing of the treatment system and optimizing operational activities around the quality of the feed water has allowed Kennecott to realize about six years of operational life on the membranes.
    • System Limitations: Requires high operating pressure. Not practical above 10,000 mg/L TDS. Requirements for pre-treatment and chemical addition to reduce scaling/fouling. Reverse osmosis permeate steam will require treatment prior to discharge to receiving waters to meet aquatic toxicity test. Frequent membrane monitoring and maintenance. May require temperature control at low and high temperatures to minimize viscosity effects.
    • Costs: For a 1 MGD system, total installed cost is estimated at $42.9 million (2013 USD). Annual O&M costs are estimated at $3.2 million (2013 USD). Total capital costs for the Bingham Canyon Water Treatment Plant: about $16.1 million (2013 USD). Total yearly O&M costs (40 percent of these costs are labor and 24-hour maintenance expenses) for the Bingham Canyon Water Treatment Plant: about $1.3 million (2013 USD).
    • Effectiveness: Kennecott site BinghamCanyon Water Treatment Plant: has consistently seen permeate production efficiencies in the range of 71 to 72 percent. Demonstrated at full scale to remove selenium to <5 μg/L. Can remove 90 to 98 percent of TDS. A TDS removal efficiency of 98.5 percent was observed during pilot-testing of the membranes tested.
• Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
  
  

  • Biological Reduction Of Selenium (BSeR™ And GE's ABMet®)
    

    This process uses specially developed biofilms that contain specific proprietary microorganisms in anaerobic bioreactors to reduce selenium (in the form of selenite and selenate) to elemental selenium. The end product is a fine precipitate of elemental selenium that is removed from the bioreactor with backflushing.

    • Treated Constituents:
      • mercury
      • metals
      • nitrate
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: ABMet® (formerly BSeR™) is a plug-flow, anaerobic bioreactor in which a selenium-reducing bacterial biofilm is supported on granular activated carbon. The system is inoculated with a mixture of proprietary and indigenous microorganisms, and reducing conditions are maintained by feeding a molasses-based nutrient mixture to the system. Systems can be custom designed for specific needs or pre-engineered as modular units for lower cost and quicker turnaround times.
    • Long-term Maintenance: The ABMet® system is designed to be relatively self-sustaining, requiring only the addition of a proprietary molasses-based nutrient. It does not require ongoing replenishment of microbial cultures or granular activated carbon.
    • System Limitations: Requires pre- and post-treatment steps to remove suspended solids, backwashing to prevent plugging and short-circuiting of flow, and temperature dependence.
    • Costs: GE estimates that for a 1 million gpd system, the estimated total installed cost would be about $32.1 million, with an annual O&M cost of about $3.2 million (2013 USD). O&M costs of $0.11 to $0.54 per 1,000 gallons of water treated (2013 USD).
    • Effectiveness: Process can treat flow rates as low as 5 gpm and as high as 1,400 gpm, while achieving up to 99 percent removal rates and discharging a treated effluent containing 5 μg/L of selenium. Nitrate (typical feed of 10-25 mg/L), possible effluent: ND<1mg/L. Selenium (typical feed of 10,000 μg/L), possible effluent: <0.005 μg/L. Mercury (typical feed of 5 μg/L), possible effluent: <0.012 μg/L.
  • Catalyzed Cementation Of Selenium
    

    Catalyzed cementation removes heavy metals from solution by cementation on an iron surface. The process is optimized by adding catalysts that increase selenium removal efficiency.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: Feed water is fed through a series of static mixers where pH is lowered before entering the elemental iron reactor. The reactor is a specialized tank designed to fluidize iron particles. The iron particles carried out are trapped in a small, cone-bottom tank and pumped back to the reactor for reuse. The processed feed water exiting the small, cone-bottom tank is routed to an 80-gallon reactor where the pH is raised again with a lime slurry and an oxidizer is added that completes the required reaction.
    • Long-term Maintenance: Solids that accumulated in the bottom of the thickener were periodically removed by a diaphragm pump. This sludge slurry was then processed by a filter press. The sludge liquid separated from the solids was returned to the thickener. The filter cake solids removed from the filter press were prepared for analysis or disposal by placing them in appropriate containers. Both filter cake samples were analyzed and found to be below the TCLP threshold value for selenium of 1 mg/L.
    • System Limitations: High chemical costs and solid waste disposal required. No long-term studies of the stability of the cementation waste have been undertaken.
    • Costs: Capital: $1,428,860 (2013 USD for all monetary values) Annual O&M Cost: $1,537,114 Net Present Value of Annual O&M Costs: $12,529,666 Total Net Present Value: $2,248,485 Net Present Value of $/1000 gallons treated: $10.78 Generic cost estimate: Based on 300 gpm plant, 2 mg/L selenium influent, Capital: $1.6 million, O&M: $1.6 million, Net Present Value: $12.5 million, $/1000 gal.: $10.78, $/kg selenium: $1,423.
    • Effectiveness: Garfield Wetlands-Kessler Springs water: water with total selenium concentrationsof 1,950 μg/L (primarily as selenate) was tested at a flow rateof 1 gpm. Even after extensive optimization in the field, the lowest effluent concentration achieved was 26 μg/L. Continued optimization in the laboratory achieved a mean effluent selenium concentration of 3 μg/L.
  • Ferrihydrite Adsorption (Iron Co-Precipitation)
    

    Ferrihydrite adsorption is a two-step physical adsorption process in which a ferric salt is added to the water source at proper conditions such that a ferric hydroxide and ferrihydrite precipitate results in concurrent adsorption of selenium on the surface. Also known as iron co-precipitation.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Full-scale
    • Example Site: Kennecott Utah Copper Corporation Garfield Wetlands-Kessler Springs Kennecott North site, Utah
    • Operations: Oxidation of ferrous iron to ferric iron and formation of ferric hydroxide is a common reaction in water that causes iron staining because the ferric hydroxide is insoluble and readily precipitates from water. Oxidation of water soluble ferrous iron to ferric iron is the most common method of removing iron from water. This process is relatively fast at pH values above 6.5 and very rapid at a pH of 8.5 or above. Pretreatment to optimize pH might be required. Flow equalization required as part of the treatment train.
    • Long-term Maintenance: Iron residuals with adsorbed selenium will require thickening and dewatering for disposal as solid waste. Will require toxicity characteristic leaching procedure (TCLP) testing to determine whether or not the sludge should be disposed of as hazardous waste.
    • System Limitations: Consistent removal to regulatory levels of selenium has not been proven. Potential release of selenium from ferrihydrite residuals. Gravity sedimentation may be required to separate iron solids and adsorbed metals from the water matrix. High operational costs typical of chemical treatment. Ion exchange capacity for selenium can be greatly reduced by competing ions (e.g., sulfates, nitrates).
    • Costs: Cost of a 1 MGD treatment system is estimated at $11.8 million (2013 USD), with an estimated annual O&M cost of about $4.3 million (2013 USD).
    • Effectiveness: At the Garfield Wetlands-Kessler Springs site, water contained 1,950 μg/L selenium, primarily as selenite. Using an iron concentration of 4,800 mg/L, the mean effluentselenium concentration was 90 μg/L. The minimum reported selenium concentration was 35 μg/L. Selenium removal is not proven to less than 5 μg/L.
• Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
  
  

  • Ceramic Microfiltration
    

    This treatment system is designed for the removal of heavy metals from an acid mine drainage system. It uses ceramic microfiltration to remove the precipitated solids.

    • Treated Constituent: metals
    • Scale: Pilot-scale
    • Example Sites:
      • Black Hawk and Central City, Colorado
      • Upper Blackfoot Mining Complex, near Lincoln, Montana
      • Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
    • Operations: Wastewater proceeds through a hydroxide precipitation step, which consists of adding sodium hydroxide. The pH will be adjusted to between 8.5 and 9.5 in a two-stage pH adjust system. The wastewater is then transferred to the concentration tank. At this point, the wastewater will be pumped through the cross-flow ceramic membrane. The absolute pore size of the membrane is 0.2 microns. Therefore, the only metals that will remain in the filtered water will be dissolved metals.
    • Long-term Maintenance: Ceramic membranes should be backwashed periodically and chemical cleaning is required at weekly to three-month intervals, depending on water quality. Backwash waste requires disposal or recycling. Chemical waste is generated during periodic cleanings.
    • System Limitations: High capital and O&M costs. Requirement of osmotic pressure. Fouling of membranes and scale production. Reliance on external power. Potential difficulty of concentrate disposal. Feed solution regarding quality predictability.
    • Costs: Pressure-driven membrane separation processes may involve higher capital and O&M costs than other water treatment technologies, depending on the size of the treatment unit, the volume of feed solution to be addressed, and the cleanup goals. The system at the Upper Blackfoot Mining Complex cost $666,192 (2013 USD).
    • Effectiveness: Ceramic microfiltration removes 99.5 percent ofthe heavy metals from wastewater streams with a system that meets the new proposedstandards. Upper Blackfoot Mining Complex: the system has been operating and meeting standards since January 2009.
• Keystone site, California
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Kittanning Run, Altoona, Pennsylvania
  
  

  • ChitoRem®
    

    ChitoRem® is a mixture of ground crab shells, calcium carbonate, and protein that can be used as the substrate in a BCR.

    • Treated Constituents:
      • aluminum
      • cadmium
      • copper
      • iron
      • zinc
    • Scale: Pilot-Scale
    • Example Sites:
      • Barker-Hughesville Mining District, Montana
      • Kittanning Run, Altoona, Pennsylvania
    • Operations: Applied as carbon substrate in BCR setup.
    • Long-term Maintenance: Not reported
    • System Limitations: Possible flow limitations.
    • Costs: Not reported
    • Effectiveness: Treatability study at the Barker site found pre-treatment with ChitoRem® removed all of the major metals to below water quality standards or to non-detect concentrations, with the exception of arsenic.
• Landusky Mine, Montana
  
  

  • Electro-biochemical Reactor
    

    The Electro-Biochemical Reactor (EBR) is a biological water treatment system based on redox reactions that directly supplies electrons to the microbes and reactor environment.

    • Treated Constituent: metals
    • Scale: Pilot-Scale
    • Example Sites:
      • Unnamed Metal Mine in the Yukon Territory, Canada
      • Landusky Mine, Montana
    • Operations: Electrons needed for microbial contaminant transformations are directly supplied using an applied voltage potential of 1 to 3 volts and very low current. These electrons represent a “free” energy source that is available independent of microbial nutrient metabolism.
    • Long-term Maintenance: Not Reported
    • System Limitations: Electrode configurations and materials are being examined with respect to electron transfer, charge density, lifespan, and observed impacts on nutrient utilization and biotransformation kinetics.
    • Costs: Not reported, but described as 40 percent lower capital costs of current biotreatment facilities.
    • Effectiveness: Average of 99 percent Se removal to ≤2.0 µg/L
      
      
      
      Average co-contaminant removals of 93.5 percent to 99.7 percent
• Latrobe wetland, Westmoreland County, Pennsylvania
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Leviathan Mine, California
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
  • Aeration Treatment Systems
    

    Aeration involves the mechanical introduction of oxygen to enhance the oxidation and decrease the solubility of metals in MIW.

    • Treated Constituents:
      • dissolved metals
      • pH
    • Scale: Full-Scale
    • Example Site: Leviathan Mine, California
    • Operations: Aeration is often applied in conjunction with acid-neutralizing agents (e.g., lime or caustic soda), chemical oxidants, flocculants, filtration, and settling basins.
    • Long-term Maintenance: Not reported
    • System Limitations: Not effective at sites where MIW has relatively high oxygen content.
    • Costs: Not reported
    • Effectiveness: Aeration has use as a sole remediation technology in limited situations, but is much more commonly applied in conjunction with other technologies.
• Lick Creek in southwestern Indiana
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Little Mill Creek site, Jefferson County, Pennsylvania
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Many sites in northwest Virginia
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• McCarty Highwall site in Preston County, West Virginia
  
  

  • Open Limestone Channels (OLCs)
    

    Open limestone channels are the simplest treatment systems, where limestone fragments are added directly to the stream channel semiannually or less frequently. These systems are typically applied when the mine drainage must be conveyed over some distance prior to treatment.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • lead
      • manganese
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Lick Creek in southwestern Indiana
      • Brandy Camp site in Pennsylvania
      • Many sites in northwest Virginia
      • Big Bear Lake near Hazelton in northeastern Preston County, West Virginia
      • Brownton, Dola, Florence, Webster and Airport sites
      • McCarty Highwall site in Preston County, West Virginia
    • Operations: An open channel conveying the MIW is lined with high-calcium limestone. The length of the channel and the channel gradient are design factors that can be varied. Optimal performance is attained on slopes exceeding 12 percent, where flow velocities keep precipitates in suspension and where suspended sediments help clean precipitates from limestone surfaces. OLCs can be used alone or in combination with other passive treatment systems. Residence time is critical to OLC performance, yet water velocity must remain high. A settling basin below the channel can be used to slow the water enough to drop out the suspended iron and aluminum hydroxides.
    • Long-term Maintenance: If properly constructed to withstand washout during high flows, OLCs should be nearly maintenance free. Open limestone channels can be useful in abandoned mine reclamation projects where one-time installation costs can be incurred and regular maintenance is not possible.
    • System Limitations: Limited success where metals are elevated and/or the acidity is also high. The design and operation of the limestone drain require special attention to accommodate the inevitable armoring and coating of the limestone. High-flow velocities to scour settled solids and clean precipitates from the limestone surfaces. Ability to periodically flush the system and clear accumulated precipitates and solids. Burial can be a more significant problem than armoring.
    • Costs: The cost of treatment varied between $32 and $9,303 per ton per year (2013 USD). Most OLCs treat water at or less than $300 per ton per year.
    • Effectiveness: The amount of alkalinity that these systems can usually generate is usually sufficient to raise the pH of the stream to at or near 6. The highest removal rates were withchannels on slopes of 45 to 60 percent and forMIW with acidity of 500 to 2,600 mg/L as calcium carbonate. OLCs can be effective as one element of a passive treatment system, but typically are not relied on for stand-alone MIW treatment.
• Metro site, Pennsylvania
  
  

  • Aluminator® Passive Treatment System
    

    The Aluminator© is an adaptation of a limestone drain in which aluminum hydroxide will accumulate for recovery.

    • Treated Constituents:
      • acidity
      • aluminum
      • iron
    • Scale: Pilot-scale
    • Example Sites:
      • Buckeye Reclamation Landfill site, Belmont County, Ohio
      • Casselman River Watershed, Somerset County, Pennsylvania
      • Little Mill Creek site, Jefferson County, Pennsylvania
      • Metro site, Pennsylvania
      • Greendale site, Clay County, West Virginia
    • Operations: Mine drainage enters the Aluminator© on the surface of the treatment unit and flows downward through the treatment column. A standing pool of water provides a buffer from flow surges, allows for a relatively even distribution of flow across the entire treatment area, and provides a positive head, essentially forcing the water down, into, and through the underlying substrates.
    • Long-term Maintenance: These systems require more operation and maintenance (O&M) than either aerobic wetlands or ALDs. Treatment effectiveness can be maintained by periodically flushing the system.
    • System Limitations: Efficiency can decrease with sustained or uncontrolled high flow events. There has been some decline in effectiveness of some of the systems over time but mainly in sites treating water with significant levels of aluminum and a low pH.
    • Costs: The total cost of the Metro site’s M1 system was $217,636. The cost of the M2 system was $131,901 (2013 USD).
    • Effectiveness: Metro site systems treated: Aluminum from 90/110 mg/L to 20/25 mg/L. Iron from 270/290 mg/L to 140/170 mg/L. pH from 2.8/2.7 to 5.8/5.8. Alkalinity from 0 to 90 and 100 mg/L CaCO3.
• Monticello Mill Tailings, Utah
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• N-Spring at DOE's Hanford Facility, Hanford, Washington
  
  

  • Colloid Polishing Filter Method (CPFM)
    

    CPFM technology uses a proprietary compound (Filter Flow [FF] 1000) that consists of inorganic, oxide based granules. FF 1000 is formulated to remove heavy metals and radionuclides from water through a combination of sorption, chemical complexing and filtration. The technology developer, Filter Flow Technology, Inc., states that sorption on the FF 1000 accounts for the majority of the removal action.

    • Treated Constituents:
      • colloidal radionuclides
      • complex non-tritium radionuclides
      • heavy metals
      • ionic radionuclides
    • Scale: Pilot-scale
    • Example Sites:
      • Rocky Flats Environmental Technology site near Golden, Colorado
      • K-Basin at DOE's Hanford Facility, Hanford, Washington
      • N-Spring at DOE's Hanford Facility, Hanford, Washington
    • Operations: Pre-treated water is pumped from the bag filters to the colloid filter press units where heavy metals and radionuclides are removed and discharged.
    • Long-term Maintenance: The only major system components that require regular maintenance are the filter packs in the colloid filter press unit. They require periodic replacement or regeneration.
    • System Limitations: A CPFM system is not designed to operate at temperatures near or below freezing. If such temperatures are anticipated, the CPFM system and associated storage tanks should be kept in a heated shelter, such as a building or shed. In addition, piping to the system must be protected from freezing. A CPFM system requires potable water, electricity and compressed air for operation.
    • Costs: Ground water remediation costs for an l00-gpm CPFM system could range from about $3.23 to $11.32 (2013 USD) per 1,000 gallons, depending on contaminated ground water characteristics and duration of the remedial action. The cost of building a system is estimated to be about $121,244 to $161,658 (2013 USD). A skid-mounted system that treats water at flow rates up to 100 gpm could be built for about $242,487 to $323,316 (2013 USD).
    • Effectiveness: Filter Flow Technology, Inc. reports that its CPFM system has effectively removed trace ionic heavy metals and non-tritium radionuclides from water that has been pre-treated to reduce suspended solids.
• Nickel Rim, Ontario
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Ohio Abandoned Bituminous Coal, southeast Ohio
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• Panoche Drainage District on the west side of the San Joaquin Valley, California
  
  

  • Algal-Bacterial Selenium Removal
    

    Algal treatment occurs via enhanced cyanobacterial and algal growth through nutrient addition. These additional nutrients increase algal biomass, thereby increasing selenium volatilization rates. In addition to treatment by volatilization, the algal biomass generated also serves as a carbon source to support microbial selenium reduction processes.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: Panoche Drainage District on the west side of the San Joaquin Valley, California
    • Operations: This system uses a combination of ponds containing algae and bacteria in which selenate is reduced to selenite and elemental selenium.
    • Long-term Maintenance: Unknown
    • System Limitations: Seasonally limited with treatment affected by duration of solar light and ambient temperatures. Difficulty of generating sufficient biomass to promote biological reduction and the inability to treat selenium to regulatory levels. Although much of the total selenium may be removed using the ABSR system, it is essential that the remaining selenium is in a form that is not readily bioavailable to aquatic organisms. In the ABSR system, if the selenium that remains has been transformed into a more bioavailable form, then the system could possibly be increasing the concentrations of selenium absorbed by aquatic life.
    • Costs: Potentially low-cost treatment, but can require large land area as well as the need for separation of the high-rate and reduction ponds. The preliminary total cost estimate for a 10-acre-foot per day ABSR facility is less than $291 (2013 USD) per acre-foot of treated drainage water. The ABSR system is one of the most economical and therefore easily adopted selenium removal systems.
    • Effectiveness: Preliminary results have shown that the method may be able to reduce the total selenium in the drainage water up to 80 percent. During 1997 and 1998, the best-performing ABSR plant configuration reduced nitrate by more than 95 percent and reduced total soluble selenium mass by 80 percent. The results of this studysuggest that the ABSR system may not be successfully reducing the bioavailability of selenium to aquatic organisms. Although microcosm data was limited, results lead to the conclusion that certain steps of the system may be increasing bioavailability.
• Richmond Hill Mine, South Dakota
  
  

  • Zero Valent Iron (ZVI)
    

    Zero valent iron (ZVI) can be used to reduce selenium oxyanions to elemental selenium. Ferrous cations can also reduce selenate to selenite and subsequently remove selenite by adsorption to iron hydroxides.

    • Treated Constituents:
      • arsenic
      • selenium
    • Scale: Pilot-scale
    • Example Sites:
      • Dry Valley Mine, Idaho
      • Richmond Hill Mine, South Dakota
    • Operations: ZVI acts as a reducing agent in the redox reaction. The iron acts as both a catalyst and an electron donor for the reaction. Systems have typically applied the media in tanks or filter vessels that hold elemental iron. Pre-treatment in the form of pH adjustment may be required. Flow equalization/diversion is required as part of the treatment train.
    • Long-term Maintenance: ZVI media is finite and will require removal, disposal and replacement. Residuals will require TCLP testing to determine whether sludge should be disposed of as hazardous waste.
    • System Limitations: Requires long contact time. Forms iron oxides and sludge. Passivation and exhaustion of the iron. ZVI treatment is pH and temperature dependent. Due to iron content and reducing environment, aeration followed by clarification is recommended.
    • Costs: For column-based system (using steel wool): total installed cost for a 1 MGD system is estimated at $13.9 million (2013 USD). For stirred-tank based system (using granular ZVI): total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). Annual O&M cost is estimated at $3.2 million (2013 USD).
    • Effectiveness: At Richmond Hill Mine, the process is able to remove selenium to concentrations of 12 μg/L to 22 μg/L. Catenary Post pilot: 5 μg/L to 14 μg/L selenium was treated to> 5 μg/L.
• Rocky Flats Environmental Technology site near Golden, Colorado
  
  

  • Colloid Polishing Filter Method (CPFM)
    

    CPFM technology uses a proprietary compound (Filter Flow [FF] 1000) that consists of inorganic, oxide based granules. FF 1000 is formulated to remove heavy metals and radionuclides from water through a combination of sorption, chemical complexing and filtration. The technology developer, Filter Flow Technology, Inc., states that sorption on the FF 1000 accounts for the majority of the removal action.

    • Treated Constituents:
      • colloidal radionuclides
      • complex non-tritium radionuclides
      • heavy metals
      • ionic radionuclides
    • Scale: Pilot-scale
    • Example Sites:
      • Rocky Flats Environmental Technology site near Golden, Colorado
      • K-Basin at DOE's Hanford Facility, Hanford, Washington
      • N-Spring at DOE's Hanford Facility, Hanford, Washington
    • Operations: Pre-treated water is pumped from the bag filters to the colloid filter press units where heavy metals and radionuclides are removed and discharged.
    • Long-term Maintenance: The only major system components that require regular maintenance are the filter packs in the colloid filter press unit. They require periodic replacement or regeneration.
    • System Limitations: A CPFM system is not designed to operate at temperatures near or below freezing. If such temperatures are anticipated, the CPFM system and associated storage tanks should be kept in a heated shelter, such as a building or shed. In addition, piping to the system must be protected from freezing. A CPFM system requires potable water, electricity and compressed air for operation.
    • Costs: Ground water remediation costs for an l00-gpm CPFM system could range from about $3.23 to $11.32 (2013 USD) per 1,000 gallons, depending on contaminated ground water characteristics and duration of the remedial action. The cost of building a system is estimated to be about $121,244 to $161,658 (2013 USD). A skid-mounted system that treats water at flow rates up to 100 gpm could be built for about $242,487 to $323,316 (2013 USD).
    • Effectiveness: Filter Flow Technology, Inc. reports that its CPFM system has effectively removed trace ionic heavy metals and non-tritium radionuclides from water that has been pre-treated to reduce suspended solids.
• San Joaquin, California
  
  

  • Evaporation
    

    Evaporation is the vaporization of pure water to concentrate contaminants as a solid or in a brine stream.

    • Treated Constituent: selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: Solar evaporation ponds and enhanced evaporation systems have been examined for selenium treatment. Enhanced evaporation system accelerates evaporation rates by spraying water in the air. The use of mechanical evaporators can produce concentrated brine followed by crystallization, drying and solid waste disposal. Requires minimal energy and no pre-treatment. Mechanical evaporation machines can rapidly increase the evaporation process, with up to 14 times more efficiency than space taken by the same area of pond.
    • Long-term Maintenance: Sediments accumulated during evaporation require disposal. Land-based mechanical evaporation machines require more attention if wind direction varies greatly and if the site is sensitive to spray droplet drift. A pond-based unit requires less operator attention.
    • System Limitations: Solar evaporation is likely unsuitable for metals removal from MIW due to the prevailing cold climate where operations are typically located. Enhanced evaporation system has not been applied to MIW treatment. Risk of infiltration to ground water (depending on liner type) could occur. May pose a risk to wildlife. An ecological risk assessment should be performed prior to implementation.
    • Costs: The cost of constructing additional storage ponds and the added cost of cleanup and revegetation are often prohibitive. Lower costs because the technology relies on solar radiation for evaporation. Evaporation pond treatment in the San Joaquin valley cost $754 USD per acre-foot of treated water, with $3.3 million/year (2013 USD) for O&M.
    • Effectiveness: Evaporation ponds reduced selenium concentrations by only 25 percent in the San Joaquin Valley.
  • Fluidized Bed Reactor (FBR)
    

    In a fluidized, or pulsed, bed reactor, contaminated water is passed through a granular solid media at high enough velocities to suspend or fluidize the media, creating a completely mixed reactor configuration for attached biological growth or biofilm.

    • Treated Constituents:
      • nitrate
      • perchlorate
      • selenium
    • Scale: Pilot-scale
    • Example Site: San Joaquin, California
    • Operations: In this type of reactor, a fluid is passed through a granular solid material at velocities sufficient to suspend or fluidize the solid media. Media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. FBRs allow for shorter residence times for treatment and a smaller overall footprint due to the vertical orientation of the vessels and the efficiency of treatment.
    • Long-term Maintenance: Requires daily cleaning of the influent strainer, tank walls, recycle tank and piping due to biological growth. Envirogen FBR systems are designed to be operated continuously – they do not require cyclical backwash operations.
    • System Limitations: Presence of excess nitrates necessitates sufficient carbon or energy source, leading to additional biomass. External carbon source may be required. Waste biomass may be hazardous waste.
    • Costs: Total installed cost for a 1 MGD system is estimated at $11.8 million (2013 USD). The annual O&M cost for the same system is estimated at $3.2 million (2013 USD). A recent third-party analysis performed for the North American Mining Council showed that initial capital costs for an FBR system can be one-third or less the cost of a packed bed reactor system designed for similar treatment requirements.
    • Effectiveness: At a pilot test with a flow rate of 1 gpm, total selenium decreased from 520 μg/L to 380 μg/L. Envirogen FBR technology demonstrated the abilityto achieve <5 ppb selenium over a 10-month period in treatingmining leachate at a U.S.-based coal mining site.
• Somerset wetland, Somerset County, Pennsylvania
  
  

  • Constructed Wetlands
    

    Constructed wetlands use soil- and water-borne microbes associated with wetland plants to remove dissolved metals from acid mine drainage. Constructed wetlands can be designed as aerobic wetlands, anaerobic horizontal-flow wetlands and vertical-flow ponds (vertical-flow wetlands).

    • Treated Constituents:
      • Iron
      • arsenic
      • cadmium
      • copper
      • dissolved aluminum
      • lead
      • manganese
      • nickel
      • selenium
      • sulfate
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Keystone site, California
      • Burleigh Tunnel wetland, Colorado
      • Asarco’s West Fork site, Missouri
      • Commerce/Mayer site, Oklahoma
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Friendship Hill wetland, Fayette County, Pennsylvania
      • Latrobe wetland, Westmoreland County, Pennsylvania
      • Somerset wetland, Somerset County, Pennsylvania
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: Design of a constructed wetland for the treatment of acid mine drainage varies based on a site’s characteristics. The most important design considerations are biochemical processes, loading rate and retention time, slope, substrate, vegetation, sediment control, morphometry, seasonality, and regulatory issues.
    • Long-term Maintenance: Constructed wetlands can operate for long periods of time with minimal O&M. The concentration of contaminants must be monitored to maintain ecological health of the system. Disposal of accumulated material is required.
    • System Limitations: Requires appropriate land for wetlands construction. High initial construction cost. Sensitivity to high throughput excursions. Disposal of accumulated material. Relatively slow performance in comparison to other treatment technologies. Dependency on local climatic conditions, which may lead to reduced efficiency during colder seasons. Potential to become a permanent feature of the ecosystem, requiring long-term maintenance.
    • Costs: The U.S. Naval Facilities Engineering Service Center’s Remediation Technology Online Help Program lists the costs of constructed wetlands treatment at between $0.15 and $1.00 (2013 USD) per gallon of water treated.
    • Effectiveness: Typical range of removal efficiencies observed in wetlands constructed to treat drainage: pH: >6 for coal mine drainage and metal mine drainage. Acidity: 75-90 percent for coal mine drainage and metal mine drainage. Sulfate: 10-30 percent for coal mine drainage and metal mine drainage. Iron: 80-90+ percent forcoal mine drainage and metal mine drainage. Aluminum: 90+ percent for coal mine drainage and metal mine drainage. Copper: 80-90+ percent for metal mine drainage. Zinc: 75-90+ percent for metal mine drainage. Cadmium: 75-90+ percent for metal mine drainage. Lead: 80-90+ percent for metal mine drainage.
• Soudan Park, Minnesota
  
  

  • Ion Exchange
    

    Ion exchange is the reversible exchange of contaminant ions from a process stream with more desirable ions of a similar charge adsorbed to solid surfaces known as ion exchange resins. This process provides hardness removal, desalination, alkalinity removal, radioactive waste removal, ammonia removal and metals removal.

    • Treated Constituents:
      • hardness
      • metals
    • Scale: Pilot-scale
    • Example Site: Soudan Park, Minnesota
    • Operations: Ion exchange is generally used as a polishing step to remove low-concentration contaminants, and often requires pre-treatment prior to application. Important considerations include type of resin, the volume and type of regenerant, the backwash water source, backwash quantities, the need for pre-filtration of solids, the column configuration, the need for pH adjustment before and after ion exchange, and the cycle length. Flow equalization/diversion is required as part of the overall system.
    • Long-term Maintenance: Once ion exchange sites on the resin are completely full, the resin must be regenerated in order to be used again. Scale removal may be required to prevent resin fouling. The higher the concentration of TDS in the water, the more frequently the resin will need to be regenerated with caustic soda and rinsed with backwash water.
    • System Limitations: Pre-filtration may be needed to remove suspended solids that would plug the resin bed. Organics, strong oxidants and high temperatures can degrade the resin. Resins may need to be disposed of if they cannot be regenerated, meaning high disposal costs. High sulfate can result in exhaustion of the resin.
    • Costs: Estimated annual costs for one site, the Soudan Mine discharge (average flow of 86,400 gpd), are about $168,993 (2013 USD).
    • Effectiveness: Generally greater than 90 percent recovery rates, given resin specificity for target constituent and regenerant and back wash requirements. A lab test was performed using process solutions fromKennecott Mining Company containing 0.93 mg/L selenium and 80 mg/L sulfate atpH 4. The resin removed selenium to less than 1 μg/L.
• Stowell Mine, Shasta Lake City, California
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.
• Summitville Mine, Colorado
  
  

  • Aquafix
    

    The Aquafix system uses the recognized effectiveness of lime addition to raise the pH of Mining-Influenced Water (MIW) to precipitate metals.

    • Treated Constituents:
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Pilot-scale
    • Example Sites:
      • Dinero Tunnel, Colorado
      • Summitville Mine, Colorado
      • Jennings Randolph Lake, Maryland
      • Crystal underground copper mine, Butte, Montana
      • Almeda Mine, near Grants Pass, Oregon
    • Operations: Water passing through the water wheel drives the auger, which distributes lime pellets into the stream at a fully adjustable rate, to ensure precise treatment levels. In a pilot study, a rock drain downstream from the treatment unit promoted dissolution of the lime. Effluent from the rock drain was further aerated in a mixing tank and subsequently sent to two settling tanks connected in series. The calculated total residence time of the system was about two days, but the flow rate in this system tended to fluctuate, affecting residence time.
    • Long-term Maintenance: Requires regular inspections to ensure that proper flow is maintained through the treatment systems. Aquafix units do not require constant monitoring. Units can operate continuously for many days without human attention.
    • System Limitations: At the Colorado site (Dinero Tunnel), the inlet hose became clogged with iron hydroxides (yellow boy), which reduced the flow and the lime dispensing rate. Revolutions per minute and pH values were consistently lower than expected. It became necessary to disconnect the hose each week and flush out the sludge. Operational problems also were encountered in Oregon with accumulation of the granular lime below the dispenser.
    • Costs: The average cost for a permanent Aquafix system designed to treat 25 gallons per minute (gpm) is expected to be about $89,531 (2013 USD) per year, based on a 15-year system life. Jennings Randolph Lake: Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1,000 gallons of water. A portable Aquafix unit costs about $21,582 (2013 USD).
    • Effectiveness: At the Oregon site, metal concentration reductions ranged from 94 percent to 99 percentfor the principal acid mine drainage metals ofaluminum, cadmium, copper, iron, lead, manganese and zinc. Removal efficiencies: Al - 97%, Cu – 99%, Fe- 99%, Mn - 97% Zn - 99%
  • Successive Alkalinity Producing System (SAPS)
    

    Successive alkalinity producing systems (SAPS) combine the use of an ALD and an organic substrate into one system. A SAPS is a pond that contains a combination of limestone and compost overlain by several feet of water. Mine drainage enters at the top of the pond and flows down through the compost, where the drainage gains alkalinity and the oxidation-reduction potential decreases. It then flows into the limestone below. Dissolution of the limestone increases the alkalinity of the water, resulting in precipitation.

    • Treated Constituents:
      • acidity
      • aluminum
      • copper
      • iron
      • manganese
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Summitville Mine, Colorado
      • Howe Bridge, REM, Schnepp Road, Filson sites, Jefferson County, Pennsylvania
    • Operations: At the Summitville Mine, after the pretreatment of the settling pond, MIW feeds into the SAPS pond for alkalinity treatment and precipitation. Precipitated metals are collected in a subsequent settling pond; discharge from the settling pond was then routed through a polishing channel for final treatment. The total treatment time through the entire treatment system was between 14 and 15 days and about four days through the SAPS ponds. Water with high metal loads can be passed through additional SAPS to reduce high acidity. Iron and aluminum clogging of limestone and pipes can be removed by flushing the system.
    • Long-term Maintenance: Compost removal and replacement. Replenishment of the compost after two to three years may extend the system’s effectiveness. Maintenance of bed permeability. Continual monitoring of both influent and effluent water chemistry and metal removal.
    • System Limitations: With high flows and high metals, more complicated designs may be needed that incorporate treatment cells in a series with increased numbers of settling ponds. More complex systems are costly to build and a larger area is needed. Successful SAPS have used mushroom compost. Other types of organic material have problems with plugging.
    • Costs: The average estimated cost for a SAPS based on a 15-year system life range from $72,439 (2013 USD) for a 5-gpm system to $150,983 (2013 USD) per year for a 100-gpm system. For the 5-gpm system, treatment cost is estimated at $0.03 per gallon of MIW. For the 100-gpm system, the cost is estimated at $0.003 per gallon (2013 USD).
    • Effectiveness: SAPS performance has been inconsistent, but can be effective. Typical observed removal efficiencies: Al – 97 percent Cu –– 90 percent Fe –– 64 percent Mn –– 11 percent Zn –– 57 percent
• Tecumseh - AML site 262, Indiana
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• Tenmile Creek, Montana
  
  

  • Permeable Reactive Barriers
    

    A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity.

    • Treated Constituents:
      • aromatics
      • arsenic
      • cadmium
      • chromium
      • cobalt
      • copper
      • ethane
      • ethene
      • iron
      • lead
      • manganese
      • methane
      • nickel
      • nitrate
      • phosphate
      • propane
      • radionuclides
      • selenium
      • sulfate
      • technetium
      • uranium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Durango site, Colorado
      • Tenmile Creek, Montana
      • Nickel Rim, Ontario
      • Monticello Mill Tailings, Utah
    • Operations: Commercial PRBs are currently built as either funnel-and-gate or continuous PRB systems. Both have required some degree of excavation and been limited to relatively shallow depths of 50 to 70 feet or less. The residence time required and the anticipated ground-water velocity through the PRB are used to determine the size of PRB needed to achieve the desired treatment level.
    • Long-term Maintenance: Minimal maintenance is required for PRBs, but performance can decline due to clogging. Depending on several site-specific conditions, PRBs are now expected to last 10 to 30 years before reactivity or hydraulic issues will result in the need for maintenance.
    • System Limitations: The barrier system may not be a stand-alone technology. The remediation timeframe may require a long treatment period, depending on the size of the contaminated area. Biofouling and mineral precipitation may limit the permeability of the wall system if not managed properly. In both designs, it is necessary to keep the reactive zone permeability equal to or greater than the permeability of the aquifer to avoid diversion of the flowing waters around the reactive zone.
    • Costs: Costs of PRB systems vary depending on site-specific circumstances. The length and especially the depth tend to be the biggest factors that drive the cost of the installation. PRB system installations typically cost more than conventional pump-and-treat technology installations. At the Durango site, treatment costs were about $29.68 (2013 USD) per 1,000 gallons treated. For a PRB installed in Monkstown, Northern Ireland, total treatment costs were $1.4 million (2013USD).
    • Effectiveness: At Monticello, Utah site, influent of 40 μg/Lselenium was treated to below detection limits. At the Durango, Colorado site, influent of 359 μg/L selenium was treated to 8 μg/L.
• Tennessee Valley Authority site, Alabama
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• Unnamed Metal Mine in the Yukon Territory, Canada
  
  

  • Electro-biochemical Reactor
    

    The Electro-Biochemical Reactor (EBR) is a biological water treatment system based on redox reactions that directly supplies electrons to the microbes and reactor environment.

    • Treated Constituent: metals
    • Scale: Pilot-Scale
    • Example Sites:
      • Unnamed Metal Mine in the Yukon Territory, Canada
      • Landusky Mine, Montana
    • Operations: Electrons needed for microbial contaminant transformations are directly supplied using an applied voltage potential of 1 to 3 volts and very low current. These electrons represent a “free” energy source that is available independent of microbial nutrient metabolism.
    • Long-term Maintenance: Not Reported
    • System Limitations: Electrode configurations and materials are being examined with respect to electron transfer, charge density, lifespan, and observed impacts on nutrient utilization and biotransformation kinetics.
    • Costs: Not reported, but described as 40 percent lower capital costs of current biotreatment facilities.
    • Effectiveness: Average of 99 percent Se removal to ≤2.0 µg/L
      
      
      
      Average co-contaminant removals of 93.5 percent to 99.7 percent
• Unspecified mine, South Africa
  
  

  • Electrodialysis Reversal (EDR)
    

    Electrodialysis (ED) is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current voltage. EDR is a variation on the ED process, which uses electrode polarity reversal to automatically clean membrane surfaces.

    • Treated Constituents:
      • arsenic
      • dissolved solids
      • nitrate
      • radium
    • Scale: Full-scale
    • Example Site: Unspecified mine, South Africa
    • Operations: EDR works the same way as ED, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed and so are the chemical reactions at the electrodes. This polarity reversal helps prevent the formation of scale on the membranes.
    • Long-term Maintenance: The ED stack must be disassembled, mechanically cleaned and reassembled at regular intervals. The concentrate waste stream, electrode cleaning flows, and residuals from the pretreatment process will be a part of a typical waste stream flow and will require disposal.
    • System Limitations: Total dissolved solids (TDS) economical up to 8,000 mg/L, but often run at waters of 1,200 mg/L pH: 2.0 to 11.0 Iron (Fe+2): 0.3 ppm Mn (+2): 0.1 ppm H2S: up to 1 ppm
    • Costs: Unknown
    • Effectiveness: When combined with reverse osmosis at South African mine, thesystem treats MIW with5,000 mg/L TDS with high calcium sulfate content down to <40 mg/L TDS.
• Upper Blackfoot Mining Complex, near Lincoln, Montana
  
  

  • Ceramic Microfiltration
    

    This treatment system is designed for the removal of heavy metals from an acid mine drainage system. It uses ceramic microfiltration to remove the precipitated solids.

    • Treated Constituent: metals
    • Scale: Pilot-scale
    • Example Sites:
      • Black Hawk and Central City, Colorado
      • Upper Blackfoot Mining Complex, near Lincoln, Montana
      • Kennecott Utah Copper, LLC, (Kennecott) Bingham Canyon Mine, Utah
    • Operations: Wastewater proceeds through a hydroxide precipitation step, which consists of adding sodium hydroxide. The pH will be adjusted to between 8.5 and 9.5 in a two-stage pH adjust system. The wastewater is then transferred to the concentration tank. At this point, the wastewater will be pumped through the cross-flow ceramic membrane. The absolute pore size of the membrane is 0.2 microns. Therefore, the only metals that will remain in the filtered water will be dissolved metals.
    • Long-term Maintenance: Ceramic membranes should be backwashed periodically and chemical cleaning is required at weekly to three-month intervals, depending on water quality. Backwash waste requires disposal or recycling. Chemical waste is generated during periodic cleanings.
    • System Limitations: High capital and O&M costs. Requirement of osmotic pressure. Fouling of membranes and scale production. Reliance on external power. Potential difficulty of concentrate disposal. Feed solution regarding quality predictability.
    • Costs: Pressure-driven membrane separation processes may involve higher capital and O&M costs than other water treatment technologies, depending on the size of the treatment unit, the volume of feed solution to be addressed, and the cleanup goals. The system at the Upper Blackfoot Mining Complex cost $666,192 (2013 USD).
    • Effectiveness: Ceramic microfiltration removes 99.5 percent ofthe heavy metals from wastewater streams with a system that meets the new proposedstandards. Upper Blackfoot Mining Complex: the system has been operating and meeting standards since January 2009.
• Valzinco Mine, Virginia
  
  

  • Anoxic Limestone Drains (ALD)
    

    ALDs are a simple treatment method – buried limestone in air-tight trenches intercepts acidic discharge water. ALDs are used to generate alkalinity and must be followed by ponds and aerobic wetlands that oxidize and remove the dissolved metals.

    • Treated Constituent: acidity
    • Scale: Full-scale
    • Example Sites:
      • Fabius Coal Preparation Plant, Alabama
      • Tennessee Valley Authority site, Alabama
      • Tecumseh - AML site 262, Indiana
      • Ohio Abandoned Bituminous Coal, southeast Ohio
      • Hartshorne/Whitlock-Jones site, Hartshorne, Oklahoma
      • Copper Basin Mining site, southeastern Tennessee
      • Valzinco Mine, Virginia
    • Operations: Construction of an ALD consists of a trench containing limestone encapsulated in a plastic liner and covered with clay or compacted soil to maintain anoxic conditions, as well as to prevent water infiltration and to keep carbon dioxide from escaping. The width and length of the trench are based on the levels of dissolved metals present in the mine drainage, the retention time needed to raise the pH, as well as the amount of area that is available for construction. The ALD may be capped with topsoil and vegetation to control erosion. The two factors that must be considered when sizing an anoxic limestone drain are the accommodation of the maximum probable flow and the desired longevity of the drain.
    • Long-term Maintenance: Routine maintenance is typically limited to inspection of the surface for evidence of leakage in the anoxic cover material, and periodic cleaning of the discharge point to remove accumulated iron oxides. The systems are generally designed for limestone replenishment every 15 to 25 years, depending on the characteristic of the drainage flow. Maintenance costs for ALDs are not expected to be significant. Apart from monitoring costs, costs should be limited to periodic inspection of the site and maintenance of the vegetation cover.
    • System Limitations: Metal removal must occur elsewhere to prevent clogging of the bed and system failure. ALDs must be kept anoxic to prevent the oxidization of soluble ferrous iron to the insoluble ferric species. Although ALDs are documented to have success in raising pH, the differing chemical characteristics of the influent mine water can cause variations in alkalinity generation and retention of metals. Most ALD systems exhibit reduced effectiveness over time and eventually require maintenance or replacement. Use of ALDs as a standalone treatments system might not achieve effluent compliance limits.
    • Costs: The cost of installing ALDs can vary, depending largely on location and chemical makeup of the influent. Operators of the Tennessee Valley Authority abandoned mine site in Alabama reported that their capital cost was about $0.27 per 1,000 gallons of water and their O&M costs were about $0.11 per 1,000 gallons of water (2013 USD). A typical ALD at most locations in Canada is expected to cost in the range of $6,000 to $37,000 (2013 USD), depending on chosen dimensions and design flow. This estimate would not apply to more remote sites or sites where an ALD would require extensive excavation or blasting.
    • Effectiveness: Where influent mine water contained less than 1 mg/L of both ferric iron and aluminum, ALDs produced consistent concentrations of alkalinity for over 10 years. Alkalinity concentrations in the effluent range from 80 mg/L to 320 mg/L as CaCO3, with near maximum levels reached after about 15 hours of detention in the ALD. An ALD receiving influent mine water containing 21 mg/L of aluminum failed within 8 months due to clogging.
• West Fork Mine, Missouri
  
  

  • Biochemical Reactors (Bioreactors)
    

    Biochemical reactors (BCRs), or bioreactors, treat MIW by using microorganisms to transform contaminants and to increase pH in the treated water. BCRs can be designed as open ponds and buried ponds or within tanks or even in trenches between mine waste and a surface water body. The most commonly used BCRs for treating mining influenced water are operated anaerobically. They are also called “sulfate-reducing” bioreactors.

    • Treated Constituents:
      • arsenic
      • cadmium
      • chromium
      • copper
      • lead
      • nickel
      • selenium
      • zinc
    • Scale: Full-scale
    • Example Sites:
      • Golinsky Mine, Shasta Lake City, California
      • Leviathan Mine, California
      • Stowell Mine, Shasta Lake City, California
      • Central City/Clear Creek Superfund Site, Idaho Springs, Colorado
      • West Fork Mine, Missouri
      • Copper Basin Mining site, southeastern Tennessee
    • Operations: The design of BCRs is controlled by the site-specific MIW characteristics of pH, flow, temperature and the type and concentration of metals. Application requires bench-scale and pilot-scale testing to estimate site- and effluent-specific parameters. Sulfate-reducing bioreactors typically require large amounts of organic materials that are usually considered waste. Enhanced sulfate-reducing bioreactor cells can consume liquid organic wastes like antifreeze or cheese whey.
    • Long-term Maintenance: Minimal maintenance is required for bioreactors, but performance can decline due to clogging. Since the passive systems typically do not require any external power and can operate without continual maintenance, they are attractive for remote and abandoned sites.
    • System Limitations: BCRs require a large footprint. Substrate degrades over time. BCR design is influenced greatly by available space, since the water to be treated must reside within the BCR for a certain period of time, called retention or residence time. The most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for sulfate-reducing bioreactor showed that a combination of organic sources is preferable over a unique source.
    • Costs: Bioreactors should have lower O&M costs than standard chemical treatment approaches. Bioreactors can be costly to construct since generally the systems are lined and often contain additional components, such as settling ponds and/or aerobic polishing cells. As constructed, the Leviathan Mine system requires 0.75 acres. The capitol costs for construction of the gravity-flow operation amounted to $1,062,100 (2013 USD) and changing to the recirculation mode added nearly $38,000, for a total of approximately $1.1 million (2013 USD). Operating at an average flow rate of 10 gpm, the O&M costs of the system are $19.51 (2013 USD) per 1,000 gallons of treated water.
    • Effectiveness: Various types of media for gravel pit seepage can result in 98 percent removal of selenium and can achieve less than 5 micrograms per liter of selenium. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed inCanada and the United States and efficiently removed sulfate and metals for periods up to5 years. Manganese and arsenic are less efficiently removed as sulfides in passive bioreactors.