cache Memory that holds copies of recently accessed data. Some Web browsers keep recently viewed pages in a cache so users can return to them quickly without suffering network delays.
CaCO3 equivalent (calcium carbonate equivalent) An expression of the concentration of specified constituents in water in terms of their molecular equivalent value to calcium carbonate. For example, the hardness of water which is caused by calcium, magnesium, and other ions is usually described as calcium carbonate equivalent.
cadmium (Cd) A heavy metal element that accumulates in the environment.
CAG Carcinogen Assessment Group.
caisson A structure or chamber which is usually sunk or lowered by digging from the inside. Used to gain access to the bottom of a stream or other body of water.
cake A dewatered mass of suspended solids and water with a dry solids content of 15 percent or more by weight.
calendar call A writ commanding a court to certify records to a superior court. When the supreme court grants certiorari (or “to be certified”), it has agreed to hear the case. If it denies certiorari, it will not hear the case. Also referred to as calling the docket.
calibration 1) A procedure which checks or adjusts an instrument's accuracy by comparison with a standard or reference. 2) The process of using historical data to estimate parameters in a hydrologic forecast techniques such as SACSMA parameters, routings, and unit hydrographs.
calorie 1) The heat required (at one atmosphere of pressure) to raise the temperature of one gram of water one degree, specifically from 4 to 5°C. 2) In nutrition, a Calorie is 1,000 calories.
Canary Current A North Atlantic Ocean current setting southward off the west coast of Portugal and along the northwest coast of Africa.
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.
cancer A disease characterized by the rapid and uncontrolled growth of aberrant cells in malignant tumors.
candela (cd) The unit of luminous intensity. One candela is defined as the luminous intensity of 1/600,000 square meter of projected area of a blackbody radiator operating at a temperature of solidification of platinum under a pressure of 101,325 newtons per square meter.
canopy The leafy cover of vegetation; the uppermost leafy layer in forests.
cap 1) A layer of clay or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize leachate. 2) A layer of relatively warm air aloft (usually several thousand feet above the ground) which suppresses or delays the development of thunderstorms. Also called Capping Inversion.
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.
capillarity 1) The degree to which a material or object containing minute openings or passages, when immersed in a liquid, will draw the surface of the liquid above the hydrostatic level. Unless otherwise defined, the liquid is generally assumed to be water. 2) The phenomenon by which water is held in interstices above the normal hydrostatic level, due to attraction between water molecules.
capillary action The movement of water through very small spaces due to molecular forces.
capillary forces The molecular forces which cause the movement of water through very small spaces.
capillary fringe The porous material just above the water table which may hold water by capillarity (a property of surface tension that draws water upwards) in the smaller void spaces. Also called the capillary zone.
capillary suction The process whereby water rises above the water table into the void spaces of a soil due to tension between the water and soil particles.
capillary zone The soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches to a few feet (few centimeters to couple of meters), and it depends on the pore sizes of the materials. Also called the capillary fringe.
capital The funds committed to an enterprise in the form of ownership equity and long-term financing.
capital costs Costs, usually long-term debt, of financing construction and equipment normally charged to fixed asset accounts. Capital costs are usually fixed, one-time expenses which are independent of the amount of water produced.
capital facilities Physical facilities used in the production, transmission, and distribution of water.
capitalization grant The assistance agreement by which EPA awards funds to Virginia for purposes of capitalizing the revolving fund.
capital planning A systematic approach to managing the risks and returns of I/T investments for a given mission.
capture efficiency The fraction of organic vapors generated by a process that are directed to an abatement or recovery device.
carbohydrate Any of the various neutral compounds consisting of carbon, hydrogen, and oxygen (as sugars, starches, celluloses) most of which are formed by green plants.
carbonaceous oxidation A biochemical process by which heterotrophic microorganisms derive energy from organic wastes, rendering more stable organics and inorganics as end-products and producing carbon dioxide and water. See biodegradable.
carbon adsorber 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 Removal of contaminants from water by filtration through granular activated carbon or by the addition of powdered activated carbon.
carbonate alkalinity That part of the total alkalinity due to the carbonate ion (CO3 –).
carbon monoxide (CO) A colorless, odorless, poisonous gas produced by incomplete fossil fuel combustion. Carboxyhemoglobin: Hemoglobin in which the iron is bound to carbon monoxide (CO) instead of oxygen.
carcinogen Any substance which tends to produce cancer in an organism.
carcinogenic Cancer producing.
carnivore An organism that eats living animals.
carrier 1) The inert liquid or solid material added to an active ingredient in a pesticide. 2) A person or animal, in which an infectious agent lives, which may not itself have any observable disease (at least at some point, and in the case of some infectious agents, not at all) caused by carrying the agent. The carrier is the potential source of infection—directly or indirectly, it is involved in transmitting the disease to humans or animals.
carrying capacity 1) The maximum population size of a given species in an area beyond which no significant increase can occur without damage occurring to the area. 2) In recreation management, the amount of use a recreation area can sustain without loss of quality.
case An infected or diseased person or animal having specific clinical, laboratory, and epidemiological characteristics. See confirmed case and presumptive case.
case-control study A type of observational analytic study. Enrollment into the study is based on presence (“case”) or absence (“control”) of disease. Characteristics such as previous exposure are then compared between cases and controls.
case definition A set of standard criteria for deciding whether a person has a particular disease or health-related condition, by specifying clinical criteria and limitations on time, place, and person.
case-fatality rate The proportion of persons with a particular condition (cases) who die from that condition. The denominator is the number of incident cases; the numerator is the number of cause-specific deaths among those cases.
cask A thick-walled container (usually lead) used to transport radioactive material. Also called a coffin.
CAS registration number A number assigned by the Chemical Abstracts Service to identify a chemical.
catadramous Living in fresh water and going to salt water to spawn.
catalase An enzyme which decomposes hydrogen peroxide to produce water and oxygen.
catalyst A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.
catalytic converter An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen and oxygen.
catalytic incinerator A control device that oxidizes volatile organic compounds (VOCs) by using a catalyst to promote the combustion process. Catalytic incinerators require lower temperatures than conventional thermal incinerators, thus saving fuel and other costs.
catalytic oxidizer An off-gas post-treatment unit for control of organic compounds. Gas enters the unit and passes over a support material coated with a catalyst (commonly a noble metal such as platinum or rhodium) that promotes oxidation of the organics. Catalytic oxidizers can also be very effective in controlling odors. High moisture content and the presence of chlorine or sulfur compounds can adversely affect the performance of the catalytic oxidizer.
catalyze To act as a catalyst or to speed up a chemical reaction.
catalyzed To be acted upon by a catalyst.
catastrophic disaster. An event that results in large numbers of deaths and injuries; causes excessive damage or destruction of facilities that provide and sustain human needs; produces an overwhelming demand on State and local response resources and mechanisms; causes a severe long-term effect on general economic activity; and severely affects State, local, and private sector capabilities to begin and sustain response activities.
catchment area An area having a common outlet for its surface runoff. Same as drainage basin.
catchment basin A drainage area. A structure that receives surface runoff flow. See drainage basin.
categorical exclusion A class of actions that 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.
categorical pretreatment standard A technology-based effluent limitation for a specific type of industrial facility discharging into a municipal sewer system. Analogous in stringency to best available technology for direct dischargers.
catharobes Organisms found in clean water.
cathode The negative pole or electrode of an electrolytic cell or system. The cathode attracts positively charged particles or ions (cations). Opposite of anode.
cathodic corrosion An unusal condition in which corrosion is accelerated at the cathode because cathodic reaction creates an alkaline condition that is corrosive to certain metals.
cathodic polarization Polarization of the cathode; a reduction from the initial potential resulting from current flow effects at or near the cathode surface. Potential becomes more active (negative) because of cathodic polarization.
cathodic protection An electrical system for prevention of rust, corrosion, and pitting of metal surfaces which are in contact with water or soil. A low-voltage current is made to flow through a liquid (water) or a soil in contact with the metal in such a manner that the external electromotive force renders the metal structure cathodic. This concentrates corrosion on auxiliary anodic parts which are allowed deliberately to corrode instead of letting the structure corrode.
cation A positively charged ion in an electrolytic solution, attracted to the cathode under the influence of a difference in electrical potential. Sodium ion (Na+) is a cation.
cationic polymer A polymer having positively charged groups of ions; often used as a coagulant aid.
cause of disease A factor (characteristic, behavior, event, etc.) that directly influences the occurrence of disease. A reduction of the factor in the population should lead to a reduction in the occurrence of disease.
cause-specific mortality rate The mortality rate from a specified cause for a population. The numerator is the number of deaths attributed to a specific cause during a specified time interval; the denominator is the size of the population at the midpoint of the time interval.
caution stage The stage at which some action needs to be taken.
cavitation The formation and collapse of a gas pocket or bubble on the blade of an impeller or the gate of a valve. The collapse of this gas pocket or bubble drives water into the impeller or gate with a terrific force than can cause pitting on the impeller or gate surface. Cavitation is accompanied by loud noises that sound like someone is pounding on the impeller or gate with a hammer.
cavitation corrosion Corrosion damage resulting from cavitation and corrosion; metal corrodes, pressure develops from collapse of the cavity and removes the corrosion product, exposing bare metal to repeated corrosion.
cavitation damage Deterioration of a surface caused by cavitation (the sudden formation and collapse of cavities in a liquid).
cavitation erosion See cavitation damage.
C-band A type of satellite transmission with less path loss than other satellite standards such as Ku-band. C-band, however, requires a relatively large antenna. C-band frequencies are shared with terrestrial microwave transmissions, which can cause interference with weaker satellite signals in certain areas.
celestial sphere An imaginary sphere of infinite radius concentric with the Earth, on which all celestial bodies except the Earth are imagined to be projected.
cell 1) A circuit consisting of an anode and a cathode in electrical contact in a solid or liquid electrolyte. Corrosion generally occurs only at anodic areas. 2) In solid waste disposal, confined areas where waste is dumped, compacted, and covered with layers of dirt on a daily basis. 3) The smallest structural part of living matter capable of functioning as an independent unit. 4) See aeration cell. 5) Convection in the form of a single updraft, downdraft, or updraft/downdraft couplet, typically seen as a vertical dome or tower as in a cumulus or towering cumulus cloud. A typical thunderstorm consists of several cells (see multi-cellular thunderstorm).
cell culture The in- vitro growth of cells isolated from multicellular organisms. These cells are usually of one type.
cell differentiation The process whereby descendants of a common parental cell achieve and maintain specialization of structure and function.
cell fusion The formation of a hybrid cell with nuclei and cytoplasm from different cells, produced by fusing two cells of the same or different species.
cell line Cells that acquire the ability to multiply indefinitely in- vitro.
cementitious Densely packed and nonfibrous friable materials.
census The enumeration of an entire population, usually with details being recorded on residence, age, sex, occupation, ethnic group, marital status, birth history, and relationship to head of household.
center The vertical axis or core of a tropical cyclone. It is usually determined by cloud vorticity patterns, wind, and/or pressure distributions.
center/vortex fix The location of the center of a tropical or subtropical cyclone obtained by reconnaissance aircraft penetration, satellite, radar, or synoptic data.
centibar The unit of pressure equal to 1 ton per meter per second per second. See decibar.
central collection point A location where a generator of regulated medical waste consolidates wastes originally generated at various locations in his or her facility. The wastes are gathered for transport elsewhere for treatment and/or disposal. This term could apply also to community hazardous waste collections or industrial (and other) waste management systems.
central nervous system The body’s organ system that originates, sends, and receives electrical signals to control movement and action consisting of the brain and spinal cord. Acute exposures over 2,200 R causes death within hours by damage to this organ system; cns.
centrate The water leaving a centrifuge after most of the solids have been removed.
centrifugal collector A mechanical system using centrifugal force to de-water sludge.
centrifugal pump A pump consisting of an impeller fixed on a rotating shaft that is enclosed in a casing and having an inlet and discharge connection. As the rotating impeller whirls the water around, centrifugal force builds up enough pressure to force the water through the discharge outlet.
centrifuge A mechanical device that uses centrifugal or rotational forces to separate solids from liquids.
certification Documentation signed by the responsible party that specific standards have been or will be met.
cesspool An underground catch basin for liquid waste, such as household waste. Also called a septic tank.
C factor A factor or value used to indicate the relative smoothness of the interior of a pipe. The higher the C Factor, the smoother the pipe, the greater the carrying capacity, and the smaller the friction or energy losses from water flowing in the pipe. To calculate the C Factor, measure the flow, pipe diameter, distance between two pressure gages, and the friction or energy loss of the water between the gages.
chain of infection A process that begins when an agent leaves its reservoir or host through a portal of exit, and is conveyed by some mode of transmission, then enters through an appropriate portal of entry to infect a susceptible host.
channel An open conduit either naturally or artificially created which periodically or continuously contains moving water. Watercourse, river, creek, run, branch, and tributary are some of the terms used to describe natural channels.
channel capacity The maximum rate of flow that may occur in a stream without causing flooding. The discharge at bankfull stage.
channel inflow Water, which at any instant, is flowing into the channel system form surface flow, subsurface flow, base flow, and rainfall that has directly fallen onto the channel.
channelization Straightening and deepening streams so that water will move faster— a marsh-drainage tactic that can interfere with waste assimilation capacity, disturb fish and wildlife habitats, and aggravate flooding.
channel lead An elongated opening in the ice cover caused by a water current.
channel routing The process of determining progressively the timing and shape of the flood wave at successive points along a river.
channel storage The volume of water at a give time in the channel or over a flood plain in a drainage basin or river reach. Channel storage is large during the progress of a flood event.
chaparral 1) The climax vegetation generally found in temperate regions which have at least moderate winter rainfall and dry summers (Mediterranean climate). 2) Small trees and shrubs characterized by hard, thick evergreen leaves.
characteristic Any one of the four categories used in defining hazardous waste: ignitability, corrosivity, reactivity, and toxicity.
charge sheet The specification of the violation attached to a notice of hearing. It is the proposed statement of charges that, should prosecution ensue, would become the government's allegation in the criminal information.
chart datum The datum to which soundings on a chart are referred. It is usually taken to correspond to a low-water elevation, and its depression below mean sea level is represented by the symbol Z .
check valve A special valve with a hinged disc or flap that opens in the direction of normal flow and is forced shut when flows attempt to go in the reverse or opposite direction of normal flow.
chelating agent
chelation A chemical complexing (forming or joining together) of metallic ions (such as copper) with certain organic compounds, such as edta (ethylene diamine tetracetic acid). Chelation is used to prevent the precipitation of metals (copper). See sequestration.
chemical oxygen demand (COD) An indirect measure of the amount of oxygen required to oxidize by inorganic and organic matter in water. The measure is a laboratory test based on a chemical oxidant and does not necessarily correlate with biochemical oxygen demand.
chemical treatment Any one of a variety of technologies that uses 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.
chemosynthesis The process by which some organisms (bacteria) obtain their energy for carbon dioxide assimilation by the chemical oxidation of simple inorganic compounds. See photosynthesis.
chemotaxis Net oriented movement in a concentration gradient of certain compounds. Various sugars and amino acids can serve as attractants while some substances such as acid or alkali serve as repellants in microbial chemotaxis. White blood cells and macrophages demonstrate chemotactic movement in the presence of bacterial products, complement proteins and antigen activated t cells to contribute to the local inflammatory reaction and resistance to pathogens.
chemotrophs Organisms that obtain energy from oxidation or reduction of inorganic or organic matter.
Chemterc The industry-sponsored Chemical Transportation Emergency Center that provides information and/or emergency assistance to emergency responders.
chilling effect The lowering of the Earth's temperature because of increased particles in the air blocking the sun's rays. (See greenhouse effect.)
chisel plowing Cropland preparation by a special implement (chisel) that avoids complete inversion of the soil (as occurs with conventional moldboard plowing). Chisel plowing can leave a protective cover of crop residues on the soil surface that helps prevent erosion and improve infiltration.
chitin A nitrogen-containing polysaccharide present in the cell walls of many fungi.
chloramines Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.
chloride index
chlorinated hydrocarbons These include a class of persistent, broad-spectrum compounds that linger in the environment and accumulate in the food chain.
chlorinated solvent An organic solvent containing chlorine atoms, e.g., methylene chloride and 1,1,1-trichloromethane, used in aerosol spray containers and in highway paint.
chlorination The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results (aiding coagulation and controlling tastes and odors).
chlorinator A metering device which is used to control the addition of chlorine to water.
chlorine Molecular or dry chlorine.
chlorine-contact chamber A basin that maintains an established residence period following chlorination as necessary to achieve disinfection.
chlorine demand The difference between the amount of chlorine added to water and the amount of residual chlorine remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of the impurities in the water.
chlorine demand, mg/L = chlorine applied, mg/L - residual, mg/L
chlorine detector Usually a mixed oxide, semi-conductor (similar to an oxygen meter) that is calibrated to detect chlorine concentrations in the air.
chlorine gas Dry chlorine in the gaseous state.
chlorine requirement The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of coliform bacteria, obtaining a particular chlorine residual, or oxidizing some substance in the water. In each case a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.
chlorine solution (chlorine water) A solution of chlorine in water. Note: the term chlorine solution is sometimes used to describe hypochlorite solutions. This use of the term is incorrect.
chlorinity The number giving the chlorinity in grams per kilogram of a seawater sample is identical with the number giving the mass in grams of atomic weight silver just necessary to precipitate the halogens in 0.328,523,3 kilogram of the seawater sample.
S(°/oo) = 1.806,55 x Cl(°/oo)
where S(°/oo) is the salinity in parts per thousand. See salinity.
chlorofluorocarbons (CFCs) A family of inert, nontoxic, and easily liquified chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere they drift into the upper atmosphere where their chlorine components destroy ozone.
chlorosis Discoloration of normally green plant parts caused by disease, lack of nutrients, or various air pollutants.
chlorophenolic Phenolic compounds combined with chlorine.
chlorophenoxy A class of herbicides that may be found in domestic water supplies and cause adverse health effects. Two widely used chlorophenoxy herbicides are 2,4-D (2,4-Dichlorophenoxy acetic acid) and 2,4,5-TP (2,4,5-Trichlorophenoxy propionic acid [silvex]).
chlorophyll The green photosynthetic coloring matter of plants found in chloroplasts and made up chiefly of a blue-black ester and a dark green ester.
chloroplast A plastid containing chlorophyll.
chlororganic Organic compounds combined with chlorine. These compounds generally originate from, or associated with, life processes such as those of algae in water.
cholinesterase An enzyme found in animals that regulates nerve impulses. Cholinesterase inhibition is associated with a variety of acute symptoms such as nausea, vomiting, blurred vision, stomach cramps, and rapid heart rate.
chromatographic Pertaining to a method for separating mixtures that makes use of the different tendencies that substances have for being adsorbed onto the surface of some stationary support following an extraction procedure.
chronic Occurring over a long period of time, either continuously or intermittently; used to describe ongoing exposures and effects that develop only after a long exposure.
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 Long-term, low-level exposure to radiation or a toxic chemical.
chronic toxicity The capacity of a substance to cause long-term poisonous human health effects.
ciliate A type of protozoan characterized by short, filamentous cilia used for motility and/or capturing food.
cilium A hair-like structure on certain cells.
circadian rhythm The regular repetition of activities (cellular or organismic) at intervals of about 24 hours, even in the absence of regular diurnal cues, such as light.
circle of influence The circular, outer edge of a depression produced in the water table produced by the pumping of water from a well. Also see cone of influence and cone of depression.
circuit The complete path of an electric current, including the generating apparatus or other source; or a specific segment or section of the complete path.
circuit breaker A safety device in an electrical circuit that automatically shuts off the circuit when it becomes overloaded. The device can be reset manually.
cistern A small tank, usually covered, or a storage facility used to store water for a home or farm. Often used to store rain water.
cistron The smallest unit of genetic material which is responsible for the synthesis of a specific polypeptide.
citation See hearing.
citee One who is cited. See hearing.
civil day A mean solar day commencing at midnight.
civil suit A lawsuit brought under the rules of civil procedure. For example, seizure, injunction, and civil contempt are actions initiated under civil rules.
civil time Time in which the day begins at midnight as distinguished from the former astronomical time in which the day began at noon.
claim A statement of interest in seized property, affirmed by sworn oath, entered by a person in response to seizure of a lot.
clarification Water or wastewater solids separation accomplished by gravity that occurs during water or wastewater treatment when solids settle out of a retained volume. This is often aided by centrifugal action and chemically induced coagulation and flocculation.
clarified wastewater
clarifier A large circular or rectangular tank or basin in which water is retained for a period of time, during which the heavier suspended solids settle to the bottom. Clarifiers are also called settling basins and sedimentation basins.
class (1) Biology. A category of biological classification ranking above the order and below the phylum or division. (2) Pipes and fittings. The working pressure rating of a specific pipe for use in water distribution systems which includes allowance for surges. This term is used for cast iron, ductile iron, asbestos cement, and some plastic pipe.
Class I Area Under the Clean Air Act, an area in which visibility is protected more stringently than under the national ambient air quality standards; includes national parks, wilderness area, monuments and other areas of special national and cultural significance.
classification See type of tide.
class interval A span of values of a continuous variable which are grouped into a single category for a frequency distribution of that variable.
clay A fine textured soil particle with a diameter of approximately one ten-thousandth of an inch.
clay soil A soil containing more than 40 percent clay, but less than 45 percent sand or 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, liquified petroleum gas, and others.
cleanup Actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and/or the environment.
clear cut Harvesting all the trees in one area at one time—a practice that encourages fast rainfall or snowmelt runoff, erosion, sedimentation of streams and lakes, and flooding and destroys vital habitat.
clear well A reservoir for the storage of filtered water of sufficient capacity to prevent the need to vary the filtration rate with variations in demand. Also used to provide chlorine contact time for disinfection.
climate The average conditions of the weather over a number of years. Macroclimate is the climate representative of a relatively large area. Microclimate is the climate of a small area, particularly that of the living space of a certain species, group, or community.
climatic climax A climax in which the regional climate is the controlling factor.
climax The final, stable community in an ecological succession that is able to reproduce itself indefinitely under existing conditions. The result of coaction.
climax community See climax.
cline A continuous series of differences (structural or functional) exhibited by a group of related organisms, usually along a line of geographic or environmental gradient.
clinical studies Studies of humans suffering from symptoms induced by chemical exposure.
clone A cell line stemming from a single ancestral cell and normally expressing all the same genes. If this is a b lymphocyte clone, they will normally produce identical antibodies, i.e. monoclonal antibodies.
cloning In biotechnology, obtaining a group of genetically identical cells from a single cell; making identical copies of a gene.
closed basin A basin draining to some depression or pond within its area, from which water is lost only by evaporation or percolation. A basin without a surface outlet for precipitation falling precipitation.
closed basin lake flooding Flooding that occurs on lakes with either no outlet or a relatively small one. Seasonal increases in rainfall cause the lake level to rise faster than it can drain. The water may stay at flood stage for weeks, months, or years.
closed-loop recycling Reclaiming or reusing wastewater for non-potable purposes in an enclosed process.
closed system An organized assemblage of system objects in which there is no exchange of material with objects outside of the system.
closest point of approach Point where hurricane eye makes closest contact to shore without actually making landfall.
closure The procedure a landfill operator must follow when a landfill reaches its legal capacity for solid waste: ceasing acceptance of solid waste and placing a cap on the landfill site.
cluster An aggregation of cases of a disease or other health-related condition, particularly cancer and birth defects, which are closely grouped in time and place. The number of cases may or may not exceed the expected number; frequently the expected number is not known.
cluster investigation An epidemiological investigation mounted to determine if there has been an unexpected increase in the number or prevalence of cases of illness. The increase can be with respect to a particular interval in time, a particular location, or both.
coaction The interaction of organisms with each other.
coagulant aid Any chemical or substance used to assist or modify coagulation.
coagulants Chemicals that cause very fine particles to clump together into larger particles. This eases separating the solids from the water by settling, skimming, draining, or filtering.
coagulation A process using coagulant chemicals and mixing by which colloidal and lighter suspended materials are destabilized and agglomerated into flocs.
coal cleaning technology 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 boundary The mean high water line (MHWL) or mean higher high water line (MHHWL) when tidal lines are used as the coastal boundary. Also, lines used as boundaries inland of and measured from (or points thereon) the MHWL or MHHWL. See marine boundary.
coastal flooding Flooding which occurs from storms where water is driven onto land from an adjacent body of water. These can be hurricanes, "nor'easters," or tropical storms, but even a strong winter storm or thunderstorm can cause this type of flooding.
coastal flood warning A warning that significant wind-forced flooding is to be expected along low-lying coastal areas if weather patterns develop as forecast.
coastal flood watch An announcement that significant wind-forced flooding is to be expected along low-lying coastal areas if weather patterns develop as forecast.
coastal zone Lands and waters adjacent to the coast that exert and influence on the uses of the sea and its ecology or whose uses and ecology are affected by the sea.
Coast and Geodetic Survey A former name of the National Ocean Service. The National Ocean Service is a component of NOAA, U.S. Department of Commerce.
coast line The low water datum line for purposes of the Submerged Lands Act (Public Law 31). See shoreline.
coccus A spherical bacterium.
cocci plural of coccus.
cocurrent line A line on a map or chart passing through places having the same current hour.
COD Chemical oxygen demand.
codec Coder/decoder equipment used to convert and compress analog video and audio signals into a digital format for transmission, then convert them back to analog signals upon reaching their destination.
Code of Federal Regulations (CFR)The Code of Federal Regulations is a codification of the published rules in the Federal Register by the executive departments and agencies of the federal government. The CFR is divided into 51 titles which represent broad areas subject to federal regulation. Each title is divided into chapters which usually bear the name of the issuing agency. Each chapter is further subdivided into parts covering specific regulatory areas.
codominant Any of equally dominant forms; one of several species that dominate a community, no one species to the exclusion of the others.
codon A group of three nucleotide bases in dna or rna that determines the composition of one amino acid in "building" a protein and also can code for chain termination.
coefficient A factor used to predict a result and used to establish numerical magnitudes in various mathematical models.
coefficient of haze (COH) A measurement of visibility interference in the atmosphere.
coefficient of permeability see hydraulic conductivity.
coefficient of storage See storativity.
coenzyme A substance that enhances or is necessary for the action of enzymes. They are generally much smaller than enzymes themselves
co-fire Burning of two fuels in the same combustion unit, e.g., coal and natural gas, or oil and coal.
cohesion Molecular attraction which holds two particles together.
cohesive termini A dna molecule with single- stranded ends with exposed (cohesive) complementary bases.
cohort A well-defined group of people who have had a common experience or exposure, who are then followed up for the incidence of new diseases or events, as in a cohort or prospective study. A group of people born during a particular period or year is called a birth cohort.
cohort study A type of observational analytic study. Enrollment into the study is based on exposure characteristics or membership in a group. Disease, death, or other health-related outcomes are then ascertained and compared.
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 front The leading edge of an advancing cold air mass that is underrunning and displacing the warmer air in its path. Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere). Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front. See occluded front and warm front.
cold temperature CO A standard for automobile carbon monoxide (CO) emissions to be met at a low temperature (i.e. 20 degrees Fahrenheit). Conventional automobile catalytic convertors are less efficient upon start-up at low temperatures.
coliform A group of bacteria found in the intestines of warm-blooded animals, including humans, and in plants, soil, and water. The presence of coliform bacteria is an indication that the water is polluted and may contain pathogens.
coliform bacteria group A group of bacteria predominantly inhabiting the intestines of man or animal but also occasionally found elsewhere. It includes all aerobic and facultative anaerobic, gram-negative, non-spore forming bacilli that ferment lactose with production of gas. Also included are all bacteria that produce a dark, purplish-green colony with metallic sheen by the membrane filter technique used for coliform identification.
coliform, fecal A specific class of bacteria which primarily inhabit the intestines of warm-blooded animals. The presence of coliform bacteria is an indication that the water is polluted and may contain pathogens. They are ONPG positive, CO negative, and consist of the family enterobacteraceae and genera Escherichia. They include fecal coliform and Klebsiella.
coliform index A rating of the purity of water based on the count of fecal bacteria.
coliform levels Numbers referring to the density of coliform bacteria in water bodies.
coliform organism Microorganism typically found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially adverse contamination by pathogens.
coliform, total A group of gram-negative, aerobic to facultative anaerobic, non-spore forming, rod-shaped bacteria that ferment lactose at 35°C producing gas and acid within 48 hours. Using the membrane technique, they develop a red colony with a green, metallic sheen within 24 hours at 35°C on an Endo-type medium containing lactose.
coliphage A virus that infects Escherichia coli.
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 (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in water have a negative electrical charge, they tend to repel each other. This repulsion prevents the particles from clumping together, becoming heavier, and settling.
colonization Propagation of a microorganism on or within a host without causing cellular injury. A colonized host can serve as a source of infection.
colonizing Of or relating to organisms that occupy areas previously barren, or at least areas currently unoccupied by that species.
colony A macroscopically visible aggregation of microbial cells grown on a solid culture medium.
colony forming unit (CFU) A colony from which one microorganism has grown. For purposes of analysis, one CFU represents one organism.
colormetric measurement A means of measuring unknown chemical concentrations in water by measuring a sample's color intensity. The specific color of the sample, developed by addition of chemical reagents, is measured with a photoelectric colorimeter or is compared with “color standards” using, or corresponding, with known concentrations of the chemical.
columnular ice Ice consisting of columnar shaped grain. The ordinary black ice is usually columnar-grained.
colluvium Rock and soil accumulated at the foot of a slope from gravitational forces.
combined available residual chlorine The concentration of residual chlorine which is combined with ammonia (NH3) and/or organic nitrogen in water as a chloramine (or other chlorinated molecule that has germicidal properties) yet is still available to oxidize organic matter and use its bactericidal properties.
combined residual chlorination The application of chlorine to water to produce combined available residual chlorine. This residual can be made up of monochloramines, dichloromines, and nitrogen trichloride.
combined sewer overflows Discharge of a mixture of stormwater and domestic waste from a combined collection system when the flow capacity of a sewer system is exceeded during rainstorms.
combined sewers A collection system that carries both sewage and stormwater runoff. Normally, the entire flow goes to a waste treatment plant, but during a heavy storm, the volume of water may be so great as to cause discharges or overflows of untreated mixtures of storm water and sewage into receiving waters.
combustible gas indicator An instrument that measures the concentration of a flammable vapor or gas in air indicating the results as a percentage of the lower explosive limit (LEL) of the calibration gas.
combustion 1) Burning, or rapid oxidation, accompanied by release of energy in the form of heat and light. 2) The 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.
cometabolism The simultaneous metabolism of two compounds, in which the degradation of the second compound (the secondary substrate) depends on the presence of the first compound (the primary substrate). For example, in the process of degrading methane, some bacteria can degrade hazardous chlorinated solvents that they would otherwise be unable to attack.
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 regulatory action or rule making after publication of a notice stating the time deadlines.
commercial water use Water for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. The water may be obtained from a public supply or may be self supplied. See also public supply and self- supplied water.
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.
comminution Mechanical shredding or pulverizing of waste. Used in both wastewater treatment and solid waste management.
comminutor A cutting screen device for the catching and shredding of heavy solid matter in the primary stage of waste treatment.
Commissioner The State Health Commissioner (see 12 VAC 5-590-40 2, Virginia Waterworks Regulations).
commodity charge See variable charge.
common source outbreak An outbreak that results from a group of persons being exposed to a common noxious influence, such as an infectious agent or toxin. If the group is exposed over a relatively brief period of time, so that all cases occur within one incubation period, then the common source outbreak is further classified as a point source outbreak. In some common source outbreaks, persons may be exposed over a period of days, weeks, or longer, with the exposure being either intermittent or continuous.
communicable disease An illness that is caused by a specific infectious agent or its toxic products and which arises through the transmission of that agent or its products from a reservoir to a susceptible host. Such transmission can be either direct (as from an infected person or animal) or indirect (through the agency of an intermediate plant or animal host, vector, or the inanimate environment).
community All the plants and animals in an area or volume; a complex association usually containing both plants and animals.
community cohesion The innate feeling of community identity that promotes actions for the common benefit (real or intangible) of the inhabitants.
community metabolism The combined metabolism (metabolic activity) of all organisms in a given area or community.
community relations A regulatory agency’s effort to establish two-way communication with the public: to create understanding of regulatory programs and related actions, to assure 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.
community respiration The combined respiration of all organisms in a community.
community water system (CWS) A public water system which serves at least 15 service connections used by yearround residents or regularly serves at least 25 year-round residents. Also see non-community water system, transient water system, and non-transient non-community water system.
compact disc (CD) High density storage media based on a 4.75" reflective optical disc. Can hold up to 650,000,000 bytes of data, that is equivalent to 12,000 images or 200,000 pages of text. CDs may all look the same, but there are numerous standards for different applications. The most common are defined below.
compact disc read-only memory (CD-ROM) Version of the CD that allows the information to be stored and retrieved. Once a CD-ROM is pressed, new data cannot be stored and the disc cannot be erased for reuse.
compact disc-recordable (CD-R) CD-ROM recording systems can be used to record data onto a compact disc-recordable like any other recordable media. However, they cannot be erased and re-recorded. For large-scale duplication of CD-ROMs, a pressing facility is preferred.
compaction Reduction of the bulk of solid waste by rolling and tamping.
comparison of simultaneous observations A reduction process in which a short series of tide or tidal current observations at any place is compared with simultaneous observations at a control station where tidal or tidal current constants have previously been determined from a long series of observations. For tides, it is usually used to adjust constants from a subordinate station to the equivalent of that which would be obtained from a 19-year series.
compass direction Direction as indicated by compass without any allowances for compass error. The direction indicated by a compass may differ by a considerable amount from true or magnetic direction.
compass error The angular difference between a compass direction and the corresponding true direction. The compass error combines the effects of deviation and variation.
compensation level Depth in a body of water at which the available light is just sufficient enough to allow photosynthesis to balance respiration over an appreciable time.
competition Of or related to the interaction of organisms that use common resources in short supply.
complainant Person registering a complaint, such as a consumer complaining about an article.
complete mix Idealized continuous flow reactor in which fluid particles are dispersed uniformly throughout the reactor so that the effluent characteristics are identical to those of the reactor.
complete treatment A method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. Also called conventional filtration.
completed test The third and final phase of the Multiple Tube Fermentation (MTF) Procedure. Suspected coliform colonies from the Confirmed Test are inoculated into Lauryl Tryptose Broth and Brilliant Green Lactose Broth tubes and incubated.
complexation A reaction in which a metal ion and one or more anionic ligands chemically bond. Complexes often prevent the precipitation of metals.
compliance coal Any coal that emits less than 1.2 pounds of sulfur dioxide per million Btu when burned. Also known as low sulfur coal.
compliance coating A coating whose volatile organic compound content does not exceed that allowed by regulation.
compliance cycle The nine-year calendar year cycle during which public water systems must monitor. Each compliance cycle consists of three three-year compliance periods. The first compliance cycle begins January 1, 1993, and ends December 31, 2001; the second begins January 1, 2002, and ends December 31, 2010; the third begins January 1, 2011 and ends December 31, 2019.
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 period A three-year calendar period within a compliance cycle. Within in the first compliance cycle, the first compliance period runs from January 1, 1993, to December 31, 1995; the second from January 1, 1996, to December 31, 1998; the third from January 1, 1999, to December 31, 2001.
compliance schedule A negotiated agreement between a pollution source owner and a government agency that specifies dates and procedures by which a source owner will reduce emissions and, thereby, comply with a regulation.
complementary dna (cdna) Dna that is complementary to messenger rna; used for cloning or as a probe in dna hybridization studies.
component (1) Same as constituent. (2) That part of a tidal current velocity which, by resolution into orthogonal vectors, is found to act in a specified direction.
composite hydrograph A stream discharge hydrograph which includes baseflow, or one which corresponds to a net rain storm of duration longer than one unit period.
composite samples Samples collected at regular intervals, sometimes in proportion to the existing flow, and then combined to form a sample representative of flow over a period of time.
compositing Combining more than one sample for analysis.
compost The relatively stable humus material that is produced from a composting process in which organisms present in degradable organic matter decompose the organics through biological oxidation processes.
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 of organic waste material with a more stable bulking material and aerating, ventilating the mixture by mechanical mixing through either a series of vertical aerated chambers, or by placing the compost in piles out in the open air and mixing or turning periodically.
compound A substance composed of two or more elements whose composition is constant. For example, table salt, sodium chloride, is a compound.
compound tide A harmonic tidal (or tidal current) constituent with a speed equal to the sum or difference of the speeds of two or more elementary constituents. The presence of compound tides is usually attributed to shallow water conditions.
compressed video A digital transmission process used to transmit a video signal. When the vast amount of information in a video transmission is compressed into a fraction of its former bandwidth by a codec, the resulting compressed video can be transmitted more economically and through existing phone lines. While compressed video requires less bandwidth, signal quality may be reduced. As a result, picture quality is generally not as good as full-motion video. Quick motions often appear somewhat blurred. This quality issue is becoming less of a concern as more and more playback systems for compressed video run at 30 frames per second.
computer-assisted instruction (CAI) See Computer-based Training (CBT).
computer-based training (CBT) An interactive instructional approach in which the computer, taking the place of an instructor, provides a series of stimuli to the student ranging from questions to be answered to choices or decisions to be made. The CBT then provides feedback based on the student's response.
computer conferencing An ongoing computer conversation via text with others in different locations. Conferencing can be done in "real time," so that messages appear as they are being keyed, or it can be "asynchronous," which means the complete message is keyed and then stored for later use by the receiver or sender.
comsumptive use Water removed from available supplies without return a water resource system (uses such as manufacturing, agricultural, and food preparation).
concentration 1) The amount of a given substance dissolved or suspended in a unit volume of solution. 2) The process of increasing the solids per unit volume in a liquid.
concentration cell A cell involving an electrolyte and two identical electrodes, with the potential resulting from differences in the chemistry of the environments adjacent to the two electrodes.
concentration factor
concentration polarization 1) The ratio of the salt concentration in the membrane boundary layer to the salt concentration in the bulk stream. The most common and serious problem resulting from concentration polarization is the increasing tendency for precipitation of sparingly soluble salts and the deposition of particulate matter on the membrane surface. 2) Used in corrosion studies to indicate a depletion of new ions near an electrode. ) The basis for chemical analysis by a polarograph.
condensate The liquid that separates from a vapor during condensation.
condensation 1) A chemical reaction in which water or another simple substance is released by the combination of two or more molecules. 2) The process in which water vapor is cooled to the liquid phase. The water film produced is referred to as condensate.
conceptual model A model which represents a physical process such as accumulation and ablation of a snowpack with explicit mathematical functions. Each significant physical component is represented separately rather than using a single index to explain several processes.
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 that a new product or use of an existing pesticide will not significantly increase the risk of unreasonable adverse effects.
conditionally exempt generators Owners 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 permitted facility for proper disposal.
conductance A rapid method of estimating the dissolved solids content of a water supply. The measurement indicates the capacity of a sample of water to carry an electrical current, which is related to the concentration of ionized substances in the water. Also called specific conductance.
conductivity The property of transmitting heat, electricity, or sound through a medium.
conductor A substance, body, device or wire that readily conducts or carries energy, such as electrical current.
cone of depression The depression, roughly conical in shape, produced in the water table by the pumping of water from a well. Also see circle of influence.
cone of influence The depression, roughly conical in shape, produced in the water table by the pumping of water from a well. Also see circle of influence.
confidence The degree of trust or assurance placed in a given result.
confidence interval The statistical upper and lower limits around an estimated value within which the actual population value is expected to fall. The confidence interval is stated as a specified level, such as 95%, of confidence. For the National Pesticide Survey, estimates for wells throughout the US, based on analysis of results for the NPS sample of wells, are given with a 95% confidence interval, indicating upper and lower limits hat EPA is reasonably confident contain the actual detection rate.
confidence level The probability that the true value of a parameter lies within a stated interval.
confidence limit The minimum or maximum value of a confidence interval.
confined aquifer An aquifer that is bounded above and below by low permeability formations or aquitards.
confined groundwater Groundwater held under an aquiclude or an aquifuge, if the pressure is positive it is called artesian.
confined water
confining bed
confining layer A geologic formation characterized by low permeability that inhibits the flow of water (see also aquitard).
confirmed case A person from whom a disease-producing agent has been isolated and identified or from whom has been obtained other laboratory evidence of the presence of an etiologic agent whether or not that person has a clinical syndrome indicative of the disease caused by the agent.
confirmed test The second phase of the Multiple Tube Fermentation (MTF) Procedure. Positive presumptive tubes are inoculated into BGLB tubes and incubated. Positive results of the Confirmed Test may be reported, but positive tubes should be submitted to the Completed Test for quality control. This test is done simultaneously with the fecal coliform test.
confluence The point at which one stream flows into another or where two streams converge and unite.
confluent A stream flowing into another to form a single stream.
confluent growth A continuous bacterial growth covering the entire filtration area of a membrane filter, or a portion thereof, in which bacterial colonies are not discrete.
confluent stream
confounding factors Variables other than chemical exposure level which can affect the incidence or degree of a parameter being measured.
conical-plug valve
conifer Pines, cedars, hemlocks, etc; any of a type of mostly evergreen trees and shrubs with botanically true cones.
coning 1) A condition that may occur in a sludge hopper during sludge withdrawal when part of the sludge moves towards the outlet while the remainder stays in place. 2) Development of a cone or channel of moving liquid surrounded by relatively stationary sludge.
conjugate depths
conjugation The fusion of two similar gametes; usually in contrast to fertilization.
consecutive waterworks A waterworks which has no water production or source facility of its own and which obtains all of its water from another permitted waterworks. See waterworks.
consent degree 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 to contamination at the site involved. The consent degree describes the actions PRPs will take and may be subject to a public comment period.
consent decree of injunction An injunction to which the defendant has agreed and which is filed in court.
conservation Supervision, management, and maintenance of natural resources.
conservation pool Storage of water for later release for usual purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.
conservation pricing Water rate structures that help achieve beneficial reductions in water usuage. See nonpromotional rates.
conservation storage Storage of water for later release for usual purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.
conservation (water-use) Any beneficial reduction in water losses, waste, or use.
conservative 1) In the case of a contaminant, one that does not degrade and the movement of which is not retarded; is unreactive. 2) In the case of an assumption, one that leads to a worst-case scenario, one that is most protective of human health and the environment.
consignee The individual or firm to which goods have been consigned.
consocial Of or related to plant species found together in a given community.
consolidated ice cover Ice cover formed by the packing and freezing together of floes, brash ice and other forms of floating ice.
constant-dollar values A series of dollar values, such as gross national product, personal income, sales, or profits, from which the effect of changes in the purchasing power of the dollar has been removed. Also called realdollar values.
constituent 1) An essential part or component of a system or group (e.g., an ingredient of a chemical mixture). For instance, benzene is one constituent of gasoline. 2) One of the harmonic elements in a mathematical expression for the tide-producing force and in corresponding formulas for the tide or tidal current. Each constituent represents a periodic change or variation in the relative positions of the earth, moon, and sun.
constituent day The time of the rotation of the Earth with respect to a fictitious celestial body representing one of the periodic elements in the tidal forces. It approximates in length the lunar or solar day and corresponds to the period of a diurnal constituent or twice the period of a semidiurnal constituent. The term is not applicable to the long-period constituents.
constituent hour One twenty-fourth part of a constituent day.
constructed wetland An artificial wetland system designed to remove waterborne contaminants through natural treatment processes.
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 The prohibition of construction or modification of any major stationery source of a pollutant for which the area is in non-attainment.
construction funds Funds appropriated for construction of an authorized project.
consumer 1) Any person who uses a product, such as drinking water. 2) An organism that consumes another. A primary consumer is an organism that consumes green plants. A secondary consumer is an organism that consumes a primary consumer.
consumer's water system Any water system located on the consumer's premises, supplied by or in any manner connected to a waterworks.
consumptive use 1) Water removed from available supplies without direct return to a water resource system for uses such as manufacturing, agriculture, and food preparation. 2) Use that permanently withdraws water from its source.
contact Exposure to a source of an infection, or a person so exposed.
contact aerator A biological unit consisting of stone, cement-asbestos, or other surfaces supported in an aeration tank in which air is diffused up and around the surfaces and settled wastewater flows through the tank.
contactor 1) An electrical switch usually magnetically operated. 2) A biological reactor in which wastewater treatment is accomplished by attached growth or fixed film biomass on the surface of reactor media.
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.
contact stabilization process A modification of the activated sludge process in which wastewater is aerated with a high concentration of activated sludge for a short period, usually less than 60 minutes, to obtain BOD removal. The biomass is subsequently separated by sedimentation and transferred to a stabilization tank where aeration is continued, starving the microorganisms before returning it to the aeration basin.
contact time The length of time water is exposed to a disinfectant.
contagious Capable of being transmitted from one person to another by contact or close proximity.
container Term used to describe a self-contained unit of various dimensions and configurations used for storage and transportation of goods.
containment A structure, found at a nuclear power plant, designed to contain any radioactive material that may be released from the nuclear reactor fuel and cooling systems.
contaminant Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil.
contamination 1) The introduction of microorganisms, chemicals, toxic substances, wastes, or wastewater into water in a concentration that makes the water unfit for either discharge or its next intended use. 2) Radioactive material found on surfaces where it is not supposed to be.
contempt of court Any act which is calculated to embarrass, hinder, or obstruct a court in the administration of justice, or which is calculated to lessen its authority or its dignity.
contents 1) The volume of water in a reservoir. Unless otherwise indicated reservoir content is computed on the basis of a level pool and does not include bank storage. 2)The actual water contained in a SACSMA soil zone.
contest To make defense to an adverse claim in a court of law; to oppose, resist, or dispute the case made by a plaintiff.
contingency plan A document setting out an organized, planned, and coordinated course of action to be followed in case of a fire, explosion, natural catastrophe, or other accident that releases toxic chemicals, hazardous waste, or radioactive materials that threaten human health or the environment. (See National Oil and Hazardous Substances Contingency Plan.)
contingency table A two-variable table with cross-tabulated data.
continuing contracts A contract extending beyond the end of a fiscal year and dependent upon further appropriations for such continuance.
continuing planning process The concept that needs will change with time. Hence, planning is a continuum that recognizes needs as a natural progression as they become apparent.
continuous discharge A routine release to the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc.
continuous noise Noise levels that vary minimally as a function of time.
continuous sample A flow of water from a particular place in a plant to the location where samples are collected for testing. This continuous stream may be used to obtain grab or composite samples. Frequently, several taps (faucets) will flow continuously in the laboratory to provide test samples from various places in a water treatment plant.
contour A line drawn on a map to join all places at the same height above sea level; a number of contours therefore depict (on a flat map) the relief of the land over the area covered. Similar lines showing the depths of the sea bed are called isobaths.
contour farming A conservation-based method of farming in which all farming operations (tilling and planting) are performed across (rather than up and down) the slope. Ideally, each crop row is planted at right angles to the ground slope. Also contour plowing.
contour interval
contour line
contour map
contour plowing Soil tilling method that follows the shape of the land to discourage erosion. See contour farming.
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 that analyzes samples taken from waste, soil, air, and water or carry out EPA- funded research projects.
control 1) A device used to verify or regulate a scientific experiment or study. 2) In a case-control study, comparison group of persons without disease. A case-control study serves as a useful example. Since patients with a specific illness are examined for various characteristics, a group of healthy individuals who otherwise have as much in common with the patients as possible must be examined in parallel for the same characteristics.
control current station A current station at which continuous velocity observations have been made over a minimum period of 29 days. Its purpose is to provide data for computing accepted values of the harmonic and nonharmonic constants essential to tidal current predictions and circulatory studies. The data series from this station serves as the control for the reduction of relatively short series from subordinate current stations through the method of comparison of simultaneous observations. See current station.
control rod A rod made of neutron absorbing material which, when inserted into a nuclear reactor, reduces the number of free neutrons available to cause the uranium atoms to fission.
control station See primary control tide station, secondary control tide station, and control current station.
controlled burn Of or related to fires used in forest or range management to secure growth and/or reproduction of desired species or to eliminate potentially dangerous fire hazards such as dry, shrubby undergrowth.
controlled reaction A chemical reaction under temperature and pressure conditions maintained within safe limits to produce a desired product or process.
controller A device which controls the starting, stopping, or operation of a device or piece of equipment.
control loop The path through the control system between the sensor, which measures a process variable, and the controller, which controls or adjusts the process variable.
control points Small monuments securely embedded in the surface of the dam. Any movement of the monument indicates a movement in the dam itself. Movements in the dam are detected by comparing control points location to location of fixed monuments located off the dam using accurate survey techniques.
control system A system which senses and controls its own operation on a close, continuous basis by various means such as step adjustments or proportional (or modulating) control.
control technique guidelines (CTG) Documents issued to assist state and local pollution control authorities achieve and maintain air quality standards for certain sources through reasonably available control technologies.
convection Atmospheric motions in the vertical direction resulting from surface heating and the subsequent rising of warm air. This lifting mechanism is capable of generating the rising motions necessary for clouds and precipitation to form.
convergence Wind movement that results in a horizontal net inflow of air into a particular region. Convergent winds at lower levels are associated with upward motion.
cooling tower A heat exchanger used to cool the water used to condense exhaust steam exiting the turbines of a power plant. Cooling towers transfer exhaust heat into the air instead of into a body of water.
corange line A line passing through places of equal tidal range.
Coriolis force A term in the relative hydrodynamic equations of motion that takes into account the effect of the Earth's rotation on moving objects (including air and water) when viewed with reference to a coordinate system attached to the rotating Earth.
corrected current A relatively short series of current observations from a subordinate station to which a factor is applied to adjust the current to a more representative value based on a relatively long series from a nearby control station. See current and total current.
cotidal hour The average interval between the moon's transit over the meridian of Greenwich and the time of the following high water at any place. This interval may be expressed either in solar or lunar time.
cotidal line A line on a chart or map passing through places having the same cotidal hour.
covariates A set of explanatory variables.
conventional Accepted as well understood and established.
conventional activated sludge process A suspended growth reactor followed by a clarifier from which settled biomass is returned back to the reactor. Activated sludge process using an aeration mixing mechanism within an aeration basin receiving primary effluent, with return biomass received at the h