A
abatement: Reducing the degree or intensity of, or eliminating, pollution.

absorption: the penetration of atoms, ions, or molecules into the bulk mass of a substance.

acceptable daily Intake (ADI): Estimate of the largest amount of chemical to which a person can be exposed on a daily basisthat is not anticipated to result in adverse effects (usually expressed in mg/kg/day). Same as RfD.

acid deposition: A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either wet or dry form. The wet forms, popularly called "acid rain," can fall as rain, snow, or fog. The dry forms are acidic gases or particulates.

acid mine drainage: Drainage of water from areas that have been mined for coal of other mineral ores; the water has low pH, sometimes less than 2.0 (is acid), because of its contact with sulfur-bearing material; acid drainage is harmful because it often kills aquatic organisms.

acid rain: Precipitation which has been rendered (made) acidic by airborne pollutants.

acidic: The condition of water or soil that contains a sufficient amount of acid substances to lower the pH below 7.0

action levels: 1. 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. As opposed to "tolerances" which are established for residues occurring as a direct result of proper usage, action levels are set for inadvertent residues resulting from previous legal use or accidental contamination. 2. In the Superfund program, the existence of a contaminant concentration in the environment high enough to warrant action or trigger a response under SARA and the National Oil and Hazardous Substances Contingency Plan. The term is also used in other regulatory programs.

activated sludge process: A sewage treatment process by which bacteria that feed on organic wastes are continuously circulated and put in contact with organic waste in the presence of oxygen to increase the rate of decomposition.

active ingredient: In any pesticide product, the component that kills, or otherwise controls, target pests. Pesticides are regulated primarily on the basis of active ingredients.

acute effect: An adverse effect on any living organism in which severe symptoms develop rapidly and often subside after the exposure stops.

adaptation: Changes in an organism's structure or habits that help it adjust to its surroundings.

additive effect: Combined effect of two or more chemicals equal to the sum of their individual effects.

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.)

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).  

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 suspension of liquid or solid particles in a gas.

aggregate: A mass or cluster of soil particles, often having a characteristic shape.

agricultural waste: Poultry and livestock manure, and residual materials in liquid or solid form generated from the production and marketing of poultry, livestock, furbearing animals, and their products. Also includes gra in, vegetable, and fruit harvest residue.

agrochemical: Synthetic chemicals (pesticide and fertilizers) used in agricultural production.

air emissions: Gas emitted into the air from industrial and chemical processes, such as ozone, carbon monoxide, nitrogen oxide, nitrogen dioxide, sulfur dioxide and others.

air mass: A large volume of air with certain meteorological or polluted characteristics, e,g, a heat inversion or smogginess-while in one location. The characteristics can change as the air mass moves away.

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. They may be in the form of solid particles, liquid droplets, gases, or in combination thereof. Generally, they fall into two main groups: (1) those emitted directly from identifiable sources and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation. Exclusive of pollen, fog, and dust, which are of natural origin, about 100 contaminants have been identified and fall into the following categories: solids, sulfur compounds, volatile organic chemicals, nitrogen compounds, oxygen compounds, halogen compounds, radioactive compounds, and odors.

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 may not be exceeded during a given time in a defined area.

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.

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. Airborne particulates include: windblown dust, emissions from industrial processes, smoke from the burning of wood and coal, and motor vehicle or non-road engine exhausts. exhaust of motor vehicles.

algae: Chiefly aquatic, eucaryotic one-celled or multicellular plants without true stems, roots and leaves, that are typically autotrophic, photosynthetic, and contain chlorophyll. Algae are not typically found in groundwater. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water.

algal bloom: Sudden, massive growths of microscopic and macroscopic plant life, such as green or bluegreen algae, which develop in lakes and reservoirs, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry.

alkali: Various soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids to form neutral salts and may be used in chemical water treatment processes.

alluvial: Relating to mud and/or sand deposited by flowing water. Alluvial deposits may occur after a heavy rain storm.

alternative fuels: Substitutes for traditional liquid, oil-derived motor vehicle fuels like gasoline and diesel. Includesmethanol, ethanol, compressed natural gas, and others.

ambient air: Any unconfined portion of the atmosphere: open air, surrounding air.

anaerobic: A biological process which occurs in the absence of oxygen.

aqueous solubility: The extent to which a compound will dissolve in water. The log of solubility is generally inversely related to molecular weight.

aquifer: An underground geological formation, or group of formations, containing usable amounts of groundwater that can supply wells and springs.

aromatic: A type of hydrocarbon, such as benzene or toluene, added to gasoline in order to increase octane. Some aromatics are toxic.

artesian: Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing.

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: 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.

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.


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B
backflow: A reverse flow condition, created by a difference in water pressures, which causes water to flow back into the distribution pipes of a potable water supply from any source or sources other than an intended source. Also see backsiphonage and cross-connection.

background level: In air pollution control, the concentration of air pollutants in a definite area during a fixed period of time prior to the starting up or on the stoppage of a source of emission under control. In toxic substances monitoring, the average presence in the environment, originally referring to naturally occurring phenomena.

bacteria: (Singular 'bacterium') Microscopic living organisms that can aid in pollution control by metabolizing organic matter in sewage, oil spills or other pollutants. However, bacteria in soil, water or air can also cause human, animal and plant health problems.

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 (water, chemical solutions, slurry).

berm: A sloped wall or embankment (typically constructed of earth, hay bales, or timber framing) used to prevent inflow or outflow of material into/from an area.

best available technology (BAT): The best technology treatment techniques, or other means which the Administrator finds, after examination for efficacy under field conditions and not solely under laboratory conditions, are available (taking cost into consideration). For the purposes of setting MCLs for synthetic organic chemicals, any BAT must be at least as effective as granular activated carbon.

best management practices (BMPs): Structural, nonstructural and managerial techniques that are recognized to be the most effective and practical means to control nonpoint source pollutants yet are compatible with the productive use of the resource to which they are applied. BMPs are used in both urban and agricultural areas.
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 method used to determine the toxicity of specific chemical contaminants. A number of individuals of a sensitive species are placed in water containing specific concentrations of the contaminant for a specified period of time.

bioaugmentation: The introduction of cultured microorganisms into the subsurface environment for the purpose of enhancing bioremediation of organic contaminants. Generally the microorganisms are selected for their ability to degrade the organic compounds present at the remediation site. The culture can be either an isolated genus or a mix of more than one genera. Nutrients are usually also blended with the aqueous solution containing the microbes to serve as a carrier and dispersant. The liquid is introduced into the subsurface under natural conditions (gravity fed) or injected under pressure.

biochemicals: Chemicals that are either naturally occurring or identical to naturally occurring substances. Examples include hormones, pheromones, and enzymes. Biochemicals function as pesticides through non-toxic, non-lethal modes of action, such as disrupting the mating pattern of insects, regulating growth, or acting as repellants. Biochemicals tend to be environmentally compatible and are thus important to Integrated Pest Management programs.

biodegradable: The ability of a substance to be broken down physically and/or chemically by microorganisms. For example, many chemicals, food scraps, cotton, wool, and paper are bio-degradable; plastics and polyester generally are not.

biodiversity: The number and variety of different organisms in the ecological complexes in which they naturally occur. Organisms are organized at many levels, ranging from complete ecosystems to the biochemical structures that are the molecular basis of heredity. Thus, the term encompasses different ecosystems, species, and genes that must be present for a healthy environment. A large number of species must characterize the food chain, representing multiple predator-prey relationships.

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.

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.

bioremediation: The use of living organisms (e.g., bacteria) to clean up oil spills or remove other pollutants from soil, water, and wastewater, use of organisms such as non-harmful insects to remove agricultural pests or counteract diseases of trees, plants, and garden soil.

biosphere: The portion of Earth and its atmosphere that can support life.

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.

black water: Water that contains animal, human, or food waste.

bloom (algal): A proliferation of algae and/or higher aquatic plants in a body of water; often related to pollution, especially when pollutants accelerate growth.

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.

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 the non-combustible materials, which may include toxics.

brackish: Mixed fresh and salt waters.

brine mud: Waste material, often associated with well-drilling or mining, composed of mineral salts or other inorganic compounds.

buffer strips: Strips of grass or other close-growing vegetation that separate a waterway (ditch, stream, creek) from an intensive land use area (subdivision, farm); also referred to as filter strips, vegetated filter strips, and grassed buffers.

by-product: Material, other than the principal product, generated as a consequence of an industrial process.

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C
cancer: A disease characterized by the rapid and uncontrolled growth of aberrant cells into malignant tumors.

cap: A fairly impermeable seal, usually composed of clay-type soil or a combination of clay soil and synthetic liner, which is placed over a landfill during closure. The cap serves to minimize leachate volume during biodegradation of the waste by keeping precipitation from percolating through the landfill. The cap also keeps odors down and animal scavengers from gathering.

carbon dioxide: A colorless, odorless, gas produced by burning fossil fuels, sometimes referred to as a green house gas because it contibutes to earth warming.

carbon monoxide: A colorless, odorless, poisonous gas produced by incomplete fossil fuel combustion.

carcinogen: Any substance that can cause or aggravate cancer.

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 and oxygen.

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.

chelation: A chemical complexing (forming or joining together) of metallic cations (such as copper) with certain organic compounds, such as EDTA (ethylene diamine tetracetic acid). Chelation is used to prevent the precipitation of metals (copper).

chisel plowing: Preparing croplands by using a special implement that avoids complete inversion of the soil as in with conventional plowing. Chisel plowing can leave a protective cover or crop residues on the soil surface to help prevent erosion and improve filtration.

chlorinated hydrocarbons: These include a class of persistent, broad-spectrum insecticides that linger in the environment and accumulate in the food chain. Among them are DDT, aldrin, dieldrin, heptachlor, chlordane, lindane, endrin, mirex, hexachloride, and toxaphene. Other examples include TCE, used as an industrial solvent.

chlorination: Adding chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results. Chlorine also is used almost universally in manufacturing processes, particularly for the plastics industry.
chlorofluorocarbons (CFCs): A family of inert, nontoxic, and easily liquified chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere they 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. Two widely used chlorophenoxy herbicides are 2,4-D (2,4-Dichlorophenoxy acetic acid) and 2,4,5-TP (2,4,5-Trichlorophenoxy propionic acid (silvex)).

chlorophyll: A chemical mixture or compound found in the chloroplasts of plant cells and gives plants their green color. Plants use chlorophyll to convert the energy of sunlight to food in the process known as photosynthesis.

chlorosis: Discoloration of normally green plant parts caused by disease, lack of nutrients, or various air pollutants.

cholinesterase: An enzyme found in animals that regulates nerve impulses. Cholinesterase inhibition is associated with a variety of acute symptoms such as nausea, vomiting, blurred vision, stomach cramps, and rapid heart rate.

chronic effect: An adverse effect on a human or animal in which symptoms recur frequently or develop slowly over a long period of time.

cistern: A small tank (usually covered) or a storage facility used to store water for a home or farm. Often used to store rain water.

clarifer: A large circular or rectangular tank or basin in which water is held for a period of time, during which the heavier suspended solids settle to the bottom. Clarifiers are also called settling basins and sedimentation basins.

class I area: Under the Clean Air Act, 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 area, monuments and other areas of special national and cultural significance.

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, liquified petroleum gas, and others.

clear cut: Harvesting all the trees in one area at one time, a practice that can encourage fast rainfall or snowmelt runoff, erosion, sedimentation of streams and lakes, flooding, and destroys vital habitat.

clear well: A reservoir for storing filtered water of sufficient quantity to prevent the need to vary the filtration rate with variations in demand. Also used to provide chlorine contact time for disinfection.

climate change: This term is commonly used interchangeably with "global warming" and "the greenhouse effect," but is a more descriptive term. Climate change refers to the buildup of man-made gases in the atmosphere that trap the suns heat, causing changes in weather patterns on a global scale. The effects include changes in rainfall patterns, sea level rise, potential droughts, habitat loss, and heat stress. The greenhouse gases of most concern are carbon dioxide, methane, and nitrous oxides. If these gases in our atmosphere double, the earth could warm up by 1.5 to 4.5 degrees by the year 2050, with changes in global precipitation having the greatest consequences.

cloning: In biotechnology, obtaining a group of genetically identical cells from a single cell; making identical copies of a gene.

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 waste: ceasing acceptance of solid waste and placing a cap on the landfill site. No more waste can be accepted and a cap usually is placed over the site. The cap is then planted with grasses and other ground covers. Post-closure care includes monitoring ground water, landfill gases, and leachate collection systems, sometimes for as long as 30 years.

coagulants: Chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids from the water by settling, skimming, draining or filtering.

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.

cohesion: Molecular attraction which holds two particles together.

coliform organism: Microorganisms found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially dangerous bacterial contamination by disease-causing microorganisms.

colloids: Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in water have a negative electrical charge, they tend to repel each other. This repulsion prevents the particles from clumping together, becoming heavier, and settling out.

combustion: 1. Burning, or rapid oxidation, accompanied by release of energy in the form of heat and light. A basic cause of air pollution. 2. Refers to controlled burning of waste, in which heat chemically alters organic compounds, converting into stable inorganics such as carbon dioxide and water.

commercial waste: All solid waste from businesses. This category includes, but is not limited to, solid waste originating in stores, markets, office buildings, restaurants, shopping centers, and theaters.

comminution: Mechanical shredding or pulverizing of waste. Used in both solid waste management and wastewater treatment.
community water system (CWS): A public water system which serves at least 15 service connections used by yearround residents or regularly serves at least 25 year-round residents. Also see non-community water system, transient water system and non-transient non-community water system.

compost: Decomposed organic material that is produced when bacteria in soil break down garbage and biodegradable trash, making organic fertilizer. Making compost requires turning and mixing and exposing the materials to air. Gardeners and farmers use compost for soil enrichment. The relatively stable humus material that is produced from a composting process in which bacteria in soil mixed with garbage and degradable trash break down the mixture into organic fertilizer.

compressed natural gas (CNG): An alternative fuel for motor vehicles; considered one of cleanest because of low hydrocarbon emissions and its vapors are relatively non-ozone producing. However, it does emit a significant quantity of nitrogen oxides.

condensation: The process by which a liquid is removed from a vapor. In the water cycle, water vapor rises, cools, and condenses, sometimes clinging to tiny particles of dust in the atmosphere. Condensed water vapor either remains a liquid or turns directly into a solid (ice, hail or snow). Clouds are formed by condensed water particles.

conductance: A rapid method of estimating the dissolvedsolids content of a water supply. The measurement indicates the capacity of a sample of water to carry an electrical current, which is related to the concentration of ionized substances in the water.

cone of depression: The area around a discharging well where the hydraulic head (potentiometric surface) in the aquifer has been lowered by pumping. In an unconfined aquifer, the cone of depression is a cone-shaped depression in the water table where the media has actually been dewatered.

confined aquifer: An aquifer in which ground water is confined under pressure which is significantly greater than atmospheric pressure. See artesian 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; cease or correct actions or processes that are polluting the environment; or otherwise comply with EPA initiated regulatory enforcement actions to resolve the contamination at the Superfund site involved. The consent decree describes the actions PRPs will take and may be subject to a public comment period.

conservation: Preserving and renewing natural resources to assure their highest economic or social benefit over the longest period of time. Clean rivers and lakes, wilderness areas, a diverse wildlife population, healthy soil, and clean air are natural resources worth conserving for future generations.

construction and demolition waste: Waste building materials, dredging materials, tree stumps, and rubble resulting from construction, remodeling, repair, and
demolition of homes, commercial buildings and other structures and pavements. May contain lead, asbestos, or other hazardous substances.

consumptive use: Water removed from available supplies without direct return to a water resource system for uses such as manufacturing, agriculture, and food preparation.

contact pesticide: A chemical that kills pests when it touches them, instead of by ingestion. Also, soil that contains the minute skeletons of certain algae that scratch and dehydrate waxy-coated insects.

contaminant: Any physical, chemical, biological, or radiological substance or matter that has an adverse affect on air, water, or soil.

continuous discharge: A permitted release of pollutants into the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc.

contour farming: A conservation-based method of farming in which all farming operations (for example, tillage and planting) are performed across (rather than up and down) the slope. Ideally, each crop row is planted at right angles to the ground slope.

contour strip farming: A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosionresistant forage crops.

conventional filtration: A method of treating water to remove particulates. The method consists of the addition of coagulant chemicals, flash mixing, coagulation flocculation, sedimentation and filtration.

conventional tillage: The traditional method of farming in which soil is prepared for planting by completely inverting it with a moldboard plow. Subsequent working of the soil with other implements is usually performed to smooth the soil surface. Bare soil is exposed to the weather for some varying length of time depending on soil and climatic conditions.

conveyance loss: Water lost in conveyance (pipe, channel, conduit, ditch) by leakage or evaporation.

core: The uranium-containing heart of a nuclear reactor, where energy is released.

cover crop: A crop that provides temporary protection for delicate seedlings and/or provides a canopy for seasonal soil protection and improvement between normal
crop production periods. Except in orchards where permanent vegetative cover is maintained, cover crops usually are grown for one year of less. When plowed under and incorporated into the soil, cover crops are also referred to as gren manure crops.

cradle-to-grave or manifest system: 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 (e.g., manifests). Commonly referred to as the cradle-to-grave system.

criteria pollutants: The 1970 amendments to the Clean Air Act required EPA to set National Ambient Air Quality Standards for certain pollutants known to be hazardous to human health. EPA has identified and set standards to protect human health and welfare for six pollutants: ozone, carbon monoxide, total suspended particulates, sulfur dioxide, lead, and nitrogen oxide. The term, "criteria pollutants" derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants. It is on the basis of these criteria that standards are set or revised.

crop rotation: A system of farming in which a regular succession of different crops are planted on the same land area, as opposed to growing the same crop time after time (monoculture).

cryptosporidium: A protozoan associated with the disease cryptosporidiosis in humans. The disease can be transmitted through ingestion of drinking water, person-to-person contact, or other exposure routes. Cryptosporidiosis may cause acute diarrhea, abdominal pain, vomiting, and fever that last 1-2 weeks in healthy adults, but may be chronic or fatal in immuno-compromised people.

cumulative exposure: The summation of exposures of an organism to a chemical over a period of time.

curie: A measure of radioactivity. One Curie of radioactivity is equivalent to 3.7 x 1010 or 37,000,000,000 nuclear disintegrations per second.

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D
DDT: The first chlorinated hydrocarboninsecticide chemical name: Dichloro-Diphenyl-Trichloroethane. It has a half-life of 15 years and 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 because of its persistence in the environment and accumulation in the food chain.

decant: To draw off the upper layer of liquid (water) after the heavier 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.

decomposition: The conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.

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: A process by which waste fluids are injected deep below the surface of the earth.

defoliant: An herbicide that removes leaves from trees and growing plants.

degasification: A water treatment process which removes dissolved gases from the water. The gases may be removed by either mechanical or chemical treatment methods or a combination of both.

degradation: Chemical or biological breakdown of a complex compound into simpler compounds.

denitrification: Bacterial reduction of nitrite to gaseous nitrogen under anaerobic conditions.

density: A measure of how heavy a solid, liquid, or gas is for its size. Density is expressed in terms of weight per unit volume, that is, grams per cubic centimeter or pounds per cubic foot. The density of water is 1.0 gram per cubic centimeter or about 62.4 pounds per cubic foot.

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.

desiccant: A chemical agent that absorbs moisture; some desiccants are capable of drying out plants or insects, causing death.

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.

destratification: The development of vertical mixing within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life. This vertical mixing can be caused by mechanical means (pumps) or through the use of forced air diffusers which release air into the lower layers of the reservoir.

detritus: Loose fragments, particles, or grains formed by the disintegration of rocks.

diatomaceous earth (diatomite): A chalk-like material (fossilized diatoms) used to filter out solid waste in wastewater treatment plants, also used as an active ingredient in some powdered pesticides.

diffusion: The movement of suspended or dissolved particles from a more concentrated to a less concentrated area. The process tends to distribute the particles more uniformly.

digestion: The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants.

dimictic: Lakes and reservoirs which freeze over and normally go through two stratification and two mixing cycles within a year.

dioxin: Any of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity and contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic man-made compounds.

direct runoff: Water that flows over the ground surface or through the ground directly into streams, rivers, or 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 discharge of liquid effluent from a facility or of chemical emissions into the air through designated venting mechanisms.

disinfectant: Any oxidant, including but not limited to chlorine, chlorine dioxide, chloramines, and ozone, that is added to water in any part of the treatment or distribution process and is intended to kill or inactivate pathogenic microorganisms.

dispersant: A chemical agent used to break up concentrations of organic material such as spilled oil.

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. Disposal may be accomplished through use of approved secure landfills, surface impoundments, land farming, deep-well injection, ocean dumping, or incineration.

dissolved oxygen: The oxygen freely available in water, vital to fish and other aquatic life and for the prevention of odors. DO levels are considered a most important indicator of a water body's ability to support desirable aquatic life. Secondary and advanced waste treatment are generally designed to ensure adequate DO in waste-receiving waters.

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 condenses to a pure liquid and the pollutants remain in a concentrated residue.

drainage: A technique to improve the productivity of some agricultural land by removing excess water from the soil; surface drainage is accomplished with open     ditches; subsurface drainage uses porous conduits (drain tile) buried beneath the soil surface.

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 toxics. Dredging activities may be subject to regulation under Section 404 of the Clean Water Act.

dump: A land site where wastes are discarded in a disorderly or haphazard fashion without regard to protecting the environment. Uncontrolled dumping is an indiscriminate and illegal form of waste disposal. Problems associated with dumps include multiplication of disease-carrying organisms and pests, fires, air and water pollution, unsightliness, loss of habitat, and personal injury.

dystrophic lakes: Acidic, shallow bodies of water that contain much humus and/or other organic matter; contain many plants but few fish.

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E
ecological impact: The effect that a man-made or natural activity has on living organisms and their non-living (abiotic) environment.

ecological indicator: A characteristic of the environment that, when measured, quantifies magnitude of stress, habitat characteristics, degree of exposure to a stressor, or ecological response to exposure. The term is a collective term for response, exposure. The term is a collective term for response, exposure, habitat, and stressor indicators.

ecological risk assessment: The application of a formal framework, 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. Such analysis includes initial hazard identification, exposure and doseresponse assessments, and risk characterization.

ecology: The study of the relationships between all living organisms and the environment, especially the totality or pattern of interactions; a view that includes all plant and animal species and their unique contributions to a particular habitat.

ecosystem: The interacting synergism of all living organisms in a particular environment; every plant, insect, aquatic animal, bird, or land species that forms a complex web of interdependency. An action taken at any level in the food chain, use of a pesticide for example, has a potential domino effect on every other occupant of that system.

effluent: Water or some other liquid-raw, partially or completely treated-flowing from a reservoir, basin, treatment process or treatment plant.

electrodialysis: A process that uses electrical current applied to permeable membranes to remove minerals from water. Often used to desalinize salty or brackish water.

electrolyte: A substance which dissociates (separates) into two or more ions when it is dissolved in water.

electrostatic precipitator (ESP): 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. Rapping on the plates causes the particles to fall into a hopper for disposal.

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 aircraft exhausts.

emission cap: A limit designed to prevent projected growth in emissions from existing and future stationary sources from eroding any mandated reduction. Generally, such provisions require any emission growth from facilities under the restrictions be offset by equivalent reductions at other facilities under the same cap.

emissions trading: The creation of surplus emission reductions at certain stacks, vents, or similar emissions sources and the use of this surplus to meet or redefine pollution requirements applicable to other emission sources. This allows one source to increase emissions when another sources reduces them, maintaining an overall constant emission level. Facilities that reduce emissions substantially may "bank" their "credits" or sell them to other industries.

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.

endangered species: Animals, birds, fish, plants, or other living organisms threatened with extinction by man-made or natural changes in their environment. Requirements for declaring a species endangered are contained in the Endangered Species Act.

endangerment assessment: A site-specific risk assessment of the actual or potential danger to human health or welfare and the environment from the release of hazardous substances or waste. The endangerment assessment document is prepared in support of enforcement actions under CERCLA or RCRA.

endemic: Something peculiar to a particular people or locality, such as a disease which is always present in the population.

Endrin: a pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies.

energy recovery: To capture energy from waste through any of a variety of processes (e.g., burning). Many new technology incinerators are waste-to-energy recovery units.

enrichment: The addition of nutrients (e.g., nitrogen, phosphorus, carbon compounds) from sewage effluent or agricultural runoff to surface water, greatly increases the growth potential for algae and other aquatic plants.

enteric: Of intestinal origin, especially applied to wastes or bacteria.

environment: The sum of all external conditions affecting the life, development and survival of an organism.

environmental assessment (EA): 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 (not conducted by EPA) of a facility's compliance policies, practices, and controls. Many pollution prevention initiatives require an audit to determine where wastes may be reduced or eliminated or energy conserved. Many supplemental environmental projects that offset a penalty use audits to identify ways to reduce the harmful effects of a violation.

environmental equity: Equal protection from environmental hazards for individuals, groups, or communities regardless of race, ethnicity, or economic status.

environmental exposure: Human exposure to pollutants originating 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 impact statement (EIS): A document prepared by or for EPA which identifies and analyzes, in detail, environmental impacts of a proposed action. As a tool for decision-making, the EIS describes positive and negative effects and lists alternatives for an undertaking, such as development of a wilderness area. (Required by NEPA : see Federal Law Section).

environmental technology: An all-inclusive term used to describe pollution control devices and systems, waste treatment processes and storage facilities, and site remediation technologies and their components that may be utilized to remove pollutants or contaminants from, or to prevent them from entering, the environment. Examples include wet scrubbers (air), soil washing (soil), granulated activated carbon unit (water), and filtration (air, water). Usually, this term applies to hardware-based systems; however, it can also apply to methods or techniques used for pollution prevention, pollutant reduction, or containment of contamination to prevent further movement of the contaminants, such as capping, solidification or vitrification, and biological treatment.

enzyme: (a) any of numerous proteins or conjugated proteins produced by living organisms and functioning as biochemical catalysts. (b) a protein that a living organism uses in the process of degrading a specific compound. The protein serves as a catalyst in the compound's biochemical transformation.

epidemic: Widespread outbreak of a disease, or a large number of cases of a disease in a single community or relatively small area. Disease may spread from person to person, and/or by the exposure of many persons to a single source, such as a water supply.

epidemiology: The study of the occurrence and causes of health effects in human populations. An epidemiological study often compares two groups of people who are alike except for one factor, such as exposure to a chemical or the presence of a health effect. The investigators try to determine if any factor is associated with thehealth effect.

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.

estuary: A complex ecosystem between a river and near-shore ocean waters where fresh and salt water mix. These brackish areas include bays, mouths of rivers, salt marshes, wetlands, and lagoons and are influenced by tides and currents. Estuaries provide valuable habitat for marine animals, birds, and other wildlife.

ethanol: An alternative automotive fuel derived from grain and corn; usually blended with gasoline to form gasohol.

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 nutritive compounds such as nitrogen and phosphorus. Human activities can accelerate the process.

evaporation: The process by which water or other liquid becomes a gas (water vapor or ammonia vapor). Water from land areas, bodies of water, and all other moist surfaces is absorbed into the atmosphere as a vapor.

evaporation ponds: Areas where sewage sludge is dumped and dried.

evapotranspiration: The combined processes of evaporation and transpiration. It can be defined as the sum of water used by vegetation and water lost by evaporation.

ex situ: Moved from its original place; excavated; removed or recovered from the subsurface.

exotic species: A species that is not indigenous to a region.

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.

exposure: Radiation or pollutants that come into contact with the body and present a potential health threat. The most common routes of exposure are through the skin, mouth, or by inhalation.

exposure assessment: The determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of
exposure to a chemical.

exposure level (chemical): The amount (concentration) of a chemical at the absorptive surfaces of an organism.

extremely hazardous substances (EHS): Any of 366 (+ or:) chemicals or hazardous substances identified by EPA on the basis of hazard or toxicity and listed under EPCRA. The list is periodically revised.

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F
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, a recommended plan, an environmental assessment of the recommendations, and descriptions of the treatment works, costs, and a completion schedule.

facultative: Used to describe organisms that are able to grow in either the presence or absence of a specific environmental factor (e.g., oxygen). See also facultative anaerobe.

feasibility study: 1. Analysis of the practicability of a proposal; e.g., a description and analysis of potential cleanup alternatives for a site such as one on the National Priorities List. The feasibility study usually recommends selection of a cost-effective alternative. It usually starts as soon as the remedial investigation is underway; together, they are commonly referred to as the "RI/FS". 2. A small-scale investigation of a problem to ascertain whether a proposed research approach is likely to provide useful data.

fecal coliform bacteria: Bacteria found in the intestinal tracts of animals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.

feedlot: A confined area for the controlled feeding of animals. Tends to concentrate large amounts of animal waste that cannot be absorbed by the soil and, hence, may be carried to nearby streams or lakes by rainfall runoff.

feedstock: Raw material supplied to a machine or processing plant from which other products can be made. For example, polyvinyl chloride and polyethylene are raw chemicals used to produce plastic tiles, mats, fenders, cushions, and traffic cones.

field capacity: The maximum amount of water that a soil can retain after excess water from saturated conditions has been drained by the force of gravity.

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 waste water.

filtration: A treatment process, under the control of qualified operators, for removing solid (particulate) matter from water by means of porous media such as sand or a man-made filter; often used to remove particles that containing pathogens.

finished water: Water that has passed through a water treatment plant; all the treatment processes are completed or "finished". This water is ready to be delivered to consumers. Also called product water.

first draw: The water that comes out when a faucet in the kitchen or bathroom is first opened, which is likely to have the highest level of lead contamination from old plumbing solder and pipes.

fish kill: When aquatic life within a river, lake, or stream dies in a mass extinction.

flare: A device that burns gaseous materials to prevent them from being released into the environment. Flares may operate continuously or intermittently and are usually found on top of a stack. Flares also burn off methane gas in a landfill.

flash point: The lowest temperature at which evaporation of a substance produces enough vapor to form an ignitable mixture with air.

flocculation: The gathering together of fine particles in water by gentle mixing after the addition of coagulant chemicals to form larger particles.

floodplain: Mostly level land along rivers and streams that may be submerged by floodwater. A 100-year floodplain is an area which can be expected to flood once in every 100 years.

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.

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.

flume: A natural or man-made channel that diverts water.

fluoridation: The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence (number) of dental caries (tooth decay) in children. Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.

fluorides: Gaseous, solid, or dissolved compounds containing fluorine that result from industrial processes. Excessive amounts in food can lead to fluorosis.

fluorocarbons (FCs): Any of a number of organic compounds analogous to hydrocarbons in which one or more hydrogen atoms are replaced by fluorine. Once used in the United States as a propellant for domestic aerosols, they are now found mainly in coolants and some industrial processes. FCs containing chlorine are called chlorofluorocarbons (CFCs). They are believed to be modifying the ozone layer in the stratosphere, thereby allowing more harmful solar radiation to reach the Earth's surface.

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 chain: A sequence of organisms, each of which uses the next, lower member of the sequence as a food source.

formaldehyde: A colorless, pungent, and irritating gas, CH20, used chiefly as a disinfectant and preservative and in synthesizing other compounds like resins.

fossil fuel: Fuel derived from ancient organic remains, e.g., peat, coal, crude oil, and natural gas.

fresh water: Water that generally contains less than 1,000 milligrams-per-liter of dissolved solids

friable: Capable of being crumbled, pulverized, 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 the energy released on combustion of a fuel that is converted into useful energy.

fugitive emissions: Air pollutants released to the air other than those from stacks or vents; typically small releases from leaks in plant equipment such as valves, pump seals, flanges, sampling connections, etc.

fume: Tiny particles trapped in vapor in a gas stream.

fumigant: A pesticide vaporized to kill pests. Used in buildings and greenhouses.

fungi: Aerobic, multicellular, nonphotosynthetic, heterotrophic microorganisms. The fungi include mushrooms, yeast, molds, and smuts. Most fungi are saprophytes, obtaining their nourishment from dead organic matter. Along with bacteria, fungi are the principal organisms responsible for the decomposition of carbon in the biosphere. Fungi have two ecological advantages over bacteria: (1) they can grow in low moisture areas, and (2) they can grow in low pH environments. gate valve: a valve regulated by the position of a circular plate.

fungicide: A pesticide used to control or destroy fungi on food or grain crops.

fungistat: A chemical that keeps fungi from growing.
furrow irrigation: Irrigation method in which water travels through the field by means of small channels between each row or groups of rows.

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G
galvanize: To coat a metal (especially iron or steel) with zinc. Galvanization is the process of coating a metal with zinc.

game fish: Species like trout, salmon, or bass, caught for sport. Many of them show more sensitivity to environmental change than "rough" fish.

garbage: Animal and vegetable waste resulting from the handling, storage, sale, preparation, cooking, and serving of foods.

gas chromatograph/mass spectrometer: Highly sophisticated instrument that identifies the molecular composition and concentrations of various chemicals in water and soil samples.

gasification: Conversion of solid material such as coal into a gas for use as a fuel.

gasohol: 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.

gastroenteritis: An inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is often associated with fever.

genetic engineering: A process of inserting new genetic information into existing cells in order to modify an organism for the purpose of changing particular characteristics.

geographic information system (GIS): A computer system designed for storing, manipulating, analyzing, and displaying data in a geographic context.

geological log: A detailed description of all underground features discovered during the drilling of a well (depth, thickness and type of formations).

germicide: A substance formulated to kill germs or microorganisms. The germicidal properties of chlorine make it an effective disinfectant.

giardia lamblia: Flagellate protozoan which is shed during its cyst stage into the feces of man and animals. When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.

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.

gram: A unit of mass equivalent to one milliliter of water at 4 degrees Celsius. 1/454 of a pound.

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.

gray water: Domestic wastewater composed of wash water from kitchen, bathroom, and laundry sinks, tubs, and washers.

greenhouse effect: The warming of Earth's atmosphere attributed to a build-up of carbon dioxide or other gases;some scientists think that this build-up allows the sun's rays to heat Earth, while infra-red radiation makes the atmosphere opaque to a counterbalancing loss of heat.

ground water: 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.
ground-water discharge: Ground water entering near coastal waters which has been contaminated by landfill leachate, deep well injection of hazardous wastes, septic tanks, etc.

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.

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H
habitat: The place where a population (e.g., human, animal, plant, microorganism) lives and its surroundings, both living and non-living.

half-life: 1. The time required for a pollutant to lose half its affect on the environment. For example, the biochemical half-life of DDT in the environment is 15 years of Radium. 1,580 years. 2. The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay. 3. The time required for the elimination of one half a total dose from the body.

halogen: One of the chemical elements chlorine, bromine, or iodine.

hard water: Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from lathering. Water may be considered hard if it has a hardness greater than the typical hardness of water from the region. Some textbooks define hard water as water with a hardness of more than 100 mgAL as calcium carbonate.

hazard evaluation: A component of risk assessment that involves gathering and evaluating data on the types of health injury or disease (e.g., cancer) that may be produced by a chemical and on the conditions of exposure under which injury or disease is produced.

hazardous air pollutants: Air pollutants which are not covered by ambient air quality standards but which, as defined in the Clean Air Act, may reasonably be expected to cause or contribute to irreversible illness or death. 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.

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 substancedesignated by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or if otherwise released into the environment.

hazardous waste: A subset of solid wastes that pose substantial or potential threats to public health or the environment and meet any of the following criteria: it is specifically listed as a hazardous waste by EPA; exhibits one or more of the characteristics of hazardous wastes (ignitability, corrosiveness, reactivity, and/or toxicity); o is generated by the treatment of hazardous waste; or is contained in a hazardous waste.

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 large margin of safety.

heat island effect: A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions.

heavy metal: 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.

herbaceous: Any of various types of non-woody plants with green stems. Herbaceous plants die down to ground level in the winter.

herbicide: A pesticide designed to control or kill plants, weeds, or grasses. Almost 70% of all pesticide used by farmers and ranchers are herbicides. These chemicals have wide-ranging effects on non-target species (other than those the pesticide is meant to control).

herbivore: An animal that feeds on plants.

heterotrophic microorganisms: Bacteria and other microorganisms that use organic matter synthesized by other organisms for energy and growth.

high-density polyethylene: A material used to make plastic bottles and other products that produces toxic fumes when burned.

high-level radioactive waste (HLW): 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.

histology: The study of the structure of cells and tissues; usually involves microscopic examination of tissue slices.

host: 1. In genetics, the organism, typically a bacterium, into which a gene from another organism is transplanted. 2. In medicine, an animal infected or parasitized by another organism.

hot spot: Localized elliptical areas with concentrations in excess of the cleanup standard, either a volume defined by the projection of the surface area through the soil zone that will be sampled or a discrete horizon within the soil zone that will be sampled.

household waste (domestic waste): Solid waste, composed of garbage and rubbish, which normally originated in a private home or apartment house. Domestic waste may contain a significant amount of toxic or hazardous waste.

humus: Organic portion of the soil remaining after prolonged microbial decomposition.

hydrocarbon: Chemicals that consist entirely of hydrogen and carbon. Hydrocarbons contribute to air pollution problems like smog.

hydrochlorination: The application of hypochlorite compounds to water for the purpose of disinfection.

hydrogen peroxide: Hydrogen peroxide is used to increase the dissolved oxygen content of groundwater to stimulate aerobic biodegradation of organic contaminants. Hydrogen peroxide is infinitely soluble in water, but rapidly dissociates to form a molecule of water [H(2)O] and one-half molecule of oxygen [O]. Dissolved oxygen concentrations of greater than 1,000 mg/L are possible using hydrogen peroxide, but high levels of D.O. can be toxic to microorganisms.
hydrogen sulfide: Gas emitted during organic decomposition. Also a byproduct of oil refining and burning. Smells like rotten eggs and, in heavy concentration, can kill or cause illness.

hydrogeology: The geology of ground water, with particular emphasis on the chemistry and movement of water.

hypoxic: A condition of low oxygen concentration, below that considered aerobic. in situ: in its original place; unmoved; unexcavated; remaining in the subsurface.

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I
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.

in situ: In place, the original location, in the natural environment.

in vitro: In glass; a laboratory experiment performed in a test tube or other vessel.

in vivo: With in a living organism; a laboratory experiment performed in which the substance under study is inserted into a living organism.

incineration: The destruction of solid, liquid, or gaseous wastes by controlled burning at high temperatures.Hazardous organic compounds are converted to ash, carbon dioxide, and water. Burning destroys organics, reduces the volume of waste, and vaporizes water and other liquids the wastes may contain. The residue ash produced may contain some hazardous material, such as non-combustible heavy metals, concentrated from the original waste.

incompatible waste: A waste unsuitable for mixing with another waste or material because it may react to form a hazard.

indigenous: Living or occurring naturally in a specific area or environment; native.

indirect discharge: Introduction of pollutants from a non-domestic source into a publicly owned waste-treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.

indoor air: Breathing air inside a habitable structure, often highly polluted because of lack of exchange with fresh oxygen from outdoors. Solvents, smoke, paints, furniture glues, carpet padding, and other synthetic chemicals trapped inside contribute to an often unhealthy environment.

indoor air pollution: Chemical, physical, or biological contaminants in indoor air.

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. Term includes equipment or technology modifications, substitution of raw materials, and improvements in housekeeping, maintenance, training or inventory control.

industrial waste: Unwanted materials produced in or eliminated from an industrial operation and categorized under a variety of headings, such as liquid wastes, sludge, solid wastes, and hazardous wastes.

inert ingredient: Substances that are not active, such as water, petroleum distillates, talc, corn meal, or soaps. When discussing pesticides, inert ingredients do not attack a particular pest, but some are chemically or biologically active, causing health and environmental problems.

infectious agent: Any organism, such as a virus or bacterium, that is pathogenic and capable of being communicated by invasion and multiplication in body tissues.

infectious waste: Hazardous waste with infectious characteristics, including: contaminated animal waste; human blood and blood products; isolation waste, pathological waste; and discarded sharps (needles, scalpels or broken medical instruments.)

infiltration gallery: A subsurface groundwater collection system, typically shallow in depth, constructed with openjointed or perforated pipes that discharge collected water into a water-tight chamber. From this chamber the water is pumped to treatment facilities and into the distribution system. Infiltration galleries are usually located close to streams or ponds and may be under the direct influence of surface water.

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.

influent: Water or other liquid-raw or partially flowing INTO a reservoir, basin, treatment process or treatment plant.

ingestion: Type of exposure through the mouth.

inhalation: Type of exposure through the lungs.

inorganic: Material such as sand, salt, iron, calcium salts and other mineral materials. Inorganic substances are of mineral origin, whereas organic substances are usually of animal or plant origin.

insecticide: A pesticide compound specifically used to kill or prevent the growth of insects.

integrated exposure assessment: A summation over time, in all media, of the magnitude of exposure to a toxic chemical.

integrated pest management (IPM): A combination of biological, cultural, and genetic pest control methods with use of pesticides as the last resort. IPM considers a targeted species' life cycle and intervenes in reproduction, growth, or development to reduce the population. Land use practices are examined for possible change; other animals, birds, or reptiles in the ecosystem are used as natural predators.

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. Also used in separate systems to collect the flows from main and trunk sewers and carry them to treatment points.

interstate carrier water supply: A source of water for drinking and sanitary use on planes, buses, trains, and ships operating in more than one state. These sources are federally regulated.

inversion: An atmospheric condition caused by increasing temperature with elevation, resulting in a layer of warm air preventing the rise of cooler air trapped beneath. This condition prevents the rise of pollutants that might otherwise be dispersed. Trapping pollutants near the ground increases ozone to harmful levels.
ion exchange treatment: A common water-softening method often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the ph to a level where the metals will precipitate out.

irradiated food: Food that has been briefly exposed to radioactivity (usually gamma rays) to kill insects, bacteria, and mold. Irradiated food can be stored without refrigeration or chemical preservatives and has a long "shelf life."

irreversible effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent.

irrigation: Applying water or wastewater to land areas to supply the water and nutrient needs of plants.

irritant: A substance that can cause irritation of the skin, eyes, or respiratory system. An irritant can cause an acute effect from a single high-level exposure, or chronic effects from repeated, low-level exposures. Some examples of irritants are chlorine, nitric acid, and various pesticides. 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.

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J/K
kinetic energy: Energy possessed by a moving body of matter, such as water, as a result of its motion.

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L
lagoon: A shallow, artificial treatment pond where sunlight, bacterial action, and oxygen work to purify wastewater; a stabilization pond. An aerated lagoon is a treatment pond that uses oxygen to speed up the natural process of biological decomposition of organic wastes. A lagoon is regulated as a point source under the Clean Water Act if there is a direct surface water discharge. Some lagoons that discharge into ground water also are regulated if they have a direct hydrogeologic connection to surface water. In other areas, lagoons were historically used to dump various liquid, solid, and hazardous wastes from manufacturing or industrial processes. These wastes typically flooded and polluted surrounding environs or seeped underground. Such lagoons are now regulated under RCRA but some must be cleaned up under Superfund.

landfill: A method for final disposal of solid waste on land. The refuse is spread and compacted and a cover of soil applied so that effects on the environment (including public health and safety) are minimized. Under current regulations, landfills are required to have liners and leachate treatment systems to prevent contamination of ground water and surface waters. An industrial landfill disposes of non-hazardous industrial wastes. A municipal landfill disposes of domestic waste including garbage, paper, etc. This waste may include toxins that are used in the home, such as insect sprays and powders, engine oil, paints, solvents, and weed killers.

large quantity generator: Person or facility which generates more than 2,200 pounds of hazardous waste per month. In 1989, only 1% of more than 20,000 generators fell into this category. Those generators produced nearly 97% of the nation's hazardous waste. These generators are subject to all requirements of RCRA.

latency: Time from the first exposure to a chemical until the appearance of a toxic effect.

laundering weir: Sedimentation basin overflow weir. A plate with V-notches along the top to assure a uniform flow rate and avoid short-circuiting.

leachate: A liquid that results from water collecting contaminants as it trickles through wastes, agricultural 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.

leaching: The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid.

lead (Pb): 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.

legionella: A genus of bacteria, some species of which have caused a type of pneumonia called Legionnaires Disease.

lesion: A pathological or traumatic discontinuity of tissue or loss of function of a part.

level of concern (LOC): 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

lifetime exposure: Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).

limestone scrubbing: Use of a limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere.

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.

liquefaction: Changing a solid into a liquid.

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. The strip of land along the shoreline between the high and low water levels.

local emergency planning committee (LEPC): A committee appointed by the State Emergency Response Commission (SERC), as required by EPCRA, which develops comprehensive emergency plans for Local Emergency Planning Districts, collects MSDS forms and chemical release reports, and provides this information to the public. Each county and some large city governments participate in an LEPC.

low-level radioactive waste (LLRW): Wastes less hazardous than most of those associated with 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 explosive limit (LEL): The concentration of a gas below which the concentration of vapors is insufficient to support an explosion. LELs for most organics are generally 1 to 5 percent by volume. magnehelic gauge: a sensitive differential pressure or vacuum gauge manufactured by Dwyer Instrument Co. that uses a precision diaphragm to measure pressure differences. This gauge is manufactured in specific pressure or vacuum ranges such as 0 to 2 inches of water column. Magnehelic gauges are typically used to measure SVE system vacuums.

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M
macroscopic organisms: Organisms big enough to be seen by the eye without the aid of a microscope.

malignant: Very dangerous or virulent, causing or likely to cause death.

manifest system: Tracking of hazardous waste from "cradle to grave" (generation through disposal) with accompanying documents known as manifests.

manufacturers 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.

margin of safety (MOS): 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 sanitation device: Any equipment or process installed on board a vessel to receive, retain, treat, or discharge sewage.

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.

material safety data sheet (MSDS): Printed material concerning a hazardous chemical, or Extremely Hazardous Substance, including its physical properties, hazards to personnel, fire and explosion potential, safe handling recommendations, health effects, fire fighting techniques, reactivity, and proper disposal. Originally established for employee safety by OSHA.

maximum contaminant level (MCL): The maximum permissible level of a contaminant in water which is delivered to the free flowing outlet of the ultimate user of a public water system, except in the case of turbidity where the maximum permissible level is measured at the point of entry to the distribution system. Contaminants added to the water under circumstances controlled by the user are excluded from this definition, except those contaminants resulting from the corrosion of piping and plumbing caused by water quality.

media: Specific environments -- air, water, soil -- which are the subject of regulatory concern and activities.

mercury: A heavy metal that can accumulate in the environment and is highly toxic if breathed or swallowed.

mesotrophic: Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.

metabolism: The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).

metabolites: Any substances produced by biological processes, such as those from pesticides.

metastatic: Pertaining to the transfer of disease from one organ or part to another not directly connected with it.

methane: A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds.

methanol: An alcohol that can be used as an alternative fuel or as a gasoline additive. It is less volatile than gasoline; when blended with gasoline it lowers the carbon monoxide emissions but increases hydrocarbon emissions. Used as pure fuel, its emissions are less ozone-forming that those from gasoline.

methoxychlor: Pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater and marine aquatic life.

microbial growth: The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton and fungi.

microcosm: A diminutive, representative system analogous to a larger system in composition, development, or configuration. As used in biodegradation treatability studies, microcosms are typically constructed in glass bottles or jars.

micrograms per liter (mg/L): One microgram of a substance dissolved in each liter of water: This unit is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.

micron: A unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.

microorganisms: Bacteria, yeasts, simple fungi, algae, protozoans, and a number of other organisms that are microscopic in size. Most are beneficial but some produce disease. Others are involved in composting and sewage treatment. Milligrams/liter (mg/l): A measure of concentration used in the measurement of fluids. Mg/l is the most common way to present a concentration in water and is roughly equivalent to parts per million.

mineralization: The release of inorganic chemicals from organic matter in the process of aerobic or anaerobic decay.

minimization: Measures or techniques that reduce the amount of wastes generated during industrial production processes; this term also is applied to recycling and other efforts to reduce the volume of waste going to landfills. This term is interchangeable with waste reduction and waste minimization.

miscible liquids: Two or more liquids that can be mixed and will remain mixed under normal conditions.
mist: Liquid particles measuring 40 to 500 microns, are formed by condensation of vapor. By comparison, fog particles are smaller than 40 microns.

mitigation: Measures taken to reduce adverse effects on the environment.

mobile source: Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, locomotives.

modeling: Use of mathematical equations to simulate and predict real events and processes.

molecular weight: The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. The molecular weight of sulfuric acid (H2SO4) in grams is 98.

molecule: The smallest division of a compound that still retains or exhibits all the properties of the substance.

monitoring wells: Wells used to collect ground-water samples for analysis to determine the amount, type, and spread of contaminants In ground water.

monomictic: Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year (usually in the fall).

morbidity: Rate of disease incidence.

motile: Capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.

mulch: Any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff.

multiple use: Use of land for more than one purpose; i.e., 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.

municipal discharge: Discharge of effluent from waste water treatment plants which receive waste water from households, commercial establishments, and industries in the coastal drainage basin. Combined sewer/separate storm overflows are included in this category.

municipal sewage: Wastes (mostly liquid) originating from a community; may be composed of domestic wastewaters and/or industrial wastewaters.

mutagen: An agent that causes a permanent genetic change in a cell other than that which occurs during normal genetic recombination.

mutagenicity: The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells.

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N
national ambient air quality standards (NAAQS): Standards established by EPA that apply for outside air throughout the country.

national emissions standards for hazardous air pollutants (NESHAP): Emission standards set by EPA for an air pollutant not covered by NAAQS that may cause an increase in deaths or serious, irreversible, or incapacitating illness. Primary standards are designed to protect human health, secondary standards to protect public welfare.

national pollutant discharge elimination system (NPDES): 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 priorities list (NPL): 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. EPA is required to update the NPL at least once a year. A site must be on the NPL to receive money from the Trust Fund for remedial action.

national response yeam (NRT): Representatives of 13 federal agencies that, as a team, coordinate federal responses to nationally significant incidents of pollution-an oil spill, a major chemical release, or a Superfund response action-and provide advice and technical assistance to the responding agency(ies) before and during a response action.

national strike force (NSF): Operated by the U.S. Coast Guard, the NSF is composed of three strategically located teams (Atlantic, Pacific, and Gulf coasts) who back up the federal On-Scene Coordinator. These teams are extensively trained and equipped to respond to major oil spills and chemical releases. These capabilities are especially suited to incidents in a marine environment but also include site assessment, safety, action plan development, and documentation for both inland and coastal zone incidents. The NSF Coordination Center is at Elizabeth City, NC.

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.

nematodes: Roundworms, any of which are pathogenic for plants and sometimes animals.

neoplasm: An abnormal growth or tissue, as a tumor.

netting: A concept in which all emissions sources in the same area that are owned or controlled by single company are treated as one large source, thereby allowing flexibility in controlling individual sources in order to meet a single emissions standard.

neurotoxicity: Exerting a destructive or poisonous effect on nerve tissue.

neutralization: Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.

nitrate: Plant nutrient and inorganic fertilizer that enters water supply sources from septic systems, animal feed lots, agricultural fertilizers, manure, industrial waste waters, sanitary landfills and garbage dumps.

nitric oxide: A gas formed by combustion under high temperature and high pressure in an internal combustion engine; changes into nitrogen dioxide in the ambient air and contributes to photochemical smog.

nitrification: The process whereby ammonia in wastewater is oxidized to nitrite and then to nitrate by bacterial or chemical reactions.

nitrogen dioxide: The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.

nitrogen fixation: The biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen.

nitrogen oxide: Product of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition.

nitrogenous: A term used to describe chemical compounds (usually organic) containing nitrogen in combined forms. Proteins and nitrates are nitrogenous compounds.

no till: Planting crops without prior seedbed preparation, into an existing cover crop, sod, or crop residues, and eliminating subsequent tillage operations.

noble metal: Chemically inactive metal (such as gold). A metal that does not corrode easily and is much scarcer (and more valuable) than the so-called useful or base metals. Also see base metal.

non-attainment area: Area that does not meet one or more of the National Ambient Air Quality Standards for the criteria pollutants designated in the Clean Air Act.

non-binding allocations of responsibility (NBAR): Process for EPA to propose a way for potentially responsible parties to allocate costs among themselves.

non-conventional pollutant: Any pollutant which is not a statutorily listed or which is poorly understood by the scientific community.

non-point source: Diffuse pollution sources (i.e., without a single point of origin or not introduced into a receiving stream from a specific outlet). The pollutants are generally carried off the land by storm water. Common nonpoint sources are agriculture, forestry, urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.

non-potable: Water that is unsafe or unpalatable to drink because in contains objectionable pollution, contamination, minerals, or infective agents.

nutrient pollution: Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern.

nutrient: Any substance assimilated by living things that promotes growth. The term is generally applied to nitrogen and phosphorus in wastewater, but is also applied to other essential and trace elements.

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O
obligate aerobes: Organisms that require the presence of molecular oxygen ([O(2)] for their metabolism.

obligate anaerobes: Organisms for which the presence of molecular oxygen is toxic. These organisms derive the oxygen needed for cell synthesis from chemical compounds.

off-site facility: A hazardous waste treatment, storage or disposal area that is located away from the generating site.

oil fingerprinting: A method that identifies sources of oil and allows spills to be traced to their source.

oil spill: An accidental or intentional discharge of oil which reaches bodies of water. Can be controlled by chemical dispersion, combustion, mechanical containment, and/or adsorption. Spills from tanks and pipelines can also occur away from water bodies, contaminating the soil, getting into sewer systems and threatening underground water sources.

olfactory fatigue: A condition in which a person's nose, after exposure to certain odors, is no longer able to detect the odor.

oligotrophic: Reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life.

on-site facility: A hazardous waste treatment, storage or disposal area that is located on the generating site.

oncology: Study of cancer.

opacity: The amount of light obscured by particulate pollution in the air; clear window glass has zero opacity, a brick wall is 100 percent opaque. Opacity is an indicator of changes in performance of particulate control systems.

organic chemicals/compounds: Animal or plant-produced substances containing mainly carbon, hydrogen, nitrogen, and oxygen.

organic matter: Carbonaceous waste contained in plant or animal matter and originating from domestic or industrial sources.

organically grown: Food, feed crops, and livestock grown within an intentionally-diversified, self-sustaining agro-ecosystem. In practice, farmers build up nutrients in the soil using compost, agricultural wastes, and cover crops instead of synthetically derived fertilizers to increase productivity, rotate crops, weed mechanically, and reduce dramatically their dependence on the entire family of pesticides. Farmers must be certified to characterize crops as organically grown and can only use approved natural and synthetic biochemicals, agents, and materials for three consecutive years prior to harvest. Live stock must be fed a diet that includes grains and forages that have been organically grown and cannot receive hormones, sub-therapeutic antibiotics, or other growth promoters.

organism: Any living being, whether plant, mammal, bird, insect, reptile, fish, crustacean, aquatic or estuarine animal, or bacterium.

organophosphates: Pesticides that contain phosphorus; short-lived, but some can be toxic when first applied.

OSHA: Occupational Safety and Health Administration, U.S. Department of Labor.

osmosis: The passage of a liquid from a weak solution to a more concentrate solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids. This process tends to equalize the conditions on either side of the membrane.

overdraft: The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin: This pumping results in a depletion or "mining" of the groundwater in the basin.

overfire air: Air forced into the top of an incinerator or boiler to fan the flames.

overturn: The almost spontaneous mixing of all layers of water in a reservoir or lake when the water temperature becomes similar from top to bottom. This may occur in the fall/winter when the surface waters cool to the same temperature as the bottom waters and also in the spring when the surface waters warms after the ice melts.

oxidant: A substance containing oxygen that reacts chemically in air to produce a new substance; the primary ingredient of photochemical smog.

oxidation: Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In the environment, organic matter is oxidized to more stable substances. The opposite of reduction

oxygenated fuels: Gasoline which has been blended with alcohols or ethers that contain oxygen in order to reduce carbon monoxide and other emissions.

ozonation: The application of ozone to water for disinfection or for taste and odor control.

ozone: Found in two layers of the atmosphere, the stratosphere and the troposphere. In the stratosphere (the atmospheric layer 7 to 10 miles or more above the earth's surface) ozone is a natural form of oxygen that provides a protective layer shielding the earth from ultraviolet radiation.In the troposphere (the layer extending up 7 to 10 miles from the earth's surface), ozone is a chemical oxidant and major component of photochemical smog. It can seriously impair the respiratory system and is one of the most widespread of all the criteria pollutants for which the Clean Air Act required EPA to set standards. Ozone in the troposphere is produced through complex chemical reactions of nitrogen oxides, which are among the primary pollutants emitted by combustion sources; hydrocarbons, released into the atmosphere through the combustion, handling and processing of petroleum products; and sunlight.

ozone depletion: Destruction of the stratospheric ozone layer which shields the earth from ultraviolet radiation harmful to life. This destruction of ozone is caused by the breakdown of certain chlorine and/or-bromine containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules.

ozone hole: Thinning break in the stratospheric ozone layer. Designation of amount of such depletion as a "ozone hole" is made when detected amount of depletion exceeds fifty percent. seasonal ozone holes have been observed over both the Antarctic region and the Arctic region and part of canada and the extreme northeastern United States.

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 reaching the earth's surface.

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P
packed bed scrubber: An air pollution control device in which emissions pass through alkaline water to neutralize hydrogen chloride gas.

packed tower aeration: A method of treating water to remove volatile organic chemical (VOCs) contaminants. As water is mixed with air, VOCs move from water to air which then passes through carbon filters to trap the contaminants.

particulate: 1. Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog found in air or emissions. 2, Very small solid suspended in water. They vary in size, shape, density, and electrical charge, can be gathered together by coagulation and flocculation.

pathogen: Microorganisms that can cause disease in other organisms or in humans, animals and plants (e.g., bacteria, viruses, or parasites) found in sewage, in runoff from farms or rural areas populated with domestic and wild animals, and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illness.

pathology: The study of disease.

perched water: Zone of unpressurized water held above the water table by impermeable rock or sediment.

percolation: 1. The movement of water downward and radially through subsurface soil layers, continuing downward to groundwater. Can also involve upward movement of the water. 2. Slow seepage of water through a filter.

periphyton: Microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings and other structures.

permeability: A qualitative description of the relative ease with which rock, soil, or sediment will transmit a fluid (liquid or gas). Often used as a synonym for hydraulic conductivity or coefficient of permeability.

permissible dose: The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result.

persistent pesticides: Pesticides that do not break down chemically or break down very slowly and remain in the environment after a growing season.

pest: An insect, rodent, nematode, fungus, weed or other form of terrestrial or aquatic plant or animal life that is injurious to health or the environment.

pesticide: Substances intended to repel, kill, or control any species designated a "pest" including weeds, insects, rodents, fungi, bacteria, or other organisms. The family of pesticides includes herbicides, insecticides, rodenticides, fungicides, and bactericides.

petroleum derivatives: Chemicals formed when gasoline breaks down in contact with ground water.

pH: A measure of the acidity of a solution. pH is equal to the negative logarithm of the concentration of hydrogen ions in a solution. A pH of 7 is neutral. Values less than 7 are acidic, and values greater than 7 are basic.

pharmacokinetics: The dynamic behavior of chemicals inside biological systems; it includes the processes of uptake, distribution, metabolism, and excretion.

phenols: Organic compounds that are byproducts of petroleum refining, tanning, and textile, dye, and resin manufacturing. Low concentrations cause taste and odor problems in water; higher concentrations can kill aquatic life and humans.

phosphates: Certain chemical compounds containing phosphorus.

phosphorus: An essential chemical food element that can contribute to the eutrophication of lakes and otherwater bodies. Increased phosphorus levels result from discharge of phosphorus-containing materials into surface waters.

photochemical oxidants: Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons.

photosynthesis: A process in which organisms, with the aid of chlorophyll (green plant enzyme), convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants grow by this process.

phototrophs: Organisms that use light to generate energy (by photosynthesis) for cellular activity, growth, and reproduction.

phytoplankton: Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.

pico: A prefix used in the metric system and other scientific systems of measurement which means 10-12 or 0.000000000001

picocurie (pCi): A measure of radioactivity. One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second.

plankton: 1) Small, usually microscopic, plants (phytoplankton) and animals (zooplankton) in aquatic systems. 2) All of the smaller floating, suspended or self-propelled organisms in a body of water.

plastics: Non-metallic chemoreactive compounds molded into rigid or pliable construction materials, fabrics, etc.

plume: 1. A visible or measurable discharge of a contaminant from a given point of origin. Can be visible or thermal in water as it extends downstream from the pollution source, or visible in air as, for example, a plume of smoke. 2. The area of radiation leaking from a damaged reactor. 3. Area downwind within which a release could be dangerous for those exposed to leaking fumes.

plutonium: A radioactive metallic element chemically similar to uranium.

point source: A stationary location or fixed facility such as an industry or municipality that discharges pollutants into air or surface water through pipes, ditches, lagoons, wells, or stacks; a single identifiable source such as a ship or a mine.

pollutant: Generally, any substance introduced into the environment that adversely affects the usefulness of a resource.

pollution: Any substances in water, soil, or air that degrade the natural quality of the environment, offend the senses of sight, taste, or smell, or cause a health hazard. The usefulness of the natural resource is usually impaired by the presence of pollutants and contaminants.

polychlorinated biphenyls (PCBs): 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.

polymer: A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes.

polyvinyl chloride: A tough, environmentally indestructible plastic that releases hydrochloric acid when burned.

porosity: Degree to which soil, gravel, sediment or rock is permeated with pores or cavities through which water or air can move.

potable water: Raw or treated water that is considered safe to drink.

potentially responsible party (PRP): Any individual or company-including owners, operators, transporters or generators-potentially responsible for, or contributing to a spill or other contamination at a Superfund site. Whenever possible, through administrative and legal actions, GPA requires PRPs to clean up hazardous sites they have contaminated.

precipitation: 1) The process by which atmospheric moisture falls onto a land or water surface as rain, snow, hail, or other forms of moisture. 2) The chemical transformation of a substance in solution into an insoluble form (precipitate).

predation: The act or practice of capturing another creature (prey) as a means for securing food.

prescriptive: Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures. These procedures include filing a request to use unused water in a strewn, river or lake with a state agency.

pretreatment: Methods used by industry and other non-household sources of wastewater to remove, reduce, or alter the pollutants in wastewater before discharge to a POTW.

prevalence study: An epidemiological study which examines the relationships between diseases and exposures as they exist in a defined population at a particular point in time.

prevention of significant deterioration (PSD): EPA program in which state and/or federal permits are required in order to restrict emissions from new or modified sources in places where air quality already meets or exceeds primary and secondary ambient air quality standards.

primary waste treatment: First steps in wastewater treatment; screens and sedimentation tanks are used to remove most materials that float or will settle. Primary treatment removes about 30 percent of carbonaceous biochemical oxygen demand from domestic sewage.

procaryotes: A cellular organism in which the nucleus has no limiting membrane.

propellant: Liquid in a self-pressurized pesticide product that expels the active ingredient from its container.

proteins: Complex nitrogenous organic compounds of high molecular weight made of amino acids; essential for growth and repair of animal tissue. Many, but not all, proteins are enzymes.

protoplast: A membrane-bound cell from which the outer wall has been partially or completely removed. The term often is applied to plant cells.

protozoa: Single-celled, eucaryotic microorganisms without cell walls. Most protozoa are free-living although many are parasitic. The majority of protozoa are aerobic or facultatively anaerobic heterotrophs.

public water system: A system for the provision to the public of piped water for human consumption, If such system has at least fifteen service connections or regularly least 60 days out of the year. Such term includes: 1) any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system, and 2) any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system. A public water system is either a "community water system" or a "non-community water system.'

putrefaction: Biological decomposition of organic matter, with the production of ill smelling and tasting products, associated with anaerobic (no oxygen present) conditions

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Q
quality control (QC): The overall system of technical activities that measures the attributes and performance of a process, item, or service against defined standards to verify that they meet the stated requirements established by the customer; operational techniques and activities that are used to fulfill requirements for quality. The system of activities and checks used to ensure that measurement systems are maintained within prescribed limits, providing protection against "out of control" conditions and ensuring the results are of acceptable quality.

quench tank: A water-filled tank used to cool incinerator residue or hot materials from industrial processes.

quicklime: A material that is mostly calcium oxide (CaO) or calcium oxide in natural association with a lesser amount of magnesium oxide. Quicklime is capable of combining with water to form hydrated lime.

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R
radiation: Transmission of energy through space or any medium. Also known as radiant energy.

radical: A group of atoms that is capable of remaining unchanged during a series of chemical reactions. Such combinations (radicals) exist in the molecules of many organic compounds; sulfate (SO42-) is an inorganic radical.

radioactive decay: Spontaneous change in an atom by emission of charged particles and/or gamma rays; also known as radioactive disintegration and radioactivity.

radioactive waste: Any waste that emits energy as rays, waves, or streams of energetic particles. Radioactive materials are often mixed with hazardous waste, usually from nuclear reactors, research institutions, or hospitals.

radioisotopes: Chemical variants of an element with potentially oncogenic, teratogenic, and mutagenic effects on the human body.

radionuclide: Any man-made or natural element which emits radiation in the form of alpha or beta particles, or as gamma rays.

radius of vulnerability zone: The maximum distance from the point of release of a hazardous substance in which the airborne concentration could reach the level of concern under specified weather conditions.

radon: A colorless, naturally occurring gas formed by radioactive decay of radium atoms. Radon accumulating in basements and other areas of buildings without proper ventilation has been identified as a leading cause of lung cancer.

radon daughters/radon progeny: Short-lived radioactive decay products of radon that decay into longer-lived lead isotopes, The daughter isotopes can attach themselves to airborne dust and other particles and, if inhaled, damage to lining of the lung. Also known as radon decay products.

ranney collector: This water collector is constructed as a dug well from 12 to 16 feet (3.5 to 5 m) in diameter that has been sunk as a caisson near the bank of a river or lake. Screens are driven radially and approximately horizontally from this well into the sand and the gravel deposits underlying the river.

raw sewage: Untreated wastewater and its contents.

raw water: 1) Water in its natural state, prior to any treatment. 2) Usually the water entering the first treatment process of a water treatment plant.

reactivity: Refers to those hazardous wastes that are normally unstable and readily undergo violent chemical change but do not explode.

reaeration: Introduction of air into the lower layers of a reservoir. As the air bubbles form and rise through the water, the oxygen from the air dissolves into the water and replenishes the dissolved oxygen. The rising bubbles also cause the lower waters to rise to the surface where they take on oxygen from the atmosphere.

reagent: A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect, or examine other substances.

recarbonation: A process in which carbon dioxide is bubbled into the water being treated to lower the pH. The pH may also be lowered by the addition of acid. Recarbonation is the final stage in the lime-soda ash softening process. This process converts carbonate ions to bicarbonate ions and stabilizes the solution against
the precipitation of carbonate compounds.

receiving waters: All distinct bodies of water that receive runoff or wastewater discharges, such as streams, rivers, ponds, lakes, and estuaries.

receptor: 1) In biochemistry: a specialized molecule in a cell that binds a specific chemical with high specificity and high affinity. 2) In exposure assessment: an organism that receives, may receive, or has received environmental exposure to a chemical.

recharge: The process by which water is added to a zone of saturation, usually by percolation from the soil surface, e.g., the recharge of an aquifer.

reclamation: (In recycling) Restoration of materials found in the waste stream to a beneficial use which may be for purposes other than the original use.

recombinant bacteria: A microorganism whose genetic makeup has been altered by deliberate introduction of new genetic elements. The offspring of these altered bacteria also contain these new genetic elements, i.e. they "breed true."

recombinant DNA: The new DNA that is formed by combining pieces of DNA from different organisms or cells.

recycling: Reusing materials and objects in original or changed forms rather than discarding them as wastes.

red tide: A proliferation of a marine plankton toxic and often fatal to fish, perhaps stimulated by the addition of nutrients. A tide can be red, green, or brown, depending on the coloration of the plankton.

reduction: Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H2S and other compounds. The opposite of oxidation.

reformulated gasoline: Gasoline with a different composition from conventional gasoline (e.g., lower aromatics content) that cuts air pollutants.

regeneration: Manipulation of cells to cause them to develop into whole plants.

release: Any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment of a hazardous or toxic chemical or extremely hazardous substance.

rem: The unit of dose equivalent from ionizing radiation to the total body or any internal organ or organ system. A millirem (mrem)" is 1/1000 of a rem.

remediation: 1. Cleanup or other methods used to remove or contain a toxic spill or hazardous materials from a Superfund site; 2. for the Asbestos Hazard Emergency Response program, abatement methods including evaluation, repair, enclosure, encapsulation, or removal of greater than 3 linear feet or square feet of asbestos-containing materials from a building.

remote sensing: The capture of information about the Earth from a distant vantage point. The term is often associated with satellite imagery but also applies to aerial photography, airborne digital sensors, ground-based detectors, and other devices.

reservoir: Any natural or artificial holding area used to store; regulate, or control water.

residual: Amount of a pollutant remaining in the environment after a natural or technological process has taken place, e.g., the sludge remaining after initial wastewater treatment, or particulates remaining in air after it passes through a scrubbing or other process.

residual risk: The extent of health risk from air pollutants remaining after application of the Maximum Achievable Control Technology (MACT).

residue: The dry solids remaining after the evaporation of a sample of water or sludge. Also see total dissolved solids

resistance: For plants and animals, the ability to withstand poor environmental conditions or attacks by chemicals or disease. May be inborn or acquired.

resource recovery: The extraction of useful materials or energy from solid waste. Such materials can include paper, glass, and metals that can be reprocessed for re-use. Resource recovery also is employed in pollution prevention.

respiration: The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.

restoration: Measures taken to return a site to pre-violation conditions.

retardation: Preferential retention of contaminant movement in the subsurface resulting from adsorptive processes or solubility differences. saturated zone: the zone in which all the voids in the rock or soil are filled with water at greater than atmospheric pressure. The water table is the top of the saturated zone in an unconfined aquifer.

retrofit: Addition of a pollution control device on an existing facility without making major changes to the generating plant.

reuse: Using a product or component of municipal solid waste in its original form more than once, e.g., refilling a glass bottle that has been returned or using a coffee can to hold nuts and bolts.

reversible effect: An effect which is not permanent, especially adverse effects which diminish when exposure to a toxic chemical is ceased.

ribonucleic acid (RNA): A molecule that carries the genetic message from DNA to a cellular protein-producing mechanisms.

riffle: A rocky shoal or sandbar lying just below the surface of a waterway. The choppy water created by such sand bars and shoals is also referred to as a riffle.

rill: A small channel eroded into the soil surface by runoff, rills easily can be smoothed out (obliterated) by normal tillage.

riparian rights: A doctrine of state water law under which a land owner is entitled to use the water on or bordering his property, including the right to prevent diversion or misuse of upstream waters. Riparian land is land that borders on surface water.

risk: A measure of the probability that damage to life, health, property, and/or the environment will occur as a result of a given hazard.

risk assessment: A qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or physical agent (pollutant); combines exposure assessment results with toxicity assessment results to estimate risk.

risk factor: A characteristic (e.g., race, sex, age, obesity) or variable (e.g., smoking, exposure) associated with increased chance of toxic effects. Some standard risk factors used in general risk assessment calculations include average breathing rates, average weight, and average human life span.

risk management: Decisions about whether an assessed risk is sufficiently high to present a public health concern and about the appropriate means for control of a risk judged to be significant. The process of evaluating and selecting alternative regulatory and non-regulatory responses to risk. The selection process necessarily requires the consideration of legal, economic, and behavioral factors.

river basin: The land area drained by a river and its tributaries.

rodenticide: A chemical or agent used to destroy rats or other rodent pests, or to prevent them from damaging food, crops, etc.

rotary kiln incinerator: An incinerator with a rotating combustion chamber that keeps waste moving, thereby allowing it to vaporize for easier burning.

rough fish: Fish not prized for eating, such as gar and suckers. Most are more tolerant of changing environmental conditions than game species.

route of exposure: The avenue by which a chemical comes into contact with an organism (e.g., inhalation, ingestion, dermal contact, injection).

run-off: That part of precipitation, snow melt, or irrigation water that runs off the land into streams or other surface water. It can carry pollutants from the air and land into the receiving waters.

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S
safe: Condition of exposure under which there is a "practical certainty" that no harm will result in exposed individuals.

safe water: Water that does not contain harmful bacteria, or toxic materials or chemicals. Water may have taste and odor problems, color and certain mineral problems and still be considered safe for drinking.

safe yield: The annual amount of water that can be taken from a source or supply over a period of years without depleting that source beyond its ability to be replenished naturally in "wet years".

salinity: 1)The relative concentration of dissolved salts, usually sodium chloride, in a given water.. 2) A measure of the concentration of dissolved mineral substances in water.

salt water intrusion: The invasion of fresh surface or ground water by salt water. If it comes from the ocean it may be called sea water intrusion.

salts: Minerals that water picks up as it passes through the air, over and under the ground, or from households and industry.

salvage: The utilization of waste materials.

sanctions: Actions taken by the federal government for failure to plan or implement a State Improvement Plan (SIP). Such action may be include withholding of highway funds and a ban on construction of new sources of potential pollution.

sand filters: Devices that remove some suspended solids from sewage. Air and bacteria decompose additional wastes filtering through the sand so that cleaner water drains from the bed.

sanitary sewer: A sewer that transports only wastewaters (from domestic residences and/or industries) to a wastewater treatment plant.

sanitary water: Water discharged from restrooms, showers, food preparation facilities, or other nonindustrial operations; also known as "gray water."

saprophytes: Organisms living on dead or decaying organic matter that help natural decomposition of organic matter in water.

saturated zone: The area below the water table where all open spaces are filled with water.

scrap: Materials discarded from manufacturing operations that may be suitable for reprocessing.

scrubber: An air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions.

secondary treatment: The second step in most publicly owned waste treatment systems in which bacteria consume the organic parts of the waste. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.

sedges: Plants of the family Cyperacae that resemble grasses, but have solid stems

sediment: Topsoil, sand, and minerals washed from the land into water, usually after rain or snow melt. Sediments collecting in rivers, reservoirs, and harbors can destroy fish and wildlife habitat and cloud the water so that sunlight cannot reach aquatic plants. Loss of topsoil from farming, mining, or building activities can be prevented through a variety of erosion-control techniques.

seepage: Percolation of water through the soil from unlined canals, ditches, laterals, watercourses, or water storage facilities.

sentinel well: A groundwater monitoring well situated between a sensitive receptor downgradient and the source of a contaminant plume upgradient. Contamination should be first detected in the sentinel well which serves as a warning that contamination may be moving closer to the receptor. The sentinel well should be located far enough upgradient of the receptor to allow enough time before the contamination arrives at the receptor to initiate other measures to prevent contamination from reaching the receptor, or in the case of a supply well, provide for an alternative water source.

septic system: An onsite system designed to treat and dispose of domestic sewage. A typical septic system consists of a tank that receives waste from a residence or business and a system of tile lines or a pit for disposal of the liquid effluent (sludge) that remains after decomposition of the solids by bacteria in the tank and must be pumped out periodically.

sequestration: The inhibition or stoppage of normal ion behavior by combination with added materials, especially the prevention of metallic ion precipitation from solution by formation of a coordination complex with a phosphate.

settling tank: A holding area for wastewater, where heavier particles sink to the bottom for removal and disposal.

sewage: The used water and solids that flow from homes through sewers to a wastewater treatment plant. The preferred term is wastewater.

sewer: An underground system of conduits (pipes and/or tunnels) that collect and transport wastewaters and/or runoff; gravity sewers carry free-flowing water and wastes; pressurized sewers carry pumped wastewaters under pressure.

shock load: The arrival at a water treatment plant of raw water containing unusual amounts of algae, colloidal mater, color, suspended solids, turbidity, ore other pollutants.

short circuiting: The entry of ambient air into an extraction well (used for SVE and bioventing) without first passing through the contaminated zone. Short circuiting may occur through utility trenches, incoherent well or surface seals, or layers of high permeability geologic materials. Also when some of the water in tanks or basins flows faster than the rest; usually undesirable since it may result in shorter contact, reaction, or settling times in comparison with the calculated or presumed detention times.

silt: Sedimentary materials composed of fine or intermediate sized mineral particles.

silviculture: Management of forest land for timber.

sink: A place in the environment where a compound or material collects. See reservoir.

sinking: Controlling oil spills by using an agent to trap the oil and sink it to the bottom of the body of water where the agent and the oil are biodegraded.

skimming: Using a machine to remove oil or scum from the surface of the water.

slake: To mix with water with a true chemical combination (hydrolysis) taking place, such as in the slaking of lime.

slow sand filtration: A process involving passage of raw water through a bed of sand at low velocity (generally less than 0.4 m/h) resulting in substantial particulate removal by physical and biological mechanisms.

sludge: A semi-solid residue from any of a number of air or water treatment processes; can be a hazardous waste.

slurry: A watery mixture or suspension of insoluble (not dissolved) matter; a thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).

smelter: A facility that melts or fuses ore, often with an accompanying chemical change, to separate its metal content. Emissions cause pollution. "Smelting" is the process involved.

smog: Dust, smoke, or chemical fumes that pollute the air and make hazy, unhealthy conditions (literally, the word is a blend of smoke and fog). Automobile, truck, bus, and other vehicle exhausts and particulates are usually trapped close to the ground, obscuring visibility and contributing to a number of respiratory problems.
soft water: Water having a low concentration of calcium and magnesium ions. According to U.S. Geological Survey guidelines, soft water is water having a hardness of 60 milligrams per liter or less.

soil adsorption field: A sub-surface area containing a trench or bed with clean stones and a system of piping through which treated sewage may seep into the surrounding soil for further treatment and disposal.

soil erodibility: A measure of the soil's susceptibility to raindrop impact, runoff and other erosional processes.

soil profile: A vertical section of the earth's highly weathered upper surface often showing several distinct layers, or horizons.

sole source aquifer: An aquifer that supplies 50 percent or more of the drinking water of an area.

solid waste: As defined under RCRA, any solid, semi-solid, liquid, or contained gaseous materials discarded from industrial, commercial, mining, or agricultural operations, and from community activities. Solid waste includes garbage, construction debris, commercial refuse, sludge from water supply or waste treatment plants, or air pollution control facilities, and other discarded materials. Solid Waste Management Facility: Any disposal or resource recovery system; any system, program, or facility for resource conservation; any facility for the treatment of solid wastes.

solidification and stabilization: Removal of wastewater from a waste or changing it chemically to make it less permeable and susceptible to transport by water.

solution: A liquid mixture of dissolved substances. In a solution it is impossible to see all the separate parts.

soot: Carbon dust formed by incomplete combustion.

source reduction: The design, manufacture, purchase, or use of materials (such as products and packaging) to reduce the amount or toxicity of garbage generated.
Source reduction can help reduce waste disposal and handling charges because the costs of recycling, municipal composting, landfilling, and combustion are avoided. Source reduction conserves resources and reduces pollution.

sparge: Injection of air below the water table to strip dissolved volatile organic compounds and/or oxygenate the groundwater to facilitate aerobic biodegradation of organic compounds.

species: A reproductively isolated aggregate of interbreeding organisms.

sphagnum: Any of various pale or ashy mosses of the genus Sphagnum, the decomposed remains of which form peat.

spore: The reproductive body of an organism which is capable of giving rise to a new organism either directly or indirectly. A viable (able to live and grow) body regarded as the resting stage of an organism. A spore is usually more resistant to disinfectants and heat than most organisms.

sprawl: Unplanned development of open land.

spray tower scrubber: A device that sprays alkaline water into a chamber where acid gases present to aid in the neutralizing of the gas.

stabilization: Conversion of the active organic matter in sludge into inert, harmless material.

STEL: Short Term Exposure Limit (ACGIH terminology). See Threshold Value

stable air: A motionless mass of air that holds instead of dispersing pollutants.

stack effect: Air, as in a chimney, that moves upward because it is warmer than the ambient atmosphere.

stagnation: Lack of motion in a mass of air or water that holds pollutants in place.

state emergency response commission (SERC): The agency appointed by the Governor to oversee the administration of EPCRA at the state level. This commission designates and appoints members to LEPCs and reviews emergency response plans for cities and counties.

state implementation plans (SIP): EPAapproved state plans for the establishment, regulation, and enforcement of air pollution standards.

stationary source: A fixed-site producer of pollution, mainly power plants and other facilities using industrial combustion processes.

sterilisation: The removal or destruction of all microorganisms, including pathogenic and other bacteria, vegetative forms and spores. Compare with disinfection.

storm sewer: A sewer that collects and transports surface runoff to a discharge point (infiltration basin, receiving stream, treatment plant).

stratification: The formation of separate layers (of temperature, plant, or animal life) in a lake or reservoir. Each layer has similar characteristics such as all water in the layer has the same temperature.

stratosphere: The portion of the atmosphere 10-to-25 miles above the earth's surface.

stratum: A horizontal layer of geologic material of similar composition, especially one of several parallel layers arranged one on top of another.

streambed: The channel through which a natural stream or river runs or once ran through.
strip cropping: A crop production system that involves planting alternating strips of row crops and close-growing forage crops; the forage strips intercept and slow runoff from the less protected row crop strips.

strip mining: A process that uses machines to scrape soil or rock away from mineral deposits just under Earth’s surface.
submerged aquatic vegetation (SAV): Aquatic vegetation, such as sea grasses, that cannot withstand excessive drying and therefore live with their leaves at or below the water surface. SAVs provide an important habitat for young fish and other aquatic organisms.

sulfur dioxide: A pungent, colorless, gaseous pollutant formed primarily by the combustion of fossil fuels.

supercritical water: A type of thermal treatment using moderate temperatures and high pressures to enhance the ability of water to break down large organic molecules into smaller, less toxic ones. Oxygen injected during this process combines with simple organic compounds to form carbon dioxide and water.

superfund: The program operated under the legislative authority of CERCLA and SARA that funds and carries out EPA solid waste emergency and long-term removal and remedial activities. These activities include establishing the National Priorities List, investigating sites for inclusion on the list, determining their priority, and conducting and/or supervising the cleanup and other remedial actions.

supernatant: Liquid removed from settled sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the water surface of a basin or container.

supersaturated: An unstable condition of a solution (water) in which the solution contains a substance at a concentration greater than the saturation concentration for the substance.

surface impoundment: Treatment, storage, or disposal of liquid hazardous wastes in ponds.

surface runoff: Precipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored in small surface depressions; runoff is a major transporter of non-point source pollutants.

surface water: All water naturally open to the atmosphere (rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors directly influenced by surface water.

suspended solids: I)Solids that either float on the surface or are suspended in water or other liquids, and which are largely removable by laboratory filtering. 2) The quantity of material removed from water in a laboratory test.

sustainable agriculture: Environmentally friendly methods of farming that allow the production of crops or livestock without damage to the farm as an ecosystem, including effects on soil, water supplies, biodiversity, or other surrounding natural resources. The concept of sustainable agriculture is an "intergenerational" one in which we pass on a conserved or improved natural resource base instead of one which has been depleted or polluted. Terms often associated with farms or ranches that are self-sustaining include "low-input," organic, "ecological," "biodynamic," and "permaculture."

swamp: A type of wetland dominated by woody vegetation but without appreciable peat deposits. Swamps may be fresh or salt water and tidal or non-tidal. (See 'wetlands')

symbiosis: The relationship of two or more different organisms in a close association that may be but is not necessarily of benefit to each.

synergism: The cooperative action of two or more organisms producing a greater total result than the sum of their independent effects; chemicals or muscles in synergy enhance the effectiveness of one another beyond what an individual could have produced.

systemic effects: Effects observed at sites distant from the entry point of a chemical due to its absorption and distribution into the body.

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T
tail water: The runoff of irrigation water from the lower end of an irrigated field.

tailings: Residue of raw material or waste separated out during the processing of crops or mineral ores.

tailpipe standards: Emissions limitations applicable to engine exhausts from mobile sources.

teratogenesis: The induction of nonhereditary congenital malformations (birth defects) in a developing fetus by exogenous factors acting in the womb; interference with normal embryonic development.

terrace: A broad channel, bench, or embankment constructed across the slope to intercept runoff and detain or channel it to protected outlets, thereby reducing erosion from agricultural areas.

tertiary treatment: An enhancement of normal sewage treatment operations to provide water of potable quality using further chemical and physical treatment; the highest drinking water standard achieved in the U.S.

thermal stratification: The formation of layers of different temperatures in a lake or reservoir.

thermocline: The middle layer in a thermally stratified lake or reservoir. In this layer there is a rapid decrease in temperature with depth. Also called the METALIMNION.

threshold: The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.

threshold level: Time-weighted average pollutant concentration values, exposure beyond which is likely to adversely affect human health. (See 'environmental exposure')

tidal marsh: Low, flat marshlands traversed by channels and tidal hollows, subject to tidal inundation; normally, the only vegetation present is salttolerant bushes and grasses.

tillage: Plowing, seedbed preparation, and cultivation practices.

time-weighted average (TWA): In air sampling, the average air concentration of contaminants during a given period.

tolerance: Permissible residue level for pesticides in raw agricultural produce and processed foods. Whenever a pesticide is registered for use on a food or feed crop, a tolerance must be established. EPA establishes the tolerance levels, which are enforced by the Food and Drug Administration and the Department of Agriculture.

tonnage: The amount of waste that a landfill accepts, usually expressed as tons per month. The rate at which a landfill accepts waste is limited by the landfill's permit.

toxaphene: A chemical that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.

toxic chemical: Substances that can cause severe illness, poisoning, birth defects, disease, or death when ingested, inhaled, or absorbed by living organisms.

toxic cloud: Airborne plume of gases, vapors, fumes, or aerosols containing toxic materials.

toxic pollutants: Materials contaminating the environment that cause death, disease. birth defects in organisms that ingest or absorb them. The quantities and length of exposure necessary to cause these effects can vary widely.

toxic release inventory (TRI): A database of annual toxic releases from certain manufacturers compiled from EPCRA Section 313 reports. Manufacturers must report annually to EPA and the states the amounts of almost 350 toxic chemicals and 22 chemical categories that they release directly to air, water, or land, inject underground, or transfer to off-site facilities. EPA compiles these reports and makes the information available to the public under the "Community Right-to-Know" portion of the law.

toxic substance: A chemical or mixture that can cause illness, death, disease, or birth defects. The quantities and exposures necessary to cause these effects can vary widely. Many toxic substances are pollutants and contaminants in the environment.

toxic waste: A waste that can produce injury if inhaled, swallowed, or absorbed through the skin.

transboundary pollutants: Air pollution that travels from one jurisdiction to another, often crossing state or international boundaries.

transient water system: A non-community water system that does not serve 25 of the same nonresident persons per day for more than six months per year. Also called a transient non-community water system (TNCWS).

transpiration: The process by which water vapor is lost to the atmosphere from living plants. The term can also be applied to the quantity of water thus dissipated.

treated wastewater: Wastewater that has been subjected to one or more physical, chemical, and biological processes to reduce its pollution of health hazard.

treatment plant: A structure built to treat wastewater before discharging it into the environment.

tributary: A stream or other body of water, surface or underground, which intermittently contributes its water in small quantities to another larger stream or body of water.

trichloroethane (TCE): A stable, low boiling-point colorless liquid, toxic if inhaled. Used as a solvent or metal decreasing agent, and in other industrial applications.

trickle irrigation: Method in which water drips to the soil from perforated tubes or emitters.

trickling filter: A coarse treatment system in which wastewater is trickled over a bed of stones or other material covered with bacteria that break down the organic waste and produce clean water.

trihalomethane (THM): One of a family of organic compounds named as derivative of methane. THMs are generally by-products of chlorination of drinking water that contains organic material.

troposphere: The layer of the atmosphere closest to the earth's surface.

tundra: A type of ecosystem dominated by lichens, mosses, grasses, and woody plants. Tundra is found at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and is usually saturated. (See 'wetlands')

turbidity: The cloudy appearance of water caused by the presence of suspended and colloidal matter. In the waterworks field, a turbidity measurement is used to indicate the clarity of water. Technically, turbidity is an optical property of the water based on the amount of light reflected by suspended particles. Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.

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U
ultraviolet rays: Radiation from the sun that can be useful or potentially harmful. UV rays from one part of the spectrum (UV-A) enhance plant life and are useful in some medical and dental procedures; UV rays from other parts of the spectrum (UV-B) can cause skin cancer or other tissue damage. The ozone layer in the atmosphere partly shields us from ultraviolet rays reaching the earth's surface.

underground storage tank (UST): A tank and any underground piping connected to the tank that has 10% or more of its volume (including pipe volume) beneath the surface of the ground. USTs are designed to hold gasoline, other petroleum products, and hazardous materials.

unsaturated: The characteristic of a carbon atom in a hydrocarbon molecule that shares a double bond with another carbon atom.

uranium mill-tailings waste piles: Licensed active mills with tailings piles and evaporation ponds created by acid or alkaline leaching processes.

urban runoff: Storm water from city streets and adjacent domestic or commercial properties that carries pollutants of various kinds into the sewer systems and receiving waters.

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V
vadose zone: The zone between land surface and the water table within which the moisture content is less than saturation (except in the capillary fringe) and pressure is less than atmospheric. Soil pore spaces also typically contain air or other gases. The capillary fringe is included in the vadose zone.

vapor: The gas given off by substances that are solids or liquids at ordinary atmospheric pressure and temperatures. Vapor Dispersion: The movement of vapor clouds or plumes in the air due to wind, gravity, spreading, and mixing.

vapor density: The amount of mass of a vapor per unit volume of the vapor.

vapor dispersion: The movement of vapor clouds in air due to wind, thermal action, gravity spreading, and mixing.

vapor plumes: Flue gases visible because they contain water droplets.

vector: 1. An organism, often an insect or rodent, that carries disease. 2. Plasmids, viruses, or bacteria used to transport genes into a host cell. A gene is placed in the vector; the vector then "infects" the bacterium.

vegetative controls: Non-point source pollution control practices that involve plants (vegetative cover) to reduce erosion and minimize the loss of pollutants.

vinyl chloride: A chemical compound, used in producing some plastics, that is believed to be oncogenic.

virgin materials: Resources extracted from nature in their raw form, such as timber or metal ore.

virus: The smallest form of microorganisms capable of causing disease. Especially, a virus of fecal origin that is infectious to humans by waterborne transmission.

viscosity: A measure of the internal friction of a fluid that provides resistance to shear within the fluid. The greater the forces of internal friction (i.e. the greater the viscosity), the less easily the fluid will flow.

volatile acids: Acids produced during digestion. Fatty acids which are soluble in water and can be steam-distilled at atmospheric pressure. Also called "organic acids." Volatile acids are commonly reported as equivalent to acetic acid.

volatile liquids: Liquids which easily vaporize or evaporate at room temperature.

volatile organic compound (VOC): Any organic compound which evaporates readily to the atmosphere. VOCs contribute significantly to photochemical smog production and certain health problems.

volatile solids: Those solids in water or other liquids that are lost on ignition of the dry solids at 550 degrees C.

vortex: A revolving mass of water which forms a whirlpool. This whirlpool is caused by water flowing out of a small opening in the bottom of a basin or reservoir. A funnelshaped opening is created downward from the water surface.

vulnerable zone: An area over which the airborne concentration of a chemical accidentally released could reach the level of concern.

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W
waste exchange: Arrangement in which companies exchange their wastes for the benefit of both parties.

waste load allocation: The maximum load of pollutants each discharger of waste is allowed to release into a particular waterway. Discharge limits are usually required for each specific water quality criterion being, or expected to be, violated. The portion of a stream's total assimilative capacity assigned to an individual discharge.

waste reduction: Using source reduction, recycling, or composting to prevent or reduce waste generation.

waste stream: The total flow of solid waste from homes, businesses, institutions, and manufacturing plants that are recycled, burned, or disposed of in landfills, or segments thereof such as the "residential waste stream" or the "recyclable waste stream."

waste water: Water carrying wastes from homes, businesses and industries that is a mixture of water and dissolved or suspended solids.

water budget: A summation of inputs, outputs, and net changes to a particular water resource system over a fixed period. (Also, water balance model).

water cycle: The process, also known as the hydrologic cycle, in which water travels in a sequence from the air through condensation to the earth as precipitation and back to the atmosphere by evaporation.

water quality criteria: Levels of water quality expected to render a body of water suitable for its designated use. Criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.

water quality standard (WQS): The combination of a designated use and the maximum concentration of a pollutant which will protect that use for any given body of water. For example, in a trout stream, the concentration of iron should not exceed 1 mg/l.

water solubility: The maximum concentration of a chemical compound which can result when it is dissolved in water. If a substance is water soluble, it can very readily disperse through the environment.

water storage pond: An impound for liquid wastes, so designated as to accomplish some degree of biochemical treatment of the wastes.

water table: The level of ground water. The upper surface of the zone of saturation of groundwater above an impermeable layer of soil or rock (through which water cannot move) as in an unconfined aquifer. This level can be very near the surface of the ground or far below it.

water vapor: Water diffused as a gas in the atmosphere.

watershed: The land area that drains into a stream. An area of land that contributes runoff to one specific delivery point; large watersheds may be composed of several smaller "subsheds", each of which contributes runoff to different locations that ultimately combine at a common delivery point.

weathering: The process during which a complex compound is reduced to its simpler component parts, transported via physical processes, or biodegraded over time.

weir (weer): 1) A wall or plate placed in an open channel and used to measure the flow of water. The depth of the flow over the weir can be used to calculate the flow rate, or a chart or conversion table may be used. 2) A wall or obstruction used to control flow (from settling tanks and clarifiers) to assure uniform flow rate and avoid short-circuiting.

well: A bored, drilled, or driven shaft, or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground.

wellhead: The area immediately surrounding the top of a well, or the top of the well casing.

wetlands: Any number of tidal and nontidal areas characterized by saturated or nearly saturated soils most of the year that form an interface between terrestrial (land-based) and aquatic environments; include freshwater marshes around ponds and channels (rivers and streams), brackish and salt marshes; other common names include swamps and bogs.

wildlife refuge: An area designated for the protection of wild animals, within which hunting and fishing are either prohibited or strictly controlled.

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X
xenobiote: Any biotum displaced from its normal habitat; a chemical foreign to a biological system.

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Y
yield: The quantity of water (expressed as a rate of flow GPM, GPH, GPD, or total quantity per year) that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations.

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Z
zone of saturation: The soil or rock located below the top of the groundwater table. By definition, the zone of saturation is saturated with water. Also see water table.

zooplankton: Small, usually microscopic animals(such as protozoan), found in lakes and reservoirs.

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