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.
Decision Support System for Evaluating Source Depletion at Chlorinated Solvent DNAPL Sites
Newell, C.J., T. McGuire, J. McDade, P. Newberry, D. Adamson, and I. Cowie, Groundwater Services, Inc., Houston, TX. Partners in Environmental Technology Technical Symposium & Workshop, 29 November - 1 December 2005, Washington, DC: Abstracts. Poster presentation No 61, p F-41, 2005
A decision support system was developed to aid the evaluation of source zone remediation at sites impacted with chlorinated solvent dense nonaqueous phase liquid (DNAPL). The decision support system consists of four modules: (1) a performance database for source depletion sites; (2) a performance database for untreated sites; (3) a cost database for source depletion sites; and (4) a literature summary of other source depletion projects. The project was one component of a project funded by SERDP focusing on DNAPL source zone remediation. The performance database for treated sites includes temporal groundwater concentration data from before and after active remediation for 144 wells at 59 chlorinated solvent sites. Sites in the database used one of the following source depletion technologies: enhanced bioremediation, chemical oxidation, thermal treatment, and surfactant/cosolvent treatment. The decision support system allows the user to generate custom concentration versus time curves using various site characteristics as selection criteria. For each custom data set, summary statistics of concentration reductions from before and after treatment are provided. The performance database for untreated sites includes temporal groundwater concentration data for 52 wells at 23 natural attenuation sites. Only sites with at least five years of monitoring data were included in the database; the length of the monitoring record for the sites in the database ranged from five to 15 years. The decision support system allows the user to generate custom concentration versus time curves using various site characteristics as selection criteria. For each custom data set, summary statistics of concentration change over the monitoring period are provided. The cost database summarizes treatment cost data for 36 sites where source depletion technologies were used to treat chlorinated solvent DNAPL source zones. The decision support system allows the user to generate custom cost data using various site characteristics as selection criteria. Cost data is summarized in terms of US dollars per cubic yard treated for each site. The literature summary module includes recent data from three other SERDP-funded DNAPL remediation research projects on the following topics: development of assessment tools for evaluating benefits of source zone treatment, mass transfer of entrapped DNAPL from sources undergoing remediation, and assessment of the benefits of partial source removal through experimentation and modeling.
Modeling Tools for Assessing the Benefits of DNAPL Source Zone Remediation
Abriola, L.M. (Tufts Univ., Medford, MA); J.A. Christ (U.S. Air Force Academy); K. Li and C.A. Ramsburg (Tufts Univ.). Partners in Environmental Technology Technical Symposium & Workshop, 29 November - 1 December 2005, Washington, DC: Abstracts. Poster presentation No 62, p F-42, 2005
Quantifying the benefits of partial mass removal from chlorinated dense nonaqueous phase liquid (DNAPL) source zones has emerged as a key issue in the decision to implement active source-zone treatment technologies. Researchers at Tufts University and Georgia Tech are collaborating under SERDP Project ER-1293 to develop assessment tools to quantify these benefits. To evaluate the utility of incorporating upscaled mass transfer coefficients into simplified transport models for the prediction of source-zone mass discharge and source longevity, predictions of flux-averaged concentrations and source longevity obtained with an upscaled model were compared to 3-D multiphase numerical simulations of tetrachloroethene (PCE)-NAPL dissolution for an ensemble of nonuniform initial PCE saturation distributions. Incorporation of a limited amount of site-specific information (e.g., initial flux-averaged concentration and source-zone ganglia-to-pool mass ratio) enhanced the accuracy of the upscaled approach, facilitating its application to remedial alternative evaluation at a broad range of sites. Modification of a compositional multiphase simulator to include metabolic reductive dechlorination kinetics has facilitated the simulation of enhancements in DNAPL dissolution due to source-zone dechlorination processes. This modeling tool has been validated against laboratory batch and 1-D column data and is being used to determine the sensitivity of bioenhanced dissolution to source zone characteristics (e.g., NAPL contaminated length, saturation), flushing conditions (e.g., ground water velocity, electron donor amendment), and biomass distribution. Results from this effort will facilitate the refinement of biostimulation and bioaugmentation strategies for enhanced source zone dechlorination. Geostatistical approaches are being used to develop and refine a tool which uses local concentration and permeability measurements to estimate downstream dissolved mass flux and to quantify the uncertainty in these estimates. The refined tool employs a multi-stage sampling strategy to overcome the limitations on estimate precision created by the presence of spatial discontinuities (hot spots) in the concentration field commonly found at DNAPL sites. Results indicate that the refined tool can rapidly improve the accuracy and precision of the derived mass flux probability distribution. Examples demonstrate that a 25% increase in sampling frequency can improve estimate accuracy and precision by more than 50%.
Monitoring the Progress of Remedial Technologies Using a Rate-limiting NAPL Dissolution Model
Benni, William C. and Mary Ann Parcher, Environmental Systems & Technology. NGWA 2006 Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Assessment, and Remediation Conference, 6-7 November 2006
Application of a rate-limiting nonaqueous phase (NAPL) dissolution model has successfully monitored the progress and effectiveness of remedial activities on NAPL sources. The approach relies on the principles of NAPL dissolution, measured groundwater concentration data, and estimates of the mass removal from each phase. When a multi-component NAPL mixture dissolves, higher soluble constituents are preferentially removed, which results in noticeable and predictable changes in the NAPL's composition. The equations for the rate-limiting mechanisms have been developed through review of laboratory studies and application of the model to several sites. The model uses the observed recovery data to calibrate an initial effective NAPL mass to the same level of certainty as the recovery data. The model estimates the amount of source mass remaining and provides real-time monitoring of the remedy's progress toward achieving the remedial objectives. The model's use of data that are readily available and frequently obtained makes it applicable to a wide range of remedial technologies and sites. Case studies for a recovery system and an innovative technology are presented to show the modeling approach for monitoring the progress of these remedial activities.
Spatial Variations of Residual NAPL Zone Concentration in Subsurface
Sun, D. and J. Zhu, Texas A&M Univ., College Station. 2004 Joint Assembly of the Canadian Geophysical Union, American Geophysical Union, Society of Exploration Geophysicists, and Environmental and Engineering Geophysical Society, 17-21 May 2004, Montreal, Canada. Eos Trans. AGU, Vol 85 No 17, Jt. Assem. Suppl., Abstract H21B-13, 2004
Improved models are presented for the prediction of the solute concentration in the zone of residual nonaqueous phase liquid (NAPL) as a result of dissolution. The models enable the pseudo-equilibrium formulation to be used and therefore the numerical simulations for field application problems can be simplified compared to the non-equilibrium counterpart. The models are especially useful for situations of small residual NAPL saturation, which are typical for many field applications. The previous screening models lumped the entire NAPL source zone together without considering the spatial distribution of NAPL source zone concentrations. The new models incorporate the fact that the NAPL mass in the upstream will dissolve first, creating a dissolution zone that will travel downstream at certain velocity and thus demonstrating that the NAPL zone concentration is dependent on both the time and the distance into the NAPL zone.
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