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.
This protocol describes a newly developed field technology—the single-well push-pull test—for evaluating the feasibility of using in situ aerobic cometabolic processes to treat ground water contaminated with chlorinated solvent mixtures. Push-pull tests have been used to obtain quantitative information on a variety of aquifer physical, chemical, and microbiological characteristics, but have not previously been used to investigate aerobic cometabolic processes. This protocol describes how push-pull tests can be used to evaluate the potential for aerobic cometabolism of chlorinated aliphatic hydrocarbons using gaseous cometabolic substrates (e.g., propane) and soluble substrates (e.g., toluene). The protocol introduces the field test methodology, describes how field push-pull tests are performed, explains how to prepare test solutions, and summarizes the analytical methods used to measure tracer, nutrient, substrate, and chlorinated solvent/transformation product concentrations in field samples collected during the tests. Case studies of field work conducted at McClellan AFB, CA, and Fort Lewis, WA, are provided to illustrate additional details about the push-pull test methodology.
Monitoring Bioaugmenation with Single Well Push-Pull Tests in Sediment Systems Contaminated with Trichloroethene
Lee, Jae Hyuk, Mark Dolan, Jonathan Istok, & Jennifer Field, Oregon State Univ., Corvallis. Fourth SETAC World Congress, 25th Annual Meeting in North America, 14-18 November 2004, Portland, Oregon. Society of Environmental Toxicology and Chemistry, Pensacola, FL. Poster PH255, 2004
Bioaugmentation can be defined as the introduction of microorganisms to degrade a target compound in a contaminated medium. Despite successful bioaugmentation in bench- and field-scale studies, it still is not clear whether dechlorinating activity is due to indigenous or bioaugmented strains and whether the injected cultures have lesser or greater distribution around the injection wells. Microcosm studies conducted to compare the reductive dechlorination rates of trichloroethene (TCE) and trichlorofluoroethene (TCFE) in control sediments and sediments bioaugmented with a dechlorinating culture produced data that were then used to design intermediate-scale (125 cm) push-pull laboratory tests conducted in physical aquifer models (PAMs). Push-pull test methodology, TCFE, and the PAMs were used to monitor the progress of bioaugmentation in PAMs containing TCE-contaminated sediment. The rate and products of TCFE transformation were determined by conducting push-pull tests in the PAM. The spatial distribution of the dechlorinating culture within the PAM correlated with concentrations of TCFE and TCE dechlorination products. No transformation products of TCFE and TCE were observed for sediment controls that did not receive the dechlorinating culture.
In situ aerobic cometabolic transformations of ethylene, propylene, and cis-1,2-dichloroethylene (c-DCE) by microorganisms stimulated on propane were examined in groundwater contaminated with c-DCE and trichloroethene (TCE). Field push/pull tests provided in situ measurements. The tests involved the injection of site groundwater amended with a bromide tracer and combinations of propane, dissolved oxygen (DO), nitrate, ethylene, propylene, c-DCE, and TCE into existing monitoring wells and sampling the same wells over time. Mass balance and transformation rate calculations were performed after adjusting for dilution losses using measured tracer concentrations. Initial rates of propane utilization were very low, but the rates increased substantially following sequential additions of propane and DO. The injected ethylene and propylene were transformed to the cometabolic byproducts ethylene oxide and propylene oxide, whereas these transformations were inhibited in the presence of co-injected acetylene, a known monoxygenase mechanism-based inactivator. These results suggest that a series of push/pull tests performed with nontoxic chemical probes can be useful for detecting and monitoring in situ aerobic cometabolism of chlorinated aliphatic hydrocarbons.
Bioaugmentation is a promising remediation approach for remediating contaminated ground water in which the aquifer is injected with a microbial community that can degrade high contaminant concentrations in situ. Successful biaugmentation requires careful monitoring. Practitioners need a way to quantitatively track changes in the microbial community, the extent of bioaugmentation, and the treatment's effectiveness. Researchers from Oregon State University--Jack Istok, Jennifer Field, and Mark Dolan--are developing a single well "push-pull" test to monitor the effectiveness of the treatment in anaerobic source zones. The push-pull test involves injecting a test solution into an aquifer and then withdrawing the test solution and ground-water mixture. Comparisons of the "pushed" and "pulled" solutions provide information about the physical, chemical, and biological conditions within the aquifer. The researchers are focusing on using the method to monitor the cleanup of high concentrations of chlorinated solvents, such as tetrachloroethene and trichloroethene, by anaerobic reductive dechlorination.
Field Push-Pull Test Protocol for Aerobic Cometabolism of Chlorinated Aliphatic Hydrocarbons
Return to "Detection and Site Characterization"
