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.
DNAPL source areas can be divided into two major categories—those that contain flowable material and those that contain residual material. Residual materials are those that cannot move as a mass because they cannot overcome the capillary pressure of the matrix they are in. Residual DNAPL may be induced to move with technologies, such as heat and surfactant/cosolvents.
Flowable masses of DNAPL are generally addressed by placing an interception trench in front of them if they are still moving or by placing an extraction well into the mass. The flowable material enters the trench where it moves to a sump and is recovered by bailing or pumping. In the case of a well, the removal of the DNAPL in the well creates an induced gradient in the DNAPL that causes the flowable mass around the well to move into it. Pumping or bailing are used to remove the DNAPL depending upon how much DNAPL is present and how fast it will flow into the well.
The Army Corps of Engineers' Multiphase extraction (MPE) engineering and design manual provides the following description of the technology:
Multiphase extraction comprises a generic category of in-situ remediation technologies that simultaneously extract more than one fluid phase from wells or trenches. These phases generally include air (i.e., gaseous phase including organic vapor) and water (i.e., aqueous phase including dissolved constituents), and may include NAPL. The terminology presented by EPA (1997), which distinguishes between dual-phase and two-phase extraction technologies, is as follows:
(1) In dual-phase extraction (DPE), soil gas and/or separate phase liquids are conveyed from the extraction well to the surface in separate conduits by separate pumps or blowers. A common �pipe within a pipe� configuration is a submersible pump suspended within the well casing that extracts liquid, which may be NAPL and/or groundwater, and delivers it through a water extraction pipe to an aboveground treatment and disposal system. Soil gas is simultaneously extracted by applying a vacuum at the well head. The extracted gas is, in turn, conveyed to a gas-liquid separator prior to gas phase treatment. DPE is in essence a rather straightforward enhancement of SVE [soil vapor extraction], with groundwater recovery being carried out within the SVE well. Other DPE configurations are also common, such as use of suction (e.g., exerted by a double-diaphragm pump at the ground surface) to remove liquids from the well, rather than a submersible pump. A line-shaft turbine pump could also be employed to remove liquids from the well, provided the water table is shallow enough.
(2) In two-phase extraction (TPE), soil gas and liquid are conveyed from the extraction well to the surface within the same conduit, which has been referred to with various names including drop tube, slurp tube, stinger, lance, or suction pipe. A single vacuum source (vacuum pump or blower) is used to extract both liquid and gaseous phases. A common configuration has the suction pipe suspended within the well casing (typically to the well's base) that can extract a combination of NAPL and/or groundwater, and soil gas. These phases are conveyed to an aboveground gas-liquid separator. If extraction of NAPL is anticipated, an oil-water separator may be installed downstream of the gas liquid separator.
MPE is most often associated with residual DNAPL remediation in the unsaturated and shallow saturated zone. If a groundwater pump is employed it can lower the water table in the vicinity of the well and potentially expose more residual for capture by the SVE system. In fine grained soils (silts and clays) the two-phase system is often employed because it can dewater the well and keep it dewatered while a high vacuum SVE system can potentially reach residual at some depth below the water table as well as the unsaturated zone. A system using a pump in fined grained soil will be much more difficult to operate since the pump can only run when there is pumpable water.
Two case studies are presented in the halogenated alkene section. One case study involves the use of a two-phase system to recover both vapor and free DNAPL. Another case study describes the use of a pump in a less permeable subsurface to draw down water and expose the formerly saturated soils to vacuum recovery. In this system the extraction wells have 65 ft screens, and sufficient groundwater entry exists over the saturated zone to allow the pump to operate without completely dewatering the well.
This report provides an engineering analysis of, and status report on, selected enhancements for the following SVE treatment technologies: air sparging, dual-phase extraction, directional drilling, pneumatic and hydraulic fracturing, and thermal enhancement. It also offers an evaluation of each technology's applicability to various site conditions, cost and performance information, a list of vendors specializing in the technologies, a discussion of relative strengths and limitations of the technologies, recommendations to keep in mind when considering the enhancements, and extensive references.
This engineering manual provides practical guidance for evaluating the feasibility and applicability of MPE for remediating contaminated soil and groundwater, and it describes the design and operational considerations for MPE systems.
Analysis of Selected Enhancements for Soil Vapor Extraction
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