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)
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Coal tars are produced from the distillation of coal to produce coke primarily for the steel industry and from making manufactured gas. The two processes can produce two distinctly different products. The coking process usually results in a viscous liquid or semi-solid material that is dark brown to black and has a naphthalene odor (ATSDR 2002). The coal tars from a manufactured gas plant (MGP), especially one using the carburetted water process, are reddish brown to black with the consistency of vegetable oil (NYDEC 2007). The difference in viscosity means that some MGP produced coal tars can move farther and quicker in the subsurface than their coking counterparts.
Coal tars are a very complex mixture of mono and polycyclic aromatic hydrocarbons, phenols, heterocyclic oxygen, sulfur, and nitrogen compounds (ATSDR 2002). The specific gravity of coal tars varies from about 1.18 g/cc to 1.23 g/cc (Lewis 2001) due to the inherent variability of these mixtures.
When released to the environment coal tars begin to partition by individual constituent. For example, soluble components like benzene, naphthalene, and phenol start dissolving into water while volatile chemicals like benzene, xylenes, and toluene partition to the vapor phase. Like the creosotes that are derived from coal tars, the various chemicals contained in coal tars have a wide range of Koc and Kow values that give them different fates. Some compounds in coal tar mixtures tend to bioaccumulate.
Several chemicals found in coal tars biodegrade readily and will do so if they dissolve into a surface or ground water body; however, as is evidenced by the presence of coal tars in the subsurface of several MGP sites that have been closed for 50 to 100 years, coal tars can be very long-lived.
For Further Information
Acid Tar Lagoons
Smith, C., X. Hao, S. Talbot, and N. Lawson.
CL:AIRE: Contaminated Land: Applications in Real Environments, Subr:im Bulletin SUB 7, 8 pp, 2008
Although similar to coal tars, acid tars are a unique and challenging waste product arising from petroleum refining processes (i.e., benzole refining, white oil production, and oil re-refining.) that now are largely obsolete. Depending on their composition, acid tars can behave as DNAPL. This bulletin provides a state-of-the-art update on the science, assessment, and remediation of acid tar lagoons based on research carried out from 2003 to 2007 and experience from two recent remediation projects carried out in Europe. This bulletin is available without charge on the CL:AIRE Web site to registered users (registration is also free).
MGP tar and wastewater solids historically discharged into the Penobscot River, Maine, accumulated in riverbed sediment over a 5-hectare area downstream from the sewer outfall. Much of the tarry sediment is a hardened mass at the bottom of the river, but in the active zone, anaerobic biodegradation of organic matter generates methane and carbon dioxide. As gas accumulates and migrates upward, it entrains tar, eventually dragging the tar from the sediment to surface water. For tar to migrate from sediment to surface water, three conditions are necessary: the sediment must contain liquid tar, the sediment must produce gas bubbles, and the gas must come into contact with the tarry sediment. Failure to consider facilitated transport of MGP tar from sediment can cause underestimation of site risk and can lead to failure of remedial measures.
Hawley's Condensed Chemical Dictionary 14th Edition
Lewis, R. John Wiley & Sons, 2001, 1223 pp
This profile covers coal tar creosote human health effects, chemical and physical properties, manufacturing volume data, potential for human exposure (environmental fate and transport), and analytical methods.
Ebullition-Facilitated Transport of Manufactured Gas Plant Tar from Contaminated Sediment 
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