Term	Definitions	Acronym	
7Q10
 	Seven-day, consecutive low flow with a ten year return frequency; the lowest stream flow for seven consecutive days that would be expected to occur once in ten years. 		
A-Scale Sound Level
 	A measurement of sound approximating the sensitivity of the human ear, used to note the intensity or annoyance level of sounds. 		
Abandoned Well
 	A well whose use has been permanently discontinued or which is in a state of such disrepair that it cannot be used for its intended purpose. 		
Abatement
 	Reducing the degree or intensity of, or eliminating, pollution. 		
Abatement Debris
 	Waste from remediation activities. 		
Absorbed Dose
 	In exposure assessment, the amount of a substance that penetrates an exposed organism's absorption barriers (e.g. skin, lung tissue, gastrointestinal tract) through physical or biological processes. The term is synonymous with internal dose. 		
Absorption
 	The uptake of water , other fluids, or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in soil). 		
Absorption Barrier
 	Any of the exchange sites of the body that permit uptake of various substances at different rates (e.g. skin, lung tissue, and gastrointestinal-tract wall). 		
Accident Site
 	The location of an unexpected occurrence, failure or loss, either at a plant or along a transportation route, resulting in a release of hazardous materials. 		
Acclimatization
 	The physiological and behavioral adjustments of an organism to changes in its environment. 		
Acid
 	A corrosive solution with a pH less than 7. 		
Acid Aerosol
 	Acidic liquid or solid particles small enough to become airborne. High concentrations can irritate the lungs and have been associated with respiratory diseases like asthma. 		
Acid Deposition
 	A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either wet or dry form. The wet forms, popularly called "acid rain," can fall to earth as rain, snow, or fog. The dry forms are acidic gases or particulates. 		
Acid Mine Drainage
 	Drainage of water from areas that have been mined for coal or other mineral ores. The water has a low pH because of its contact with sulfur-bearing material and is harmful to aquatic organisms. 		
Acid Neutralizing Capacity
 	Measure of ability of a base (e.g. water or soil) to resist changes in pH. 		
Acid Rain
 			
Acidic
 	The condition of water or soil that contains a sufficient amount of acid substances to lower the pH below 7.0. 		
Action Levels
 	Definition 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. 
Definition 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 Carbon
 	A highly adsorbent form of carbon used to remove odors and toxic substances from liquid or gaseous emissions. In waste treatment, it is used to remove dissolved organic matter from waste drinking water. It is also used in motor vehicle evaporative control systems. 		
Activated Sludge
 	Product that results when primary effluent is mixed with bacteria-laden sludge and then agitated and aerated to promote biological treatment, speeding the breakdown of organic matter in raw sewage undergoing secondary waste treatment. 		
Activator
 	A chemical added to a pesticide to increase its activity. 		
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. 		
Activity Plans
 	Written procedures in a school's asbestos-management plan that detail the steps a Local Education Agency (LEA) will follow in performing the initial and additional cleaning, operation and maintenance-program tasks; periodic surveillance; and reinspection required by the Asbestos Hazard Emergency Response Act (AHERA). 		
Acute Effect
 	An adverse effect on any living organism which results in severe symptoms that develop rapidly; symptoms often subside after the exposure stops. 		
Acute Exposure
 	A single exposure to a toxic substance which may result in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day, as compared to longer, continuing exposure over a period of time. 		
Acute Toxicity
 	The ability of a substance to cause severe biological harm or death soon after a single exposure or dose. Also, any poisonous effect resulting from a single short-term exposure to a toxic substance. 		
Adaptation
 	Changes in an organism's physiological structure or function or habits that allow it to survive in new surroundings. 		
Add-on Control Device
 	An air pollution control device such as carbon absorber or incinerator that reduces the pollution in an exhaust gas. The control device usually does not affect the process being controlled and thus is "add-on" technology, as opposed to a scheme to control pollution through altering the basic process itself. 		
Adequately Wet
 	Asbestos containing material that is sufficiently mixed or penetrated with liquid to prevent the release of particulates. 		
Administered Dose
 	In exposure assessment, the amount of a substance given to a test subject (human or animal) to determine dose-response relationships. Since exposure to chemicals is usually inadvertent, this quantity is often called potential dose. 		
Administrative Order
 	A legal document signed by EPA directing an individual, business, or other entity to take corrective action or refrain from an activity. It describes the violations and actions to be taken, and can be enforced in court. Such orders may be issued, for example, as a result of an administrative complaint whereby the respondent is ordered to pay a penalty for violations of a statute. 		
Administrative Order On Consent
 	A legal agreement signed by EPA and an individual, business, or other entity through which the violator agrees to pay for correction of violations, take the required corrective or cleanup actions, or refrain from an activity. It describes the actions to be taken, may be subject to a comment period, applies to civil actions, and can be enforced in court. 		
Administrative Procedures Act
 	A law that spells out procedures and requirements related to the promulgation of regulations. 		
Administrative Record
 	All documents which EPA considered or relied on in selecting the response action at a Superfund site, culminating in the record of decision for remedial action or, an action memorandum for removal actions. 		
Adsorption
 	Removal of a pollutant from air or water by collecting the pollutant on the surface of a solid material; e.g., an advanced method of treating waste in which activated carbon removes organic matter from waste-water. 		
Adsorption Partition Coefficient
 			
Adulterants
 	Chemical impurities or substances that by law do not belong in a food, or pesticide. 		
Adulterated
 	Definition 1: Any pesticide whose strength or purity falls below the quality stated on its label. 
Definition 2: A food, feed, or product that contains illegal pesticide residues. 
		
Advanced Treatment
 	A level of wastewater treatment more stringent than secondary treatment; requires an 85-percent reduction in conventional pollutant concentration or a significant reduction in non-conventional pollutants. Sometimes called tertiary treatment. 		
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. 		
Adverse Effects Data
 	FIFRA requires a pesticide registrant to submit data to EPA on any studies or other information regarding unreasonable adverse effects of a pesticide at any time after its registration. 		
Advisory
 	A non-regulatory document that communicates risk information to those who may have to make risk management decisions. 		
Aerated Lagoon
 	A holding and/or treatment pond that speeds up the natural process of biological decomposition of organic waste by stimulating the growth and activity of bacteria that degrade organic waste. 		
Aeration
 	A process which promotes biological degradation of organic matter in water. The process may be passive (as when waste is exposed to air), or active (as when a mixing or bubbling device introduces the air). 		
Aeration Tank
 	A chamber used to inject air into water. 		
Aerobic
 	Life or processes that require, or are not destroyed by, the presence of oxygen. 		
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
 	Definition 1: Small droplets or particles suspended in the atmosphere, typically containing sulfur. They are usually emitted naturally (e.g. in volcanic eruptions) and as the result of anthropogenic (human) activities such as burning fossil fuels. 
Definition 2: The pressurized gas used to propel substances out of a container. 
Definition 3: A finely divided material suspended in air or other gaseous environment. 
		
Affected Landfill
 	Under the Clean Air Act, landfills that meet criteria for capacity, age, and emissions rates set by the EPA. They are required to collect and combust their gas emissions. 		
Affected Public
 	Definition 1: The people who live and/or work near a hazardous waste site. 
Definition 2: The human population adversely impacted following exposure to a toxic pollutant in food, water, air, or soil. 
		
Afterburner
 	In incinerator technology, a burner located so that the combustion gases are made to pass through its flame in order to remove smoke and odors. It may be attached to or be separated from the incinerator proper. 		
Age Tank
 	A tank used to store a chemical solution of known concentration for feed to a chemical feeder. 		
Agent
 	Any physical, chemical, or biological entity that can be harmful to an organism (synonymous with stressors). 		
Agent Orange
 	A toxic herbicide and defoliant used in the Vietnam conflict, containing 2,4,5-trichlorophen-oxyacetic acid (2,4,5-T) and 2-4 dichlorophenoxyacetic acid (2,4-D) with trace amounts of dioxin. 		
Agricultural Pollution
 	Farming wastes, including runoff and leaching of pesticides and fertilizers; erosion and dust from plowing; improper disposal of animal manure and carcasses; crop residues, and debris. 		
Agricultural Waste
 	Poultry and livestock manure, and residual materials in liquid or solid form generated from the production and marketing of poultry, livestock or fur-bearing animals; also includes grain, vegetable, and fruit harvest residue. 		
Agroecosystem
 	Land used for crops, pasture, and livestock; the adjacent uncultivated land that supports other vegetation and wildlife; and the associated atmosphere, the underlying soils, groundwater, and drainage networks. 		
AHERA Designated Person
 	A person designated by a Local Education Agency to ensure that the AHERA requirements for asbestos management and abatement are properly implemented. 	ADP 	
Air Binding
 	Situation where air enters the filter media and harms both the filtration and backwash processes. 		
Air Changes Per Hour
 	The movement of a volume of air in a given period of time; if a house has one air change per hour, it means that the air in the house will be replaced in a one-hour period. 	ACH 	
Air Cleaning
 	Indoor-air quality-control strategy to remove various airborne particulates and/or gases from the air. Most common methods are particulate filtration, electrostatic precipitation, and gas sorption. 		
Air Contaminant
 	Any particulate matter, gas, or combination thereof, other than water vapor. 		
Air Curtain
 	A method of containing oil spills. Air bubbling through a perforated pipe causes an upward water flow that slows the spread of oil. It can also be used to stop fish from entering polluted water. 		
Air Exchange Rate
 	The rate at which outside air replaces indoor air in a given space. 		
Air Gap
 	Open vertical gap or empty space that separates drinking water supply to be protected from another water system in a treatment plant or other location. The open gap protects the drinking water from contamination by backflow or back siphonage. 		
Air Handling Unit
 	Equipment that includes a fan or blower, heating and/or cooling coils, regulator controls, condensate drain pans, and air filters. 		
Air Mass
 	A large 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 Monitoring
 			
Air/Oil Table
 	The surface between the vadose zone and ambient oil; the pressure of oil in the porous medium is equal to atmospheric pressure. 		
Air Padding
 	Pumping dry air into a container to assist with the withdrawal of liquid or to force a liquefied gas such as chlorine out of the container. 		
Air Permeability
 	Permeability of soil with respect to air. Important to the design of soil-gas surveys. Measured in darcys or centimeters-per-second. 		
Air Plenum
 	Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum. 		
Air Pollutant
 	Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. 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. Air pollutants are often grouped in categories for ease in classification; some of the categories are: solids, sulfur compounds, volatile organic chemicals, particulate matter, nitrogen compounds, oxygen compounds, halogen compounds, radioactive compounds, and odors. 		
Air Pollution
 	The presence of contaminants or pollutant substances in the air that interfere with human health or welfare, or produce other harmful environmental effects. 		
Air Pollution Control Device
 	Mechanism or equipment that cleans emissions generated by a source (e.g. an incinerator, industrial smokestack, or an automobile exhaust system) by removing pollutants that would otherwise be released to the atmosphere. 		
Air Pollution Episode
 	A period of abnormally high concentration of air pollutants, often due to low winds and temperature inversion, that can cause illness and death. 		
Air Quality Control Region
 			
Air Quality Criteria
 	The levels of pollution and lengths of exposure above which adverse health and welfare effects may occur. 		
Air Quality Standards
 	The level of pollutants prescribed by regulations that are not to be exceeded during a given time in a defined area. 		
Air Sparging
 	Injecting air or oxygen into an aquifer to strip or flush volatile contaminants as air bubbles up through the ground water and is captured by a vapor extraction system. 		
Air Stripping
 	A treatment system that removes volatile organic compounds (VOCs) from contaminated ground water or surface water by forcing an airstream through the water and causing the compounds to evaporate. 		
Air Toxics
 	Any air pollutant for which a national ambient air quality standard (NAAQS) does not exist (i.e. excluding ozone, carbon monoxide, PM-10, sulfur dioxide, nitrogen oxide) that may reasonably be anticipated to cause cancer; respiratory, cardiovascular, or developmental effects; reproductive dysfunctions, neurological disorders, heritable gene mutations, or other serious or irreversible chronic or acute health effects in humans. 		
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. Sources of airborne particulates include: dust, emissions from industrial processes, combustion products from the burning of wood and coal, combustion products associated with motor vehicle or non-road engine exhausts, and reactions to gases in the atmosphere. 		
Airborne Release
 	Release of any pollutant into the air. 		
Alachlor
 	A herbicide, marketed under the trade name Lasso, used mainly to control weeds in corn and soybean fields. 		
Alar
 	Trade name for daminozide, a pesticide that makes apples redder, firmer, and less likely to drop off trees before growers are ready to pick them. It is also used to a lesser extent on peanuts, tart cherries, concord grapes, and other fruits. 		
Aldicarb
 	An insecticide sold under the trade name Temik. It is made from ethyl isocyanate. 		
Algae
 	Simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals. 		
Algal Blooms
 	Sudden spurts of algal growth, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry. 		
Algicide
 	Substance or chemical used specifically to kill or control algae. 		
Aliquot
 	A measured portion of a sample taken for analysis. One or more aliquots make up a sample. 		
Alkaline
 	The condition of water or soil which contains a sufficient amount of alkali substance to raise the pH above 7.0. 		
Alkalinity
 	The capacity of bases to neutralize acids. An example is lime added to lakes to decrease acidity. 		
Allergen
 	A substance that causes an allergic reaction in individuals sensitive to it. 		
Alluvial
 	Relating to and/or sand deposited by flowing water. 		
Alternate Method
 	Any method of sampling and analyzing for an air or water pollutant that is not a reference or equivalent method but that has been demonstrated in specific cases-to EPA's satisfaction-to produce results adequate for compliance monitoring. 		
Alternative Compliance
 	A policy that allows facilities to choose among methods for achieving emission-reduction or risk-reduction instead of command-and control regulations that specify standards and how to meet them. Use of a theoretical emissions bubble over a facility to cap the amount of pollution emitted while allowing the company to choose where and how (within the facility) it complies. 		
Alternative Fuels
 	Substitutes for traditional liquid, oil-derived motor vehicle fuels like gasoline and diesel. Includes mixtures of alcohol-based fuels with gasoline, methanol, ethanol, compressed natural gas, and others. 		
Alternative Remedial Contract Strategy Contractors
 	Government contractors who provide project management and technical services to support remedial response activities at National Priorities List sites. 		
Ambient Air
 	Any unconfined portion of the atmosphere: open air, surrounding air. 		
Ambient Air Quality Standards
 			
Ambient Background Samples
 			
Ambient Measurement
 	A measurement of the concentration of a substance or pollutant within the immediate environs of an organism; taken to relate it to the amount of possible exposure. 		
Ambient Medium
 	Material surrounding or contacting an organism (e.g. outdoor air, indoor air, water, or soil, through which chemicals or pollutants can reach the organism. 		
Ambient Temperature
 	Temperature of the surrounding air or other medium. 		
Amprometric Titration
 	A way of measuring concentrations of certain substances in water using an electric current that flows during a chemical reaction. 		
Anaerobic
 	A life or process that occurs in, or is not destroyed by, the absence of oxygen. 		
Anaerobic Decomposition
 	Reduction of the net energy level and change in chemical composition of organic matter caused by microorganisms in an oxygen-free environment. 		
Animal Dander
 	Tiny scales of animal skin, a common indoor air pollutant. 		
Animal Studies
 	Investigations using animals as surrogates for humans with the expectation that the results are pertinent to humans. 		
Anisotropy
 	In hydrology, the conditions under which one or more hydraulic properties of an aquifer vary from a reference point. 		
Annular Space
 	The space between two concentric tubes or casings, or between the casing and the borehole wall. 		
Annulus
 			
Antagonism
 	Interference or inhibition of the effect of one chemical by the action of another. 		
Antarctic "Ozone Hole"
 	Refers to the seasonal depletion of ozone in the upper atmosphere above a large area of Antarctica. 		
Anti-Degradation Clause
 	Part of federal air quality and water quality requirements prohibiting deterioration where pollution levels are above the legal limit. 		
Anti-Microbial
 	An agent that kills microbes. 		
Applicable or Relevant and Appropriate Requirements
 	Any state or federal statute that pertains to protection of human life and the environment in addressing specific conditions or use of a particular cleanup technology at a Superfund site, 	ARARs 	
Applied Dose
 	In exposure assessment, the amount of a substance in contact with the primary absorption boundaries of an organism (e.g. skin, lung tissue, gastrointestinal track) and available for absorption. 		
Aqueous
 	Something made up of water. 		
Aqueous Solubility
 	The maximum concentration of a chemical that will dissolve in pure water at a reference temperature. 		
Aquifer
 	An underground geological formation, or group of formations, containing water. Are sources of groundwater for wells and springs. 		
Aquifer Test
 	A test to determine hydraulic properties of an aquifer. 		
Aquitard
 	Geological formation that may contain groundwater but is not capable of transmitting significant quantities of it under normal hydraulic gradients. May function as confining bed. 		
Architectural Coatings
 	Coverings such as paint and roof tar that are used on exteriors of buildings. 		
Area of Review
 	In the UIC program, the area surrounding an injection well that is reviewed during the permitting process to determine if flow between aquifers will be induced by the injection operation. 		
Area Source
 	Any source of air pollution that is released over a relatively small area but which cannot be classified as a point source. Such sources may include vehicles and other small engines, small businesses and household activities, or biogenic sources such as a forest that releases hydrocarbons. 		
Aromatics
 	A type of hydrocarbon, such as benzene or toluene, with a specific type of ring structure. Aromatics are sometimes added to gasoline in order to increase octane. Some aromatics are toxic. 		
Arsenicals
 	Pesticides containing arsenic. 		
Artesian Aquifer
 	Water held under pressure in porous rock or soil confined by impermeable geological formations. 		
Artesian Well
 			
Asbestos
 	A mineral fiber that can pollute air or water and cause cancer or asbestosis when inhaled. EPA has banned or severely restricted its use in manufacturing and construction. 		
Asbestos Abatement
 	Procedures to control fiber release from asbestos-containing materials in a building or to remove them entirely, including removal, encapsulation, repair, enclosure, encasement, and operations and maintenance programs. 		
Asbestos Assessment
 	In the asbestos-in-schools program, the evaluation of the physical condition and potential for damage of all friable asbestos containing materials and thermal insulation systems. 		
Asbestos-Containing Waste Materials
 	Mill tailings or any waste that contains commercial asbestos and is generated by a source covered by the Clean Air Act Asbestos NESHAPS. 	ACWM 	
Asbestos Program Manager
 	A building owner or designated representative who supervises all aspects of the facility asbestos management and control program. 		
Asbestosis
 	A disease associated with inhalation of asbestos fibers. The disease makes breathing progressively more difficult and can be fatal. 		
Ash
 	The mineral content of a product remaining after complete combustion. 		
Assay
 	A test for a specific chemical, microbe, or effect. 		
Assessment Endpoint
 	In ecological risk assessment, an explicit expression of the environmental value to be protected; includes both an ecological entity and specific attributed thereof entity (e.g. salmon are a valued ecological entity; reproduction and population maintenance--the attribute--form an assessment endpoint). 		
Assimilation
 	The ability of a body of water to purify itself of pollutants. 		
Assimilative Capacity
 	The capacity of a natural body of water to receive wastewaters or toxic materials without deleterious effects and without damage to aquatic life or humans who consume the water. 		
Association of Boards of Certification
 	An international organization representing boards which certify the operators of waterworks and wastewater facilities. 		
Attainment Area
 	An area considered to have air quality as good as or better than the national ambient air quality standards as defined in the Clean Air Act. An area may be an attainment area for one pollutant and a non-attainment area for others. 		
Attenuation
 	The process by which a compound is reduced in concentration over time, through absorption, adsorption, degradation, dilution, and/or transformation. Can also be the decrease with distance of sight caused by attenuation of light by particulate pollution. 		
Attractant
 	A chemical or agent that lures insects or other pests by stimulating their sense of smell. 		
Attrition
 	Wearing or grinding down of a substance by friction. Dust from such processes contributes to air pollution. 		
Availability Session
 	Informal meeting at a public location where interested citizens can talk with EPA and state officials on a one-to-one basis. 		
Available Chlorine
 	A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials used as a source of chlorine when compared with that of liquid or gaseous chlorines. 		
Avoided Cost
 	The cost a utility would incur to generate the next increment of electric capacity using its own resources; many landfill gas projects' buy back rates are based on avoided costs. 		
Back Pressure
 	A pressure that can cause water to backflow into the water supply when a user's waste water system is at a higher pressure than the public system. 		
Back Siphonage
 			
Backfit
 			
Backflow
 	A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one. 		
Background Level
 	Definition 1: The concentration of a substance in an environmental media (air, water, or soil) that occurs naturally or is not the result of human activities. 
Definition 2: In exposure assessment, the concentration of a substance in a defined control area, during a fixed period of time before, during, or after a data-gathering operation. 
		
Backwashing
 	Reversing the flow of water back through the filter media to remove entrapped solids. 		
Backyard Composting
 	Diversion of organic food waste and yard trimmings from the municipal waste stream by composting hem in one's yard through controlled decomposition of organic matter by bacteria and fungi into a humus-like product. It is considered source reduction, not recycling, because the composted materials never enter the municipal waste stream. 		
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. 		
Bactericide
 	A pesticide used to control or destroy bacteria, typically in the home, schools, or hospitals. 		
Bacterium
 			
Baffle
 	A flat board or plate, deflector, guide, or similar device constructed or placed in flowing water or slurry systems to cause more uniform flow velocities to absorb energy and to divert, guide, or agitate liquids. 		
Baffle Chamber
 	In incinerator design, a chamber designed to promote the settling of fly ash and coarse particulate matter by changing the direction and/or reducing the velocity of the gases produced by the combustion of the refuse or sludge. 		
Baghouse Filter
 	Large fabric bag, usually made of glass fibers, used to eliminate intermediate and large (greater than 20 PM in diameter) particles. This device operates like the bag of an electric vacuum cleaner, passing the air and smaller particles while entrapping the larger ones. 		
Bailer
 	Definition 1: A pipe with a valve at the lower end, used to remove slurry from the bottom or side of a well as it is being drilled, or to collect groundwater samples from wells or open boreholes. 
Definition 2: A tube of varying length. 
		
Baling
 	Compacting solid waste into blocks to reduce volume and simplify handling. 		
Ballistic Separator
 	A machine that sorts organic from inorganic matter for composting. 		
Band Application
 	The spreading of chemicals over, or next to, each row of plants in a field. 		
Banking
 	A system for recording qualified air emission reductions for later use in bubble, offset, or netting transactions. 		
Bar Screen
 	In wastewater treatment, a device used to remove large solids. 		
Barrel Sampler
 	Open-ended steel tube used to collect soil samples. 		
Barrier Coating
 	A layer of a material that obstructs or prevents passage of something through a surface that is to be protected; e.g., grout, caulk, or various sealing compounds; sometimes used with polyurethane membranes to prevent corrosion or oxidation of metal surfaces, chemical impacts on various materials, or, for example, to prevent radon infiltration through walls, cracks, or joints in a house. 		
Barrier Coatings
 			
Basal Application
 	In pesticides, the application of a chemical on plant stems or tree trunks just above the soil line. 		
Basalt
 	Consistent year-round energy use of a facility; also refers to the minimum amount of electricity supplied continually to a facility. 		
Bean Sheet
 	Common term for a pesticide data package record. 		
Bed Load
 	Sediment particles resting on or near the channel bottom that are pushed or rolled along by the flow of water. 		
BEN
 	EPA's computer model for analyzing a violator's economic gain from not complying with the law. 		
Bench-Scale Tests
 	Laboratory testing of potential cleanup technologies 		
Benefit-Cost Analysis
 	An economic method for assessing the benefits and costs of achieving alternative health-based standards at given levels of health protection. 		
Benthic
 	An organism that feeds on the sediment at the bottom of a water body such as an ocean, lake, or river. 		
Benthos
 			
Bentonite
 	A colloidal clay, expansible when moist, commonly used to provide a tight seal around a well casing. 		
Beryllium
 	An metal hazardous to human health when inhaled as an airborne pollutant. It is discharged by machine shops, ceramic and propellant plants, and foundries. 		
Best Available Control Measures
 	A term used to refer to the most effective measures (according to EPA guidance) for controlling small or dispersed particulates and other emissions from sources such as roadway dust, soot and ash from woodstoves and open burning of rush, timber, grasslands, or trash. 	BACM 	
Best Available Control Technology
 	Definition 1: An emission limitation based on the maximum degree of emission reduction (considering energy, environmental, and economic impacts) achievable through application of production processes and available methods, systems, and techniques. BACT does not permit emissions in excess of those allowed under any applicable Clean Air Act provisions. Use of the BACT concept is allowable on a case by case basis for major new or modified emissions sources in attainment areas and applies to each regulated pollutant. 
Definition 2: For any specific source, the currently available technology producing the greatest reduction of air pollutant emissions, taking into account energy, environmental, economic, and other costs. 
Definition 3: The most stringent technology available for controlling emissions; major sources are required to use BACT, unless it can be demonstrated that it is not feasible for energy, environmental, or economic reasons. 
	BACT 	
Best Demonstrated Available Technology
 	As identified by EPA, the most effective commercially available means of treating specific types of hazardous waste. The BDATs may change with advances in treatment technologies. 	BDAT 	
Best Management Practice
 	Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from non-point sources. 	BMP 	
BIAX Lamps
 			
Bimetal
 	Beverage containers with steel bodies and aluminum tops; handled differently from pure aluminum in recycling. 		
Bioaccumulants
 	Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. 		
Bioassay
 	A test to determine the relative strength of a substance by comparing its effect on a test organism with that of a standard preparation. 		
Bioavailability
 	Degree of ability to be absorbed and ready to interact in organism metabolism. 		
Biochemical Oxygen Demand
 	A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. The greater the BOD, the greater the degree of pollution. 	BOD 	
Bioconcentration
 	The accumulation of a chemical in tissues of a fish or other organism to levels greater than in the surrounding medium. 		
Biodegradable
 	Capable of decomposing under natural conditions. 		
Biodiversity
 	Refers to the variety and variability among living organisms and the ecological complexes in which they occur. Diversity can be defined as the number of different items and their relative frequencies. For biological diversity, these items 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. 		
Biological Contaminants
 	Living organisms or derivates (e.g. viruses, bacteria, fungi, and mammal and bird antigens) that can cause harmful health effects when inhaled, swallowed, or otherwise taken into the body. 		
Biological Control
 	In pest control, the use of animals and organisms that eat or otherwise kill or out-compete pests. 		
Biological Integrity
 	The ability to support and maintain balanced, integrated, functionality in the natural habitat of a given region. Concept is applied primarily in drinking water management. 		
Biological Magnification
 	Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. 		
Biological Measurement
 	A measurement taken in a biological medium. For exposure assessment, it is related to the measurement is taken to related it to the established internal dose of a compound. 		
Biological Medium
 	One of the major component of an organism; e.g. blood, fatty tissue, lymph nodes or breath, in which chemicals can be stored or transformed. 		
Biological Oxidation
 	Decomposition of complex organic materials by microorganisms. Occurs in self-purification of water bodies and in activated sludge wastewater treatment. 		
Biological Oxygen Demand
 	An indirect measure of the concentration of biologically degradable material present in organic wastes. It usually reflects the amount of oxygen consumed in five days by biological processes breaking down organic waste. 	BOD 	
Biological pesticides
 	Certain microorganism, including bacteria, fungi, viruses, and protozoa that are effective in controlling pests. These agents usually do not have toxic effects on animals and people and do not leave toxic or persistent chemical residues in the environment. 		
Biological Stressors
 	Organisms accidentally or intentionally dropped into habitats in which they do not evolve naturally; e.g. gypsy moths, Dutch elm disease, certain types of algae, and bacteria. 		
Biological Treatment
 	A treatment technology that uses bacteria to consume organic waste. 		
Biologically Effective Dose
 	The amount of a deposited or absorbed compound reaching the cells or target sites where adverse effect occur, or where the chemical interacts with a membrane. 		
Biologicals
 	Vaccines, cultures and other preparations made from living organisms and their products, intended for use in diagnosing, immunizing, or treating humans or animals, or in related research. 		
Biomass
 	All of the living material in a given area; often refers to vegetation. 		
Biome
 	Entire community of living organisms in a single major ecological area. 		
Biomonitoring
 	Definition 1: The use of living organisms to test the suitability of effluents for discharge into receiving waters and to test the quality of such waters downstream from the discharge. 
Definition 2: Analysis of blood, urine, tissues, etc. to measure chemical exposure in humans. 
		
Bioremediation
 	Use of living organisms to clean up oil spills or remove other pollutants from soil, water, or wastewater; use of organisms such as non-harmful insects to remove agricultural pests or counteract diseases of trees, plants, and garden soil. 		
Biosensor
 	Analytical device comprising a biological recognition element (e.g. enzyme, receptor, DNA, antibody, or microorganism) in intimate contact with an electrochemical, optical, thermal, or acoustic signal transducer that together permit analyses of chemical properties or quantities. Shows potential development in some areas, including environmental monitoring. 		
Biosphere
 	The portion of Earth and its atmosphere that can support life. 		
Biostabilizer
 	A machine that converts solid waste into compost by grinding and aeration. 		
Biota
 	The animal and plant life of a given region. 		
Biotechnology
 	Techniques that use living organisms or parts of organisms to produce a variety of products (from medicines to industrial enzymes) to improve plants or animals or to develop microorganisms to remove toxics from bodies of water, or act as pesticides. 		
Biotic Community
 	A naturally occurring assemblage of plants and animals that live in the same environment and are mutually sustaining and interdependent. 		
Biotransformation
 	Conversion of a substance into other compounds by organisms; includes biodegradation. 		
Blackwater
 	Water that contains animal, human, or food waste. 		
Blood Products
 	Any product derived from human blood, including but not limited to blood plasma, platelets, red or white corpuscles, and derived licensed products such as interferon. 		
Bloom
 	A proliferation of algae and/or higher aquatic plants in a body of water; often related to pollution, especially when pollutants accelerate growth. 		
BOD5
 	The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter. 		
Body Burden
 	The amount of a chemical stored in the body at a given time, especially a potential toxin in the body as the result of exposure. 		
Bog
 	A type of wetland that accumulates appreciable peat deposits. Bogs depend primarily on precipitation for their water source, and are usually acidic and rich in plant residue with a conspicuous mat of living green moss. 		
Boiler
 	A vessel designed to transfer heat produced by combustion or electric resistance to water. Boilers may provide hot water or steam. 		
Boom
 	Definition 1: A floating device used to contain oil on a body of water. 
Definition 2: A piece of equipment used to apply pesticides from a tractor or truck. 
		
Borehole
 	Hole made with drilling equipment. 		
Botanical Pesticide
 	A pesticide whose active ingredient is a plant-produced chemical such as nicotine or strychnine. 		
Bottle Bill
 	Proposed or enacted legislation which requires a returnable deposit on beer or soda containers and provides for retail store or other redemption. Such legislation is designed to discourage use of throw-away containers. 		
Bottom Ash
 	The non-airborne combustion residue from burning pulverized coal in a boiler; the material which falls to the bottom of the boiler and is removed mechanically; a concentration of non-combustible materials, which may include toxics. 		
Bottom Land Hardwoods
 	Forested freshwater wetlands adjacent to rivers in the southeastern United States, especially valuable for wildlife breeding, nesting and habitat. 		
Bounding Estimate
 	An estimate of exposure, dose, or risk that is higher than that incurred by the person in the population with the currently highest exposure, dose, or risk. Bounding estimates are useful in developing statements that exposures, doses, or risks are not greater than an estimated value. 		
Brackish
 	Mixed fresh and salt water. 		
Breakpoint Chlorination
 	Addition of chlorine to water until the chlorine demand has been satisfied. 		
Breakthrough
 	A crack or break in a filter bed that allows the passage of floc or particulate matter through a filter; will cause an increase in filter effluent turbidity. 		
Breathing Zone
 	Area of air in which an organism inhales. 		
Brine Mud
 	Waste material, often associated with well-drilling or mining, composed of mineral salts or other inorganic compounds. 		
British Thermal Unit
 	Unit of heat energy equal to the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. 		
Broadcast Application
 	The spreading of pesticides over an entire area. 		
Brownfields
 	Abandoned, idled, or under used industrial and commercial facilities/sites where expansion or redevelopment is complicated by real or perceived environmental contamination. They can be in urban, suburban, or rural areas. EPA's Brownfields initiative helps communities mitigate potential health risks and restore the economic viability of such areas or properties. 		
Bubble
 	A system under which existing emissions sources can propose alternate means to comply with a set of emissions limitations; under the bubble concept, sources can control more than required at one emission point where control costs are relatively low in return for a comparable relaxation of controls at a second emission point where costs are higher. 		
Bubble Policy
 			
Buffer
 	A solution or liquid whose chemical makeup is such that it minimizes changes in pH when acids or bases are added to it. 		
Buffer Strips
 	Strips of grass or other erosion-resisting vegetation between or below cultivated strips or fields. 		
Building Cooling Load
 	The hourly amount of heat that must be removed from a building to maintain indoor comfort (measured in British thermal units (Btus). 		
Building Envelope
 	The exterior surface of a building's construction--the walls, windows, floors, roof, and floor. 		
Building Related Illness
 	Diagnosable illness whose cause and symptoms can be directly attributed to a specific pollutant source within a building (e.g. Legionnaire's disease, hypersensitivity, pneumonitis). 		
Building Shell
 			
Bulk Sample
 	A small portion (usually thumbnail size) of a suspect asbestos-containing building material collected by an asbestos inspector for laboratory analysis to determine asbestos content. 		
Bulky Waste
 	Large items of waste materials, such as appliances, furniture, large auto parts, trees, stumps. 		
Burial Ground
 	A disposal site for radioactive waste materials that uses earth or water as a shield. 		
Buy-Back Center
 	Facility where individuals or groups bring reyclables in return for payment. 		
By-product
 	Material, other than the principal product, generated as a consequence of an industrial process or as a breakdown product in a living system. 		
Cadmium
 	A heavy metal that accumulates in the environment. 	Cd 	
Cancellation
 	Refers to Section 6 (b) of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) which authorizes cancellation of a pesticide registration if unreasonable adverse effects to the environment and public health develop when a product is used according to widespread and commonly recognized practice, or if its labeling or other material required to be submitted does not comply with FIFRA provisions. 		
Cap
 	A layer of clay, or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize leachate. 		
Capacity Assurance Plan
 	A statewide plan which supports a state's ability to manage the hazardous waste generated within its boundaries over a twenty year period. 		
Capillary Action
 	Movement of water through very small spaces due to molecular forces called capillary forces. 		
Capillary Fringe
 	Definition 1: The porous material just above the water table which may hold water by capillarity (a property of surface tension that draws water upwards) in the smaller void spaces. 
Definition 2: The zone above the water table within which the porous medium is saturated by water under less than atmospheric pressure. 
		
Capture Efficiency
 	The fraction of organic vapors generated by a process that are directed to an abatement or recovery device. 		
Carbon Absorber
 	An add-on control device that uses activated carbon to absorb volatile organic compounds from a gas stream. (The VOCs are later recovered from the carbon.) 		
Carbon Adsorption
 	A treatment system that removes contaminants from ground water or surface water by forcing it through tanks containing activated carbon treated to attract the contaminants. 		
Carbon Monoxide
 	A colorless, odorless, poisonous gas produced by incomplete fossil fuel combustion. 	CO 	
Carbon Tetrachloride
 	Compound consisting of one carbon atom ad four chlorine atoms, once widely used as a industrial raw material, as a solvent, and in the production of CFCs. Use as a solvent ended when it was discovered to be carcinogenic. 	CC14 	
Carboxyhemoglobin
 	Hemoglobin in which the iron is bound to carbon monoxide(CO) instead of oxygen. 		
Carcinogen
 	Any substance that can cause or aggravate cancer. 		
Carrier
 	Definition 1: The inert liquid or solid material in a pesticide product that serves as a delivery vehicle for the active ingredient. Carriers do not have toxic properties of their own. 
Definition 2: Any material or system that can facilitate the movement of a pollutant into the body or cells. 
		
Carrying Capacity
 	Definition 1: In recreation management, the amount of use a recreation area can sustain without loss of quality. 
Definition 2: In wildlife management, the maximum number of animals an area can support during a given period. 
		
CAS Registration Number
 	A number assigned by the Chemical Abstract Service to identify a chemical. 		
Case Study
 	A brief fact sheet providing risk, cost, and performance information on alternative methods and other pollution prevention ideas, compliance initiatives, voluntary efforts, etc. 		
Cask
 	A thick-walled container (usually lead) used to transport radioactive material. 		
Catalyst
 	A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction. 		
Catalytic Converter
 	An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen. 		
Catalytic Incinerator
 	A control device that oxidizes volatile organic compounds (VOCs) by using a catalyst to promote the combustion process. Catalytic incinerators require lower temperatures than conventional thermal incinerators, thus saving fuel and other costs. 		
Categorical Exclusion
 	A class of actions which either individually or cumulatively would not have a significant effect on the human environment and therefore would not require preparation of an environmental assessment or environmental impact statement under the National Environmental Policy Act (NEPA). 		
Categorical Pretreatment Standard
 	A technology-based effluent limitation for an industrial facility discharging into a municipal sewer system. Analogous in stringency to Best Availability Technology (BAT) for direct dischargers. 		
Cathodic Protection
 	A technique to prevent corrosion of a metal surface by making it the cathode of an electrochemical cell. 		
Cavitation
 	The formation and collapse of gas pockets or bubbles on the blade of an impeller or the gate of a valve; collapse of these pockets or bubbles drives water with such force that it can cause pitting of the gate or valve surface. 		
Cells
 	Definition 1: In solid waste disposal, holes where waste is dumped, compacted, and covered with layers of dirt on a daily basis. 
Definition 2: The smallest structural part of living matter capable of functioning as an independent unit. 
		
Cementitious
 	Densely packed and nonfibrous friable materials. 		
Central Collection Point
 	Location were a generator of regulated medical waste consolidates wastes originally generated at various locations in his facility. The wastes are gathered together for treatment on-site or for transportation elsewhere for treatment and/or disposal. This term could also apply to community hazardous waste collections, industrial and other waste management systems. 		
Centrifugal Collector
 	A mechanical system using centrifugal force to remove aerosols from a gas stream or to remove water from sludge. 		
CERCLIS
 	The federal Comprehensive Environmental Response, Compensation, and Liability Information System is a database that includes all sites which have been nominated for investigation by the Superfund program. 		
Channelization
 	Straightening and deepening streams so water will move faster, a marsh-drainage tactic that can interfere with waste assimilation capacity, disturb fish and wildlife habitats, and aggravate flooding. 		
Characteristic
 	Any one of the four categories used in defining hazardous waste: ignitability, corrosivity, reactivity, and toxicity. 		
Characterization of Ecological Effects
 	Part of ecological risk assessment that evaluates ability of a stressor to cause adverse effects under given circumstances. 		
Characterization of Exposure
 	Portion of an ecological risk assessment that evaluates interaction of a stressor with one or more ecological entities. 		
Check-Valve Tubing Pump
 	Water sampling tool. 		
Chemical Case
 	For purposes of review and regulation, the grouping of chemically similar pesticide active ingredients (e.g. salts and esters of the same chemical) into chemical cases. 		
Chemical Compound
 	A distinct and pure substance formed by the union or two or more elements in definite proportion by weight. 		
Chemical Element
 	A fundamental substance comprising one kind of atom; the simplest form of matter. 		
Chemical Oxygen Demand
 	A measure of the oxygen required to oxidize all compounds, both organic and inorganic, in water. 	COD 	
Chemical Stressors
 	Chemicals released to the environment through industrial waste, auto emissions, pesticides, and other human activity that can cause illnesses and even death in plants and animals. 		
Chemical Treatment
 	Any one of a variety of technologies that use chemicals or a variety of chemical processes to treat waste. 		
Chemnet
 	Mutual aid network of chemical shippers and contractors that assigns a contracted emergency response company to provide technical support if a representative of the firm whose chemicals are involved in an incident is not readily available. 		
Chemosterilant
 	A chemical that controls pests by preventing reproduction. 		
Chemtrec
 	The industry-sponsored Chemical Transportation Emergency Center; provides information and/or emergency assistance to emergency responders. 		
Child Resistant Packaging
 	Packaging that protects children or adults from injury or illness resulting from accidental contact with or ingestion of residential pesticides that meet or exceed specific toxicity levels. Required by FIFRA regulations. Term is also used for protective packaging of medicines. 	CRP 	
Chiller
 	A device that generates a cold liquid that is circulated through an air-handling unit's cooling coil to cool the air supplied to the building. 		
Chilling Effect
 	The lowering of the Earth's temperature because of increased particles in the air blocking the sun's rays. 		
Chisel Plowing
 	Preparing croplands by using a special implement that avoids complete inversion of the soil as in conventional plowing. Chisel plowing can leave a protective cover or crops residues on the soil surface to help prevent erosion and improve filtration. 		
Chlorinated Hydrocarbons
 	Definition 1: Chemicals containing only chlorine, carbon, and hydrogen. 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. 
Definition 2: Any chlorinated organic compounds including chlorinated solvents such as dichloromethane, trichloromethylene, chloroform. 
		
Chlorinated Solvent
 	An organic solvent containing chlorine atoms(e.g. methylene chloride and 1,1,1-trichloromethane). Uses of chlorinated solvents are include aerosol spray containers, in highway paint, and dry cleaning fluids. 		
Chlorination
 	The application of chlorine to drinking water, sewage, or industrial waste to disinfect or to oxidize undesirable compounds. 		
Chlorinator
 	A device that adds chlorine, in gas or liquid form, to water or sewage to kill infectious bacteria. 		
Chlorine-Contact Chamber
 	That part of a water treatment plant where effluent is disinfected by chlorine. 		
Chlorofluorocarbons
 	A family of inert, nontoxic, and easily liquefied 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. 	CFCs 	
Chlorophenoxy
 	A class of herbicides that may be found in domestic water supplies and cause adverse health effects. 		
Chlorosis
 	Discoloration of normally green plant parts caused by disease, lack of nutrients, or various air pollutants. 		
Cholinesterase
 	An enzyme found in animals that regulates nerve impulses by the inhibition of acetylcholine. Cholinesterase inhibition is associated with a variety of acute symptoms such as nausea, vomiting, blurred vision, stomach cramps, and rapid heart rate. 		
Chromium
 			
Chronic Effect
 	An adverse effect on a human or animal in which symptoms recur frequently or develop slowly over a long period of time. 		
Chronic Exposure
 	Multiple exposures occurring over an extended period of time or over a significant fraction of an animal's or human's lifetime (Usually seven years to a lifetime.) 		
Chronic Toxicity
 	The capacity of a substance to cause long-term poisonous health effects in humans, animals, fish, and other organisms. 		
Circle of Influence
 	The circular outer edge of a depression produced in the water table by the pumping of water from a well. 		
Cistern
 	Small tank or storage facility used to store water for a home or farm; often used to store rain water. 		
Clarification
 	Clearing action that occurs during wastewater treatment when solids settle out. This is often aided by centrifugal action and chemically induced coagulation in wastewater. 		
Clarifier
 	A tank in which solids settle to the bottom and are subsequently removed as sludge. 		
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 areas, monuments, and other areas of special national and cultural significance. 		
Class I Substance
 	One of several groups of chemicals with an ozone depletion potential of 0.2 or higher, including CFCS, Halons, Carbon Tetrachloride, and Methyl Chloroform (listed in the Clean Air Act), and HBFCs and Ethyl Bromide (added by EPA regulations). 		
Class II Substance
 	A substance with an ozone depletion potential of less than 0.2. All HCFCs are currently included in this classification. 		
Clay Soil
 	Soil material containing more than 40 percent clay, less than 45 percent sand, and less than 40 percent silt. 		
Clean Coal Technology
 	Any technology not in widespread use prior to the Clean Air Act Amendments of 1990. This Act will achieve significant reductions in pollutants associated with the burning of coal. 		
Clean Fuels
 	Blends or substitutes for gasoline fuels, including compressed natural gas, methanol, ethanol, and liquefied petroleum gas. 		
Cleaner Technologies Substitutes Assessment
 	A document that systematically evaluates the relative risk, performance, and cost trade-offs of technological alternatives; serves as a repository for all the technical data (including methodology and results) developed by a DfE or other pollution prevention or education project. 		
Cleanup
 	Actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and/or the environment. The term "cleanup" is sometimes used interchangeably with the terms remedial action, removal action, response action, or corrective action. (See: Response Action (2)) 		
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, and 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
 	The term 'climate change' is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, 'climate change' has been used synonymously with the term, 'global warming'; scientists however, tend to use the term in the wider sense to also include natural changes in climate. 		
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 ceasing acceptance of solid waste and placing a cap on the landfill site. 		
Co-fire
 	Burning of two fuels in the same combustion unit; e.g., coal and natural gas, or oil and coal. 		
Coagulation
 	Clumping of particles in wastewater to settle out impurities, often induced by chemicals such as lime, alum, and iron salts. 		
Coal Cleaning Technology
 	A precombustion process by which coal is physically or chemically treated to remove some of its sulfur so as to reduce sulfur dioxide emissions. 		
Coal Gasification
 	Conversion of coal to a gaseous product by one of several available technologies. 		
Coastal Zone
 	Lands and waters adjacent to the coast that exert an influence on the uses of the sea and its ecology, or whose uses and ecology are affected by the sea. 		
Code of Federal Regulations
 	Document that codifies all rules of the executive departments and agencies of the federal government. It is divided into fifty volumes, known as titles. Title 40 of the CFR (referenced as 40 CFR) lists all environmental regulations. 	CFR 	
Coefficient of Haze
 	A measurement of visibility interference in the atmosphere. 	COH 	
Coffin
 			
Cogeneration
 	The consecutive generation of useful thermal and electric energy from the same fuel source. 		
Coke Oven
 	An industrial process which converts coal into coke, one of the basic materials used in blast furnaces for the conversion of iron ore into iron. 		
Cold Temperature CO
 	A standard for automobile emissions of carbon monoxide (CO) emissions to be met at a low temperature (i.e. 20 degrees Fahrenheit). Conventional automobile catalytic converters are not efficient in cold weather until they warm up. 		
Coliform Index
 	A rating of the purity of water based on a count of fecal bacteria. 		
Coliform Organism
 	Microorganisms found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially adverse contamination by pathogens. 		
Collector
 	Public or private hauler that collects nonhazardous waste and recyclable materials from residential, commercial, institutional and industrial sources. 		
Collector Sewers
 	Pipes used to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility. 		
Colloids
 	Very small, finely divided solids (that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. 		
Combined Sewer Overflows
 	Discharge of a mixture of storm water and domestic waste when the flow capacity of a sewer system is exceeded during rainstorms. 		
Combined Sewers
 	A sewer system that carries both sewage and storm-water runoff. Normally, its entire flow goes to a waste treatment plant, but during a heavy storm, the volume of water may be so great as to cause overflows of untreated mixtures of storm water and sewage into receiving waters. Storm-water runoff may also carry toxic chemicals from industrial areas or streets into the sewer system. 		
Combustion
 	Definition 1: Burning, or rapid oxidation, accompanied by release of energy in the form of heat and light. 
Definition 2: Refers to controlled burning of waste, in which heat chemically alters organic compounds, converting into stable inorganics such as carbon dioxide and water. 
		
Combustion Chamber
 	The actual compartment where waste is burned in an incinerator. 		
Combustion Product
 	Substance produced during the burning or oxidation of a material. 		
Command-and-Control Regulations
 	Specific requirements prescribing how to comply with specific standards defining acceptable levels of pollution. 		
Command Post
 	Facility located at a safe distance upwind from an accident site, where the on-scene coordinator, responders, and technical representatives make response decisions, deploy manpower and equipment, maintain liaison with news media, and handle communications. 		
Comment Period
 	Time provided for the public to review and comment on a proposed EPA action or rulemaking after publication in the Federal Register. 		
Commercial Waste
 	All solid waste emanating from business establishments such as stores, markets, office buildings, restaurants, shopping centers, and theaters. 		
Commercial Waste Management Facility
 	A treatment, storage, disposal, or transfer facility which accepts waste from a variety of sources, as compared to a private facility which normally manages a limited waste stream generated by its own operations. 		
Commingled Recyclables
 	Mixed recyclables that are collected together. 		
Comminuter
 	A machine that shreds or pulverizes solids to make waste treatment easier. 		
Comminution
 	Mechanical shredding or pulverizing of waste. Used in both solid waste management and wastewater treatment. 		
Common Sense Initiative
 	Voluntary program to simplify environmental regulation to achieve cleaner, cheaper, smarter results, starting with six major industry sectors. (See: Pollution Prevention (2)) 		
Community
 	In ecology, an assemblage of populations of different species within a specified location in space and time. Sometimes, a particular subgrouping may be specified, such as the fish community in a lake or the soil arthropod community in a forest. 		
Community Relations
 	The EPA effort to establish two-way communication with the public to create understanding of EPA programs and related actions, to ensure public input into decision-making processes related to affected communities, and to make certain that the Agency is aware of and responsive to public concerns. Specific community relations activities are required in relation to Superfund remedial actions. 		
Community Water System
 	A public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. 		
Compact Fluorescent Lamp
 	Small fluorescent lamps used as more efficient alternatives to incandescent lighting. 	CFL 	
Compaction
 	Reduction of the bulk of solid waste by rolling and tamping. 		
Comparative Risk Assessment
 	Process that generally uses the judgment of experts to predict effects and set priorities among a wide range of environmental problems. 		
Complete Treatment
 	A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. 		
Compliance Coal
 	Any coal that emits less than 1.2 pounds of sulfur dioxide per million Btu when burned. 		
Compliance Coating
 	A coating whose volatile organic compound content does not exceed that allowed by regulation. 		
Compliance Cycle
 	The 9-year calendar year cycle, beginning January 1, 1993, during which public water systems must monitor. Each cycle consists of three 3-year compliance periods. 		
Compliance Monitoring
 	Collection and evaluation of data, including self-monitoring reports, and verification to show whether pollutant concentrations and loads contained in permitted discharges are in compliance with the limits and conditions specified in the permit. 		
Compliance Schedule
 	A negotiated agreement between a pollution source and a government agency that specifies dates and procedures by which a source will reduce emissions and, thereby, comply with a regulation. 		
Composite Sample
 	A series of water samples taken over a given period of time and weighted by flow rate. 		
Compost
 	A humus or soil-like material created from aerobic, microbial decomposition of organic materials such as food scraps, yard trimmings, and manure. 		
Composting
 	The controlled biological decomposition of organic material in the presence of air to form a humus-like material. Controlled methods of composting include mechanical mixing and aerating, ventilating the materials by dropping them through a vertical series of aerated chambers, or placing the compost in piles out in the open air and mixing it or turning it periodically. 		
Composting Facilities
 	Definition 1: An offsite facility where the organic component of municipal solid waste is decomposed under controlled conditions. 
Definition 2: An aerobic process in which organic materials are ground or shredded and then decomposed to humus in windrow piles or in mechanical digesters, drums, or similar enclosures. 
		
Compressed Natural Gas
 	An alternative fuel for motor vehicles; considered one of the cleanest because of low hydrocarbon emissions and its vapors are relatively non-ozone producing. However, vehicles fueled with CNG do emit a significant quantity of nitrogen oxides. 	CNG 	
Concentration
 	The relative amount of a substance mixed with another substance. An example is five ppm of carbon monoxide in air or 1 mg/l of iron in water. 		
Condensate
 	Definition 1: Liquid formed when warm landfill gas cools as it travels through a collection system. 
Definition 2: Water created by cooling steam or water vapor. 
		
Condensate Return System
 	System that returns the heated water condensing within steam piping to the boiler and thus saves energy. 		
Conditional Registration
 	Under special circumstances, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) permits registration of pesticide products that is "conditional" upon the submission of additional data. These special circumstances include a finding by the EPA Administrator that a new product or use of an existing pesticide will not significantly increase the risk of unreasonable adverse effects. A product containing a new (previously unregistered) active ingredient may be conditionally registered only if the Administrator finds that such conditional registration is in the public interest, that a reasonable time for conducting the additional studies has not elapsed, and the use of the pesticide for the period of conditional registration will not present an unreasonable risk. 		
Conditionally Exempt Generators
 	Persons or enterprises which produce less than 220 pounds of hazardous waste per month. Exempt from most regulation, they are required merely to determine whether their waste is hazardous, notify appropriate state or local agencies, and ship it by an authorized transporter to a permitted facility for proper disposal. 	CE 	
Conductance
 	A rapid method of estimating the dissolved solids content of water supply by determining the capacity of a water sample to carry an electrical current. Conductivity is a measure of the ability of a solution to carry and electrical current. 		
Conductivity
 	A measure of the ability of a solution to carry an electrical current. 		
Cone of Depression
 	A depression in the water table that develops around a pumped well. 		
Cone of Influence
 	The depression, roughly conical in shape, produced in a water table by the pumping of water from a well. 		
Cone Penetrometer Testing
 	A direct push system used to measure lithology based on soil penetration resistance. Sensors in the tip of the cone of the DP rod measure tip resistance and side-wall friction, transmitting electrical signals to digital processing equipment on the ground surface. 	CPT 	
Confidential Business Information
 	Material that contains trade secrets or commercial or financial information that has been claimed as confidential by its source (e.g. a pesticide or new chemical formulation registrant). EPA has special procedures for handling such information. 	CBI 	
Confidential Statement of Formula
 	A list of the ingredients in a new pesticide or chemical formulation. The list is submitted at the time for application for registration or change in formulation. 	CSF 	
Confined Aquifer
 	An aquifer in which ground water is confined under pressure which is significantly greater than atmospheric pressure. 		
Confluent Growth
 	A continuous bacterial growth covering all or part of the filtration area of a membrane filter in which the bacteria colonies are not discrete. 		
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, when possible, human and natural resources. The use, protection, and improvement of natural resources according to principles that will ensure their highest economic or social benefits. 		
Conservation Easement
 	Easement restricting a landowner to land uses that are compatible with long-term conservation and environmental values. 		
Constituent of Concern
 	Specific chemicals that are identified for evaluation in the site assessment process. 		
Constituents of Concern
 			
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. 		
Construction Ban
 	If, under the Clean Air Act, EPA disapproves an area's planning requirements for correcting nonattainment, EPA can ban the construction or modification of any major stationary source of the pollutant for which the area is in nonattainment. 		
Consumptive Water Use
 	Water removed from available supplies without return to a water resources system, e.g. water used in manufacturing, agriculture, and food preparation. 		
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 effect on air, water, or soil. 		
Contamination
 	Introduction into water, air, and soil of microorganisms, chemicals, toxic substances, wastes, or wastewater in a concentration that makes the medium unfit for its next intended use. Also applies to surfaces of objects, buildings, and various household and agricultural use products. 		
Contamination Source Inventory
 	An inventory of contaminant sources within delineated State Water-Protection Areas. Targets likely sources for further investigation. 		
Contingency Plan
 	A document setting out an organized, planned, and coordinated course of action to be followed in case of a fire, explosion, or other accident that releases toxic chemicals, hazardous waste, or radioactive materials that threaten human health or the environment. 		
Continuous Discharge
 	A routine release to the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc. 		
Continuous Sample
 	A flow of water, waste or other material from a particular place in a plant to the location where samples are collected for testing. May be used to obtain grab or composite samples. 		
Contour Plowing
 	Soil tilling method that follows the shape of the land to discourage erosion. 		
Contour Strip Farming
 	A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosion-resistant forage crops. 		
Contract Labs
 	Laboratories under contract to EPA, which analyze samples taken from waste, soil, air, and water or carry out research projects. 		
Control Technique Guidelines
 	EPA documents designed to assist state and local pollution authorities to achieve and maintain air quality standards for certain sources (e.g. organic emissions from solvent metal cleaning known as degreasing) through reasonably available control technologies (RACT). 	CTG 	
Controlled Reaction
 	A chemical reaction under temperature and pressure conditions maintained within safe limits to produce a desired product or process. 		
Conventional Filtration
 			
Conventional Pollutants
 	Statutorily listed pollutants understood well by scientists. These may be in the form of organic waste, sediment, acid, bacteria, viruses, nutrients, oil and grease, or heat. 		
Conventional Site Assessment
 	Assessment in which most of the sample analysis and interpretation of data is completed off-site; process usually requires repeated mobilization of equipment and staff in order to fully determine the extent of contamination. 		
Conventional Systems
 	Systems that have been traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant prior to discharge to surface waters. 		
Conventional Tilling
 	Tillage operations considered standard for a specific location and crop and that tend to bury the crop residues; usually considered as a base for determining the cost effectiveness of control practices. 		
Conveyance Loss
 	Water loss in pipes, channels, conduits, ditches by leakage or evaporation. 		
Cooling Electricity Use
 	Amount of electricity used to meet the building cooling load. 		
Cooling Tower
 	Definition 1: A structure that helps remove heat from water used as a coolant; e.g., in electric power generating plants. 
Definition 2: Device which dissipates the heat from water-cooled systems by spraying the water through streams of rapidly moving air. 
		
Cooperative Agreement
 	An assistance agreement whereby EPA transfers money, property, services or anything of value to a state, university, non-profit, or not-for-profit organization for the accomplishment of authorized activities or tasks. 		
Core
 	The uranium-containing heart of a nuclear reactor, where energy is released. 		
Core Program Cooperative Agreement
 	An assistance agreement whereby EPA supports states or tribal governments with funds to help defray the cost of non-item-specific administrative and training activities. 		
Corrective Action
 	EPA can require treatment, storage and disposal (TSDF) facilities handling hazardous waste to undertake corrective actions to clean up spills resulting from failure to follow hazardous waste management procedures or other mistakes. The process includes cleanup procedures designed to guide TSDFs toward in spills. 		
Corrosion
 	The dissolution and wearing away of metal caused by a chemical reaction such as between water and the pipes, chemicals touching a metal surface, or contact between two metals. 		
Corrosive
 	A chemical agent that reacts with the surface of a material causing it to deteriorate or wear away. 		
Cost/Benefit Analysis
 	A quantitative evaluation of the costs which would have incurred by implementing an environmental regulation versus the overall benefits to society of the proposed action. 		
Cost-Effective Alternative
 	An alternative control or corrective method identified after analysis as being the best available in terms of reliability, performance, and cost. Although costs are one important consideration, regulatory and compliance analysis does not require EPA to choose the least expensive alternative. For example, when selecting or approving a method for cleaning up a Superfund site, the Agency balances costs with the long-term effectiveness of the methods proposed and the potential danger posed by the site. 		
Cost Recovery
 	A legal process by which potentially responsible parties who contributed to contamination at a Superfund site can be required to reimburse the Trust Fund for money spent during any cleanup actions by the federal government. 		
Cost Sharing
 	A publicly financed program through which society, as a beneficiary of environmental protection, shares part of the cost of pollution control with those who must actually install the controls. In Superfund, for example, the government may pay part of the cost of a cleanup action with those responsible for the pollution paying the major share. 		
Cover Crop
 	A crop that provides temporary protection for delicate seedlings and/or provides a cover canopy for seasonal soil protection and improvement between normal crop production periods. 		
Cover Material
 	Soil used to cover compacted solid waste in a sanitary landfill. 		
Cradle-to-Grave 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). 		
Criteria
 	Descriptive factors taken into account by EPA in setting standards for various pollutants. These factors are used to determine limits on allowable concentration levels, and to limit the number of violations per year. When issued by EPA, the criteria provide guidance to the states on how to establish their standards. 		
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. 		
Critical Effect
 	The first adverse effect, or its known precursor, that occurs as a dose rate increases. Designation is based on evaluation of overall database. 		
Crop Consumptive Use
 	The amount of water transpired during plant growth plus what evaporated from the soil surface and foliage in the crop area. 		
Crop Rotation
 	Planting a succession of different crops on the same land as opposed to planting the same crop time after time. 		
Cross-Connection
 	Any actual or potential connection between a drinking water system and an unapproved water supply or other source of contamination. 		
Cross Contamination
 	The movement of underground contaminants from one level or area to another due to invasive subsurface activities. 		
Crumb Rubber
 	Ground rubber fragments the size of sand or silt used in rubber or plastic products, or processed further into reclaimed rubber or asphalt products. 		
Cryptosporidium
 	A protozoan microbe associated with the disease cryptosporidiosis in man. The disease can be transmitted through ingestion of drinking water, person-to-person contact, or other pathways, and can cause acute diarrhea, abdominal pain, vomiting, fever, and can be fatal as it was in the Milwaukee episode. 		
Cubic Feet Per Minute
 	A measure of the volume of a substance flowing through air within a fixed period of time. With regard to indoor air, refers to the amount of air, in cubic feet, that is exchanged with outdoor air in a minute's time; i.e. the air exchange rate. 	CFM 	
Cullet
 	Crushed glass. 		
Cultural Eutrophication
 	Increasing rate at which water bodies "die" by pollution from human activities. 		
Cultures and Stocks
 	Infectious agents and associated biologicals including cultures from medical and pathological laboratories; cultures and stocks of infectious agents from research and industrial laboratories; waste from the production of biologicals; discarded live and attenuated vaccines; and culture dishes and devices used to transfer, inoculate, and mix cultures. 		
Cumulative Ecological Risk Assessment
 	Consideration of the total ecological risk from multiple stressors to a given eco-zone. 		
Cumulative Exposure
 	The sum of exposures of an organism to a pollutant over a period of time. 		
Cumulative Working Level Months
 	The sum of lifetime exposure to radon working levels expressed in total working level months. 	CWLM 	
Curb Stop
 	A water service shutoff valve located in a water service pipe near the curb and between the water main and the building. 		
Curbside Collection
 	Method of collecting recyclable materials at homes, community districts or businesses. 		
Cutie-Pie
 	An instrument used to measure radiation levels. 		
Cuttings
 	Spoils left by conventional drilling with hollow stem auger or rotary drilling equipment. 		
Cyclone Collector
 	A device that uses centrifugal force to remove large particles from polluted air. 		
Data Call-In
 	A part of the Office of Pesticide Programs (OPP) process of developing key required test data, especially on the long-term, chronic effects of existing pesticides, in advance of scheduled Registration Standard reviews. Data Call-In from manufacturers is an adjunct of the Registration Standards program intended to expedite re-registration. 		
Data Quality Objectives
 	Qualitative and quantitative statements of the overall level of uncertainty that a decision-maker will accept in results or decisions based on environmental data. They provide the statistical framework for planning and managing environmental data operations consistent with user's needs. 	DQOs 	
Day Tank
 			
Dead End
 	The end of a water main which is not connected to other parts of the distribution system. 		
Deadmen
 	Anchors drilled or cemented into the ground to provide additional reactive mass for DP sampling rigs. 		
Deaerating Tank
 			
Decant
 	To draw off the upper layer of liquid after the heaviest material (a solid or another liquid) has settled. 		
Decay Products
 	Degraded radioactive materials, often referred to as "daughters" or "progeny"; radon decay products of most concern from a public health standpoint are polonium-214 and polonium-218. 		
Dechlorination
 	Removal of chlorine from a substance. 		
Decomposition
 	The breakdown of matter by bacteria and fungi, changing the chemical makeup and physical appearance of materials. 		
Decontamination
 	Removal of harmful substances such as noxious chemicals, harmful bacteria or other organisms, or radioactive material from exposed individuals, rooms and furnishings in buildings, or the exterior environment. 		
Deep-Well Injection
 	Deposition of raw or treated, filtered hazardous waste by pumping it into deep wells, where it is contained in the pores of permeable subsurface rock. 		
Deflocculating Agent
 	A material added to a suspension to prevent settling. 		
Deflouridation
 	The removal of excess fluoride in drinking water to prevent the staining of teeth. 		
Defoliant
 	An herbicide that removes leaves from trees and growing plants. 		
Degasification
 	A water treatment that removes dissolved gases from the water. 		
Degree-Day
 	A rough measure used to estimate the amount of heating required in a given area; is defined as the difference between the mean daily temperature and 65 degrees Fahrenheit. Degree-days are also calculated to estimate cooling requirements. 		
Delegated State
 	A state (or other governmental entity such as a tribal government) that has received authority to administer an environmental regulatory program in lieu of a federal counterpart. As used in connection with NPDES, UIC, and PWS programs, the term does not connote any transfer of federal authority to a state. 		
Delist
 	Use of the petition process to have a facility's toxic designation rescinded. 		
Demand-side Waste Management
 	Prices whereby consumers use purchasing decisions to communicate to product manufacturers that they prefer environmentally sound products packaged with the least amount of waste, made from recycled or recyclable materials, and containing no hazardous substances. 		
Demineralization
 	A treatment process that removes dissolved minerals from water. 		
Denitrification
 	The biological reduction of nitrate to nitrogen gas by denitrifying bacteria in soil. 		
Dense Non-Aqueous Phase Liquid
 	Non-aqueous phase liquids such as chlorinated hydrocarbon solvents or petroleum fractions with a specific gravity greater than 1.0 that sink through the water column until they reach a confining layer. Because they are at the bottom of aquifers instead of floating on the water table, typical monitoring wells do not indicate their presence. 	DNAPL 	
Density
 	A measure of how heavy a specific volume of a solid, liquid, or gas is in comparison to water. depending on the chemical. 		
Depletion Curve
 	In hydraulics, a graphical representation of water depletion from storage-stream channels, surface soil, and groundwater. A depletion curve can be drawn for base flow, direct runoff, or total flow. 		
Depressurization
 	A condition that occurs when the air pressure inside a structure is lower that the air pressure outdoors. Depressurization can occur when household appliances such as fireplaces or furnaces, that consume or exhaust house air, are not supplied with enough makeup air. Radon may be drawn into a house more rapidly under depressurized conditions. 		
Dermal Absorption
 	Process by which a chemical penetrates the skin and enters the body as an internal dose. 		
Dermal Exposure
 	Contact between a chemical and the skin. 		
Dermal Penetration
 			
Dermal Toxicity
 	The ability of a pesticide or toxic chemical to poison people or animals by contact with the skin. 		
DES
 	A synthetic estrogen, diethylstilbestrol is used as a growth stimulant in food animals. Residues in meat are thought to be carcinogenic. 		
Desalination
 	Definition 1: Removing salts from ocean or brackish water by using various technologies. 
Definition 2: Removal of salts from soil by artificial means, usually leaching. 
		
Desalinization
 			
Desiccant
 	A chemical agent that absorbs moisture; some desiccants are capable of drying out plants or insects, causing death. 		
Design Capacity
 	The average daily flow that a treatment plant or other facility is designed to accommodate. 		
Design Value
 	The monitored reading used by EPA to determine an area's air quality status; e.g., for ozone, the fourth highest reading measured over the most recent three years is the design value. 		
Designated Pollutant
 	An air pollutant which is neither a criteria nor hazardous pollutant, as described in the Clean Air Act, but for which new source performance standards exist. The Clean Air Act does require states to control these pollutants, which include acid mist, total reduced sulfur (TRS), and fluorides. 		
Designated Uses
 	Those water uses identified in state water quality standards that must be achieved and maintained as required under the Clean Water Act. Uses can include cold water fisheries, public water supply, and irrigation. 		
Designer Bugs
 	Popular term for microbes developed through biotechnology that can degrade specific toxic chemicals at their source in toxic waste dumps or in ground water. 		
Destination Facility
 	The facility to which regulated medical waste is shipped for treatment and destruction, incineration, and/or disposal. 		
Destratification
 	Vertical mixing within a lake or reservoir to totally or partially eliminate separate layers of temperature, plant, or animal life. 		
Destroyed Medical Waste
 	Regulated medical waste that has been ruined, torn apart, or mutilated through thermal treatment, melting, shredding, grinding, tearing, or breaking, so that it is no longer generally recognized as medical waste, but has not yet been treated (excludes compacted regulated medical waste). 		
Destruction and Removal Efficiency
 	A percentage that represents the number of molecules of a compound removed or destroyed in an incinerator relative to the number of molecules entering the system (e.g. a DRE of 99.99 percent means that 9,999 molecules are destroyed for every 10,000 that enter; 99.99 percent is known as "four nines." For some pollutants, the RCRA removal requirement may be as stringent as "six nines"). 	DRE 	
Destruction Facility
 	A facility that destroys regulated medical waste. 		
Desulfurization
 	Removal of sulfur from fossil fuels to reduce pollution. 		
Detectable Leak Rate
 	The smallest leak (from a storage tank), expressed in terms of gallons- or liters-per-hour, that a test can reliably discern with a certain probability of detection or false alarm. 		
Detection Criterion
 	A predetermined rule to ascertain whether a tank is leaking or not. Most volumetric tests use a threshold value as the detection criterion. 		
Detection Limit
 	The lowest concentration of a chemical that can reliably be distinguished from a zero concentration. 		
Detention Time
 	Definition 1: The theoretical calculated time required for a small amount of water to pass through a tank at a given rate of flow. 
Definition 2: The actual time that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber. 
Definition 3: In storage reservoirs, the length of time water will be held before being used. 
		
Detergent
 	Synthetic washing agent that helps to remove dirt and oil. Some contain compounds which kill useful bacteria and encourage algae growth when they are in wastewater that reaches receiving waters. 		
Development Effects
 	Adverse effects such as altered growth, structural abnormality, functional deficiency, or death observed in a developing organism. 		
Dewater
 	Definition 1: Remove or separate a portion of the water in a sludge or slurry to dry the sludge so it can be handled and disposed of. 
Definition 2: Remove or drain the water from a tank or trench. 
		
Diatomaceous Earth
 	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. 		
Diatomite
 			
Diazinon
 	An insecticide. In 1986, EPA banned its use on open areas such as sod farms and golf courses because it posed a danger to migratory birds. The ban did not apply to agricultural, home lawn or commercial establishment uses. 		
Dibenzofurans
 	A group of organic compounds, some of which are toxic. 		
Dichloro-Diphenyl-Trichloroethane
 		DDT 	
Dicofol
 	A pesticide used on citrus fruits. 		
Diffused Air
 	A type of aeration that forces oxygen into sewage by pumping air through perforated pipes inside a holding tank. 		
Diffusion
 	The movement of suspended or dissolved particles (or molecules) from a more concentrated to a less concentrated area. The process tends to distribute the particles or molecules more uniformly. 		
Digester
 	In wastewater treatment, a closed tank; in solid-waste conversion, a unit in which bacterial action is induced and accelerated in order to break down organic matter and establish the proper carbon to nitrogen ratio. 		
Digestion
 	The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants. 		
Dike
 	A low wall that can act as a barrier to prevent a spill from spreading. 		
Diluent
 	Any liquid or solid material used to dilute or carry an active ingredient. 		
Dilution Ratio
 	The relationship between the volume of water in a stream and the volume of incoming water. It affects the ability of the stream to assimilate waste. 		
Dimictic
 	Lakes and reservoirs that freeze over and normally go through two stratifications and two mixing cycles a year. 		
Dinocap
 	A fungicide used primarily by apple growers to control summer diseases. EPA proposed restrictions on its use in 1986 when laboratory tests found it caused birth defects in rabbits. 		
Dinoseb
 	A herbicide that is also used as a fungicide and insecticide. It was banned by EPA in 1986 because it posed the risk of birth defects and sterility. 		
Dioxin
 	Any of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity as contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic anthropogenic (man-made) compounds. 		
Direct Discharger
 	A municipal or industrial facility which introduces pollution through a defined conveyance or system such as outlet pipes; a point source. 		
Direct Drive
 			
Direct Filtration
 	A method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. Sedimentation is not uses. 		
Direct Push
 	Technology used for performing subsurface investigations by driving, pushing, and/or vibrating small-diameter hollow steel rods into the ground. 		
Direct Runoff
 	Water that flows over the ground surface or through the ground directly into streams, rivers, and lakes. 		
Discharge
 	Flow of surface water in a stream or canal or the outflow of ground water from a flowing artesian well, ditch, or spring. Can also apply to discharge of liquid effluent from a facility or to chemical emissions into the air through designated venting mechanisms. 		
Disinfectant
 	A chemical or physical process that kills pathogenic organisms in water, air, or on surfaces. Chlorine is often used to disinfect sewage treatment effluent, water supplies, wells, and swimming pools. 		
Disinfectant By-Product
 	A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply; a chemical byproduct of the disinfection process. 		
Disinfectant Time
 	The time it takes water to move from the point of disinfectant application (or the previous point of residual disinfectant measurement) to a point before or at the point where the residual disinfectant is measured. In pipelines, the time is calculated by dividing the internal volume of the pipe by the maximum hourly flow rate; within mixing basins and storage reservoirs it is determined by tracer studies of an equivalent demonstration. 		
Dispersant
 	A chemical agent used to break up concentrations of organic material such as spilled oil. 		
Displacement Savings
 	Saving realized by displacing purchases of natural gas or electricity from a local utility by using landfill gas for power and heat. 		
Disposables
 	Consumer products, other items, and packaging used once or a few times and discarded. 		
Disposal
 	Final placement or destruction of toxic, radioactive, or other wastes; surplus or banned pesticides or other chemicals; polluted soils; and drums containing hazardous materials from removal actions or accidental releases. Disposal may be accomplished through use of approved secure landfills, surface impoundments, land farming, deep-well injection, ocean dumping, or incineration. 		
Disposal Facilities
 	Repositories for solid waste, including landfills and combustors intended for permanent containment or destruction of waste materials. Excludes transfer stations and composting facilities. 		
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. 	DO 	
Dissolved Solids
 	Disintegrated organic and inorganic material in water. Excessive amounts make water unfit to drink or use in industrial processes. 		
Distillation
 	The act of purifying liquids through boiling, so that the steam or gaseous vapors condense to a pure liquid. Pollutants and contaminants may remain in a concentrated residue. 		
Disturbance
 	Any event or series of events that disrupt ecosystem, community, or population structure and alters the physical environment. 		
Diversion
 	Definition 1: Use of part of a stream flow as water supply. 
Definition 2: A channel with a supporting ridge on the lower side constructed across a slope to divert water at a non-erosive velocity to sites where it can be used and disposed of. 
		
Diversion Rate
 	The percentage of waste materials diverted from traditional disposal such as landfilling or incineration to be recycled, composted, or re-used. 		
DNA Hybridization
 	Use of a segment of DNA, called a DNA probe, to identify its complementary DNA; used to detect specific genes. 		
Dobson Unit
 	Units of ozone level measurement. measurement of ozone levels. If, for example, 100 DU of ozone were brought to the earth's surface they would form a layer one millimeter thick. Ozone levels vary geographically, even in the absence of ozone depletion. 	DU 	
Domestic Application
 	Pesticide application in and around houses, office buildings, motels, and other living or working areas. 		
Domestic Waste
 			
Dosage
 	Definition 1: The actual quantity of a chemical administered to an organism or to which it is exposed. 
Definition 2: The amount of a substance that reaches a specific tissue (e.g. the liver). 
Definition 3: The amount of a substance available for interaction with metabolic processes after crossing the outer boundary of an organism. 
		
Dose
 			
Dose Equivalent
 	The product of the absorbed dose from ionizing radiation and such factors as account for biological differences due to the type of radiation and its distribution in the body in the body. 		
Dose Rate
 	In exposure assessment, dose per time unit (e.g. mg/day), sometimes also called dosage. 		
Dose Response
 	Shifts in toxicological responses of an individual (such as alterations in severity) or populations (such as alterations in incidence) that are related to changes in the dose of any given substance. 		
Dose-Response Assessment
 	Definition 1: Estimating the potency of a chemical. 
Definition 2: In exposure assessment, the process of determining the relationship between the dose of a stressor and a specific biological response. 
Definition 3: Evaluating the quantitative relationship between dose and toxicological responses. 
		
Dose Response Curve
 	Graphical representation of the relationship between the dose of a stressor and the biological response thereto. 		
Dose-Response Relationship
 	The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease produced. 		
Dosimeter
 	An instrument to measure dosage; many so-called dosimeters actually measure exposure rather than dosage. Dosimetry is the process or technology of measuring and/or estimating dosage. 		
DOT Reportable Quantity
 	The quantity of a substance specified in a U.S. Department of Transportation regulation that triggers labeling, packaging and other requirements related to shipping such substances. 		
Downgradient
 	The direction that groundwater flows; similar to "downstream" for surface water. 		
Downstream Processors
 	Industries dependent on crop production (e.g. canneries and food processors). 		
DP Hole
 	Hole in the ground made with DP equipment. 		
Draft
 	Definition 1: The act of drawing or removing water from a tank or reservoir. 
Definition 2: The water which is drawn or removed. 
		
Draft Permit
 	A preliminary permit drafted and published by EPA; subject to public review and comment before final action on the application. 		
Drainage
 	Improving the productivity of agricultural land by removing excess water from the soil by such means as ditches or subsurface drainage tiles. 		
Drainage Basin
 	The area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel. 		
Drainage Well
 	A well drilled to carry excess water off agricultural fields. Because they act as a funnel from the surface to the groundwater below. Drainage wells can contribute to groundwater pollution. 		
Drawdown
 	Definition 1: The drop in the water table or level of water in the ground when water is being pumped from a well. 
Definition 2: The amount of water used from a tank or reservoir. 
Definition 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. 		
Drilling Fluid
 	Fluid used to lubricate the bit and convey drill cuttings to the surface with rotary drilling equipment. Usually composed of bentonite slurry or muddy water. Can become contaminated, leading to cross contamination, and may require special disposal. Not used with DP methods 		
Drinking Water Equivalent Level
 	Protective level of exposure related to potentially non-carcinogenic effects of chemicals that are also known to cause cancer. 		
Drinking Water State Revolving Fund
 	The Fund provides capitalization grants to states to develop drinking water revolving loan funds to help finance system infrastructure improvements, assure source-water protection, enhance operation and management of drinking-water systems, and otherwise promote local water-system compliance and protection of public health. 		
Drive Casing
 	Heavy duty steel casing driven along with the sampling tool in cased DP systems. Keeps the hole open between sampling runs and is not removed until last sample has been collected. 		
Drive Point
 			
Drive Point Profiler
 	An exposed groundwater DP system used to collect multiple depth-discrete groundwater samples. Ports in the tip of the probe connect to an internal stainless steel or teflon tube that extends to the surface. Samples are collected via suction or airlift methods. Deionized water is pumped down through the ports to prevent plugging while driving the tool to the next sampling depth. 		
Drop-off
 	Recyclable materials collection method in which individuals bring them to a designated collection site. 		
Dual-Phase Extraction
 	Active withdrawal of both liquid and gas phases from a well usually involving the use of a vacuum pump. 		
Dump
 	A site used to dispose of solid waste without environmental controls. 		
Duplicate
 	A second aliquot or sample that is treated the same as the original sample in order to determine the precision of the analytical method. 		
Dustfall Jar
 	An open container used to collect large particles from the air for measurement and analysis. 		
Dynamometer
 	A device used to place a load on an engine and measure its performance. 		
Dystrophic Lakes
 	Acidic, shallow bodies of water that contain much humus and/or other organic matter; contain many plants but few fish. 		
Ecological Entity
 	In ecological risk assessment, a general term referring to a species, a group of species, an ecosystem function or characteristic, or a specific habitat or biome. 		
Ecological Exposure
 	Exposure of a non-human organism to a stressor. 		
Ecological Impact
 	The effect that a man-caused or natural activity has on living organisms and their non-living (abiotic) environment. 		
Ecological Indicator
 	A characteristic of an ecosystem that is related to, or derived from, a measure of biotic or abiotic variable, that can provide quantitative information on ecological structure and function. An indicator can contribute to a measure of integrity and sustainability. 		
Ecological Integrity
 	A living system exhibits integrity if, when subjected to disturbance, it sustains and organizes self-correcting ability to recover toward a biomass end-state that is normal for that system. End-states other than the pristine or naturally whole may be accepted as normal and good. 		
Ecological Risk
 			
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 dose-response assessments, and risk characterization. 		
Ecological Sustainability
 	Maintenance of ecosystem components and functions for future generations. 		
Ecology
 	The relationship of living things to one another and their environment, or the study of such relationships. 		
Economic Poisons
 	Chemicals used to control pests and to defoliate cash crops such as cotton. 		
Ecosphere
 	The "bio-bubble" that contains life on earth, in surface waters, and in the air. 		
Ecosystem
 	The interacting system of a biological community and its non-living environmental surroundings. 		
Ecosystem Structure
 	Attributes related to the instantaneous physical state of an ecosystem; examples include species population density, species richness or evenness, and standing crop biomass. 		
Ecotone
 	A habitat created by the juxtaposition of distinctly different habitats; an edge habitat; or an ecological zone or boundary where two or more ecosystems meet. 		
Effluent
 	Wastewater--treated or untreated--that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters. 		
Effluent Guidelines
 	Technical EPA documents which set effluent limitations for given industries and pollutants. 		
Effluent Limitation
 	Restrictions established by a state or EPA on quantities, rates, and concentrations in wastewater discharges. 		
Effluent Standard
 			
Ejector
 	A device used to disperse a chemical solution into water being treated. 		
Electrodialysis
 	A process that uses electrical current applied to permeable membranes to remove minerals from water. Often used to desalinize salty or brackish water. 		
Electromagnetic Geophysical Methods
 	Ways to measure subsurface conductivity via low-frequency electromagnetic induction. 		
Electrostatic Precipitator
 	A device that removes particles from a gas stream (smoke) after combustion occurs. The ESP imparts an electrical charge to the particles, causing them to adhere to metal plates inside the precipitator. Rapping on the plates causes the particles to fall into a hopper for disposal. 	ESP 	
Eligible Costs
 	The construction costs for wastewater treatment works upon which EPA grants are based. 		
EMAP Data
 	Environmental monitoring data collected under the auspices of the Environmental Monitoring and Assessment Program. All EMAP data share the common attribute of being of known quality, having been collected in the context of explicit data quality objectives (DQOs) and a consistent quality assurance program. 		
Emergency and Hazardous Chemical Inventory
 	An annual report by facilities having one or more extremely hazardous substances or hazardous chemicals above certain weight limits. 		
Emergency (Chemical)
 	A situation created by an accidental release or spill of hazardous chemicals that poses a threat to the safety of workers, residents, the environment, or property. 		
Emergency Episode
 			
Emergency Exemption
 	Provision in FIFRA under which EPA can grant temporary exemption to a state or another federal agency to allow the use of a pesticide product not registered for that particular use. Such actions involve unanticipated and/or severe pest problems where there is not time or interest by a manufacturer to register the product for that use. (Registrants cannot apply for such exemptions.) 		
Emergency Removal Action
 	Definition 1: Steps take to remove contaminated materials that pose imminent threats to local residents (e.g. removal of leaking drums or the excavation of explosive waste.) 
Definition 2: The state record of such removals. 
		
Emergency Response Values
 	Concentrations of chemicals, published by various groups, defining acceptable levels for short-term exposures in emergencies. 		
Emergency Suspension
 	Suspension of a pesticide product registration due to an imminent hazard. The action immediately halts distribution, sale, and sometimes actual use of the pesticide involved. 		
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 reductions. Generally, such provisions require that any emission growth from facilities under the restrictions be offset by equivalent reductions at other facilities under the same cap. 		
Emission Factor
 	The relationship between the amount of pollution produced and the amount of raw material processed. For example, an emission factor for a blast furnace making iron would be the number of pounds of particulates per ton of raw materials. 		
Emission Inventory
 	A listing, by source, of the amount of air pollutants discharged into the atmosphere of a community; used to establish emission standards. 		
Emission Standard
 	The maximum amount of air polluting discharge legally allowed from a single source, mobile or stationary. 		
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 emissions sources. This allows one source to increase emissions when another source reduces them, maintaining an overall constant emission level. Facilities that reduce emissions substantially may "bank" their "credits" or sell them to other facilities or industries. 		
Emulsifier
 	A chemical that aids in suspending one liquid in another. Usually an organic chemical in an aqueous solution. 		
Encapsulation
 	The treatment of asbestos-containing material with a liquid that covers the surface with a protective coating or embeds fibers in an adhesive matrix to prevent their release into the air. 		
Enclosure
 	Putting an airtight, impermeable, permanent barrier around asbestos-containing materials to prevent the release of asbestos fibers into the air. 		
End-of-the-pipe
 	Technologies such as scrubbers on smokestacks and catalytic convertors on automobile tailpipes that reduce emissions of pollutants after they have formed. 		
End-use Product
 	A pesticide formulation for field or other end use. The label has instructions for use or application to control pests or regulate plant growth. The term excludes products used to formulate other pesticide products. 		
End User
 	Consumer of products for the purpose of recycling. Excludes products for re-use or combustion for energy recovery. 		
Endangered Species
 	Animals, birds, fish, plants, or other living organisms threatened with extinction by anthropogenic (man-caused) or other natural changes in their environment. Requirements for declaring a species endangered are contained in the Endangered Species Act. 		
Endangerment Assessment
 	A study to determine the nature and extent of contamination at a site on the National Priorities List and the risks posed to public health or the environment. EPA or the state conducts the study when a legal action is to be taken to direct potentially responsible parties to clean up a site or pay for it. An endangerment assessment supplements a remedial investigation. 		
Endrin
 	A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies. 		
Energy Management System
 	A control system capable of monitoring environmental and system loads and adjusting HVAC operations accordingly in order to conserve energy while maintaining comfort. 		
Energy Recovery
 	Obtaining energy from waste through a variety of processes (e.g. combustion). 		
Enforceable Requirements
 	Conditions or limitations in permits issued under the Clean Water Act Section 402 or 404 that, if violated, could result in the issuance of a compliance order or initiation of a civil or criminal action under federal or applicable state laws. If a permit has not been issued, the term includes any requirement which, in the Regional Administrator's judgement, would be included in the permit when issued. Where no permit applies, the term includes any requirement which the RA determines is necessary for the best practical waste treatment technology to meet applicable criteria. 		
Enforcement
 	EPA, state, or local legal actions to obtain compliance with environmental laws, rules, regulations, or agreements and/or obtain penalties or criminal sanctions for violations. Enforcement procedures may vary, depending on the requirements of different environmental laws and related implementing regulations. Under CERCLA, for example, EPA will seek to require potentially responsible parties to clean up a Superfund site, or pay for the cleanup, whereas under the Clean Air Act the Agency may invoke sanctions against cities failing to meet ambient air quality standards that could prevent certain types of construction or federal funding. In other situations, if investigations by EPA and state agencies uncover willful violations, criminal trials and penalties are sought. 		
Enforcement Decision Document
 	A document that provides an explanation to the public of EPA's selection of the cleanup alternative at enforcement sites on the National Priorities List. Similar to a Record of Decision. 	EDD 	
Engineered Controls
 	Method of managing environmental and health risks by placing a barrier between the contamination and the rest of the site, thus limiting exposure pathways. 		
Enhanced Inspection and Maintenance
 	An improved automobile inspection and maintenance program--aimed at reducing automobile emissions---that contains, at a minimum, more vehicle types and model years, tighter inspection, and better management practices. It may also include annual computerized or centralized inspections, under-the-hood inspection--for signs of tampering with pollution control equipment--and increased repair waiver cost. 	Enhanced I&M 	
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. 		
Entrain
 	To trap bubbles in water either mechanically through turbulence or chemically through a reaction. 		
Environment
 	The sum of all external conditions affecting the life, development and survival of an organism. 		
Environmental Assessment
 	An environmental analysis prepared pursuant to the National Environmental Policy Act to determine whether a federal action would significantly affect the environment and thus require a more detailed environmental impact statement. 		
Environmental Audit
 	An independent assessment of the current status of a party's compliance with applicable environmental requirements or of a party's environmental compliance policies, practices, and controls. 		
Environmental Equity
 	Equal protection from environmental hazards for individuals, groups, or communities regardless of race, ethnicity, or economic status. This applies to the development, implementation, and enforcement of environmental laws, regulations, and policies, and implies that no population of people should be forced to shoulder a disproportionate share of negative environmental impacts of pollution or environmental hazard due to a lack of political or economic strength levels. 		
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 Fate
 	The destiny of a chemical or biological pollutant after release into the environment. 		
Environmental Fate Data
 	Data that characterize a pesticide's fate in the ecosystem, considering factors that foster its degradation (light, water, microbes), pathways and resultant products. 		
Environmental Impact Statement
 	A document required of federal agencies by the National Environmental Policy Act for major projects or legislative proposals significantly affecting the environment. A tool for decision making, it describes the positive and negative effects of the undertaking and cites alternative actions. 		
Environmental Indicator
 	A measurement, statistic or value that provides a proximate gauge or evidence of the effects of environmental management programs or of the state or condition of the environment. 		
Environmental Justice
 	The fair treatment of people of all races, cultures, incomes, and educational levels with respect to the development and enforcement of environmental laws, regulations, and policies. 		
Environmental Lien
 	A charge, security, or encumbrance on a property's title to secure payment of cost or debt arising from response actions, cleanup, or other remediation of hazardous substances or petroleum products. 		
Environmental Medium
 	A major environmental category that surrounds or contacts humans, animals, plants, and other organisms (e.g. surface water, ground water, soil or air) and through which chemicals or pollutants move. 		
Environmental Monitoring for Public Access and Community Tracking
 	Joint EPA, NOAA, and USGS program to provide timely and effective communication of environmental data and information through improved and updated technology solutions that support timely environmental monitoring reporting, interpreting, and use of the information for the benefit of the public. 		
Environmental Response Team
 	EPA experts located in Edison, N.J., and Cincinnati, OH, who can provide around-the-clock technical assistance to EPA regional offices and states during all types of hazardous waste site emergencies and spills of hazardous substances. 		
Environmental Risk
 	The potential for adverse effects on living organisms associated with pollution of the environment by effluents, emissions, wastes, or accidental chemical releases; energy use; or the depletion of natural resources. 		
Environmental Site Assessment
 	The process of determining whether contamination is present on a parcel of real property. 		
Environmental Sustainability
 	Long-term maintenance of ecosystem components and functions for future generations. 		
Environmental Tobacco Smoke
 	Mixture of smoke from the burning end of a cigarette, pipe, or cigar and smoke exhaled by the smoker. 		
EP Toxic
 			
EPA I.D. Number
 			
Epidemiology
 	Study of the distribution of disease, or other health-related states and events in human populations, as related to age, sex, occupation, ethnicity, and economic status in order to identify and alleviate health problems and promote better health. 		
Epilimnion
 	Upper waters of a thermally stratified lake subject to wind action. 		
Episode (Pollution)
 	An air pollution incident in a given area caused by a concentration of atmospheric pollutants under meteorological conditions that may result in a significant increase in illnesses or deaths. May also describe water pollution events or hazardous material spills. 		
Equilibrium
 	In relation to radiation, the state at which the radioactivity of consecutive elements within a radioactive series is neither increasing nor decreasing. 		
Equivalent Method
 	Any method of sampling and analyzing for air pollution which has been demonstrated to the EPA Administrator's satisfaction to be, under specific conditions, an acceptable alternative to normally used reference methods. 		
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. 		
Established Treatment Technologies
 	Technologies for which cost and performance data are readily available. 		
Estimated Environmental Concentration
 	The estimated pesticide concentration in an ecosystem. 		
Estuary
 	Region of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Such areas include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife. 		
Ethanol
 	An alternative automotive fuel derived from grain and corn; usually blended with gasoline to form gasohol. 		
Ethylene Dibromide
 	A chemical used as an agricultural fumigant and in certain industrial processes. Extremely toxic and found to be a carcinogen in laboratory animals, EDB has been banned for most agricultural uses in the United States. 	EDB 	
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 Ponds
 	Areas where sewage sludge is dumped and dried. 		
Evapotranspiration
 	The loss of water from the soil both by evaporation and by transpiration from the plants growing in the soil. 		
Exceedance
 	Violation of the pollutant levels permitted by environmental protection standards. 		
Exclusion
 	In the asbestos program, one of several situations that permit a Local Education Agency (LEA) to delete one or more of the items required by the Asbestos Hazard Emergency Response Act (AHERA); e.g. records of previous asbestos sample collection and analysis may be used by the accredited inspector in lieu of AHERA bulk sampling. 		
Exclusionary Ordinance
 	Zoning that excludes classes of persons or businesses from a particular neighborhood or area. 		
Exempt Solvent
 	Specific organic compounds not subject to requirements of regulation because they are deemed by EPA to be of negligible photochemical reactivity. 		
Exempted Aquifer
 	Underground bodies of water defined in the Underground Injection Control program as aquifers that are potential sources of drinking water though not being used as such, and thus exempted from regulations barring underground injection activities. 		
Exemption
 	A state (with primacy) may exempt a public water system from a requirement involving a Maximum Contaminant Level (MCL), treatment technique, or both, if the system cannot comply due to compelling economic or other factors, or because the system was in operation before the requirement or MCL was instituted; and the exemption will not create a public health risk. 		
Exotic Species
 	A species that is not indigenous to a region. 		
Experimental Use Permit
 	Definition 1: Obtained by manufacturers for testing new pesticides or uses thereof whenever they conduct experimental field studies to support registration on 10 acres or more of land or one acre or more of water. 
Definition 2: A permit granted by EPA that allows a producer to conduct tests of a new pesticide, product and/or use outside the laboratory. The testing is usually done on ten or more acres of land or water surface. 
		
Explosive Limits
 	The amounts of vapor in the air that form explosive mixtures; limits are expressed as lower and upper limits and give the range of vapor concentrations in air that will explode if an ignition source is present. 		
Exports
 	In solid waste program, municipal solid waste and recyclables transported outside the state or locality where they originated. 		
Exposure
 	The amount of radiation or pollutant present in a given environment that represents a potential health threat to living organisms. 		
Exposure Assessment
 	Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed. 		
Exposure Concentration
 	The concentration of a chemical or other pollutant representing a health threat in a given environment. 		
Exposure Indicator
 	A characteristic of the environment measured to provide evidence of the occurrence or magnitude of a response indicator's exposure to a chemical or biological stress. 		
Exposure Level
 	The amount (concentration) of a chemical at the absorptive surfaces of an organism. 		
Exposure Pathway
 	The path from sources of pollutants via, soil, water, or food to man and other species or settings. 		
Exposure-Response Relationship
 	The relationship between exposure level and the incidence of adverse effects. 		
Exposure Route
 	The way a chemical or pollutant enters an organism after contact; i.e. by ingestion, inhalation, or dermal absorption. 		
Extraction Procedure
 	Determining toxicity by a procedure which simulates leaching; if a certain concentration of a toxic substance can be leached from a waste, that waste is considered hazardous, i.e."EP Toxic." 		
Extraction Well
 	A discharge well used to remove groundwater or air. 		
Extremely Hazardous Substances
 	Any of 406 chemicals identified by EPA as toxic, and listed under SARA Title III. The list is subject to periodic revision. 		
Fabric Filter
 	A cloth device that catches dust particles from industrial emissions. 		
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. 		
Facility Emergency Coordinator
 	Representative of a facility covered by environmental law (e.g., a chemical plant) who participates in the emergency reporting process with the Local Emergency Planning Committee (LEPC). 		
Facultative Bacteria
 	Bacteria that can live under aerobic or anaerobic conditions. 		
Feasibility Study
 	Definition 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". 
Definition 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 mammals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens. 		
Federal Implementation Plan
 	Under current law, a federally implemented plan to achieve attainment of air quality standards, used when a state is unable to develop an adequate plan. 		
Federal Motor Vehicle Control Program
 	All federal actions aimed at controlling pollution from motor vehicles by such efforts as establishing and enforcing tailpipe and evaporative emission standards for new vehicles, testing methods development, and guidance to states operating inspection and maintenance programs. Federally designated area that is required to meet and maintain federal ambient air quality standards. May include nearby locations in the same state or nearby states that share common air pollution problems. 		
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. 		
Fen
 	A type of wetland that accumulates peat deposits. Fens are less acidic than bogs, deriving most of their water from groundwater rich in calcium and magnesium. 		
Ferrous Metals
 	Magnetic metals derived from iron or steel; products made from ferrous metals include appliances, furniture, containers, and packaging like steel drums and barrels. Recycled products include processing tin/steel cans, strapping, and metals from appliances into new products. 		
FIFRA Pesticide Ingredient
 	An ingredient of a pesticide that must be registered with EPA under the Federal Insecticide, Fungicide, and Rodenticide Act. Products making pesticide claims must register under FIFRA and may be subject to labeling and use requirements. 		
Fill
 	Man-made deposits of natural soils or rock products and waste materials. 		
Filling
 	Depositing dirt, mud or other materials into aquatic areas to create more dry land, usually for agricultural or commercial development purposes, often with ruinous ecological consequences. 		
Filter Strip
 	Strip or area of vegetation used for removing sediment, organic matter, and other pollutants from runoff and wastewater. 		
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 contain pathogens. 		
Financial Assurance for Closure
 	Documentation or proof that an owner or operator of a facility such as a landfill or other waste repository is capable of paying the projected costs of closing the facility and monitoring it afterwards as provided in RCRA regulations. 		
Finding of No Significant Impact
 	A document prepared by a federal agency showing why a proposed action would not have a significant impact on the environment and thus would not require preparation of an Environmental Impact Statement. An FNSI is based on the results of an environmental assessment. 		
Finished Water
 	Water is "finished" when it has passed through all the processes in a water treatment plant and is ready to be delivered to consumers. 		
First Draw
 	The water that comes out when a tap is first opened, likely to have the highest level of lead contamination from plumbing materials. 		
Fix a Sample
 	A sample is "fixed" in the field by adding chemicals that prevent water quality indicators of interest in the sample from changing before laboratory measurements are made. 		
Fixed-Location Monitoring
 	Sampling of an environmental or ambient medium for pollutant concentration at one location continuously or repeatedly. 		
Flammable
 	Any material that ignites easily and will burn rapidly. 		
Flare
 	A control device that burns hazardous materials to prevent their release into the environment; may operate continuously or intermittently, usually on top of a stack. 		
Flash Point
 	The lowest temperature at which evaporation of a substance produces sufficient vapor to form an ignitable mixture with air. 		
Floc
 	A clump of solids formed in sewage by biological or chemical action. 		
Flocculation
 	Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage. 		
Floodplain
 	The flat or nearly flat land along a river or stream or in a tidal area that is covered by water during a flood. 		
Floor Sweep
 	Capture of heavier-than-air gases that collect at floor level. 		
Flow Rate
 	The rate, expressed in gallons -or liters-per-hour, at which a fluid escapes from a hole or fissure in a tank. Such measurements are also made of liquid waste, effluent, and surface water movement. 		
Flowable
 	Pesticide and other formulations in which the active ingredients are finely ground insoluble solids suspended in a liquid. They are mixed with water for application. 		
Flowmeter
 	A gauge indicating the velocity of wastewater moving through a treatment plant or of any liquid moving through various industrial processes. 		
Flue Gas
 	The air coming out of a chimney after combustion in the burner it is venting. It can include nitrogen oxides, carbon oxides, water vapor, sulfur oxides, particles and many chemical pollutants. 		
Flue Gas Desulfurization
 	A technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide from the gases produced by burning fossil fuels. Flue gas desulfurization is current state-of-the art technology for major SO2 emitters, like power plants. 		
Fluidized
 	A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water treatment, a bed of filter media is fluidized by backwashing water through the filter. 		
Fluidized Bed Incinerator
 	An incinerator that uses a bed of hot sand or other granular material to transfer heat directly to waste. Used mainly for destroying municipal sludge. 		
Flume
 	A 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 reduce the incidence of tooth decay. 		
Fluorides
 	Gaseous, solid, or dissolved compounds containing fluorine that result from industrial processes. Excessive amounts in food can lead to fluorosis. 		
Fluorocarbons
 	Any of a number of organic compounds 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. 	FCs 	
Flush
 	Definition 1: To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux. 
Definition 2: To force large amounts of water through a system to clean out piping or tubing, and storage or process tanks. 
		
Flux
 	Definition 1: A flowing or flow. 
Definition 2: A substance used to help metals fuse together. 
		
Fly Ash
 	Non-combustible residual particles expelled by flue gas. 		
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. 		
Food Processing Waste
 	Food residues produced during agricultural and industrial operations. 		
Food Waste
 	Uneaten food and food preparation wastes from residences and commercial establishments such as grocery stores, restaurants, and produce stands, institutional cafeterias and kitchens, and industrial sources like employee lunchrooms. 		
Food Web
 	The feeding relationships by which energy and nutrients are transferred from one species to another. 		
Formaldehyde
 	A colorless, pungent, and irritating gas, CH20, used chiefly as a disinfectant and preservative and in synthesizing other compounds like resins. 		
Formulation
 	The substances comprising all active and inert ingredients in a pesticide. 		
Fossil Fuel
 	Fuel derived from ancient organic remains; e.g. peat, coal, crude oil, and natural gas. 		
Fracture
 	A break in a rock formation due to structural stresses; e.g. faults, shears, joints, and planes of fracture cleavage. 		
Free Product
 	A petroleum hydrocarbon in the liquid free or non aqueous phase. 		
Freeboard
 	Definition 1: Vertical distance from the normal water surface to the top of a confining wall. 
Definition 2: Vertical distance from the sand surface to the underside of a trough in a sand filter. 
		
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. 		
Friable Asbestos
 	Any material containing more than one-percent asbestos, and that can be crumbled or reduced to powder by hand pressure. (May include previously non-friable material which becomes broken or damaged by mechanical force.) 		
Fuel Economy Standard
 	The Corporate Average Fuel Economy Standard (CAFE) effective in 1978. It enhanced the national fuel conservation effort imposing a miles-per-gallon floor for motor vehicles. 		
Fuel Efficiency
 	The proportion of energy released by fuel combustion that is converted into useful energy. 		
Fuel Switching
 	Definition 1: A precombustion process whereby a low-sulfur coal is used in place of a higher sulfur coal in a power plant to reduce sulfur dioxide emissions. 
Definition 2: Illegally using leaded gasoline in a motor vehicle designed to use only unleaded. 
		
Fugitive Emissions
 	Emissions not caught by a capture system. 		
Fume
 	Tiny particles trapped in vapor in a gas stream. 		
Fumigant
 	A pesticide vaporized to kill pests. Used in buildings and greenhouses. 		
Functional Equivalent
 	Term used to describe EPA's decision-making process and its relationship to the environmental review conducted under the National Environmental Policy Act (NEPA). A review is considered functionally equivalent when it addresses the substantive components of a NEPA review. 		
Fungi
 			
Fungicide
 	Pesticides which are used to control, deter, or destroy fungi. 		
Fungistat
 	A chemical that keeps fungi from growing. 		
Fungus
 	Molds, mildews, yeasts, mushrooms, and puffballs, a group of organisms lacking in chlorophyll (i.e. are not photosynthetic) and which are usually non-mobile, filamentous, and multicellular. Some grow in soil, others attach themselves to decaying trees and other plants whence they obtain nutrients. Some are pathogens, others stabilize sewage and digest composted waste. 		
Furrow Irrigation
 	Irrigation method in which water travels through the field by means of small channels between each groups of rows. 		
Future Liability
 	Refers to potentially responsible parties' obligations to pay for additional response activities beyond those specified in the Record of Decision or Consent Decree. 		
Game Fish
 	Species like trout, salmon, or bass, caught for sport. Many of them show more sensitivity to environmental change than "rough" fish. 		
Garbage
 	Animal and vegetable waste resulting from the handling, storage, sale, preparation, cooking, and serving of foods. 		
Gas Chromatograph/Mass Spectrometer
 	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. 		
Gasoline Volatility
 	The property of gasoline whereby it evaporates into a vapor. Gasoline vapor is a mixture of volatile organic compounds. 		
General Permit
 	A permit applicable to a class or category of dischargers. 		
General Reporting Facility
 	A facility having one or more hazardous chemicals above the 10,000 pound threshold for planning quantities. Such facilities must file MSDS and emergency inventory information with the SERC, LEPC, and local fire departments. 		
Generally Recognized as Safe
 	Designation by the FDA that a chemical or substance (including certain pesticides) added to food is considered safe by experts, and so is exempted from the usual FFDCA food additive tolerance requirements. 	GRAS 	
Generator
 	Definition 1: A facility or mobile source that emits pollutants into the air or releases hazardous waste into water or soil. 
Definition 2: Any person, by site, whose act or process produces regulated medical waste or whose act first causes such waste to become subject to regulation. Where more than one person (e.g. doctors with separate medical practices) are located in the same building, each business entity is a separate generator. 
		
Genetic Engineering
 	A process of inserting new genetic information into existing cells in order to modify a specific organism for the purpose of changing one of its characteristics. 		
Genotoxic
 	Damaging to DNA; pertaining to agents known to damage DNA. 		
Geographic Information System
 	A computer system designed for storing, manipulating, analyzing, and displaying data in a geographic context. 	GIS 	
Geological Log
 	A detailed description of all underground features (depth, thickness, type of formation) discovered during the drilling of a well. 		
Geophysical Log
 	A record of the structure and composition of the earth encountered when drilling a well or similar type of test hold or boring. 		
Geothermal/Ground Source Heat Pump
 	These heat pumps are underground coils to transfer heat from the ground to the inside of a building. 		
Germicide
 	Any compound that kills disease-causing microorganisms. 		
Giardia Lamblia
 	Protozoan in the feces of humans and animals that can cause severe gastrointestinal ailments. It is a common contaminant of surface waters. 		
Glass Containers
 	For recycling purposes, containers like bottles and jars for drinks, food, cosmetics and other products. When being recycled, container glass is generally separated into color categories for conversion into new containers, construction materials or fiberglass insulation. 		
Global Climate Change
 			
Global Warming
 	An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the Earth's surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas. 		
Global Warming Potential
 	The ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. CFC-12, for example, has a GWP of 8,500, while water has a GWP of zero. 		
Glovebag
 	A polyethylene or polyvinyl chloride bag-like enclosure affixed around an asbestos-containing source (most often thermal system insulation) permitting the material to be removed while minimizing release of airborne fibers to the surrounding atmosphere. 		
Gooseneck
 	A portion of a water service connection between the distribution system water main and a meter. Sometimes called a pigtail. 		
Grab Sample
 	A single sample collected at a particular time and place that represents the composition of the water, air, or soil only at that time and place. 		
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. 		
Granular Activated Carbon Treatment
 	A filtering system often used in small water systems and individual homes to remove organics. Also used by municipal water treatment plants. GAC can be highly effective in lowering elevated levels of radon in water. 		
Grasscycling
 	Source reduction activities in which grass clippings are left on the lawn after mowing. 		
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. 		
Graveyard
 			
Gray Water
 	Domestic wastewater composed of wash water from kitchen, bathroom, and laundry sinks, tubs, and washers. 		
Greenhouse Effect
 	The warming of the Earth's atmosphere attributed to a buildup of carbon dioxide or other gases; some scientists think that this build-up allows the sun's rays to heat the Earth, while making the infra-red radiation atmosphere opaque to infra-red radiation, thereby preventing a counterbalancing loss of heat. 		
Greenhouse Gas
 	A gas, such as carbon dioxide or methane, which contributes to potential climate change. 		
Grinder Pump
 	A mechanical device that shreds solids and raises sewage to a higher elevation through pressure sewers. 		
Gross Alpha/Beta Particle Activity
 	The total radioactivity due to alpha or beta particle emissions as inferred from measurements on a dry sample. 		
Gross Power-Generation Potential
 	The installed power generation capacity that landfill gas can support. 		
Ground Cover
 	Plants grown to keep soil from eroding. 		
Ground-Penetrating Radar
 	A geophysical method that uses high frequency electromagnetic waves to obtain subsurface information. 		
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. 		
Ground-Water Disinfection Rule
 	A 1996 amendment of the Safe Drinking Water Act requiring EPA to promulgate national primary drinking water regulations requiring disinfection as for all public water systems, including surface waters and ground water systems. 		
Ground Water UDI of Surface Water
 			
Ground Water Under the Direct Influence of Surface Water
 	Any water beneath the surface of the ground with: 1. significant occurrence of insects or other microorganisms, algae, or large-diameter pathogens; 2. significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions. Direct influence is determined for individual sources in accordance with criteria established by a state. 		
Groundwater Mining
 			
Gully Erosion
 	Severe erosion in which trenches are cut to a depth greater than 30 centimeters (a foot). Generally, ditches deep enough to cross with farm equipment are considered gullies. 		
Habitat
 	The place where a population (e.g. human, animal, plant, microorganism) lives and its surroundings, both living and non-living. 		
Habitat Indicator
 	A physical attribute of the environment measured to characterize conditions necessary to support an organism, population, or community in the absence of pollutants; e.g. salinity of estuarine waters or substrate type in streams or lakes. 		
Half-Life
 	Definition 1: The time required for a pollutant to lose one-half of its original coconcentration or for example, the biochemical half-life of DDT in the environment is 15 years. 
Definition 2: The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years). 
Definition 3: The time required for the elimination of half a total dose from the body. 
		
Halogen
 	A type of incandescent lamp with higher energy-efficiency that standard ones. 		
Halon
 	Bromine-containing compounds with long atmospheric lifetimes whose breakdown in the stratosphere causes depletion of ozone. Halons are used in firefighting. 		
Hammer Mill
 	A high-speed machine that uses hammers and cutters to crush, grind, chip, or shred solid waste. 		
Hard Water
 	Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from sudsing. 		
Hauler
 	Garbage collection company that offers complete refuse removal service; many will also collect recyclables. 		
Hazard
 	Definition 1: Potential for radiation, a chemical or other pollutant to cause human illness or injury. 
Definition 2: In the pesticide program, the inherent toxicity of a compound. Hazard identification of a given substances is an informed judgment based on verifiable toxicity data from animal models or human studies. 
		
Hazard Assessment
 	Evaluating the effects of a stressor or determining a margin of safety for an organism by comparing the concentration which causes toxic effects with an estimate of exposure to the organism. 		
Hazard Communication Standard
 	An OSHA regulation that requires chemical manufacturers, suppliers, and importers to assess the hazards of the chemicals that they make, supply, or import, and to inform employers, customers, and workers of these hazards through MSDS information. 		
Hazard Evaluation
 	A component of risk evaluation that involves gathering and evaluating data on the types of health injuries or diseases that may be produced by a chemical and on the conditions of exposure under which such health effects are produced. 		
Hazard Identification
 	Determining if a chemical or a microbe can cause adverse health effects in humans and what those effects might be. 		
Hazard Quotient
 	The ratio of estimated site-specific exposure to a single chemical from a site over a specified period to the estimated daily exposure level, at which no adverse health effects are likely to occur. 		
Hazard Ratio
 	A term used to compare an animal's daily dietary intake of a pesticide to its LD 50 value. A ratio greater than 1.0 indicates that the animal is likely to consume an a dose amount which would kill 50 percent of animals of the same species. 		
Hazardous Air Pollutants
 	Air pollutants which are not covered by ambient air quality standards but which, as defined in the Clean Air Act, may present a threat of adverse human health effects or adverse environmental effects. Such pollutants include asbestos, beryllium, mercury, benzene, coke oven emissions, radionuclides, and vinyl chloride. 		
Hazardous Chemical
 	An EPA designation for any hazardous material requiring an MSDS under OSHA's Hazard Communication Standard. Such substances are capable of producing fires and explosions or adverse health effects like cancer and dermatitis. Hazardous chemicals are distinct from hazardous waste. 		
Hazardous Ranking System
 	The principal screening tool used by EPA to evaluate risks to public health and the environment associated with abandoned or uncontrolled hazardous waste sites. The HRS calculates a score based on the potential of hazardous substances spreading from the site through the air, surface water, or ground water, and on other factors such as density and proximity of human population. This score is the primary factor in deciding if the site should be on the National Priorities List and, if so, what ranking it should have compared to other sites on the list. 		
Hazardous Substance
 	Definition 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. 
Definition 2: Any substance designated by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or is otherwise released into the environment. 
		
Hazardous Waste
 	By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed. Possesses at least one of four characteristics (ignitability, corrosivity, reactivity, or toxicity), or appears on special EPA lists. 		
Hazardous Waste Landfill
 	An excavated or engineered site where hazardous waste is deposited and covered. 		
Hazardous Waste Minimization
 	Reducing the amount of toxicity or waste produced by a facility via source reduction or environmentally sound recycling. 		
Hazards Analysis
 	Procedures used to: (1) identify potential sources of release of hazardous materials from fixed facilities or transportation accidents; (2) determine the vulnerability of a geographical area to a release of hazardous materials; and (3) compare hazards to determine which present greater or lesser risks to a community. 		
Hazards Identification
 	Providing information on which facilities have extremely hazardous substances, what those chemicals are, how much there is at each facility, how the chemicals are stored, and whether they are used at high temperatures. 		
Headspace
 	The vapor mixture trapped above a solid or liquid in a sealed vessel. 		
Health Advisory Level
 	A non-regulatory health-based reference level of chemical traces (usually in ppm) in drinking water at which there are no adverse health risks when ingested over various periods of time. Such levels are established for one day, 10 days, long-term and life-time exposure periods. They contain a wide margin of safety. 		
Health Assessment
 	An evaluation of available data on existing or potential risks to human health posed by a Superfund site. The Agency for Toxic Substances and Disease Registry (ATSDR) of the Department of Health and Human Services (DHHS) is required to perform such an assessment at every site on the National Priorities List. 		
Heat Island Effect
 	A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions. 		
Heat Pump
 	An electric device with both heating and cooling capabilities. It extracts heat from one medium at a lower (the heat source) temperature and transfers it to another at a higher temperature (the heat sink), thereby cooling the first and warming the second. 		
Heavy Metals
 	Metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend to accumulate in the food chain. 		
Heptachlor
 	An insecticide that was banned on some food products in 1975 and in all of them 1978. It was allowed for use in seed treatment until 1983. More recently it was found in milk and other dairy products in Arkansas and Missouri where dairy cattle were illegally fed treated seed. 		
Herbicide
 	A chemical pesticide designed to control or destroy plants, weeds, or grasses. 		
Herbivore
 	An animal that feeds on plants. 		
Heterotrophic Organisms
 	Species that are dependent on organic matter for food. 		
High-Density Polyethylene
 	A material used to make plastic bottles and other products that produces toxic fumes when burned. 		
High End Exposure (dose) Estimate
 	An estimate of exposure, or dose level received anyone in a defined population that is greater than the 90th percentile of all individuals in that population, but less than the exposure at the highest percentile in that population. A high end risk descriptor is an estimate of the risk level for such individuals. Note that risk is based on a combination of exposure and susceptibility to the stressor. 		
High Intensity Discharge
 	A generic term for mercury vapor, metal halide, and high pressure sodium lamps and fixtures. 		
High-Level Nuclear Waste Facility
 	Plant designed to handle disposal of used nuclear fuel, high-level radioactive waste, and plutonium waste. 		
High-Level Radioactive Waste
 	Waste generated in core fuel of a nuclear reactor, found at nuclear reactors or by nuclear fuel reprocessing; is a serious threat to anyone who comes near the waste without shielding. 	HLRW 	
High-Line Jumpers
 	Pipes or hoses connected to fire hydrants and laid on top of the ground to provide emergency water service for an isolated portion of a distribution system. 		
High-Risk Community
 	A community located within the vicinity of numerous sites of facilities or other potential sources of environmental exposure/health hazards which may result in high levels of exposure to contaminants or pollutants. 		
High-Sulfur Coal
 			
High-to-Low-Dose Extrapolation
 	The process of prediction of low exposure risk to humans and animals from the measured high-exposure-high-risk data involving laboratory animals. 		
Highest Dose Tested
 	The highest dose of a chemical or substance tested in a study. 		
Holding Pond
 	A pond or reservoir, usually made of earth, built to store polluted runoff. 		
Holding Time
 	The maximum amount of time a sample may be stored before analysis. 		
Hollow Stem Auger Drilling
 	Conventional drilling method that uses augurs to penetrate the soil. As the augers are rotated, soil cuttings are conveyed to the ground surface via augur spirals. DP tools can be used inside the hollow augers. 		
Homeowner Water System
 	Any water system which supplies piped water to a single residence. 		
Homogeneous Area
 	In accordance with Asbestos Hazard and Emergency Response Act (AHERA) definitions, an area of surfacing materials, thermal surface insulation, or miscellaneous material that is uniform in color and texture. 		
Hood Capture Efficiency
 	Ratio of the emissions captured by a hood and directed into a control or disposal device, expressed as a percent of all emissions. 		
Host
 	Definition 1: In genetics, the organism, typically a bacterium, into which a gene from another organism is transplanted. 
Definition 2: In medicine, an animal infected or parasitized by another organism. 
		
Household Hazardous Waste
 	Hazardous products used and disposed of by residential as opposed to industrial consumers. Includes paints, stains, varnishes, solvents, pesticides, and other materials or products containing volatile chemicals that can catch fire, react or explode, or that are corrosive or toxic. 		
Household Waste
 	Solid waste, composed of garbage and rubbish, which normally originates in a private home or apartment house. Domestic waste may contain a significant amount of toxic or hazardous waste. 		
Human Equivalent Dose
 	A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals. 		
Human Exposure Evaluation
 	Describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure. 		
Human Health Risk
 	The likelihood that a given exposure or series of exposures may have damaged or will damage the health of individuals. 		
Hydraulic Conductivity
 	The rate at which water can move through a permeable medium. (i.e. the coefficient of permeability.) 		
Hydraulic Gradient
 	In general, the direction of groundwater flow due to changes in the depth of the water table. 		
Hydrocarbons
 	Chemical compounds that consist entirely of carbon and hydrogen. 	HC 	
Hydrogen Sulfide
 	Gas emitted during organic decomposition. Also a by-product of oil refining and burning. Smells like rotten eggs and, in heavy concentration, can kill or cause illness. 	H2S 	
Hydrogeological Cycle
 	The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again. 		
Hydrogeology
 	The geology of ground water, with particular emphasis on the chemistry and movement of water. 		
Hydrologic Cycle
 	Movement or exchange of water between the atmosphere and earth. 		
Hydrology
 	The science dealing with the properties, distribution, and circulation of water. 		
Hydrolysis
 	The decomposition of organic compounds by interaction with water. 		
Hydronic
 	A ventilation system using heated or cooled water pumped through a building. 		
Hydrophilic
 	Having a strong affinity for water. 		
Hydrophobic
 	Having a strong aversion for water. 		
Hydropneumatic
 	A water system, usually small, in which a water pump is automatically controlled by the pressure in a compressed air tank. 		
Hypersensitivity Diseases
 	Diseases characterized by allergic responses to pollutants; diseases most clearly associated with indoor air quality are asthma, rhinitis, and pneumonic hypersensitivity. 		
Hypolimnion
 	Bottom waters of a thermally stratified lake. The hypolimnion of a eutrophic lake is usually low or lacking in oxygen. 		
Hypoxia/Hypoxic Waters
 	Waters with dissolved oxygen concentrations of less than 2 ppm, the level generally accepted as the minimum required for most marine life to survive and reproduce. 		
Identification Code
 	The unique code assigned to each generator, transporter, and treatment, storage, or disposal facility by regulating agencies to facilitate identification and tracking of chemicals or hazardous waste. 		
Ignitable
 	Capable of burning or causing a fire. 		
IM240
 	A high-tech, transient dynamometer automobile emissions test that takes up to 240 seconds. 		
Imhoff Cone
 	A clear, cone-shaped container used to measure the volume of settleable solids in a specific volume of water. 		
Immediately Dangerous to Life and Health
 	The maximum level to which a healthy individual can be exposed to a chemical for 30 minutes and escape without suffering irreversible health effects or impairing symptoms. Used as a "level of concern." 	IDLH 	
Imminent Hazard
 	One that would likely result in unreasonable adverse effects on humans or the environment or risk unreasonable hazard to an endangered species during the time required for a pesticide registration cancellation proceeding. 		
Imminent Threat
 	A high probability that exposure is occurring. 		
Immiscibility
 	The inability of two or more substances or liquids to readily dissolve into one another, such as soil and water. Immiscibility The inability of two or more substances or liquids to readily dissolve into one another, such as soil and water. 		
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. 		
Imports
 	Municipal solid waste and recyclables that have been transported to a state or locality for processing or final disposition (but that did not originate in that state or locality). 		
Impoundment
 	A body of water or sludge confined by a dam, dike, floodgate, or other barrier. 		
In-Line Filtration
 	Pre-treatment method in which chemicals are mixed by the flowing water; commonly used in pressure filtration installations. Eliminates need for flocculation and sedimentation. 		
In Situ
 	In its original place; unmoved unexcavated; remaining at the site or in the subsurface. 		
In-Situ Flushing
 	Introduction of large volumes of water, at times supplemented with cleaning compounds, into soil, waste, or ground water to flush hazardous contaminants from a site. 		
In-Situ Oxidation
 	Technology that oxidizes contaminants dissolved in ground water, converting them into insoluble compounds. 		
In-Situ Stripping
 	Treatment system that removes or "strips" volatile organic compounds from contaminated ground or surface water by forcing an airstream through the water and causing the compounds to evaporate. 		
In-Situ Vitrification
 	Technology that treats contaminated soil in place at extremely high temperatures, at or more than 3000 degrees Fahrenheit. 		
In Vitro
 	Testing or action outside an organism (e.g. inside a test tube or culture dish.) 		
In Vivo
 	Testing or action inside an organism. 		
Incident Command Post
 	A facility located at a safe distance from an emergency site, where the incident commander, key staff, and technical representatives can make decisions and deploy emergency manpower and equipment. 		
Incident Command System
 	The organizational arrangement wherein one person, normally the Fire Chief of the impacted district, is in charge of an integrated, comprehensive emergency response organization and the emergency incident site, backed by an Emergency Operations Center staff with resources, information, and advice. 	ICS 	
Incineration
 	A treatment technology involving destruction of waste by controlled burning at high temperatures; e.g., burning sludge to remove the water and reduce the remaining residues to a safe, non-burnable ash that can be disposed of safely on land, in some waters, or in underground locations. 		
Incineration at Sea
 	Disposal of waste by burning at sea on specially-designed incinerator ships. 		
Incinerator
 	A furnace for burning waste under controlled conditions. 		
Incompatible Waste
 	A waste unsuitable for mixing with another waste or material because it may react to form a hazard. 		
Indemnification
 	In the pesticide program, legal requirement that EPA pay certain end-users, dealers, and distributors for the cost of stock on hand at the time a pesticide registration is suspended. 		
Indicator
 	Definition 1: In biology, any biological entity or processes, or community whose characteristics show the presence of specific environmental conditions. 
Definition 2: In chemistry, a substance that shows a visible change, usually of color, at a desired point in a chemical reaction. 
Definition 3: A device that indicates the result of a measurement; e.g. a pressure gauge or a moveable scale. 
		
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. 		
Indirect Source
 	Any facility or building, property, road or parking area that attracts motor vehicle traffic and, indirectly, causes pollution. 		
Indoor Air
 	The breathable air inside a habitable structure or conveyance. 		
Indoor Air Pollution
 	Chemical, physical, or biological contaminants in indoor air. 		
Indoor Climate
 	Temperature, humidity, lighting, air flow and noise levels in a habitable structure or conveyance. Indoor climate can affect indoor air pollution. 		
Industrial Pollution Prevention
 	Combination of industrial source reduction and toxic chemical use substitution. 		
Industrial Process Waste
 	Residues produced during manufacturing operations. 		
Industrial Sludge
 	Semi-liquid residue or slurry remaining from treatment of industrial water and wastewater. 		
Industrial Source Reduction
 	Practices that reduce the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment. Also reduces the threat to public health and the environment associated with such releases. Term includes equipment or technology modifications, substitution of raw materials, and improvements in housekeeping, maintenance, training or inventory control. 		
Industrial Waste
 	Unwanted materials from an industrial operation; may be liquid, sludge, solid, or hazardous waste. 		
Inert Ingredient
 	Pesticide components such as solvents, carriers, dispersants, and surfactants that are not active against target pests. Not all inert ingredients are innocuous. 		
Inertial Separator
 	A device that uses centrifugal force to separate waste particles. 		
Infectious Agent
 	Any organism, such as a pathogenic virus, parasite, or bacterium, that is capable of invading body tissues, multiplying, and causing disease. 		
Infectious Waste
 	Hazardous waste capable of causing infections in humans, including: contaminated animal waste; human blood and blood products; isolation waste, pathological waste; and discarded sharps (needles, scalpels or broken medical instruments). 		
Infiltration
 	Definition 1: The penetration of water through the ground surface into sub-surface soil or the penetration of water from the soil into sewer or other pipes through defective joints, connections, or manhole walls. 
Definition 2: The technique of applying large volumes of waste water to land to penetrate the surface and percolate through the underlying soil. 
		
Infiltration Gallery
 	A sub-surface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a watertight chamber from which the water is pumped to treatment facilities and into the distribution system. Usually located close to streams or ponds. 		
Infiltration Rate
 	The quantity of water that can enter the soil in a specified time interval. 		
Inflow
 	Entry of extraneous rain water into a sewer system from sources other than infiltration, such as basement drains, manholes, storm drains, and street washing. 		
Influent
 	Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant. 		
Information Collection Request
 	A description of information to be gathered in connection with rules, proposed rules, surveys, and guidance documents that contain information-gathering requirements. The ICR describes what information is needed, why it is needed, how it will be collected, and how much collecting it will cost. The ICR is submitted by the EPA to the Office of Management and Budget (OMB) for approval. 	ICR 	
Information File
 	In the Superfund program, a file that contains accurate, up-to-date documents on a Superfund site. The file is usually located in a public building (school, library, or city hall) convenient for local residents. 		
Inhalable Particles
 	All dust capable of entering the human respiratory tract. 		
Initial Compliance Period (Water)
 	The first full three-year compliance period which begins at least 18 months after promulgation. 		
Injection Well
 	A well into which fluids are injected for purposes such as waste disposal, improving the recovery of crude oil, or solution mining. 		
Injection Zone
 	A geological formation receiving fluids through a well. 		
Innovative Technologies
 	New or inventive methods to treat effectively hazardous waste and reduce risks to human health and the environment. 		
Innovative Treatment Technologies
 	Technologies whose routine use is inhibited by lack of data on performance and cost. 		
Inoculum
 	Definition 1: Bacteria or fungi injected into compost to start biological action. 
Definition 2: A medium containing organisms, usually bacteria or a virus, that is introduced into cultures or living organisms. 
		
Inorganic Chemicals
 	Chemical substances of mineral origin, not of basically carbon structure. 		
Insecticide
 	A pesticide compound specifically used to kill or prevent the growth of insects. 		
Inspection and Maintenance
 	Definition 1: Activities to ensure that vehicles' emission controls work properly. 
Definition 2: Also applies to wastewater treatment plants and other anti-pollution facilities and processes. 
	I/M, I&M 	
Institutional Waste
 	Waste generated at institutions such as schools, libraries, hospitals, prisons, etc. 		
Instream Use
 	Water use taking place within a stream channel; e.g., hydro-electric power generation, navigation, water quality improvement, fish propagation, recreation. 		
Integrated Exposure Assessment
 	Cumulative summation (over time) of the magnitude of exposure to a toxic chemical in all media. 		
Integrated Pest Management
 	A mixture of chemical and other, non-pesticide, methods to control pests. 	IPM 	
Integrated Risk Information System
 	An electronic data base containing the Agency's latest descriptive and quantitative regulatory information on chemical constituents. 	IRIS 	
Integrated Waste Management
 	Using a variety of practices to handle municipal solid waste; can include source reduction, recycling, incineration, and landfilling. 		
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. 		
Interface
 	The common boundary between two substances such as a water and a solid, water and a gas, or two liquids such as water and oil. 		
Interfacial Tension
 	The strength of the film separating two immiscible fluids (e.g. oil and water) measured in dynes per, or millidynes per centimeter. 		
Interim (Permit) Status
 	Period during which treatment, storage and disposal facilities coming under RCRA in 1980 are temporarily permitted to operate while awaiting a permanent permit. Permits issued under these circumstances are usually called "Part A" or "Part B" permits. 		
Internal Dose
 	In exposure assessment, the amount of a substance penetrating the absorption barriers (e.g. skin, lung tissue, gastrointestinal tract) of an organism through either physical or biological processes. 		
Interstate 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. 		
Interstate Commerce Clause
 	A clause of the U.S. Constitution which reserves to the federal government the right to regulate the conduct of business across state lines. Under this clause, for example, the U.S. Supreme Court has ruled that states may not inequitably restrict the disposal of out-of-state wastes in their jurisdictions. 		
Interstate Waters
 	Waters that flow across or form part of state or international boundaries; e.g. the Great Lakes, the Mississippi River, or coastal waters. 		
Interstitial Monitoring
 	The continuous surveillance of the space between the walls of an underground storage tank. 		
Intrastate Product
 	Pesticide products once registered by states for sale and use only in the state. All intrastate products have been converted to full federal registration or canceled. 		
Inventory (TSCA)
 	Inventory of chemicals produced pursuant to Section 8 (b) of the Toxic Substances Control Act. 		
Inversion
 	A layer of warm air that prevents the rise of cooling air and traps pollutants beneath it; can cause an air pollution episode. 		
Ion
 	An electrically charged atom or group of atoms. 		
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. 		
Ionization Chamber
 	A device that measures the intensity of ionizing radiation. 		
Ionizing Radiation
 	Radiation that can strip electrons from atoms; e.g. alpha, beta, and gamma radiation. 		
Irradiated Food
 	Food subject to brief radioactivity, usually gamma rays, to kill insects, bacteria, and mold, and to permit storage without refrigeration. 		
Irradiation
 	Exposure to radiation of wavelengths shorter than those of visible light (gamma, x-ray, or ultra- violet), for medical purposes, to sterilize milk or other foodstuffs, or to induce polymerization of monomers or vulcanization of rubber. 		
Irreversible Effect
 	Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent. 		
Irrigation
 	Applying water or wastewater to land areas to supply the water and nutrient needs of plants. 		
Irrigation Efficiency
 	The amount of water stored in the crop root zone compared to the amount of irrigation water applied. 		
Irrigation Return Flow
 	Surface and subsurface water which leaves the field following application of irrigation water. 		
Irritant
 	A substance that can cause irritation of the skin, eyes, or respiratory system. Effects may be acute from a single high level exposure, or chronic from repeated low-level exposures to such compounds as chlorine, nitrogen dioxide, and nitric acid. 		
Isoconcentration
 	More than one sample point exhibiting the same isolate concentration. 		
Isopleth
 	The line or area represented by an isoconcentration. 		
Isotope
 	A variation of an element that has the same atomic number of protons but a different weight because of the number of neutrons. Various isotopes of the same element may have different radioactive behaviors, some are highly unstable. 		
Isotropy
 	The condition in which the hydraulic or other properties of an aquifer are the same in all directions. 		
Jar Test
 	A laboratory procedure that simulates a water treatment plant's coagulation/flocculation units with differing chemical doses, mix speeds, and settling times to estimate the minimum or ideal coagulant dose required to achieve certain water quality goals. 		
Joint and Several Liability
 	Under CERCLA, this legal concept relates to the liability for Superfund site cleanup and other costs on the part of more than one potentially responsible party (i.e. if there were several owners or users of a site that became contaminated over the years, they could all be considered potentially liable for cleaning up the site.) 		
Karst
 	A geologic formation of irregular limestone deposits with sinks, underground streams, and caverns. 		
Kinetic Energy
 	Energy possessed by a moving object or water body. 		
Kinetic Rate Coefficient
 	A number that describes the rate at which a water constituent such as a biochemical oxygen demand or dissolved oxygen rises or falls, or at which an air pollutant reacts. 		
Laboratory Animal Studies
 	Investigations using animals as surrogates for humans. 		
Lagoon
 	Definition 1: A shallow pond where sunlight, bacterial action, and oxygen work to purify wastewater; also used for storage of wastewater or spent nuclear fuel rods. 
Definition 2: Shallow body of water, often separated from the sea by coral reefs or sandbars. 
		
Land Application
 	Discharge of wastewater onto the ground for treatment or reuse. 		
Land Ban
 	Phasing out of land disposal of most untreated hazardous wastes, as mandated by the 1984 RCRA amendments. 		
Land Disposal Restrictions
 	Rules that require hazardous wastes to be treated before disposal on land to destroy or immobilize hazardous constituents that might migrate into soil and ground water. 		
Land Farming (of Waste)
 	A disposal process in which hazardous waste deposited on or in the soil is degraded naturally by microbes. 		
Landfills
 	Definition 1: Sanitary landfills are disposal sites for non-hazardous solid wastes spread in layers, compacted to the smallest practical volume, and covered by material applied at the end of each operating day. 
Definition 2: Secure chemical landfills are disposal sites for hazardous waste, selected and designed to minimize the chance of release of hazardous substances into the environment. 
		
Landscape
 	The traits, patterns, and structure of a specific geographic area, including its biological composition, its physical environment, and its anthropogenic or social patterns. An area where interacting ecosystems are grouped and repeated in similar form. 		
Landscape Characterization
 	Documentation of the traits and patterns of the essential elements of the landscape. 		
Landscape Ecology
 	The study of the distribution patterns of communities and ecosystems, the ecological processes that affect those patterns, and changes in pattern and process over time. 		
Landscape Indicator
 	A measurement of the landscape, calculated from mapped or remotely sensed data, used to describe spatial patterns of land use and land cover across a geographic area. Landscape indicators may be useful as measures of certain kinds of environmental degradation such as forest fragmentation. 		
Langelier Index
 	An index reflecting the equilibrium pH of a water with respect to calcium and alkalinity; used in stabilizing water to control both corrosion and scale deposition. 	LI 	
Large Quantity Generator
 	Person or facility generating more than 2200 pounds of hazardous waste per month. Such generators produce about 90 percent of the nation's hazardous waste, and are subject to all RCRA requirements. 		
Large Water System
 	A water system that services more than 50,000 customers. 		
Laser Induced Fluorescence
 	A method for measuring the relative amount of soil and/or groundwater with an in-situ sensor. 		
Latency
 	Time from the first exposure of a chemical until the appearance of a toxic effect. 		
Lateral Sewers
 	Pipes that run under city streets and receive the sewage from homes and businesses, as opposed to domestic feeders and main trunk lines. 		
Laundering Weir
 	Sedimentation basin overflow weir. 		
Leachate
 	Water that collects contaminants as it trickles through wastes, pesticides or fertilizers. Leaching may occur in farming areas, feedlots, and landfills, and may result in hazardous substances entering surface water, ground water, or soil. 		
Leachate Collection System
 	A system that gathers leachate and pumps it to the surface for treatment. 		
Leaching
 	The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid. 		
Lead
 	A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations. 	Pb 	
Lead Service Line
 	A service line made of lead which connects the water to the building inlet and any lead fitting connected to it. 		
Legionella
 	A genus of bacteria, some species of which have caused a type of pneumonia called Legionnaires Disease. 		
Lethal Concentration
 	Median level concentration, a standard measure of toxicity. It tells how much of a substance is needed to kill half of a group of experimental organisms in a given time. 	LC50, LC 50 	
Lethal Concentration 50
 	Also referred to as LC50, a concentration of a pollutant or effluent at which 50 percent of the test organisms die; a common measure of acute toxicity. 	LC50, LC 50 	
Lethal Dose
 			
Lethal Dose 50
 	Also referred to as LD50, the dose of a toxicant that will kill 50 percent of test organisms within a designated period of time; the lower the LD 50, the more toxic the compound. 	LD50, LD 50 	
Lethal Dose Low
 	the lowest dose in an animal study at which lethality occurs. 	Ldlo 	
Level of Concern
 	The concentration in air of an extremely hazardous substance above which there may be serious immediate health effects to anyone exposed to it for short periods 	LOC 	
Life Cycle of a Product
 	All stages of a product's development, from extraction of fuel for power to production, marketing, use, and disposal. 		
Lifetime Average Daily Dose
 	Figure for estimating excess lifetime cancer risk. 		
Lifetime Exposure
 	Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years). 		
Lift
 	In a sanitary landfill, a compacted layer of solid waste and the top layer of cover material. 		
Lifting Station
 			
Light-Emitting Diode
 	A long-lasting illumination technology used for exit signs which requires very little power. 		
Light Non-Aqueous Phase Liquid
 	A non-aqueous phase liquid with a specific gravity less than 1.0. Because the specific gravity of water is 1.0, most LNAPLs float on top of the water table. Most common petroleum hydrocarbon fuels and lubricating oils are LNAPLs. 	LNAPL 	
Limestone Scrubbing
 	Use of a limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere. 		
Limit of Detection
 	The minimum concentration of a substance being analyzed test that has a 99 percent probability of being identified. 	LOD 	
Limited Degradation
 	An environmental policy permitting some degradation of natural systems but terminating at a level well beneath an established health standard. 		
Limiting Factor
 	A condition whose absence or excessive concentration, is incompatible with the needs or tolerance of a species or population and which may have a negative influence on their ability to thrive. 		
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. 		
Liner
 	Definition 1: A relatively impermeable barrier designed to keep leachate inside a landfill. Liner materials include plastic and dense clay. 
Definition 2: An insert or sleeve for sewer pipes to prevent leakage or infiltration. 
		
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. 		
Liquid Injection Incinerator
 	Commonly used system that relies on high pressure to prepare liquid wastes for incineration by breaking them up into tiny droplets to allow easier combustion. 		
List
 	Shorthand term for EPA list of violating facilities or firms debarred from obtaining government contracts because they violated certain sections of the Clean Air or Clean Water Acts. The list is maintained by The Office of Enforcement and Compliance Monitoring. 		
Listed Waste
 	Wastes listed as hazardous under RCRA but which have not been subjected to the Toxic Characteristics Listing Process because the dangers they present are considered self-evident. 		
Lithology
 	Mineralogy, grain size, texture, and other physical properties of granular soil, sediment, or rock. 		
Litter
 	Definition 1: The highly visible portion of solid waste carelessly discarded outside the regular garbage and trash collection and disposal system. 
Definition 2: Leaves and twigs fallen from forest trees. 
		
Littoral Zone
 	Definition 1: That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 
Definition 2: A strip of land along the shoreline between the high and low water levels. 
		
Local Education Agency
 	In the asbestos program, an educational agency at the local level that exists primarily to operate schools or to contract for educational services, including primary and secondary public and private schools. A single, unaffiliated school can be considered an LEA for AHERA purposes. 	LEA 	
Local Emergency Planning Committee
 	A committee appointed by the state emergency response commission, as required by SARA Title III, to formulate a comprehensive emergency plan for its jurisdiction. 	LEPC 	
Low Density Polyethylene
 	Plastic material used for both rigid containers and plastic film applications. 	LOPE 	
Low Emissivity Windows
 	New window technology that lowers the amount of energy loss through windows by inhibiting the transmission of radiant heat while still allowing sufficient light to pass through. 	Low-E Windows 	
Low-Level Radioactive Waste
 	Wastes less hazardous than most of those associated with a nuclear reactor; generated by hospitals, research laboratories, and certain industries. The Department of Energy, Nuclear Regulatory Commission, and EPA share responsibilities for managing them. 	LLRW 	
Low NOx Burners
 	One of several combustion technologies used to reduce emissions of Nitrogen Oxides (NOx.) 		
Low Sulfur Coal
 			
Lower Detection Limit
 	The smallest signal above background noise an instrument can reliably detect. 		
Lower Explosive Limit
 	The concentration of a compound in air below which the mixture will not catch on fire. 	LEL 	
Lowest Acceptable Daily Dose
 	The largest quantity of a chemical that will not cause a toxic effect, as determined by animal studies. 		
Lowest Achievable Emission Rate
 	Under the Clean Air Act, the rate of emissions that reflects (1) the most stringent emission limitation in the implementation plan of any state for such source unless the owner or operator demonstrates such limitations are not achievable; or (2) the most stringent emissions limitation achieved in practice, whichever is more stringent. A proposed new or modified source may not emit pollutants in excess of existing new source standards. 		
Lowest Observed Adverse Effect Level
 	The lowest level of a stressor that causes statistically and biologically significant differences in test samples as compared to other samples subjected to no stressor. 	LOAEL 	
Macropores
 	Secondary soil features such as root holes or desiccation cracks that can create significant conduits for movement of NAPL and dissolved contaminants, or vapor-phase contaminants. 		
Magnetic Separation
 	Use of magnets to separate ferrous materials from mixed municipal waste stream. 		
Major Modification
 	This term is used to define modifications of major stationary sources of emissions with respect to Prevention of Significant Deterioration and New Source Review under the Clean Air Act. 		
Major Stationary Sources
 	Term used to determine the applicability of Prevention of Significant Deterioration and new source regulations. In a nonattainment area, any stationary pollutant source with potential to emit more than 100 tons per year is considered a major stationary source. In PSD areas the cutoff level may be either 100 or 250 tons, depending upon the source. 		
Majors
 	Larger publicly owned treatment works (POTWs) with flows equal to at least one million gallons per day (mgd) or servicing a population equivalent to 10,000 persons; certain other POTWs having significant water quality impacts. 		
Man-Made (Anthropogenic) Beta Particle and Photon Emitters
 	All radionuclides emitting beta particles and/or photons listed in Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and Water for Occupational Exposure. 		
Management Plan
 	Under the Asbestos Hazard Emergency Response Act (AHERA), a document that each Local Education Agency is required to prepare, describing all activities planned and undertaken by a school to comply with AHERA regulations, including building inspections to identify asbestos-containing materials, response actions, and operations and maintenance programs to minimize the risk of exposure. 		
Managerial Controls
 	Methods of nonpoint source pollution control based on decisions about managing agricultural wastes or application times or rates for agrochemicals. 		
Mandatory Recycling
 	Programs which by law require consumers to separate trash so that some or all recyclable materials are recovered for recycling rather than going to landfills. 		
Manifest
 	A one-page form used by haulers transporting waste that lists EPA identification numbers, type and quantity of waste, the generator it originated from, the transporter that shipped it, and the storage or disposal facility to which it is being shipped. It includes copies for all participants in the shipping process. 		
Manifest System
 	Tracking of hazardous waste from "cradle-to-grave" (generation through disposal) with accompanying documents known as manifests. 		
Manual Separation
 	Hand sorting of recyclable or compostable materials in waste. 		
Manufacturer's Formulation
 	A list of substances or component parts as described by the maker of a coating, pesticide, or other product containing chemicals or other substances. 		
Manufacturing Use Product
 	Any product intended (labeled) for formulation or repackaging into other pesticide products. 		
Margin of Exposure
 	The ratio of the no-observed adverse-effect-level to the estimated exposure dose. 	MOE 	
Margin of Safety
 	Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population. 		
Marine 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 Category
 	In the asbestos program, broad classification of materials into thermal surfacing insulation, surfacing material, and miscellaneous material. 		
Material Safety Data Sheet
 	A compilation of information required under the OSHA Communication Standard on the identity of hazardous chemicals, health, and physical hazards, exposure limits, and precautions. Section 311 of SARA requires facilities to submit MSDSs under certain circumstances. 	MSDS 	
Material Type
 	Classification of suspect material by its specific use or application; e.g., pipe insulation, fireproofing, and floor tile. 		
Materials Recovery Facility
 	A facility that processes residentially collected mixed recyclables into new products available for market. 	MRF 	
Maximally Exposed Individual
 	The person with the highest exposure in a given population. 		
Maximum Acceptable Toxic Concentration
 	For a given ecological effects test, the range (or geometric mean) between the No Observable Adverse Effect Level and the Lowest Observable Adverse Effects Level. 		
Maximum Available Control Technology
 	The emission standard for sources of air pollution requiring the maximum reduction of hazardous emissions, taking cost and feasibility into account. Under the Clean Air Act Amendments of 1990, the MACT must not be less than the average emission level achieved by controls on the best performing 12 percent of existing sources, by category of industrial and utility sources. 	MACT 	
Maximum Contaminant Level
 	The maximum permissible level of a contaminant in water delivered to any user of a public system. MCLs are enforceable standards. 	MCL 	
Maximum Contaminant Level Goal
 	Under the Safe Drinking Water Act, a non-enforceable concentration of a drinking water contaminant, set at the level at which no known or anticipated adverse effects on human health occur and which allows an adequate safety margin. The MCLG is usually the starting point for determining the regulated Maximum Contaminant Level. 	MCLG 	
Maximum Exposure Range
 	Estimate of exposure or dose level received by an individual in a defined population that is greater than the 98th percentile dose for all individuals in that population, but less than the exposure level received by the person receiving the highest exposure level. 		
Maximum Residue Level
 	Comparable to a U.S. tolerance level, the Maximum Residue Level the enforceable limit on food pesticide levels in some countries. Levels are set by the Codex Alimentarius Commission, a United Nations agency managed and funded jointly by the World Health Organization and the Food and Agriculture Organization. 		
Maximum Tolerated Dose
 	The maximum dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity. 		
Measure of Effect/ Measurement Endpoint
 	A measurable characteristic of ecological entity that can be related to an assessment endpoint; e.g. a laboratory test for eight species meeting certain requirements may serve as a measure of effect for an assessment endpoint, such as survival of fish, aquatic, invertebrate or algal species under acute exposure. 		
Measure of Exposure
 	A measurable characteristic of a stressor (such as the specific amount of mercury in a body of water) used to help quantify the exposure of an ecological entity or individual organism. 		
Mechanical Aeration
 	Use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen. 		
Mechanical Separation
 	Using mechanical means to separate waste into various components. 		
Mechanical Turbulence
 	Random irregularities of fluid motion in air caused by buildings or other nonthermal, processes. 		
Media
 	Specific environments--air, water, soil--which are the subject of regulatory concern and activities. 		
Medical Surveillance
 	A periodic comprehensive review of a worker's health status; acceptable elements of such surveillance program are listed in the Occupational Safety and Health Administration standards for asbestos. 		
Medical Waste
 	Any solid waste generated in the diagnosis, treatment, or immunization of human beings or animals, in research pertaining thereto, or in the production or testing of biologicals, excluding hazardous waste identified or listed under 40 CFR Part 261 or any household waste as defined in 40 CFR Sub-section 261.4 (b)(1). 		
Medium-size Water System
 	A water system that serves 3,300 to 50,000 customers. 		
Meniscus
 	The curved top of a column of liquid in a small tube. 		
Mercury
 	Heavy metal that can accumulate in the environment and is highly toxic if breathed or swallowed. 	Hg 	
Mesotrophic
 	Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life. 		
Metabolites
 	Any substances produced by biological processes, such as those from pesticides. 		
Metalimnion
 	The middle layer of a thermally stratified lake or reservoir. In this layer there is a rapid decrease in temperature with depth. Also called thermocline. 		
Methane
 	A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds. A major component of natural gas used in the home. 		
Methanol
 	An alcohol that can be used as an alternative fuel or as a gasoline additive. It is less volatile than gasoline; when blended with gasoline it lowers the carbon monoxide emissions but increases hydrocarbon emissions. Used as pure fuel, its emissions are less ozone-forming than those from gasoline. Poisonous to humans and animals if ingested. 		
Method 18
 	An EPA test method which uses gas chromatographic techniques to measure the concentration of volatile organic compounds in a gas stream. 		
Method 24
 	An EPA reference method to determine density, water content and total volatile content (water and VOC) of coatings. 		
Method 25
 	An EPA reference method to determine the VOC concentration in a gas stream. 		
Method Detection Limit
 		MDL 	
Methoxychlor
 	Pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater and marine aquatic life. 		
Methyl Orange Alkalinity
 	A measure of the total alkalinity in a water sample in which the color of methyl orange reflects the change in level. 		
Microbial Growth
 	The amplification or multiplication of microorganisms such as bacteria, algae, diatoms, plankton, and fungi. 		
Microbial Pesticide
 	A microorganism that is used to kill a pest, but is of minimum toxicity to humans. 		
Microclimate
 	Definition 1: Localized climate conditions within an urban area or neighborhood. 
Definition 2: The climate around a tree or shrub or a stand of trees. 
		
Microenvironmental Method
 	A method for sequentially assessing exposure for a series of microenvironments that can be approximated by constant concentrations of a stressor. 		
Microenvironments
 	Well-defined surroundings such as the home, office, or kitchen that can be treated as uniform in terms of stressor concentration. 		
Million-Gallons Per Day
 	A measure of water flow. 	MGD 	
Minimization
 	A comprehensive program to minimize or eliminate wastes, usually applied to wastes at their point of origin. 		
Mining of an Aquifer
 	Withdrawal over a period of time of ground water that exceeds the rate of recharge of the aquifer. 		
Mining Waste
 	Residues resulting from the extraction of raw materials from the earth. 		
Minor Source
 	New emissions sources or modifications to existing emissions sources that do not exceed NAAQS emission levels. 		
Minors
 	Publicly owned treatment works with flows less than 1 million gallons per day. 		
Miscellaneous ACM
 	Interior asbestos-containing building material or structural components, members or fixtures, such as floor and ceiling tiles; does not include surfacing materials or thermal system insulation. 		
Miscellaneous Materials
 	Interior building materials on structural components, such as floor or ceiling tiles. 		
Miscible Liquids
 	Two or more liquids that can be mixed and will remain mixed under normal conditions. 		
Missed Detection
 	The situation that occurs when a test indicates that a tank is "tight" when in fact it is leaking. 		
Mist
 	Liquid particles measuring 40 to 500 micrometers (pm), are formed by condensation of vapor. By comparison, fog particles are smaller than 40 micrometers (pm). 		
Mitigation
 	Measures taken to reduce adverse impacts on the environment. 		
Mixed Funding
 	Settlements in which potentially responsible parties and EPA share the cost of a response action. 		
Mixed Glass
 	Recovered container glass not sorted into categories (e.g. color, grade). 		
Mixed Liquor
 	A mixture of activated sludge and water containing organic matter undergoing activated sludge treatment in an aeration tank. 		
Mixed Metals
 	Recovered metals not sorted into categories such as aluminum, tin, or steel cans or ferrous or non-ferrous metals. 		
Mixed Municipal Waste
 	Solid waste that has not been sorted into specific categories (such as plastic, glass, yard trimmings, etc.) 		
Mixed Paper
 	Recovered paper not sorted into categories such as old magazines, old newspapers, old corrugated boxes, etc. 		
Mixed Plastic
 	Recovered plastic unsorted by category. 		
Mobile Incinerator Systems
 	Hazardous waste incinerators that can be transported from one site to another. 		
Mobile Source
 	Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, and locomotives. 		
Model Plant
 	A hypothetical plant design used for developing economic, environmental, and energy impact analyses as support for regulations or regulatory guidelines; first step in exploring the economic impact of a potential NSPS. 		
Modified Bin Method
 	Way of calculating the required heating or cooling for a building based on determining how much energy the system would use if outdoor temperatures were within a certain temperature interval and then multiplying the energy use by the time the temperature interval typically occurs. 		
Modified Source
 	The enlargement of a major stationary pollutant sources is often referred to as modification, implying that more emissions will occur. 		
Moisture Content
 	Definition 1: The amount of water lost from soil upon drying to a constant weight, expressed as the weight per unit of dry soil or as the volume of water per unit bulk volume of the soil. For a fully saturated medium, moisture content indicates the porosity. 
Definition 2: Water equivalent of snow on the ground; an indicator of snowmelt flood potential. 
		
Molecule
 	The smallest division of a compound that still retains or exhibits all the properties of the substance. 		
Molten Salt Reactor
 	A thermal treatment unit that rapidly heats waste in a heat-conducting fluid bath of carbonate salt. 		
Monitoring
 	Periodic or continuous surveillance or testing to determine the level of compliance with statutory requirements and/or pollutant levels in various media or in humans, plants, and animals. 		
Monitoring Well
 	Definition 1: A well used to obtain water quality samples or measure groundwater levels. 
Definition 2: A well drilled at a hazardous waste management facility or Superfund site to collect ground-water samples for the purpose of physical, chemical, or biological analysis to determine the amounts, types, and distribution of contaminants in the groundwater beneath the site. 
		
Monoclonal Antibodies
 	Definition 1: Man-made (anthropogenic) clones of a molecule, produced in quantity for medical or research purposes. 
Definition 2: Molecules of living organisms that selectively find and attach to other molecules to which their structure conforms exactly. This could also apply to equivalent activity by chemical molecules. 
	MABs, MCAs 	
Monomictic
 	Lakes and reservoirs which are relatively deep, do not freeze over during winter, and undergo a single stratification and mixing cycle during the year (usually in the fall). 		
Montreal Protocol
 	Treaty, signed in 1987, governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCS. Under the Protocol, various research groups continue to assess the ozone layer. The Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies. 		
Moratorium
 	During the negotiation process, a period of 60 to 90 days during which EPA and potentially responsible parties may reach settlement but no site response activities can be conducted. 		
Morbidity
 	Rate of disease incidence. 		
Mortality
 	Death rate. 		
Most Exposed Individual
 			
Most Probable Number
 	An estimate of microbial density per unit volume of water sample, based on probability theory. 		
Muck Soils
 	Earth made from decaying plant materials. 		
Mudballs
 	Round material that forms in filters and gradually increases in size when not removed by backwashing. 		
Mulch
 	A layer of material (wood chips, straw, leaves, etc.) placed around plants to hold moisture, prevent weed growth, and enrich or sterilize the soil. 		
Multi-Media Approach
 	Joint approach to several environmental media, such as air, water, and land. 		
Multiple Chemical Sensitivity
 	A diagnostic label for people who suffer multi-system illnesses as a result of contact with, or proximity to, a variety of airborne agents and other substances. 		
Multiple Use
 	Use of land for more than one purpose; e.g., grazing of livestock, watershed and wildlife protection, recreation, and timber production. Also applies to use of bodies of water for recreational purposes, fishing, and water supply. 		
Multistage Remote Sensing
 	A strategy for landscape characterization that involves gathering and analyzing information at several geographic scales, ranging from generalized levels of detail at the national level through high levels of detail at the local scale. 		
Municipal 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 discharges. 		
Municipal Sludge
 	Semi-liquid residue remaining from the treatment of municipal water and wastewater. 		
Municipal Solid Waste
 	Common garbage or trash generated by industries, businesses, institutions, and homes. 		
Municipal-Waste Combustor
 	See: Waste-to-Energy Facility 		
Mutagen
 	An agent that causes a permanent genetic change in a cell other than that which occurs during normal growth. 		
Mutagenicity
 	Mutagenicity is the capacity of a chemical or physical agent to cause such permanent changes. 		
National Ambient Air Quality Standards
 	Standards established by EPA that apply for outdoor air throughout the country. 	NAAQS 	
National Emissions Standards for Hazardous Air Pollutants
 	Emissions standards set by EPA for an air pollutant not covered by NAAQS that may cause an increase in fatalities or in serious, irreversible, or incapacitating illness. Primary standards are designed to protect human health, secondary standards to protect public welfare (e.g. building facades, visibility, crops, and domestic animals). 	NESHAPS 	
National Environmental Performance Partnership Agreements
 	System that allows states to assume greater responsibility for environmental programs based on their relative ability to execute them. 		
National Estuary Program
 	A program established under the Clean Water Act Amendments of 1987 to develop and implement conservation and management plans for protecting estuaries and restoring and maintaining their chemical, physical, and biological integrity, as well as controlling point and nonpoint pollution sources. 		
National Municipal Plan
 	A policy created in 1984 by EPA and the states in 1984 to bring all publicly owned treatment works (POTWs) into compliance with Clean Water Act requirements. 		
National Oil and Hazardous Substances Contingency Plan
 	The federal regulation that guides determination of the sites to be corrected under both the Superfund program and the program to prevent or control spills into surface waters or elsewhere. 	NOHSCP/NCP 	
National Pollutant Discharge Elimination System
 	A provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation. 	NPDES 	
National Priorities List
 	EPA's list of the most serious uncontrolled or abandoned hazardous waste sites identified for possible long-term remedial action under Superfund. The list is based primarily on the score a site receives from the Hazard Ranking System. 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. 	NPL 	
National Response Center
 	The federal operations center that receives notifications of all releases of oil and hazardous substances into the environment; open 24 hours a day, is operated by the U.S. Coast Guard, which evaluates all reports and notifies the appropriate agency. 		
National Response Team
 	Representatives of 13 federal agencies that, 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. 	NRT 	
National Secondary Drinking Water Regulations
 	Commonly referred to as NSDWRs. 	NSDWRs 	
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. 		
Negotiations (Under Superfund)
 	After potentially responsible parties are identified for a site, EPA coordinates with them to reach a settlement that will result in the PRP paying for or conducting the cleanup under EPA supervision. If negotiations fail, EPA can order the PRP to conduct the cleanup or EPA can pay for the cleanup using Superfund monies and then sue to recover the costs. 		
Nematocide
 	A chemical agent which is destructive to nematodes. 		
Nephelometric
 	Method of measuring turbidity in a water sample by passing light through the sample and measuring the amount of the light that is deflected. 		
Netting
 	A concept in which all emissions sources in the same area that owned or controlled by a single company are treated as one large source, thereby allowing flexibility in controlling individual sources in order to meet a single emissions standard. 		
Neutralization
 	Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively. 		
New Source
 	Any stationary source built or modified after publication of final or proposed regulations that prescribe a given standard of performance. 		
New Source Performance Standards
 	Uniform national EPA air emission and water effluent standards which limit the amount of pollution allowed from new sources or from modified existing sources. 	NSPS 	
New Source Review
 	A Clean Air Act requirement that State Implementation Plans must include a permit review that applies to the construction and operation of new and modified stationary sources in nonattainment areas to ensure attainment of national ambient air quality standards. 	NSR 	
Nitrate
 	A compound containing nitrogen that can exist in the atmosphere or as a dissolved gas in water and which can have harmful effects on humans and animals. Nitrates in water can cause severe illness in infants and domestic animals. A plant nutrient and inorganic fertilizer, nitrate is found in 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; it is converted by sunlight and photochemical processes in ambient air to nitrogen oxide. NO is a precursor of ground-level ozone pollution, or smog. 	NO 	
Nitrification
 	The process whereby ammonia in wastewater is oxidized to nitrite and then to nitrate by bacterial or chemical reactions. 		
Nitrilotriacetic Acid
 	A compound now replacing phosphates in detergents. 	NTA 	
Nitrite
 	Definition 1: An intermediate in the process of nitrification. 
Definition 2: Nitrous oxide salts used in food preservation. 
		
Nitrogen Dioxide
 	The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog. 	NO2 	
Nitrogen Oxide
 	The result of photochemical reactions of nitric oxide in ambient air; major component of photochemical smog. Product of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition. 	NOx 	
Nitrogenous Wastes
 	Animal or vegetable residues that contain significant amounts of nitrogen. 		
Nitrophenols
 	Synthetic organopesticides containing carbon, hydrogen, nitrogen, and oxygen. 		
No Further Remedial Action Planned
 	Determination made by EPA following a preliminary assessment that a site does not pose a significant risk and so requires no further activity under CERCLA. 		
No Observable Adverse Effect Level
 	An exposure level at which there are no statistically or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered as adverse, or as precursors to adverse effects. In an experiment with several NOAELs, the regulatory focus is primarily on the highest one, leading to the common usage of the term NOAEL as the highest exposure without adverse effects. 	NOAEL 	
No-Observed-Effect-Level
 	Exposure level at which there are no statistically or biological significant differences in the frequency or severity of any effect in the exposed or control populations. 	NOEL 	
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; does not corrode easily. 		
Noise
 	Product-level or product-volume changes occurring during a test that are not related to a leak but may be mistaken for one. 		
Non-Aqueous Phase Liquid
 	Contaminants that remain undiluted as the original bulk liquid in the subsurface, e.g. spilled oil. 	NAPL 	
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
 	A process for EPA to propose a way for potentially responsible parties to allocate costs among themselves. 	NBAR 	
Non-Community Water System
 	A public water system that is not a community water system; e.g. the water supply at a camp site or national park. 		
Non-Compliance Coal
 	Any coal that emits greater than 3.0 pounds of sulfur dioxide per million BTU when burned. 		
Non-Contact Cooling Water
 	Water used for cooling which does not come into direct contact with any raw material, product, byproduct, or waste. 		
Non-Conventional Pollutant
 	Any pollutant not statutorily listed or which is poorly understood by the scientific community. 		
Non-Degradation
 	An environmental policy which disallows any lowering of naturally occurring quality regardless of preestablished health standards. 		
Non-Ferrous Metals
 	Nonmagnetic metals such as aluminum, lead, and copper. Products made all or in part from such metals include containers, packaging, appliances, furniture, electronic equipment and aluminum foil. 		
Non-ionizing Electromagnetic Radiation
 	Definition 1: Radiation that does not change the structure of atoms but does heat tissue and may cause harmful biological effects. 
Definition 2: Microwaves, radio waves, and low-frequency electromagnetic fields from high-voltage transmission lines. 
		
Non-Methane Hydrocarbon
 	The sum of all hydrocarbon air pollutants except methane; significant precursors to ozone formation. 	NMHC 	
Non-Methane Organic Gases
 	The sum of all organic air pollutants. Excluding methane; they account for aldehydes, ketones, alcohols, and other pollutants that are not hydrocarbons but are precursors of ozone. 	NMOG 	
Non-Point Sources
 	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 non-point 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 it contains pollutants, contaminants, minerals, or infective agents. 		
Non-Road Emissions
 	Pollutants emitted by combustion engines on farm and construction equipment, gasoline-powered lawn and garden equipment, and power boats and outboard motors. 		
Non-Transient Non-Community Water System
 	A public water system that regularly serves at least 25 of the same non-resident persons per day for more than six months per year. 		
Nondischarging Treatment Plant
 	A treatment plant that does not discharge treated wastewater into any stream or river. Most are pond systems that dispose of the total flow they receive by means of evaporation or percolation to groundwater, or facilities that dispose of their effluent by recycling or reuse (e.g. spray irrigation or groundwater discharge). 		
Nonfriable Asbestos-Containing Materials
 	Any material containing more than one percent asbestos (as determined by Polarized Light Microscopy) that, when dry, cannot be crumbled, pulverized, or reduced to powder by hand pressure. 		
Nonhazardous Industrial Waste
 	Industrial process waste in wastewater not considered municipal solid waste or hazardous waste under RARA. 		
Notice of Deficiency
 	An EPA request to a facility owner or operator requesting additional information before a preliminary decision on a permit application can be made. 		
Notice of Intent to Cancel
 	Notification sent to registrants when EPA decides to cancel registration of a product containing a pesticide. 		
Notice of Intent to Deny
 	Notification by EPA of its preliminary intent to deny a permit application. 		
Notice of Intent to Suspend
 	Notification sent to a pesticide registrant when EPA decides to suspend product sale and distribution because of failure to submit requested data in a timely and/or acceptable manner, or because of imminent hazard. 		
Nuclear Reactors and Support Facilities
 	Uranium mills, commercial power reactors, fuel reprocessing plants, and uranium enrichment facilities. 		
Nuclear Winter
 	Prediction by some scientists that smoke and debris rising from massive fires of a nuclear war could block sunlight for weeks or months, cooling the earth's surface and producing climate changes that could, for example, negatively affect world agricultural and weather patterns. 		
Nuclide
 	An atom characterized by the number of protons, neutrons, and energy in the nucleus. 		
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. 		
Nutrient Pollution
 	Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern. 		
Ocean Discharge Waiver
 	A variance from Clean Water Act requirements for discharges into marine waters. 		
Odor Threshold
 	The minimum odor of a water or air sample that can just be detected after successive dilutions with odorless water. 		
OECD Guidelines
 	Testing guidelines prepared by the Organization of Economic and Cooperative Development of the United Nations. They assist in preparation of protocols for studies of toxicology, environmental fate, etc. 		
Off-Site Facility
 	A hazardous waste treatment, storage or disposal area that is located away from the generating site. 		
Office Paper
 	High grade papers such as copier paper, computer printout, and stationary almost entirely made of uncoated chemical pulp, although some ground wood is used. Such waste is also generated in homes, schools, and elsewhere. 		
Offsets
 	A concept whereby emissions from proposed new or modified stationary sources are balanced by reductions from existing sources to stabilize total emissions. 		
Offstream Use
 	Water withdrawn from surface or groundwater sources for use at another place. 		
Oil and Gas Waste
 	Gas and oil drilling muds, oil production brines, and other waste associated with exploration for, development and production of crude oil or natural gas. 		
Oil Desulfurization
 	Widely used precombustion method for reducing sulfur dioxide emissions from oil-burning power plants. The oil is treated with hydrogen, which removes some of the sulfur by forming hydrogen sulfide gas. 		
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. 		
Oligotrophic Lakes
 	Deep clear lakes with few nutrients, little organic matter and a high dissolved-oxygen level. 		
On-Scene Coordinator
 	The predesignated EPA, Coast Guard, or Department of Defense official who coordinates and directs Superfund removal actions or Clean Water Act oil- or hazardous-spill response actions. 	OSC 	
On-Site Facility
 	A hazardous waste treatment, storage or disposal area that is located on the generating site. 		
Onboard Controls
 	Devices placed on vehicles to capture gasoline vapor during refueling and route it to the engines when the vehicle is starting so that it can be efficiently burned. 		
Onconogenicity
 	The capacity to induce cancer. 		
One-hit Model
 	A mathematical model based on the biological theory that a single "hit" of some minimum critical amount of a carcinogen at a cellular target such as DNA can start an irreversible series events leading to a tumor. 		
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. 		
Open Burning
 	Uncontrolled fires in an open dump. 		
Open Dump
 	An uncovered site used for disposal of waste without environmental controls. 		
Operable Unit
 	Term for each of a number of separate activities undertaken as part of a Superfund site cleanup. A typical operable unit would be removal of drums and tanks from the surface of a site. 		
Operating Conditions
 	Conditions specified in a RCRA permit that dictate how an incinerator must operate as it burns different waste types. A trial burn is used to identify operating conditions needed to meet specified performance standards. 		
Operation and Maintenance
 	Definition 1: Activities conducted after a Superfund site action is completed to ensure that the action is effective. 
Definition 2: Actions taken after construction to ensure that facilities constructed to treat waste water will be properly operated and maintained to achieve normative efficiency levels and prescribed effluent limitations in an optimum manner. 
Definition 3: On-going asbestos management plan in a school or other public building, including regular inspections, various methods of maintaining asbestos in place, and removal when necessary. 
		
Operator Certification
 	Certification of operators of community and nontransient noncommunity water systems, asbestos specialists, pesticide applicators, hazardous waste transporter, and other such specialists as required by the EPA or a state agency implementing an EPA-approved environmental regulatory program. 		
Optimal Corrosion Control Treatment
 	An erosion control treatment that minimizes the lead and copper concentrations at users' taps while also ensuring that the treatment does not cause the water system to violate any national primary drinking water regulations. 		
Oral Toxicity
 	Ability of a pesticide to cause injury when ingested. 		
Organic
 	Definition 1: Referring to or derived from living organisms. 
Definition 2: In chemistry, any compound containing carbon. 
		
Organic Chemicals/Compounds
 	Naturally occurring (animal or plant-produced or synthetic) 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. 		
Organism
 	Any form of animal or plant life. 		
Organophosphates
 	Pesticides that contain phosphorus; short-lived, but some can be toxic when first applied. 		
Organophyllic
 	A substance that easily combines with organic compounds. 		
Organotins
 	Chemical compounds used in anti-foulant paints to protect the hulls of boats and ships, buoys, and pilings from marine organisms such as barnacles. 		
Original AHERA Inspection/Original Inspection/Inspection
 	Examination of school buildings arranged by Local Education Agencies to identify asbestos-containing-materials, evaluate their condition, and take samples of materials suspected to contain asbestos; performed by EPA-accredited inspectors. 		
Original Generation Point
 	Where regulated medical or other material first becomes waste. 		
Ortho P
 			
Osmosis
 	The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids. 		
Other Ferrous Metals
 	Recyclable metals from strapping, furniture, and metal found in tires and consumer electronics but does not include metals found in construction materials or cars, locomotives, and ships. 		
Other Glass
 	Recyclable glass from furniture, appliances, and consumer electronics. Does not include glass from transportation products (cars trucks or shipping containers) and construction or demolition debris. 		
Other Nonferrous Metals
 	Recyclable nonferrous metals such as lead, copper, and zinc from appliances, consumer electronics, and nonpackaging aluminum products. Does not include nonferrous metals from industrial applications and construction and demolition debris. 		
Other Paper
 	For Recyclable paper from books, third-class mail, commercial printing, paper towels, plates and cups; and other nonpackaging paper such as posters, photographic papers, cards and games, milk cartons, folding boxes, bags, wrapping paper, and paperboard. Does not include wrapping paper or shipping cartons. 		
Other Plastics
 	Recyclable plastic from appliances, eating utensils, plates, containers, toys, and various kinds of equipment. Does not include heavy-duty plastics such as yielding materials. 		
Other Solid Waste
 	Recyclable nonhazardous solid wastes, other than municipal solid waste, covered under Subtitle D of RARA. 		
Other Wood
 	Recyclable wood from furniture, consumer electronics cabinets, and other nonpackaging wood products. Does not include lumber and tree stumps recovered from construction and demolition activities, and industrial process waste such as shavings and sawdust. 		
Outdoor Air Supply
 	Air brought into a building from outside. 		
Outfall
 	The place where effluent is discharged into receiving waters. 		
Overburden
 	Rock and soil cleared away before mining. 		
Overdraft
 	The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin; 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. 		
Overflow Rate
 	One of the guidelines for design of the settling tanks and clarifiers in a treatment plant; used by plant operators to determine if tanks and clarifiers are over or under-used. 		
Overland Flow
 	A land application technique that cleanses waste water by allowing it to flow over a sloped surface. As the water flows over the surface, contaminants are absorbed and the water is collected at the bottom of the slope for reuse. 		
Oversized Regulated Medical Waste
 	Medical waste that is too large for plastic bags or standard containers. 		
Overturn
 	One complete cycle of top to bottom mixing of previously stratified water masses. This phenomenon may occur in spring or fall, or after storms, and results in uniformity of chemical and physical properties of water at all depths. 		
Oxidant
 	A collective term for some of the primary constituents of photochemical smog. 		
Oxidation
 	The chemical addition of oxygen to break down pollutants or organic waste; e.g., destruction of chemicals such as cyanides, phenols, and organic sulfur compounds in sewage by bacterial and chemical means. 		
Oxidation Pond
 	A man-made (anthropogenic) body of water in which waste is consumed by bacteria, used most frequently with other waste-treatment processes; a sewage lagoon. 		
Oxidation-Reduction Potential
 	The electric potential required to transfer electrons from one compound or element (the oxidant) to another compound (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems. 		
Oxygenated Fuels
 	Gasoline which has been blended with alcohols or ethers that contain oxygen in order to reduce carbon monoxide and other emissions. 		
Oxygenated Solvent
 	An organic solvent containing oxygen as part of the molecular structure. Alcohols and ketones are oxygenated compounds often used as paint solvents. 		
Ozonation
 	Application of ozone to water for disinfection or for taste and odor control. The ozonator is the device that does this. 		
Ozonator
 	See: Ozonation 		
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 wide- spread 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. 	O3 	
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
 	A thinning break in the stratospheric ozone layer. Designation of amount of such depletion as an "ozone hole" is made when the detected amount of depletion exceeds fifty percent. Seasonal ozone holes have been observed over both the Antarctic and Arctic regions, 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 that reaches the earth's surface. 		
Packaging
 	The assembly of one or more containers and any other components necessary to ensure minimum compliance with a program's storage and shipment packaging requirements. Also, the containers, etc. involved. 		
Packed Bed Scrubber
 	An air pollution control device in which emissions pass through alkaline water to neutralize hydrogen chloride gas. 		
Packed Tower
 	A pollution control device that forces dirty air through a tower packed with crushed rock or wood chips while liquid is sprayed over the packing material. The pollutants in the air stream either dissolve or chemically react with the liquid. 		
Packer
 	An inflatable gland, or balloon, used to create a temporary seal in a borehole, probe hole, well, or drive casing. It is made of rubber or non-reactive materials. 		
Palatable Water
 	Water, at a desirable temperature, that is free from objectionable tastes, odors, colors, and turbidity. 		
Pandemic
 	A widespread epidemic throughout an area, nation or the world. 		
Paper
 	In the recycling business, refers to products and materials, including newspapers, magazines, office papers, corrugated containers, bags and some paperboard packaging that can be recycled into new paper products. 		
Paper Processor/Plastics Processor
 	Intermediate facility where recovered paper or plastic products and materials are sorted, decontaminated, and prepared for final recycling. 		
Parameter
 	A variable, measurable property whose value is a determinant of the characteristics of a system; e.g. temperature, pressure, and density are parameters of the atmosphere. 		
Paraquat
 	A standard herbicide used to kill various types of crops, including marijuana. Causes lung damage if smoke from the crop is inhaled. 		
Parshall Flume
 	Device used to measure the flow of water in an open channel. 		
Part A Permit
 			
Part B Permit
 			
Participation Rate
 	Portion of population participating in a recycling program. 		
Particle Count
 	Results of a microscopic examination of treated water with a special "particle counter" that classifies suspended particles by number and size. 		
Particulate Loading
 	The mass of particulates per unit volume of air or water. 		
Particulates
 	Definition 1: Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog, found in air or emissions. 
Definition 2: Very small solids suspended in water; they can vary in size, shape, density and electrical charge and can be gathered together by coagulation and flocculation. 
		
Partition Coefficient
 	Measure of the sorption phenomenon, whereby a pesticide is divided between the soil and water phase. 		
Parts Per Billion
 	Units commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in water, land, or air. 	ppb 	
Parts Per Million
 	Units commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in water, land, or air. 	ppm 	
Passive Smoking
 	Inhalation of others' tobacco smoke. 		
Passive Treatment Walls
 	Technology in which a chemical reaction takes place when contaminated ground water comes in contact with a barrier such as limestone or a wall containing iron filings. 		
Pathogens
 	Microorganisms (e.g., bacteria, viruses, or parasites) that can cause disease in humans, animals and plants. 		
Pathway
 	The physical course a chemical or pollutant takes from its source to the exposed organism. 		
Pay-As-You-Throw
 	Systems under which residents pay for municipal waste management and disposal services by weight or volume collected, not a fixed fee. 		
Peak Electricity Demand
 	The maximum electricity used to meet the cooling load of a building or buildings in a given area. 		
Peak Levels
 	Levels of airborne pollutant contaminants much higher than average or occurring for short periods of time in response to sudden releases. 		
Percent Saturation
 	The amount of a substance that is dissolved in a solution compared to the amount that could be dissolved in it. 		
Perched Water
 	Zone of unpressurized water held above the water table by impermeable rock or sediment. 		
Percolating Water
 	Water that passes through rocks or soil under the force of gravity. 		
Percolation
 	Definition 1: The movement of water downward and radially through subsurface soil layers, usually continuing downward to ground water. Can also involve upward movement of water. 
Definition 2: Slow seepage of water through a filter. 
		
Performance Bond
 	Cash or securities deposited before a landfill operating permit is issued, which are held to ensure that all requirements for operating and subsequently closing the landfill are faithful performed. The money is returned to the owner after proper closure of the landfill is completed. If contamination or other problems appear at any time during operation, or upon closure, and are not addressed, the owner must forfeit all or part of the bond which is then used to cover clean-up costs. 		
Performance Data (For Incinerators)
 	Information collected, during a trial burn, on concentrations of designated organic compounds and pollutants found in incinerator emissions. Data analysis must show that the incinerator meets performance standards under operating conditions specified in the RCRA permit. 		
Performance Standards
 	Definition 1: Regulatory requirements limiting the concentrations of designated organic compounds, particulate matter, and hydrogen chloride in emissions from incinerators. 
Definition 2: Operating standards established by EPA for various permitted pollution control systems, asbestos inspections, and various program operations and maintenance requirements. 
		
Periphyton
 	Microscopic underwater plants and animals that are firmly attached to solid surfaces such as rocks, logs, and pilings. 		
Permeability
 	The rate at which liquids pass through soil or other materials in a specified direction. 		
Permissible Dose
 	The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result. 		
Permissible Exposure Limit
 	Federal limits for workplace exposure to contaminants as established by OSHA. 	PEL 	
Permit
 	An authorization, license, or equivalent control document issued by EPA or an approved state agency to implement the requirements of an environmental regulation; e.g. a permit to operate a wastewater treatment plant or to operate a facility that may generate harmful emissions. 		
Persistence
 	Refers to the length of time a compound stays in the environment, once introduced. A compound may persist for less than a second or indefinitely. 		
Persistent Pesticides
 	Pesticides that do not break down chemically or break down very slowly and remain in the environment after a growing season. 		
Personal Air Samples
 	Air samples taken with a pump that is directly attached to the worker with the collecting filter and cassette placed in the worker's breathing zone (required under OSHA asbestos standards and EPA worker protection rule). 		
Personal Measurement
 	A measurement collected from an individual's immediate environment. 		
Personal Protective Equipment
 	Clothing and equipment worn by pesticide mixers, loaders and applicators and re-entry workers, hazmat emergency responders, workers cleaning up Superfund sites, et. al., which is worn to reduce their exposure to potentially hazardous chemicals and other pollutants. 		
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. 		
Pest Control Operator
 	Person or company that applies pesticides as a business (e.g. exterminator); usually describes household services, not agricultural applications. 		
Pesticide
 	Substances or mixture there of intended for preventing, destroying, repelling, or mitigating any pest. Also, any substance or mixture intended for use as a plant regulator, defoliant, or desiccant. 		
Pesticide Regulation Notice
 	Formal notice to pesticide registrants about important changes in regulatory policy, procedures, regulations. 		
Pesticide Tolerance
 	The amount of pesticide residue allowed by law to remain in or on a harvested crop. EPA sets these levels well below the point where the compounds might be harmful to consumers. 		
Petroleum
 	Crude oil or any fraction thereof that is liquid under normal conditions of temperature and pressure. The term includes petroleum-based substances comprising a complex blend of hydrocarbons derived from crude oil through the process of separation, conversion, upgrading, and finishing, such as motor fuel, jet oil, lubricants, petroleum solvents, and used oil. 		
Petroleum Derivatives
 	Chemicals formed when gasoline breaks down in contact with ground water. 		
pH
 	An expression of the intensity of the basic or acid condition of a liquid; may range from 0 to 14, where 0 is the most acid and 7 is neutral. Natural waters usually have a pH between 6.5 and 8.5. 		
Pharmacokinetics
 	The study of the way that drugs move through the body after they are swallowed or injected. 		
Phenolphthalein Alkalinity
 	The alkalinity in a water sample measured by the amount of standard acid needed to lower the pH to a level of 8.3 as indicated by the change of color of the phenolphthalein from pink to clear. 		
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. 		
Phosphogypsum Piles
 	Principal byproduct generated in production of phosphoric acid from phosphate rock. These piles may generate radioactive radon gas. 		
Phosphogypsum Stacks
 			
Phosphorus
 	An essential chemical food element that can contribute to the eutrophication of lakes and other water bodies. Increased phosphorus levels result from discharge of phosphorus-containing materials into surface waters. 		
Phosphorus Plants
 	Facilities using electric furnaces to produce elemental phosphorous for commercial use, such as high grade phosphoric acid, phosphate-based detergent, and organic chemicals use. 		
Photochemical Oxidants
 	Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons. 		
Photochemical Smog
 	Air pollution caused by chemical reactions of various pollutants emitted from different sources. 		
Photosynthesis
 	The manufacture by plants of carbohydrates and oxygen from carbon dioxide mediated by chlorophyll in the presence of sunlight. 		
Physical and Chemical Treatment
 	Processes generally used in large-scale wastewater treatment facilities. Physical processes may include air-stripping or filtration. Chemical treatment includes coagulation, chlorination, or ozonation. The term can also refer to treatment of toxic materials in surface and ground waters, oil spills, and some methods of dealing with hazardous materials on or in the ground. 		
Phytoplankton
 	That portion of the plankton community comprised of tiny plants; e.g. algae, diatoms. 		
Phytoremediation
 	Low-cost remediation option for sites with widely dispersed contamination at low concentrations. 		
Phytotoxic
 	Harmful to plants. 		
Phytotreatment
 	The cultivation of specialized plants that absorb specific contaminants from the soil through their roots or foliage. This reduces the concentration of contaminants in the soil, but incorporates them into biomasses that may be released back into the environment when the plant dies or is harvested. 		
Picocuries Per Liter
 	A unit of measure for levels of radon gas; becquerels per cubic meter is metric equivalent. 	pCi/L 	
Piezometer
 	A nonpumping well, generally of small diameter, for measuring the elevation of a water table. 		
Pigtail
 			
Pilot Tests
 	Testing a cleanup technology under actual site conditions to identify potential problems prior to full-scale implementation. 		
PL
 			
Plankton
 	Tiny plants and animals that live in water. 		
Plant-Derived Pesticide
 			
Plasma Arc Reactors
 	devices that use an electric arc to thermally decompose organic and inorganic materials at ultra-high temperatures into gases and a vitrified slag residue. A plasma arc reactor can operate as any of the following: (1) integral component of chemical, fuel, or electricity production systems, processing high or medium value organic compounds into a synthetic gas used as a fuel. (2) materials recovery device, processing scrap to recover metal from the slag. (3) destruction or incineration system, processing waste materials into slag and gases ignited inside of a secondary combustion chamber that follows the reactor. 		
Plasmid
 	A circular piece of DNA that exists apart from the chromosome and replicates independently of it. Bacterial plasmids carry information that renders the bacteria resistant to antibiotics. Plasmids are often used in genetic engineering to carry desired genes into organisms. 		
Plastics
 	Non-metallic chemoreactive compounds molded into rigid or pliable construction materials, fabrics, etc. 		
Plate Tower Scrubber
 	An air pollution control device that neutralizes hydrogen chloride gas by bubbling alkaline water through holes in a series of metal plates. 		
Plug Flow
 	Type of flow the occurs in tanks, basins, or reactors when a slug of water moves through without ever dispersing or mixing with the rest of the water flowing through. 		
Plugging
 	Act or process of stopping the flow of water, oil, or gas into or out of a formation through a borehole or well penetrating that formation. 		
Plume
 	Definition 1: A visible or measurable discharge of a contaminant from a given point of origin. Can be visible or thermal in water, or visible in the air as, for example, a plume of smoke. 
Definition 2: The area of radiation leaking from a damaged reactor. 
Definition 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. 		
PM-10/PM-2.5
 	PM 10 is measure of particles in the atmosphere with a diameter of less than ten or equal to a nominal 10 micrometers. PM-2.5 is a measure of smaller particles in the air. PM-10 has been the pollutant particulate level standard against which EPA has been measuring Clean Air Act compliance. On the basis of newer scientific findings, the Agency is considering regulations that will make PM-2.5 the new "standard". 		
Pneumoconiosis
 	Health conditions characterized by permanent deposition of substantial amounts of particulate matter in the lungs and by the tissue reaction to its presence; can range from relatively harmless forms of sclerosis to the destructive fibrotic effect of silicosis. 		
Point-of-Contact Measurement of Exposure
 	Estimating exposure by measuring concentrations over time (while the exposure is taking place) at or near the place where it is occurring. 		
Point-of-Disinfectant Application
 	The point where disinfectant is applied and water downstream of that point is not subject to recontamination by surface water runoff. 		
Point-of-Use Treatment Device
 	Treatment device applied to a single tap to reduce contaminants in the drinking water at the one faucet. 		
Point Source
 	A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution; e.g. a pipe, ditch, ship, ore pit, factory smokestack. 		
Pollen
 	The fertilizing element of flowering plants; background air pollutant. 		
Pollutant
 	Generally, any substance introduced into the environment that adversely affects the usefulness of a resource or the health of humans, animals, or ecosystems. 		
Pollutant Pathways
 	Avenues for distribution of pollutants. In most buildings, for example, HVAC systems are the primary pathways although all building components can interact to affect how air movement distributes pollutants. 		
Pollutant Standard Index
 	Indicator of one or more pollutants that may be used to inform the public about the potential for adverse health effects from air pollution in major cities. 	PSI 	
Pollution
 	Generally, the presence of a substance in the environment that because of its chemical composition or quantity prevents the functioning of natural processes and produces undesirable environmental and health effects. Under the Clean Water Act, for example, the term has been defined as the man-made or man-induced alteration of the physical, biological, chemical, and radiological integrity of water and other media. 		
Pollution Prevention
 	Definition 1: Identifying areas, processes, and activities which create excessive waste products or pollutants in order to reduce or prevent them through, alteration, or eliminating a process. Such activities, consistent with the Pollution Prevention Act of 1990, are conducted across all EPA programs and can involve cooperative efforts with such agencies as the Departments of Agriculture and Energy. 
Definition 2: EPA has initiated a number of voluntary programs in which industrial, or commercial or "partners" join with EPA in promoting activities that conserve energy, conserve and protect water supply, reduce emissions or find ways of utilizing them as energy resources, and reduce the waste stream. Among these are: Agstar, to reduce methane emissions through manure management. Climate Wise, to lower industrial greenhouse-gas emissions and energy costs. Coalbed Methane Outreach, to boost methane recovery at coal mines. Design for the Environment, to foster including environmental considerations in product design and processes. Energy Star programs, to promote energy efficiency in commercial and residential buildings, office equipment, transformers, computers, office equipment, and home appliances. Environmental Accounting, to help businesses identify environmental costs and factor them into management decision making. Green Chemistry, to promote and recognize cost-effective breakthroughs in chemistry that prevent pollution. Green Lights, to spread the use of energy-efficient lighting technologies. Indoor Environments, to reduce risks from indoor-air pollution. Landfill Methane Outreach, to develop landfill gas-to-energy projects. Natural Gas Star, to reduce methane emissions from the natural gas industry. Ruminant Livestock Methane, to reduce methane emissions from ruminant livestock. Transportation Partners, to reduce carbon dioxide emissions from the transportation sector. Voluntary Aluminum Industrial Partnership, to reduce perfluorocarbon emissions from the primary aluminum industry. WAVE, to promote efficient water use in the lodging industry. Wastewi$e, to reduce business-generated solid waste through prevention, reuse, and recycling. 
		
Polonium
 	A radioactive element that occurs in pitchblende and other uranium-containing ores. 		
Polychlorinated Biphenyls
 	A group of toxic, persistent chemicals used in electrical transformers and capacitors for insulating purposes, and in gas pipeline systems as lubricant. The sale and new use of these chemicals, also known as PCBs, were banned by law in 1979. 	PCBs 	
Polyelectrolytes
 	Synthetic chemicals that help solids to clump during sewage treatment. 		
Polyethylene Terepthalate
 	Thermoplastic material used in plastic soft drink and rigid containers. 	PETE 	
Polymer
 	A natural or synthetic chemical structure where two or more like molecules are joined to form a more complex molecular structure (e.g. polyethylene in plastic). 		
Polyvinyl Chloride
 	A tough, environmentally indestructible plastic that releases hydrochloric acid when burned. 	PVC 	
Population
 	A group of interbreeding organisms occupying a particular space; the number of humans or other living creatures in a designated area. 		
Population at Risk
 	A population subgroup that is more likely to be exposed to a chemical, or is more sensitive to the chemical, than is the general population. 		
Porosity
 	Degree to which soil, gravel, sediment, or rock is permeated with pores or cavities through which water or air can move. 		
Portal-of-Entry Effect
 	A local effect produced in the tissue or organ of first contact between a toxicant and the biological system. 		
Post-Chlorination
 	Addition of chlorine to plant effluent for disinfectant purposes after the effluent has been treated. 		
Post-Closure
 	The time period following the shutdown of a waste management or manufacturing facility; for monitoring purposes, often considered to be 30 years. 		
Post-Consumer Materials
 	Materials or finished products that have served their intended use and have been diverted or recovered from waste destined for disposal, having completed their lives as consumer items. Postconsumer materials are part of the broader category of recovered materials. 		
Post-Consumer Recycling
 	Use of materials generated from residential and consumer waste for new or similar purposes; e.g. converting wastepaper from offices into corrugated boxes or newsprint. 		
Post-Consumer Waste
 			
Potable Water
 	Water that is safe for drinking and cooking. 		
Potential Dose
 	The amount of a compound contained in material swallowed, breathed, or applied to the skin. 		
Potentially Responsible Party
 	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, EPA requires PRPs to clean up hazardous sites they have contaminated. 	PRP 	
Potentiation
 	The ability of one chemical to increase the effect of another chemical. 		
Potentiometric Surface
 	The surface to which water in an aquifer can rise by hydrostatic pressure. 		
Pre-Consumer Materials
 	Materials generated in manufacturing and converting processes such as manufacturing scrap and trimmings and cuttings. Includes print overruns, overissue publications, and obsolete inventories. 		
Pre-Consumer Waste
 			
Pre-Harvest Interval
 	The time between the last pesticide application and harvest of the treated crops. 		
Precautionary Principle
 	When information about potential risks is incomplete, basing decisions about the best ways to manage or reduce risks on a preference for avoiding unnecessary health risks instead of on unnecessary economic expenditures. 		
Prechlorination
 	The addition of chlorine at the headworks of a treatment plant prior to other treatment processes. Done mainly for disinfection and control of tastes, odors, and aquatic growths, and to aid in coagulation and settling. 		
Precipitate
 	A substance separated from a solution or suspension by chemical or physical change. 		
Precipitation
 	Removal of hazardous solids from liquid waste to permit safe disposal; removal of particles from airborne emissions as in rain (e.g. acid precipitation). 		
Precipitator
 	Pollution control device that collects particles from an air stream. 		
Precursor
 	In photochemistry, a compound antecedent to a pollutant. For example, volatile organic compounds (VOCs) and nitric oxides of nitrogen react in sunlight to form ozone or other photochemical oxidants. As such, VOCs and oxides of nitrogen are precursors. 		
Preliminary Assessment
 	The process of collecting and reviewing available information about a known or suspected waste site or release. 		
Prescriptive
 	Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures; e.g. filing a request with a state agency to use unused water in a stream, river, or lake. 		
Pressed Wood Products
 	Materials used in building and furniture construction that are made from wood veneers, particles, or fibers bonded together with an adhesive under heat and pressure. 		
Pressure Sewers
 	A system of pipes in which water, wastewater, or other liquid is pumped to a higher elevation. 		
Pressure, Static
 	In flowing air, the total pressure minus velocity pressure, pushing equally in all directions. 		
Pressure, Total
 	In flowing air, the sum of the static and velocity pressures. 		
Pressure, Velocity
 	In flowing air, the pressure due to velocity and density of air. 		
Pretreatment
 	Processes used to reduce, eliminate, or alter the nature of wastewater pollutants from non-domestic sources before they are discharged into publicly owned treatment works (POTWs). 		
Prevalent Level Samples
 	Air samples taken under normal conditions. 		
Prevalent Levels
 	Levels of airborne contaminant occurring under normal conditions. 		
Prevention of Significant Deterioration
 	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. 	PSD 	
Primacy
 	Having the primary responsibility for administering and enforcing regulations. 		
Primary Drinking Water Regulation
 	Applies to public water systems and specifies a contaminant level, which, in the judgment of the EPA Administrator, will not adversely affect human health. 		
Primary Effect
 	An effect where the stressor acts directly on the ecological component of interest, not on other parts of the ecosystem. 		
Primary Standards
 	National ambient air quality standards designed to protect human health with an adequate margin for safety. 		
Primary Treatment
 	First stage of wastewater treatment in which solids are removed by screening and settling. 		
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. 		
Principal Organic Hazardous Constituents
 	Hazardous compounds monitored during an incinerator's trial burn, selected for high concentration in the waste feed and difficulty of combustion. 	POHCs 	
Prions
 	Microscopic particles made of protein that can cause disease. 		
Prior Appropriation
 	A doctrine of water law that allocates the rights to use water on a first-come, first-served basis. 		
Probability of Detection
 	The likelihood, expressed as a percentage, that a test method will correctly identify a leaking tank. 		
Process Variable
 	A physical or chemical quantity which is usually measured and controlled in the operation of a water treatment plant or industrial plant. 		
Process Verification
 	Verifying that process raw materials, water usage, waste treatment processes, production rate and other facts relative to quantity and quality of pollutants contained in discharges are substantially described in the permit application and the issued permit. 		
Process Wastewater
 	Any water that comes into contact with any raw material, product, byproduct, or waste. 		
Process Weight
 	Total weight of all materials, including fuel, used in a manufacturing process; used to calculate the allowable particulate emission rate. 		
Producers
 	Plants that perform photosynthesis and provide food to consumers. 		
Product Level
 	The level of a product in a storage tank. 		
Product Water
 	Water that has passed through a water treatment plant and is ready to be delivered to consumers. 		
Products of Incomplete Combustion
 	Organic compounds formed by combustion. Usually generated in small amounts and sometimes toxic, PICs are heat-altered versions of the original material fed into the incinerator (e.g. charcoal is a P.I.C. from burning wood). 	PICs 	
Project XL
 	An EPA initiative to give states and the regulated community the flexibility to develop comprehensive strategies as alternatives to multiple current regulatory requirements in order to exceed compliance and increase overall environmental benefits. (Pollution Prevention (2)) 		
Propellant
 	Liquid in a self-pressurized pesticide product that expels the active ingredient from its container. 		
Proportionate Mortality Ratio
 	The number of deaths from a specific cause in a specific period of time per 100 deaths from all causes in the same time period. 	PMR 	
Proposed Plan
 	A plan for a site cleanup that is available to the public for comment. 		
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. 		
Protocol
 	A series of formal steps for conducting a test. 		
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
 	One-celled animals that are larger and more complex than bacteria. May cause disease. 		
Public Comment Period
 	The time allowed for the public to express its views and concerns regarding an action by EPA (e.g. a Federal Register Notice of proposed rule-making, a public notice of a draft permit, or a Notice of Intent to Deny). 		
Public Health Approach
 	Regulatory and voluntary focus on effective and feasible risk management actions at the national and community level to reduce human exposures and risks, with priority given to reducing exposures with the biggest impacts in terms of the number affected and severity of effect. 		
Public Health Context
 	The incidence, prevalence, and severity of diseases in communities or populations and the factors that account for them, including infections, exposure to pollutants, and other exposures or activities. 		
Public Hearing
 	A formal meeting wherein EPA officials hear the public's views and concerns about an EPA action or proposal. EPA is required to consider such comments when evaluating its actions. Public hearings must be held upon request during the public comment period. 		
Public Notice
 	Definition 1: Notification by EPA informing the public of Agency actions such as the issuance of a draft permit or scheduling of a hearing. EPA is required to ensure proper public notice, including publication in newspapers and broadcast over radio and television stations. 
Definition 2: In the safe drinking water program, water suppliers are required to publish and broadcast notices when pollution problems are discovered. 
		
Public Water System
 	A system that provides piped water for human consumption to at least 15 service connections or regularly serves 25 individuals. 		
Publicly Owned Treatment Works
 	A waste-treatment works owned by a state, unit of local government, or Indian tribe, usually designed to treat domestic wastewaters. 	POTWs 	
Pumping Station
 	Mechanical device installed in sewer or water system or other liquid-carrying pipelines to move the liquids to a higher level. 		
Pumping Test
 	A test conducted to determine aquifer or well characteristics. 		
Purging
 	Removing stagnant air or water from sampling zone or equipment prior to sample collection. 		
Push Technology
 			
Putrefaction
 	Biological decomposition of organic matter; associated with anaerobic conditions. 		
Putrescible
 	Able to rot quickly enough to cause odors and attract flies. 		
Pyrolysis
 	Decomposition of a chemical by extreme heat. 		
Qualitative Use Assessment
 	Report summarizing the major uses of a pesticide including percentage of crop treated, and amount of pesticide used on a site. 		
Quality Assurance
 			
Quality Control
 	A system of procedures, checks, audits, and corrective actions to ensure that all EPA research design and performance, environmental monitoring and sampling, and other technical and reporting activities are of the highest achievable quality. 		
Quench Tank
 	A water-filled tank used to cool incinerator residues or hot materials during industrial processes. 		
Radiant Energy
 			
Radiation
 	Transmission of energy though space or any medium. 		
Radiation Standards
 	Regulations that set maximum exposure limits for protection of the public from radioactive materials. 		
Radio Frequency Radiation
 			
Radioactive Decay
 	Spontaneous change in an atom by emission of charged particles and/or gamma rays. 		
Radioactive Disintegration
 			
Radioactive Substances
 	Substances that emit ionizing radiation. 		
Radioactive Waste
 	Any waste that emits energy as rays, waves, streams or energetic particles. Radioactive materials are often mixed with hazardous waste, from nuclear reactors, research institutions, or hospitals. 		
Radioactivity
 			
Radioisotopes
 	Chemical variants of radioactive elements with potentially oncogenic, teratogenic, and mutagenic effects on the human body. 		
Radionuclide
 	Radioactive particle, man-made (anthropogenic) or natural, with a distinct atomic weight number. Can have a long life as soil or water pollutant. 		
Radius of Influence
 	Definition 1: The radial distance from the center of a wellbore to the point where there is no lowering of the water table or potentiometric surface (the edge of the cone of depression). 
Definition 2: The radial distance from an extraction well that has adequate air flow for effective removal of contaminants when a vacuum is applied to the extraction well. 
		
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, radioactive, inert gas formed by radioactive decay of radium atoms in soil or rocks. 		
Radon Daughters
 	Short-lived radioactive decay products of radon that decay into longer-lived lead isotopes that can attach themselves to airborne dust and other particles and, if inhaled, damage the linings of the lungs. 		
Radon Decay Products
 	A term used to refer collectively to the immediate products of the radon decay chain. These include Po-218, Pb-214, Bi-214, and Po-214, which have an average combined half-life of about 30 minutes. 		
Radon Progeny
 			
Rainbow Report
 	Comprehensive document giving the status of all pesticides now or ever in registration or special reviews. Known as the "rainbow report" because chapters are printed on different colors of paper. 		
Rasp
 	A machine that grinds waste into a manageable material and helps prevent odor. 		
Raw Agricultural Commodity
 	An unprocessed human food or animal feed crop (e.g., raw carrots, apples, corn, or eggs.) 		
Raw Sewage
 	Untreated wastewater and its contents. 		
Raw Water
 	Intake water prior to any treatment or use. 		
Re-entry
 	(In indoor air program) Refers to air exhausted from a building that is immediately brought back into the system through the air intake and other openings. 		
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 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. 		
Real-Time Monitoring
 	Monitoring and measuring environmental developments with technology and communications systems that provide time-relevant information to the public in an easily understood format people can use in day-to-day decision-making about their health and the environment. 		
Reasonable Further Progress
 	Annual incremental reductions in air pollutant emissions as reflected in a State Implementation Plan that EPA deems sufficient to provide for the attainment of the applicable national ambient air quality standards by the statutory deadline. 		
Reasonable Maximum Exposure
 	The maximum exposure reasonably expected to occur in a population. 		
Reasonable Worst Case
 	An estimate of the individual dose, exposure, or risk level received by an individual in a defined population that is greater than the 90th percentile but less than that received by anyone in the 98th percentile in the same population. 		
Reasonably Available Control Measures
 	A broadly defined term referring to technological and other measures for pollution control. 	RACM 	
Reasonably Available Control Technology
 	Control technology that is reasonably available, and both technologically and economically feasible. Usually applied to existing sources in nonattainment areas; in most cases is less stringent than new source performance standards. 	RACT 	
Recarbonization
 	Process in which carbon dioxide is bubbled into water being treated to lower the pH. 		
Receiving Waters
 	A river, lake, ocean, stream or other watercourse into which wastewater or treated effluent is discharged. 		
Receptor
 	Ecological entity exposed to a stressor. 		
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. 		
Recharge Area
 	A land area in which water reaches the zone of saturation from surface infiltration, e.g., where rainwater soaks through the earth to reach an aquifer. 		
Recharge Rate
 	The quantity of water per unit of time that replenishes or refills 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. 		
Recommended Maximum Contaminant Level
 	The maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on human health would occur, and that includes an adequate margin of safety. Recommended levels are nonenforceable health goals. 	RMCL 	
Reconstructed Source
 	Facility in which components are replaced to such an extent that the fixed capital cost of the new components exceeds 50 percent of the capital cost of constructing a comparable brand-new facility. New-source performance standards may be applied to sources reconstructed after the proposal of the standard if it is technologically and economically feasible to meet the standards. 		
Reconstruction of Dose
 	Estimating exposure after it has occurred by using evidence within an organism such as chemical levels in tissue or fluids. 		
Record of Decision
 	A public document that explains which cleanup alternative(s) will be used at National Priorities List sites where, under CERCLA, Trust Funds pay for the cleanup. 	ROD 	
Recovery Rate
 	Percentage of usable recycled materials that have been removed from the total amount of municipal solid waste generated in a specific area or by a specific business. 		
Recycle
 	Minimizing waste generation by recovering and reprocessing usable products that might otherwise become waste (.i.e. recycling of aluminum cans, paper, and bottles, etc.). 		
Recycling and Reuse Business Assistance Centers
 	Located in state solid-waste or economic-development agencies, these centers provide recycling businesses with customized and targeted assistance. 		
Recycling Economic Development Advocates
 	Individuals hired by state or tribal economic development offices to focus financial, marketing, and permitting resources on creating recycling businesses. 		
Recycling Mill
 	Facility where recovered materials are remanufactured into new products. 		
Recycling Technical Assistance Partnership National Network
 	A national information-sharing resource designed to help businesses and manufacturers increase their use of recovered materials. 		
Red Bag Waste
 			
Red Border
 	An EPA document undergoing review before being submitted for final management decision-making. 		
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. 		
Redemption Program
 	Program in which consumers are monetarily compensated for the collection of recyclable materials, generally through prepaid deposits or taxes on beverage containers. In some states or localities legislation has enacted redemption programs to help prevent roadside litter. 		
Reduction
 	The addition of hydrogen, removal of oxygen, or addition of electrons to an element or compound. 		
Reentry Interval
 	The period of time immediately following the application of a pesticide during which unprotected workers should not enter a field. 		
Reference Dose
 	The RfD is a numerical estimate of a daily oral exposure to the human population, including sensitive subgroups such as children, that is not likely to cause harmful effects during a lifetime. RfDs are generally used for health effects that are thought to have a threshold or low dose limit for producing effects. 	RfD 	
Reformulated Gasoline
 	Gasoline with a different composition from conventional gasoline (e.g., lower aromatics content) that cuts air pollutants. 		
Refueling Emissions
 	Emissions released during vehicle re-fueling. 		
Refuse
 			
Refuse Reclamation
 	Conversion of solid waste into useful products; e.g., composting organic wastes to make soil conditioners or separating aluminum and other metals for recycling. 		
Regeneration
 	Manipulation of cells to cause them to develop into whole plants. 		
Regional Response Team
 	Representatives of federal, local, and state agencies who may assist in coordination of activities at the request of the On-Scene Coordinator before and during a significant pollution incident such as an oil spill, major chemical release, or Superfund response. 	RRT 	
Registrant
 	Any manufacturer or formulator who obtains registration for a pesticide active ingredient or product. 		
Registration
 	Formal listing with EPA of a new pesticide before it can be sold or distributed. Under the Federal Insecticide, Fungicide, and Rodenticide Act, EPA is responsible for registration (pre-market licensing) of pesticides on the basis of data demonstrating no unreasonable adverse effects on human health or the environment when applied according to approved label directions. 		
Registration Standards
 	Published documents which include summary reviews of the data available on a pesticide's active ingredient, data gaps, and the Agency's existing regulatory position on the pesticide. 		
Regulated Asbestos-Containing Material
 	Friable asbestos material or nonfriable ACM that will be or has been subjected to sanding, grinding, cutting, or abrading or has crumbled, or been pulverized or reduced to powder in the course of demolition or renovation operations. 	RACM 	
Regulated Medical Waste
 	Under the Medical Waste Tracking Act of 1988, any solid waste generated in the diagnosis, treatment, or immunization of human beings or animals, in research pertaining thereto, or in the production or testing of biologicals. Included are cultures and stocks of infectious agents; human blood and blood products; human pathological body wastes from surgery and autopsy; contaminated animal carcasses from medical research; waste from patients with communicable diseases; and all used sharp implements, such as needles and scalpels, and certain unused sharps. 		
Relative Ecological Sustainability
 	Ability of an ecosystem to maintain relative ecological integrity indefinitely. 		
Relative Permeability
 	The permeability of a rock to gas, NAIL, or water, when any two or more are present. 		
Relative Risk Assessment
 	Estimating the risks associated with different stressors or management actions. 		
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. 		
Remedial Action
 	The actual construction or implementation phase of a Superfund site cleanup that follows remedial design. 	RA 	
Remedial Design
 	A phase of remedial action that follows the remedial investigation/feasibility study and includes development of engineering drawings and specifications for a site cleanup. 		
Remedial Investigation
 	An in-depth study designed to gather data needed to determine the nature and extent of contamination at a Superfund site; establish site cleanup criteria; identify preliminary alternatives for remedial action; and support technical and cost analyses of alternatives. The remedial investigation is usually done with the feasibility study. Together they are usually referred to as the "RI/FS". 		
Remedial Project Manager
 	The EPA or state official responsible for overseeing on-site remedial action. 	RPM 	
Remedial Response
 	Long-term action that stops or substantially reduces a release or threat of a release of hazardous substances that is serious but not an immediate threat to public health. 		
Remediation
 	Definition 1: Cleanup or other methods used to remove or contain a toxic spill or hazardous materials from a Superfund site. 
Definition 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 collection and interpretation of information about an object without physical contact with the object; e.g., satellite imaging, aerial photography, and open path measurements. 		
Removal Action
 	Short-term immediate actions taken to address releases of hazardous substances that require expedited response. 		
Renewable Energy Production Incentive
 	Incentive established by the Energy Policy Act available to renewable energy power projects owned by a state or local government or nonprofit electric cooperative. 	REPI 	
Repeat Compliance Period
 	Any subsequent compliance period after the initial one. 		
Reportable Quantity
 	Quantity of a hazardous substance that triggers reports under CERCLA. If a substance exceeds its RQ, the release must be reported to the National Response Center, the SERC, and community emergency coordinators for areas likely to be affected. 	RQ 	
Repowering
 	Rebuilding and replacing major components of a power plant instead of building a new one. 		
Representative Sample
 	A portion of material or water that is as nearly identical in content and consistency as possible to that in the larger body of material or water being sampled. 		
Reregistration
 	The reevaluation and relicensing of existing pesticides originally registered prior to current scientific and regulatory standards. EPA reregisters pesticides through its Registration Standards Program. 		
Reserve Capacity
 	Extra treatment capacity built into solid waste and wastewater treatment plants and interceptor sewers to accommodate flow increases due to future population growth. 		
Reservoir
 	Any natural or artificial holding area used to store, regulate, or control water. 		
Residential Use
 	Pesticide application in and around houses, office buildings, apartment buildings, motels, and other living or working areas. 		
Residential Waste
 	Waste generated in single and multi-family homes, including newspapers, clothing, disposable tableware, food packaging, cans, bottles, food scraps, and yard trimmings other than those that are diverted to backyard composting. 		
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). 		
Residual Saturation
 	Saturation level below which fluid drainage will not occur. 		
Residue
 	The dry solids remaining after the evaporation of a sample of water or sludge. 		
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 process of obtaining matter or energy from materials formerly discarded. 		
Response Action
 	Definition 1: Generic term for actions taken in response to actual or potential health-threatening environmental events such as spills, sudden releases, and asbestos abatement/management problems. 
Definition 2: A CERCLA-authorized action involving either a short-term removal action or a long-term removal response. This may include but is not limited to: removing hazardous materials from a site to an EPA-approved hazardous waste facility for treatment, containment or treating the waste on-site, identifying and removing the sources of ground-water contamination and halting further migration of contaminants. 
Definition 3: Any of the following actions taken in school buildings in response to AHERA to reduce the risk of exposure to asbestos: removal, encapsulation, enclosure, repair, and operations and maintenance. 
		
Responsiveness Summary
 	A summary of oral and/or written public comments received by EPA during a comment period on key EPA documents, and EPA's response to those comments. 		
Restoration
 	Measures taken to return a site to pre-violation conditions. 		
Restricted Entry Interval
 	The time after a pesticide application during which entry into the treated area is restricted. 		
Restricted Use
 	A pesticide may be classified (under FIFRA regulations) for restricted use if it requires special handling because of its toxicity, and, if so, it may be applied only by trained, certified applicators or those under their direct supervision. 		
Restriction Enzymes
 	Enzymes that recognize specific regions of a long DNA molecule and cut it at those points. 		
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. 		
Reverse Osmosis
 	A treatment process used in water systems by adding pressure to force water through a semi-permeable membrane. Reverse osmosis removes most drinking water contaminants. Also used in wastewater treatment. Large-scale reverse osmosis plants are being developed. 		
Reversible Effect
 	An effect which is not permanent; especially adverse effects which diminish when exposure to a toxic chemical stops. 		
Ribonucleic Acid
 	A molecule that carries the genetic message from DNA to a cellular protein-producing mechanism. 	RNA 	
Rill
 	A small channel eroded into the soil by surface runoff; can be easily smoothed out or obliterated by normal tillage. 		
Ringlemann Chart
 	A series of shaded illustrations used to measure the opacity of air pollution emissions, ranging from light grey through black; used to set and enforce emissions standards. 		
Riparian Habitat
 	Areas adjacent to rivers and streams with a differing density, diversity, and productivity of plant and animal species relative to nearby uplands. 		
Riparian Rights
 	Entitlement of a land owner to certain uses of water on or bordering the property, including the right to prevent diversion or misuse of upstream waters. Generally a matter of state law. 		
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 (Adverse) for Endangered Species
 	Risk to aquatic species if anticipated pesticide residue levels equal one-fifth of LD10 or one-tenth of LC50; risk to terrestrial species if anticipated pesticide residue levels equal one-fifth of LC10 or one-tenth of LC50. 		
Risk Assessment
 	Qualitative and quantitative evaluation of the risk posed to human health and/or the environment by the actual or potential presence and/or use of specific pollutants. 		
Risk-based Targeting
 	The direction of resources to those areas that have been identified as having the highest potential or actual adverse effect on human health and/or the environment. 		
Risk Characterization
 	The last phase of the risk assessment process that estimates the potential for adverse health or ecological effects to occur from exposure to a stressor and evaluates the uncertainty involved. 		
Risk Communication
 	The exchange of information about health or environmental risks among risk assessors and managers, the general public, news media, interest groups, etc. 		
Risk Estimate
 	A description of the probability that organisms exposed to a specific dose of a chemical or other pollutant will develop an adverse response, e.g., cancer. 		
Risk Factor
 	Characteristics (e.g., race, sex, age, obesity) or variables (e.g., smoking, occupational exposure level) associated with increased probability of a toxic effect. 		
Risk for Non-Endangered Species
 	Risk to species if anticipated pesticide residue levels are equal to or greater than LC50. 		
Risk Management
 	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. 		
Risk-Specific Dose
 	The dose associated with a specified risk level. 		
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 sport or eating, such as gar and suckers. Most are more tolerant of changing environmental conditions than are game or food species. 		
Route of Exposure
 	The avenue by which a chemical comes into contact with an organism, e.g., inhalation, ingestion, dermal contact, injection. 		
Rubbish
 	Solid waste, excluding food waste and ashes, from homes, institutions, and workplaces. 		
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 receiving waters. 		
Running Losses
 	Evaporation of motor vehicle fuel from the fuel tank while the vehicle is in use. 		
Sacrificial Anode
 	An easily corroded material deliberately installed in a pipe or intake to give it up (sacrifice it) to corrosion while the rest of the water supply facility remains relatively corrosion-free. 		
Safe
 	Condition of exposure under which there is a practical certainty that no harm will result to exposed individuals. 		
Safe Water
 	Water that does not contain harmful bacteria, toxic materials, or chemicals, and is considered safe for drinking even if it may have taste, odor, color, and certain mineral problems. 		
Safe Yield
 	The annual amount of water that can be taken from a source of supply over a period of years without depleting that source beyond its ability to be replenished naturally in "wet years." 		
Safener
 	A chemical added to a pesticide to keep it from injuring plants. 		
Salinity
 	The percentage of salt 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. 		
Sampling Frequency
 	The interval between the collection of successive samples. 		
Sanctions
 	Actions taken by the federal government for failure to provide or implement a State Implementation Plan (SIP). Such action may 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 Landfill
 			
Sanitary Sewers
 	Underground pipes that carry off only domestic or industrial waste, not storm water. 		
Sanitary Survey
 	An on-site review of the water sources, facilities, equipment, operation and maintenance of a public water system to evaluate the adequacy of those elements for producing and distributing safe drinking water. 		
Sanitary Water
 	Water discharged from sinks, showers, kitchens, or other non-industrial operations, but not from commodes. 		
Sanitation
 	Control of physical factors in the human environment that could harm development, health, or survival. 		
Saprolite
 	A soft, clay-rich, thoroughly decomposed rock formed in place by chemical weathering of igneous or metamorphic rock. Forms in humid, tropical, or subtropical climates. 		
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 under pressure equal to or greater than that of the atmosphere. 		
Saturation
 	The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance at a given temperature and pressure. 		
Science Advisory Board
 	A group of external scientists who advise EPA on science and policy. 	SAB 	
Scrap
 	Materials discarded from manufacturing operations that may be suitable for reprocessing. 		
Scrap Metal Processor
 	Intermediate operating facility where recovered metal is sorted, cleaned of contaminants, and prepared for recycling. 		
Screening
 	Use of screens to remove coarse floating and suspended solids from sewage. 		
Screening Risk Assessment
 	A risk assessment performed with few data and many assumptions to identify exposures that should be evaluated more carefully for potential risk. 		
Scrubber
 	An air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions. 		
Secondary Drinking Water Regulations
 	Non-enforceable regulations applying to public water systems and specifying the maximum contamination levels that, in the judgment of EPA, are required to protect the public welfare. These regulations apply to any contaminants that may adversely affect the odor or appearance of such water and consequently may cause people served by the system to discontinue its use. 		
Secondary Effect
 	Action of a stressor on supporting components of the ecosystem, which in turn impact the ecological component of concern. 		
Secondary Materials
 	Materials that have been manufactured and used at least once and are to be used again. 		
Secondary Standards
 	National ambient air quality standards designed to protect welfare, including effects on soils, water, crops, vegetation, man-made (anthropogenic) materials, animals, wildlife, weather, visibility, and climate; damage to property; transportation hazards; economic values, and personal comfort and well-being. 		
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. 		
Secondhand Smoke
 			
Secure Chemical Landfill
 			
Secure Maximum Contaminant Level
 	Maximum permissible level of a contaminant in water delivered to the free flowing outlet of the ultimate user, or of contamination resulting from corrosion of piping and plumbing caused by water quality. 		
Sediment
 	Topsoil, sand, and minerals washed from the land into water, usually after rain or snow melt. 		
Sediment Yield
 	The quantity of sediment arriving at a specific location. 		
Sedimentation
 	Letting solids settle out of wastewater by gravity during treatment. 		
Sedimentation Tanks
 	Wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal. 		
Sediments
 	Soil, sand, and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish and wildlife habitat, and clouding the water so that sunlight cannot reach aquatic plants. Careless farming, mining, and building activities will expose sediment materials, allowing them to wash off the land after rainfall. 		
Seed Protectant
 	A chemical applied before planting to protect seeds and seedlings from disease or insects. 		
Seepage
 	Percolation of water through the soil from unlined canals, ditches, laterals, watercourses, or water storage facilities. 		
Selective Pesticide
 	A chemical designed to affect only certain types of pests, leaving other plants and animals unharmed. 		
Semi-Confined Aquifer
 	An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur. 		
Semivolatile Organic Compounds
 	Organic compounds that volatilize slowly at standard temperature (20 degrees C and 1 atm pressure). 		
Senescence
 	The aging process. Sometimes used to describe lakes or other bodies of water in advanced stages of eutrophication. Also used to describe plants and animals. 		
Septic System
 	An on-site system designed to treat and dispose of domestic sewage. A typical septic system consists of 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. 		
Septic Tank
 	An underground storage tank for wastes from homes not connected to a sewer line. Waste goes directly from the home to the tank. 		
Service Connector
 	The pipe that carries tap water from a public water main to a building. 		
Service Line Sample
 	A one-liter sample of water that has been standing for at least 6 hours in a service pipeline and is collected according to federal regulations. 		
Service Pipe
 	The pipeline extending from the water main to the building served or to the consumer's system. 		
Set-Back
 	Setting a thermometer to a lower temperature when the building is unoccupied to reduce consumption of heating energy. Also refers to setting the thermometer to a higher temperature during unoccupied periods in the cooling season. 		
Settleable Solids
 	Material heavy enough to sink to the bottom of a wastewater treatment tank. 		
Settling Chamber
 	A series of screens placed in the way of flue gases to slow the stream of air, thus helping gravity to pull particles into a collection device. 		
Settling Tank
 	A holding area for wastewater, where heavier particles sink to the bottom for removal and disposal. 		
Sewage
 	The waste and wastewater produced by residential and commercial sources and discharged into sewers. 		
Sewage Lagoon
 			
Sewage Sludge
 	Sludge produced at a Publicly Owned Treatment Works, the disposal of which is regulated under the Clean Water Act. 		
Sewer
 	A channel or conduit that carries wastewater and storm-water runoff from the source to a treatment plant or receiving stream. "Sanitary" sewers carry household, industrial, and commercial waste. "Storm" sewers carry runoff from rain or snow. "Combined" sewers handle both. 		
Sewerage
 	The entire system of sewage collection, treatment, and disposal. 		
Shading Coefficient
 	The amount of the sun's heat transmitted through a given window compared with that of a standard 1/8- inch-thick single pane of glass under the same conditions. 		
Sharps
 	Hypodermic needles, syringes (with or without the attached needle), Pasteur pipettes, scalpel blades, blood vials, needles with attached tubing, and culture dishes used in animal or human patient care or treatment, or in medical, research or industrial laboratories. Also included are other types of broken or unbroken glassware that were in contact with infectious agents, such as used slides and cover slips, and unused hypodermic and suture needles, syringes, and scalpel blades. 		
Shock Load
 	The arrival at a water treatment plant of raw water containing unusual amounts of algae, colloidal matter. color, suspended solids, turbidity, or other pollutants. 		
Short-Circuiting
 	When some of the water in tanks or basins flows faster than the rest; may result in shorter contact, reaction, or settling times than calculated or presumed. 		
Sick Building Syndrome
 	Building whose occupants experience acute health and/or comfort effects that appear to be linked to time spent therein, but where no specific illness or cause can be identified. Complaints may be localized in a particular room or zone, or may spread throughout the building. 		
Signal
 	The volume or product-level change produced by a leak in a tank. 		
Signal Words
 	The words used on a pesticide label--Danger, Warning, Caution--to indicate level of toxicity. 		
Significant Deterioration
 	Pollution resulting from a new source in previously "clean" areas. 		
Significant Municipal Facilities
 	Those publicly owned sewage treatment plants that discharge a million gallons per day or more and are therefore considered by states to have the potential to substantially affect the quality of receiving waters. 		
Significant Non-Compliance
 			
Significant Potential Source of Contamination
 	A facility or activity that stores, uses, or produces compounds with potential for significant contaminating impact if released into the source water of a public water supply. 		
Significant Violations
 	Violations by point source dischargers of sufficient magnitude or duration to be a regulatory priority. 		
Silt
 	Sedimentary materials composed of fine or intermediate-sized mineral particles. 		
Silviculture
 	Management of forest land for timber. 		
Single-Breath Canister
 	Small one-liter canister designed to capture a single breath. Used in air pollutant ingestion research. 		
Sink
 	Place in the environment where a compound or material collects. 		
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. 		
SIP Call
 	EPA action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the require national ambient air quality standards within the statutory deadline. A SIP Revision is a revision of a SIP altered at the request of EPA or on a state's initiative. 		
Site
 	An area or place within the jurisdiction of the EPA and/or a state. 		
Site Assessment Program
 	A means of evaluating hazardous waste sites through preliminary assessments and site inspections to develop a Hazard Ranking System score. 		
Site Inspection
 	The collection of information from a Superfund site to determine the extent and severity of hazards posed by the site. It follows and is more extensive than a preliminary assessment. The purpose is to gather information necessary to score the site, using the Hazard Ranking System, and to determine if it presents an immediate threat requiring prompt removal. 		
Site Safety Plan
 	A crucial element in all removal actions, it includes information on equipment being used, precautions to be taken, and steps to take in the event of an on-site emergency. 		
Siting
 	The process of choosing a location for a facility. 		
Skimming
 	Using a machine to remove oil or scum from the surface of the water. 		
Slow Sand Filtration
 	Passage of raw water through a bed of sand at low velocity, resulting in substantial removal of chemical and biological contaminants. 		
Sludge
 	A semi-solid residue from any of a number of air or water treatment processes; can be a hazardous waste. 		
Sludge Digester
 	Tank in which complex organic substances like sewage sludges are biologically dredged. During these reactions, energy is released and much of the sewage is converted to methane, carbon dioxide, and water. 		
Slurry
 	A watery mixture of insoluble matter resulting from some pollution control techniques. 		
Small Quantity Generator
 	Persons or enterprises that produce 220-2200 pounds per month of hazardous waste; they are required to keep more records than conditionally exempt generators. The largest category of hazardous waste generators, SQGs, include automotive shops, dry cleaners, photographic developers, and many other small businesses. 	SQG 	
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
 	Air pollution typically associated with oxidants. 		
Smoke
 	Particles suspended in air after incomplete combustion. 		
Soft Detergents
 	Cleaning agents that break down in nature. 		
Soft Water
 	Any water that does not contain a significant amount of dissolved minerals such as salts of calcium or magnesium. 		
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 and Water Conservation Practices
 	Control measures consisting of managerial, vegetative, and structural practices to reduce the loss of soil and water. 		
Soil Conditioner
 	An organic material like humus or compost that helps soil absorb water, build a bacterial community, and take up mineral nutrients. 		
Soil Erodibility
 	An indicator of a soil's susceptibility to raindrop impact, runoff, and other erosive processes. 		
Soil Gas
 	Gaseous elements and compounds in the small spaces between particles of the earth and soil. Such gases can be moved or driven out under pressure. 		
Soil Moisture
 	The water contained in the pore space of the unsaturated zone. 		
Soil Sterilant
 	A chemical that temporarily or permanently prevents the growth of all plants and animals. 		
Solder
 	Metallic compound used to seal joints between pipes. Until recently, most solder contained 50 percent lead. Use of solder containing more than 0.2 percent lead in pipes carrying drinking water is now prohibited. 		
Sole-Source Aquifer
 	An aquifer that supplies 50-percent or more of the drinking water of an area. 		
Solid Waste
 	Non-liquid, non-soluble materials ranging from municipal garbage to industrial wastes that contain complex and sometimes hazardous substances. Solid wastes also include sewage sludge, agricultural refuse, demolition wastes, and mining residues. Technically, solid waste also refers to liquids and gases in containers. 		
Solid Waste Disposal
 	The final placement of refuse that is not salvaged or recycled. 		
Solid Waste Management
 	Supervised handling of waste materials from their source through recovery processes to disposal. 		
Solidification and Stabilization
 	Removal of wastewater from a waste or changing it chemically to make it less permeable and susceptible to transport by water. 		
Solubility
 	The amount of mass of a compound that will dissolve in a unit volume of solution. Aqueous Solubility is the maximum concentration of a chemical that will dissolve in pure water at a reference temperature. 		
Soluble P
 			
Soot
 	Carbon dust formed by incomplete combustion. 		
Sorption
 	The action of soaking up or attracting substances; process used in many pollution control systems. 		
Source Area
 	The location of liquid hydrocarbons or the zone of highest soil or groundwater concentrations, or both, of the chemical of concern. 		
Source Characterization Measurements
 	Measurements made to estimate the rate of release of pollutants into the environment from a source such as an incinerator, landfill, etc. 		
Source Reduction
 	Reducing the amount of materials entering the waste stream from a specific source by redesigning products or patterns of production or consumption (e.g., using returnable beverage containers). Synonymous with waste reduction. 		
Source Separation
 	Segregating various wastes at the point of generation (e.g., separation of paper, metal and glass from other wastes to make recycling simpler and more efficient). 		
Source-Water Protection Area
 	The area delineated by a state for a Public Water Supply or including numerous such suppliers, whether the source is ground water or surface water or both. 		
Sparge
 	Injection of air below the water table to strip dissolved volatile organic compounds and/or oxygenate ground water to facilitate aerobic biodegradation of organic compounds. 		
Sparging
 			
Special Local-Needs Registration
 	Registration of a pesticide product by a state agency for a specific use that is not federally registered. However, the active ingredient must be federally registered for other uses. The special use is specific to that state and is often minor, thus may not warrant the additional cost of a full federal registration process. SLN registration cannot be issued for new active ingredients, food-use active ingredients without tolerances, or for a canceled registration. The products cannot be shipped across state lines. 		
Special Review
 	Formerly known as Rebuttable Presumption Against Registration (RPAR), this is the regulatory process through which existing pesticides suspected of posing unreasonable risks to human health, non-target organisms, or the environment are referred for review by EPA. Such review requires an intensive risk/benefit analysis with opportunity for public comment. If risk is found to outweigh social and economic benefits, regulatory actions can be initiated, ranging from label revisions and use-restriction to cancellation or suspended registration. 		
Special Waste
 	Items such as household hazardous waste, bulky wastes (refrigerators, pieces of furniture, etc.) tires, and used oil. 		
Species
 	Definition 1: A reproductively isolated aggregate of interbreeding organisms having common attributes and usually designated by a common name. 
Definition 2: An organism belonging to such a category. 
		
Specific Conductance
 	Rapid method of estimating the dissolved solid content of a water supply by testing its capacity to carry an electrical current. 		
Specific Yield
 	The amount of water a unit volume of saturated permeable rock will yield when drained by gravity. 		
Spill Prevention, Containment, and Countermeasures Plan
 	Plan covering the release of hazardous substances as defined in the Clean Water Act. 	SPCP 	
Spoil
 	Dirt or rock removed from its original location--destroying the composition of the soil in the process--as in strip-mining, dredging, or construction. 		
Sporicide
 			
Sprawl
 	Unplanned development of open land. 		
Spray Tower Scrubber
 	A device that sprays alkaline water into a chamber where acid gases are present to aid in neutralizing the gas. 		
Spring
 	Ground water seeping out of the earth where the water table intersects the ground surface. 		
Spring Melt
 	The process whereby warm temperatures melt winter snow and ice. Because various forms of acid deposition may have been stored in the frozen water, the melt can result in abnormally large amounts of acidity entering streams and rivers, sometimes causing fish kills. 		
Spring Thaw
 			
Squeegee
 			
Stabilization
 	Conversion of the active organic matter in sludge into inert, harmless material. 		
Stabilization Ponds
 			
Stable Air
 	A motionless mass of air that holds, instead of dispersing, pollutants. 		
Stack
 	A chimney, smokestack, or vertical pipe that discharges used air. 		
Stack Effect
 	Definition 1: Air, as in a chimney, that moves upward because it is warmer than the ambient atmosphere. 
Definition 2: Flow of air resulting from warm air rising, creating a positive pressure area at the top of a building and negative pressure area at the bottom. This effect can overpower the mechanical system and disrupt building ventilation and air circulation. 
		
Stack Gas
 			
Stage II Controls
 	Systems placed on service station gasoline pumps to control and capture gasoline vapors during refuelling. 		
Stagnation
 	Lack of motion in a mass of air or water that holds pollutants in place. 		
Stakeholder
 	Any organization, governmental entity, or individual that has a stake in or may be impacted by a given approach to environmental regulation, pollution prevention, energy conservation, etc. 		
Standard Industrial Classification Code
 	Also known as SIC Codes, a method of grouping industries with similar products or services and assigning codes to these groups. 	SIC Code 	
Standard Sample
 	The part of finished drinking water that is examined for the presence of coliform bacteria. 		
Standards
 	Norms that impose limits on the amount of pollutants or emissions produced. EPA establishes minimum standards, but states are allowed to be stricter. 		
Start of a Response Action
 	The point in time when there is a guarantee or set-aside of funding by EPA, other federal agencies, states or Principal Responsible Parties in order to begin response actions at a Superfund site. 		
State Emergency Response Commission
 	Commission appointed by each state governor according to the requirements of SARA Title III. The SERCs designate emergency planning districts, appoint local emergency planning committees, and supervise and coordinate their activities. 	SERC 	
State Environmental Goals and Indication Project
 	Program to assist state environmental agencies by providing technical and financial assistance in the development of environmental goals and indicators. 		
State Implementation Plans
 	EPA approved state plans for the establishment, regulation, and enforcement of air pollution standards. 	SIP 	
State Management Plan
 	Under FIFRA, a state management plan required by EPA to allow states, tribes, and U.S. territories the flexibility to design and implement ways to protect ground water from the use of certain pesticides. 		
Static Water Depth
 	The vertical distance from the centerline of the pump discharge down to the surface level of the free pool while no water is being drawn from the pool or water table. 		
Static Water Level
 	Definition 1: Elevation or level of the water table in a well when the pump is not operating. 
Definition 2: The level or elevation to which water would rise in a tube connected to an artesian aquifer or basin in a conduit under pressure. 
		
Stationary Source
 	A fixed-site producer of pollution, mainly power plants and other facilities using industrial combustion processes. 		
Sterilization
 	The removal or destruction of all microorganisms, including pathogenic and other bacteria, vegetative forms, and spores. 		
Sterilizer
 	One of three groups of anti-microbials registered by EPA for public health uses. EPA considers an antimicrobial to be a sterilizer when it destroys or eliminates all forms of bacteria, viruses, and fungi and their spores. Because spores are considered the most difficult form of microorganism to destroy, EPA considers the term sporicide to be synonymous with sterilizer. 		
Storage
 	Temporary holding of waste pending treatment or disposal, as in containers, tanks, waste piles, and surface impoundments. 		
Storm Sewer
 	A system of pipes (separate from sanitary sewers) that carries water runoff from buildings and land surfaces. 		
Stratification
 	Separating into layers. 		
Stratigraphy
 	Study of the formation, composition, and sequence of sediments, whether consolidated or not. 		
Stratosphere
 	The portion of the atmosphere 10-to-25 miles above the earth's surface. 		
Stressors
 	Physical, chemical, or biological entities that can induce adverse effects on ecosystems or human health. 		
Strip-Cropping
 	Growing crops in a systematic arrangement of strips or bands that serve as barriers to wind and water erosion. 		
Strip-Mining
 	A process that uses machines to scrape soil or rock away from mineral deposits just under the earth's surface. 		
Structural Deformation
 	Distortion in walls of a tank after liquid has been added or removed. 		
Subchronic
 	Of intermediate duration, usually used to describe studies or periods of exposure lasting between 5 and 90 days. 		
Subchronic Exposure
 	Multiple or continuous exposures lasting for approximately ten percent of an experimental species lifetime, usually over a three-month period. 		
Submerged Aquatic Vegetation
 	Vegetation that lives at or below the water surface; an important habitat for young fish and other aquatic organisms. 		
Subwatershed
 	Topographic perimeter of the catchment area of a stream tributary. 		
Suction
 	See: Ventilation 		
Sulfur Dioxide
 	A pungent, colorless, gasformed primarily by the combustion of fossil fuels; becomes a pollutant when present in large amounts. 	SO2 	
Sump
 	A pit or tank that catches liquid runoff for drainage or disposal. 		
Superchlorination
 	Chlorination with doses that are deliberately selected to produce water free of combined residuals so large as to require dechlorination. 		
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 cleanup and other remedial actions. 		
Superfund Innovative Technology Evaluation Program
 	EPA program to promote development and use of innovative treatment and site characterization technologies in Superfund site cleanups. 	SITE Program 	
Supplemental Registration
 	An arrangement whereby a registrant licenses another company to market its pesticide product under the second company's registration. 		
Supplier of Water
 	Any person who owns or operates a public water supply. 		
Surface Impoundment
 	Treatment, storage, or disposal of liquid hazardous wastes in ponds. 		
Surface Runoff
 	Precipitation, snow melt, or irrigation water in excess of what can infiltrate the soil surface and be stored in small surface depressions; a major transporter of non-point source pollutants in rivers, streams, and lakes.. 		
Surface Uranium Mines
 	Strip mining operations for removal of uranium-bearing ore. 		
Surface Water
 	All water naturally open to the atmosphere (rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries, etc.) 		
Surface-Water Treatment Rule
 	Rule that specifies maximum contaminant level goals for Giardia lamblia, viruses, and Legionella and promulgates filtration and disinfection requirements for public water systems using surface-water or ground-water sources under the direct influence of surface water. The regulations also specify water quality, treatment, and watershed protection criteria under which filtration may be avoided. 		
Surfacing ACM
 	Asbestos-containing material that is sprayed or troweled on or otherwise applied to surfaces, such as acoustical plaster on ceilings and fireproofing materials on structural members. 		
Surfacing Material
 	Material sprayed or troweled onto structural members (beams, columns, or decking) for fire protection; or on ceilings or walls for fireproofing, acoustical or decorative purposes. Includes textured plaster, and other textured wall and ceiling surfaces. 		
Surfactant
 	A detergent compound that promotes lathering. 		
Surrogate Data
 	Data from studies of test organisms or a test substance that are used to estimate the characteristics or effects on another organism or substance. 		
Surveillance System
 	A series of monitoring devices designed to check on environmental conditions. 		
Susceptibility Analysis
 	An analysis to determine whether a Public Water Supply is subject to significant pollution from known potential sources. 		
Suspect Material
 	Building material suspected of containing asbestos; e.g., surfacing material, floor tile, ceiling tile, thermal system insulation. 		
Suspended Loads
 	Specific sediment particles maintained in the water column by turbulence and carried with the flow of water. 		
Suspended Solids
 	Small particles of solid pollutants that float on the surface of, or are suspended in, sewage or other liquids. They resist removal by conventional means. 		
Suspension
 	Suspending the use of a pesticide when EPA deems it necessary to prevent an imminent hazard resulting from its continued use. An emergency suspension takes effect immediately; under an ordinary suspension a registrant can request a hearing before the suspension goes into effect. Such a hearing process might take six months. 		
Suspension Culture
 	Cells growing in a liquid nutrient medium. 		
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. 		
Synergism
 	An interaction of two or more chemicals that results in an effect greater than the sum of their separate effects. 		
Synthetic Organic Chemicals
 	Man-made (anthropogenic) organic chemicals. Some SOCs are volatile; others tend to stay dissolved in water instead of evaporating. 	SOCs 	
System With a Single Service Connection
 	A system that supplies drinking water to consumers via a single service line. 		
Systemic Pesticide
 	A chemical absorbed by an organism that interacts with the organism and makes the organism toxic to pests. 		
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 mobile source engine exhausts. 		
Tampering
 	Adjusting, negating, or removing pollution control equipment on a motor vehicle. 		
Technical Assistance Grant
 	As part of the Superfund program, Technical Assistance Grants of up to $50,000 are provided to citizens' groups to obtain assistance in interpreting information related to clean-ups at Superfund sites or those proposed for the National Priorities List. Grants are used by such groups to hire technical advisors to help them understand the site-related technical information for the duration of response activities. 	TAG 	
Technical-Grade Active Ingredient
 	A pesticide chemical in pure form as it is manufactured prior to being formulated into an end-use product (e.g. wettable powders, granules, emulsifiable concentrates). Registered manufactured products composed of such chemicals are known as Technical Grade Products. 	TGA 	
Technology-Based Limitations
 	Industry-specific effluent limitations based on best available preventive technology applied to a discharge when it will not cause a violation of water quality standards at low stream flows. Usually applied to discharges into large rivers. 		
Technology-Based Standards
 	Industry-specific effluent limitations applicable to direct and indirect sources which are developed on a category-by-category basis using statutory factors, not including water-quality effects. 		
Teratogen
 	A substance capable of causing birth defects. 		
Teratogenesis
 	The introduction of nonhereditary birth defects in a developing fetus by exogenous factors such as physical or chemical agents acting in the womb to interfere with normal embryonic development. 		
Terracing
 	Dikes built along the contour of sloping farm land that hold runoff and sediment to reduce erosion. 		
Tertiary Treatment
 	Advanced cleaning of wastewater that goes beyond the secondary or biological stage, removing nutrients such as phosphorus, nitrogen, and most BOD and suspended solids. 		
Theoretical Maximum Residue Contribution
 	The theoretical maximum amount of a pesticide in the daily diet of an average person. It assumes that the diet is composed of all food items for which there are tolerance-level residues of the pesticide. The TMRC is expressed as milligrams of pesticide/kilograms of body weight/day. 		
Therapeutic Index
 	The ratio of the dose required to produce toxic or lethal effects to the dose required to produce nonadverse or therapeutic response. 		
Thermal Pollution
 	Discharge of heated water from industrial processes that can kill or injure aquatic organisms. 		
Thermal Stratification
 	The formation of layers of different temperatures in a lake or reservoir. 		
Thermal System Insulation
 	Asbestos-containing material applied to pipes, fittings, boilers, breeching, tanks, ducts, or other interior structural components to prevent heat loss or gain or water condensation. 	TSI 	
Thermal Treatment
 	Use of elevated temperatures to treat hazardous wastes. 		
Thermocline
 	The middle layer of a thermally stratified lake or reservoir. In this layer, there is a rapid decrease in temperatures in a lake or reservoir. 		
Threshold
 	Definition 1: The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed. 
Definition 2: The dose or exposure level below which a significant adverse effect is not expected. 
		
Threshold Level
 	Time-weighted average pollutant concentration values, exposure beyond which is likely to adversely affect human health. 		
Threshold Limit Value
 	The concentration of an airborne substance to which an average person can be repeatedly exposed without adverse effects. TLVs may be expressed in three ways: (1) TLV-TWA--Time weighted average, based on an allowable exposure averaged over a normal 8-hour workday or 40-hour work- week; (2) TLV-STEL--Short-term exposure limit or maximum concentration for a brief specified period of time, depending on a specific chemical (TWA must still be met); and (3) TLV-C--Ceiling Exposure Limit or maximum exposure concentration not to be exceeded under any circumstances. (TWA must still be met.) 	TLV 	
Threshold Odor
 			
Threshold Planning Quantity
 	A quantity designated for each chemical on the list of extremely hazardous substances that triggers notification by facilities to the State Emergency Response Commission that such facilities are subject to emergency planning requirements under SARA Title III. 		
Tidal Marsh
 	Low, flat marshlands traversed by channels and tidal hollows, subject to tidal inundation; normally, the only vegetation present is salt-tolerant bushes and grasses. 		
Tillage
 	Plowing, seedbed preparation, and cultivation practices. 		
Time-weighted Average
 	In air sampling, the average air concentration of contaminants during a given period. 	TWA 	
Tire Processor
 	Intermediate operating facility where recovered tires are processed in preparation for recycling. 		
Tires
 	As used in recycling, passenger car and truck tires (excludes airplane, bus, motorcycle and special service military, agricultural, off-the-road and-slow speed industrial tires). Car and truck tires are recycled into rubber products such as trash cans, storage containers, rubberized asphalt or used whole for playground and reef construction. 		
Tolerance Petition
 	A formal request to establish a new tolerance or modify an existing one. 		
Tolerances
 	Permissible residue levels for pesticides in raw agricultural produce and processed foods. Whenever a pesticide is registered for use on a food or a feed crop, a tolerance (or exemption from the tolerance requirement) must be established. EPA establishes the tolerance levels, which are enforced by the Food and Drug Administration and the Department of Agriculture. (See: Action Levels (2)) 		
Tonnage
 	The amount of waste that a landfill accepts, usually expressed in tons per month. The rate at which a landfill accepts waste is limited by the landfill's permit. 		
Topography
 	The physical features of a surface area including relative elevations and the position of natural and man-made (anthropogenic) features. 		
Total Dissolved Phosphorous
 	The total phosphorous content of all material that will pass through a filter, which is determined as orthophosphate without prior digestion or hydrolysis. 		
Total Dissolved Solids
 	All material that passes the standard glass river filter; now called total filterable residue. Term is used to reflect salinity. 	TDS 	
Total Maximum Daily Load
 	A calculation of the highest amount of a pollutant that a water body can receive and safely meet water quality standards set by the state, territory, or authorized tribe. 	TMDL 	
Total Petroleum Hydrocarbons
 	Measure of the concentration or mass of petroleum hydrocarbon constituents present in a given amount of soil or water. The word "total" is a misnomer--few, if any, of the procedures for quantifying hydrocarbons can measure all of them in a given sample. Volatile ones are usually lost in the process and not quantified and non-petroleum hydrocarbons sometimes appear in the analysis. 	TPH 	
Total Recovered Petroleum Hydrocarbon
 	A method for measuring petroleum hydrocarbons in samples of soil or water. 		
Total Suspended Particles
 	A method of monitoring airborne particulate matter by total weight. 	TSP 	
Total Suspended Solids
 	A measure of the suspended solids in wastewater, effluent, or water bodies, determined by tests for "total suspended non-filterable solids." 	TSS 	
Toxaphene
 	Chemical that causes adverse health effects in domestic water supplies and is toxic to fresh water and marine aquatic life. 		
Toxic Chemical
 	Any chemical listed in EPA rules as "Toxic Chemicals Subject to Section 313 of the Emergency Planning and Community Right-to-Know Act of 1986." 		
Toxic Chemical Release Form
 	Information form required of facilities that manufacture, process, or use (in quantities above a specific amount) chemicals listed under SARA Title III. 		
Toxic Chemical Use Substitution
 	Replacing toxic chemicals with less harmful chemicals in industrial processes. 		
Toxic Cloud
 	Airborne plume of gases, vapors, fumes, or aerosols containing toxic materials. 		
Toxic Concentration
 	The concentration at which a substance produces a toxic effect. 		
Toxic Dose
 	The dose level at which a substance produces a toxic effect. 		
Toxic Pollutants
 	Materials that cause death, disease, or birth defects in organisms that ingest or absorb them. The quantities and exposures necessary to cause these effects can vary widely. 		
Toxic Release Inventory
 	Database of toxic releases in the United States compiled from SARA Title III Section 313 reports. 		
Toxic Substance
 	A chemical or mixture that may present an unreasonable risk of injury to health or the environment. 		
Toxic Waste
 	A waste that can produce injury if inhaled, swallowed, or absorbed through the skin. 		
Toxicant
 	A harmful substance or agent that may injure an exposed organism. 		
Toxicity
 	The degree to which a substance or mixture of substances can harm humans or animals. Acute toxicity involves harmful effects in an organism through a single or short-term exposure. Chronic toxicity is the ability of a substance or mixture of substances to cause harmful effects over an extended period, usually upon repeated or continuous exposure sometimes lasting for the entire life of the exposed organism. Subchronic toxicity is the ability of the substance to cause effects for more than one year but less than the lifetime of the exposed organism. 		
Toxicity Assessment
 	Characterization of the toxicological properties and effects of a chemical, with special emphasis on establishment of dose-response characteristics. 		
Toxicity Testing
 	Biological testing (usually with an invertebrate, fish, or small mammal) to determine the adverse effects of a compound or effluent. 		
Toxicological Profile
 	An examination, summary, and interpretation of a hazardous substance to determine levels of exposure and associated health effects. 		
Transboundary Pollutants
 	Air pollution that travels from one jurisdiction to another, often crossing state or international boundaries. Also applies to water pollution. 		
Transfer Station
 	Facility where solid waste is transferred from collection vehicles to larger trucks or rail cars for longer distance transport. 		
Transient Water System
 	A non-community water system that does not serve 25 of the same nonresidents per day for more than six months per year. 		
Transmission Lines
 	Pipelines that transport raw water from its source to a water treatment plant, then to the distribution grid system. 		
Transmissivity
 	The ability of an aquifer to transmit water. 		
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. 		
Transportation Control Measures
 	Steps taken by a locality to reduce vehicular emission and improve air quality by reducing or changing the flow of traffic; e.g. bus and HOV lanes, carpooling and other forms of ride-sharing, public transit, bicycle lanes. 	TCMs 	
Transporter
 	Hauling firm that picks up properly packaged and labeled hazardous waste from generators and transports it to designated facilities for treatment, storage, or disposal. Transporters are subject to EPA and DOT hazardous waste regulations. 		
Trash
 	Material considered worthless or offensive that is thrown away. Generally defined as dry waste material, but in common usage it is a synonym for garbage, rubbish, or refuse. 		
Trash-to-Energy Plan
 	Burning trash to produce energy. 		
Treatability Studies
 	Tests of potential cleanup technologies conducted in a laboratory. 		
Treated Regulated Medical Waste
 	Medical waste treated to substantially reduce or eliminate its pathogenicity, but that has not yet been destroyed. 		
Treated Wastewater
 	Wastewater that has been subjected to one or more physical, chemical, and biological processes to reduce its potential of being health hazard. 		
Treatment
 	Definition 1: Any method, technique, or process designed to remove solids and/or pollutants from solid waste, waste-streams, effluents, and air emissions. 
Definition 2: Methods used to change the biological character or composition of any regulated medical waste so as to substantially reduce or eliminate its potential for causing disease. 
		
Treatment Plant
 	A structure built to treat wastewater before discharging it into the environment. 		
Treatment, Storage, and Disposal Facility
 	Site where a hazardous substance is treated, stored, or disposed of. TSD facilities are regulated by EPA and states under RCRA. 		
Tremie
 	Device used to place concrete or grout under water. 		
Trial Burn
 	An incinerator test in which emissions are monitored for the presence of specific organic compounds, particulates, and hydrogen chloride. 		
Trichloroethylene
 	A stable, low boiling-point colorless liquid, toxic if inhaled. Used as a solvent or metal degreasing agent, and in other industrial applications. 	TCE 	
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
 	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. 	THM 	
Trophic Levels
 	A functional classification of species that is based on feeding relationships (e.g. generally aquatic and terrestrial green plants comprise the first trophic level, and herbivores comprise the second.) 		
Troposphere
 	The layer of the atmosphere closest to the earth's surface. 		
Trust Fund (CERCLA)
 	A fund set up under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) to help pay for cleanup of hazardous waste sites and for legal action to force those responsible for the sites to clean them up. 		
Tube Settler
 	Device using bundles of tubes to let solids in water settle to the bottom for removal by conventional sludge collection means; sometimes used in sedimentation basins and clarifiers to improve particle removal. 		
Tuberculation
 	Development or formation of small mounds of corrosion products on the inside of iron pipe. These tubercules roughen the inside of the pipe, increasing its resistance to water flow. 		
Tundra
 	A type of treeless 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 water saturated. 		
Turbidimeter
 	A device that measures the cloudiness of suspended solids in a liquid; a measure of the quantity of suspended solids. 		
Turbidity
 	Definition 1: Haziness in air caused by the presence of particles and pollutants. 
Definition 2: A cloudy condition in water due to suspended silt or organic matter. 
		
Twin-Tube Lamps
 			
Ultra Clean Coal
 	Coal that is washed, ground into fine particles, then chemically treated to remove sulfur, ash, silicone, and other substances; usually briquetted and coated with a sealant made from coal. 	UCC 	
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. 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. 		
Uncertainty Factor
 	One of several factors used in calculating the reference dose from experimental data. UFs are intended to account for (1) the variation in sensitivity among humans; (2) the uncertainty in extrapolating animal data to humans; (3) the uncertainty in extrapolating data obtained in a study that covers less than the full life of the exposed animal or human; and (4) the uncertainty in using LOAEL data rather than NOAEL data. 		
Unconfined Aquifer
 	An aquifer containing water that is not under pressure; the water level in a well is the same as the water table outside the well. 		
Underground Injection Control
 	The program under the Safe Drinking Water Act that regulates the use of wells to pump fluids into the ground. 	UIC 	
Underground Injection Wells
 	Steel- and concrete-encased shafts into which hazardous waste is deposited by force and under pressure. 		
Underground Sources of Drinking Water
 	Aquifers currently being used as a source of drinking water or those capable of supplying a public water system. They have a total dissolved solids content of 10,000 milligrams per liter or less, and are not "exempted aquifers." 		
Underground Storage Tank
 	A tank located at least partially underground and designed to hold gasoline or other petroleum products or chemicals. 	UST 	
Unit-Based Pricing
 	Systems under which residents pay for municipal waste management and disposal services by weight or volume collected, not a fixed fee. 		
Unreasonable Risk
 	Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), "unreasonable adverse effects" means any unreasonable risk to man or the environment, taking into account the medical, economic, social, and environmental costs and benefits of any pesticide. 		
Unsaturated Zone
 	The area above the water table where soil pores are not fully saturated, although some water may be present. 		
Untreated Medical Waste
 			
Upper Detection Limit
 	The largest concentration that an instrument can reliably detect. 		
Uranium Mill Tailings Piles
 	Former uranium ore processing sites that contain leftover radioactive materials (wastes), including radium and unrecovered uranium. 		
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. 		
Urea-Formaldehyde Foam Insulation
 	A material once used to conserve energy by sealing crawl spaces, attics, etc.; no longer used because emissions were found to be a health hazard. 		
Use Cluster
 	A set of competing chemicals, processes, and/or technologies that can substitute for one another in performing a particular function. 		
Used Oil
 	Spent motor oil from passenger cars and trucks collected at specified locations for recycling (not included in the category of municipal solid waste). 		
User Fee
 	Fee collected from only those persons who use a particular service, as compared to one collected from the public in general. 		
Utility Load
 	The total electricity demand for a utility district. 		
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 space also typically contains air or other gases. The capillary fringe is included in the vadose zone. 		
Valued Environmental Attributes/Components
 	Those aspects(components/processes/functions) of ecosystems, human health, and environmental welfare considered to be important and potentially at risk from human activity or natural hazards. Similar to the term "valued environmental components" used in environmental impact assessment. 		
Vapor
 	The gas given off by substances that are solids or liquids at ordinary atmospheric pressure and temperatures. 		
Vapor Capture System
 	Any combination of hoods and ventilation system that captures or contains organic vapors so they may be directed to an abatement or recovery device. 		
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. 		
Vapor Pressure
 	A measure of a substance's propensity to evaporate, vapor pressure is the force per unit area exerted by vapor in an equilibrium state with surroundings at a given pressure. It increases exponentially with an increase in temperature. A relative measure of chemical volatility, vapor pressure is used to calculate water partition coefficients and volatilization rate constants. 		
Vapor Recovery System
 	A system by which the volatile gases from gasoline are captured instead of being released into the atmosphere. 		
Variance
 	Government permission for a delay or exception in the application of a given law, ordinance, or regulation. 		
Vector
 	Definition 1: An organism, often an insect or rodent, that carries disease. 
Definition 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 vegetative cover to reduce erosion and minimize loss of pollutants. 		
Vehicle Miles Travelled
 	A measure of the extent of motor vehicle operation; the total number of vehicle miles travelled within a specific geographic area over a given period of time. 	VMT 	
Ventilation
 	The act of admitting fresh air into a space in order to replace stale or contaminated air; achieved by blowing air into the space. Similarly, suction represents the admission of fresh air into an interior space by lowering the pressure outside of the space, thereby drawing the contaminated air outward. 		
Ventilation Rate
 	The rate at which indoor air enters and leaves a building. Expressed as the number of changes of outdoor air per unit of time (air changes per hour (ACH), or the rate at which a volume of outdoor air enters in cubic feet per minute (CFM). 		
Venturi Scrubbers
 	Air pollution control devices that use water to remove particulate matter from emissions. 		
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. 		
Viscosity
 	The molecular friction within a fluid that produces flow resistance. 		
Volatile
 	Any substance that evaporates readily. 		
Volatile Liquids
 	Liquids which easily vaporize or evaporate at room temperature. 		
Volatile Organic Compound
 	Any organic compound that participates in atmospheric photochemical reactions except those designated by EPA as having negligible photochemical reactivity. 	VOC 	
Volatile Solids
 	Those solids in water or other liquids that are lost on ignition of the dry solids at 550° centigrade. 		
Volatile Synthetic Organic Chemicals
 	Chemicals that tend to volatilize or evaporate. 		
Volume Reduction
 	Processing waste materials to decrease the amount of space they occupy, usually by compacting, shredding, incineration, or composting. 		
Volumetric Tank Test
 	One of several tests to determine the physical integrity of a storage tank; the volume of fluid in the tank is measured directly or calculated from product-level changes. A marked drop in volume indicates a leak. 		
Vulnerability Analysis
 	Assessment of elements in the community that are susceptible to damage if hazardous materials are released. 		
Vulnerable Zone
 	An area over which the airborne concentration of a chemical accidentally released could reach the level of concern. 		
Waste
 	Definition 1: Unwanted materials left over from a manufacturing process. 
Definition 2: Refuse from places of human or animal habitation. 
		
Waste Characterization
 	Identification of chemical and microbiological constituents of a waste material. 		
Waste Exchange
 	Arrangement in which companies exchange their wastes for the benefit of both parties. 		
Waste Feed
 	The continuous or intermittent flow of wastes into an incinerator. 		
Waste Generation
 	The weight or volume of materials and products that enter the waste stream before recycling, composting, landfilling, or combustion takes place. Also can represent the amount of waste generated by a given source or category of sources. 		
Waste-Heat Recovery
 	Recovering heat discharged as a byproduct of one process to provide heat needed by a second process. 		
Waste Load Allocation
 	Definition 1: 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. 
Definition 2: The portion of a stream's total assimilative capacity assigned to an individual discharge. 
		
Waste Minimization
 	Measures or techniques that reduce the amount of wastes generated during industrial production processes; term is also applied to recycling and other efforts to reduce the amount of waste going into the waste stream. 		
Waste Piles
 	Non-containerized, lined or unlined accumulations of solid, nonflowing waste. 		
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 is recycled, burned, or disposed of in landfills, or segments thereof such as the "residential waste stream" or the "recyclable waste stream." 		
Waste-to-Energy Facility
 	Facility where recovered municipal solid waste is converted into a usable form of energy, usually via combustion. 		
Waste Treatment Lagoon
 	Impoundment made by excavation or earth fill for biological treatment of wastewater. 		
Waste Treatment Plant
 	A facility containing a series of tanks, screens, filters and other processes by which pollutants are removed from water. 		
Waste Treatment Stream
 	The continuous movement of waste from generator to treater and disposer. 		
Wastewater
 	The spent or used water from a home, community, farm, or industry that contains dissolved or suspended matter. 		
Wastewater Infrastructure
 	The plan or network for the collection, treatment, and disposal of sewage in a community. The level of treatment will depend on the size of the community, the type of discharge, and/or the designated use of the receiving water. 		
Wastewater Operations and Maintenance
 	Actions taken after construction to ensure that facilities constructed to treat wastewater will be operated, maintained, and managed to reach prescribed effluent levels in an optimum manner. 		
Wastewater Treatment Plan
 	A facility containing a series of tanks, screens, filters, and other processes by which pollutants are removed from water. Most treatments include chlorination to attain safe drinking water standards. 		
Water Pollution
 	The presence in water of enough harmful or objectionable material to damage the water's quality. 		
Water Pump
 			
Water Purveyor
 	A public utility, mutual water company, county water district, or municipality that delivers drinking water to customers. 		
Water Quality-Based Limitations
 	Effluent limitations applied to dischargers when mere technology-based limitations would cause violations of water quality standards. Usually applied to discharges into small streams. 		
Water Quality-Based Permit
 	A permit with an effluent limit more stringent than one based on technology performance. Such limits may be necessary to protect the designated use of receiving waters (e.g. recreation, irrigation, industry or water supply). 		
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 Standards
 	State-adopted and EPA-approved ambient standards for water bodies. The standards prescribe the use of the water body and establish the water quality criteria that must be met to protect designated uses. 		
Water Solubility
 	The maximum possible concentration of a chemical compound dissolved in water. If a substance is water soluble it can very readily disperse through the environment. 		
Water-Soluble Packaging
 	Packaging that dissolves in water; used to reduce exposure risks to pesticide mixers and loaders. 		
Water-Source Heat Pump
 	Heat pump that uses wells or heat exchangers to transfer heat from water to the inside of a building. Most such units use ground water. 		
Water Storage Pond
 	An impound for liquid wastes designed to accomplish some degree of biochemical treatment. 		
Water Supplier
 	One who owns or operates a public water system. 		
Water Supply System
 	The collection, treatment, storage, and distribution of potable water from source to consumer. 		
Water Table
 	The level of groundwater. 		
Water Treatment Lagoon
 	An impound for liquid wastes designed to accomplish some degree of biochemical treatment. 		
Water Well
 	An excavation where the intended use is for location, acquisition, development, or artificial recharge of ground water. 		
Waterborne Disease Outbreak
 	The significant occurrence of acute illness associated with drinking water from a public water system that is deficient in treatment, as determined by appropriate local or state agencies. 		
Watershed
 	The land area that drains into a stream; the watershed for a major river may encompass a number of smaller watersheds that ultimately combine at a common point. 		
Watershed Approach
 	A coordinated framework for environmental management that focuses public and private efforts on the highest priority problems within hydrologically-defined geographic areas taking into consideration both ground and surface water flow. 		
Watershed Area
 	A topographic area within a line drawn connecting the highest points uphill of a drinking water intake into which overland flow drains. 		
Weight of Scientific Evidence
 	Considerations in assessing the interpretation of published information about toxicity--quality of testing methods, size and power of study design, consistency of results across studies, and biological plausibility of exposure-response relationships and statistical associations. 		
Weir
 	Definition 1: A wall or plate placed in an open channel to measure the flow of water. 
Definition 2: A wall or obstruction used to control flow from settling tanks and clarifiers to ensure a 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. 		
Well Field
 	Area containing one or more wells that produce usable amounts of water or oil. 		
Well Injection
 	The subsurface emplacement of fluids into a well. 		
Well Monitoring
 	Measurement by on-site instruments or laboratory methods of well water quality. 		
Well Plug
 	A watertight, gastight seal installed in a bore hole or well to prevent movement of fluids. 		
Well Point
 	A hollow vertical tube, rod, or pipe terminating in a perforated pointed shoe and fitted with a fine-mesh screen. 		
Wellhead Protection Area
 	A protected surface and subsurface zone surrounding a well or well field supplying a public water system to keep contaminants from reaching the well water. 		
Wetlands
 	An area that is saturated by surface or ground water with vegetation adapted for life under those soil conditions, as swamps, bogs, fens, marshes, and estuaries. 		
Wettability
 	The relative degree to which a fluid will spread into or coat a solid surface in the presence of other immiscible fluids. 		
Wettable Powder
 	Dry formulation that must be mixed with water or other liquid before it is applied. 		
Wheeling
 	The transmission of electricity owned by one entity through the facilities owned by another (usually a utility). 		
Whole-Effluent-Toxicity Tests
 	Tests to determine the toxicity levels of the total effluent from a single source as opposed to a series of tests for individual contaminants. 		
Wildlife Refuge
 	An area designated for the protection of wild animals, within which hunting and fishing are either prohibited or strictly controlled. 		
Wire-to-Wire Efficiency
 	The efficiency of a pump and motor together. 		
Wood-Burning-Stove Pollution
 	Air pollution caused by emissions of particulate matter, carbon monoxide, total suspended particulates, and polycyclic organic matter from wood-burning stoves. 		
Wood Packaging
 	Wood products such as pallets, crates, and barrels. 		
Wood Treatment Facility
 	An industrial facility that treats lumber and other wood products for outdoor use. The process employs chromated copper arsenate, which is regulated as a hazardous material. 		
Working Level
 	A unit of measure for documenting exposure to radon decay products, the so-called "daughters." One working level is equal to approximately 200 picocuries per liter. 	WL 	
Working Level Month
 	A unit of measure used to determine cumulative exposure to radon. 	WLM 	
Xenobiota
 	Any biotum displaced from its normal habitat; a chemical foreign to a biological system. 		
Yard Waste
 	The part of solid waste composed of grass clippings, leaves, twigs, branches, and other garden refuse. 		
Yellow-Boy
 	Iron oxide flocculant (clumps of solids in waste or water); usually observed as orange-yellow deposits in surface streams with excess iron content. 		
Yield
 	The quantity of water (expressed as a rate of flow or total quantity per year) that can be collected for a given use from surface or groundwater sources. 		
Zero Air
 	Atmospheric air purified to contain less than 0.1 ppm total hydrocarbons. 		
Zone of Saturation
 	The layer beneath the surface of the land containing openings that may fill with water. 		
Zooplankton
 	Small (often microscopic) free-floating aquatic plants or animals.