SOS 6262 Soil Contamination & Remediation
for glossary provided below
Asante-Duah, D.K. 1995. Management of contaminated site problems. Lewis Pub.,
Pollution Engineering. 2001-2002.
Abatement: Reducing the degree or intensity of, or eliminating, pollution.
Absorption -- The transport of a substance through the outer boundary of a medium. Sometimes used to refer to the uptake of a chemical by a cell or an organism, including the flow into the bloodstream following exposure through the skin, lungs, and/or gastrointestinal tract.
Absorbed dose -- The amount of a chemical substance actually entering an exposed organism via the lungs (for inhalation exposures), the gastrointestinal tract (for ingestion exposures), and/or the skin (for dermal exposures). It represents the amount penetrating the exchange boundaries of the organism after contact. It is calculated from the intake and the absorption efficiency, expressed in mg/kg-day.
Absorption factor -- The percent or fraction of a chemical in contact with an organism that becomes absorbed into the receptor.
Acceptable daily intake (ADI) -- An estimate of the maximum amount of a chemical (in mg/kg body weight/day) to which a potential receptor can be exposed on a daily basis over an extended period of time - usually a lifetime – without suffering a deleterious effect, or without anticipating an adverse effect.
Acceptable Risk -- A risk level generally deemed by society to be acceptable.
Acid Deposition: A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either wet or dry form. The wet forms, popularly called “acid rain,” can fall to earth as rain, snow or fog. The dry forms are acidic gases or particulates.
Action level (
Activated carbon -- A highly adsorbent form of carbon used to remove contaminants from fluidal emissions or discharges. It is a special form of carbon, often derived from charcoal, and treated to make it capable of adsorbing and retaining certain chemical substances.
Activated carbon adsorption -- A treatment technology based on the principle that certain organic constituents preferentially adsorb to organic carbon.
Acute exposure -- A single large exposure or dose to a chemical, generally occurring over a short period (usually 24 to 96 h).
Acute toxicity -- The development of symptoms of poisoning or the occurrence of adverse health effects after exposure to a single dose or multiple doses of a chemical within a short period of time.
Adsorption -- The removal of contaminants from a fluid stream by concentration of the constituents onto a solid material. It is the physical process of attracting and holding molecules of other chemical substances on the surface of a solid, usually by the formation of chemical bonds. A substance is said to be adsorbed if the concentration in the boundary region of a solid (e.g., soil) particle is greater than in the interior of the contiguous phase.
Air Sparging -- The process of blowing air through a liquid for mixing purposes in order strip volatile materials (i.e., VOCs) or to add oxygen. Usually refers to the highly controlled injection of air into a contaminant plume in the soil saturated zone.
Air Stripping -- A remediation technique that involves the physical removal of dissolved-phase contamination from a water stream.
Aliphatic compounds -- Organic compounds in which the carbon atoms exist as either straight or branched-chains; examples include pentane, hexane and octane.
Antagonism -- The interference or inhibition of the effects of one chemical substance by the action of other chemicals.
Aquifer -- A geological formation, group of formations, or part of a formation which is capable of yielding significant/usable quantities of groundwater to wells and/or springs.
Arithmetic mean (also, Average) -- A measure of central tendency for data from a normal distribution, defined for a set of n values by the sum of values divided by n: Xm = SXI/N
Aromatic Compounds -- Organic compounds that contain carbon molecular ring structures; examples include benzene, toluene, ethylbenzene, and xylenes. These compounds are reasonably soluble, volatile, and mobile in the subsurface environment, and are a very useful indicator of contaminant migration.
Asphalt batching -- Also referred to as asphalt incorporation. A method for treating hydrocarbon-contaminated soils. It is a relatively new remedial technique that involves the incorporation of petroleum-laden soils into hot asphalt mixes as a substitute for stone aggregate. This mixture can then be utilized for paving.
Attenuation -- Any decrease in the amount or concentration of a pollutant in an environmental matrix as it moves in time and space. It is the reduction or removal of contaminant constituents by a combination of physical, chemical, and/or biological factors acting upon the contaminated media.
Average concentration -- A mathematical average of contaminant concentration(s) from more than one sample, typically represented by the arithmetic mean or the geometric mean for environmental samples.
Average daily dose (ADD) -- The average dose calculated for the duration of exposure, and used to estimate risks for chronic noncarcinogenic effects of environmental contaminants. This is defined by:
Background level -- The normal ambient environmental concentration of a chemical constituent. It may include both naturally occurring concentrations and elevated levels resulting from non-site-related human activities.
BACT-Best Available Control Technology: An emission limitation based on the maximum degree of emission reduction (considering energy, environmental and economic impacts) achievable through application of production processes, and available methods, systems and techniques. BACT does not permit emissions in excess of those allowed under any applicable Clean Air Act provisions. Use of the BACT concept is allowable on a case by case basis for major new or modified emissions sources in attainment areas and applies to each regulated pollutant.
BDAT -Best Demonstrated Available Technology: As identified by EPA, the most effective commercially available means of treating specific types of hazardous waste. The BDATs may change with advances in treatment technologies.
Benchmark risk -- A threshold level of risk, typically prescribed by regulations, above which corrective measures will almost certainly have to be implemented to mitigate the risks.
Bioaccumulation -- The retention and concentration of a chemical by an organism. It is a build-up of a chemical in a living organism, which occurs when the organism takes in more of the chemical than it can rid itself of in the same length of time and stores the chemical in its tissue, etc.
Bioassay -- Measuring the effect(s) of environmental exposures by intentional exposure of living organisms to a chemical.
Bioaugmentation -- A process in which specially selected bacteria cultures that are predisposed to metabolize some target compound(s) are added to impacted media, along with the nutrient materials, to encourage degradation of the contaminants of concern.
Bioconcentration -- The accumulation of a chemical substance in tissues of organisms (such as fish) to levels greater than levels in the surrounding media (such as water) for the organism’s habitat; often used synonymously with bioaccumulation.
Bioconcentration factor (BCF) -- A measure of the amount of selected chemical substances that accumulates in humans or in biota. It is the ratio of the concentration of a chemical substance in an organism at equilibrium to the concentration of the substance in the surrounding environmental medium.
Biodegradation -- Decomposition of a substance into simpler substances by the action of microorganisms, usually in soil. It may or may not detoxify the material which is decomposed.
Biomagnification -- The serial accumulation of a chemical by organisms in the food chain, higher concentrations occurring at each successive trophic level.
Bioremediation -- Also called biorestoration, is a viable and cost-effective remediation technique for treating a wide variety of contaminants (such as petroleum and aromatic hydrocarbons, chlorinated solvents, and pesticides). It relies on microorganisms (especially bacteria and fungi) to transform hazardous compounds found in environmental matrices into innocuous or less toxic metabolic products. Natural in situ bioremediation involves the attenuation of contaminants by indigenous (native) microorganisms without any manipulation.
Bioremediation: Use of living organisms to clean up oil spills or remove other pollutants from soil, water or wastewater; use of organisms such as non-harmful insects to remove agricultural pests of counteract diseases of trees, plants and garden soil.
Biostimulation -- A process whereby the addition of selected amounts of nutrient materials stimulate or encourage the growth of the indigenous bacteria in soil, resulting in the degradation of some target contaminant(s).
Biota -- All living organisms which are found within a prescribed volume or space.
BMP -Best Management Practice: Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from non-point sources.
Bottom Ash: The non-airborne combustion residue from burning pulverized coal in a boiler; the material which falls to the bottom of the boiler and is removed mechanically; a concentration of non-combustible materials, which may include toxics.
Brownfields: Abandoned, idled or underused industrial and commercial facilities/sites where expansion or redevelopment is complicated by real or perceived environmental contamination. Brownfields can be in urban, suburban or rural areas. .
Cancer -- A disease characterized by malignant, uncontrolled invasive growth of body tissue cells. It refers to the development of a malignant tumor or abnormal formation of tissue.
Cancer potency factor -- Health effect information factor commonly used to evaluate health hazard potentials for carcinogens. It is usually represented by the cancer slope factor.
Capillary zone -- The unsaturated area between the ground surface and the water table.
Carcinogen – A chemical or substance capable of producing cancer in living organisms.
Carcinogen Assessment Group (CAG) -- A group within the U.S. EPA responsible for the evaluation of carcinogen bioassay results and also estimates of the carcinogenic potency of various chemicals.
Carcinogenic -- Capable of causing, and tending to produce or incite cancer in living organisms.
Carcinogenicity -- The ability of a chemical to cause cancer in a living organism.
Chronic -- Of long-term duration.
Chronic daily intake (CDI) -- The receptor exposure, expressed in mg/kg-day, averaged over a long period of time.
Chronic exposure -- The long-term, usually low-level exposure to chemicals, i.e., the repeated exposure or doses to a chemical over a long period of time. It may cause latent damage that does not appear until a later period in time.
Chronic toxicity -- The occurrence of symptoms, diseases, or other adverse health effects that develop and persist over time, after exposure to a single dose or multiple doses of a chemical delivered over a relatively long period of time.
Class I Substance: One of several groups of chemicals with an ozone depletion potential of 0.2 or higher, including CFCs, Halons, Carbon Tetrachloride, and Methyl Chloroform (listed in the Clean Air Act), and HBFCs and Ethyl Bromide (added by EPA regulations).
Class II Substance: A substance with an ozone depletion potential of less than 0.2. All HCFCs are currently included in this classification.
Cleanup -- Actions taken to abate the situation involving the release or threat of release of contaminants that could potentially affect human health and/or the environment. This typically involves a process to remove or attenuate contamination levels, in order to restore the impacted media to a useable state.
Cleanup: Actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and/or the environment. This term is sometimes used interchangeably with the terms “remedial action,” “response action” or “corrective action.”
Cleanup level - The contaminant concentration goal of a remedial action, i.e., the media contaminant level to be attained through a remedial action.
Closure - All activities involved in taking a hazardous waste facility out of service and securing it for the time required by applicable regulations and laws. Site closures follow the implementation of appropriate site restoration and monitoring programs.
Co-fire: Burning of two fuels in the same combustion unit; e.g., coal and natural gas, or oil and coal.
Confidence interval (CI) - A statistical parameter used to specify a range and the probability that an uncertain quantity falls within this range.
Confidence limits - The upper and lower boundary values of a range of statistical probability numbers.
Confidence limits, 95 percent (95% CL) - The limits of the range of values within which a single evaluation/analysis will be included 95% of the time. For large samples (i.e., n >30),
95%CL = Xm ± 1.96s/n0.5
where CL is the confidence level, and s is the estimate of the standard deviation of the mean (Xm). For a limited number of samples (n < 30), a confidence limit or confidence interval may be estimated from:
CL = Xm ± ts /n0.5
where t is the value of the student r-distribution (refer to standard statistical texts) for the desired confidence level and degrees of freedom, (n - 1).
Consequence - The impacts resulting from a receptor response due to specified exposures, or loading or stress conditions.
Contaminant - Any physical, chemical, biological, or radiological material that can potentially have adverse impacts on environmental media, or that can adversely impact public health and the environment. It represents any undesirable substance/material that normally is not present in the environmental media of concern.
Contaminant migration - The movement of a contaminant from its source through other matrices/media such as air, water, or soil. A contaminant migration pathway is the path taken by the contaminants as they travel from the contaminated site through various environmental media.
Contaminant plume - A body of contaminated groundwater or vapor originating from a specific source and spreading out due to influences of factors such as local groundwater conditions or soil vapor flow patterns. It represents the volume of groundwater or vapor that contains the contaminants released from a pollution source.
Contaminant release -The ability of a contaminant to enter into other environmental media/matrices (e.g., air, water or soil) from its place/point of origin.
Corrective action - Action taken to correct a problematic situation. A typical example involves the remediation of chemical contamination in soil and groundwater.
Cross contamination: The movement of underground contaminants from one level or area to another due to invasive subsurface activities.
Cost-effective alternative - The most cost-effective alternative is the lowest cost alternative that is technologically feasible and reliable, and which effectively mitigates and minimizes environmental damage. It generally provides adequate protection of public health, welfare, or the environment.
Data quality objectives (DQOs) - Qualitative and quantitative statements developed by analysts to specify the quality of data that, at a minimum, is needed and expected from a particular data collection activity (or site characterization activity). It is determined based on the end use of the data to be collected.
Decision analysis - A process of systematic evaluation of alternative solutions to a problem where the decision is made under uncertainty. The approach is comprised of a conceptual and systematic procedure for analyzing complex sets of alternative solutions in a rational manner in order to improve the overall performance of a decision-making process.
Decision framework - A management tool designed to facilitate rational decision making on environmental contamination problems.
Degradation - The physical, chemical, or biological breakdown of a complex compound into simpler compounds and byproducts.
de Minimus - A legal doctrine dealing with levels associated with insignificant vs. significant issues relating to human exposures to chemicals that present very low risk. It is the level below which one need not be concerned.
Detection Limit - The minimum concentration or weight of analyte that can be detected by a single measurement with a known confidence level. Instrument detection limit (IDL) represents the lowest amount that can be distinguished from the normal “noise” of an analytical instrument, i.e., the smallest amount of a chemical detectable by an analytical instrument under ideal conditions. Method detection limit (MDL) represents the lowest amount that can be distinguished from the normal “noise” of an analytical method, i.e., the smallest amount of a chemical detectable by a prescribed or specified method of analysis.
Diffusion – The migration of molecules, atoms, or ions from one fluid to another in a direction tending to equalize concentrations.
Dissolved product – The water-soluble fuel components of contaminant releases.
Dose –The amount of a chemical taken in by potential receptors on exposure. It is a measure of the amount of the substance received by the receptor, whether human or animal, as a result of exposure, expressed as an amount of exposure (in mg) per unit body weight of the receptor (in kg).
Dose-response – The quantitative relationship between the dose of a chemical and an effect caused by exposure to such substance.
Dose-response curve – A graphical representation of the relationship between the degree of exposure to a chemical substance and the observed or predicted biological effects or response.
Dose-response evaluation – The process of quantitatively evaluating toxicity information and characterizing the relationship between the dose of a chemical administered or received and the incidence of adverse health effects in the exposed population.
Ecological/environmental sustainability: Maintenance of ecosystem components and functions for future generations.
Ecosystem – The interacting system of a biological community and its abiotic (i.e., nonliving) environment.
Ecotoxicity assessment – The measurement of effects of environmental toxicants on indigenous populations of organisms.
Effect (local) – The response produced from a chemical contact with an exposed receptor that occurs at the site of first contact.
Effect (systematic) – The response produced from a chemical contact with an exposed receptor that requires absorption and distribution of the chemical and tends to affect the receptor at sites away from the entry point(s).
Effective porosity – The ratio of the volume of interconnected voids through which fluid can flow to the total volume of material.
Endangerment assessment – A site-specific risk assessment of the actual or potential danger to human health and welfare, and also the environment, from the release of hazardous chemicals into various environmental media.
Environmental assessment: An environmental analysis prepared pursuant to the National Environmental Policy Act to determine whether a federal action would significantly affect the environment and thus require a more detailed environmental impact statement.
Environmental audit: An independent assessment of the current status of a party’s compliance with applicable environmental requirements or of a party’s environmental compliance policies, practices and controls.
Environmental fate – The ultimate and intermediary destinies of a chemical after release or escape into the environment, and following transport through various environmental compartments. It is the movement of a chemical through the environment by transport in water, soil, and air culminating in exposures to living organisms. It represents the disposition of a material in various environmental compartments (e.g., soil, sediment, water, air, biota) as result of transport, transformation, and degradation.
Event tree analysis – A procedure that uses deductive logic to evaluate series of events which lead to an upset or accident scenario.
Exposure - The situation of receiving a dose of a chemical substance (or physical agent), or coming in contact with a hazard. It represents the contact of an organism with a chemical or physical agent available at the exchange boundary (e.g., lungs, gut, skin) during a specified time period.
Exposure assessment - The qualitative or quantitative estimation, or the measurement, of the dose or amount of a chemical to which potential receptors have been exposed, or could potentially be exposed. It comprises the determination of the magnitude, frequency, duration, route, and extent of exposure (to the chemicals or hazards of potential concern).
Exposure conditions - Factors (such as location, time, etc.) that may have significant effects on an exposed population's response to a hazard situation.
Exposure duration - The length of time that a potential receptor is exposed to the contaminants of concern in a defined exposure scenario.
Exposure parameters - Variables used in the calculation of intake (e.g., exposure duration, inhalation rate, average body weight).
Exposure pathway -The course a chemical or physical agent takes from a source to an exposed population or organism. It describes a unique mechanism by which an individual or population is exposed to chemicals or physical agents at or originating from a contaminated site.
Exposure point - A location of potential contact between an organism and a chemical or physical agent.
Exposure route - The avenue by which an organism contacts a chemical, such as inhalation, ingestion, or dermal contact.
Exposure scenario - A set of conditions or assumptions about sources, exposure pathways, concentrations of chemicals, and potential receptors that aid in the evaluation and quantification of exposure in a given situation.
Feasibility study (FS) -The analysis and selection of alternative remedial or corrective actions for hazardous waste or contaminated sites. The process identifies and evaluates remedial alternatives by utilizing a variety of appropriate environmental, engineering, and economic criteria.
Feasibility study: 1. Analysis of the practicability of a proposal; e.g., a description and analysis of potential cleanup alternatives for a site such as one on the National Priorities List. The feasibility study usually recommends selection of a cost-effective alternative. It usually starts as soon as the remedial investigation is underway; together, they are commonly referred to as the “RI/FS”. 2. A small-scale investigation of a problem to ascertain whether a proposed research approach is likely to provide useful data.
Field sampling plan (FSP) -A documentation that defines in detail the sampling and data gathering activities to be used in the investigation of a potentially contaminated site.
Flue Gas: The air coming out of a chimney after combustion in the burner it is venting. It can include nitrogen oxides, carbon oxides, water vapor, sulfur oxides, particles and many chemical pollutants.
Flue Gas Desulfurization: A technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide from the gases produced by burning fossil fuels. Flue gas desulfurization is current state-of-the art technology for major SO2 emitters, like power plants.
Free product - Chemical constituents that floats on groundwater, or that remains unadulterated as a contaminant pool in the environment.
Fugitive dust - Atmospheric dust arising from disturbances of particulate matter exposed to the air. Fugitive dust emissions consist of the release of chemicals from contaminated surface soil into the air, attached to dust particles.
Gasification: Conversion of solid material such as coal into a gas for use as a fuel.
Geometric mean - A measure of the central tendency for data from a positively skewed distribution (lognormal), given by:
Xgm = [(X1)(X2)(X3)
Xgm = antilog (SnlogXi / n) , where i = l.
Hazard - The inherent adverse effect that a chemical or other object poses. It is that innate character which has the potential for creating adverse and/or undesirable consequences. It defines the chance that a particular substance will have an adverse effect on human health or the environment in a particular set of circumstances which creates an exposure to that substance.
Hazard assessment - The evaluation of system performance and associated consequences over a range of operating and/or failure conditions. It involves gathering and evaluating data on types of injury or consequences that may be produced by a hazardous situation or substance.
Hazard assessment: Evaluating the effects of a stressor or determining a margin of safety for an organism by comparing the concentration that causes effects with an estimate of exposure to the organism.
Hazard identification - The systematic identification of potential accidents, upset conditions, etc. It is the recognition that a hazard exists and the definition of its characteristics. The process involves determining whether exposure to an agent can cause an increase in the incidence of a particular adverse health effect in receptors of interest.
Hazard index (HI) - The sum of several hazard quotients for multiple substances and/or multiple exposure pathways.
Hazard quotient (HQ) -The ratio of a single substance exposure level for a specified time period to a reference dose of that substance derived from a similar exposure period.
Hazard Ranking System (HRS) - A scoring system used by the EPA to assess the relative threat associated with actual or potential releases of hazardous substances at contaminated sites. The HRS is the primary way of determining whether a site is to be included on the National Priorities List (NPL).
Hazardous waste - Wastes that are ignitable, explosive, corrosive, reactive, toxic, radioactive, pathological, or have some other properties that produces substantial risk to life. It is that byproduct which has the potential of causing detrimental effects on human health and/or the environment if not managed efficiently.
Heavy metals - Members of a group of metallic elements which are recognized as toxic and generally bioaccumulative. The term arises from the relatively high atomic weights of these elements.
High-risk community: A community located within the vicinity of numerous sites of facilities or other potential sources of environmental health hazards that may result in high levels of exposure to contaminants or pollutants.
Hot spot -Term used to denote zones where contaminants are present at much higher concentrations than the immediate surrounding areas. It represents a relatively small area which is highly contaminated within a study area.
Human equivalent dose - A dose which, when administered to humans, produces effects comparable to that produced by a dose in experimental animals.
Human health risk - The likelihood (or probability) that a given exposure or series of exposures to a hazardous substance will cause adverse health impacts on individual receptors experiencing the exposures.
Hydraulic conductivity - A measure of the ability of earth materials to transmit fluid, that is dependent on the type of fluid passing through the material.
Hydrocarbon - Organic chemicals/compounds, such as benzene, that contain atoms of both hydrogen and carbon.
Hydrophilic - Having greater affinity for water, or water-loving. Hydrophilic compounds tend to become dissolved in water.
Hydrophobic -Tending not to combine with water, or having less affinity for water. Hydrophobic compounds tend to avoid being dissolved in water and are more attracted to nonpolar liquids (e.g., oils) or solids.
Incineration - A thermal treatment/degradation process by which contaminated materials are exposed to excessive heat in a variety of incinerator types. The incineration process typically involves the thermal destruction of contaminants by burning under controlled conditions. Depending on the intensity of the heat, the contaminants of concern are volatilized and/or destroyed during the incineration process.
Incompatible wastes - Wastes, which when mixed with other materials without controls, may create fire, explosion, or other severe hazards.
Individual excess lifetime cancer risk - An upper bound estimate of the increased cancer risk, expressed as a probability, that an individual receptor could expect from exposure over a lifetime. It is a statistical concept and is not necessarily dependent on the average residency time in an area.
Ingestion - An exposure type whereby chemical substances enter the body through the mouth, and into the gastrointestinal system.
Inhalation - The intake of a substance by receptors through the respiratory tract system.
In-situ: In its original place; unmoved unexcavated; remaining at the site or in the subsurface.
In-situ flushing: Introduction of large volumes of water, at times supplemented with cleaning compounds, into soil, waste or ground water to flush hazardous contaminants from a site.
In-situ oxidation: Technology that oxidizes contaminants dissolved in ground water, converting them into insoluble compounds.
In-situ stripping: Treatment system that removes or “strips” volatile organic compounds from contaminated ground or surface water by forcing an airstream through the water and causing the compounds to evaporate.
Intake - The amount of material inhaled, ingested, or dermally absorbed during a specified time period. It is a measure of exposure, expressed in mg/kg-day.
Integrated Risk Information System (IRIS) - A EPA database containing verified reference doses (RfDs) and slop factors (SFs), and up-to-date health risk and EPA regulatory information for numerous chemicals. It serves as a source of toxicity information for human health and environmental risk assessment.
Interim action - An action that initiates remediation of a contaminated site, but may also constitute part of the final remedy.
Investigation-derived wastes (IDWs) - Wastes generated in the process of collecting samples during a remedial investigation or site characterization activity. Such wastes must be handled according to all relevant and appropriate regulatory requirements. The wastes may include soil, groundwater, used personal protective equipment, decontamination fluids, and disposable sampling equipment.
Kd (soil/water partition coefficient) - Provides a soil- or sediment-specific measure of the extent of chemical partitioning between soil or sediment and water, unadjusted for the dependence on organic carbon.
Koc (organic carbon adsorption coefficient) - Provides a measure of the extent of chemical partitioning between organic carbon and water at equilibrium.
Kow (octanol/water partition coefficient)- Provides a measure of the extent of chemical partitioning between water and octanol at equilibrium.
Land farming - The application of biodegradable organic wastes onto a land surface and their incorporation into the surface soil so that they degrade more readily.
Landfill - A controlled site for the disposal of wastes on land, generally operated in accordance with regulatory safety and environmental compliance requirements.
Landfills: 1.) Sanitary landfills are disposal sites for non-hazardous solid wastes spread in layers, compacted to the smallest practical volume and covered by material applied at the end of each operating day. 2.) Secure chemical landfills are disposal sites for hazardous waste, selected and designed to minimize the chance of release of hazardous substances into the environment.
Latent period - The time between the initial induction of a health effect from first exposure to a chemical and the manifestation or detection of actual health effects.
LC50 (mean lethal concentration) - The lowest concentration of a chemical in air or water that will be fatal to 50% of test organisms living in that media.
LD50 (mean lethal dose) - The median lethal dose, i.e., the single dose (ingested or dermally absorbed) required to kill 50% of a test animal group.
Leachate - Aqueous, often-contaminated, liquid generated when water percolates or trickles through waste materials or contaminated sites and collects components of those wastes. Leaching usually occurs at landfills as a result of infiltration of rainwater or snowmelt, and may result in hazardous chemicals entering soils, surface water, or groundwater.
Lifetime average daily dose (LADD) - The exposure, expressed as mass of a substance contacted and absorbed per unit body weight per unit time, averaged over a lifetime. It is usually used to calculate carcinogenic risks; it takes into account the fact that, whereas carcinogenic risk values are determined with an assumption of lifetime exposure, actual exposures may be for a shorter period of time.
Lifetime exposure - The total amount of exposure to a substance that a human would be subjected to in a lifetime.
Lifetime risk - Risk which results from lifetime exposure to a chemical substance.
LOAEL (lowest-observed-adverse-effect level) - The chemical dose rate causing statistically or biologically significant increases in frequency or severity of adverse effects between the exposed and control groups. It is the lowest dose level, expressed in mg/kg body weight/day, at which adverse effects are noted in the exposed population.
LOAELa - LOAEL values adjusted by dividing by one or more safety factors.
Matrix (or medium) -The predominant material comprising the environmental sample being investigated (e.g., soils, water, and air).
Maximum Daily Dose (MDD) - The maximum dose calculated for the duration of receptor exposure, and used to estimate risks for subchronic or acute noncarcinogenic effects of environmental contaminants.
MCL (maximum contaminant level) - A legally enforceable maximum chemical concentration standard that is allowable in drinking water, issued by the U.S. EPA under authority of the SDWA.
MCLG (maximum contaminant level goal) - A nonenforceable health goal for public drinking water systems issued by the U.S. EPA under authority of the SDWA. It is also referred to as the recommended maximum contaminant level (RMCL).
Methane: A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds. A major component of natural gas used in the home.
Methanol: An alcohol that can be used as an alternative fuel or as a gasoline additive. It is less volatile than gasoline; when blended with gasoline it lowers the carbon monoxide emissions but increases hydrocarbon emissions. Used as pure fuel, its emissions are less ozone-forming than those from gasoline.
Microbe - A microscopic or ultramicroscopic organism (e.g., bacterium or virus).
Mitigation - The process of reducing or alleviating a problem situation.
Modeling - The use of mathematical equations to simulate and predict real events and processes.
Monitoring - The measurement of concentrations of chemicals in environmental media or in tissues of humans and other biological receptors/organisms.
Monitoring: Periodic or continuous surveillance or testing to determine the level of compliance with statutory requirements and/or pollutant levels in various media or in humans, plants and animals.
National Contingency Plan (NCP) - The National Oil and Hazardous Substances Pollution Contingency Plan, commonly known as the NCP, is a regulation that establishes roles, responsibilities, and authorities for responding to hazardous substance releases. The NCP established the HRS as the principal mechanism for placing sites on the NPL.
National Priorities List - A list of waste sites for which the U.S. EPA has at of a site contamination on air, surface and groundwater, soil, and the population potentially at risk; this site listing, which is found under CERCLA (Section 105), is updated three times a year.
Neurotoxicity - Hazard effects that are poisonous to the nerve cells.
NOAEL (no-observed-adverse-effect level) -The chemical intakes at which there are no statistically or biologically significant increases in frequency or severity of adverse effects between the exposed and control groups (which means that statistically significant effects are observed at this level, but they are not considered to be adverse). It is the highest level at which a chemical causes no observable adverse effect in the species being tested or the exposed population.
NOAELa - NOAEL values adjusted by dividing by one or more safety factors.
NOEL (no-observed-effect level) - The dose rate of chemical at which there are no statistically or biologically significant increases in frequency or severity of any effects between the exposed and control groups. It is the highest level at which a chemical causes no observable changes in the species or exposed populations under investigation.
Nonparanzetric statistics - Statistical techniques whose application is independent of the actual distribution of the underlying population from which the data were collected.
Off-site - Areas outside the boundaries or limits of a presumed contaminated site.
On-site - The boundaries or limits of a presumed contaminated site.
Organic carbon content of soils or sediments (%) - This reflects the amount of organic matter present, and generally correlates with the tendency of chemicals to accumulate in the soil or sediment. The accumulation of chemicals in soils or sediments is frequently the result of adsorption onto organic matter. In general, the higher the organic carbon content of the soil or sediment, the more a contaminant will be adsorbed to the soil particles, rather than be dissolved in the water or gases permeating the soil or sediment.
Pathway - Any specific route which environmental contaminants take in order to travel away from the source and to reach potential receptors or individuals.
PEL (permissible exposure limit) - A maximum (legally enforceable) allowable level for a chemical in workplace air.
Permeability - A measure of a material’s ability to transmit fluid. It is the capacity of a porous medium to transmit a fluid subjected to an energy gradient (the hydraulic gradient, in the case of water).
pH - A measure of the acidity or alkalinity of a material or medium, with a value of 7 representing neutral; a low pH means a highly acidic medium, whereas a high pH indicates an alkaline medium.
Pica - The behavior in toddlers and children (usually under age 6 years) involving the intentional eating/mouthing of large quantities of dirt and other objects.
Pollution prevention: Identifying areas, processes and activities which create excessive waste products or pollutants in order to reduce or prevent them through alteration, or eliminating a process. Such activities, consistent with the Pollution Prevention Act of 1990, are conducted across all EPA programs and can involve cooperative efforts with such agencies as the Departments of Agriculture and Energy.
Population-at-risk (PAR) - A population subgroup that is more susceptible to hazard or chemical exposures. It represents that group which is more sensitive to a hazard or chemical than is the general population.
Population excess cancer burden -An upper bound estimate of the increase in cancer cases in a population as a result of exposure to a carcinogen.
Porosity -The ratio of the volume of void spaces in earth materials to the total volume of the material. The wider the range of grain sizes, the lower the porosity.
Potency - A measure of the relative toxicity of a chemical.
Potentially responsible party (PRP) - Those identified by the U.S. EPA as potentially liable under CERCLA for cleanup costs at specified waste sites.
ppb (parts per billion)- An amount of substance in a billion parts of another material; also expressed by mg/kg or mg/L.
ppm (parts per million) - An amount of substance in a million parts of another material; also expressed by mg/kg or mg/L
Practical quantitation limit (PQL) - Also called sample quantitation limit (SQL). It is the lowest level that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions. It represents a detection limit that has been corrected for sample characteristics, sample preparation, and analytical adjustments such as dilution. Typically, the PQL or SQL will be about 5 to 10 times the chemical-specific detection limit.
Preliminary assessment (PA) - A survey and evaluation whereby sites are characterized with respect to their potential to release significant amounts of contaminants into the environment.
Preliminary site appraisal - Process used for quick assessment of a site’s potential to adversely affect the environment and/or public health.
Probability - The likelihood of an event occurring.
Promoter - A chemical that, when administered after an initiator has been given, promotes the change of an initiated cell, culminating in a cancer.
Qualitative - Description of a situation without numerical specifications.
Quality assurance (QA) - A system of activities designed to assure that the quality control system is performing adequately. It consists of the management of investigation data to assure that they meet the data quality objectives. This commonly includes designing appropriate protocols, ensuring they are carried out, and independently testing data quality.
Quality assurance project plan (QAPP) - A plan that describes protocols necessary to achieve the data quality objectives defined for a remedial investigation or site characterization.
Quality control (QC) - A system of specific efforts designed to test and control the quality of data obtained in an investigation. It consists of the management of activities involved in the collection and analysis of data to assure they meet the data quality objectives. It is the system of activities required to provide information as to whether the quality assurance system is performing adequately. Activities include following the sampling protocols, and routinely checking calibration of laboratory equipment.
Quantitation limit (QL) -The lowest level at which a chemical can be accurately and reproducibly quantitated. It usually is equal to the instrument detection limit (JDL) multiplied by a factor of 3 to 5 , but varies for different chemicals and different samples.
Real-time monitoring: Monitoring and measuring environmental developments with technology and communications systems that provide time-relevant information to the public in an easily understood format people can use in day-to-day decision-making about their health and the environment.
Receptor - Members of a potentially exposed population, such as persons or organisms that are potentially exposed to concentrations of a particular chemical compound.
Reference concentration (RfC) - A concentration of a chemical substance in an environmental medium to which exposure can occur over a prolonged period without an expected adverse effect. The medium in this case is usually air, with the concentration expressed in mg of chemical per m3 of air.
Reference dose (RfD) - The maximum amount of a chemical that the human body can absorb without experiencing chronic health effects, expressed in mg of chemical per kg body weight per day. It is the estimate of lifetime daily exposure of a noncarcinogenic substance for the general human population (including sensitive receptors) which appears to be without an appreciable risk of deleterious effects, consistent with the threshold concept.
Remedial action -Those actions consistent with a permanent remedy in the event of a release of a hazardous substance into the environment, meant to prevent or minimize such releases so that they do not migrate to cause substantial danger to present or future public health or welfare or the environment.
Remedial alternative - An action considered in the feasibility study, that is intended to reduce or eliminate significant risks to human health and/or the environment at a contaminated site.
Remedial design: A phase of remedial action that follows the remedial investigation/feasibility study and includes development of engineering drawings and specifications for a site cleanup.
Remedial investigation (RI) - The field investigation of hazardous waste sites to determine pathways, nature, and extent of contamination, as well as to identify preliminary alternative remedial actions. It addresses data collection and site characterization to identify and assess threats or potential threats to human health and the environment posed by a site.
Remedial investigation: An in-depth study designed to gather data needed to determine the nature and extent of contamination at a Superfund site; establish site cleanup criteria; identify preliminary alternatives for remedial action; and support technical and cost analyses of alternatives. The remedial investigation is usually done with the feasibility study. Together they are usually referred to as the “RI/FS”.
Remedial response: Long-term action that stops or substantially reduces a release or threat of a release of hazardous substances that is serious but not an immediate threat to public health.
Remediation -The process of cleaning up of a potentially contaminated site, in order to prevent or minimize the potential release and migration of hazardous substances from the impacted media that could cause adverse impacts to present or future public health and welfare, or the environment.
Remediation: Cleanup or other methods used to remove or contain a toxic spill or hazardous materials from a Superfund site.
Removal action - An action that is implemented to address a direct threat to human health or the environment.
Representative sample - A sample that is assumed not to be significantly different than the population of samples available.
Residual risk -The risk of adverse consequences that remains after corrective actions have been implemented.
Response -The reaction of a body or organ to a chemical substance or other physical, chemical, or biological agent.
Risk - The probability or likelihood of an adverse consequence from a hazardous situation or hazard, or the potential for the realization of undesirable adverse consequences from impending events. It is a measure of the probability and severity of an adverse effect to health, property, or the environment.
Risk acceptance - The willingness of an individual, group, or society to accept a specific level of risk in order to obtain some gain or benefit.
Risk appraisal - The assessment of whether existing or potential biologic receptors are presently, or may in the future, be at risk of adverse effects as a result of exposures to contaminants originating at a contaminated site.
Risk assessment - A methodology that combines exposure assessment with health and environmental effects data to estimate risks to human or environmental target organisms which results from exposure to pollutants.
Risk control -The process to manage risks associated with a hazard situation. It may involve the implementation, enforcement, and reevaluation of the effectiveness of corrective measures from time to time.
Risk decision - The process used for making complex public policy decisions relating to the control of risks associated with hazardous situations.
Risk determination - The evaluation of the environmental and health impacts of contaminant releases.
Risk estimate - A description of the probability that a potential receptor exposed to a specified dose of a chemical will develop an adverse response.
Risk estimation - The process of quantifying the probability and consequence values for a hazard situation. It is the process, used to determine the extent and probability of adverse effects of the hazards identified, and to produce a measure of the level of health, property, or environmental risks being assessed.
Risk evaluation - The complex process of developing acceptable levels of risk to individuals or society. It is the stage at which values and judgments enter into the decision process.
Risk management - The steps and processes taken to reduce, abate, or eliminate the risk that has been revealed by a risk assessment. It is an activity concerned with decisions about whether an assessed risk is sufficiently high to present a public health concern, and about the appropriate means for controlling the risks judged to be significant.
Risk perception - The magnitude of the risk as it is perceived by an individual or population. It consists of the measured risk and the preconceptions of the observer.
Risk reduction - The action of lowering the probability of occurrence and/or the value of a risk consequence, thereby reducing the magnitude of the risk.
Risk-specific dose (RSD) -An estimate of the daily dose of a carcinogen which, over a lifetime, will result in an incidence of cancer equal to a given risk level. It is the dose associated with a specified risk level.
Sample Blank - Blanks are samples considered to be the same as the environmental samples of interest except with regard to one factor whose influence on the samples is being evaluated. Blanks are used to ensure that contaminant concentrations actually reflect site conditions, and are not artifacts of the sample handling processes. The blanks consist of laboratory-prepared sample bottles of distilled or deionized water that accompany the empty sample bottles to the field as well as the samples returning to the laboratory, and are not opened until both the blanks and the actual site samples are analyzed.
Sample Duplicate - Two samples taken from the same source at the same time and analyzed under identical conditions.
Sampling and analysis plan (SAP) - Documentation that consists of a quality assurance project plan (QAPP) and a field sampling plan (FSP).
Saturated Zone - An underground geologic formation in which the pore spaces or interstitial spaces in the formation are filled with water under a pressure equal to or greater than atmospheric pressure.
Sediment- Soil that is normally covered with water. It generally is considered to provide a direct exposure pathway to aquatic life
Sediments: Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish and wildlife habitat, and clouding the water so that sunlight cannot reach aquatic plants.
Sensitive receptor - Individual in a population who is particularly susceptible to health impacts due to exposure to a chemical pollutant.
Sensitivity analysis- A method used to examine the operation of a system by measuring the deviation of its nominal behavior due to pertubations in the performance of its components from their nominal values.
Sewage sludge: Sludge produced at a Publicly Owned Treatment Works, the disposal of which is regulated under the Clean Water Act.
Sewage: The waste and wastewater produced by residential and commercial sources and discharged into sewers.
Sewer: A channel or conduit that carries wastewater and stormwater runoff from the source to a treatment plant or receiving stream. Sanitary sewers carry household, industrial, and commercial waste. Storm sewers carry runoff from rain or snow. Combined sewers handle both.
Sewerage: The entire system of sewage collection, treatment and disposal.
Site assessment - Process used to identify toxic substances that may be present at a site and to present site-specific characteristics that influence the migration of contaminants.
Site categorization - A classification of sites to reflect the uniqueness of each site.
Site cleanup - The decontamination of a site, initiated as a result of the discovery of contamination at a site or property.
Site mitigation - The process of cleaning up a contaminated site in order to return it to an environmentally acceptable state.
Slope factor (SF) -A plausible upper bound estimate of the probability of a response per unit intake of a chemical over a lifetime. It is used to estimate an upper bound probability of an individual developing cancer as a result of a lifetime of exposure to a particular level of a carcinogen.
Soil gas - The vapor or gas found in the unsaturated soil zone.
Soil vapor extraction (SVE) - Also known as in situ soil venting, subsurface venting, vacuum extraction, or in situ soil stripping, is a technique that uses soil aeration to treat subsurface zones of VOC contamination in soils.
Solubility - A measure of the ability of a substance to dissolve in a fluid.
Stabilization -The conversion of a substance into a form that will not readily change its physical or chemical characteristics.
Standard - A general term used to describe legally established values above which regulatory action will be required.
Standard deviation - The most widely used measure to describe the dispersion of a data set, defined for a set of n values as follows: where Xm is the arithmetic mean for the data set of n values.
Storm sewer: A system of pipes (separate from sanitary sewers) that carries water runoff from buildings and land surfaces.
Subchronic - Relating to intermediate duration, usually used to describe studies or exposure levels spanning 5 to 90 days duration.
Subchronic daily intake (SDI) The exposure, expressed in mg/kg-day, averaged over a portion of a lifetime.
Subchronic exposure - The short-term, high-level exposure to chemicals, i.e., the maximum exposure or doses to a chemical over a portion of a lifetime.
Superfund - A commonly used name for the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also referred to as the “Trust Fund.”
Surface runoff: Precipitation, snow melt, or irrigation water in excess of what can infiltrate the soil surface and be stored in small surface depressions; a major transporter of non-point source pollutants in rivers, streams and lakes.
Surface water: All water naturally open to the atmosphere (rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries, etc.).
Surface-water treatment rule: Rule that specifies maximum contaminant level goals for Giardia lamblia, viruses and Legionella, and promulgates filtration and disinfection requirements for public water systems using surface-water or ground-water sources under the direct influence of surface water. The regulations also specify water quality, treatment, and watershed protection criteria under which filtration may be avoided.
Surfactant - A surface-active chemical agent, usually made up of phosphates, used in detergents to produce lathering.
Synergism - An interaction of two or more chemicals that results in an effect that is greater than the sum of their effects taken independently. It is the effects from a combination of two or more events, efforts, or substances that are greater than would be expected from adding the individual effects.
Threshold - The lowest dose or exposure of a chemical at which a specified measurable effect is observed and below which such effect is not observed. Threshold dose is the minimum exposure dose of a chemical that will evoke a stipulated toxicological response. Toxicological threshold refers to the concentration at, which a compound exhibits toxic effects.
Threshold chemical -Also, non-zero threshold chemical, refers to a substance which is known or assumed to have no adverse effects below a certain dose.
Threshold limit - A chemical concentration above which adverse health and/or environmental effects may occur.
Tolerance limit- The level or concentration of a chemical residue in media of concern above which adverse health effects are possible, and above which corrective action should therefore be undertaken.
Toxicant - Any synthetic or natural chemical with an ability to produce adverse health effects. It is a poisonous contaminant that may injure an exposed organism.
Toxicity - The harmful effects produced by a chemical substance. It is the quality or degree of being poisonous or harmful to human or ecological receptors. It represents the property of a substance to cause any adverse physiological effects (on living organisms).
Toxicity assessment - Evaluation of the toxicity of a chemical based on all available human and animal data. It is the characterization of the toxicological properties and effects of a chemical substance, with special emphasis on the establishment of dose-response characteristics.
Toxic substance -Any material or mixture that is capable of causing an unreasonable threat to human health or the environment.
Treatment - A change in the composition or concentration of a waste substance so as to make it less hazardous, or to make it acceptable at disposal and re-use facilities. It involves the application of technological process to a contaminant or waste in order to render it nonhazardous or less hazardous or more suitable for resource recovery.
Trip blank - A trip blank is transported just like actual samples, but does not contain the chemicals to be analyzed. The purpose of this blank is to evaluate the possibility that a chemical could seep into samples (to adulterate them) during transportation to the laboratory.
Uncertainty - The lack of confidence in the estimate of a variable’s magnitude or probability of occurrence.
Uncertainty factor (UF) - Also called safety factor, refers to a factor that is used to provide a margin of error when extrapolating from experimental animals to estimate human health risks.
Underground storage tank (UST) -A tank fully or partially located below the ground surface that is designed to hold gasoline or other petroleum products, or indeed other chemical products.
Unit cancer risk (UCR) - The excess lifetime risk of cancer due to a continuous lifetime exposure/dose of one unit of carcinogenic chemical concentration (caused by one unit of exposure in the low exposure region).
Unit Risk (
Upper confidence limit, 95% (95% UCL) -The upper limit on a normal distribution curve below which the observed mean of a data set will occur 95% of the time. This is also equivalent to stating that there is, at most, a 5% chance of the true mean being greater than the observed value.
Vadose Zone - Also called the unsaturated soil zone, is the zone between the ground surface and the top of the groundwater table.
Volatile organic compound (VOC) - Any organic compound that has a great tendency to vaporize, and is susceptible to atmospheric photochemical reactions.
Volatility - A measure of the tendency of a compound to vaporize from the liquid state.
Water table - The top of the saturated zone where confined groundwater is under atmospheric pressure.