| Abandoned Well | A well whose use has been permanently discontinued or which is in a state of such disrepair that it cannot be used for its intended purpose. | Abatement | Reducing the degree or intensity of, or eliminating pollution. | Abatement Debris | Waste from remediation activities. | Abiotic | Nonliving,Not caused by or resulting from the activity of living organisms. | Aboveground storage tanks | Any tank or other container that is aboveground, partially buried, bunkered, or in a subterranean vault. This includes floating fuel systems. | Absorbed Dose | The amount of a substance that penetrates an exposed organism's absorption barriers (e.g.,, skin, lung tissue, gastrointestinal tract) through physical or biological processes. The term is synonymous with internal dose. | Absorption | The uptake of water, other fluids, or dissolved chemicals by a cell or an organism (e.g. Tree roots absorb dissolved nutrients in soil). | Absorption Barrier | Any of the exchange sites of the body that permit uptake of various substances at different rates (e.g. skin, lung tissue, and gastrointestinal-tract wall). | Accelerated Growth | On a plot of bacterial growth versus time, the point at which the bacteria begin to divide, and the population increase is gradual. | Accident Site | The location of an unexpected occurrence, failure or loss, either at a plant or along a transportation route, resulting in a release of hazardous materials. | Acclimatization | The physiological and behavioral adjustments of an organism to changes in its environment. | Accumulation | Accumulation refers to change in mass or moles within a system with respect to time. This change can be either positive or negative and accordingly accumulation is positive or negative. | Accuracy | Accuracy is a degree, or measurement, of closeness to a target value. Accuracy should not be confused with precision. A sample is accurate if the absolute value of the bias of the total sampling error is within a specified acceptable level of accuracy. | Acid | A corrosive solution with a pH less than 7. | Acid Aerosol | Acidic liquid or solid particles small enough to become airborne. High concentrations can irritate the lungs and have been associated with respiratory diseases like asthma. | Acid Deposition | A complex atmospheric phenomenon that occurs when sulfur and nitrogen compounds 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 (e.g. acid rain). | Acid Mine Drainage | Drainage of water from areas that have been mined for coal or other mineral ores. The water has a low pH because of its contact with sulfur-bearing material and is harmful to aquatic organisms. | Acid Neutralizing Capacity | Measure of ability of a base (e.g., water or soil) to resist changes in pH. | Acid Rain | Precipitation having a ph lower than the natural range of ~5.2 - 5.6; caused by sulfur and nitrogen acids derived from anthropogenic emissions. | Acidic | The condition of water or soil that contains a sufficient amount of acidic substances to lower the pH below 7.0. | Acidity | A measure of how acid a solution may be. A solution with a pH of less than 7.0 is considered acidic. | ACScale Sound Level | A measurement of sound approximating the sensitivity of the human ear, used to note the intensity or annoyance level of sounds. | Action Levels | Regulatory levels recommended by EPA for enforcement by FDA and USDA when pesticide residues occur in food or feed commodities for reasons other than the direct application of the pesticide. Action levels are set for inadvertent residues. | Activated Carbon | A highly adsorbent form of carbon used to remove odors and toxic substances from liquid or gaseous emissions. In waste treatment, it is used to remove dissolved organic matter from waste drinking water. | Activated Sludge | Product that results when primary effluent is mixed with bacteria-laden sludge and then agitated and aerated to promote biological treatment, speeding the breakdown of organic matter in raw sewage undergoing secondary waste treatment. | Activated Sludge Process | An sewage treatment process by which bacteria that feed on organic wastes are continuously circuated and put in contact with organic waste in the presence of oxygen to increase the rate of decomposition. | Activator | A chemical added to a pesticide to increase its activity. | Active Ingredient | An agent that is specifically intended to kill, repel, or otherwise deter a target organism. Active ingredients are listed on pesticide product labels. | Acute Exposure | A single exposure to a toxic substance which may result in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day, as compared to longer, continuing exposure over a period of time. | Acute Toxicity | The ability of a substance to cause severe biological harm or death soon after a single exposure or dose. Also, any poisonous effect resulting from a single short-term exposure to a toxic substance. | Adaptation | Changes in an organism's physiological structure or function or habits that allow it to survive in new surroundings. | Add-on Control Device | An air pollution control device that reduces the pollution in an exhaust gas. The control device usually does not affect the process being controlled and thus is "add-on" technology. | Adequately Wet | Asbestos containing material that is sufficiently mixed or penetrated with liquid to prevent the release of particulates. | Administered Dose | In exposure assessment, the amount of a substance given to a test subject (human or animal) to determine dose-response relationships. Since exposure to chemicals is usually inadvertent, this quantity is often called potential dose. | Administrative Order | A legal document signed by EPA directing an individual, business, or other entity to take corrective action or refrain from an activity. It describes the violations and actions to be taken, and can be enforced in court. | Administrative Order by Consent for Response Activity and Site Redevelopment | A three party agreement between the state, a liable party under NREPA Part 201, and a non-liable party that has an interest in the property. | Administrative Order On Consent | A legal agreement signed by EPA and an individual, business, or other entity through which the violator agrees to pay for correction of violations, take the required corrective or cleanup actions, or refrain from an activity. | Administrative Procedures Act | A law that spells out procedures and requirements related to the promulgation of regulations. | Administrative Record | All documents which EPA considered or relied on in selecting the response action at a Superfund site, culminating in the record of decision for remedial action or, an action memorandum for removal actions. | Adsorb | Accumulation of a substance at an interface, i.e. is held at or on the surface.
A chemical process where a molecule attaches loosely to the surface of another phase, without becoming incorporated into that phase. | Adsorption | Removal of a pollutant from air or water by collecting the pollutant on the surface of a solid material; e.g., an advanced method of treating waste in which activated carbon removes organic matter from waste-water. | Adulterants | Chemical impurities or substances that by law do not belong in a food, or pesticide. | Adulterated | The addition of inactive ingredients to a food that cause the food to have toxic effects when ingested. | Advance (of a beach) | A continuing seaward movement of the shoreline. Also Progression. | Advanced Wastewater Treatment | Any treatment of sewage that goes beyond the secondary or biological water treatment stage and includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. (See primary, secondary treatment.) | Advection | Advection is one of the two processes by which solutes are transported in a fluid. Advective transport is the bulk movement of solute as a direct result of cocurrent movement of the fluid elements. | Adverse Effects Data | FIFRA requires a pesticide registrant to submit data to EPA on any studies or other information regarding unreasonable adverse effects of a pesticide at any time after its registration. | Advisory | A non-regulatory document that communicates risk information to those who may have to make risk management decisions. | Aerated Lagoon | A holding and/or treatment pond that speeds up the natural process of biological decomposition of organic waste by stimulating the growth and activity of bacteria that degrade organic waste. | Aeration | A process which promotes biological degradation of organic matter in water. The process may be passive (as when waste is exposed to air), or active (as when a mixing or bubbling device introduces the air). | Aeration Tank | A chamber used to inject air into water. | Aerobic | Life or processes that require, or are not destroyed by, the presence of oxygen. (See: anaerobic). | Aerobic Organisms | Organisms that survive in oxygen-rich environments and use oxygen as the terminal electron acceptor. | Aerobic Respiration | The breakdown of organic chemicals by molecular oxygen to form gaseous carbon dioxide. | Aerobic Treatment | Process by which microbes decompose complex organic compounds in the presence of oxygen and use the liberated energy for reproduction and growth. (Such processes include extended aeration, trickling filtration, and rotating biological contactors). | Aerosol | A finely divided material suspended in air or other gaseous environment. | Affected Landfill | Under the Clean Air Act, landfills that meet criteria for capacity, age, and emissions rates set by the EPA. They are required to collect and combust their gas emissions. | Affected Public | 1.The people who live and/or work near a hazardous waste site. 2. The human population adversely impacted following exposure to a toxic pollutant in food, water, air, or soil. | Afterburner | In incinerator technology, a burner located so that the combustion gases are made to pass through its flame in order to remove smoke and odors. It may be attached to or be separated from the incinerator proper. | Age Tank | A tank used to store a chemical solution of known concentration for feed to a chemical feeder. Also called a day tank. | Agent | Any physical, chemical, or biological entity that can be harmful to an organism(synonymous with stressor). | Aggradation | The general smoothing of the earth's surface by deposition due to air or aquatic transport of material. | Agricultural Pollution | Farming wastes, including runoff and leaching of pesticides and fertilizers; erosion and dust from plowing; improper disposal of animal manure and carcasses; crop residues, and debris. | Agroecosystem | Land used for crops, pasture, and livestock; the adjacent uncultivated land that supports other vegetation and wildlife; and the associated atmosphere, the underlying soils, groundwater, and drainage networks. | AHERA Designated Person | A person designated by a Local Education Agency to ensure that the AHERA requirements for asbestos management and abatement are properly implemented. | Air Binding | Situation where air enters the filter media and harms both the filtration and backwash processes. | Air Changes Per Hour | The movement of a volume of air in a given period of time; if a house has one air change per hour, it means that the air in the house will be replaced in a one-hour period. | Air Cleaning | Indoor-air quality-control strategy to remove various airborne particulates and/or gases from the air. Most common methods are particulate filtration, electrostatic precipitation, and gas sorption. | Air Contaminant | Any particulate matter, gas, or combination thereof, other than water vapor. (See: Air Pollutant.) | Air Curtain | A method of containing oil spills. Air bubbling through a perforated pipe causes an upward water flow that slows the spread of oil. It can also be used to stop fish from entering polluted water. | Air Exchange Rate | The rate at which outside air replaces indoor air in a given space. | Air Gap | Open vertical gap or empty space that separates drinking water supply to be protected from another water system in a treatment plant or other location. The open gap protects the drinking water from contamination by backflow or back siphonage. | Air Handling Unit | Equipment that includes a fan or blower, heating and/or cooling coils, regulator controls, condensate drain pans, and air filters. | Air Mass | A large body of air with similar temperature and moisture characteristics as a result of having come from the same source region. | Air Padding | Pumping dry air into a container to assist with the withdrawal of liquid or to force a liquefied gas such as chlorine out of the container. | Air Permeability | The degree to which a given material or substance will permit the passage of air. Important to the design of soil-gas surveys. Measured in darcys or centimeters-per-second. | Air Plenum | Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum. | Air Pollutant | Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. | Air Pollution Control Device | Mechanism or equipment that cleans emissions generated by a source (e.g., an incinerator, industrial smokestack, or an automobile exhaust system) by removing pollutants that would otherwise be released to the atmosphere. | Air Pollution Episode | A period of abnormally high concentration of air pollutants, often due to low winds and temperature inversion, that can cause illness and death. (See: Episode, Pollution.). | Air Quality Criteria | The levels of pollution and lengths of exposure above which adverse health and welfare effects may occur. | Air Quality Standards | The level of pollutants prescribed by regulations that are not be exceeded during a given time in a defined area. | Air Sparging | Injecting air or oxygen into an aquifer to strip or flush volatile contaminants as air bubbles up through the ground water and is captured by a vapor extraction system. | Air Stripping | A treatment system that removes volatile organic compounds (VOCs) from contaminated ground water or surface water by forcing an airstream through the water and causing the compounds to evaporate. | Air Toxics | Any air pollutant for which a national ambient air quality standard (NAAQS) does not exist that may reasonably be anticipated to cause cancer; respiratory, cardiovascular or other serious or irreversible chronic or acute health effects in humans. | Air/Oil Table | The surface between the vadose zone and ambient oil; the pressure of oil in the porous medium is equal to atmospheric pressure. | Airborne Particulates | Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets. Chemical composition of particulates varies widely, depending on location and time of year (dust, emissions, combustion products, etc.). | Airborne Release | Release of any pollutant into the air. | Alachlor | A herbicide, marketed under the trade name Lasso, used mainly to control weeds in in corn, soybeans, peanuts, cotton, woody fruits, and certain ornamentals. | Alar | Trade name for daminozide, a pesticide that makes apples redder, firmer, and less likely to drop off trees before growers are ready to pick them. It is also used to a lesser extent on peanuts, tart cherries, concord grapes, and other fruits. | Aldicarb | An insecticide sold under the trade name Temik. It is made from ethyl isocyanate. | Algae | Simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals. | Algal Blooms | Sudden spurts of algal growth, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry. | Algicide | Substance or chemical used specifically to kill or control algae. | Aliphatic | Organic compound that is an alkane or alkene or alkyne or their derivative. | Aliquot | A measured portion of a sample taken for analysis. One or more aliquots make up a sample. (See: Duplicate.). | Alkaline | The condition of water or soil which contains a sufficient amount of alkali substance to raise the pH above 7.0. | Alkalinity | 1. The capacity of bases to neutralize acids. An example is lime added to lakes to decrease acidity. 2. A water's ability to resist changes in pH on the addition of acid. | Allergen | A substance that causes an allergic reaction in individuals sensitive to it. | Alluvial | Relating to and/or sand deposited by flowing water. | Alongshore | Parallel to and near the shoreline; same as LONGSHORE. | Alternative Compliance | A policy that allows facilities to choose among methods for achieving emission-reduction or risk-reduction instead of command and control regulations that specify standards and how to meet them. | Alternative Remedial Contract Strategy Contractors | Government contractors who provide project management and technical services to support remedial response activities at National Priorities List sites. | Ambient Air | Any unconfined portion of the atmosphere: open air, surrounding air. | Ambient Measurement | A measurement of the concentration of a substance or pollutant within the immediate environs of an organism; taken to relate it to the amount of possible exposure. | Ambient Medium | Material surrounding or contacting an organism (e.g., outdoor air, indoor air, water, or soil, through which chemicals or pollutants can reach the organism. (See: Biological medium, Environmental medium.) | Amphoteric | Substances with the ability to act as either an acid or a base. | Amplitude | The vertical distance that a wave causes water to be displaced from a mean value. An ocean wave has an amplitude equal to the vertical distance from STILLWATER LEVEL to wave crest. | Amprometric Titration | A way of measuring concentrations of certain substances in water using an electric current that flows during a chemical reaction. | Anaerobic | A life or process that occurs in, or is not destroyed by, the absence of oxygen. | Anaerobic Decomposition | Reduction of the net energy level and change in chemical composition of organic matter caused by microorganisms in an oxygen-free environment. | Anaerobic Respiration | Respiration that can only occur in the absence of oxygen or nitrate. | Analysis | Separation and measurement of component parts. | Analyte | The chemical for which a sample is analyzed. | Analytical Error | This error component arises from imperfections in the analysis (chemical or
physical) operation. It includes errors associated with such activities as chemically extracting the
analyte from the sample matrix, instrumentation error, operator errors, moisture analysis, gravimetric
errors, and other measurement errors. | Animal Dander | Tiny scales of animal skin, a common indoor air pollutant. | Anion | A negatively charged ion. | Anisotropy | Having properties which vary depending on the direction of measurement. | Annular Space, Annulus | The space between two concentric tubes or casings, or between the casing and the borehole wall. | Anoxic Denitrification | Conversion of oxidised forms of nitrogen, such as NO3- to nitrogen gas (N2) by anaerobic bacteria. | Anoxic Environment | An environment that contains low concentrations of oxygen. | Anti-Degradation Clause | Part of federal air quality and water quality requirements prohibiting deterioration where pollution levels are above the legal limit. | Applicable or Relevant and Appropriate Requirements | Any state or federal statute that pertains to protection of human life and the environment in addressing specific conditions or use of a particular cleanup technology at a Superfund site. | Applied Dose | In exposure assessment, the amount of a substance in contact with the primary absorption boundaries of an organism (e.g., skin, lung tissue, gastrointestinal track) and available for absorption. | Aqueous Solubility | The maximum concentration of a chemical that will dissolve in pure water at a reference temperature. | Aquiclude | A confining layer in an aquifer that is essentially impermeable to water flow. | Aquifer | The water-yeilding earthen layer where water is stored. The geologic formation, thorough which water can flow horizontally and be pumped. | Aquifer test | A test to determine hydraulic properties of an aquifer. | Aquitard | Geological formation that may contain groundwater but is not capable of transmitting significant quantities of it under normal hydraulic gradients. May function as confining bed. | Architectural Coatings | Coverings such as paint and roof tar that are used on exteriors of buildings. | Area of Concern | An environment identified as a potential pollution risk. | Area of Review | In the UIC program, the area surrounding an injection well that is reviewed during the permitting process to determine if flow between aquifers will be induced by the injection operation. | Area Source | Any source of air pollution that is released over a relatively small area but which cannot be classified as a point source. Such sources may include vehicles and other small engines, small businesses and household activities, or biogenic sources. | Aromatics | A type of hydrocarbon, such as benzene or toluene, with a specific type of ring structure. Aromatics are sometimes added to gasoline in order to increase octane. Some aromatics are toxic. | Arsenicals | Pesticides containing arsenic. | Artesian Aquifer or Well | Water held under pressure in porous rock or soil confined by impermeable geological formations. | Asbestos | A mineral fiber that can pollute air or water and cause cancer or asbestosis when inhaled. EPA has banned or severely restricted its use in manufacturing and construction. | Asbestos Abatement | Procedures to control fiber release from asbestos-containing materials in a building or to remove them entirely, including removal, encapsulation, repair, enclosure, encasement, and operations and maintenance programs. | Asbestos Assessment | In the asbestos-in-schools program, the evaluation of the physical condition and potential for damage of all friable asbestos containing materials and thermal insulation systems. | Asbestos Program Manager | A building owner or designated representative who supervises all aspects of the facility asbestos management and control program. | Asbestos-Containing Waste Materials | Mill tailings or any waste that contains commercial asbestos and is generated by a source covered by the Clean Air Act Asbestos NESHAPS. | Asbestosis | A disease associated with inhalation of asbestos fibers. The disease makes breathing progressively more difficult and can be fatal. | Assay | Determination of the purity of a substance or the amount of any particular constituent of a mixture. | Assemblage | An association of interacting populations of organisms in a given waterbody. Examples of assemblages used for biological assessments include : algae, amphibians, birds, fish, herps (reptiles and amphibians), macroinvertebrates (insects, crayfish, clams, snails, etc.), and vascular plants. | Assessment Endpoint | In ecological risk assessment, an explicit expression of the environmental value to be protected; includes both an ecological entity and specific attributed thereof. Entity. | Assimilation | The ability of a body of water to purify itself of pollutants. | Assimilative Capacity | The capacity of a natural body of water to receive wastewaters or toxic materials without deleterious effects and without damage to aquatic life or humans who consume the water. | Association of Boards of Certification | An international organization representing boards which certify the operators of waterworks and wastewater facilities. | Atmospheric emissions | Release or discharge of fumes, dust or particulates into the air. | Atomic Number | The number of protons in the nucleus of an atom. | Atomic Weight | Of an element, is the average atomic mass for the naturally occurring element. | Attainment Area | An area considered to have air quality as good as or better than the national ambient air quality standards as defined in the Clean Air Act. An area may be an attainment area for one pollutant and a non-attainment area for others. | Attenuation | The process by which a compound is reduced in concentration over time, through absorption, adsorption, degradation, dilution, and/or transformation. an also be the decrease with distance of sight caused by attenuation of light by particulate pollution. | Attractant | A chemical or agent that lures insects or other pests by stimulating their sense of smell. | Attrition | Wearing or grinding down of a substance by friction. Dust from such processes contributes to air pollution. | Autotrophic Organisms | Primary producers that obtain their carbon from inorganic sources. | Availability Session | Informal meeting at a public location where interested citizens can talk with EPA and state officials on a one-to-one basis. | Available Chlorine | A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials used as a source of chlorine when compared with that of liquid or gaseous chlorines. | Avoided Cost | The cost a utility would incur to generate the next increment of electric capacity using its own resources; many landfill gas projects' buy back rates are based on avoided costs. | Awash | Being intermittently washed over by waves. | Back Pressure | A pressure that can cause water to backflow into the water supply when a user's waste water system is at a higher pressure than the public system. | Backfill | To refill an excavated area with fill or soil; or, the material itself that is used to refill an excavated area. | Backflow/Back Siphonage | A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one. | Background Level | The concentration of a substance in an environmental media (air, water, or soil) that occurs naturally or is not the result of human activities. | Backwashing | Reversing the flow of water back through the filter media to remove entrapped solids. | Baffle | A flat board or plate, deflector, guide, or similar device constructed or placed in flowing water or slurry systems to cause more uniform flow velocities to absorb energy and to divert, guide, or agitate liquids. | Baffle Chamber | In incinerator design, a chamber designed to promote the settling of fly ash and coarse particulate matter by changing the direction and/or reducing the velocity of the gases produced by the combustion of the refuse or sludge. | Baghouse Filter | Large fabric bag, usually made of glass fibers, used to eliminate intermediate and large (greater than 20 PM in diameter) particles. This device operates like the bag of an electric vacuum cleaner. | Bailer | A pipe with a valve at the lower end, used to remove slurry from the bottom or side of a well as it is being drilled, or to collect ground-water samples from wells or open boreholes. | Baling | Compacting solid waste into blocks to reduce volume and simplify handling. | Ballistic Separator | A machine that sorts organic from inorganic matter for composting. | Band Application | The spreading of chemicals over, or next to, each row of plants in a field. | Banking | A system for recording qualified air emission reductions for later use in bubble, offset, or netting transactions. (See: Emissions trading.) | Barrel Sampler | Open-ended steel tube used to collect soil samples. | Basal Application | In pesticides, the application of a chemical on plant stems or tree trunks just above the soil line. | Basalt | Consistent year-round energy use of a facility; also refers to the minimum amount of electricity supplied continually to a facility. | Base-Neutralizing Capacity | The ability of a water to resist changes in pH due to the addition of a base. | Baseflow | A portion of the streamflow that would be present even during periods of drought. | Baseline Environmental Assessment | An evaluation of environmental conditions which exist at a facility at the time of purchase, occupancy, or foreclosure that reasonably defines the existing conditions. | Basin | Larger systems that include lakes, rivers, the surrounding land, and even the groundwater lying in the geological materials below the land. | Batch System | Batch system or a Closed system is one in which there is no transfer of material across the system boundary , during the time interval of interest. | Beach erosion | The carrying away of beach materials by wave action, currents, or wind. | Bean Sheet | Common term for a pesticide data package record. | Bed Load | Sediment particles resting on or near the channel bottom that are pushed or rolled along by the flow of water. | Bedrock | A general term for the rock layer that lies beneath soil, loose sediments, or other unconsolidated material. Groundwater often is found in the bedrock layer. | BEN-EPA's Computer model | EPA's computer model for analyzing a violator's economic gain from not complying with the law. | Bench-scale Tests | Laboratory testing of potential cleanup technologies (See: Treatability studies.) | Benefit-Cost Analysis | An economic method for assessing the benefits and costs of achieving alternative health-based standards at given levels of health protection. | Benthic Organism | Any of a diverse group of aquatic plants and animals that live on the bottom of marine and/or fresh water. Presence or absence of certain benthic organisms can be used as an indicator of water quality. | Benthic Zone | The bottom sediments of a lake. | Bentonite | A colloidal clay, expansible when moist, commonly used to provide a tight seal around a well casing. | Berm | A ledge, wall or mound of soil used to prevent the migration of contaminants. | Beryllium | An metal hazardous to human health when inhaled as an airborne pollutant. It is discharged by machine shops, ceramic and propellant plants, and foundries. | Best Available Control Measures | A term used to refer to the most effective measures (according to EPA guidance) for controlling small or dispersed particulates and other emissions from various sources. | 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. | Best Demonstrated Available Technology | The most effective commercially available means of treating specific types of hazardous waste. The BDATs may change with advances in treatment technologies. | Best Management Practice | Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from non-point sources. | Bias | The systematic or persistent distortion of a measurement process that causes errors in one
direction along a metric away the true value; that is, bias is a function of systematic error (e.g., the
average measured mass differs from the true mass by +0.034 g). | Bimetal | Beverage containers with steel bodies and aluminum tops; handled differently from pure aluminum in recycling. | Bin vent filter | Used on Minergy storage silos to minimize emission of particulate matter. | Bioaccumulants | Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. | Bioassay | A test to determine the relative strength of a substance by comparing its effect on a test organism with that of a standard peparation. | Bioavailability | Degree of ability to be absorbed and ready to interact in organism metabolism. | Biochemical Oxygen Demand | A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. The greater the BOD, the greater the degree of pollution. | Bioconcentration | The accumulation of a chemical in tissues of a fish or other organism to levels greater than in the surrounding medium. | Biodegradable | Capable of decomposing under natural conditions. | Biodiversity | Refers to the variety and variability among living organisms and the ecological complexes in which they occur. Diversity can be defined as the number of different items and their relative frequencies. | Biological Assessment (bioassessment) | Using biomonitoring data of samples of living organisms to evaluate the condition or health of a place (e.g., a stream, wetland, or woodlot). | Biological Contaminants | Living organisms or derivates(e.g., viruses, bacteria, fungi, and mammal and bird) antigens that can cause harmful health effects when inhaled, swallowed, or otherwise taken into the body. | Biological Control | In pest control, the use of animals and organisms that eat or otherwise kill or out-compete pests. | Biological Indicators of Exposure Study | A study designed to use biomedical testing or the measurement of a chemical (analyte), its metabolite, or another marker of exposure in human body fluids or tissues in order to validate human exposure to a hazardous substance. | Biological Integrity | The ability to support and maintain balanced, integrated, functionality in the natural habitat of a given region. Concept is applied primarily in drinking water management. | Biological Magnification | Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. | Biological Measurement | A measurement taken in a biological medium. For exposure assessment, it is related to the measurement is taken to related it to the established internal dose of a compound. | Biological Medium | One of the major component of an organism; e.g., blood, fatty tissue, lymph nodes or breath, in which chemicals can be stored or transformed. | Biological Oxidation | Decomposition of complex organic materials by microorganisms. Occurs in self-purifi- cation of water bodies and in activated sludge wastewater treatment. | Biological Oxygen Demand | The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter. | Biological Stressors | Organisms accidently or intentionally dropped into habitats in which they do not evolve naturally; e.g. gypsy moths, Dutch elm disease, certain types of algae, and bacteria. | Biological Treatment | A treatment technology that uses bacteria to consume organic waste. | Biological Uptake | The transfer of hazardous substances from the environment to plants, animals, and humans. | Biologically Effective Dose | The amount of a deposited or absorbed compound reaching the cells or target sites where adverse effect occur, or where the chemical interacts with a membrane. | Biologicals | Vaccines, cultures and other preparations made from living organisms and their products, intended for use in diagnosing, immunizing, or treating humans or animals, or in related research. | Biomagnification | The process that results in the accumulation of a chemical in an organism at higher levels than are found in its own food. | Biomass | All of the living material in a given area; often refers to vegetation. | Biome | Entire community of living organisms in a single major ecological area. | Biomonitoring | The use of living organisms to test the suitability of effluents for discharge into receiving waters and to test the quality of such waters downstream from the discharge. | 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 or counteract diseases of trees, plants, and garden soil. | Biosensor | Analytical device comprising a biological recognition element (e.g., enzyme, DNA) in intimate contact with an electrochemical, optical, thermal, or acoustic signal transducer that together permit analyses of chemical properties or quantities. | Biostabilizer | A machine that converts solid waste into compost by grinding and aeration. | Biota | The animal and plant life of a given region. | Biotechnology | Techniques that use living organisms or parts of organisms to produce a variety of products (from medicines to industrial enzymes) to improve plants or animals or to develop microorganisms to remove toxics from bodies of water, or act as pesticides. | Biotic Community | A naturally occurring assemblage of plants and animals that live in the same environment and are mutually sustaining and interdependent. (See: Biome.) | Biotransformation | Conversion of a substance into other compounds by organisms; includes biodegredation. | Bioturbation | The natural activity of living organisms, such as worms, to move particles and porewater from inside soil or sediment beds toward the surface and circulate them in the upper layers. | Blackwater | Water that contains animal, human, or food waste. | Bloom | A proliferation of algae and/or higher aquatic plants in a body of water; often related to pollution, especially when pollutants accelerate growth. | Body Burden | The amount of a chemical stored in the body at a given time, especially a potential toxin in the body as the result of exposure. | Bog | A type of wetland that accumulates appreciable peat deposits. Bogs depend primarily on precipitation for their water source, and are usually acidic and rich in plant residue with a conspicuous mat of living green moss. | Boom | A floating device used to contain oil on a body of water. | Borehole | Hole made by inserting a hollow tube with drilling equipment to draw up a core of soil. The soil samples are collected for testing to determine the site geology and to learn if the soil has been contaminated. | Boring (or Soil Boring) | A circular hole made in the ground by an auger or mechanical drill rig to collect soil samples deep in the ground. Representative samples are collected for testing to see if the subsoil has been contaminated. Sometimes these borings are converted into groundwater monitoring wells. | Boring logs | The record of formations penetrated, drilling progress, record of depth of water, location of contaminants, and other recorded information having to do with the drilling well. | Botanical Pesticide | A pesticide whose active ingredient is a plant-produced chemical such as nicotine or strychnine. Also called a plant-derived pesticide. | 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. | Bottom Land Hardwoods | Forested freshwater wetlands adjacent to rivers in the southeastern United States, especially valuable for wildlife breeding, nesting and habitat. | Bounding Estimate | An estimate of exposure, dose, or risk that is higher than that incurred by the person in the population with the currently highest exposure, dose, or risk. | Brackish | Mixed fresh and salt water. | Break water | A structure that protects a shoreline, harbor, anchorage, or basin from waves. | Breakdown products | Most contaminants are combinations of specific substances. Contaminants are degraded, or separated, into these individual substances through chemical or physical means. | Breakpoint Chlorination | Addition of chrlorine to water until the chlorine demand has been satisfied. | Breakthrough | A crack or break in a filter bed that allows the passage of floc or particulate matter through a filter; will cause an increase in filter effluent turbidity. | Breathing Zone | Area of air in which an organism inhales. | Brine Mud | Waste material, often associated with well-drilling or mining, composed of mineral salts or other inorganic compounds. | British Thermal Unit | A measure of the amount of energy produced from a material that is being combusted. | Brownfield | Abandoned, idled, or under-used industrial and commercial facilities where expansion or redevelopment is complicated by real or perceived environmental contamination. | Brownfield Plan | A plan approved by the local governing body that includes the specific brownfield properties. | Brownfield Revelopment Authority | A local governing body that provides decision making and control of brownfield redevelopment projects. | Bubble | Under the bubble concept, sources can control more than required at one emission point where control costs are relatively low in return for a comparable relaxation of controls at a second emission point where costs are higher. | Buffer | A solution or liquid whose chemical makeup is such that it minimizes changes in pH when acids or bases are added to it. | Buffering Capacity | The ability of a water to resist change in pH when an acid or base is added. | Building Related Illness | Diagnosable illness whose cause and symptoms can be directly attributed to a specific pollutant source within a building (e.g., Legionnaire's disease, hypersensitivity, pneumonitis.) | Bulk head | A shoreline protection structure or partition intended to retain land from sliding into a water body. | Bulk Sample | A small portion (usually thumbnail size) of a suspect asbestos-containing building material collected by an asbestos inspector for laboratory analysis to determine asbestos content. | Cadmium | A heavy metal that accumulates in the environment. | Cap | A layer of clay, or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize leachate. | Capacity Assurance Plan | A statewide plan which supports a state's ability to manage the hazardous waste generated within its boundaries over a twenty year period. | Capillary Action | The process of soil drawing water above its static level. | Capillary Fringe | The porous material just above the water table which may hold water by capillarity (a property of surface tension that draws water upwards) in the smaller void spaces. | Capture Efficiency | The fraction of organic vapors generated by a process that are directed to an abatement or recovery device. | Carbon Absorber | An add-on control device that uses activated carbon to absorb volatile organic compounds from a gas stream. (The VOCs are later recovered from the carbon.) | Carbon Adsorption | A treatment system that removes contaminants from ground water or surface water by forcing it through tanks containing activated carbon treated to attract the contaminants. | Carbon Monoxide | A colorless, odorless, poisonous gas produced by incomplete fossil fuel combustion. | Carbon Tetrachloride | Compound consisting of one carbon atom ad four chlorine atoms, once widely used as a industrial raw material, as a solvent, and in the production of CFCs. Use as a solvent ended when it was discovered to be carcinogenic. | Carcinogen | Any substance that can cause or aggravate cancer. | Carrier | Any material or system that can facilitrate the movement of a pollutant into the body or cells. | Carrying Capacity | On a plot of bacterial growth versus time, the point at which the bacteria begin to die faster than they reproduce. | Cask | A thick-walled container (usually lead) used to transport radioactive material. Also called a coffin. | Catalyst | A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction. | Catalytic Converter | An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen. | Catalytic Incinerator | A control device that oxidizes volatile organic compounds (VOCs) by using a catalyst to promote the combustion process. Catalytic incinerators require lower temperatures than conventional thermal incinerators, thus saving fuel and other costs. | Categorical Exclusion | A class of actions which either individually or cumulatively would not have a significant effect on the human environment and therefore would not require preparation of an environmental assessment or environmental impact statement. | Categorical Pretreatment Standard | A technology-based effluent limitation for an industrial facility discharging into a municipal sewer system. Analogous in stringency to Best Availability Technology (BAT) for direct dischargers. | Cation | A positively charged ion. | Cementitious | Densely packed and nonfibrous friable materials. | Central Collection Point | Location were a generator of regulated medical waste consolidates wastes originally generated at various locations in his facility. The wastes are gathered together for treatment on-site or for transportation elsewhere for treatment and/or disposal. | Centrifugal Collector | A mechanical system using centrifugal force to remove aerosols from a gas stream or to remove water from sludge. | Channel Precipitation | The symbolic representation of a chemical reaction in terms of chemical formulas. | Channelization | Straightening and deepening streams so water will move faster, a marsh-drainage tactic that can interfere with waste assimilation capacity, disturb fish and wildlife habitats, and aggravate flooding. | Characteristic | Any one of the four categories used in defining hazardous waste: ignitability, corrosivity, reactivity, and toxicity. | Characterization of Ecological Effects | Part of ecological risk assessment that evaluates ability of a stressor to cause adverse effects under given circumstances. | Characterization of Exposure | Portion of an ecological risk assessment that evaluates interaction of a stressor with one or more ecological entities. | Check-Valve Tubing Pump | Water sampling tool also referred to as a water Pump. | Chemical | A chemical is any element, chemical compound or mixture of elements and/or compounds. | Chemical Case | For purposes of review and regulation, the grouping of chemically similar pesticide active ingredients (e.g., salts and esters of the same chemical) into chemical cases. | Chemical Oxygen Demand | A measure of the oxygen required to oxidize all compounds, both organic and inorganic, in water. | Chemical spill | Accident release occurring during the production, transportation or handling of hazardous chemical substances. | Chemical Stressors | Chemicals released to the environment through industrial waste, auto emissions, pesticides, and other human activity that can cause illnesses and even death in plants and animals. | Chemnet | Mutual aid network of chemical shippers and contractors that assigns a contracted emergency response company to provide technical support if a representative of the firm whose chemicals are involved in an incident is not readily available. | Chemotroph | Organisms that obtain their energy from organic or inorganic carbon rather than from light. | Chemtrec | The industry-sponsored Chemical Transportation Emergency Center; provides information and/or emergency assistance to emergency responders. | Chlorinated Hydrocarbons | Chemicals containing only chlorine, carbon, and hydrogen or any chlorinated organic compounds including chlorinated solvents. Includes DDT, aldrin, dieldrin, heptachlor, chlordane, dichloromethane, trichloromethylene, chloroform. | Chlorinated Solvent | An organic solvent containing chlorine atoms(e.g., methylene chloride and 1,1,1-trichloromethane). Uses of chlorinated solvents are include aerosol spray containers, in highway paint, and dry cleaning fluids. | Chlorofluorocarbons | A family of inert, nontoxic, and easily liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. CFCs drift into the upper atmosphere where their chlorine components destroy ozone. | Chlorophenoxy | A class of herbicides that may be found in domestic water supplies and cause adverse health effects. | Chlorosis | Discoloration of normally green plant parts caused by disease, lack of nutrients, or various air pollutants. | Chronic Effect | An adverse effect on a human or animal in which symptoms recur frequently or develop slowly over a long period of time. | Chronic Exposure | Multiple exposures occurring over an extended period of time or over a significant fraction of an animal's or human's lifetime (Usually seven years to a lifetime.) | Chronic Toxicity | The capacity of a substance to cause long-term poisonous health effects in humans, animals, fish, and other organisms.(See: Acute toxicity.) | Circle of Influence | The circular outer edge of a depression produced in the water table by the pumping of water from a well. | Class I Area | A Class I area is one in which visibility is protected more stringently than under the national ambient air quality standards; includes national parks, wilderness areas, monuments, and other areas of special national and cultural significance. | 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). | Class II Substance | A substance with an ozone depletion potential of less than 0.2. All HCFCs are currently included in this classification. | Clay Soil | Soil material containing more than 40 percent clay, less than 45 percent sand, and less than 40 percent silt. | Clean Air Act | The comprehensive federal law, which regulates air emissions. | Clean Coal Technology | Any technology not in widespread use prior to the Clean Air Act Amendments of 1990. This Act will achieve significant reductions in pollutants associated with the burning of coal. | Clean Fuels | Blends or substitutes for gasoline fuels, including compressed natural gas, methanol, ethanol, and liquified petroleum gas. | Clean Water Act | The Clean Water Act (CWA) is the cornerstone of surface water quality protection in the United States. (The Act does not deal directly with ground water nor with water quantity issues). The law employs a variety of regulatory and nonregulatory tools to sharply reduce direct pollutant discharges into waterways, finance municipal wastewater treatment facilities, and manage polluted runoff. | Cleaner Technologies Substitutes Assessment | A document that systematically evaluates the relative risk, performance, and cost trade-offs of technological alternatives; serves as a repository for all the technical data. | Cleanup | Actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and/or the environment. | Cleanup Process | A comprehensive program for the clean up (or remediation) of a polluted site. It involves investigation, analysis, and development of a cleanup plan and implementation of that plan. | Climate Change | The term "climate change" is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. | Climatology | The science of studying climatic conditions. Climatic conditions studied are usually within a region of the earth over an extended period of time. | Closed-Loop Recycling | Reclaiming or reusing wastewater for non-potable purposes in an enclosed process. | Closure | The procedure a landfill operator must follow when a landfill reaches its legal capacity for solid ceasing acceptance of solid waste and placing a cap on the landfill site. | Co-fire | Burning of two fuels in the same combustion unit; e.g., coal and natural gas, or oil and coal. | Coal Cleaning Technology | A precombustion process by which coal is physically or chemically treated to remove some of its sulfur so as to reduce sulfur dioxide emissions. | Coastal Zone | Lands and waters adjacent to the coast that exert an influence on the uses of the sea and its ecology, or whose uses and ecology are affected by the sea. | Code of Federal Regulations | Document that codifies all rules of the executive departments and agencies of the federal government. It is divided into fifty volumes, known as titles. Title 40 of the CFR (referenced as 40 CFR) lists all environmental regulations. | Coefficient of Haze | A measurement of visibility interference in the atmosphere. | Coke Oven | An industrial process which converts coal into coke, one of the basic materials used in blast furnaces for the conversion of iron ore into iron. | Cold Temperature CO | A standard for automobile emissions of carbon monoxide (CO) emissions to be met at a low temperature (i.e. 20 degrees Fahrenheit). Conventional automobile catalytic converters are not efficient in cold weather until they warm up. | Coliform Index | A rating of the purity of water based on a count of fecal bacteria. | Coliform Organism | Microorganisms found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially adverse contamination by pathogens. | Collector Sewers | Pipes used to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility. | Combined Sewer Overflows | Discharge of a mixture of storm water and domestic waste when the flow capacity of a sewer system is exceeded during rainstorms. | Combined Sewers | A sewer system that carries both sewage and storm-water runoff. During a heavy storm, the volume of water may be so great as to cause overflows of untreated mixtures of storm water and sewage into receiving waters. | Combustion | Burning accompanied by release of energy in the form of heat and light. Refers to controlled burning of waste, in which heat chemically alters organic compounds, converting into stable inorganics such as carbon dioxide and water. | Combustion Product | Substance produced during the burning or oxidation of a material. | Command-and-Control Regulations | Specific requirements prescribing how to comply with specific standards defining acceptable levels of pollution. | Comment Period | Time provided for the public to review and comment on a proposed EPA action or rulemaking after publication in the Federal Register. | Commingled Recyclables | Mixed recyclables that are collected together. | Comminuter | A machine that shreds or pulverizes solids to make waste treatment easier. | Common Sense Initiative | Voluntary program to simplify environmental regulation to achieve cleaner, cheaper, smarter results, starting with six major industry sectors. | Community Water System | A public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. | Comparative Risk Assessment | Process that generally uses the judgement of experts to predict effects and set priorities among a wide range of environmental problems. | Complex | A compound consisting of either complex ions with other ions of opposite charge or a neutral complex species. | Complex Ion | A metal ion with Lewis bases attached to it through coordinate covalent bonding. | Compliance Monitoring | Collection and evaluation of data, including self-monitoring reports, and verification to show whether pollutant concentrations and loads contained in permitted discharges are in compliance with the limits and conditions specified in the permit. | Compliance Schedule | A negotiated agreement between a pollution source and a government agency that specifies dates and procedures by which a source will reduce emissions and, thereby, comply with a regulation. | Composite Sample | A series of water samples taken over a given period of time and weighted by flow rate. | Composite sample | A sample created by combining several distinct subsamples. | Compounds | Substances containing two or more elements that are combined chemically. | Comprehensive Environmental Response, Compensation, and Liability Act | Federal law passed in 1980 that created a tax to fund Superfund, a trust fund used to investigate and clean up abandoned or uncontrolled hazardous waste sites. | Concentration | The relative amount of a substance mixed with another substance. An example is five ppm of carbon monoxide in air or 1 mg/l of iron in water. | Conditional Registration | Under special circumstances, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) permits registration of pesticide products that is "conditional" upon the submission of additional data. | Conditionally Exempt Generators | Persons or enterprises which produce less than 220 pounds of hazardous waste per month. Exempt from most regulation, they are required merely to determine whether their waste is hazardous, notify appropriate state or local agencies, and ship it offsite. | Conductance | A rapid method of estimating the dissolved solids content of water supply by determining the capacity of a water sample to carry an electrical current. Conductivity is a measure of the ability of a solution to carry and electrical curerent. | Cone of Depression | A depression in the water table that develops around a pumped well. | Cone of Influence | The depression, roughly conical in shape, produced in a water table by the pumping of water from a well. | Cone Penterometer Testing | A direct push system used to measure lithology based on soil penetration resistance. Sensors in the tip of the cone of the DP rod measure tip resistance and side-wall friction, transmitting electrical signals to digital processing equipment. | Confidential Business Information | Material that contains trade secrets or commercial or financial information that has been claimed as confidential by its source (e.g., a pesticide or new chemical formulation registrant). EPA has special procedures for handling such information. | Confidential Statement of Formula | A list of the ingredients in a new pesticide or chemical formulation. The list is submitted at the time for application for registration or change in formulation. | Confined Aquifer | An aquifer in which ground water is confined under pressure which is significantly greater than atmospheric pressure. | Confining Layer | The impermeable layers in an aquifer. | Consent Decree | A legal document, approved by a judge, that formalizes an agreement reached between EPA and potentially responsible parties (PRPs) through which PRPs will conduct all or part of a cleanup action at a Superfund site. | Conservation Easement | Easement restricting a landowner to land uses that are compatible with long-term conservation and environmental values. | Conservative Chemical | Most of the chemicals undergo chemical, biological or radioactive decay in the environment. Substances which do not undergo these types of reaction are called conservative substances. | Constituent(s) of Concern | Specific chemicals that are identified for evaluation in the site assessment process. | Construction Ban | If, under the Clean Air Act, EPA disapproves an area's planning requirements for correcting nonattainment, EPA can ban the construction or modification of any major stationary source of the pollutant for which the area is in nonattainment. | Consumption | Consumption is the rate of disappearance of a substance in a reaction. It can be defined as the moles or mass of a substance reacted with respect to time. Consumption terms contribute to disappearance of mass and thus are given a negative sign in a mass balance equation. | Consumptive Water Use | Water removed from available supplies without return to a water resources system, e.g., water used in manufacturing, agriculture, and food preparation. | Contaminant | Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil. | Contamination | Introduction into water, air, and soil of microorganisms, chemicals, toxic substances, wastes, or wastewater in a concentration that makes the medium unfit for its next intended use. | Contamination Source Inventory | An inventory of contaminant sources within delineated State Water Protection Areas. Targets likely sources for further investigation. | Contingency Plan | A document setting out an organized, planned, and coordinated course of action to be followed in case of a fire, explosion, or other accident that releases toxic chemicals, hazardous waste, or radioactive materials. | Continuous Discharge | A routine release to the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc. | Continuous Emission Monitoring Systems | Machines that measure, on a continuous basis, how much pollution is being released into the air. For specific locations or stacks, CEMS measure the pollutants released (emitted) by that source into the air. | Continuous Opacity Monitoring Systems | Equipment used to sample and condition, analyze and provide permanent record of emissions or process parameters that reduce the transmission of light and obscure the view of a background object. | Continuous Sample | A flow of water, waste or other material from a particular place in a plant to the location where samples are collected for testing. May be used to obtain grab or composite samples. | Contour Plowing | Soil tilling method that follows the shape of the land to discourage erosion. | Control Technique Guidelines | EPA documents designed to assist state and local pollution authorities to achieve and maintain air quality standards for certain sources through reasonably available control technologies. | Control technology; control measures | Equipment, processes or actions used to reduce air pollution. The extent of pollution reduction varies among technologies and measures. | Control Volume | Control Volume is the region of space over which our attention is focussed. It is any arbitrary portion of system set out specifically for analysis. It is common to break down a larger system such as a Water Treatment Plant into smaller blocks, each being a control volume. | Controlled Reaction | A chemical reaction under temperature and pressure conditions maintained within safe limits to produce a desired product or process. | Conventional Pollutants | Statutorily listed pollutants understood well by scientists. These may be in the form of organic waste, sediment, acid, bacteria, viruses, nutrients, oil and grease, or heat. | Conventional Site Assessment | Assessment in which most of the sample analysis and interpretation of data is completed off-site; process usually requires repeated mobilization of equipment and staff in order to fully determine the extent of contamination. | Convergence | As two waves merge the wave height will increase totaling the height of both individual waves. Increased wave heights will also occur when the depth of water in which they are travelling decreases. The opposite of DIVERGENCE. | Conveyance Loss | Water loss in pipes, channels, conduits, ditches by leakage or evaporation. | Cooperative Agreement | An assistance agreement whereby EPA transfers money, property, services or any- thing of value to a state, university, non-profit, or not-for-profit organization for the accomplishment of authorized activities or tasks. | Core Program Cooperative Agreement | An assistance agreement whereby EPA supports states or tribal governments with funds to help defray the cost of non-item-specific administrative and training activities. | Corrective Action | EPA can require treatment, storage and disposal (TSDF) facilities handling hazardous waste to undertake corrective actions to clean up spills resulting from failure to follow hazardous waste management procedures or other mistakes. | Corrective Measures Implementation | Part of the RCRA Process. The CMI phase involves the design and implementation of a chosen remedy. | Cost Recovery | A legal process by which potentially responsible parties who contributed to contamination at a Superfund site can be required to reimburse the Trust Fund for money spent during any cleanup actions by the federal government. | Cost Sharing | A publicly financed program through which society, as a beneficiary of environmental protection, shares part of the cost of pollution control with those who must actually install the controls. | Cost/Benefit Analysis | A quantitative evaluation of the costs which would bve incurred by implementing an environmental regulation versus the overall benefits to society of the proposed action. | Covalent Bond | A bond formed by the sharing of a pair of electrons between atoms. | Cradle-to-Grave | A procedure in which hazardous materials are identified and followed as they are produced, treated, transported, and disposed of by a series of permanent, linkable, descriptive documents. | Criteria | Descriptive factors taken into account by EPA in setting standards for various pollutants. These factors are used to determine limits on allowable concentration levels, and to limit the number of violations per year. | Criteria Air Pollutants | A group of very common air pollutants regulated by EPA on the basis of criteria (information on health and/or environmental effects of pollution. | Critical Effect | The first adverse effect, or its known precursor, that occurs as a dose rate increases. Designation is based on evaluation of overall database. | Cross Contamination | The movement of underground contaminants from one level or area to another due to invasive subsurface activities. | Cryptosporidium | A protozoan microbe associated with the disease cryptosporidiosis in man. The disease can be transmitted through ingestion of drinking water or person-to-person and can cause acute diarrhea, abdominal pain, vomiting, fever, and can be fatal. | Cubic Feet Per Minute | A measure of the volume of a substance flowing through air within a fixed period of time. With regard to indoor air, refers to the amount of air, in cubic feet, that is exchanged with outdoor air in a minute's time; i.e., the air exchange rate. | Cultural Eutrophication | Increasing rate at which water bodies "die" by pollution from human activities. | Cumulative Ecological Risk Assessment | Consideration of the total ecological risk from multiple stressors to a given eco-zone. | Cumulative Exposure | The sum of exposures of an organism to a pollutant over a period of time. | Current | The part of a fluid body (air or water) that moves continuously in a certain direction. | Cutie-Pie | An instrument used to measure radiation levels. | Cyclone Collector | A device that uses centrifugal force to remove large particles from polluted air. | Cyclone furnace | The type of furnace used in the Minergy Clear Horizons process. It is where the wastewater sludge (and coal and limestone flux) is combusted to form the glass aggregate. | Data quality objective (DQO) process | A systematic planning tool to facilitate the planning of
environmental data collection activities (see: U.S. EPA, 1994, 1996a, 1996c, 1997, 2000a, and
2000d). The DQO process allows planners to focus their planning efforts by specifying the intended
use of the data, the decision criteria, and the decision maker’s tolerable decision error rates. Data
quality objects are the qualitative and quantitative outputs from the DQO process. | Data Quality Objectives | Statements of the overall level of uncertainty that a decision-maker will accept in results or decisions based on environmental data. They provide the statistical framework for planning and managing environmental data operations. | Data Quality Objectives | Qualitative and quantitative statements derived from the DQO
process that clarify study objectives, define the appropriate types of data, and specify tolerable levels
of potential decision errors that will be used as the basis for establishing the quality and quantity of
the data needed to support decisions. | Datum | A chosen point used as a basis for calculating or measuring. | Day Tank | Another name for deaerating tank. (See: Age tank). | Death Rate | The number of organisms that die per unit time divided by the number of organisms alive at the beginning of that time period. | Debris | Broken, scattered remains; rubble; pieces of rubbish or litter. | Decant | To draw off the upper layer of liquid after the heaviest material (a solid or another liquid) has settled. | Decay Products | Degraded radioactive materials, often referred to as "daughters" or "progeny"; radon decay products of most concern from a public health standpoint are polonium-214 and polonium-218. | Decontamination | Removal of harmful substances such as noxious chemicals, harmful bacteria or other organisms, or radioactive material from exposed individuals, rooms and furnishings in buildings, or the exterior environment. | Deep-Well Injection | Deposition of raw or treated, filtered hazardous waste by pumping it into deep wells, where it is contained in the pores of permeable subsurface rock. | Deflation | The removal of loose material from a beach or other land surface by wind or wave action. | Defoliant | An herbicide that removes leaves from trees and growing plants. | Deforestation | Those practices or processes that result in the change of forested lands to non-forest uses. | Delegated State | A state (or other governmental entity such as a tribal government) that has received authority to administer an environmental regulatory program in lieu of a federal counterpart. The term does not connote any transfer of federal authority to a state. | Delist | Use of the petition process to have a facility's toxic designation rescinded. | Denitrification | The biological reduction of nitrate to nitrogen gas by denitrifying bacteria in soil. | Denitrification | The process in which nitrate is reduced by bacteria to nitrogen gas and lost from the system. | Dense Non-Aqueous Phase Liquid | Non-aqueous phase liquids that sink through the water column until they reach a confining layer. Because they are at the bottom of aquifers instead of floating on the water table, typical monitoring wells do not indicate their presence. | Density | A measure of how heavy a specific volume of a solid, liquid, or gas is in comparison to water. | Depletion Curve | In hydraulics, a graphical representation of water depletion from storage-stream channels, surface soil, and groundwater. A depletion curve be drawn for base flow, direct runoff, or total flow. | Depressurization | A condition that occurs when the air pressure inside a structure is lower that the air pressure outdoors. Radon may be drawn into a house more rapidly under depressurized conditions. | Dermal Absorption/Penetration | Process by which a chemical penetrates the skin and enters the body as an internal dose. | Dermal Toxicity | The ability of a pesticide or toxic chemical to poison people or animals by contact with the skin. | Desalination | 1) Removing salts from ocean or brackish water by using various technologies. 2) Removal of salts from soil by artificial means, usually leaching. | Description of Current Conditions | A document required by the EPA before a site investigation begins that includes what is known about the background and existing state of the site. | Desiccant | A chemical agent that absorbs moisture; some desiccants are capable of drying out plants or insects, causing death. | Design Value | The monitored reading used by EPA to determine an area's air quality status; e.g., for ozone, the fourth highest reading measured over the most recent three years is the design value. | Designated Pollutant | An air pollutant which is not a hazardous pollutant described in the Clean Air Act, but for which source performance standards exist. The Clean Air Act does require states to control these pollutants which include acid mist and total reduced sulfur (TRS). | Designated Uses | Those water uses identified in state water quality standards that must be achieved and maintained as required under the Clean Water Act. Uses can include cold water fisheries, public water supply, and irrigation. | Designer Bugs | Popular term for microbes developed through biotechnology that can degrade specific toxic chemicals at their source in toxic waste dumps or in ground water. | Destination Facility | The facility to which regulated medical waste is shipped for treatment and destruction, incineration, and/or disposal. | Destratification | Vertical mixing within a lake or reservoir to totally or partially eliminate separate layers of temperature, plant, or animal life. | Destruction and Removal Efficiency | A percentage that represents the number of molecules of a compound removed or destroyed in an incinerator relative to the number of molecules entering the system. For some pollutants, the RCRA removal requirement may be as stringent as 99.9999 percent. | Desulfurization | Removal of sulfur from fossil fuels to reduce pollution. | Detection Criterion | A predetermined rule to ascertain whether a tank is leaking or not. Most volumetric tests use a threshold value as the detection criterion. | Detection Limit | The lowest concentration of a chemical that can reliably be distinguished from a zero concentration. | Detergent | Synthetic washing agent that helps to remove dirt and oil. Some contain compounds which kill useful bacteria and encourage algae growth when they are in wastewater that reaches receiving waters. | Development Effects | Adverse effects such as altered growth, structural abnormality, functional deficiency, or death observed in a developing organism. | Dewater | 1. Remove or separate a portion of the water in a sludge or slurry to dry the sludge so it can be handled and disposed off. 2.Remove or drain the water from a tank or trench. | Diatom | Microscopic algae with cell walls made of silicon and of two separating halves. | Diazinon | An insecticide. In 1986, EPA banned its use on open areas such as sod farms and golf courses because it posed a danger to migratory birds. The ban did not apply to agricultural, home lawn or commercial establishment uses. | Dibenzofurans | A group of organic compounds, some of which are toxic. | Dichloro-Diphenyl-Trichloroethane | Insecticide that can collect in fatty tissues of certain animals. EPA banned registration and interstate sale of DDT for virtually all but emergency uses in the United States in 1972. | Dicofol | A pesticide used on citrus fruits. | Diethylstilbestrol | A synthetic estrogen, diethylstilbestrol is used as a growth stimulant in food animals. Residues in meat are thought to be carcinogenic. | Diffused Air | A type of aeration that forces oxygen into sewage by pumping air through perforated pipes inside a holding tank. | Diffusion | The movement of suspended or dissolved particles (or molecules) from a more concentrated to a less concentrated area. The process tends to distribute the particles or molecules more uniformly. | Digestion | The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants. | Dike | A low wall that can act as a barrier to prevent a spill from spreading. | Dilution Ratio | The relationship between the volume of water in a stream and the volume of incoming water. It affects the ability of the stream to assimilate waste. | Dimictic | Lakes and reservoirs that freeze over and normally go through two stratifications and two mixing cycles a year. | Dinocap | A fungicide used primarily by apple growers to control summer diseases. EPA proposed restrictions on its use in 1986 when laboratory tests found it caused birth defects in rabbits. | Dinoseb | A herbicide that is also used as a fungicide and insecticide. It was banned by EPA in 1986 because it posed the risk of birth defects and sterility. | Dioxin | Any of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity as contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic man-made compounds. | Direct Discharger | A municipal or industrial facility which introduces pollution through a defined conveyance or system such as outlet pipes; a point source. | Direct Push | Technology used for performing subsurface investigations by driving, pushing, and/or vibrating small-diameter hollow steel rods into the ground. Also known as direct drive, drive point, or push technology. | Direct Runoff | Water that flows over the ground surface or through the ground directly into streams, rivers, and lakes. | Discharge | Flow of surface water in a stream or canal or the outflow of ground water from a flowing artesian well, ditch, or spring. Can also apply to of liquid effluent from a facility or to chemical emissions into the air through designated venting mechanisms. | Disinfectant | A chemical or physical process that kills pathogenic organisms in water, air, or on surfaces. Chlorine is often used to disinfect sewage treatment effluent, water supplies, wells, and swimming pools. | Disinfectant By-Product | A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply; a chemical byproduct of the disinfection process. | Dispersal | The movement of an animal from the location of it birth to a new area where it lives and reproduces. | Dispersant | A chemical agent used to break up concentrations of organic material such as spilled oil. | Dispersion | Dispersion is the spreading of the solute from the path that it is expected to follow according to advective hydraulics. Dispersion can be classified into two Categories: Turbulent diffusion and Hydrodynamic dispersion. | Disposables | Consumer products, other items, and packaging used once or a few times and discarded. | Disposal | Final placement or destruction of toxic, radioactive, or other wastes; surplus or banned pesticides or other chemicals; polluted soils; and drums containing hazardous materials from removal actions or accidental releases. | Dissolution Reaction | A procedure by which one substance is dissolved in another to form a solution. | Dissolved Oxygen | The oxygen freely available in water, vital to fish and other aquatic life and for the prevention of odors. DO levels are most important indicator of a water body's ability to support desirable aquatic life. | Dissolved Solids | Disintegrated organic and inorganic material in water. Excessive amounts make water unfit to drink or use in industrial processes. | Distillation | The act of purifying liquids through boiling, so that the steam or gaseous vapors condense to a pure liquid. Pollutants and contaminants may remain in a concentrated residue. | Divergence | When a wave separates creating two waves, the wave height of each wave will decrease as the distance between them increases. Decreased wave heights will also occur as the depth of water in which they are travelling increases. | Diversion Rate | The percentage of waste materials diverted from traditional disposal such as landfilling or incineration to be recycled, composted, or re-used. | Domestic Application | Pesticide application in and around houses, office buildings, motels, and other living or working areas. | Dosage/Dose | The actual quantity of a chemical administered to an organism or to which it is exposed. 2. The amount of a substance that reaches a specific tissue. | Dose Rate | In exposure assessment, dose per time unit (e.g., mg/day), sometimes also called dosage. | Dose Response | Shifts in toxicological responses of an individual (such as alterations in severity) or populations (such as alterations in incidence) that are related to changes in the dose of any given substance. | Dose Response Curve | Graphical representation of the relationship between the dose of a stressor and the biological response thereto. | Dose-Response Assessment | 1. Estimating the potency of a chemical. 2. In exposure assessment, the process of determining the relationship between the dose of a stressor and a specific biological response. | Dose-Response Relationship | The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease produced. | Dosimeter | An instrument to measure dosage; many so-called dosimeters actually measure exposure rather than dosage. Dosimetry is the process or technology of measuring and/or estimating dosage. | DOT Reportable Quantity | The quantity of a substance specified in a U.S. Department of Transportation regulation that triggers labeling, packaging and other requirements related to shipping such substances. | Downdrift | The predominant direction of movement of shoreline materials, such as sand. | Downgradient | The direction the groundwater flows; similar to "downstream" for surface water. | Draft | 1. The act of drawing or removing water from a tank or reservoir. 2. The water which is drawn or removed. | Drainage Basin | The area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel. | Drainage Well | A well drilled to carry excess water off agricultural fields. Because they act as a funnel from the surface to the groundwater below. Drainage wells can contribute to groundwater pollution. | Drawdown | 1. The drop in the water table or level of water in the ground when water is being pumped from a well. 2. The amount of water used from a tank or reservoir. 3. The drop in the water level of a tank or reservoir. | Dredging | Removal of mud from the bottom of water bodies. This can disturb the ecosystem and causes silting that kills aquatic life. Dredging of contaminated muds can expose biota to heavy metals and other toxins. | Drilling Fluid | Fluid used to lubricate the bit and convey drill cuttings to the surface with rotary drilling equipment. Usually composed of bentonite slurry muddy water. Can become contaminated, leading to cross contamination, and may require special disposal. | Drinking Water Equivalent Level | Protective level of exposure related to potentially non-carcinogenic effects of chemicals that are also known to cancer. | Drinking Water State Revolving Fund | Grants to help finance system infrastructure improvements, assure source-water protection, enhance operation and management of drinking-water systems, and otherwise promote local water-system compliance and protection of public health. | Drive Casing | Heavy duty steel casing driven along with the sampling tool in cased DP systems. Keeps the hole open between sampling runs and is not removed until last sample has been collected. | Drive Point Profiler | A system used to collect multiple depth-discrete groundwater samples. Ports in the tip of the probe connect to an internal stainless steel or teflon tube that extends to the surface. Samples are collected via suction or airlift methods. | Dry Scrubbing | The removal of sulfur dioxide (SO2) and toxics by using lime and minimal amounts of water to provide humidification. | Dual-Phase Extraction | Active withdrawal of both liquid and gas phases from a well usually involving the use of a vacuum pump. | Due Care | Due Care:1. prevent exacerbation of existing contamination 2. eliminate unacceptable exposure to occupants 3. take reasonable precautions against acts or omissions of a third party. | Due Care compliance Plan | Once the property is determined a facility, and the owner complies with BEA, they must comply with Due Care to maintain protection from liability. | Dustfall Jar | An open container used to collect large particles from the air for measurement and analysis. | Dystrophic Lakes | Acidic, shallow bodies of water that contain much humus and/or other organic matter; contain many plants but few fish. | Ecological Entity | In ecological risk assessment, a general term referring to a species, a group of species, an ecosystem function or characteristic, or a specific habitat or biome. | Ecological Exposure | Exposure of a non-human organism to a stressor. | Ecological Impact | The effect that a man-caused or natural activity has on living organisms and their non-living (abiotic) environment. | Ecological Indicator | A characteristic of an ecosystem that is related to a measure of biotic or abiotic variable, that can provide quantitative information on ecological structure and function. An indicator can contribute to a measure of integrity and sustainability. | Ecological Integrity | A living system exhibits integrity if, when subjected to disturbance, it sustains and organizes self-correcting ability to recover toward a biomass end-state that is normal for that system. | Ecological Risk Assessment | The application of an analytical process or model to estimate the effects of human actions(s) on a natural resource and to interpret the significance of those effects in light of the uncertainties identified in each component of the assessment process. | Ecological System | A community of organisms that interact with one another and with their physical environnent, including sunlight, rainfall, and soil nutrients. | Ecological/Environmental Sustainability | Maintenance of ecosystem components and functions for future generations. | Ecology | The science that studies the relationship of living organisms to each other and to their environment. | Ecoregion | Regions defined by similarity of climate, landform, soil, potential natural vegetation, hydrology, and other ecologically relevant variables. | Ecosystem | The biotic community and abiotic environment within a specified location and time including the chemical, physical and biological relationships among the biotic and abiotic components. | Ecosystem Structure | Attributes related to the instantaneous physical state of an ecosystem; examples include species population density, species richness or evenness, and standing crop biomass. | Ecotone | A habitat created by the juxtaposition of distinctly different habitats; an edge habitat; or an ecological zone or boundary where two or more ecosystems meet. | Effluent | Wastewater--treated or untreated--that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters. | Ejector | A device used to disperse a chemical solution into water being treated. | Electrode | Conducting body at which the electrochemical reaction occurs. | Electrodialysis | A process that uses electrical current applied to permeable membranes to remove minerals from water. Often used to desalinize salty or brackish water. | Electromagnetic Geophysical Methods | Ways to measure subsurface conductivity via low-frequency electromagnetic induction. | Electromagnetic Radiation | A traveling wave motion resulting from changing electric or magnetic fields. Types of electromagnetic radiation include x-rays, gamma rays, radar and radio waves. | Electrostatic Precipitator | A device that removes particles from a gas stream (smoke) after combustion occurs. The ESP imparts an electrical charge to the particles, causing them to adhere to metal plates inside the precipitator. | Element | All substances are made up of elements, which are the basic components, or parts, of all materials. Elements cannot be separated or broken down into smaller units by ordinary chemical means. (Examples include: calcium, carbon, mercury, etc.) | Emergency (Chemical) | A situation created by an accidental release or spill of hazardous chemicals that poses a threat to the safety of workers, residents, the environment, or property. | Emergency Exemption | Provision in FIFRA under which EPA can grant temporary exemption to a state or another federal agency to allow the use of a pesticide product not registered for that particular use. Such actions involve unanticipated and/or severe pest problems. | Emergency Removal Action | 1. Steps take to remove contaminated materials that pose Imminent threats to local residents (e.g.,removal of leaking drums or the excavation of explosive waste.) 2. The state records such removals. | Emergency Response Values | Concentrations of chemicals, published by various groups, defining acceptable levels for short-term exposures in emergencies. | Emergency Suspension | Suspension of a pesticide product registration due to an imminent hazard. The action immediately halts distribution, sale, and sometimes actual use of the pesticide involved. | Eminent Domain | The right of the government or a public utility to acquire property for necessary public use by condemnation, with proper compensation to the owner. | Emission | Pollution discharged into the atmosphere from smokestacks, other vents, and surface areas of commercial or industrial facilities; from residential chimneys; and from motor vehicle, locomotive, or air- craft exhausts. | Emission Cap | A limit designed to prevent projected growth in emissions from existing and future stationary sources from eroding any mandated reductions. | Emission Factor | The relationship between the amount of pollution produced and the amount of raw material processed. For example, an emission factor for a blast furnace making iron would be the number of pounds of particulates per ton of raw materials. | Emission Inventory | A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies. | Emission Standard | The maximum amount of air polluting discharge legally allowed from a single source, mobile or stationary. | Emissions Trading | This allows one source to increase emissions when another source reduces them, maintaining an overall constant emission level. Facilities that reduce substantially may "bank" their "credits" or sell them to other facilities or industries. | Emulsifier | A chemical that aids in suspending one liquid in another. Usually an organic chemical in an aqueous solution. | Encapsulation | The treatment of asbestos-containing material with a liquid that covers the surface with a protective coating or embeds fibers in an adhesive matrix to prevent their release into the air. | Enclosure | Putting an airtight, impermeable, permanent barrier around asbestos-containing materials to prevent the release of asbestos fibers into the air. | End-of-the-pipe | Technologies such as scrubbers on smokestacks and catalytic converters on automobile tailpipes that reduce emissions of pollutants after they have formed. | Endangered Species | Animals, birds, fish, plants, or other living organisms threatened with extinction by anthropogenic (man-caused) or other natural changes in their environment. Requirements for declaring a species endangered are contained in the Endangered Species Act. | Endangerment Assessment | A study to determine the nature and extent of contamination at a site on the National Priorities List and the risks posed to public health or the environment. EPA or the state conducts the study when a legal action is to be taken. | Endrin | A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies. | Enforceable Requirements | Conditions or limitations in permits issued under the Clean Water Act Section 402 or 404 that, if violated, could result in the issuance of a compliance order or initiation of a civil or criminal action under federal or applicable state laws. | Enforcement | EPA, state, or local legal actions to obtain compliance with environmental laws, rules, regulations, or agreements and/or obtain penalties or criminal sanctions for violations. | Enforcement Decision Document | A document that provides an explanation to the public of EPA's selection of the cleanup alternative at enforcement sites on the National Priorities List. Similar to a Record of Decision. | Engineered Controls | Method of managing environmental and health risks by placing a barrier between the contamination and the rest of the site, thus limiting exposure pathways. | Enhanced Inspection and Maintenance | An improved automobile inspection and maintenance program--aimed at reducing automobile emissions---that contains, at a minimum, more vehicle types and model years, tighter inspection, and better management practices. | Entrain | To trap bubbles in water either mechanically through turbulence or chemically through a reaction. | Environment | The sum of all external conditions affecting the life, development and survival of an organism. | 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 Equity | Equal protection from environmental hazards for individuals groups, or communities regardless of race, enthicity, or economic status. | Environmental Equity/Justice | Equal protection from environmental hazards for individuals, groups, or communities regardless of race, ethnicity, or economic status. | Environmental Exposure | Human exposure to pollutants orginating from facility emissions. Threshold levels are not necessarily surpassed, but low-level chronic pollutant exposure is one of the most common forms of environmental exposure. | Environmental Fate | The destiny of a chemical or biological pollutant after release into the environment. | Environmental Fate Data | Data that characterize a pesticide's fate in the ecosystem, considering factors that foster its degradation (light, water, microbes), pathways and resultant products. | Environmental Impact Statement | A document required of federal agencies by the National Environmental Policy Act for major projects or legislative proposals significantly affecting the environment. The document describes the positive and negative effects of alternative actions. | Environmental Indicator | A measurement, statistic or value that provides a proximate gauge or evidence of the effects of environmental management programs or of the state or condition of the environment. | Environmental Lien | A charge, security, or encumbrance on a property's title to secure payment of cost or debt arising from response actions, cleanup, or other remediation of hazardous substances or petroleum products. | Environmental Medium | A major environmental category that surrounds or contacts humans, animals, plants, and other organisms (e.g., surface water, ground water, soil or air) and through which chemicals or pollutants move. | Environmental Monitoring for Public Access Data | Joint EPA, NOAA, and USGS program to provide timely and effective communication of environmental data and information through improved and updated technology solutions that support timely environmental monitoring reporting, interpeting, and use of the information for the benefit of the public. (See: Real-time monitoring.) | Environmental Receptors | Any organism, including site employees, building occupants, the public at large, the atmosphere, animals, plants and microorganisms that may be affected by a release of a contaminant or pollutant. | Environmental Response Team | EPA experts located in Edison, N.J., and Cincinnati, OH, who can provide around-the-clock technical assistance to EPA regional offices and states during all types of hazardous waste site emergencies and spills of hazardous substances. | Environmental Site Assessment | The process of determining whether contamination is present on a parcel of real property. | Environmental Sustainability | Long-term maintenance of ecosystem components and functions for future generations. | Environmental Tobacco Smoke | Mixture of smoke from the burning end of a cigarette, pipe, or cigar and smoke exhaled by the smoker. | Environmental/Ecological Risk | The potential for adverse effects on living organisms associated with pollution of the environment by effluents, emissions, wastes, or accidental chemical releases; energy use; or the depletion of natural resources. | EPA Risk Assessor | The risk assessor responsible for reviewing the risk assessment on behalf of EPA. The individual may be an EPA employee or contractor, a State employee, or some other party, as appropriate for an individual site. | Epidemiology | Study of the distribution of disease, or other health-related states and events in human populations, as related to age, sex, occupation, ethnicity, and economic status in order to identify and alleviate health problems and promote better health. | Epilimnion | Upper waters of a thermally stratified lake subject to wind action. | Episode (Pollution) | An air or water pollution incident in a given area caused by a concentration of atmospheric pollutants under meteorological conditions that may result in a significant increase in illnesses or deaths. | Equilibrium | When the reactants and products are in a constant ratio. The forward reaction and the reverse reactions occur at the same rate when a system is in equilibrium. | Equilibrium Constant | A constant derived from chemical thermodynamic data that is numerically equilivalent to the product of the concentrations of the products divided by the product of the reactants, with each of the concentration terms raised to a power equilivalent to the stoichiometric coefficient from the chemical reaction. | Equivalent drinking water levels | A standard of protection to prevent exposure to potentially non-carcinogenic or carcinogenic chemicals in potable water. EDWLs are derived using EPA toxicity standards for chemicals without established MCLs. | Equivalent Method | Any method of sampling and analyzing for air pollution which has been demonstrated to the EPA Administrator's satisfaction to be, under specific conditions, an acceptable alternative to normally used reference methods. | Equivalent Weight | The molecular weight divided by the number of electrons transferred in redox reactions or by the number of protons transferred in acid-base reactions. | Erosion | The wearing away of land surface by wind or water, intensified by land-clearing practices related to farming, residential or industrial development, road building, or logging. | Escarpment | A more or less continuous line of cliffs or steep slopes facing in one general direction which are caused by erosion or faulting. Also SCARP. | Established Treatment Technologies | Technologies for which cost and performance data are readily available. | Estimated Environmental Concentration | Predicted concentration of a pesticide within an environmental compartment based on estimates of quantities released, discharge patterns and substance inherent properties (fate and distribution) as well as the nature of the specific receiving ecosystems. | Estuary | Region where tidal action and river flow mix fresh and salt water. Such areas include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife. | Estuary (estuarine) | Areas where fresh water from rivers and salt water from near-shore ocean waters are mixed. These areas may include bays, mouths of rivers, salt marshes, and lagoons. These water ecosystems shelter and feed marine life, birds, and wildlife. | Ethanol | Otherwise known as ethyl alcohol or "alcohol," or "grain-spirits." Ethanol can be produced chemically from ethylene or biologically from the fermentation of various sugars from carbohydrates found in agricultural crops and cellulosic residues from crops or wood. Used in the United States as a gasoline octane enhancer and oxygenate, it increases octane 2.5 to 3.0 numbers at ten percent concentration. Ethanol also can be used in higher concentration in vehicles optimized for its use. | Ethylene Dibromide | A chemical used as an agricultural fumigant and in certain industrial processes. Extremely toxic and found to be a carcinogen in laboratory animals, EDB has been banned for most agricultural uses in the United States. | Euphotic Zone | The upper layer of water in a lake through which sunlight can penetrate. | Eutrophic Lake | Lakes that have a high productivity because of an abundant supply of nutrients. | Eutrophic Lakes | Shallow, murky bodies of water with concentrations of plant nutrients causing excessive production of algae. | Eutrophication | The slow aging process during which a lake, estuary, or bay evolves into a bog or marsh and eventually disappears. During the later stages of eutrophication the water body is choked by abundant plant life due to higher levels of nutrients. | Evaporation | The conversion of liquid water from lakes, streams, and other bodies of waer to water vapor. | Evaporation Ponds | Areas where sewage sludge is dumped and dried. | Evapotranspiration | The loss of water from the soil both by evaporation and by transpiration from the plants growing in the soil. | Ex-situ | Ex-situ is Latin for "out of place." Ex-situ cleanup strategies for environmental media that involve excavating or otherwise removing the contaminated media, treating where appropriate, and disposing of these wastes in a facility that isolates the waste from the environment. | Exacerbation | Refers to activities by the owner or operator that cause existing contamination to migrate beyond the boundaries of the source of contamination or cause an increased response cost. | Exceedance | Violation of the pollutant levels permitted by environmental protection standards. | Exchange Capacity | The total ionic charge of the adsorption complex that is active in the adsorption of ions. | Exclusion | In the asbestos program, one of several situations that permit a Local Education Agency (LEA) to delete one or more of the items required by the Asbestos Hazard Emergency Response Act (AHERA). | Exempt Solvent | Specific organic compounds not subject to requirements of regulation because they are deemed by EPA to be of negligible photochemical reactivity. | Exempted Aquifer | Underground bodies of water defined in the Underground Injection Control program as aquifers that are potential sources of drinking water though not being used as such, and thus exempted from regulations barring underground injection activities. | Exemption | Public water systems may be exempt from Maximum Contaminant Level (MCL), treatment technique, or both, if the system cannot comply due to economic factors or preceding the MCL and the exemption will not create a public health risk. | Exemption | State or EPA permission for a water system not to meet a certain drinking water standard. An exemption allows a system additional time to obtain financial assistance or make improvements in order to come into compliance with the standard. The system must prove that: (1) there are compelling reasons (including economic factors) why it cannot meet a MCL or Treatment Technique; (2) it was in operation on the effective date of the requirement, and (3) the exemption will not create an unreasonable risk to public health. The state must set a schedule under which the water system will comply with the standard for which it received an exemption. | Exotic Species | A species that is not indigenous to a region. | Experimental Use Permit | A permit granted by EPA that allows a producer to conduct tests of a new pesticide, product and/or use outside the laboratory. The testing is usually done on ten or more acres of land or water surface. | Explosive Limits | The amounts of vapor in the air that form explosive mixtures; limits are expressed as lower and upper limits and give the range of vapor concentrations in air that will explode if an ignition source is present. | Exports | In solid waste program, municipal solid waste and recyclables transported outside the state or locality where they originated. | Exposure | The amount of radiation or pollutant present in a given environment that represents a potential health threat to living organisms. | Exposure Assessment | Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed. | Exposure Concentration | The concentration of a chemical or other pollutant representing a health threat in a given environment. | Exposure Indicator | A characteristic of the environment measured to provide evidence of the occurrence or magnitude of a response indicator's exposure to a chemical or biological stress. | Exposure Level | The amount (concentration) of a chemical at the absorptive surfaces of an organism. | Exposure Pathways | The course a chemical or physical agent takes from the source to the exposed organism. An exposure pathway describes a unique mechanism by which an individual or population is exposed to chemicals or physical agents at or originating from the site. | Exposure Point | An exact location of potential contact between a person and a chemical within an exposure medium. | Exposure Point Concentration | The value that represents a conservative estimate of the chemical concentration available from a particular medium or route of exposure. See definitions for Medium EPC and Route EPC, which follow. | Exposure Route | The way a chemical or pollutant enters an organism after contact; i.e., by ingestion, inhalation, or dermal absorption. | Exposure-Response Relationship | The relationship between exposure level and the incidence of adverse effects. | Extraction Procedure (EP Toxic) | Determining toxicity by a procedure which simulates leaching; if a certain concentration of a toxic substance can be leached from a waste, that waste is considered hazardous, i.e., "EP Toxic." | Extraction Well | A discharge well used to remove groundwater or air. | Extremely Hazardous Substances | Any of 406 chemicals identified by EPA as toxic, and listed under SARA Title III. The list is subject to periodic revision. | Fabric Filter | Fabric Filters are made of Teflon, Nylon, cotton, or glass fiber which are used to remove particulate matter. The accumulation of material collected can be periodically disposed, shaken off and then washed for reuse. | Facilities Plans | Plans and studies related to the construction of treatment works necessary to comply with the Clean Water Act or RCRA. A facilities plan investigates needs and provides information on the cost-effectiveness of alternatives. | Facility | A facility is defined by the boundaries of an area in which one or more sources of pollution may be located. | Facility Emergency Coordinator | Representative of a facility covered by environmental law (e.g, a chemical plant) who participates in the emergency reporting process with the Local Emergency Planning Committee (LEPC). | Facultative Bacteria | Bacteria that can live under aerobic or anaerobic conditions. | Farmland | A rural area where farming is practiced. | Feasibility Study | 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. | Fecal Coliform Bacteria | Bacteria found in the intestinal tracts of mammals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens. | Federal Implementation Plan | Under current law, a federally implemented plan to achieve attainment of air quality standards, used when a state is unable to develop an adequate plan. | Federal Motor Vehicle Control Program | All federal actions aimed at controlling pollution from motor vehicles by such efforts as establishing and enforcing tailpipe and evaporative emission standards for new vehicles, testing methods development, and guidance to state. | Feed | The raw supply liquid to the filtration unit. | Fen | A type of wetland that accumulates peat deposits. Fens are less acidic than bogs, deriving most of their water from groundwater rich in calcium and magnesium. | Fenton's reagent | Fenton's Reagent is a solution of hydrogen peroxide and an iron catalyst that is used to oxidize contaminants or waste waters. It can destroy organic compounds such as trichloroethylene (TCE) and perchloroethylene (PCE). | Ferrous Metals | Magnetic metals derived from iron or steel; products made from ferrous metals include appliances, furniture, containers, and packaging like steel drums and barrels. | FIFRA Pesticide Ingredient | An ingredient of a pesticide that must be registered with EPA under the Federal Insecticide, Fungicide, and Rodenticide Act. Products making pesticide claims must register under FIFRA and may be subject to labeling and use requirements. | Fill | Man-made deposits of natural soils or rock products and waste material. | Filling | Depositing dirt, mud or other materials into aquatic areas to create more dry land, usually for agricultural or commercial development purposes, often with ruinous ecological consequences. | Filter Strip | Strip or area of vegetation used for removing sediment, organic matter, and other pollutants from runoff and wastewater. | Filtrate | The liquid which has passed through the filter; the fluid that has been separated from the solids in the slurry being filtered. Also referred to as discharge liquor, effluent, mother liquor, solute or strong liquor. | Filtration | Removal of particles, normally solids, from a fluid. These can be contaminants or valuable products. | Financial Assurance for Closure | Documentation or proof that an owner or operator of a facility such as a landfill or other waste repository is capable of paying the projected costs of closing the facility and monitoring it afterwards as provided in RCRA regulations. | Finding of No Significant Impact | A document prepared by a federal agency showing why a proposed action would not have a significant impact on the environment and thus would not require preparation of an Environmental Impact Statement. | Finished Water | Water is "finished" when it has passed through all the processes in a water treatment plant and is ready to be delivered to consumers. | First Draw | The water that comes out when a tap is first opened, likely to have the highest level of lead contamination from plumbing materials. | Fix a Sample | A sample is "fixed" in the field by adding chemicals that prevent water quality indicators of interest in the sample from changing before laboratory measurements are made. | Fixed-Location Monitoring | Sampling of an environmental or ambient medium for pollutant concentration at one location continuously or repeatedly. | Flanking | The effective redirection of waves around an object. | Flare | A control device that burns hazardous materials to prevent their release into the environment; may operate continuously or intermittently, usually on top of a stack. | Flash Point | The lowest temperature at which evaporation of a substance produces sufficient vapor to form an ignitable mixture with air. | Floodplain | The flat or nearly flat land along a river or stream or in a tidal area that is covered by water during a flood. | Floor Sweep | Capture of heavier-than-air gases that collect at floor level. | Flow | The total volume of water that flows past a point on the river during some fixed time interval. | Flow Rate | The rate, expressed in gallons -or liters-per-hour, at which a fluid escapes from a hole or fissure in a tank. Such measurements are also made of liquid waste, effluent, and surface water movement. | Flowable | Pesticide and other formulations in which the active ingredients are finely ground insoluble solids suspended in a liquid. They are mixed with water for application. | Flowing Artesian Aquifer | An aquifer in which the water pressure is sufficiently high to push the water up through the geologic materials of the aquifer and overlying unsaturated zone an out onto the ground surface. | Flowmeter | A gauge indicating the velocity of wastewater moving through a treatment plant or of any liquid moving through various industrial processes. | 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. | Fluidized | A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water treatment, a bed of filter media is fluidized by backwashing water through the filter. | Fluidized Bed Incinerator | An incinerator that uses a bed of hot sand or other granular material to transfer heat directly to waste. Used mainly for destroying municipal sludge. | Flume | A sloped channel that is utilized to convey water and is commonly constructed of wood or concrete. Some specialized flumes are used to measure flow (e.g. Parshall flume) by means of a calibrated throat or cross section. | Fluoridation | The addition of a chemical to increase the concentration of fluoride ions in drinking water to reduce the incidence of tooth decay. | Fluorides | Gaseous, solid, or dissolved compounds containing fluorine that result from industrial processes. Excessive amounts in food can lead to fluorosis. | Fluorocarbons | Any of a number of organic compounds in which one or more hydrogen atoms are replaced by fluorine. FCs containing chlorine are called chlorofluorocarbons (CFCs). They are believed to be modifying the ozone layer in the stratosphere. | Flush | To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes or to force large amounts of water through a system to clean out piping or tubing, and storage or process tanks. | Fly Ash | The noncombustible residue from the burning of pulverized coal. Fly ash is pozzolanic and is frequently used to replace a portion of the cement and reduce its density. | Fogging | Applying a pesticide by rapidly heating the liquid chemical so that it forms very fine droplets that resemble smoke or fog. Used to destroy mosquitoes, black flies, and similar pests. | Food Web | A description of the complex relationship between organisms in an ecosystem. | Formaldehyde | A colorless, pungent, and irritating gas, CH20, used chiefly as a disinfectant and preservative and in synthesizing other compounds like resins. | Fossil Fuel | Carbon based remains of organic matter that has been geologically transformed into coal, oil and natural gas. Combustion of these substances releases large amounts of energy. Currently, humans are using fossil fuels to supply much of their energy needs. | Fracture | A break in a rock formation due to structural stresses. Faults, shears, joints, and planes of fracture cleavage are all types of fractures. | Free Product | A petroleum hydrocarbon in the liquid free or non aqueous phase. | Freeboard | 1. Vertical distance from the normal water surface to the top of a confining wall. 2. Vertical distance from the sand surface to the underside of a trough in a sand filter. | Friable | Capable of being crumbled, pulverized, or reduced to powder by hand pressure. | Friable Asbestos | Any material containing more than one-percent asbestos, and that can be crumbled or reduced to powder by hand pressure. | Fuel Economy Standard | The Corporate Average Fuel Economy Standard (CAFE) effective in 1978. It enhanced the national fuel conservation effort imposing a miles-per-gallon floor for motor vehicles. | Fuel Efficiency | The proportion of energy released by fuel combustion that is converted into useful energy. | Fuel Switching | 1.A precombustion process whereby a low-sulfur coal is used in place of a higher sulfur coal in a power plant to reduce sulfur dioxide emissions. 2. Illegally using leaded gasoline in a motor vehicle designed to use only unleaded. | Fugitive Emissions | Species like trout, salmon, or bass, caught for sport. Many of them show more sensitivity to environmental change than "rough" fish. | Fume | Tiny particles trapped in vapor in a gas stream. | Fumigant | A chemical that forms vapors (gases) which is used to destroy weeds, plant pathogens, insects or other pests. | Functional Equivalent | Term used to describe EPA's decision-making process and its relationship to the environmental review conducted under the National Environmental Policy Act (NEPA). | Fungicide | Pesticides which are used to control, deter, or destroy fungi. | Fungistat | A compound that inhibits or prevents fungal growth. | Fungus (Fungi) | Molds, mildews, yeasts, mushrooms, and puffballs, a group of organisms lacking in chlorophyll. They grow in soil, on trees and other plants where they obtain nutrients. Some are pathogens, others stabilize sewage and digest composted waste. | Furrow Irrigation | Irrigation method in which water travels through the field by means of small channels between each groups of rows. | Future Liability | Refers to potentially responsible parties' obligations to pay for additional response activities beyond those specified in the Record of Decision or Consent Decree. | Game Fish | Species like trout, salmon, or bass, caught for sport. Many of them show more sensitivity to environmental change than "rough" fish. | Gas Chromatograph/Mass Spectrometer | Instrument that identifies the molecular composition and concentrations of various chemicals in water and soil samples. | Gasahol | Mixture of gasoline and ethanol derived from fermented agricultural products containing at least nine percent ethanol. Gasohol emissions contain less carbon monoxide than those from gasoline. | Gaseous State | The state of matter in which a substance has no definite shape and a volume defined largely by the size of its container (as well as the temperature and pressure); molecules are widely separated and in constant random motion. Examples include water vapor and air (a mixture of gases). | Gasification | Conversion of solid material such as coal into a gas for use as a fuel. | Gasoline | A viscous fluid refined from crude oil which is made up of fossilized plant and animal remains and burned in internal combustion engines. | Gasoline Volatility | The property of gasoline whereby it evaporates into a vapor. Gasoline vapor is a mixture of volatile organic compounds. | Gender Ratio | The proportion of males to females within a population. | General Permit | A set of conditions that can be standardized for a number of facilities; use of general permits where possible eliminates individualized permits for similar situations and is cheaper and less burdensome administratively than individual permits. | General Reporting Facility | A facility having one or more hazardous chemicals above the 10,000 pound threshold for planning quantities. Such facilities must file MSDS and emergency inventory information with the SERC, LEPC, and local fire departments. | Generally Recognized as Safe | Designation by the FDA that a chemical or substance (including certain pesticides) added to food is considered safe by experts, and so is exempted from the usual FFDCA food additive tolerance requirements. | Generation | As the name implies generation refers to the appearance of a substance due to a reaction. It is the number of moles or mass of the substance accumulating with respect to time. Generation terms are added when used in mass balance equations. | Generator | 1. A facility or mobile source that emits pollutants into the air or releases hazardous waste into water or soil. 2. Any person, by site, whose act first causes such waste to become subject to regulation. | Geological | Relating to or based on the study of rocks, rock formations, and structure of the earth. | Geological Log | A detailed description of all underground features (depth, thickness, type of formation) discovered during the drilling of a well. | Geomembrane | A synthetic membrane, often made of polyvinyl chloride (PVC) or high density polyethylene (HDPE). Often used to line landfills. | Geophysical Log | A record of the structure and composition of the earth encountered when drilling a well or similar type of test hold or boring. | Geophysical Study | Methods of investigating the formations below the surface that involve the analysis of electrical measurements on the land surface or the analysis of subsurface vibrations that are created by an energy source on the land surface. | Geoprobe | A machine used to make soil borings and to create temporary groundwater monitoring wells. | Geothermal/Ground Source Heat Pump | These heat pumps are underground coils to transfer heat from the ground to the inside of a building. (See: Heat pump; Water source heat pump). | Germicide | Any compound that kills disease-causing microorganisms. | Giardia Lamblia | Protozoan in the feces of humans and animals that can cause severe gastrointestinal ailments. It is a common contaminant of surface waters. | Global Extinction | The complete and permanent loss of an animal species across the entire planet. | Global Warming | The progressive gradual rise of the earth's surface temperature thought to be caused by the greenhouse effect and responsible for changes in global climate patterns. An increase in the near surface temperature of the Earth. | Global Warming Potential | The ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. CFC-12, for example, has a GWP of 8,500, while water has a GWP of zero. | Glovebag | A polyethylene or polyvinyl chloride bag-like enclosure affixed around an asbestos-containing source (most often thermal system insulation) permitting the material to be removed while minimizing release of airborne fibers to the surrounding atmosphere. | Grab Sample | A single sample collected at a particular time and place that represents the composition of the water, air, or soil only at that time and place. | Grab Sampling | A nonprobabilistic selection of a sample (really, a specimen), usually chosen on the
basis of being the most accessible or by some judgement of the operator. A grab sample is taken
with no consideration for obtaining a representative sample. Grab sampling has been shown to be
associated with very high uncertainty and bias. | Gradient | 1. With reference to winds or currents, the rates of increase or decrease in speed. 2. With reference to chemicals or water levels, the difference between two concentrations or levels. (Also, see SLOPE.) | Grain Loading | The rate at which particles are emitted from a pollution source. Measurement is made by the number of grains per cubic foot of gas emitted. | Grand fathering | A term used to describe an exemption from an Air Use Permit for equipment that meets two requirements: 1) installed prior to the passage of Michigan Air Quality Rule 201 in August 15, 1967, and 2) has never been modified. | Granular Activated Carbon Treatment | A filtering system often used in small water systems and individual homes to remove organics. Also used by municipal water treatment plants. GAC can be highly effective in lowering elevated levels of radon in water. | Grassed Waterway | Natural or constructed watercourse or outlet that is shaped or graded and established in suitable vegetation for the disposal of runoff water without erosion. | Gravity | The force of attraction due to mass. All matter has gravity which influences its surroundings. The amount of gravity between two objects is dependent on their masses and the distance between their centers. The greater the mass, the greater the force due to gravity. | Gravity wave | A wave whose speed is controlled primarily by gravity. Water waves more than 2 inches long are considered gravity waves. | Gray Water | Ground water entering near coastal waters which has been contaminated by landfill leachate, deep well injection of hazardous wastes, septic tanks, etc. | Greenfields | A parcel of land not previously developed for a higher use beyond that of agriculture or forestry. | Greenhouse Effect | The trapping and build-up of heat in the lower atmosphere near a planet's surface. Some of the heat flowing back towards space from the Earth's surface is absorbed by water vapour, carbon dioxide, methane and other gases in the atmosphere. If the atmospheric concentrations of these gases rises, then theory predicts that the average temperature of the lower atmosphere will gradually increase. | Greenhouse Gases | Gases responsible for the greenhouse effect. These gases include: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); chlorofluorocarbons (CFxClx); and tropospheric ozone (O3). | Grinder Pump | A mechanical device that shreds solids and raises sewage to a higher elevation through pressure sewers. | Gross Alpha/Beta Particle Activity | The total radioactivity due to alpha or beta particle emissions as inferred from measurements on a dry sample. | Gross Power-Generation Potential | The installed power generation capacity that landfill gas can support. | Ground Cover | A groundcover is a low-lying plant, usually chosen with aesthetic considerations in mind and requiring minimal maintenance. A groundcover may cover large expanses of ground on the landscape, so economic considerations may also have to be taken into account. | Ground-Penetrating Radar | GPR is a technology that emits pulses of electromagnetic energy into the ground to measure its reflection and refraction by subsurface layers and other features, such as buried debris. | Ground-Water Discharge | 1. Ground water entering near coastal waters which has been contaminated by landfill leachate, deep well injection of hazardous wastes, septic tanks, etc. 2.The removal of water from the saturated zone is called groundwater discharge. The discharge area is simply the geographic area in which discharge occurs. | Ground-Water Disinfection Rule | A 1996 amendment of the Safe Drinking Water Act requiring EPA to promulgate national primary drinking water regulations requiring disinfection as for all public water systems, including surface waters and ground water systems. | Groundwater | The supply of fresh water found beneath the Earth's surface, usually in aquifers, which supply wells and springs. Because ground water is a major source of drinking water, there is growing concern over contamination from leaching agricultural or industrial pollutants or leaking underground storage tanks. | Groundwater Recharge | Land surfaces where water enters the ground and replenishes groundwater. This process occurs naturally when precipitation infiltrates down through the soil or rock into an aquifer. It can also occur unnaturally as artificial recharge. | Groundwater Under the Direct Influence (UDI) of Surface Water | Any water beneath the surface of the ground with: 1. significant occurence of insects or other microorganisms, algae, or large-diameter pathogens; 2. significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions. Direct influence is determined for individual sources in accordance with criteria established by a state. | Gully Erosion | Severe erosion in which trenches are cut to a depth greater than 30 centimeters (a foot). Generally, ditches deep enough to cross with farm equipment are considered gullies. | Habitat | The place where a population (e.g. human, animal, plant, microorganism) lives and its surroundings, both living and non-living. | Habitat Indicator | A physical attribute of the environment measured to characterize conditions necessary to support an organism, population, or community in the absence of pollutants; e.g. salinity of estuarine waters or substrate type in streams or lakes. | Half-Life | 1. The time required for a pollutant to lose one-half of its original coconcentrationor example, the biochemical half-life of DDT in the environment is 15 years. 2. The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years). 3. The time required for the elimination of half a total dose from the body. | Halon | Bromine-containing compounds with long atmospheric lifetimes whose breakdown in the stratosphere causes depletion of ozone. Halons are used in firefighting. | Hazard | 1. Potential for radiation, a chemical or other pollutant to cause human illness or injury. 2. In the pesticide program, the inherent toxicity of a compound. Hazard identification of a given substances is an informed judgment based on verifiable toxicity data from animal models or human studies. | Hazard Assessment | Evaluating the effects of a stressor or determining a margin of safety for an organism by comparing the concentration which causes toxic effects with an estimate of exposure to the organism. | Hazard Communication Standard | An OSHA regulation that requires chemical manufacturers, suppliers, and importers to assess the hazards of the chemicals that they make, supply, or import, and to inform employers, customers, and workers of these hazards through MSDS information. | Hazard Evaluation | Component of risk evaluation that involves gathering and evaluating data on the types of health injuries or diseases that may be produced by a chemical and on the conditions of exposure under which such health effects are produced. | Hazard Identification | Determination of substances of concern, their adverse effects, target populations, and conditions of exposure, taking into account toxicity data and knowledge of effects on human health, other organisms and their environment. | Hazard Quotient | The ratio of estimated site-specific exposure to a single chemical from a site over a specified period to the estimated daily exposure level, at which no adverse health effects are likely to occur. | Hazard Ratio | A term used to compare an animal's daily dietary intake of a pesticide to its LD 50 value. A ratio greater than 1.0 indicates that the animal is likely to consume an a dose amount which would kill 50 percent of animals of the same species. | Hazardous Air Pollutants | Air pollutants which are not covered by ambient air quality standards but which, as defined in the Clean Air Act, may present a threat of adverse human health effects or adverse environmental effects.Such pollutants include asbestos, beryllium, mercury, benzene, coke oven emissions, radionuclides, and vinyl chloride. | Hazardous Chemical | An EPA designation for any hazardous material requiring an MSDS under OSHA's Hazard Communication Standard. Such substances are capable of producing fires and explosions or adverse health effects like cancer and dermatitis. Hazardous chemicals are distinct from hazardous waste.(See: Hazardous Waste.) | Hazardous Ranking System | The principal screening tool used by EPA to evaluate risks to public health and the environment associated with abandoned or uncontrolled hazardous waste sites. The HRS calculates a score based on the potential of hazardous substances spreading from the site through the air, surface water, or ground water, and on other factors such as density and proximity of human population. This score is the primary factor in deciding if the site should be on the National Priorities List and, if so, what ranking it should have compared to other sites on the list. | Hazardous Substance | 1. Any material that poses a threat to human health and/or the environment. Typical hazardous substances are toxic, corrosive, ignitable, explosive, or chemically reactive. 2. Any substance designated by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or is otherwise released into the environment. | Hazardous Waste | By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed. Possesses at least one of four characteristics (ignitability, corrosivity, reactivity, or toxicity), or appears on special EPA lists. | Hazardous Waste Landfill | An excavated or engineered site where hazardous waste is deposited and covered. | Hazardous Waste Minimization | Reducing the amount of toxicity or waste produced by a facility via source reduction or environmentally sound recycling. | Hazards Analysis | Procedures used to (1) identify potential sources of release of hazardous materials from fixed facilities or transportation accidents; (2) determine the vulnerability of a geographical area to a release of hazardous materials; and (3) compare hazards to determine which present greater or lesser risks to a community. | Headspace | The vapor mixture trapped above a solid or liquid in a sealed vessel. | Health Advisory Level | A non-regulatory health-based reference level of chemical traces (usually in ppm) in drinking water at which there are no adverse health risks when ingested over various periods of time. Such levels are established for one day, 10 days, long-term and life-time exposure periods. They contain a wide margin of safety. | Health Assessment | An evaluation of available data on existing or potential risks to human health posed by a Superfund site. The Agency for Toxic Substances and Disease Registry (ATSDR) of the Department of Health and Human Services (DHHS) is required to perform such an assessment at every site on the National Priorities List. | Heat Island Effect | A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions. | Heavy Metals | Metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend to accumulate in the food chain. | Heptachlor | An insecticide that was banned on some food products in 1975 and in all of them 1978. More recently it was found in milk and other dairy products in Arkansas and Missouri where dairy cattle were illegally fed treated seed. | Herbicide | A chemical pesticide designed to control or destroy plants, weeds, or grasses. | Heterogeneity | The condition of a population (or a lot) when all of the individual items are not
identical with respect to the characteristic of interest. For this guidance, the focus is on the
differences in the chemical and physical properties (which are responsible for the constitution
heterogeneity, CH) of the particulate material and the distribution of the particles (which leads to the
distribution heterogeneity, DH). | High End Exposure (dose) Estimate | An estimate of exposure, or dose level received anyone in a defined population that is greater than the 90th percentile of all individuals in that population, but less than the exposure at the highest percentile in that population. | High-Density Polyethylene | A material used to make plastic bottles and other products that produce toxic fumes when burned. | High-Level Radioactive Waste | Waste generated in core fuel of a nuclear reactor, found at nuclear reactors or by nuclear fuel reprocessing; is a serious threat to anyone who comes near the waste without shielding. | High-Risk Community | A community located within the vicinity of numerous sites of facilities or other potential sources of environmental exposure/health hazards which may result in high levels of exposure to contaminants or pollutants. | High-to-Low-Dose Extrapolation | The process of prediction of low exposure risk to humans and animals from the measured high-exposure-high-risk data involving laboratory animals. | Holding Pond | A pond or reservoir, usually made of earth, built to store polluted runoff. | Holding Time | The maximum amount of time a sample may be stored before analysis. | Hollow stem auger drilling | Conventional drilling method that uses a rotary drill with a screw device (auger) to penetrate the soil. As the augers are rotated, soil cuttings are conveyed to the surface by auger spirals. | Homogeneity | The condition of a population (or a lot) when all of the individual items are identical
with respect to the characteristic of interest. It is the lower bound of heterogeneity as the difference
between the individual items of a population approach zero (which cannot be practically achieved). | Homogeneous Area | In accordance with Asbestos Hazard and Emergency Response Act (AHERA) definitions, an area of surfacing materials, thermal surface insulation, or miscellaneous material that is uniform in color and texture. | Household Hazardous Waste | Hazardous products used and disposed of by residential as opposed to industrial consumers. Includes paints, stains, varnishes, solvents, pesticides, and other products containing chemicals that can catch fire, react or explode, or are corrosive or toxic. | Human Equivalent Dose | A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals. | Human Exposure Evaluation | Describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure. | Human Health Risk | The likelihood that a given exposure or series of exposures may have damaged or will damage the health of individuals. | Hydraulic Conductivity | The rate at which water can move through a permeable medium. Aquifers with high hydraulic conductivity yield and transmit more water than similar aquifers with low hydraulic conductivity. | Hydraulic Gradient | In general, the direction of groundwater flow due to changes in the depth of the water table. The difference in hydraulic head between two measuring points within a porous medium, divided by the distance between the two points. | Hydrocarbons | Chemical compounds that consist entirely of carbon and hydrogen. | Hydrogen Sulfide | Gas emitted during organic decomposition. Also a by-product of oil refining and burning. Smells like rotten eggs and, in heavy concentration, can kill or cause illness. | Hydrogeological Cycle | The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again. | Hydrogeology | The geology of ground water, with particular emphasis on the chemistry and movement of water. | Hydrogeomorphic (HGM) Approach | A functional assessment method which compares a wetland's condition to similar wetland types (as defined by HGM classification) that are relatively unaltered. HGM functions normally fall into one of three major categories: (1) hydrologic (e.g., storage of surface water), (2) biogeochemical (e.g., removal of elements and compounds), and (3) habitat (e.g., maintenance of plant and animal communities). | Hydrogeomorphic (HGM) Classification | A wetland classification system based on the position of a wetland in the landscape (geomorphic setting), dominant sources of water, and the flow and fluctuation of water once in the wetland. Hydrogeomorphic classes include riverine, depressional, slope, mineral soil flats, organic soil flats, estuarine fringe, and lacustrine fringe. | Hydrology | The science dealing with the properties, distribution, and circulation of water. | Hydrolysis | The decomposition of organic compounds by interaction with water. | Hydronic | A ventilation system using heated or cooled water pumped through a building. | Hydrophilic | Having a strong affinity for water. | Hydrophobic | Having a strong aversion for water. | Hydropneumatic | A water system, usually small, in which a water pump is automatically controlled by the pressure in a compressed air tank. | Hypereutrophic Lake | Lakes that are extremely eutrophic, with a high algal productivity level and intense algal blooms. | Hypersensitivity Diseases | Diseases characterized by allergic responses to pollutants; diseases most clearly associated with indoor air quality are asthma, rhinitis, and pneumonic hypersensitivity. | Hypolimnion | Bottom waters of a thermally stratified lake. The hypolimnion of a eutrophic lake is usually low or lacking in oxygen. | Hypoxia/Hypoxic Waters | Waters with dissolved oxygen concentrations of less than 2 ppm, the level generally accepted as the minimum required for most marine life to survive and reproduce. | Identification Code or EPA I.D. Number | The unique code assigned to each generator, transporter, and treatment, storage, or disposal facility by regulating agencies to facilitate identification and tracking of chemicals or hazardous waste. | Ignitable | Capable of burning or causing a fire. | IM240 | A high-tech, transient dynamometer automobile emissions test that takes up to 240 seconds. | Imhoff Cone | A clear, cone-shaped container used to measure the volume of settable solids in a specific volume of water. | Immediately Dangerous to Life and Health | The maximum level to which a healthy individual can be exposed to a chemical for 30 minutes and escape without suffering irreversible health effects or impairing symptoms. Used as a "level of concern.". | Imminent Hazard | One that would likely result in unreasonable adverse effects on humans or the environment or risk unreasonable hazard to an endangered species during the time required for a pesticide registration cancellation proceeding. | Imminent Threat | A high probability that exposure is occurring. | Immiscibility | The inability of two or more substances or liquids to readily dissolve into one another, such as soil and water. | Immobilization | The conversion of an element from the inorganic to the organic form in microbial tissues so that the element is not readily available to other organisms or plants. | Impermeable | Not easily penetrated. The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water. | Impoundment | A body of water or sludge confined by a dam, dike, floodgate, or other barrier. | In Situ | Refers to treatment of contaminated areas without excavation or other removal, as in the in situ treatment of soils through biodegradation of contaminants. | In Vitro | Testing or action outside an organism (e.g., inside a test tube or culture dish.). | In Vivo | Testing or action inside an organism. | 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 air stream through the water and causing the compounds to evaporate. | In-Situ Vitrification | Technology that treats contaminated soil in place at extremely high temperatures, at or more than 3000 degrees Fahrenheit. | Incident Command Post | A facility located at a safe distance from an emergency site, where the incident commander, key staff, and technical representatives can make decisions and deploy emergency manpower and equipment. | Incident Command System | The organizational arrangement where one person is in charge of a comprehensive emergency response on the emergency incident site, backed by an Emergency Operations Center staff with resources, information, and advice. | Incineration | A treatment technology involving destruction of waste by controlled burning at high temperatures; e.g., burning sludge to remove the water and reduce the remaining residues to a safe, non-burnable ash that can be disposed of safely. | Incineration at Sea | Disposal of waste by burning at sea on specially-designed incinerator ships. | Incompatible Waste | A waste unsuitable for mixing with another waste or material because it may react to form a hazard. | Indemnification | In the pesticide program, legal requirement that EPA pay certain end-users, dealers, and distributors for the cost of stock on hand at the time a pesticide registration is suspended. | Indirect Discharge | Introduction of pollutants from a non-domestic source into a publicly owned waste-treatment system. Indirect discharges can be commercial or industrial facilities whose wastes enter local sewers. | Indirect Source | Any facility or building, property, road or parking area that attracts motor vehicle traffic and, indirectly, causes pollution. | Indoor Air | The breathable air inside a habitable structure or conveyance. | Indoor Air Pollution | Chemical, physical, or biological contaminants in indoor air. | Industrial Sludge | Semi-liquid residue or slurry remaining from treatment of industrial water and wastewater. | Industrial Source Reduction | Practices that reduce the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment. Also reduces the threat to public health and the environment associated with such releases. | Industrial Waste | Unwanted materials from an industrial operation; may be liquid, sludge, solid, or hazardous waste. | Inert | Innocuous, undamaging, nontoxic. Something that is not detrimental to health or the environment. | Inert Ingredient | Pesticide components such as solvents, carriers, dispersants, and surfactants that are not active against target pests. Not all inert ingredients are innocuous. | Inertial Separator | A device that uses centrifugal force to separate waste particles. | Infectious Agent | Any organism, such as a pathogenic virus, parasite, or bacterium, that is capable of invading body tissues, multiplying, and causing disease. | Infectious Waste | Hazardous waste capable of causing infections in humans, including: contaminated animal waste; human blood and blood products; isolation waste, pathological waste; and discarded sharps (needles, scalpels or broken medical instruments). | Infiltration | The penetration of water through the ground surface into sub-surface soil or the penetration of water from the soil into sewer or other pipes through defective joints, connections, or manhole walls. | Infiltration Gallery | A sub-surface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a watertight chamber from which the water is pumped to treatment facilities. | Infiltration Rate | The quantity of water that can enter the soil in a specified time interval. | Inflow | Entry of extraneous rain water into a sewer system from sources other than infiltration, such as basement drains, manholes, storm drains, and street washing. | Information Collection Request | A description of information to be gathered in connection with rules, proposed rules, surveys, and guidance documents that contain information-gathering requirements. | Information File | In the Superfund program, a file that contains accurate, up-to-date documents on a Superfund site. The file is usually located in a public building (school, library, or city hall) convenient for local residents. | Ingestion | The taking in of a substance through the mouth for digestion. | Inhalable Particles | All dust capable of entering the human respiratory tract. | Inhalation | The breathing in of a substance in the form of a gas, vapor, fume, mist, or dust. | Initial Risk Screening Level | A Michigan health based level for a carcinogenic effect that is defined as an increased cancer risk of one in one million (i.e., ‘ten to the minus six’ or 10-6 ). | Initial Threshold Screening Level | A Michigan health-based screening level designed to be protective for non-carcinogenic effects (an illness that threatens health but is not cancer). It is based on toxicological data. | Injection Well | A well into which fluids are injected for purposes such as waste disposal, improving the recovery of crude oil, or solution mining. | Injection Zone | A geological formation receiving fluids through a well. | Inoculum | 1. Bacteria or fungi injected into compost to start biological action. 2. A medium containing organisms, usually bacteria or a virus, that is introduced into cultures or living organisms. | Inorganic Chemicals | Chemical substances of mineral origin, not of basically carbon structure. | Inorganic Contaminants | Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. EPA has set legal limits on 15 inorganic contaminants. | Insecticide | A pesticide compound specifically used to kill or prevent the growth of insects. | Instream Use | Water use taking place within a stream channel; e.g., hydro-electric power generation, navigation, water quality improvement, fish propagation, recreation. | Integrated Exposure Assessment | Cumulative summation (over time) of the magnitude of exposure to a toxic chemical in all media. | Integrated Risk Information System | EPA's Integrated Risk Information System, an electronic data base containing the Agency's latest descriptive and quantitative regulatory information on chemical constituents. | Interagency Agreement | A written agreement between the U.S. Environmental Protection Agency (EPA) and a federal agency that has the lead for site cleanup activities (e.g., U. S. Department of Energy), that sets forth the roles and responsibilities of the agencies for performing and overseeing the activities. States are often parties to interagency agreements, as the New York State Department of Environmental Conservation is regarding Brookhaven National Laboratory. | Interceptor Sewers | Large sewer lines that, in a combined system, control the flow of sewage to the treatment plant. In a storm, they allow some of the sewage to flow directly into a receiving stream, thus keeping it from overflowing onto the streets. | Interflow | That portion of precipitation that infiltrates into the soil and moves horizontally through the shallow soil horizon without ever reaching the water table. | Intermolecular Forces | Forces that can hold molecules together. | Internal Dose | In exposure assessment, the amount of a substance penetrating the absorption barriers (e.g., skin,, lung tissue, gastrointestinal tract) of an organism through either physical or biological processes. | Interstate Air Pollution | In many areas, two or more states share the same air. We say these states are in the same air basin defined by geography and wind patterns. Often, air pollution moves out of the state in which it is produced into another state. | Interstate Waters | Waters that flow across or form part of state or international boundaries; e.g., the Great Lakes, the Mississippi River, or coastal waters. | Interstitial Monitoring | The continuous surveillance of the space between the walls of an underground storage tank. | Inversion | A layer of warm air that prevents the rise of cooling air and traps pollutants beneath it; can cause an air pollution episode. | Ion | An electrically charged atom or molecule. | Ion exchange | A reversible chemical reaction between a solid (ion exchanger) and a fluid (usually a water solution) by means of which ions may be interchanged from one substance to another. | Ionic Bond | A chemical bond formed by electrostatic attraction between positive and negative ions. | Ionizing Radiation | Radiation that can strip electrons from atoms; e.g., alpha, beta, and gamma radiation. | Irradiation | Exposure to radiation of wavelengths shorter than those of visible light (gamma, x-ray, or ultra- violet), for medical purposes, to sterilize milk or other foodstuffs, or to induce polymerization of monomers or vulcanization of rubber. | Irreversible Effect | Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent. | Irritant | A substance that can cause irritation of the skin, eyes, or respiratory system. Effects may be acute from a single high level exposure, or chronic from repeated low-level. More than one sample point exhibiting the same isolate concentration. | Isoconcentration | More than one sample point exhibiting the same isolate concentration. | Isopleth | The line or area represented by an isoconcentration. | Isotope | A variation of an element that has the same atomic number of protons but a different weight because of the number of neutrons. Various isotopes of the same element may have different radioactive behaviors, some are highly unstable. | Isotropy | The condition in which the hydraulic or other properties of an aquifer are the same in all directions. | Jasonite | Substance that is likable. | Joint and Several Liability | A legal concept for Superfund site cleanup liability and other costs on the part of more than one potentially responsible party (i.e., if there were several owners or users could all be considered potentially liable for cleaning up the site.) | Joint Implementation | Agreements made between two or more nations under the auspices of the United Nations Framework Convention on Climate Change to help reduce greenhouse gas emissions. | Karst | A geologic formation of irregular limestone deposits with sinks, underground streams, and caverns. | Kinetic Rate Coefficient | A number that describes the rate at which a water constituent such as a biochemical oxygen demand or dissolved oxygen rises or falls, or at which an air pollutant reacts. | Lacustrine | Wetlands and deepwater habitats with all the following characteristics: 1) situated in a topographic depression or a dammed river channel, 2) less than 30 percent areal coverages by trees, shrubs, persistent emergent vegetation, emergent mosses, or lichens, and 3) total area exceeds 8 hectares. Lakes typify lacustrine wetland systems. | Lacustrine Deposits | Stratified materials deposited in lake waters that later become exposed either by the lowering of the water level or by the elevation of the land. | Lag Phase | The stage of growth of microbial cells in which nucleic acids and proteins are synthesized, but in which there is no cell division. | Lagoon | 1. A shallow pond where sunlight, bacterial action, and oxygen work to purify wastewater; also used for storage of wastewater or spent nuclear fuel rods. 2. Shallow body of water, often separated from the sea by coral reefs or sandbars. | Land Ban | Phasing out of land disposal of most untreated hazardous wastes, as mandated by the 1984 RCRA amendments. | Land Disposal Restrictions | Rules that require hazardous wastes to be treated before disposal on land to destroy or immobilize hazardous constituents that might migrate into soil and ground water. | Land Farming | A disposal process in which hazardous waste deposited on or in the soil is degraded naturally by microbes. | Land Reclamation | The process of making land, previously used for other economic activity such as mining, suitable for human habitation. | Land Reuse | The process of turning contaminated land into a clean, productive resource. | Land treatment | Any activity or project to improve conservation of soil, water, or other resources and improve productive use of the resource. | 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. | Landscape | The traits, patterns, and structure of a specific geographic area, including its biological composition, its physical environment, and its anthropogenic or social patterns. An area where interacting ecosystems are grouped and repeated in similar form. | Landscape Ecology | The study of the distribution patterns of communities and ecosystems, the ecological processes that affect those patterns, and changes in pattern and process over time. | Landscape Indicator | A measurement of the landscape, calculated from mapped or remotely sensed data, used to describe spatial patterns of land use and land cover across a geographic area. | Langelier Index | An index reflecting the equilibrium pH of water with respect to calcium and alkalinity; used in stabilizing water to control both corrosion and scale deposition. | Large Quantity Generator | Person or facility generating more than 2200 pounds of hazardous waste per month. Such generators produce about 90 percent of the nation's hazardous waste, and are subject to all RCRA requirements. | Laser Induced Fluorescence | A method for measuring the relative amount of soil and/or groundwater with an in-situ sensor. | Latency | Time from the first exposure of a chemical until the appearance of a toxic effect. | Lateral Sewers | Pipes that run under city streets and receive the sewage from homes and businesses, as opposed to domestic feeders and main trunk lines. | Laundering Weir | Sedimentation basin overflow weir. | Law of Mass Action | The value of the equilibrium constant expression is a constant for a particular reaction at a given temperature, and that this value is independent of the equilibrium concentrations of the chemicals substituted into the equation. | LC 50/Lethal Concentration | Median level concentration, a standard measure of toxicity. It tells how much of a substance is needed to kill half of a group of experimental organisms in a given time. | LD 50/ Lethal Dose | The dose of a toxicant or microbe that will kill 50 percent of the test organisms within a designated period. The lower the LD 50, the more toxic the compound. | Ldlo | Lethal dose low; the lowest dose in an animal study at which lethality occurs. | Leachate | Water that collects contaminants as it trickles through wastes, pesticides or fertilizers. Leaching may occur in farming areas, feedlots, and landfills, and may result in hazardous substances entering surface water, ground water, or soil. | Leachate Collection System | A system that gathers leachate and pumps it to the surface for treatment. | Leaching | The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid. | Lead | A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations. | Lead Service Line | A service line made of lead which connects the water to the building inlet and any lead fitting connected to it. | Leaded gasoline | Gasoline containing tetraethyl lead, an important constituent in antiknock gasoline. | Legionella | A genus of bacteria, some species of which have caused a type of pneumonia called Legionaires Disease. | Level of Concern | The concentration in air of an extremely hazardous substance above which there may be serious immediate health effects to anyone exposed to it for short periods. | Life Cycle of a Product | All stages of a product's development, from extraction of fuel for power to production, marketing, use, and disposal. | Lifetime Average Daily Dose | Figure for estimating excess lifetime cancer risk. | Lifetime Exposure | Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years). | Ligands | The Lewis bases attached to the metal atom in a complex. | Light Compensation Point | In a lake, the transition between the euphotic zone and the profundal zone. At this depth, the amount of carbon dioxide being converted to sugars by photosynthesis is equal to that being released during respiration. | Light Non-Aqueous Phase Liquid | A non-aqueous phase liquid with a specific gravity less than 1.0. Because the specific gravity of water is 1.0, most LNAPLs float on top of the water table. Most common petroleum hydrocarbon fuels and lubricating oils are LNAPLs. | Lignite | A brownish-black coal of low rank with high inherent moisture and volatile matter content, used almost exclusively for electric power generation. Also referred to as brown coal. | Limestone flux | The addition of calcium chloride (limestone) to the combustion process to reduce the formation of acid rain contaminates (SO2 and NOx, also see acid rain). | Limestone Scrubbing | Use of a limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere. | Limit of Detection | The minimum concentration of a substance being analyzed test that has a 99 percent probability of being identified. | Limit of quantification (Lo) | The analyte concentration below which there is an unacceptable error in determining a quantitative value. It is commonly set at "y+s", where y is the measurement of the average value of the blank (no analyte) and s is the standard
deviation of the blank measurements. | Limited Degradation | An environmental policy permitting some degradation of natural systems but terminating at a level well beneath an established health standard. | Limiting Factor | A condition whose absence or excessive concentration, is incompatible with the needs or tolerance of a species or population and which may have a negative influence on their ability to thrive. | Limnetic Zone | A layer of open water in a lake, where photosynthesis can occur. | Limnology | The study of the physical, chemical, hydrological, and biological aspects of fresh water bodies. | Lindane | A pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater fish and aquatic life. | Lipid Solubility | The maximum concentration of a chemical that will dissolve in fatty substances. Lipid soluble substances are insoluble in water. They will very selectively disperse through the environment via uptake in living tissue. | Liquid Extraction | Process of separating a substance from water or a solid by extracting it into another liquid. | Liquid Injection Incinerator | Commonly used system that relies on high pressure to prepare liquid wastes for incineration by breaking them up into tiny droplets to allow easier combustion. | List | Term for EPA list of violating facilities debarred from obtaining government contracts because of violations of the Clean Air or Clean Water Acts. The list is maintained by The Office of Enforcement and Compliance Monitoring. | Listed Waste | Wastes listed as hazardous under RCRA but which have not been subjected to the Toxic Characteristics Listing Process because the dangers they present are considered self-evident. | Lithology | Mineralogy, grain size, texture, and other physical properties of granular soil, sediment, or rock. | Litter | Undecomposed plant residues on the soil surface. | Littoral Zone | 1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2. A strip of land along the shoreline between the high and low water levels. | Local Education Agency | In the asbestos program, an educational agency at the local level that exists primarily to operate schools, including primary and secondary public and private schools. A single, unaffiliated school can be considered a LEA for AHERA purposes. | Local Emergency Planning Committee | A committee appointed by the state emergency response commission, as required by SARA Title III, to formulate a comprehensive emergency plan for its jurisdiction. | Log Growth | On a plot of bacterial growth versus time, the phase of growth plotted using a logarithmic scale. | Lot | All of the material (the population) being characterized or studied. Anything from a single sample
to a truck load of material to an entire Superfund site could be a single lot. A lot is the material that
is to be represented by the sample. | Low Density Polyethylene | Plastic material used for both rigid containers and plastic film applications. | Low Emission Value | A vehicle meeting the low-emission vehicle standards. | Low NOx Burners | One of several combustion technologies used to reduce emissions of Nitrogen Oxides (NOx.). | Low-Level Radioactive Waste | Wastes less hazardous than most of those associated with a nuclear reactor; generated by hospitals, research laboratories, and certain industries. The Department of Energy, Nuclear Regulatory Commission, and EPA share responsibilities for managing them. | Lower Detection Limit | The smallest signal above background noise an instrument can reliably detect. | Lower Explosive Limit | The concentration of a compound in air below which the mixture will not catch on fire. | Lowest Acceptable Daily Dose | The largest quantity of a chemical that will not cause a toxic effect, as determined by animal studies. | Lowest Achievable Emission Rate | Under the Clean Air Act, the rate of emissions that reflects (1) The most stringent emission limitation in the implementation plan of any state for such source unless the owner or operator demonstrates such limitations are not achievable; or (2) The most stringent emissions limitation achieved in practice, whichever is more stringent. A proposed new or modified source may not emit pollutants in excess of existing new source standards. | Lowest Observed Adverse Effect Level | The lowest level of a stressor that causes statistically and biologically significant differences in test samples as compared to other samples subjected to no stressor. | Macropores | Secondary soil features such as root holes or desiccation cracks that can create significant conduits for movement of NAPL and dissolved contaminants, or vapor-phase contaminants. | Magnetic Separation | Use of magnets to separate ferrous materials from mixed municipal waste stream. | Major Modification | This term is used to define modifications of major stationary sources of emissions with respect to Prevention of Significant Deterioration and New Source Review under the Clean Air Act. | Major Stationary Sources | Term used to determine the applicability of source regulations. In a nonattainment area, any source with potential to emit 100 tons per year is a major stationary source. In PSD areas the cutoff level may be 100 or 250 tons, depending upon the source. | Management Plan | Under the Asbestos Hazard Emergency Response Act (AHERA), a document that each Local Education Agency is required to prepare, describing all activities planned and undertaken by a school to comply with AHERA regulations. | Mandatory Recycling | Programs which by law require consumers to separate trash so that some or all recyclable materials are recovered for recycling rather than going to landfills. | Manifest | A one-page form used by haulers transporting waste that lists EPA identification numbers, type and quantity of waste, the generator it originated from, the transporter that shipped it, and the storage or disposal facility to which it is being shipped. | Manifest System | Tracking of hazardous waste from "cradle-to-grave” (generation through disposal) with accompanying documents known as manifests.(See: cradle to grave.) | Manufacturer's Formulation | A list of substances or component parts as described by the maker of a coating, pesticide, or other product containing chemicals or other substances. | Manufacturing Use Product | Any product intended (labeled) for formulation or repackaging into other pesticide products. | Margin of Exposure | The ratio of the no-observed adverse-effect-level to the estimated exposure dose. | Margin of Safety | Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population. | Marine | Open ocean overlying the continental shelf and associated high-energy coast line. Examples of wetland types within this system are subtidal and intertidal aquatic beds, reefs, and rocky shores. | Marsh | A type of wetland that does not accumulate appreciable peat deposits and is dominated by herbaceous vegetation. Marshes may be either fresh or saltwater, tidal or non-tidal. | Mass Density | Mass per unit volume of a substance. | Mass Number | Of an element, is the sum of the number of protons and neutrons in the nucleus of that particular element. | Material Category | In the asbestos program, broad classification of materials into thermal surfacing insulation, surfacing material, and miscellaneous material. | Material Safety Data Sheet | Information required under the OSHA Communication Standard on the identity of hazardous chemicals, health, and physical hazards, exposure limits, and precautions. Section 311 of SARA requires facilities to submit MSDSs under certain circumstances. | Material Type | Classification of suspect material by its specific use or application; e.g., pipe insulation, fire- proofing, and floor tile. | Materials Recovery Facility | A facility that processes residentially collected mixed recyclables into new products available for market. | Matter | All objects that have mass and occupy space. | Maximally Exposed Individual | The person with the highest exposure in a given population. | Maximum Acceptable Toxic Concentration | For a given ecological effects test, the range (or geometric mean) between the No Observable Adverse Effect Level and the Lowest Observable Adverse Effects Level. | Maximum Available Control Technology | The emission standard for sources of air pollution requiring the maximum reduction of hazardous emissions, taking cost and feasibility into account. The MACT must not be less than the average emissions achieved by the best 12 percent of existing sources. | Maximum Contaminant Level | The maximum permissible level of a contaminant in water delivered to any user of a public system. MCLs are enforceable standards. | Maximum Contaminant Level Goal | Under the Safe Drinking Water Act, a non-enforceable concentration of a drinking water contaminant, set at the level at which no known or anticipated adverse effects on human health occur and which allows an adequate safety margin. | Maximum Exposure Range | Estimate of exposure level received by an individual in a defined population greater than the 98th percentile dose for all individuals in that population, but less than the exposure level received by the person receiving the highest exposure level. | Maximum Residue Level | Comparable to a U.S. tolerance level, the Maximum Residue Level the enforceable limit on food pesticide levels in some countries. Levels are set by the Codex Alimentarius Commission, a United Nations agency. | Maximum Tolerated Dose | The maximum dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity. | Measure of Effect/ Measurement Endpoint | A measurable characteristic of ecological entity that can be related to an assessment endpoint., such as survival of fish under acute exposure. | Measure of Exposure | A measurable characteristic of a stressor (such as the specific amount of mercury in a body of water) used to help quantify the exposure of an ecological entity or individual organism. | Mechanical Aeration | Use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen. | Mechanical Separation | Using mechanical means to separate waste into various components. | Mechanical Turbulence | The erratic movement of air or water influenced by local obstructions. | Media | Specific environments--air, water, soil--which are the subject of regulatory concern and activities. | Medical Surveillance | A periodic comprehensive review of a worker's health status; acceptable elements of such surveillance program are listed in the Occupational Safety and Health Administration standards for asbestos. | Memoranda of Agreement | An agreement between the Environmental Protection Agency and the Michigan Department of Environmental Quality in which the EPA promised not to plan or anticipate any federal action against an owner, operator, generator or transporter. | Mercury | Heavy metal that can accumulate in the environment and is highly toxic if breathed or swallowed. | Mesotrophic | The amount of water lost from soil upon drying to a constant weight, expressed as the weight per unit of dry soil or as the volume of water per unit bulk volume of the soil. For a fully saturated medium, moisture content indicates the porosity. | Metabolism | A chemical and physical process in which substances (such as sugar) are transformed into energy and waste products. | Metabolites | Any substances produced by biological processes. | Metalimnion | 1. A well used to obtain water quality samples or measure groundwater levels. 2. A well drilled at a hazardous waste management facility or Superfund site to collect ground-water samples for the purpose of physical, chemical, or biological analysis. | 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. | Method 18 | An EPA test method which uses gas chromatographic techniques to measure the concentration of volatile organic compounds in a gas stream. | Method 24 | An EPA reference method to determine density, water content and total volatile content (water and VOC) of coatings. | Method 25 | An EPA reference method to determine the VOC concentration in a gas stream. | Method Detection Limit | Refer to limit of detection. | Methoxychlor | Pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater and marine aquatic life. | Methyl Orange Alkalinity | A measure of the total alkalinity in a water sample in which the color of methyl orange reflects the change in level. | Microbial Pesticide | A microorganism that is used to kill a pest, but is of minimum toxicity to humans. | Microclimate | 1. Localized climate conditions within an urban area or neighborhood. 2. The climate around a tree or shrub or a stand of trees. | Microenvironmental Method | A method for sequentially assessing exposure for a series of microenvironments that can be approximated by constant concentrations of a stressor. | Microenvironments | Well-defined surroundings such as the home, office, or kitchen that can be treated as uniform in terms of stressor concentration. | Microorganisms | Tiny living organisms that can be seen only with the aid of a microscope. Some microorganisms can cause acute health problems when consumed in drinking water. Also known as microbes. | Milligrams per liter (mg/L) | The measure of concentration used in the measurement of chemicals in fluids. This is the most common way to present a concentration in water and is roughly equivalent to parts per million. | Million-Gallons Per Day | A measure of water flow. | Mining of an Aquifer | Withdrawal over a period of time of ground water that exceeds the rate of recharge of the aquifer. | Minor Source | New emissions sources or modifications to existing emissions sources that do not exceed NAAQS emission levels. | Miscellaneous ACM | Interior asbestos-containing building material or structural components, members or fixtures, such as floor and ceiling tiles; does not include surfacing materials or thermal system insulation. | Miscible Liquids | Two or more liquids that can be mixed and will remain mixed under normal conditions. | Mist | Liquid particles measuring 40 to 500 micrometers (pm), are formed by condensation of vapor. By comparison, fog particles are smaller than 40 micrometers (pm). | Mitigation | Measures taken to reduce adverse impacts on the environment. | Mixed Funding | Settlements in which potentially responsible parties and EPA share the cost of a response action. | Mixture | A material, having variable composition, which can be separated by physical means. | Mobile Incinerator Systems | Hazardous waste incinerators that can be transported from one site to another. | Mobile Source | Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, and locomotives. | Mobility | Ability of contaminants to move. A highly mobile contaminant will spread quickly. | Model Plant | A hypothetical plant design used for developing economic, environmental, and energy impact analyses as support for regulations or regulatory guidelines; first step in exploring the economic impact of a potential NSPS. | Modified Source | The enlargement of a major stationary pollutant sources is often referred to as modification, implying that more emissions will occur. | Moisture Content | 1.The amount of water lost from soil upon drying to a constant weight, expressed as the weight per unit of dry soil or as the volume of water per unit bulk volume of the soil. For a fully saturated medium, moisture content indicates the porosity. | Molarity | The number of moles per liter of solution. | Mole | Avogadro's number of molecules of a substance. | Molecular Formula | A chemical formula that gives the exact number of the different atoms of an element found in the molecule. | Molten Salt Reactor | A thermal treatment unit that rapidly heats waste in a heat-conducting fluid bath of carbonate salt. | Monitoring | Periodic or continuous sampling to determine the level of pollution or radioactivity. | Monitoring Well | A well used to obtain water quality samples or measure groundwater levels. 2. A well drilled at a hazardous waste management facility or Superfund site to collect ground-water samples for the purpose of physical, chemical, or biological analysis. | Monoclonal Antibodies | 1. Man-made (anthropogenic) clones of a molecule, produced in quantity for medical or research purposes. 2. Molecules of living organisms that selectively find and attach to other molecules to which their structure conforms exactly. | Monomictic | Lakes and reservoirs which are relatively deep, do not freeze over during winter, and undergo a single stratification and mixing cycle during the year (usually in the fall). | Montreal Protocol | Treaty, signed in 1987, governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCS. | Moratorium | During the negotiation process, a period of 60 to 90 days during which EPA and potentially responsible parties may reach settlement but no site response activities can be conducted. | Morbidity | Rate of disease incidence. | Mortality | Death rate. | Most Probable Number | An estimate of microbial density per unit volume of water sample, based on probability theory. | Muck Soils | Earth made from decaying plant materials. | Multi-Media Approach | Joint approach to several environmental media, such as air, water, and land. | Multiple Chemical Sensitivity | A diagnostic label for people who suffer multi-system illnesses as a result of contact with, or proximity to, a variety of airborne agents and other substances. | Multiple Use | Use of land for more than one purpose; e.g., grazing of livestock, watershed and wildlife protection, recreation, and timber production. Also applies to use of bodies of water for recreational purposes, fishing, and water supply. | Multistage Remote Sensing | A strategy for landscape characterization that involves gathering and analyzing information at several geographic scales, ranging from generalized levels of detail at the national level through high levels of detail at the local scale. | Municipal Sewage | Wastes that are permitted to be discharged into the sanitary sewers. | Municipal Solid Waste | Residential solid waste and some non-hazardous commercial, institutional, and industrial wastes. This material is generally sent to municipal landfills for disposal. | Mutagen | An agent that causes a permanent genetic change in a cell other than that which occurs during normal growth. | Mutagenicity | Mutagenicity is the capacity of a chemical or physical agent to cause such permanent changes. | National Ambient Air Quality Standards | Standards established by EPA that apply for outdoor air throughout the country. | National Emissions Standards for Hazardous Air Pollutants | Emissions standards set by EPA for an air pollutant not covered by NAAQS that may cause an increase in fatalities or in serious, irreversible, or incapacitating illness. Primary standards protect human health, secondary standards protect public welfare. | National Environmental Performance Partnership Agreements | System that allows states to assume greater responsibility for environmental programs based on their relative ability to execute them. | National Estuary Program | A program established by Clean Water Act Amendment of 1987 to develop and implement conservation and management plans for protecting estuaries and restoring and maintaining their chemical, physical, and biological integrity. | National Municipal Plan | A policy created in 1984 by EPA and the states in 1984 to bring all publicly owned treatment works (POTWs) into compliance with Clean Water Act requirements. | National Oil and Hazardous Substances Contingency Plan | The federal regulation that guides determination of the sites to be corrected under both the Superfund program and the program to prevent or control spills into surface waters or elsewhere. | National Pollutant Discharge Elimination System | A provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation. | National Pollution Discharge Elimination System | The primary permitting program under the Clean Water Act which regulates al discharges to the surface water. | National Primary Drinking Water Regulations | Applies to public water systems and specifies a contaminant level, which, in the judgment of the EPA Administrator, will not adversely affect human health. | National Priorities List | EPA's list of the most serious uncontrolled or abandoned hazardous waste sites identified for possible long-term remedial action under Superfund. The list is based primarily on the score a site receives from the Hazard Ranking System. | National Response Center | The federal operations center that receives notifications of all releases of oil and hazardous substances into the environment; open 24 hours a day, is operated by the U.S. Coast Guard, which evaluates all reports and notifies the appropriate agency. | National Response Team | Representatives of 13 federal agencies that coordinate federal responses to nationally significant incidents of pollution-- oil spills, major chemical releases --and provide advice and technical assistance to the responding agency. | National Secondary Drinking Water Regulations | The regulations define secondary maximum contaminant levels, the maximum concentrations of certain substances in drinking water that affect its aesthetic quality. While the NSDWR set aesthetic standards for drinking water, i.e., color, odor, taste, etc., the National Primary Drinking Water Regulations (NPDWR) set standards protective of the public health. | Navigable Waters | Traditionally, waters sufficiently deep and wide for navigation by all, or specified vessels; such waters in the United States come under federal jurisdiction and are protected by certain provisions of the Clean Water Act. | Necrosis | Death of plant or animal cells or tissues. In plants, necrosis can discolor stems or leaves or kill a plant entirely. | Negative pressure | Condition thatexists when less air is supplied to a spacethan is exhausted from the space, so the airpressure within that space is less than thatin surrounding areas. | Negotiations | After potentially responsible parties are identified for a site, EPA coordinates with them to reach a settlement that will result in the PRP paying for or conducting the cleanup under EPA supervision. | Nematocide | The term 'nematocide' includes all preparations intended for preventing, destroying, repelling or mitigating any invertebrate animals (Nematoda), inhabiting soil, water, plants or plants parts. | Nematode | Microscopic unsegmented worms, many of which are parasites on plant roots. Un-segmented round worms with elongated, fusiform, or sac-like bodies covered with cuticle, and inhabiting soil, water, plants and animals. | Nephelometric | Method of measuring turbidity in a water sample by passing light through the sample and measuring the amount of the light that is deflected. | Net Primary Productivity | Total amount of chemical energy fixed by the processes of photosynthesis minus the chemical energy lost through respiration. | Netting | A concept in which all emissions sources in the same area that owned or controlled by a single company are treated as one large source, thereby allowing flexibility in controlling individual sources in order to meet a single emissions standard. | Neutron | A particle having a mass almost equal to that of a proton, but no charge. | New Source | Any stationary source built or modified after publication of final or proposed regulations that prescribe a given standard of performance. | New Source Performance Standards | Uniform national EPA air emission and water effluent standards which limit the amount of pollution allowed from new sources or from modified existing sources. | New Source Review | A Clean Air Act requirement that State Implementation Plans include a permit review that applies to the operation of new and modified stationary sources in nonattainment areas to ensure attainment of national ambient air quality standards. | Nitrate | A compound containing nitrogen that can exist in the atmosphere or as a dissolved gas in water and which can have harmful effects on humans and animals. Nitrates in water can cause severe illness in infants and domestic animals. | Nitrates | Plant nutrient and fertilizer that enters water supply sources from fertilizers, animal feed lots, manures, sewage, septic systems, industrial wastewaters, sanitary landfills, and garbage dumps. | Nitric Oxide | A gas formed by combustion under high temperature and high pressure in an internal combustion engine; it is converted by sunlight and photochemical processes in ambient air to nitrogen oxide. NO is a precursor of ground-level ozone pollution, or smog. | Nitrification | The process whereby ammonia in wastewater is oxidized to nitrite and then to nitrate by bacterial or chemical reactions. | Nitrilotriacetic Acid | A compound now replacing phosphates in detergents. | Nitrite | An intermediate in the process of nitrification. 2. Nitrous oxide salts used in food preservation Nitrogen Dioxide (NO2): The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog. | Nitrogen Cycle | Cyclic movement of nitrogen in different chemical forms from the environment, to organisms, and then back to the environment. | Nitrogen dioxide | The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog. | Nitrogen fixation | Conversion of atmospheric nitrogen gas into forms useful to plants and other organisms by lightning, bacteria, and blue-green algae; it is part of the nitrogen cycle. | Nitrogen Oxide | The result of photochemical reactions of nitric oxide in ambient air; major component of photochemical smog. Product of combustion from transportation and stationary sources and a major contributor to the formation of ozone and to acid deposition. | Nitrogenous Wastes | Animal or vegetable residues that contain significant amounts of nitrogen. | No Further Remedial Action Planned | Determination made by EPA following a preliminary assessment that a site does not pose a significant risk and so requires no further activity under CERCLA. | Non attainment area | A geographic area in which the level of a criteria air pollutant is higher than the level allowed by the federal standards (i.e., does not meet one or more of the NAAQS for the criteria pollutants). | Non-Aqueous Phase Liquid | Liquids, commonly a mixture of several different chemicals that are either denser or less dense than water. Dense NAPL (DNAPL), such as chlorinated solvents, will sink if it enters groundwater; less dense, or light NAPL (LNAPL), such as gasoline, will float on the water table. NAPL in the subsurface can be a persistent source of groundwater contamination due to its low solubility and viscosity. | Non-Conservative Chemical | Chemicals which react chemically , biologically or undergo radioactive decay are called Non-Conservative chemicals. Most chemicals fall under this category. | Non-Point Source | Source of pollution which is discharged into the natural water body at multiple points is called Non-Point Source of pollution. Urban and Agriculture runoff are examples of Non-Point Source of Pollution. | Non-Transient, Non-Community Water System | A water system which supplies water to 25 or more of the same people at least six months per year in places other than their residences. Some examples are schools, factories, office buildings, and hospitals which have their own water systems. | Normality | The number of gram-equilivants of a substance per liter. | Offset | A method established by the 1990 Clean Air Act to give companies, which own or operate large (major) sources in nonattainment areas flexibility in meeting overall pollution reduction requirements when changing production processes. | Oligotrophic Lake | Lakes that have a low level of productivity due to severely limited supply of nutrients to support algal growth. | Opacity | A measure of the amount of light obscured by very small particles in the air; clear window glass has a zero opacity, a brick wall has 100 percent opacity. Opacity is used when measuring fugitive dust. | Open System | An open system is one in which material is transferred across the system boundary, that is, enters the system, leaves the system or both. It is also refered to as a flow system or a continuous system. | Operable unit (OU) | The cleanup of a site can be divided into a number of operable units, depending on the complexity of the problems associated with a site. Operable units may address geographical portions of a site, specific site problems, or initial phases of an action, or may consist of any set of actions performed over time or any actions that are concurrent but located in different parts of a site. | Order of Reaction | The order of a reaction identifies the type of equation that expresses the rate at which a reaction occurs. It also indicates the apparent mechanism of the reaction itself. | Organic | A class of compounds containing mainly carbon, hydrogen and oxygen. | Organic Chemicals | Chemical compounds made of carbon and hydrogen as the basic building blocks. | Organic Chemicals/Compounds | Naturally occurring (animal or plant-produced or synthetic) substances containing mainly carbon, hydrogen, nitrogen, and oxygen. | Organic Contaminants | Carbon-based chemicals, such as solvents and pesticides, which can get into water through runoff from cropland or discharge from factories. EPA has set legal limits on 56 organic contaminants. | Outlier | A statistical outlier is an observation that can be shown to belong to a population distribution
other than the population distribution in question (usually the underlying dominant population) or
shown not to belong to the population distribution in question. An outlier sample is a sample that is
not representative of the distribution of the results from a particular population of samples. | Overfire air | A control technology used to reduce NOx emissions and control CO emissions where air is forced into the top of an incinerator or boiler to fan the flames that encourages the formation of nitrogen gas. | Overland Flow | Flow due to surface runoff and is that portion of precipitation that neither inflitrates into the soil nor evaporates nor evaportranspirates. | Oxygen-Demanding Material | Anything that can be oxidized in the receiving water resulting in the consumption of dissolved molecular oxygen. | Oxygenated fuel/Oxyfuel | A special type of gasoline, which burns more completely than regular gasoline in cold start conditions; more complete burning results in reduced production of carbon monoxide. | Ozonation | A treatment process in which ozone is applied to the water for disinfection, or for taste and odor control. | Ozone | A gas, which is a variety of oxygen. The oxygen gas (O2) found in the air consists of two oxygen atoms stuck together; this is molecular oxygen. Ozone consists of three oxygen atoms stuck together into an ozone molecule (or O3). | Ozone depletion | Destruction of the stratospheric ozone layer, which shields the earth from ultraviolet radiation harmful to life. | Ozone layer | The protective layer in the atmosphere, about 15 miles above the ground, that absorbs some of the sun's ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the earth's surface. | Ozone precursors | Chemical compounds, such as carbon monoxide, methane, non-methane hydrocarbons, and nitrogen oxides, which in the presence of solar radiation react with other chemical compounds to form ozone, mainly in the troposphere. | Palustrine | All nontidal wetlands dominated by trees, shrubs, persistent emergent vegetation, emergent mosses or lichens, and all such wetlands that occurs in tidal areas where salinity due to ocean-derived salts is below 5 ppt. This system also includes wetlands lacking such vegetation if they are less that 8 hectares, lack wave-action or bedrock shoreline features, and are no deeper that 2 meters at low water in their deepest spot. Examples include ponds, bogs, and prairie potholes. | Pan Evaporation | The rate of evaporation using a standard National Weather Service Class A pan. | Particulates / Particulate matter | A Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog, found in air or emissions. Particulate matter includes dust, soot and other tiny bits of solid materials that are released into and move around in the air. | Parts per billion | The number of parts of a substance per billion parts of another substance into which it is combined. One ppb is comparable to one kernel of corn in a filled, 45-foot silo, 16 feet in diameter. A part per billion is roughly equivalent to one-thousandth teaspoon of water in a 21-foot diameter, 4-foot deep swimming pool. | Parts per million | The number of parts of a substance per million parts of another substance into which it is combined. Parts per million may also be expressed as micrograms per gram, milligrams per kilogram or milligrams per liter. A part per million is roughly equivalent to one teaspoon of water in a 21 foot diameter, 4 foot deep swimming pool. | Percentile | The specific value of a distribution that divides the distribution such that p percent of the
distribution is equal to or below that value. For p = 95, “The 95th percentile is X” means that 95% of
the values of the population (or sample) are less or equal to X. | Performance standards | 1. Regulatory requirements limiting the concentrations of designated compounds. 2.Operating standards established by EPA for various permitted pollution control systems, asbestos inspections, and various program operations and maintenance requirements. | Permit | A document that resembles a license, required by the Clean Air Act for big (major) sources of air pollution, such as power plants, chemical factories and, in some cases, smaller polluters. | Permit fees | Fees paid by businesses required to have a permit. Permit fees are like the fees drivers pay to register their cars. The money from permit fees will help pay for state air pollution control activities. | Petroleum | A complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. | Phase I Environmental Assessment | Determine if hazardous substances MAY have been released onto the property. Includes historical use of property and a visual inspection. | Phase I Environmental Audit | An initial environmental investigation that is limited to a historical records search to determine ownership of a site and to identify the kinds of chemical processes that were carried out at the site. | Phase II Environmental Assessment | Determine if the property meets the definition of a FACILITY under Part 201 of the MNREPA and developing enough information for preparation of a BEA and possible due care compliance plan. | Phase II Environmental Audit | An investigation that includes tests performed at the site to confirm the location and identity of environmental hazards. The audit includes preparation of a report that includes recommendations for cleanup alternatives. | Photoautrotrophic Organisms | Photosynthetic organisms that obtain their carbon from inorganic sources. | Photochemical Oxidants | Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons. | Photochemical Smog | Air pollution caused by chemical reactions of various pollutants emitted from different sources. (See: photochemical oxidants). | Photoheterotroph | Organisms that obtain energy through photosynthesis but are not capable of reducing carbon dioxide. | Photosynthesis | The process by which organisms are able to convert energy from sunight into chemical energy. | Phreatic Aquifer | Aquifers that are not confined by impermeable geologic materials. | Phreatic Zone | A level in an aquifer at which all of the openings or voids in the soils are filled with water, that is, the region beneath the water table. | Phytoremediation | Phytoremediation is the use of plants to remediate contamination by the uptake (transpiration) of contaminated water by plants. Plants can be used to contain, remove, or degrade contaminants. | Piezometer | An instrument for measuring the pressure-head of liquids, especially of the water pressure in an aquifer. | Piezometric Head | head corresponding to the height to which water would rise in an observation well penetrating an aquifer.The measure of the pressure in the aquifer. | Piezometric Surface | An imaginary plane drawn through the points of equilibrium in several piezometers. | Plume | A volume of a substance that moves from its source to places farther away from the source. Plumes can be described by the volume of air or water they occupy and the direction they move. For example, a plume can be a column of smoke from a chimney or a substance moving with groundwater. | Point of Exposure | The place where someone can come into contact with a substance present in the environment. | Point Precipitation Analysis | The analysis of data from a single rain gauge. | Point Source | A single identifiable source that discharges pollutants into the environment. Examples are smokestack, sewer, ditch, or pipe. | Polar Covalent Bond | A covalent bond in which the bonding electrons are not shared equally. | Pollutants/Pollution | Unwanted chemicals or other materials found in the air. Pollutants can harm health, the environment and property. Many air pollutants occur as gases or vapors, but some are very tiny solid particles: dust, smoke or soot. | Polychlorinated Biphenyls | A group of toxic, persistent chemicals used in electrical transformers and capacitors for insulating purposes, and in gas pipeline systems as a lubricant. The sale and new use of PCBs were banned by law in 1979. | Polychlorinated Biphenyls | A group of synthetic, organic, chlorinated, aromatic hydrocarbons having various industrial applications. They are highly toxic, poisonous and potentially carcinogenic environmental pollutants known to cause skin diseases. They tend to accumulate in animal tissues and are suspect of causing birth defects and cancer. | Polynuclear Aromatic Hydrocarbon | A group of chemical compounds that contain more than one fused benzene ring. Commonly found in petroleum fuels, coal products, and tar. | Potentially Responsible Party | Any individual or company that is potentially responsible for or has contributed to a spill or other contamination at a Superfund site. Whenever possible, EPA requires PRPs to clean up sites they have contaminated. | Precipitate | A substance separated from a solution or suspension by chemical or physical change. | Precipitation | Removal of hazardous solids from liquid waste to permit safe disposal; removal of particles from airborne emissions as in rain (e.g. acid precipitation). | Precipitation Reaction | The phase-change reaction by which dissolved chemicals form insoluble solids. | Precision | Sometimes referred to as reproducibility, precision is a measure of the mutual agreement
among individual measurements of the same property, usually under prescribed similar conditions
expressed generally in terms of the standard deviation or variance, which is a function of random
error. | Prevention of Significant Deterioration | These are federal regulations concerning air pollution. It states that there is no significant deterioration of air quality in a region from a new source of pollutants. | Primary Consumer | The herbivore organisms that eat plant material. | Primary Producers | Organisms that use sunlight as a source of energy. | Primary Standard | Pollution limit based on health effects. Primary standards are set for criteria air pollutants. | Primary Treatment | Mechanical separation of solids, grease and scum from waste water. With the aid of flocculating agents, primary treatment can eliminate 50 to 65% of the suspended solids. Solids removed by primary treatment may comprise as much as 30 to 40% of the original BOD of the water. | Priority pollutants | A group of toxic chemicals or classes of chemicals listed under section 307(a)(1) of the Clean Water Act of 1977 (U.S.C. 466). | Probabilistic Analysis | Calculation and expression of health risks using multiple risk descriptors to provide the likelihood of various risk levels. Probabilistic risk results approximate a full range of possible outcomes and the likelihood of each, which often is presented as a frequency distribution graph, thus allowing uncertainty or variability to be expressed quantitatively. | Process Controls | Modifications to the fuel, process or equipment to maximize the combustion efficiency; these are forms of pollution prevention. | Products | The chemical compounds to the right of the reaction arrow in a chemical equation. | Profundal Zone | In a lake, the zone that lies below the euphotic zone. | Proprietary Chemicals | Chemicals that have been developed under the protection of a patent. | Proton | A positively charged particle having a mass more than 1800 times that of an electron. | Protozoa | One-celled animals, usually microscopic, that are larger and more complex that bacteria. May cause disease. | Public Water System | Any water system which provides water to at least 25 people for at least 60 days annually. There are more than 170,000 PWSs providing water from wells, rivers and other sources to about 250 million Americans. The others drink water from private wells. There are differing standards for PWSs of different sizes and types. | Pyrolysis | Transformation of a compound into one or more other substances by heat alone, i.e., without oxidation. | Quality Assurance (QA) | An integrated system of activities involving planning, quality control, quality
assessment, reporting, and quality improvement. It is the activity of providing, to all concerned, the
evidence needed to establish confidence that the quality function is being performed adequately to
provide fitness for use. | Quality Assurance and Quality Control | A system of procedures, checks, audits, and corrective actions applied to ensure that all research, design and performance, environmental sampling, and other technical reporting activities are of the highest achievable quality. | Quality Control | The overall system of activities that measure the attributes (quality
characteristics) and performance of a process. For example, a measurement of the collection of data
(or data analysis) is compared with standards and an action may be taken depending on the
magnitude of the difference. | Radionuclides | Any man-made or natural element that emits radiation and that may cause cancer after many years of exposure through drinking water. | Radon | A colorless, odorless naturally occuring radioactive gas formed by the breakdown or decay of radium or uranium in soil or rocks like granite. Radon is fairly soluble in water, so well water may contain radon. | Reactants | Substances consumed in a chemical reaction. | Reaction Rate Constant | The proportionality term of a reaction, generally dependent on the temperature and pressure. | 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. | Reasonable Available Control Technology | Reductions on a source category basis as reasonable further progress towards attaining ambient air quality standards. | Recalcitrant | Difficult to degrade under natural conditions and usually not responsive to treatment. | Receptor Age | The description of the exposed individual as defined by the EPA region or dictated by the site. | Receptors | Mitigation employees, building occupants, the public at large, the building and its parts, and even an atmosphere, that may be effected by a release of a contaminant or pollutant. | Recharge | The process of infiltration and migration, renewing the supply of groundwater. | Recharge Area | The land area through or over which rainwater and other surface water soaks through the earth to replenish an aquifer, lake, stream, river or marsh. | Record of decision (ROD) | Documents the regulators' decision for the selected remedial action, and includes the responsiveness summary and a bibliography of documents that were used to reach the remedial decision. When the ROD is finalized, remedial design and construction can begin. | Recycling | Collecting and reprocessing a resource so it can be used again. An example is collecting aluminum cans, melting them down, and using the aluminum to make new cans or other aluminum products. | Reformulated gasoline | Specially refined gasoline with low levels of smog-forming volatile organic compounds (VOCs) and low levels of hazardous air pollutants. | Remedial Action Plan | A work plan for the cleanup, removal, containment, isolation, treatment, or monitoring of hazardous substances released into the environment. Or taking actions to prevent, minimize, or reduce injury to the public or environmental health from a release of a hazardous substances or a potential release of a hazardous substance. | Remedial actions | The actual construction or implementation phase of a Superfund site cleanup that follows remedial design. | Remedial Design and Remedial Action | The step in the cleanup process that follows the RI/ FS and selection of a remedy. A RD is the preparation of the engineering plans and specifications to implement the remedy. The RA is the actual construction or implementation of the remedy. | Remedial investigation (RI) | Through extensive sampling and laboratory analyses, the RI characterizes the nature and extent of contamination, defines the pathways of migration and measures the degree of contamination in surface water, groundwater, soils, air, plants and animals. Information gathered during the RI attempts to fully describes the contamination problem at the site so that the appropriate remedial action can be developed. | Remedial Investigation and Feasibility Study | The RI/FS is the step in the cleanup process that is conducted to gather sufficient information to support the selection of a site remedy that will reduce or eliminate the risks associated with the contamination at the site. | Renaissance Zone | Michigan's tax free zones created as an incentive for redevelopment. These zones waive most state and local taxes on a Michigan business. | Residence Time | For flow reactors, residence time is used as a measure of the processing rate. Residence time is defined as the time required to process one reactor volume of feed i.e. input. | Resource Conservation and Recovery Act | RCRA is a Federal law that established a regulatory system to track hazardous substances from their generation to their disposal. It requires the use of safe and secure procedures in treating, transporting, storing and disposing of hazardous substances. | Retention time | The length of time the material is held in the system. How long from beginning to end. | Risk | A measure of the chance (probability) that damage to life, health, property, or the environment will occur. | Risk Assessment | A scientific process that estimates the type and magnitude of risk to human health posed by exposure to chemical substances. | Riverine | Wetland and deepwater habitats contained within a channel with two exceptions: 1) wetlands dominated by trees, shrubs, persistent emergent plants, emergent mossess, or lichens, and 2) habitat with water containing ocean-derived salts in excess of 5 ppt. Rivers and streams fall within this system and subsystems included tidal, perennial, and intermittent watercourses. | Sample | Since it is often too difficult to analyze an entire population (or lot), a sample (a portion) is
taken from the population in order to make estimations about the characteristics of that population. To
be truly representative, the sample must mimic (be representative of) the population in every way,
including the distribution of the individual items or members (particles, analytes, and other fragments
or materials) of that population. | Sampling | Sampling is the process of selecting units (e.g., people, organizations) from a population of interest so that by studying the sample we may fairly generalize our results back to the population from which they were chosen. | Saturated | At reaction equilibrium, in a dissolution reaction, no additional ions can go into solution. | Saturated Zone | A geological area below the ground surface in which all pores and cracks are filled with water under pressure equal to or greater than that of the atmosphere.A well placed in this zone will be able to pump ground water. | Screening Levels | The intervals in a groundwater monitoring well where the samples are taken or the interval between the upper and the lower extents of the screen of a groundwater well through which the sample is taken. Maximum screening interval usually is 5 ft. | Scrubbing | Common method of reducing stack air emissions; removal of impurities by spraying a liquid that concentrates the impurities into waste. | Secondary Consumer | The carnivore organisms that eat the flesh of animals. | Secondary Risk Screening Level | Secondary Risk Screening Level is designed to be protective for carcinogenic effects. | Secondary standard | A pollution limit based on environmental effects such as damage to property, plants, visibility, etc. Secondary standards are set for criteria air pollutants. | Sediment Budget | To account for all sediments that flow into and out of a defined system, such as a park beach. Sediments that flow in are considered to come from a 'SOURCE' while all sediments leaving the system are considered to be lost to a 'SINK.' | Seepage Velocity | The rate of discharge of ground water per unit area of a porous medium measured at right angle to the direction of flow (Lohman and others, 1972). | Selective Non-Catalytic Reduction | Injecting ammonia or urea to control NOx emissions by reacting nitric oxide (NO) with a nitrogen-bearing compound to form nitrogen gas (N2). | Semivolatile Organic Compound | A substance that evaporates slowly at standard temperature (20° C and 1 atm pressure). | Septic system | A tank used to hold domestic wastes when a sewer line is not available to carry them to a treatment plant. It stores the solid waste until bacteria breaks it down and the relatively clean water is absorbed by the ground. | Sewage | The organic waste and waste water produced by residential and commercial establishments. | Shape factor | Also known as the coefficient of cubicity, the shape factor summarizes the average
shape of the particles with respect to a cube (which has a shape factor of 1.0). | Sheet pile wall | Interlocking sheets of steel that are driven into the ground one at a time by workers on the surface using specialized pile-driving equipment to create a continuous wall of steel. Sheet piles are typically used to build bulkheads, retaining walls, cofferdams, and barriers to control surface and/or groundwater flows. | Sludge | A semi-solid residue from any of a number of air or water treatment processes; can be a hazardous waste. | Slurry | A water containing a high concentration of suspended solids, usually over 5000 mg/L. A pourable mixture of solid and liquid. | Smog | A mixture of pollutants, principally ground-level ozone, produced by chemical reactions in the air involving smog-forming chemicals. A major portion of smog-formers comes from burning of petroleum-based fuels such as gasoline. | Soil Boring (or Boring) | A circular hole made in the ground by an auger or mechanical drill rig to collect soil samples deep in the ground. Representative samples are collected for testing to see if the subsoil has been contaminated. Sometimes these borings are converted into groundwater monitoring wells. | Soil washing | Soil washing is a treatment technology that uses liquids (usually water, sometimes combined with chemical additives) and a mechanical process to removes hazardous contaminants from soil. | Solidification | The change of phase from a liquid to a solid. | Solubility | Ability of a substance to dissolve in liquid. Sugar is soluble in water but oil is not water-soluble. | Solvent | A substance (usually liquid) capable of dissolving or dispersing one or more other substance. Water can be a solvent. | Solvent extraction | Solvent extraction (also known as chemical extraction) is a cleanup method that uses solventsto extract or remove harmful chemicals from polluted materials. | Sorption | The attachment of a chemical to either the mineral or organic portions of soil particles. | Source | Any place or object from which pollutants are released. A source can be a power plant, factory, dry cleaning business, gas station or farm. | Specific Gravity | Mass density of a substance per unit mass density of water. | Specific Weight | Weight (force) per unit volume. | Specimen | A specimen is a portion of the lot taken without regard to correct sampling practices and
therefore should never be used as a representative sample of the lot. It is a nonprobabilistic
sample; that is, each item (particle, fragment) does not have an equal and constant probability of
being selected from the lot to be part of the sample. | Specimen | A summary value calculated from a sample, usually as an estimator (e.g., the sample mean or
the sample variance) of a population parameter (e.g., the population mean or the population
variance). | Stabilization | Conversion of the active organic matter in sludge into inert, harmless material. | Stakeholders | A person or group of people who have a vested interest in the success of an organization and the environment in which the organization operates. | Standard Deviation | A measure of the dispersion or imprecision of a sample or population distribution
expressed as the positive square root of the variance and has the same unit of measurement as the
mean. | State Implementation Plan | EPA approved state plans for the establishment, regulation, and enforcement of air pollution standards. | Stationary Phase | The phase on a bacterial growth versus time plot where the population of bacteria becomes constant either as a result of cessation of fission or a balance in death and reproduction rates. | Stationary source | A place or object from which pollutants are released and which does not move around. Stationary sources include power plants, gas stations, incinerators, houses etc. | Steady-State | Steady State means that the values of the variables within the system such as volume, concentration etc. do not change with respect to time. This happens when the inputs and outputs are held constant for a long time and hence the system gets poised in a condition for which no net change in its composition is realized from the ongoing process. | Storage Problem | The net amount of water that is gained or lost in the lake within a given period. | Stratosphere | The layer of the atmosphere located between the troposphere and the mesosphere, characterized by a slight temperature increase and absence of clouds. It extends between 11 and 31 miles (17 to 50 kilometers) above the earth's surface. It is the location of the earth's ozone layer. | Stream-Gauging Station | A location on the channel where the flow is measured. | Streamflow | Discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation. | Structural Isomers | Compounds that have the same molecular formula but different structures. | Subsample | A subsample is simply a sample of a sample. This term is used when one wants to
distinguish the parent sample (from which the subsample is taken) from the primary lot. An example
would be that the site is the primary lot, the bottle coming to the laboratory is the (parent) sample,
and the portion taken for analysis is the subsample. | Sulfur dioxide | A criteria air pollutant. Sulfur dioxide is a gas produced by burning coal, most notably in power plants. Some industrial processes, such as production of paper and smelting of metals, produce sulfur dioxide. | Superfund | A trust fund that provides for the cleanup of hazardous substances released into the environment, regardless of fault. Established under CERCLA, Superfund also refers to cleanup programs designed and conducted under CERCLA and amendments. | Superfund Amendments and Reauthorization Act | SARA reflected EPA's experience in administering the complex Superfund program during its first six years and made several important changes and additions to the Superfund program. | Superfund Program | The program that funds the EPA solid waste emergency and long-term removal and remedial activities. | Supersaturated | In a dissolution reaction, at reaction equilibrium higher concentrations of the dissolved ions are obtained than what is predicted using the equilibrium constant. | Surface Water | All water naturally open to the atmosphere (rivers, lakes, reservoirs, ponds, streams, seas, estuaries). | Surfactant | A chemical that acts as a surface active agent. It lowers the surface or interfacial tension of the medium in which it is dissolved. | Suspensions | Mixtures of a liquid and suspended particles. | Synthetic Organic Compound | Man-made organic chemicals, some of which are volatile, while others tend to stay dissolved in water instead of evaporating. | Tax Increment Financing | Tax Increment Financing is the ability of an eligible agency to capture from all eligible taxing jurisdictions a defined portion of the property tax revenues on real and personal property in a designated area. | Technical Advisory Committees | TACs have representation from a wide range of agency, stakeholder and public groups interested in, and/or affected by, environmental issues. | Temperature inversion | One of the weather conditions that are often associated with serious smog episodes in some portions of the country. In a temperature inversion, air doesn't rise because it is trapped near the ground by a layer of warmer air above it. | Theoretical Oxygen Demand | The amount of oxygen required to oxidize a substance to carbon dioxide and water. | Thermal desorption | An innovative treatment technology that heats soil to release contaminants. | Threshold Level | The minimum concentration of a substance at which negative health effects begin to appear. | Total Fertility Rate | The number of children a woman will have over her entire lifetime. | Toxic Air Contaminates | These are toxic chemicals found in the air stream. Air toxic rules do not apply to existing sources. Concentrations of the toxic air contaminants emitted must not exceed the applicable health based screening level. | Toxic Substance | A chemical or mixture that can cause illness, death, disease or bith defects. The quantities and exposures necessary to cause these effects can vary widely. Many toxic substances are pollutants and contaminants in the environment. | Toxic Substances Control Act | Provides EPA with comprehensive authority to regulate or prohibit the manufacture, use of chemical substances that pose unreasonable risks; requires premanufacture notification of EPA for new chemicals or significant new uses of existing chemaicals. | Toxicity | A measure of the poisonous or harmful nature of a substance. | Toxicity Characteristic Leaching Procedure | A test designed to determine the potential for toxic chemicals to move through soils and groundwater. Determines the effectiveness of treatment processes designed to contain wastes or toxic chemicals in a solid matrix such as concrete or polyethylene. | Toxicology | The study of adverse effects of chemicals on living organisms. | Traceability | This is the ability to trace the history, application, or location of an entity to its origin,
such as a field sample or a calibration sample. | Transient, Non-Community Water System | A water system which provides water in a place such as a gas station or campground where people do not remain for long periods of time. These systems do not have to test or treat their water for contaminants which pose long-term health risks because fewer than 25 people drink the water over a long period. They still must test their water for microbes and several chemicals. | Transpiration | The process by which water is emitted from plants through the stomata. | Troposphere | The layer of the atmosphere closest to the earth's surface. | Turbidity | The cloudy appearance of water caused by the presence of tiny particles. High levels of turbidity may interfere with proper water treatment and monitoring. | Ultraviolet B | A type of sunlight. The ozone in the stratosphere, high above the Earth, filters out ultraviolet B rays and keeps them from reaching the Earth. Ultraviolet B exposure has been associated with skin cancer, eye cataracts and damage to the environment. | Uncertainty | This is a term with multiple meanings. As such, it should always be defined when used.
For this document, uncertainty refers to variation from the correct or expected value due to all factors
affecting the measurement process. It is often characterized as the combination of effects that cause
bias or variance components. | Underground Storage Tank | A UST is a tank located entirely or partially underground that is designed to hold gasoline or other petroleum products or chemical solutions. | Undersaturated | In a dissolution reaction, at equilibrium additional ions can go into solution. | Unsaturated Zone | The unsaturated zone is the area between the land surface and the uppermost aquifer (or saturated zone). The soils in an unsaturated zone may contain air and water. | Unsteady-State | A system that is in a transient state at the time of a measurement. Unsteady state conditions occur when the variables within the system such as the concentration and the control volume change with time. | Vadose Zone | The vadose zone is the area between the surface of the land and the aquifer water table in which the moisture content is less than the saturation point and the pressure is less than atmospheric. | Van der Waals Forces | These are week forces. It includes both dipole-dipole interaction and dispersion forces. | Vapor | Gaseous phase of any substance that is liquid or solid at atmospheric pressures and temperatures. For example, steam is a vapor. | Vaporize | Change the state from liquid to gas. | Variability | Observed differences attributable to the heterogeneity or diversity in a population (or lot),
the influence of outliers, or in the measurements made to estimate population (or lot) parameters.
Sources of variability are the results of random or systematic processes. | Variance | State or EPA permission not to meet a certain drinking water standard. The water system must prove that: (1) it cannot meet a MCL, even while using the best available treatment method, because of the characteristics of the raw water, and (2) the variance will not create an unreasonable risk to public health. The State or EPA must review, and allow public comment on, a variance every three years. States can also grant variances to water systems that serve small populations and which prove that they are unable to afford the required treatment, an alternative water source, or otherwise comply with the standard. | Viruses | Submicroscopic disease-causing organisms that grow only inside living cells. | Viscosity | The molecular friction within a fluid that produces flow resistance. | Vitrification | Vitrification is the process of converting materials into a glass-like substance, typically through a thermal process. | Volatile | Any substance which evaporates quickly. | Volatile Organic Compound | Any organic compound which evaporates readily to the atmosphere. VOCs contribute significantly to photochemical smog production and certain health problems. | Volatilization | A process by which a chemical evaporates. | Vulnerability Assessment | An evaluation of drinking water source quality and its vulnerability to contamination by pathogens and toxic chemicals. | Wastewater | Spent or used water from an individual home, community, farm or an industry that contains dissolved or suspended substances. | Water Table | The upper surface of the saturated zone in aquifers that are not confined by impermeable geologic material. | Water Table Aquifer | Aquifers that are not confined by impermeable geologic materials. | Watershed | Larger systems that include lakes, rivers, the surrounding land, and even the groundwater lying in the geological materials below the land. | Weight Percent | Grams of substance per 100 grams of solution. | Well cap | A tight-fitting, verminproof seal designed to prevent contaminants from flowing down inside of the well casing. | Well casing | The tubular lining of a well. Also a steel or plastic pipe installed during construction to prevent collapse of the well hole. | Wellhead | The top-of a structure built over a well. | Wet scrubber | A control technology using water to remove particulates still suspended in the gas stream, by making them larger. | Wetlands | An area that is saturated by surface or ground water with vegetation adapted for life under those soil conditions, as swamps, bogs, fens, marshes, and estuaries. | Zeroth Order Reaction | A reaction is of zero order when the rate of reaction is independent of the concentration of materials. Generally reactions are of zero order in higher concentrations. |
