The cost of a remedial technology is one of the key factors in determining its applicability. More specifically, a technology’s cost versus the benefits it provides compared to other alternatives will often be the deciding factor in its implementation. The costs and benefits of a particular technology must be assessed on a site-specific basis.
The objectives of this chapter are to provide information on the factors that drive the economics of surfactant/cosolvent systems, to provide information that can be used to develop site-specific cost estimates, and to provide a range of costs that can be expected for these technologies. A general discussion of the components contributing to remediation system costs is presented first, followed by two hypothetical examples and, finally, a summary of the costs analysis. The hypothetical examples have been developed to illustrate the most important components influencing system costs and to provide a range of possible costs. Because little information is available on full-scale surfactant/cosolvent flushing systems, there is no actual cost data available. Consequently, we must rely on cost estimates for example sites to provide a range of possible costs.
Relevance
This section presents information on the components that typically make up a surfactant/cosolvent flushing project and that should be itemized in the cost estimate. This section can be skipped if the reader is interested only in evaluating the applicability of surfactant/cosolvent flushing. Readers who have already decided to implement a surfactant/cosolvent project should read this section.
Key Concepts
• Components included in a cost estimate could include site characterization, laboratory testing, numerical simulations, field demonstrations, and full-scale design, construction, operations and maintenance, and monitoring.
• The design approach and cost can vary depending on the project.
• Construction costs typically include the cost for the actual facilities (direct capital costs) plus a number of indirect capital costs, including mechanical/electrical installation, general requirements, permitting and legal fees, services during construction, operations and maintenance (O&M) manual preparation, startup, demolition and site restoration, equipment salvage, and contingencies.
• The O&M and monitoring costs include costs for labor, materials, chemicals, utilities, laboratory analysis, and disposal of residues.
As discussed in Chapter 5, additional site characterization often will be necessary prior to the full-scale implementation of a surfactant/cosolvent flushing system. The cost for this site characterization will depend on the amount of information previously obtained and the design requirements. For example, a partitioning tracer test to estimate the volume and spatial extent of NAPL can be conducted once a decision is made to implement surfactant/cosolvent flushing at a site.
Chapter 5 described the laboratory testing that could be conducted to select, design, and evaluate a surfactant/cosolvent system. Site-specific laboratory testing also is necessary and must be included in the overall project cost. A specialized laboratory, such as a University facility or a specialty consulting firm, is usually required to perform these tests.
Numerical simulations can be helpful in evaluating the potential removal capacity of a full-scale system, in designing a field demonstration, and in designing the full-scale system. The types and complexity of numerical simulations are discussed in Section 5.4. The amount of numerical simulation required as part of the design phase will depend on the geological and chemical complexity of the site.
As discussed in Section 5.5, field demonstrations are a necessary component of a surfactant/cosolvent project. The cost for field demonstrations can be substantial, partly due to the need to collect sufficient performance data to verify the effectiveness of the system. The impact on the overall project cost can be minimized somewhat by reusing field demonstration components in the full-scale system. For example, wells can be reused and a portion of the site could even be remediated during the field demonstration.
When the field demonstration is complete and the data have been evaluated, the full-scale system can be designed. The type of design required will depend on the complexity of the system; the requirements of the site owner; and the contractual relationship between the owner, designer, constructor, and operator. For example, if the designer, constructor, and operator are one entity and the work is to be performed under a lump sum performance contract, the level of design detail may be fairly small. For a more traditional competitive bidding approach (often required for Federal contracts), the designer, constructor, and operator all may be different entities. In this case, fairly detailed designs are needed so that the constructor and operator can prepare accurate bids and the number of change orders can be kept to a minimum.
Under the traditional approach, the design will typically be performed in several phases, with detail added to the design at each phase. The sequence and number of design phases may vary and are sometimes dictated by the client. The following are three typical design phases:
• Conceptual or Preliminary Design. This phase is also referred to as the 15-percent design or schematic design. The design at this phase will include calculations or modeling to lay out the main process components, including the groundwater injection and recovery systems. Tank and vessel sizes are defined and the systems are laid out on site maps. Design memoranda typically are prepared to describe the intent of the design. This is the best phase in the design process to review and obtain agreement on the design concepts. The major concepts should be frozen at this point in order to minimize design costs. However, this is sometimes not possible when implementing an emerging technology such as surfactant/cosolvent flushing at a site.
• Design Development. This phase includes what is referred to as the 30- and 60-percent design. At this stage, design drawings are prepared and drafts are made of all specifications. The design is reviewed again and all facility layouts are frozen in order to minimize design costs. Again, this is sometimes not possible when implementing an emerging technology such as surfactant/cosolvent flushing.
• Construction Document Preparation. This phase is also referred to as the 100-percent design. It involves finalizing the design drawings, preparing final specifications, and preparing all contract documents for bidding.
The design costs will depend on the complexity and type of design required. For typical civil construction projects (for example, road construction), the design may run 3 to 10 percent of the total construction cost. For remediation projects, the design costs are likely to be a higher percentage of the total because the design is less standard, and the review process by the owner and regulators may be more rigorous and costly. The quantity of similar work (e.g., miles of road with basically the same design) is also less. For remediation projects, the design costs may range from 6 to 20 percent of the total construction cost.
There are numerous components that make up a project’s construction or capital costs. These components will be project specific. For surfactant/cosolvent flushing projects, they will generally include injection/recovery systems, chemical mixing systems, produced fluids handling and treatment, field piping, the site containment system, and general site preparation.
In addition to these major components, other indirect capital costs are typically applied as a percentage of the total of the direct costs. Indirect capital costs may include the following:
• Mechanical/Electrical Installation. If uninstalled equipment costs are used, some allowance must be provided for installation of the equipment by a mechanical contractor and wiring of the equipment and its instrumentation by an electrical contractor. Factors for installation may range from 20 to 50 percent, depending on how mechanically or electrically intensive the work is. If a detailed cost estimate is being prepared based on a detailed design, actual labor hours and rates can be estimated.
• General Requirements. These include costs for contractor mobilization and demobilization, bonds, and insurance. Civil construction projects often use a factor of 5 percent to cover these costs. At hazardous waste sites, a factor of 5 to 10 percent is more appropriate due to the additional mobilization, hazardous waste training, preparation of health and safety plans, decontamination, and demobilization required.
• Permitting and Legal Fees. These costs include permits and all legal fees associated with the project. A factor of 3 to 5 percent is typical for remediation projects. A larger percentage may be needed to cover permits or regulatory approvals required for the use of surfactants or cosolvents. A larger percentage also may be required if off-site construction or permanent easements are required or if off-site water treatment and discharge will occur.
• Services During Construction. These services often run between 5 and 10 percent and include the following:
– Bidding and contract administration
– Construction management and onsite observation
– Change order negotiations
– Prepurchase of equipment and expedition of deliveries
– Submittal review and office services
– Record drawings
– Minor design modifications during construction
– Review of manufacturers’ operation and maintenance manuals
• Operations and Maintenance Manual Preparation. A site-specific O&M manual will be needed for the site that includes instructions for all aspects of the operations. The preparation of the O&M manual may range from 1 to 4 percent of the construction cost.
• Startup. Startup costs include testing and debugging equipment and operator training. Factors of 2 to 5 percent are often applied.
• Demolition, Site Restoration, and Equipment Salvage. At the completion of the remediation, the remediation equipment and piping will need to be dismantled, decontaminated, and disposed. Treatment wells may need to be abandoned. Cost factors for demolition and dismantling may range from 1 to 4 percent of the total capital cost. If the remediation period is short (less than 3 years), there may be some salvage value in the equipment. Salvage values can range from 5 to 30 percent of the equipment capital costs, depending on the market value of the equipment and the life of the project. These costs should be applied at the end of the project.
• Contingency. A general contingency factor is typically included in cost estimates of this level as a provision for unforseeable additional costs. Contingency costs have two components: bid contingency and scope contingency. Bid contingency covers the unknown costs associated with constructing a given project, such as adverse weather conditions, strikes by materials suppliers, geotechnical unknowns, existing utilities unknowns, and unfavorable construction market conditions. Scope contingency covers limited scope changes that invariably occur during remediation implementation. Contingency factors ranging from 10 to 30 percent are common, depending on the amount of design detail available at the time of the estimate.
Annual O&M and monitoring costs are post-construction costs necessary to ensure the ongoing effectiveness of the project. Typical components include the following:
• Labor. O&M, monitoring, and engineering labor are required to operate the system. The number of operators needed will depend on the size and complexity of the system. For relatively new technologies, such as surfactant/cosolvent flushing, a significant amount of time may be required for monitoring and engineering to evaluate the operation of the system and prepare reports of the operations.
• Materials. This includes costs for lubricants, replacement parts, and other materials necessary for routine maintenance of the facilities and equipment. These costs are often assumed to be between 3 and 5 percent of the equipment capital costs on an annual basis.
• Chemicals. These costs include the purchase and delivery of required chemicals, including surfactants and cosolvents.
• Utilities. This includes costs for electric power, gas, telephone, water, sewer discharge, and other miscellaneous utilities.
• Laboratory Analysis. This covers the cost of analyzing samples collected to monitor the system.
• Disposal of residues. Residuals, such as recovered NAPL and surfactant, must be treated and disposed off-site. Personal protective equipment also must be disposed.
A contingency also is typically applied to the operations costs to cover unforeseeable additional costs.
Relevance
This section presents conceptual designs for three hypothetical examples of surfactant/cosolvent flushing projects. These conceptual designs are the basis for the cost estimates discussed in Section 6.3. Readers interested only in evaluating the applicability of surfactant/cosolvent flushing do not need to read this section. Readers who have already decided to implement a surfactant/cosolvent project should read this section. The conceptual designs provide good illustrations of the costs involved in surfactant/cosolvent flushing projects.
Key Concepts
• No new concepts are presented in this section. Rather, this section presents illustrations of concepts discussed in previous sections of the manual.
Tables 6-1, 6-2, and 6-3 summarize the three hypothetical sites and the
designs of the surfactant/cosolvent systems. Detailed cost spreadsheets and
design spreadsheets for the examples are provided in Appendix C. These
spreadsheets can be modified for other site sizes, configurations, and
surfactant types, but care must be taken in applying them to
| Table 6-1 | |
| Site Characteristics and System Design for Site A | |
| Type of Site | Disposal site for waste solvents. Estimated 1,000 55-gal drums released in the 1960s. The site is currently the back yard of an active maintenance shop. |
| Contaminants | Chlorinated Solvents (80% wt TCE, 5% wt PCE, 15% wt waste oil and grease), a DNAPL |
| Size of Target Area | 0.40-hectare (1-acre), "L" shaped plot, 60 m by 90 m approximately |
| Hydrogeologic Setting | Eolian sand, 10 m deep, overlying moderately jointed shale, depth to groundwater 6 m, aquifer porosity 0.30 |
| Target Depth | DNAPL in 1 m above shale deposit |
| Objective | Mass reduction to be followed by further treatment or natural attenuation |
| Removal Mechanism Utilized | Solubilization without mobility control |
| Chemical System | 4% wt isopropyl alcohol, 4% wt sodium dihexyl sulfosuccinate, 1% wt NaCl. Food-grade surfactant. |
| Delivery Recovery System | See Figure 6-1. 25 chemical injection wells, 4 gradient control wells, 40 recovery wells. All wells are 11 m deep. |
| Chemical Delivery Sequence | (1) 20 PV water flooding DNAPL recovery at 173 m3/d
(31.7 gpm) over 156 days 2) 8 PV of chemical system at 173 m3/d (31.7 gpm) over 63 days 3) 10 PV of post water flooding at 173 m3/d (31.7 gpm) over 78 days |
| Chemical Mix System | Chemicals delivered in concentrated form, diluted on site and
mixed in two solution mix and storage tanks each 265 m3 (70,000 gal)
540 m3 (143,000 gal) total of 80% wt Isopropyl Alcohol stored in two 19 m3 (5,000 gal) tanks, which is a storage capacity for 4.4 days 147 m3 (38,900 gal) total of 80% wt sodium dihexyl sulfosuccinate stored in two 19 m3 (5,000 gal) tanks, which is a storage capacity for 16.1 days 32,400 kg (71,300 lb) NaCl made up at 20% wt stock solution, stored in 19 m3 (5,000 gal) tanks, which is a storage capacity for 16.1 days |
| Produced Fluids Management | Equalization, steam stripping with condensation, off-site incineration of condensate, recycling of a portion of treated fluids, biological treatment of bleed stream, POTW discharge |
| Table 6-2 | |
| Site Characteristics and System Design for Site B | |
| Type of Site | Waste disposal site for waste oil, fuels, and solvents. Disposal activities occurred between 1955 and 1975 in this 10.8-hectare (27-acre) industrial site. The site is currently an inactive, formal industrial disposal site. |
| Contaminants | Petroleum hydrocarbon from waste oils and fuels, with small amount of chlorinated solvents (1% wt TCE, 1% wt PCE, 98% wt waste oil and grease), an LNAPL |
| Size of Target Area | 10.8 hectare (27 acres) |
| Hydrogeologic Setting | Coarse sand (hydraulic conductivity of 0.1 cm/sec) with occasional clay stringers, 3 m deep. Water table at 1.5 m. Underlying clay stone. |
| Target Depth | LNAPL in the top 1 m at the water table |
| Objective | Mass reduction to be followed by natural attenuation |
| Removal Mechanism Utilized | Mobilization with mobility control |
| Chemical System | 2 % wt Aerosol OT, 2 % wt Tween-80, 0.1 % wt xanthan gum polymer |
| Delivery Recovery System | Horizontal injection and recovery drain lines spaced 30 m on centers. Constructed in units consisting of an injection and recovery drain lines 60 m long. Construct and operate 5 units at one time. Each unit takes an average of 1 year to construct and operate. Remediation performed in stages over 6 years. |
| Chemical Delivery Sequence (flows for each drain line) | (1) 20 PV water flooding/LNAPL recovery, at 1,700
m3/d (320 gpm) for 5 units over 63 days (2) 4 PV of surfactant injection at 170 m3/d (32 gpm) for 5 units over 125 days (3) 4 PV of polymer taper at 350 m3/d (63 gpm) for 5 units over 63 days (4) 10 PV of post water flooding at 1,700 m3/d (320 gpm) for 5 units over 31 days |
| Chemical Mix System | Chemicals delivered in concentrated form, diluted on site, and
mixed in two solution mix and storage tanks, each 95 m3 (25,000 gal)
2,600 metric tons (2,900 tons) total for the project of 2% wt AOT stored in 38 m3 (10,000 gal) tank, which is a storage capacity for 10 days 3,500 metric tons (3,800 tons) total for the project of 2% wt Tween-80 stored in 38 m3 (10,000 gal) tank, which is a storage capacity for 7.5 days 360 metric tons (400 tons) total for the project of 0.1 % wt Xanthan gum stored in 55-gal drums |
| Produced Fluids Management | Oil-water separation, membrane concentration of surfactant and NAPL, off-site incineration of these waste, POTW discharge |
| Table 6-3 | |
| Site Characteristics and System Design for Site C | |
| Type of Site | Disposal site for waste solvents. Estimated 1,000 55-gal drums released in the 1960s. The site is currently the backyard of an active maintenance shop. |
| Contaminants | Chlorinated Solvents (80% wt TCE, 5% wt PCE, 15% wt waste oil and grease), a DNAPL |
| Size of Target Area | 0.4-hectare (1-acre), "L" shaped plot, 60 m by 90 m approximately |
| Hydrogeologic Setting | Eolian sand, 10 m deep, overlying moderately jointed shale, depth to groundwater of 6 m, aquifer porosity 0.30 |
| Target Depth | DNAPL in 1 m above shale deposit |
| Objective | Mass reduction to be followed by further treatment or natural attenuation |
| Removal Mechanism Utilized | Solubilization |
| Chemical System | 90% wt ethanol |
| Delivery Recovery System | 25 chemical injection wells, 40 recovery wells, and 4 gradient control wells. All wells are 11 m deep. |
| Chemical Delivery Sequence | (1) 20 PV water flooding DNAPL recovery, at 173 m3/d
(31.7 gpm) over 156 days (2) 1 PV of chemical system at 34.6 m3/d (6.34 gpm) over 39 days (alcohol flood will be performed on one unit at a time) (3) 10 PV of post water flooding at 173 m3/d (31.7 gpm) over 78 days |
| Chemical Mix System | Ethanol delivered at concentration to be delivered. Stored and
delivered from two storage tanks of 19 m3 (5,000 gal), which is a
storage capacity of 1.1 days 1,080,000 kg (2,376,000 lb) total ethanol needed |
| Produced Fluids Management | Distillation to concentrate ethanol and contaminants, off-site incineration of concentrate, and discharge to POTW. |
different conditions. They are not designed to be universally applicable, so specific changes to the design and costs may be necessary. The text in Appendix C provides additional details.
The cost estimates were developed based on information from a number of sources. Costs for specific pieces of equipment and activities were obtained from vendors when possible, from reports on past projects, and from the Remedial Action Cost Engineering and Requirements (RACER) system. RACER is an environmental cost estimating system produced by the U.S. Air Force. The source of the information presented is listed in the detailed cost spreadsheet in Appendix C.
It should be noted that the cost estimates developed here are at what would typically be considered an order-of-magnitude level. Estimates of this type are generally accurate within "plus 50 percent or minus 30 percent." The accuracy of the estimates is subject to substantial variation because the details of the specific designs will not be known until the projects are actually implemented. Factors that may impact the cost include site conditions, final project scope and schedule, design details, the bidding climate and other competitive market conditions, changes during construction and operations, productivity, interest rates, labor and equipment rates, tax effects, and other variables. As a result, actual costs will likely vary from these estimates.
The total project costs for these examples is expressed as a present worth. A real interest rate of 5 percent (meaning that the difference between the nominal interest rate and inflation is 5 percent) and a constant value based on 1996 rates for materials, expenses, and services was used to calculate the present worth.
This site has been relatively well characterized in the Remedial Investigation (RI) and Feasibility Study (FS) phases. Four additional soil borings and monitoring wells will be installed to further define the nature of the sand-bedrock interface. Soil samples and DNAPL will be collected for laboratory testing from these samples.
Solubilization has been targeted as the primary removal mechanism desired for this site. This is based partly on the fear that reducing the interfacial tension to very low values, as required for a mobilization mechanism, could result in downward migration of the DNAPL. While laboratory testing will focus on solubilization, additional information on the ability of the surfactants to reduce interfacial tension also will be collected. It is recognized that any lowering of interfacial tension may mobilize DNAPL pools.
It is assumed that the following laboratory analytical testing will be necessary:
• Initial groundwater, NAPL, and soil analysis (tested for density, viscosity, interfacial tension, and contaminant concentrations)
• Surfactant interfacial test screening
• Surfactant phase behavior test screening and solubilization potential tests
• Linear column tests
• Two-dimensional sandpack tests using sand from the site (tested for sorption, mobility, and rate-limited transfer)
• Bench-scale testing of steam stripping produced fluids treatment
• Bench-scale testing of fixed film bioreactor
A numerical model will be used to simulate the performance of the full-scale system. This model also will be used to aid in the design of the system (e.g., flow rates, timing, and well spacing). The cost for running the simulation model includes costs for the software, operator time, and computer time.
For Site A, the field demonstration will consist of a single injection well and a single extraction well surrounded by three additional injection wells spaced at 5 m around the extraction well. Water will be injected into these three wells at a low rate to hydraulically contain the injected fluids. Three nested monitoring piezometers will be installed between the injection and extraction wells. The extraction well will be used as one of the extraction wells for the full-scale system, and the other three wells will be used for monitoring the full-scale system.
The produced fluids will be sampled frequently to evaluate the performance of the system. The samples will be analyzed for DNAPL constituents, water chemistry, and surfactant properties.
Soil samples will be collected from all of the wells to determine the baseline contaminant concentrations. Eight soil borings will be installed after the field demonstration is completed to evaluate removals. Dual tracer tests also will be conducted prior to and after the field demonstration to evaluate the mass of DNAPL.
The produced fluids from the field demonstration will be stored in temporary tanks, and pilot testing of steam stripping and biological treatment will be conducted on about one-fourth of the fluids. The remaining fluids will be sent for off-site incineration as hazardous waste.
It is assumed for this example that the objective of the surfactant flushing system is mass reduction. Complete mass removal is not thought to be feasible at this site, and natural attenuation (or enhanced biodegradation) is expected to keep the remaining mass from posing a risk to human health or the environment.
The surfactant system developed in the laboratory studies for this site includes 4 percent by weight (% wt) isopropyl alcohol (a cosolvent), 4% wt sodium dihexyl sulfosucciante, and 1% wt sodium chloride. This surfactant has direct food additive status as defined by the U.S. Food and Drug Administration (FDA). Mobility control (e.g., polymers) will not be provided at this site because the other chemicals at these concentrations provide a solution of relatively high viscosity even without polymer.
The design, construction, and operations for this site will be performed by one entity on a turnkey basis. This entity could be a team comprised of a consulting engineering firm that performs turnkey remediation and another firm that specializes in surfactant/cosolvent technology development. The contract likely would have been procured on a competitive basis, but cost would be only one of the selection criteria.
Because this project will be designed and constructed on a turnkey basis, the design does not need to be detailed. The design will be partially developed in the field as the work progresses, thereby reducing design costs. On the other hand, because surfactant/cosolvent systems are designed relatively infrequently, the costs will be higher than for typical civil construction projects. A design cost of 10 percent of the total construction cost will be used for this example.
Injection/Recovery System. Because Site A is relatively small, wells will be used to inject and recover fluids. Figure 6-1 presents a layout of the proposed system, which includes 25 injection wells, four gradient-control injection wells, and 40 recovery wells. The injection wells will be laid out in rows with the recovery wells in two rows on either side. The gradient-control wells will have tap water injected into them to maintain a higher head on the edges of the surfactant injection wells, thereby forcing the injected chemicals to the recovery wells. Sheet pile walls will not be provided for containment. The wells will be about 11 m (33 ft) deep to intercept the target DNAPL zone located at about 10 m (30 ft). A series of monitoring wells also will be constructed on the site. These wells will be screened primarily in the target zone. All wells will be constructed of stainless steel to be compatible with all the injected chemicals and the DNAPL.
Chemical Mix System. The surfactant and alcohol will be purchased and delivered in concentrated form. Fiberglass storage tanks with a volume of 19 m3 (5,000 gal) will be used to store the concentrated chemicals. The sodium chloride will be made up as a concentrate in a 19-m3 (5,000-gal) tank. The concentrated chemicals will be mixed in one of two mix/storage tanks, which will be sized so that the chemicals need only be mixed approximately once every 3 days. Two tanks will be provided so that one can be filled while the other is in operation.
It is assumed that the surfactant system used is not sensitive to calcium and that the tap water has reasonably low hardness, so that tap water can be used without softening. It is also assumed that a portion of the recovered produced fluids can be recycled to the mix/storage tanks. This will require the steam stripping, which is the first stage of treatment, to remove a large fraction of the volatile contaminants from the fluids while not significantly changing the chemical makeup of the surfactant or the sodium chloride. The alcohol is likely to be stripped with the volatile contaminants, so that it cannot be reused. For these cost estimates, it was assumed that the volume of surfactant and sodium chloride needed would be equal to the volume of the first pore volume injected, plus a 20 percent loss for each subsequent pore volume injected.
The surfactant solution will be pumped from the storage tanks to each injection well by variable-speed pumps. Before entering the wells, the fluids will be passed through a bag filter to remove any particulates that may have entered the system. A level-control system will be placed in each well to regulate the fluid elevations in the wells at constant levels, or constant flow, with a high-level shut off. The entire chemical makeup system will be constructed within a temporary building (a tent system), which will be located within a secondary containment system consisting of a liner and earthen berms. The surfactant piping outside the secondary containment berms will be double walled to capture any leaks. Figure 6-2 provides a flow diagram of the chemical makeup system and produced fluids handling for Site A.
Produced Fluids Handling. Recovered fluids will be handled and pretreated as described below before being discharged to a publicly owned treatment works (POTW).
Fluids will be recovered from the system using individual diaphragm pumps in each recovery well. The rate of recovery will be 1.3 times the injection rate to ensure that all of the injected fluids are recovered. This recovery rate was determined using numerical simulation. From the recovery wells, the produced fluids will be piped in double-walled pipes to the produced fluids handling area. This area also will be within a temporary building and secondary containment. The produced fluids will be stored in a storage tank with a 1.7-day capacity. The fluids will be treated in a package steam stripper that includes a condenser to recover the volatile compounds for off-site incineration. The condensate storage tank has a 3-day capacity. The steam-stripped fluids will be recycled back to the solution mix/storage tanks. The excess fluids beyond what can be injected will be fed continuously to a fixed-film bioreactor to biodegrade the remaining surfactant and any remaining alcohol. The bioreactor will have fairly large packing openings and an effective air scouring system to prevent plugging by excessive biofilm growth. Off-gas from the bioreactor will be captured and treated with activated carbon to ensure that no volatile compounds escape from the steam stripper. As a final step, a clarifier will remove any solids from the liquid stream.
Site Preparation. Site preparation for Site A includes construction of gravel access roads, construction of the secondary containment system, construction of the temporary buildings, installation of utilities to the site (i.e., water, electrical, and sewer), and installation of temporary site facilities, including office trailers and decontamination facilities.
As presented in Table 6-1, site operations will include waterflooding the formation with 20 pore volumes of water. This waterflood will significantly reduce the amount of remaining mobile DNAPL. A partitioning tracer test also will be conducted. The waterflood will be followed by 8 pore volumes of surfactant flushing. It is assumed that 8 pore volumes are adequate to remove a significant fraction (between 50 and 85 percent) of the mass of DNAPL. A greater number of pore volumes will be needed to achieve greater removal. There is a non-linear increase in the number of pore volumes required to remove successively more DNAPL. In other words, if 4 pore volumes can remove 50 percent of the DNAPL, it might require 20 pore volumes to remove the next 25 percent and then 50 more pore volumes to get the last 25 percent. The operation will be concluded by flushing the formation with 10 pore volumes of water. The flow rate will be assumed to be constant (no plugging) at 173 m3/day (31.7 gpm) per unit during all operations. The flow rate is relatively low because of the low gradient (1 m per 15 m) assumed and the relatively wide spacing between wells. A higher head could possibly be used to create higher flow rates, and a higher head may also be necessary if plugging occurs.
Site operations will take place during a period of less than 1 year. During this year, the operations will be fairly intensive. It is assumed that two full-time (48 hours per week each) operators will be required. Weekend coverage will be 4 hours per day. These two operators will also perform the site monitoring functions. Given the short duration of operations, there should be little need for maintenance of the equipment. It is assumed that a maintenance technician will be needed 8 hours per week. Because surfactant/cosolvent flushing is a relatively new technology, a significant amount of engineering time will be required to monitor the system, evaluate the operating data, and suggest changes to the operations. Therefore, engineering time equivalent to 20 hours per week is assumed.
The cost of the chemicals for a surfactant/cosolvent flushing system will be a significant portion of the total costs. Chemical costs as of 1996 were used in this estimate, assuming the reuse of chemicals described above.
The utility costs for this operation will include the costs to run the pumps, mixers, and steam stripper. The steam stripper represents the most significant power consumption. The effluent from the bioreactor will be discharged to a POTW. It is assumed that the POTW charges $0.291 per cubic meter ($1.10 per 1,000 gal) with a surcharge of $0.064 per kilogram ($0.14 per pound) for BOD levels over 300 mg/L. It is assumed that the bioreactor is successful in reducing the BOD in the produced fluids from about 10,000 mg/L to about 1,000 mg/L. The surcharge then is calculated to be $0.306 per cubic meter ($1.16 per 1,000 gal) of effluent.
The fluids condensed from the steam stripper will be sent off-site for incineration. Biological solids produced during the treatment of produced fluids also will be sent off-site for incineration after dewatering by a contract dewatering service.
The laboratory analyses required for both operational and performance monitoring will be relatively substantial. Some of the measurements can be performed on-site by the operators, but much of it must be sent off-site. These analyses includes the following:
• Analysis of injected fluid quality. This includes viscosity (on site), fluid density, pH, conductivity, surfactant concentration, and alcohol concentration.
• Analysis of recovered fluids. This includes viscosity, fluid density, pH, conductivity, surfactant concentration, alcohol concentration, total hydrocarbons, and volatile organic compounds.
• Analysis of treated produced fluids (both final effluent and recycled). This includes COD, total suspended solids, conductivity, fluid density, surfactant concentration, alcohol concentration, and volatile organics.
• Analysis of monitoring well fluids. This includes viscosity, fluid density, pH, conductivity, surfactant concentration, alcohol concentration, and total hydrocarbons.
Site B has been relatively well characterized to define the zone of LNAPL. Eight additional soil borings and monitoring wells will be installed to collect soil and LNAPL samples for laboratory testing.
The laboratory testing required will be a function of the type of surfactant system to be used and will be somewhat independent of the size of the site. For this site, mobilization is the main removal mechanism, requiring more phase behavior tests and fewer solubilization tests. Ultrafiltration is the targeted treatment method of the produced fluids, so they will be tested rather than steam stripped and biologically treated.
For this site, a one-dimensional model will be used to model the performance of the surfactant system. A standard groundwater flow model will be used to model the full-scale system to aid in the design of the system.
The field demonstration for Site B will be conducted in two phases. The first phase will be a well-based system very similar to that described above for Site A. The second phase will involve installation of one of the full-scale units described below. The second phase will verify the performance of the system prior to committing the significant funds required for full-scale implementation. The field demonstration will yield further design information beneficial in designing the remainder of the units and will result in one unit being remediated.
A series of soil borings/monitoring wells will be installed prior to the startup of the second-phase field demonstration to collect baseline contaminant concentration data. Extensive coring also will be conducted at the end of the field demonstration. The second phase is too large to practically conduct dual tracer tests.
The produced fluids from the first phase of the field demonstration will be stored on-site, and pilot tests of ultrafiltration will be conducted. The majority of the fluids will be sent off-site for incineration. For the second phase of the demonstration, the produced fluids will be treated by ultrafiltration, the retained fluids will be sent off-site for incineration, and the passing fluids will be reused to the extent possible. The excess water and the water left at the end of the demonstration will be sent to a POTW.
It is assumed for this example that the objective of the surfactant flushing is significant mass removal. Nearly complete mass removal is desired by the regulatory agencies.
Because of the large size of the site and the related high cost of remediation, Site B can be assumed to require design and construction using a traditional detailed design/bidding approach. Most owners will assume that this type of contract gives them the greatest potential to reduce costs by competitively bidding the construction. In addition, after the completion of the field demonstration, enough information should be available about both the site and the process that a detailed design can be prepared for the first year of operation. For each subsequent year, the design can be modified slightly based on lessons learned the previous year.
The cost of the design is likely to be relatively high as a percentage of the construction cost the first year. However, the design cost should be significantly smaller in subsequent years, so that the total design cost over the life of the project is well within the range of typical remediation design costs. For this example, design is assumed to be 10 percent of the total construction cost.
Injection/Recovery System. Because the depth to contamination is relatively shallow at this site, and the site is quite large, horizontal drain lines are likely to be the most cost-effective approach to injecting and recovering fluids. These drain lines will be corrugated high-density polyethylene (HDPE) installed with continuous trenching machines. Tests have been conducted to ensure that the HDPE is compatible with all injected and recovered fluids.
A practical drainline length of 60 m (197 ft) will be used for this example. With the types of soils found at the site, it should be possible to space the drain lines at 30 m (98 ft) intervals. Less permeable soils would require tighter spacing. A treatment unit will consist of an injection drain line and two recovery drain lines, as shown in Figure 6-3. The recovery drain lines will be shared between two back-to-back units. Assuming this spacing, a total of 30 units will be required to cover the 10.8-hectare (27-acre) site.
Given the large size of the site, it is not practical to treat the entire site at one time. Instead, the site will be treated in modules, with one module constructed and operated each year. A module will consist of five units. At this rate, it will take a total of 6 years to complete the remediation.
Chemical Mix/System. The surfactants will be purchased and delivered as concentrated chemicals. They will be stored in 38 m3 (10,000 gal) storage tanks. Because relatively little polymer is needed, it will be delivered and stored in drums. All of the concentrated chemical tanks will be provided with mixers. The concentrated chemicals will be diluted, mixed, and stored in one of two 95 m3 (25,000 gal) mix/storage tanks. It is assumed that the surfactant system used is not sensitive to calcium and that the tap water has reasonably low hardness, so that tap water can be used without softening.
The surfactant solution will be pumped from the storage tanks through a bag filter to each of the five injection drain lines by five variable-speed pumps. The bag filter will remove any particulates that may be in the fluids. A level-control system will be placed in each drain line to regulate the fluid elevations in the wells at constant levels, or constant flow, with a high-level shut off. The pumping systems of the chemical makeup system will be constructed within a building. The storage tanks will be located outside. The chemical makeup system will be enclosed by a secondary containment system consisting of a liner and earthen berms. The surfactant piping outside the secondary containment berms will be double walled to capture any leaks. Figure 6-4 provides a flow diagram of the chemical makeup system and produced fluids handling for Site B.
Produced Fluids Handling. Recovered fluids will be handled and pretreated as described below before being discharged to a POTW.
The fluids will be recovered from the system using individual progressing cavity pumps (to reduce emulsification) at each recovery drain line. The recovery rate will be 1.3 times the injection rate to contain the fluids. This recovery rate was determined using numerical simulation. From the recovery drain lines, the produced fluids will be piped in double-walled pipes to a central produced fluids handling area. This area also will be within secondary containment. The produced fluids will be passed through an oil-water separator and stored in a 770-m3 (200,000-gal) storage tank with a retention time of 3 days. The fluids then will be treated in a package ultrafiltration unit. Seventy-five percent of the recovered and treated water will be recycled and 25 percent will be discharged to a POTW.
It is assumed for this example that the produced fluids cannot be treated to separate the recovered NAPL from the surfactant, and a portion of the surfactant will be recycled. With a NAPL that is mostly semi-volatile, relatively simple technologies, such as air or steam stripping, cannot be used. More complex technologies, such as liquid-liquid extraction, may be shown to be effective, but at this time they are not proven and are not off-the-shelf technologies available from vendors.
Site Preparation. Site preparation for Site B includes construction of gravel access roads, construction of roads to the units within the site, construction of the secondary containment system, construction of the buildings, installation of utilities to the site (i.e., water, electrical, and sewer), and installation of site facilities, including office trailers and decontamination facilities.
As presented in Table 6-2, the site operations will include waterflooding the formation with 20 pore volumes of water. This waterflood will significantly reduce the volume of remaining mobile NAPL. The waterflood will be followed by 4 pore volumes of surfactant flushing. It is expected that the surfactant flood will remove between 60 to 90 percent of the mass of NAPL. Fewer pore volumes could be used if less removal is desired. After the surfactant flushing is complete, the remaining surfactant will be flushed out during a "polymer taper" flush. Polymer will be injected for 4 pore volumes, with the concentration of polymer tapered down every quarter of a pore volume. The operation will be concluded by flushing the formation with 10 pore volumes of water. The flow rate during these operations will vary depending on the fluids to be injected. During the injection of water, it is assumed that fluids can be injected at 1,700 m3/d (320 gpm) through five units. During the injection of the surfactant solution, it is assumed that the flow rate will decrease by a factor of 10, to 170 m3/d (30 gpm) for the five units, because of the higher viscosity of the solution (in part, a result of the polymer). During the polymer taper, it is assumed that the flow rate will be 340 m3/d (60 gpm).
At these flow rates, it will take approximately 1 year to complete the operation of one module (made up of five units). While the first module is nearing completion, the second module will be set up for operation. It may be possible to overlap some of the operations. One new module will be constructed each year for a total of 6 years. This will allow the design to be improved upon each year and will allow the equipment to be reused. All of the drain lines will be constructed in 1 year to take advantage of efficiencies of scale.
During the 6 years of remediation, the operations will be fairly intensive, with five units operating at one time. It is assumed that six full-time (40 hours per week each) operators will be required. These six operators also will perform the monitoring functions. One full-time maintenance technician will be required to keep the equipment running. Because surfactant/cosolvent flushing is a relatively new technology and Site B is large, a significant amount of engineering time will be required to monitor the system, evaluate the operating data, suggest changes to the operations, and write reports. Therefore, engineering time equivalent to 60 hours per week will be needed. It is also assumed that one full-time laboratory technician will be hired to perform much of the operational laboratory analysis.
The cost of the chemicals for a surfactant/cosolvent flushing system will be a significant portion of the total costs. Chemical costs for 1996 were used for this estimate.
The utility costs for this operation will include the costs to run the pumps and mixers. The fluids concentrated from the ultrafiltration units will be sent off-site for incineration. The water from the ultrafiltration unit will be recycled and the remainder sent to a POTW. It is assumed that the POTW charges $0.291 per cubic meter ($1.10 per 1,000 gal) with a surcharge of $0.064 per kilogram ($0.14 per pound) for BOD levels over 300 mg/L. It is assumed that the effluent from the ultrafiltration unit has a BOD of about 1,000 mg/L. The surcharge then is calculated to be $0.306 per cubic meter ($1.16 per 1,000 gal) of effluent.
The laboratory analyses required for both operational and performance monitoring will be relatively substantial. Most of the measurements can be performed on-site by the laboratory technician, with analysis requiring GC or GC/MS instruments being sent off-site. The analyses will include the following:
• Analysis of injected fluid quality. This includes viscosity (on site), density, pH, conductivity, and surfactant concentration.
• Analysis of recovered fluids. This includes viscosity, density, pH, conductivity, surfactant concentration, NAPL-water interfacial tension, COD, total hydrocarbons, and volatile organics.
• Analysis of treated produced fluids (both concentrate and water phase). This includes density, COD, total suspended solids, conductivity, surfactant concentration, and volatile organics.
• Analysis of monitoring well fluids. This includes viscosity, density, pH, conductivity, surfactant concentration, alcohol concentration, NAPL - water interfacial tension, and total hydrocarbons.
The site characterization, laboratory testing, numerical simulations, and field demonstrations will be assumed to be the same for this example as for Site A, the small, chlorinated solvent site with surfactant flooding.