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 such a state of disrepair that it cannot be used for its intended purpose.

abate To put an end to; demolish; to do away with, to nullify, to make void.

abatement Reduction of the degree or intensity (or elimination) of pollution.

ABC See Association of Boards of Certification.

abiotic Nonliving; pertaining to physico-chemical factors only.

ablation The process by which ice and snow waste away owing to melting and evaporation.

abrasion The wearing away of surfaces by mechanical action.

absolute mean sea level change An eustatic change in mean sea level relative to the geographic center of the Earth.

absolute viscosity A measure of a fluid's resistance to tangential or shear stress. Also referred to as dynamic viscosity; see also viscosity. Units are usually given in centipoise.

absorbed dose The amount of chemical that enters the body of an exposed organism.

absorption The uptake of water or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients).

absorption coefficient

absorption factor The fraction of a chemical making contact with an organism that is absorbed by the organism.

abutment seepage Reservoir water which moves through seams or pores in the natural abutment material and exits as seepage.

abutment 1) The part of a valley or canyon wall against which a dam is constructed. Right and left abutments are those on respective sides of an observer looking downstream. 2)

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

accepted values Tidal datums and Greenwich high and low water intervals obtained through primary determination or simultaneous observational comparisons made with a primary control tide station in order to derive the equivalent of a 19-year value.

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 material.

acclimation Adjustment to environmental change on the part of the individual. The physiological adjustment or increased tolerance shown by an organism to change.

acclimatization The physiological and behavioral adjustments of an organism to changes in its environment.

accretion The process of growth or enlargement by external accumulation.

accuracy How closely an instrument measures the true or actual value of the process variable being measured or sensed.

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

acid A sour substance , typically soluble in water, which neutralizes bases to form salts.. A compound containing hydrogen atoms (H) which are capable of being replaced by a positive element or radical. A substance which gives up H to another substance.

acid rain Precipitation which has been made acidic by airborne pollutants. See acid deposition.

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

acid neutralizing capacity Measure of the ability of water or soil to resist changes in pH, sometimes referred to as buffer capacity.

acidic The condition of water or soil which contains a sufficient amount of acid substances to lower the ph below 7.0.

acidified The addition of an acid (usually nitric or sulfuric) to lower the ph below 2.0. The purpose of acidification is to fix a sample so it will not change until it is analyzed.

acidity Quality of being acid or sour; having a pH less than 7.0.

acidophilic 1) Preferring or thriving in a relatively acidic environment. 2) Staining readily with acid stains.

acoustic Doppler current profiler (ADCP) A current measuring instrument employing the transmission of high frequency acoustic signals in the water. The current is determined by a Doppler shift in the backscatter echo from plankton, suspended sediment, and bubbles, all assumed to be moving with the mean speed of the water. Time gating circuitry is employed which uses differences in acoustic travel time to divide the water column into range intervals, called bins. The bin determinations allow development of a profile of current speed and direction over the entire water column. The ADCP can be deployed from a moving vessel, tow, buoy, or bottom platform. In the latter configuration, it is nonobtrusive in the water column and thus can be deployed in shipping channels.

acre-foot A volume of water that covers one acre to a depth of one foot or 43,560 cubic feet (1,233.5 cubic meters).

actinomycetes Any of numerous, generally filamentous, and often pathogenic, microorganisms resembling both bacteria and fungi.

action level 1) The concentration of lead or copper in water specified at Code of Federal Regulations 141.80© which determines, in some cases, the treatment requirements that a water system is required to complete. 2) The concentration of lead or copper in water specified in 12 VAC 5-590-410 5, which determines, in some cases, the treatment requirements contained in 12 VAC 5-590-420 C, D ,E, and F that a waterworks is required to complete. 3) 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. 4) 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. 5) The term is also used in other regulatory programs. See tolerances.

activated sludge process A biological wastewater treatment process in which a a mixture of wastewater and biomass is agitated and aerated for aerobic treatment. The suspended biomass or floc is substantially separated from the treated wastewater (mixed liquor) by clarification and wasted or returned to the process as needed to maintain an optimum amount of biomass in the reactor to accomplish biological oxidation.

activated sludge loading The pounds of biochemical oxygen demand (BOD) in the applied liquid per unit volume of aeration capacity or per pound of activated sludge per day. See mean cell residence time.

activated carbon Adsorptive particles or granules of carbon usually obtained by heating carbon (such as wood, coal, or coconut shells). These particles or granules have a high capacity to selectively remove certain trace and soluble materials from water.

activated silica

activated sludge A suspended diverse biomass primarily composed of bacteria and protozoa produced in raw or settled wastewater by biological oxidation resulting in the growth of additional microorganisms in the presence of dissolved oxygen. The term “activated” comes from the fact that the biomass is teaming with active, or living, microorgansims.

activated solids

activator A chemical added to a pesticide to increase its activity.

active metal A metal ready to corrode or being corroded.

active (usable) storage capacity The total amount of reservoir capacity normally available for release from a reservoir below the maximum storage level. It is total or reservoir capacity minus inactive storage capacity. More specifically, it is the volume of water between the outlet works and the spillway crest.

active transport An energy-expending mechanism by which a cell moves a chemical across the cell membrane from a point of lower concentration to a point of higher concentration, against the diffusion gradient.

active A state in which metal tends to corrode; opposite of passive.

active conservation storage The portion of water stored in a reservoir that can be released for all useful purposes such as municipal water supply, power, irrigation, recreation, fish, wildlife, etc. Conservation storage is the volume of water stored between the inactive pool elevation and flood control stage.

active ingredient The specific chemical in a product that is biologically active against pest organisms. 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 reinspections required by the Asbestos Hazard Emergency Response Act (AHERA).

acute toxicity The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose. Also, ant severe poisonous effect resulting from a single short-term exposure to a toxic substance.

acute phase A short, sharp, and relatively severe course of a disease; not chronic.

acute 1) Occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure. 2) Used to describe certain MCL violations, such as nitrate and coliform bacteria, that can pose an immediate (acute) risk.

acute exposure A single exposure to a toxic substance which results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

adaptable Capable of undergoing inheritable (and/or non-inheritable) structural or functional changes.

adaptation The result of the process of long-term evolutionary adjustment of a population to environmental changes.

add-on control device An air pollution control device such as a carbon adsorber 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.

additional sample A physical sample collected from a previously sampled lot bearing the same sample number as the original sample.

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

additive A substance added in a small amount, usually to a fluid, for a special purpose— such as to reduce friction or corrosion.

adequately wet Asbestos containing material that is sufficiently mixed or penetrated with liquid to prevent the release of particulates.

adhesion The molecular attraction exerted between the surfaces of bodies in contact.

adhesive water

adjournment Putting off or postponing of business or of a session until another time or place; the act of a court.

adjudicate To make a final judgment in a lawsuit.

adjudication The judgment of the court.

administrative order A legal document signed by a regulatory agency 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 Procedures Act A law that spells out procedures and requirements related to the promulgation of regulations.

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 record All documents that a regulatory agency considered or relied on in selecting the response action to a permit violation or illegal activity, culminating in the record of decision for remedial action or an action memorandum for removal actions.

admonition A reprimand from a judge to a person accused, on being discharged, warning of the consequences of his conduct and should he be guilty of same fault, he will be punished with greater severity.

ADR gauge Analog to Digital Recording tide gauge. A float or pressure actuated tide gauge that records the heights at regular time intervals in digital format.

adsorbate The material being removed by the adsorption process.

adsorbent The material (e.g., activated carbon) that is responsible for removing the undesirable substance in the adsorption process.

adsorption The attraction and adhesion of a layer of ions from an aqueous solution to the solid mineral surfaces with which it is in contact.

adulterants Chemical impurities or substances that by law do not belong in a food or pesticide.

adulterated 1) Any pesticide whose strength or purity falls below the quality stated on its label. 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 or more reduction in conventional pollutant concentration or a significant reduction in non-conventional pollutants. May be referred to as tertiary treatment.

advanced wastewater treatment Any treatment of wastewater that goes beyond the secondary or biological treatment stage; may include the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. See primary and secondary treatment.

advection The process by which solutes are transported by the bulk motion of flowing ground water.

adventitious organism Bacteria, yeast, mold, mycoplasma or viruses that can potentially contaminate prokaryote or eukaryote cells used in production. Potential sources of adventitious organisms include the serum used in cell culture media, persistently or latently infected cells, or the environment.

advisory A non-regulatory information source that communicates information to those who may have to make regulatory 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 through mechanical aeration.

aeration period The theoretical time, usually expressed in hours, during which biomass, referred to as mixed liquor, is subjected to aeration in an aeration tank while undergoing activated sludge treatment. It is equal to the volume of the tank divided by the volumetric rate of flow of the wastewater and the return rate of biological sludge.

aeration zone A portion of the lithosphere in which the functional interstices of permeable rock or earth are not filled with water under hydrostatic pressure. The interstices either are not filled with water or are filled with water that is no held by capillarity.

aeration cell A portion of an aeration tank or basin; an oxygen concentration cell; an electrolytic cell resulting from differences in dissolved oxygen at two points.

aeration The process of adding air to a liquid ( water) for the purpose of increasing the dissolved oxygen level. Air can be added to the liquid by either passing air through the liquid, passing the liquid through air, or agitating the liquid to promote surface absorption of air.

aeration tank 1) A chamber or basin used to introduce air into water at a controlled rate of amount per volume per time. 2) The tank where raw or settled wastewater is mixed with return sludge and aerated. Also called aeration basin.

aerator

aerial photography Photographs of the earth taken from either high or low altitudes and used to interpret natural and manmade surface features.

aerie The nest of a bird on a cliff or mountain top, usually applied to birds of prey.

aerobacteraerogenes

aerobe An organism which grows best in the presence of molecular oxygen (O₂).

aerobic treatment A process by which microbes decompose complex organic compounds in the presence of oxygen and use liberated energy for reproduction and growth. (Such processes include activated sludge such as extended aeration and contactors, such as filtration beds, and rotating biological contactors.).

aerobic process See aerobic treatment.

aerobic decomposition Decomposition and decay of organic material in the presence of free or dissolved oxygen.

aerobic A condition in which free (atmospheric) or dissolved oxygen (O₂) is present in the water.

aerochlorination

aerosol A suspension of fine solid or liquid particles in a gas, having small diamters ranging from 0.01 to 50 microns.

aesthetic standards Water quality standards which involve those physical, biological, and chemical properties of water that adversely affect the palatability and consumer acceptability of water through taste, odor, appearance or chemical reaction.

affected public The people who live and or work near a hazardous waste site.

affidavit A written statement made voluntarily under oath. An affidavit may be made (a) on personal knowledge, or (b) on information and belief.

affinity The thermodynamic quantity defining the energy interaction or binding of two molecules, usually that of antibody with its corresponding antigenic determinant.

afforestation The process of allowing or encouraging the development of forests. Syn. with reforestation.

afterbay The tail race of a hydroelectric power plant at the outlet of the turbines. The term may be applied to a short stretch of stream or conduit, or to a pond or reservoir.

afterburner In incinerator terminology, a burner located so that 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.

agar-agar A gelatinous polysaccharide extract of red algae (Rhodophyceae) used to prepare solid microbiological media. Usually referred to as agar.

age of parallax inequality The time interval between perigee of the moon and the maximum effect of parallax upon range of tide or speed of the tidal current.

age of diurnal inequality The time interval between the maximum semimonthly north or south declination of the moon and the maximum effect of the declination upon range of tide or speed of the current.

age of moon The time elapsed since the preceding new moon.

age of tide Same as age of phase inequality.

age tank A tank used to store a chemical solution of known concentration for feed to a chemical feeder. Also called a day tank.

age of phase inequality The time interval between new or full moon and the maximum effect of these phases upon range of tide or speed of the tidal current.

agent A biological, physical, or chemical entity capable of causing disease.

agger Same as double tide.

agglomerate An ice cover of floe formed by the freezing together of various forms of ice.

agglomeration The growing or coming together of dispersed suspended matter into larger flocs or particles that settle rapidly.

aggregate 1) A mass or cluster of soil particles, often having a characteristic shape. 2) Coarse mineral material (e.g., sand, gravel) that is mixed with either cement to form concrete or tarry hydrocarbons to form asphalt.

aggressive A property of water that favors the corrosion of its conveying structure.

Aggressive Index (ai) The corrosion index established by the American Works Association Standard C-400; established as a criterion for determining the corrosive tendency of the water relative to asbestos-cement pipe; calculated from pH, calcium hardness and total alkalinity.

agricultural pollution Farming wastes, including runoff and leaching of pesticides and fertilizer; erosion and dust from plowing; improper disposal of animal manure and carcasses; crop residues; and debris.

agro-ecosystem Land used for crops, pasture, and livestock; the adjacent uncultivated land that supports other vegetation and wildlife; and the associated atmosphere, the underlying soild, groundwater, and drainage networks.

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

agronomy The science of crop production.

AHERA designated person (ADP) A person designated by a Local Education Agency to ensure that the AHERA requirements for asbestos management and abatement are properly implemented.

air acoustic ranging sensor A pulsed, acoustic ranging device using the air column in a tube as the acoustic sound path. The fundamental measurement is the time it takes for the acoustic signal to travel from a transmitter to the water surface and then back to the receiver. The distance from a reference point to the water surface is derived from the travel time. A calibration point is set at a fixed distance from the acoustic transducer and is used to correct the measured distance using the calibrated sound velocity in the tube.

air binding A situation where air enters filter media and is detrimental to both the filtration and backwash processes by preventing the passage of water during the filtration process and resulting in the loss of filter media during the backwash process.

airborne release Release of any chemical into the air.

airborne particulates Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets. Airborne particulates include: windblown dust, emissions from industrial processes, smoke from the burning of wood and coal, and motor vehicle or non-road engine exhausts.

air changes per hour (ACH) 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 all of the air in the house will be replaced in a one-hour period.

air contaminant Any particulate matter, gas, or combination thereof, other than water vapor. See air pollutant.

air curtain Compressed air forced through a perorated pipe or diffuser arm, placed on a chamber or basin floor, that causes an upward water flow followed by a ??? flow. It can also be used: to stop fish from entering polluted water, containing oil spills, or to form aeration cells.

air gap An open vertical drop, or vertical empty space, that separates a drinking (potable) water supply to be protected from another water system in a water treatment plant or other location. This open gap prevents the contamination of drinking water by backsiphonage or backflow because there is no raw water or any other water that can reach the drinking water in the supply line.

air gap separation The unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying pure water to a tank, plumbing fixture, or other device and the rim of the receptacle.

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 padding Pumping dry air into a container to assist with the withdrawal of a liquid or to force a liquefied gas, such as chlorine, out of a container.

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 any combination. 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.

air pollution The presence of contaminant or pollutant substances in the air that do not disperse properly and interfere with human health or welfare, or produce other harmful environmental effects.

air pollution control device Equipment or a mechanism that cleans emissions generated by an incinerator 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 A designated area that is required to meet and maintain ambient air quality standards. It may include nearby locations in the same state or nearby states that share common air pollution problems.

air quality criteria The levels of pollution and lengths of exposure above which adverse health and welfare effects may occur.

air quality standards The level of pollutants prescribed by regulations that may not be exceeded during a given time in a defined area.

air stripping A treatment process used to remove dissolved gases and volatile substances from water. Large volumes of air are bubbled through the water being treated to remove (strip out) the dissolved gases and volatile substances. See packed tower aeration.

air temperature sensors Sensors located in the protective well for the purpose of verifying uniformity of temperature for measurements taken by the air acoustic ranging sensor.

air valve

air vent

air wash

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.

alarm contact A switch that operates when some pre-set low, high, or abnormal condition exists.

albedo The portion of incoming radiation which is reflected by a surface.

aldehyde A class of organic compounds. A hydrocarbon in which a hydrogen atom has been replaced with the CHO group.

aldicarb An insecticide sold under the trade name Temik. It is made from ethyl isocynate.

ALERT Flood Warning System A cooperative, community-operated flood warning system. The acronym stands for Automated Local Evaluation (in) Real Time.

algae Simple plants, without roots, stems, or leaves, containing chlorophyll. Algae vary in size from less than 1.0 micrometer to brown algae (kelp) over 700 feet long.

algal bloom Sudden, massive growths of microscopic and macroscopic plant life, such as green or blue-green algae, which develops in lakes and reservoirs.

algicide Any substance or chemical specifically formulated to kill or control algae.

aliphatic hydroxy acids Organic acids with carbon atoms arranged in branched or unbranched open chains rather than in rings.

aliphatic Of or pertaining to a broad category of carbon compounds distinguished by a straight, or branched, open chain arrangement of the constituent carbon atoms. The carbon-carbon bonds may be either saturated or unsaturated. Alkanes, alkenes, and alkynes are aliphatic hydrocarbons.

aliquot Portion of a sample.

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

alkaline phosphatase A group of enzymes that belong to the class known as hydrolases. They are thought to play an important role in the transport of sugars and phosphates in the intestine, bone, kidney and placenta. Elevated serum levels of alkaline phosphatase activity may indicate liver disease.

alkaline The condition of water or soil which contains a sufficient amount of alkali substances to raise the ph above 7.0.

alkalinity The capacity of water to neutralize acids. This capacity is caused by the water's content of carbonate, bicarbonate, hydroxide, and occasionally borate, silicate, and phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium carbonate. Alkalinity is not the same as ph because water does not have to be strongly basic (a high ph) to have a high alkalinity. Alkalinity is a measure of how much acid can be added to a liquid without causing a great change in ph.

alkaliphobic Avoiding alkaline solutions.

alkanes The homologous group of linear saturated aliphatic hydrocarbons having the general formula C(n)H(2n+2). Alkanes can be straight chains, branched chains, or ring structures. Also referred to as paraffins.

alkenes The group of unsaturated hydrocarbons having the general formula C(n)H(2n) and characterized by being highly chemically reactive. Also referred to as olefins.

alkynes The group of unsaturated hydrocarbons with a triple Carbon-Carbon bond having the general formula C(n)H(2n-2).

allegation An assertion or statement, made in a pleading, setting forth what its maker intends to prove.

allochthonous Of or relating to material derived from outside the habitat or environment under consideration; e.g., allochthonnous detritus of a lake is that derived from the surrounding terrestrial environment or from influent streams.

allopatry Two or more, usually closely related, species, not occurring in the same region.

alloy A substance composed of two or more metals.

alluvial Relating to small sized, fine texture (silt) and/or course textured soil particles (sand) deposited by flowing water. Alluvial deposits may occur after a heavy rain storm.

alluvial clay

alluvial deposit

alluvial soil

alluvial terrace

alluviation

alluvium Sediments, usually mineral or inorganic, deposited by running water.

alpha decay

alpha particle

alpha rays

alpine The region that is above the montane timberline, characterized by the presence of herbs and grass-like plants and low, slow-growing shrubs.

alternate method Any method of sampling and analyzing for an air pollutant that is not a reference or equivalent method but that has been demonstrated in specific cases to produce results adequate for compliance monitoring.

alternating current An electric current that reverses its direction (positive/negative values) at regular intervals.

alternating device

alternative technology The approach that aims to use resources efficiently or to substitute resources in order to do minimum damage to the environment. This approach permits a large degree of personal user control over the technology.

alternative fuels Substitutes, such as methanol, ethanol, or compressed natural gas, for traditional liquid, oil-derived motor vehicle fuels like gasoline and diesel.

altitude-control valve

alum A widely used coagulant in water and wastewater treatment composed of aluminum sulfate.

amalgam An alloy that consists chiefly of silver mixed with mercury and variable amounts of other metals and is used as dental filling.

ambient air quality standards See Criteria Pollutants and National Ambient Air Quality Standards.

ambient temperature Temperature of the surrounding air (or other medium). For example, temperature of the room where a gas chlorinator is installed.

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

ambient Outdoor environmental or surrounding conditions.

ambient conditions Conditions surrounding on all sides.

American Standard [fittings]

American Standard Code for Information Interchange (ASCII) Standard eight-bit code used in data communications. Many files interchanged from one software program to another and from IBM to Mac formats go through translation into ASCII.

amicus curiae A friend of the court. A person who, although not a party in a suit, is allowed to intervene to protect his interests.

amino acid A family of modified organic acids that serve as building blocks for the synthesis of proteins.

ammoniator

ammonification The production of ammonia in decomposition of nitrogen-containing compounds, such as protein.

ammonium (NH₃) One form of nitrogen used by plants.

amoeba A protozoan microorganism of which some types are pathogenic.

amortization rate The percentage rate at which the net investment, allowing for salvage, is recoverable.

amortization The economic process of repaying or liquidating a debt or recovering the wealth invested in a project over a determined period of time.

amortization period The period of time assumed or selected for economic recovery of the net investment in a project. The period of analysis is the lesser of either 1) the period of time over which the plan can reasonably be expected to serve a useful purpose considering probable technological trends affecting various alternatives or 2) the period of time when further discounting of beneficial and adverse effects will have no appreciable effects on design. Because of the difficulty in defining the more remote future conditions and discounting of long-deferred values, 100 years in normally the upper limit of the period of analysis.

amperage The strength of an electric current measured in amperes. The amount of electric current flow, similar to the flow of water in gallons per minute.

ampere The unit used to measure current strength. The current produced by an electromagnetic force of one volt acting through a resistance of one ohm.

amperometric titration A means of measuring concentrations of certain substances in water (such as strong oxidizers) based on the electric current that flows during a chemical reaction. See titrate.

amperometric Based on the electric current that flows between two electrodes in a solution.

amphibian Any of a class of vertebrate. Animals most of which pass through an aquatic larval stage with gills and then through a terrestrial stage with lungs; e.g., salamanders, frogs, and toads.

amphidromic region An area surrounding an amphidromic point from which the radiating cotidal lines progress through all hours of the tidal cycle.

amphidromic point A point of no amplitude of the observed or a constituent tide.

amplitude One-half the range of a constituent tide. By analogy, it may be applied also to the maximum speed of a constituent current.

amylase An enzyme that breaks down complex carbohydrates such as starch.

anabranch A diverging branch of a river which re-enters the main stream, characteristic of braided streams.

anaclinal stream

anadromous Of or relating to fish, such as salmon, that ascend fresh water streams from saltwater to spawn.

anaerobe An organism that grows best in the absence of free oxygen.

anaerobic Capable of living in the absence of air or free oxygen.

anaerobic A condition in which free or dissolved oxygen is not present in water.

anaerobic digestion A process in which wastewater solids and water are placed in a large tank where bacteria decompose the solids in the absence of dissolved oxygen. At least two general groups of of bacteri act in balance: saprophytic bacteria break down complex solids to volatile acids and methane fermenters break down the acids to methane, carbon dioxide, and water.

anaerobic decomposition Reduction of the net energy level and change in chemical composition of organic matter caused by microorganisms in an oxygen-free environment.

analog communication A communication format in which information is transmitted by modulating a continuous signal, such as a sound wave. Current TV and radio signals are analog, as are many telephone lines. See also Digital Communication.

analog 1) The readout of an instrument by a pointer (or other indicator) against a dial or scale. 2) In chemistry, a structural derivative of a parent compound.

analysis, harmonic See harmonic analysis.

analysis An examination of a sample of matter or information.

analyte stability study An analysis of a laboratory sample in which a known quantity of an analyte has been placed (a “spiked” sample). The sample is analyzed at a predetermined time to assess the stability and recovery of the analyte.

analyte One of 127 chemicals that the National Pesticide Survey analytical methods were chosen or designed to identify. The Survey analytes include 101 pesticides, 25 pesticide degradates, and nitrate. Analytes were selected on the basis of expected leaching potential, occurrence in groundwater, volume of use, and other considerations.

analytic study A comparative study intended to identify and quantify associations, test hypotheses, and identify causes. Two common types are cohort study and case-control study.

analytic epidemiology The aspect of epidemiology concerned with the search for health-related causes and effects. Uses comparison groups, which provide baseline data, to quantify the association between exposures and outcomes, and test hypotheses about causal relationships.

analyzer, harmonic See harmonic analyzer.

analyzer A device which conducts periodic or continuous measurement of some factor such as chlorine, fluoride, or turbidity. Analyzers operate by any of several methods including photocells, conductivity or complex instrumentation.

anchor ice Submerged frazil ice attached or anchored to the river bottom, irrespective of its formation.

anchor ice dam An accumulation of anchor ice which acts as a dam and raises the water level.

angle of current

angle of incidence

angle of repose

angstrom unit

angularity

angular velocity of the earth's rotation Time rate of change of angular displacement relative to the fixed stars. It is equal to 0.729,211 x 10^-4 radian/second.

animal studies Investigations using animals as surrogates for humans, on the expectation that results in animals are pertinent to humans.

anion A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride (CL-) is an anion.

anionic polymer A polymer having negatively charged groups of ions, often used as a filter aid and for dewatering sludges.

anionic surfactant

anisotropic The condition in which hydraulic properties of an aquifer are not equal when measured in all directions.

annual Pertaining to yearly occurrence.

annual financial cost Sum of the annual equivalent of the investment cost, the annual operation and maintenance costs, and the annual equivalent of major replacement cost; includes interest during construction.

annual flood

annual inequality Seasonal variation in water level or current, more or less periodic, due chiefly to meteorological causes.

annual plant A plant that grows from seed and reproduces in one year.

annual review 1) 2) EPA’s assessment of the success of Virginia’s Drinking Water State Revolving Fund program.

annual daily water demand The average rate of daily water usage over at least the most recent three year period.

annual increment That which is added or gained in one year.

annual flood The maximum discharge peak during a peak during a given water year.

annular space A ring-shaped space located between two circular objects, such as two pipes.

anode The positive pole or electrode of an electrolytic system, such as a battery. The anode attracts negatively charged particles or ions (anions).

anodic polarization Polarization of an anode, i.e., the decrease in the initial anode potential resulting from current flow effects at or near the anode surface. Potential becomes more noble (more positive) because of anodic polarization.

anodic protection An appreciable reduction in corrosion by making a metal an anode and maintaining this highly polarized condition with very little current flow.

anomalistic Pertaining to the periodic return of the moon to its perigee or the earth to its perihelion. The anomalistic month is the average period of the revolution of the Moon around the Earth with respect to lunar perigee, and is approximately 27.554,550 days in length. The anomalistic year is the average period of the revolution of the Earth around the Sun with respect to perihelion, and is approximately 365.259,6 days in length.

anomaly 1) As applied to astronomy, the anomaly is the angle made at any time by the radius vector of a planet or moon with its line of apsides, the angle being reckoned from perihelion or perigee in the direction of the body's motion. It is called the true anomaly when referred to the actual position of the body, and mean anomaly when referred to a fictitious body moving with a uniform angular velocity equal to the average velocity of the real body and passing perihelion or perigee at the same time.

anomorphic zone

anoxic Pertaining to conditions of oxygen deficiency.

antagonism Interference or inhibition of the effect of one chemical by the action of another chemical.

antecedent

antecedent moisture

antecedent precipitation index (API) An index to soil moisture within a drainage basin.

antecedent precipitation index (API) method A statistical method to estimate the amount of surface runoff which will occur from a drainage basin from a given rain storm based on the antecedent precipitation index, physical characteristics of the drainage basin, time of year, storm duration, rainfall amount, and rainfall intensity.

antecedent stream

anthropogenic mercury emissions The atmospheric emission of geologically bound mercury by human activity (e.g. emission of mercury in fossil fuels such as coal).

anthropogenic Man-made.

antibiosis

anticyclone

anti-degradation clause Part of federal air and water quality requirements prohibiting deterioration where pollution levels are above the legal limit.

antibody A globulin, found in tissue fluids and blood serum, produced in response to the stimulus of a specific antigen and capable of combining with that antigen to neutralize or destroy it. Globulins are often referred to as “immune substances.”

anticyclonic ring A meander breaking off from the main current and spinning in a clockwise direction in the northern hemisphere (counter-clockwise in southern).

antifouling A coating process or the like that prevents the accumulation of aquatic animals and plants.

antigen That portion of a biologic agent capable of stimulating the formation of specific antibodies.

antigenic determinant The specific part of a structure of an antigen which will induce an immune response, i.e. will fit to the receptors on T and B lymphocytes and will also be able to react with the antibodies produced.

antigenicity Ability of an agent or its products to stimulate the formation of antibodies.

Antilles Current A North Atlantic Ocean current setting northwestward along the northeast coasts of the Bahama Islands.

antisepsis The prevention of sepsis by inhibition or destruction of the causative organism.

antiserum Blood serum which contains antibodies against a particular antigen (or immunogen). This frequently means serum from an animal that has been inoculated with the antigen.

antitoxin Antibody to the toxin of a microorganism, usually a bacterial exotoxin. Antitoxin combines with a specific toxin with the subsequent neutralization of the toxicity.

aphelion The point in the orbit of the Earth (or other planet, etc.) farthest from the sun.

aphotic Lightless, as below the photic zone in oceans and lakes.

aphotic zone The lower portion of bodies of water not reached by light.

apogean tides or tidal currents Tides of decreased range or currents of decreased speed occurring monthly as the result of the moon being in apogee. The apogean range (An) of the tide is the average range occurring at the time of apogean tides and is most conveniently computed from the harmonic constants. It is smaller than the mean range, where the type of tide is either semidiurnal or mixed, and is of no practical significance where the type of tide is predominantly diurnal.

apogee The point in the orbit of the moon or man-made satellite farthest from the earth. The point in the orbit of a satellite farthest from its companion body.

apparent density

apparent secular trend The nonperiodic tendency of sea level to rise, fall, or remain stationary with time. Technically, it is frequently defined as the slope of a least-squares line of regression through a relatively long series of yearly mean sea-level values. The word "apparent" is used since it is often not possible to know whether a trend is truly nonperiodic or merely a segment of a very long (relative to the length of the series) oscillation.

apparent specific gravity

apparent time Time based upon the true position of the sun as distinguished from mean time, which is measured by a fictitious sun moving at a uniform rate. Apparent time is that shown by the sundial, and its noon is the time when the sun crosses the meridian. The difference between apparent time and mean time is known as the equation of time. Although quite common many years ago, apparent time is seldom used now.

available dilution

available moisture

available oxygen

available water

average

average daily flow

average efficiency

average flow

average stream flow

average velocity

axial-flow pump

axis

axis of equilibrium

appeal The formal review by a higher court of a lower court's disposition of a lawsuit.

Applicable or Appropriate Requirements (arars) Any state or federal statute that pertains to protection of human life and the environment in addressing specific conditions or use of a particular cleanup technology at a Superfund site.

applied epidemiology The application or practice of epidemiology to address public health issues.

applied water Water that is ready for filtration.

apportionments A full year's requirements on projects and activities.

appraisal

appreciation

appropriation bill The bill which, when enacted by Congress and approved by the President, makes funds available for specific activities during a given fiscal year. After such a bill has been approved by the President, it becomes an Act.

appropriation The right to withdraw water from its source.

appropriations Statutory authority that allows government agencies to obligate funds and make payments from the treasury for specified purposes.

appropriative Water rights to or ownership of a water supply which is acquired for the beneficial use of water by following a specific legal procedure.

approved Material, equipment, workmanship, process or method that has been accepted as suitable for the proposed use.

appurtanance Machinery, appliances, structures and other parts of the main structure necessary to allow it to operate as intended, but not considered part of the main structure.

apron

apsides The points in the orbit of a planet or moon which are the nearest and farthest from the center of attraction. In the Earth's orbit these are called perihelion and aphelion, and in the moon's orbit, perigee and apogee. The line passing through the apsides of an orbit is called the line of apsides.

aquaculture water use Water used for farming of organisms that live in water, such as fish, excluding fish hatcheries (commercial water use), shrimp, and other shellfish.

aquaculture Production of food from managed aquatic systems.

aquatic Plants or animal life living in, growing in, or adapted to water.

aquatic growth

aquatic habitat A habitat located in water.

aqueduct

aqueous Something made up of, similar to, or containing water; watery.

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

aquiclude A geologic formation which, although porous and capable of absorbing water slowly, will not transmit it rapidly enough to furnish an appreciable supply for a well or spring.

aquifer test Pumping of a well at a constant rate for a fixed period of time with concurrent water-level measurements in one or more nearby observation wells. The time-drawdown data are analyzed to yield quantitative aquifer parameter values.

aquifer discharge area An area of land where the zone of saturation is in direct contact with the ground surface. Discharging ground water may appear as springs, seeps, or in baseflow of streams.

aquifer depletion Condition of declining water levels within the aquifer's structure because natural recharging from surface water and precipitation is inadequate to maintain normal level. Can be caused by withdrawal rates exceeding recharge rates.

aquifer recharge area An area of land above or remote from an aquifer that allows infiltration of water to that aquifer.

aquifer Rock or sediment in a formation, group of formations, or part of a formation that is saturated and sufficiently permeable to transmit economic quantities of water to wells or springs.

aquifuge A geologic formation which has no interconnected openings and cannot hold or transmit water.

aquitard A geologic unit of low permeability that can store and slowly transmit ground water from one aquifer to another. Aquitards act as confining units of aquifers.

arable land Land fit for cultivation.

arch dam A concrete arch dam is used in sites where the ratio of width between abutments to height is not great and where the foundation at the abutments is solid rock capable of resisting great forces. The arch provides resistance to movement. When combined with the weight of concrete (arch-gravity dam), both the weight and shape of the structure provide great resistance to the pressure of water.

arctic Of, or characteristic of, the region around the north pole to approximately 65 ° north latitude; all regions north of the boreal timber line.

area-capacity curve A graph showing the relation between the surface area of the water in a reservoir, the corresponding volume, and elevation.

area curve

area drain

area of diversion

area of influence The area covered by the drawdown curves of a given pumping well or combination of wells at a particular time.

area of review In the underground injection control (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 small source of man-made air pollution that is released over a relatively small area but cannot be classified as a point source. Such sources may include vehicles and other small engines, small businesses, and household activities.

argument See equilibrium argument.

arid An adjective which describes regions where precipitation is so deficient in quantity, or occurs at such times, that agriculture is impracticable without irrigation.

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

arraignment The appearance of the defendant (in any criminal prosecution) before the court to answer the allegations made against him and to enter his plea (guilty or not guilty).

arroyo A water-carved channel or gully in arid country, usually rather small with steep banks, dry most of the time, due to infrequent rainfall and the shallowness of the cut which does not penetrate below the level of permanent groundwater.

arsenicals Pesticides containing arsenic.

arterial discharge

arterial flow

arterial spring

arterial waste

arterial water

arterial well

artesian well A well drilled into a confined aquifer with enough hydraulic pressure for the water to flow to the surface without pumping. Also called a flowing well.

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

arthropods

artificial recharge

asbestos program manager A building owner or designated representative who supervises all aspects of the facility asbestos management and control program.

asbestos A mineral fiber that can pollute air and water and whose use in manufacturing and construction is banned or severely restricted.

asbestos-containing waste materials (ACWM) Mill tailings or any waste that contains commercial asbestos.

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.

asbestosis A disease associated with inhalation of asbestos fibers. The disease makes breathing progressively more difficult and can be fatal.

asepsis Absence of microorganisms capable of causing infection or contamination.

ash The mineral content of a product remaining after complete combustion.

aspect

aspection Periodic, i.e., seasonal changes in the appearance of a group of species, associated with periods of foliation or flowering, which are reflected in the appearance of the community as a whole or its members.

aspirator

assay A test for a particular chemical or effect.

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.

asset A physical or intangible item of value to an organization or individual.

assimilation 1) Transformation of absorbed nutrients into body substances (cell protoplasm). 2) 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 water.

associated costs The value of goods or services needed, over and above those included in the project costs, to make products or services of the project available for use or sale.

association 1) Statistical relationship between two or more events, characteristics, or other variables. 2) A definite or characteristic assemblage of plants living together in an area essentially uniform in environmental conditions; any ecological unit of more than one species.

association constant A reaction between antibody and its determinant which comprises a measure of affinity. The constant is quantitated by mass action law rate constants for association and for dissociation.

Association of Boards of Certification An international organization representing over 150 boards which certify the operators of waterworks and wastewater facilities.

associes An association constituting a temporary stage of plant succession; a non-climax community to be replaced by another in the process of succession.

astronomical time Time formerly used in astronomical calculations in which the day began at noon rather than midnight. The astronomical day commenced at noon of the civil day of the same date.

astronomical tide Same as tide.

astronomical day See astronomical time.

asymmetric Not similar in size, shape, form, or arrangement of parts on opposite sides of a line, point, or plane.

asymptote A line that is considered to be the limit to a curve. As the curve approaches the asymptote, the distance separating the curve and the asymptote continues to decrease, but the curve never actually intersects the asymptote.

asynchronous transfer mode (ATM) Communication technology that uses high-bandwidth, low-delay transport technology, and multiplexing techniques. Through dedicated media connections it provides simultaneous transport of voice, video, and data signals more than 50 times faster than current technology. May be used in phone and computer networks of the future.

asynchronous A type of two-way communication that occurs with a time delay, allowing participants to respond at their own convenience. Literally not synchronous, in other words, not at the same time. Example of an application of asynchronous communication is electronic bulletin board.

atmosphere The gaseous layer that surrounds the earth (air). One atmosphere of pressure equals 14.7 pounds per square inch, 33.9 feet of water or 29.92 inches of mercury.

atmospheric moisture

atmospheric pressure

atmospheric water

atom The smallest unit of a chemical element; composed of protons, neutrons, and electrons.

atomization

attached growth Fixed film growth on a contact media.

attack rate A variant of an incident rate, applied to a narrowly defined population observed for a limited period of time, such as during an epidemic.

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.

attenuate (electrically)

attenuation 1) The process by which a compound is reduced in concentration over time through one or more of the following processes: adsorption, degradation, dilution, or transformation. 2) The process where the flood crest is reduced as it progresses downstream.

Atterberg limits The moisture contents which define a soil's liquid limit, plastic limit, and sticky limit.

attractant A chemical or agent that lures insects or other pests by stimulating their sense of smell.

attributable proportion A measure of the public health impact of a causative factor; proportion of a disease in a group that is exposed to a particular factor which can be attributed to their exposure to that factor.

attrition Wearing or grinding down of a substance by friction. Dust from such processes contribute to air pollution.

audio bridge Specialized equipment that interconnects three or more telephone lines (usually operator assisted) to enable conference calls. The audioconferencing equipment needed to connect multiple sites can be provided by companies specializing in bridge services.

audioconference An electronic meeting in which participants in different locations use telephones or audioconferencing equipment to interactively communicate with each other in real time. The number of participants may be as small as 3 or as large as 100 or more.

audiogram A graph or table obtained from an audiometric test showing hearing level as a function of frequency.

audit sample A sample collected to verify the analytical results of a private laboratory and to validate the private sector evaluation process. An audit sample is collected from the same or similar units as those tested by the private laboratory.

audit (end-use) A systematic accounting of water used by end users (residential, commercial, and industrial), often used to identify potential areas for water reduction, conservation, or efficiency improvement.

audit (system) A systematic accounting of water throughout the production, transmission, and distribution facilities of the system.

auger A tool for drilling/boring into unconsolidated earth materials (soil) consisting of a spiral blade wound around a central stem or shaft that is commonly hollow (hollow-stem auger). Augers commonly are available in flights (sections) that are connected together to advance the depth of the borehole.

augmenting factor A factor used in connection with the harmonic analysis of tides or tidal currents to allow for the fact that the tabulated hourly heights or speeds used in the summation for any constituent, other than S, do not in general occur on the exact constituent hours to which they are assigned, but may differ from the same by as much as a half hour.

autochthon A native species; indigenous.

autoclave A device using steam under pressure for sterilization.

autoignition temperature The temperature at which a substance will spontaneously ignite. Autoignition temperature is an indicator of thermal stability for petroleum hydrocarbons.

automated clearing house A Federal payment mechanism that transfers cash to states using electronic transfers from the Treasury through the Federal Reserve System.

automatic recording gauge

automatic sprinkler

automatic tide gauge An instrument that automatically registers the rise and fall of the tide. In some instruments, the registration is accomplished by recording the heights at regular time intervals in digital format; in others, by a continuous graph of height against time.

automatic valve

autoradiography Detection of radioactively labeled molecules on X- ray film.

autotroph A microorganism that utilizes inorganic materials as a source of nutrients for growth. Carbon dioxide is the sole source of carbon.

autotrophic Having the ability to utilize carbon dioxide as the sole source of oxygen.

auxiliary supply

auxiliary water system Any water system on or available to the premises other than the waterworks. These auxiliary waters may include water from a source such as wells, lakes, or streams; process fluids; or used water. They may be polluted, contaminated, or objectionable or constitute an unapproved water source or system over which the water purveyor does not have control.

availability session An informal meeting at a public location where interested citizens can talk with EPA and state officials on a one-to-one basis.

available moisture The part of the water in the soil that can be taken up by plants at rates significant to their growth; the moisture content of the soil in excess of the ultimate wilting point.

available expansion The vertical distance from the sand surface to the underside of a trough in a sand filter. This distance is also called freeboard.

available supply The maximum amount of reliable water supply, including surface water, groundwater, and purchases under secure contracts.

available chlorine A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials that are used as a source of chlorine when compared with that of elemental (liquid or gaseous) chlorine.

available oxygen The quantity of dissolved oxygen available for oxidation of organic matter in a body of water.

available A quantity that can be used to produce some result.

average discharge The arithmetic average of all complete years of record whether or not they are consecutive. The term “average” is generally reserved for the average of record and “mean” is used for average of shorter periods, namely, daily mean discharge.</