Valence state: The combining capacity of an atom or radical determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.
free product: A NAPL found in the subsurface in sufficient quantity that it can be partially recovered by pumping or gravity drain.
aerobic: Direct aerobic metabolism involves microbial reactions that require oxygen to go forward. The bacteria uses a carbon substrate as the electron donor and oxygen as the electron acceptor. Degradation of contaminants that are susceptible to aerobic degradation but not anaerobic often ceases in the vicinity of the source zone because of oxygen depletion. This can sometimes be reversed by adding oxygen in the form of air (air sparging, bioventing), ozone, or slow oxygen release compound (e.g., ORC(r)).
Aerobic dechlorination may also occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal. For aerobic cometabolism to occur there must be sufficient oxygen and a suitable substrate which allows the microbe to produce the appropriate enzyme. These conditions may be present naturally but often in the presence of a source area oxygen and a substrate such as methane or propane will need to be introduced.
Adapted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites
anaerobic: Direct anaerobic metabolism involves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, sulfate-reducing activities, and denitrification. Depending on the contaminant of concern, a subset of these activities may be cultivated. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized metals, or organic compounds may replace oxygen as the electron acceptor.
Anaerobic dechlorination also may occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal.
Quoted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites
architecture: "Architecture" refers to the physical distribution of the contaminant in the subsurface. Residuals that take the form of long thin ganglia or small dispersed globules provide a larger surface area that will dissolve much faster than if the same amount of liquid were concentrated in a competent pool.
Sources: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.
source zone: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.
focal ulceration: The process or fact of a localized area being eroded away.
metaplasia of the glandular stomach: A change of cells to a form that does not normally occur in the tissue in which it is found.
hyperplasia of the glandular stomach: A condition in which there is an increase in the number of normal cells in a tissue or organ.
histiocytic: Degenerative.
duodenum: First part of the small intestine.
microcytic: Any abnormally small cell.
squamous cell papillomas: A small solid benign tumor with a clear-cut border that projects above the surrounding tissue.
squamous cell carcinomas: Cancer that begins in squamous cells-thin, flat cells that look under the microscope like fish scales. Squamous cells are found in the tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts. Squamous cell carcinomas may arise in any of these tissues.
jejunum: The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum.
ileum: The distal and narrowest portion of the small intestine.
squamous: Flat cells that look like fish scales.
metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.
ossification: The process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone.
clastogenesis: Any process resulting in the breakage of chromosomes.
neoplastic: Abnormal and uncontrolled growth of cells.
ulceration: The process or fact of being eroded away.
leucocytosis: An elevation of the total number of white cells in blood.
neutrophils: A type of white blood cell.
chromodulin: A small protein that binds four trivalent chromium ions.
biomagnification: The increased accumulation and concentration of a contaminant at higher levels of the food chain; organisms higher on the food chain will have larger amounts of contaminants than those lower on the food chain, because the contaminants are not eliminated or broken down into other chemicals within the organisms.
exencephaly: Cerebral tissue herniation through a congenital or acquired defect in the skull.
everted viscera: Rotated body organs in the chest cavity.
To Be Considered: Documents, such as federal or state guidances, that are not legally binding but may be relevant to the topic in question.
gaining: A gaining surface water body is one where groundwater flows into it.
losing: A surface water body is losing when there is a permeable sediment bed that is not in contact with the groundwater allowing the surface water to seep through it.
fluvial: Of or pertaining to flow in rivers and streams.
lacustrine: Of or pertaining to a lake as in lacustrine sediments—sediments at the bottom of a lake.
lipid: Any class of fats that are insoluble in water.
lipophilic: Able to dissolve in lipids—in this case fatty tissue.
organelles: A part of a cell such as mitochondrion, vacuole, or chloroplast that plays a specific role in how the cell functions and membranes.
RfD: The RfD is an estimate of a daily exposure of the human population (including sensitive sub-groups) to a substance that is likely to be without "the appreciable risk of deleterious effects during a lifetime." An RfD is expressed in units of mg/kg-day.
autonomic: That part of the nervous system that controls non-conscious actions such as heart rate, perspiration and digestion.
ataxia: Lack of muscle coordination.
funnel-and-gate configuration: A system where low-permeability walls (the funnel) placed in the saturated zone direct contaminated ground-water toward a permeable treatment zone (the gate)
Hekster, F.M., R.W.P.M. Laane, and P. de Voogt. 2003. Environmental and toxicity effects of perfluoroalkylated substances. Reviews of Environmental Contamination and Toxicology 179:99-121.
Higgins, C. and R. Luthy. 2006. Sorption of perfluorinated surfactants on sediments. Environmental Science & Technology 40(23):7251-7256.
Kaiser, M.A., B.S. Larsen, C-P.C. Kao, and R.C. Buck. 2005. Vapor pressures of perfluorooctanoic, -nonanoic, -decanoic, -undecanoic, and -dodecanoic acids. Journal of Chemical and Engineering Data 50(6):1841-1843.
Kauck, E.A. and A.R. Diesslin. 1951. Some properties of perfluorocarboxylic acids. Industrial and Engineering Chemical Research 43(10):2332-2334.
In situ vitrification (ISV) is a thermal treatment process that converts contaminated soil to stable glass and crystalline solids. The commercial method uses electrodes and electrical resistance to vitrify materials by applying high voltage to electrodes (typically four) placed in the soil. Starter frit (generally graphite) is placed on the soil surface and electrical current heats the soil from the top down to temperatures between 1,400 and 2,000°C. Typical melt sizes range from 200 to 1,200 tons, with a processing rate of four to six tons per hour (U.S. EPA 1995). Maximum treatment depth is approximately 20 feet in a single setup. The process depends upon the presence of 1.4 to 15 percent alkali metal oxides in the material to be treated to ensure a proper balance between electrical conductivity and melting temperature. Too much alkali metal content increases the conductivity to a point where insufficient heating occurs.
If the silica content of the soil is sufficiently high, contaminated soil can be converted into glass. Heating vaporizes or pyrolyzes organic contaminants. Most inorganic contaminants are encased in the glass-like monolith that results when the soil cools after treatment. The system requires a vapor hood that traps offgases and channels them to a treatment train that generally consists of a quencher to cool the 100 to 400�C gases and, depending upon what is being treated, a scrubber, activated carbon unit, or thermal oxidizer (U.S. EPA 1997a). The scrubber and quench water may require secondary treatment.
The ISV process can destroy or remove organics and immobilize most inorganics in contaminated soil, sludge, or other earthen materials. The process has been used on a broad range of VOCs and SVOCs, other organics including dioxins and PCBs, and on most priority pollutant metals and radionuclides (FRTR 2002). SVOCs and VOCs can be treated with this process, with about 97 percent of the VOCs destroyed and the remainder captured by the offgas treatment system (U.S. EPA 1997a). ISV is applicable to sites with high clay and moisture content, although treatment costs increase with increasing moisture content. Treatment of materials in a permeable aquifer may require dewatering, and if the treatment area is expected to contain large voids, dynamic compaction is recommended (U.S. EPA 1997a). ISV has been tested in the field several times, including a SITE Program demonstration (U.S. EPA 1995), a demonstration at DOE's Hanford Reservation (FRTR 2002), and Superfund cleanups at the Wasatch Chemical Company Lot 6 site (U.S. EPA 1997b) and General Electric Spokane Shop (U.S. EPA 2005). Costs are estimated at $400/ton (U.S. EPA 1997a). The technology is licensed to only one vendor.
Planar melting is a modification of the conventional ISV method. It differs in that the starter material is injected in a vertical plane between electrodes at depth. Generally, two electrode pairs are used with a starter plane between each pair. As the melt proceeds, it grows vertically and horizontally away from the starter planes. Because the melts are initially separated and only merge late in the process, the potential for driving gases down into the formation is greatly reduced as compared with conventional ISV. The maximum established treatment depth is 26 feet, but deeper melts are theoretically possible. The cost of the process is estimated at between $355 and $460 per ton (Thompson 2002). A successful field demonstration of the planar technique was carried out at the Los Alamos National Laboratory in 2000 (Coel-Roback et al. 2003).
Provides an example of ISV for dioxins and other organics, including residual soils from the landfarming remedial action in excess of hydrocarbon cleanup levels. A clean soil cap was placed over the treatment zone and a clean soil berm was placed around the concrete evaporation pond. Thirty-seven melts occurred to complete the ISV process for the entire area of the former evaporation pond. Sample results showed that the ISV process had been effective in reducing chemical concentrations, primarily via thermal destruction, to levels that were below the risk-based remedial action goals established for the site. Approximately 5,200 tons of soil and sludge contaminated with various organics were remediated. The RA work for the ISV was completed on January 15, 1996.
No case studies of the vitrification of compounds from the classes of Halogenated Alkenes or Multi-Component Waste have been located.
Engineering Forum Issue Paper: In Situ Treatment Technologies for Contaminated Soil, EPA 542-F-06-013, 2006.
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