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Drinking Water Glossary A thru D - Chehalis River Council

Office Of Water

Drinking Water Glossary

A Dictionary of Technical and Legal Terms Related to Drinking Water

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A

ABC. See Association of Boards of Certification.
absorbed dose. The amount of a 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 in the soil).
absorption factor. The fraction of a chemical making contact with an organism that is absorbed by the organism.
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.
accuracy. How closely an instrument measures the true or actual value of the process variable being measured or sensed.
acid mine drainage. Drainage of water from areas that have been mined for coal of other mineral ores; the water has low pH, sometimes less than 2.0 (is acid), because of its contact with sulfur-bearing material; acid drainage is harmful because it often kills aquatic organisms.
acid rain. Precipitation which has been rendered (made) acidic by airborne pollutants.
acidic (uh-SID-ick). The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.
acidified (uh-SID-uh-FIE-d). The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. The purpose of acidification is to "fix" a sample so it won't change until it is analyzed.
acre-foot A volume of water that covers one acre to a depth of one foot, or 43,560 cubic feet (1233.5 cubic meters).
activated carbon. Adsorptive particles or granules of carbon usually obtained by heating carbon (such as wood). These particles or granules have a high capacity to selectively remove certain trace and soluble materials from water.
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.
action level. The concentration of lead or copper in water specified at Code of Federal Regulations 141.80(c) which determines, in some cases, the treatment requirements contained in subpart I of this part that a water system is required to complete.
acute. Occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure.
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.
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, any severe poisonous effect resulting from a single short-term exposure to a toxic substance.
additive effect. Combined effect of two or more chemicals equal to the sum of their individual effects.
adsorbate (add-SORE-bait). The material being removed by the adsorption process.
adsorbent (add-SORE-bent). The material (activated carbon) that is responsible for removing the undesirable substance in the adsorption process.
adsorption. The process by which chemicals are held on the surface of a mineral or soil particle (compare with Absorption).
aeration (air-A-shun). The process of adding air to water. Air can be added to water by either passing air through water or passing water through air.
aerobic (air-0-bick). A condition in which free" (atmospheric) or dissolved oxygen is present in the water.
age tank. A tank used to store a chemical solution of known concentration for feed to a chemical feeder. Also called a day tank.
aggregate. A mass or cluster of soil particles, often having a characteristic shape.
agrochemical. Synthetic chemicals (pesticide and fertilizers) used in agricultural production.
air binding. A situation where air enters the filter media. Air is harmful to both the filtration and backwash processes. Air can prevent the passage of water during the filtration process and can cause the loss of filter media during the backwash process.
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 way raw water or any other water can reach the drinking water.
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 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. Also see packed tower aeration.
alarm contact. A switch that operates when some pre-set low, high or abnormal condition exists.
algae. Microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water.
algal bloom (AL-gull). Sudden, massive growths of microscopic and macroscopic plant life, such as green or bluegreen algae, which develop in lakes and reservoirs.
algicide (AL-gi-SIDE). Any substance or chemical specifically formulated to kill or control algae.
aliphatic hydroxy acids (Al-uh-FAT-ick). Organic acids with carbon atoms arranged in branched or unbranched open chains rather than in rings.
aliquot (AL-li-kwot). Portion of a sample.
alkali (AL-ka-lie). Various soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids to form neutral salts and may be used in chemical water treatment processes.
alkaline (Al-ka-LINE). The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.
alkalinity (AL-ka-LIN-it-tee). 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 (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.
alluvial (uh-LOU-vee-ul). Relating to mud and/or sand deposited by flowing water. Alluvial deposits may occur after a heavy rain storm.
alternating current (A.C.). An electric current that reverses its direction (positive/negative values) at regular intervals.
ambient. Environmental or surrounding conditions.
ambient temperature (AM-bee-ent). Temperature of the surrounding air (or other medium). For example, temperature of the room where a gas chlorinator is installed.
ammonium. One form of nitrogen that is usable by plants.
amperage (AM-purr-age). 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 (AM-peer). The unit used to measure current strength. The current produced by electromotive force of one volt acting through a resistance of one ohm
amperometric (am-PURR-o-MET-rick). Based on the electric current that flows between two electrodes in a solution.
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.
anaerobic (AN-air-O-bick). A condition in which "free" (atmospheric) or dissolved oxygen is NOT present in water.
analog. The readout of an instrument by a pointer (or other indicating means) against a dial or scale.
analyzer. A device which conducts periodic or continuous measurement of some factor such as chlorine, fluoride or turgidity. Analyzers operate by any of several methods including photocells, conductivity or complex instrumentation.
animal studies. Investigations using animals as surrogates for humans, on the expectation that results in animals are pertinent to humans.
anion (AN-EYE-en). A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride (CI-) is an anion.
anionic polymer (AN-eye-ON-ick). A polymer having negatively charged groups of ions; often used as a filter aid and for dewatering sludges.
annular space (AN-you-ler). A ring-shaped space located between two circular objects, such as two pipes.
anode (an-0-d). The positive pole or electrode of an electrolytic system, such as a battery. The anode attracts negatively charged particles or ions (anions).
antagonism. Interference or inhibition of the effect of one chemical by the action of another chemical.
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.
appurtenance (uh-PURR-ten-nans). 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.
aquatic. Plants of animal life living in, growing in, or adapted to water.
aqueous (A-kwee-us). Something made up of, similar to, or containing water; watery.
aquifer (ACK-wi-fer). A natural underground layer of porous, water-bearing materials (sand, gravel) usually capable of yielding a large amount or supply of water.
artesian (are-TEE-zhun - aquifer or well). Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing. See confined aquifer .
aseptic (a-SEP-tick). Free from the living germs of disease, fermentation or putrefaction. Sterile.
assay. A test for a particular chemical or effect.
Association of Boards of Certification. An international organization representing over 150 boards which certify the operators of waterworks and waste water facilities. For information on ABC publications regarding the preparation of and how to study for operator certification examinations, contact ABC, 4261/2 Fifth Street, P.O. Box 786, Ames, Iowa 50010-0786.
asymmetric (A-see-MET-rick). Not similar in size, shape, form or arrangement of parts on opposite sides of a line, point or plane.
atom. The smallest unit of a chemical element; composed of protons, neutrons and electrons.
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 expansion. The vertical distance from the sand surface to the underside of a trough in a sand filter. This distance is also called FREEBOARD.
axial to impeller. The direction in which material being pumped flows around the impeller or flow parallel to the impeller shaft.
axis of impeller. An imaginary line running along the center of a shaft (such as an impeller shaft).

B

back pressure. A pressure that can cause water to backflow into the water supply when a user's water system is at a higher pressure than the public water system.
backflow. A reverse flow condition, created by a difference in water pressures, which causes water to flow back into the distribution pipes of a potable water supply from any source or sources other than an intended source. Also see backsiphonage and cross-connection.
background level. In toxic substances monitoring, the average presence of a substance in the environment, originally referring to naturally occurring phenomena.
backsiphonage. A form of backflow caused by a negative or below atmospheric pressure within a water system. Also see backflow and cross-connection.
backwashing. The process of reversing the flow of water back through the filter media to remove the entrapped solids.
bacteria (back-TEER-e-uh). Singular: bacterium. Microscopic living organisms usually consisting of a single cell. Bacteria can aid in pollution control by consuming or breaking down organic matter in sewage, or by similarly acting on oil spills or other water pollutants. Some bacteria in soil, water or air may also cause human, animal and plant health problems.
baffle. A flat board or plate, deflector, guide or similar device constructed or placed in flowing water or slurry systems to cause more uniform flow velocities, to absorb energy, and to divert, guide, or agitate liquids (water, chemical solutions, slurry).
bailer (BAY-ler). A 10- to 20-foot-long pipe equipped with a valve at the lower end. A bailer is used to remove slurry from the bottom or the side of a well as it is being drilled.
base metal. A metal (such as iron) which reacts with dilute hydrochloric acid to form hydrogen. Also see noble metal.
batch process. A treatment process in which a tank or reactor is filled, the water is treated or a chemical solution is prepared, and the tank is emptied. The tank may then be filled and the process repeated.
best available technology (BAT). The best technology treatment techniques, or other means which the Administrator finds, after examination for efficacy under field conditions and not solely under laboratory conditions, are available (taking cost into consideration). For the purposes of setting MCLs for synthetic organic chemicals, any BAT must be at least as effective as granular activated carbon.
best management practices (BMPs). Structural, nonstructural and managerial techniques that are recognized to be the most effective and practical means to control nonpoint source pollutants yet are compatible with the productive use of the resource to which they are applied. BMPs are used in both urban and agricultural areas.
bias. An inadequacy in experimental design that leads to results or conclusions not representative of the population under study.
bioaccumulation. The retention and concentration of a substance by an organism.
bioassay. Test which determines the effect of a chemical on a living organism.
biochemical oxygen demand (BOD). The amount of oxygen consumed by microorganisms (mainly bacteria) and by chemical reactions in the biodegradation of organic matter.
bioconcentration. The accumulation of a chemical in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides (see bioaccumulation).
biodegradation. Decomposition of a substance into more elementary compounds by the action of microorganisms such as bacteria.
biological growth. The activity and growth of any and all living organisms.
bioremediation. A process of adding nutrient to ground water to speed up the natural process in which bacteria break down gasoline into harmless compounds.
biotransformation. Conversion of a substance into other compounds by organisms; includes biodegradation.
Black water. Liquid and solid human body waste and the carriage water generated through toilet usage.
blank. A bottle containing only dilution water or distilled water; the sample being tested is not added. Tests are frequently run on a SAMPLE and a BLANK and the differences are compared.
BOD. See biochemical oxygen demand.
bonnet (BON-it). The cover on a gate valve.
brackish. Mixed fresh and salt waters.
brake horsepower. 1) The horsepower required at the top or end of a pump shaft (input to a pump). 2) The energy provided by a motor or other power source.
breakpoint chlorination. Addition of chlorine to water until the chlorine demand has been satisfied. At this point, further additions of chlorine will result in a free residual chlorine that is directly proportional to the amount of chlorine added beyond the breakpoint.
breakthrough. A crack or break in a filter bed allowing the passage of floc or particulate matter through a filter. This will cause an increase in filter effluent turbidity. A breakthrough can occur: 1) when a filter is first placed in service, 2) when the effluent valve suddenly opens or closes, and 3) during periods of excessive head loss through the filter (including when the filter is exposed to negative heads).
brinelling (bruh-NEL-ing). Tiny indentations (dents) high on the shoulder of the bearing race or bearing. A type of bearing failure.
buffer. A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
buffer capacity. A measure of the capacity of a solution or liquid to neutralize acids or bases. This is a measure of the capacity of water for offering a resistance to changes in pH.
buffer strips. Strips of grass or other close-growing vegetation that separate a waterway (ditch, stream, creek) from an intensive land use area (subdivision, farm); also referred to as filter strips, vegetated filter strips, and grassed buffers.
bw. Body weight.

C

C factor. A factor of value used to indicate the 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. C Factor = Flow (GPM)/193.75 (Diameter, ft)2.63 (Slope)0.54
caisson (KAY-sawn). 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.
CAG. Carcinogen Assessment Group.
calcium carbonate (CACO3 ) equivalent. An expression of the concentration of specified constituents in water in terms of their equivalent value to calcium carbonate. For example, the hardness in water which is caused by calcium, magnesium and other ions is usually described as calcium carbonate equivalent.
calibration. A procedure which checks or adjusts an instrument's accuracy by comparison with a standard or reference.
cancer. A disease characterized by the rapid and uncontrolled growth of aberrant cells into malignant tumors.
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.
capital costs. Costs (usually long-term debt) of financing construction and equipment. Capital costs are usually fixed, one-time expenses which are independent of the amount of water produced.
carcinogen (car-SIN-o-jen). Any substance which tends to produce cancer in an organism.
carcinogenic. Cancer-producing.
CAS registration number. A number assigned by the Chemical Abstracts Service to identify a chemical.
catalyst (CAT-uh-LIST). A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.
catalyze (CAT-uh-LIZE). To act as a catalyst. Or, to speed up a chemical reaction.
catalyzed (CAT-uh-LIZED). To be acted upon by a catalyst.
cathode (KA-thow-d). The negative pole or electrode of an electrolytic cell or system. The cathode attracts positively charged particles or ions (cations).
cathodic protection (ca-THOD-ick). An electrical system for prevention of rust, corrosion, and pitting of metal surfaces which are in contact with water or soil. A lowvoltage 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 deliberately allowed to corrode instead of letting the structure corrode.
cation (CAT-EYE-en). A positively charged ion in an electrolyte 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.
cavitation (CAV-uh-TAY-shun). 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 that 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.
central nervous system. Portion of the nervous system which consists of the brain and spinal cord; CNS.
centrate. The water leaving a centrifugal after most of the solids have been removed.
centrifugal pump (sen-TRIF-h-gull). 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.
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.
chelation (key-LAY-shun). A chemical complexing (forming or joining together) of metallic cations (such as copper) with certain organic compounds, such as EDTA (ethylene diamine tetracetic acid). Chelation is used to prevent the precipitation of metals (copper). Also see sequestration.
chemical oxygen demand (COD). An indirect measure of the amount of oxygen used by inorganic and organic matter in water. The measure is a laboratory test based on a chemical oxidant and therefore does not necessarily correlate with biochemical oxygen demand.
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.
chloramines (KLOR-uh-means). Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.
chlorination (KLOR-uh-NAY-shun). 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 (KLOR-uh-NAY-ter). A metering device which is used to add chlorine to water.
chlorine-contact chamber. That part of a water treatment plant where effluent is disinfected by chlorine.
chlorine demand. Chlorine demand is 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 requirement. The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of coliform bacteria (Most Probable Number), 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.
chlorophenolic (klor-o-FEE-NO-lick). Chlorophenolic compounds are phenolic compounds (carbolic acid) combined with chlorine.
chlorophenoxy (KLOR-o-fuh-KNOX-ee). 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)).
chlororganic (klor-or-GAN-nick). Organic compounds combined with chlorine. These compounds generally originate from, or are associated with, life processes such as those of algae in water.
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 exposure. Long-term, low-level exposure to a toxic chemical.
circle of influence. The circular outer edge of a depression produced in the water table 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 manually reset.
cistern (SIS-turn). A small tank (usually covered) or a storage facility used to store water for a home or farm. Often used to store rain water.
clarifer (KLAIR-uh-fire). A large circular or rectangular tank or basin in which water is held for a period of time, during which the heavier suspended solids settle to the bottom. Clarifiers are also called SETTLING BASINS and SEDIMENTATION BASINS.
class (pipe and fittings). The working pressure rating of a specific pipe for use in water distribution systems which i includes allowances for surges. This term is used for cast iron, ductile iron, asbestos cement and some plastic pipe.
clay. One type of 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, and less than 40 percent silt.
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.
clinical
studies. Studies of humans suffering from symptoms induced by chemical exposure.
coagulant aid. Any chemical or substance used to assist or modify coagulation.
coagulants (co-AGG-you-lents). Chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids from the water by settling, skimming, draining or filtering.
coagulation (co-AGG-yoo-LAY-shun). The clumping together of very fine particles into larger particles caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of the fine particles and cause destabilization of the particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.
cohesion. Molecular attraction which holds two particles together.
coliform (COAL-i-form). A group of bacteria found in the intestines of warm-blooded animals (including humans) also in plants, soil, air and water. Fecal coliforms are a specific class of bacteria which only inhibit the intestines of warm-blooded animals. The presence of coliform a is an indication that the water is polluted and may contain pathogenic organisms.
coliform organism. Microorganisms found in the intestinal tract of humans and animals. Their presence in water indicates fecal pollution and potentially dangerous bacterial contamination by disease-causing microorganisms.
colloids (CALL-loids). Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in water have a negative electrical charge, they tend to repel each other. This repulsion prevents the particles from clumping together, becoming heavier, and settling out.
colorimetric 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.
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 chloro derivative) yet is still available to oxidize organic matter and utilize 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, dichloramines, and nitrogen trichloride.
combined sewer. A sewer that transports surface runoff and human domestic wastes (sewage), and sometimes industrial wastes. Wastewater and runoff in a combined sewer may occur in excess of the sewer capacity and cannot be treated immediately. The excess is frequently discharged directly to a receiving stream without treatment, or to a holding basin for subsequent treatment and disposal.
community water system (C.W.S.). 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.
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.
compliance cycle. Thee nine-year calendar year cycle during which public water systems must monitor. Each compliance cycle consists of three three-year compliance periods. The first calendar year cycle begins January 1, 1993 and ends December 31, 2001; the second begins January 1, 2002 and ends December 31, 2010; the third from January 1, 2011 to December 31, 2019, etc.
compliance period. A three year calendar period within a compliance cycle. Each compliance cycle has three three- year compliance periods. Within 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.
composite (proportional) samples (come-PAH-zit). A composite sample is a collection of individual samples obtained at regular intervals, usually every one or two hours during a 24-hour time span. Each individual sample is combined with the others in proportion to the rate of flow when the sample was collected The resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average conditions during the sampling period.
composting. A controlled microbial degradation of organic waste yield an environmentally sound, nuisance-free product of potential value as a soil conditioner.
compound. A substance composed of two or more elements whose composition is constant. For example, table salt (sodium chloride NACl) is a compound.
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 ions near an electrode. 3) The basis for chemical analysis by a polarograph.
conductance. A rapid method of estimating the dissolvedsolids content of a water supply. The measurement indicates the capacity of a sample of water to carry an electrical current, which is related to the concentration of ionized substances in the water. Also called SPECIFIC CONDUCTANCE.
conductivity. A measure of the ability of a solution (water) to carry an electric current.
conductor. A substance, body, device or wire that readily conducts or carries 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 and cone 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 and cone of depression
confined aquifer. An aquifer in which ground water is confined under pressure which is significantly greater than atmospheric pressure. See artesian aquifer.
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.
confounding factors. Variables other than chemical exposure level which can affect the incidence or degree of a parameter being measured.
consumptive use. Water removed from available supplies without direct return to a water resource system for uses such as manufacturing, agriculture, and food preparation.
contactor. An electrical switch, usually magnetically operated.
contaminant Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil.
contamination. The introduction into water of microorganisms, chemicals, toxic substances, wastes, or wastewater in a concentration that makes the water unfit for its next intended use.
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 farming. A conservation-based method of farming in which all farming operations (for example, tillage and planting) are performed across (rather than up and down) the slope. Ideally, each crop row is planted at right angles to the ground slope.
contour strip farming. A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosion resistant forage (grass, grain, hay) crops.
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 system. A system which senses and controls its own operation on a close, continuous basis in what is called proportional (or modulating) control.
controller. A device which controls the starting, stopping, or operation of a device or piece of equipment.
conventional filtration. A method of treating water to remove particulates. The method consists of the addition of coagulant chemicals, flash mixing, coagulation flocculation, sedimentation and filtration. Also called COMPLETE TREATMENT. Also see direct filtration and in-line filtration.
conventional filtration treatment A series of processes including coagulation, flocculation, sedimentation, and filtration resulting in substantial particulate removal.
conventional tillage. The traditional method of farming in which soil is prepared for planting by completely inverting it with a moldboard plow. Subsequent working of the soil with other implements is usually performed to smooth the soil surface. Bare soil is exposed to the weather for some varying length of time depending on soil and climatic conditions.
conventional treatment See conventional filtration Also called COMPLETE TREATMENT.
conveyance loss. Water lost in conveyance (pipe, channel, conduit, ditch) by leakage or evaporation.
corporation stop. A water service shutoff valve located at a street water main. This valve cannot be operated from the ground surface because it is buried and there is no valve box. Also called a CORPORATION COCK.
corrosion. The gradual decomposition or destruction of a material by chemical action, often due to an electrochemical reaction. Corrosion may be caused by: 1) stray current electrolysis, 2) galvanic corrosion caused by dissimilar metals, or 3) differential concentration cells. Corrosion starts at the surface of a material and moves inward.
corrosion inhibitor. A substances that slows the rate of corrosion of metal plumbing materials by water, especially lead and copper materials, by forming a protective film on the interior surface of those materials.
corrosivity. An indication of the corrosiveness of a water. The corrosiveness of a water is described by the water's pH, alkalinity, hardness, temperature, total dissolved solids, dissolved oxygen concentration, and the Langelier Index.
cost/beneflt analysis. A quantitative evaluation of the costs which would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of a toxic chemical.
cost sharing. A publicly financed program through which society, as the beneficiary of environment protection, shares part of the cost of pollution control with those who must actually install the controls.
coulomb (COO-lahm). A measurement of the amount of electrical charge conveyed in one second by an electric current of one ampere. One coulomb equals about 6.25 x 1018electrons (6,250,000,000,000,000,000 electrons).
coupon. A steel specimen inserted into water to measure the corrosiveness of water. The rate of corrosion is measured as the loss of weight of the coupon (in milligrams) per surface area (in square decimeters) exposed to the water per day. 10 decimeters = 1 meter = 100 centimeters
cover crop. A crop that provides temporary protection for delicate seedlings and/or provides a canopy for seasonal soil protection and improvement between normal crop production periods. Except in orchards where permanent vegetative cover is maintained, cover crops usually are grown for one year of less. When plowed under and incorporated into the soil, cover crops are also referred to as gren manure crops.
crop rotation. A system of farming in which a regular succession of different crops are planted on the same land area, as opposed to growing the same crop time after time (monoculture).
cross connection. Any actual or potential connection between a drinking (potable) water system and an unapproved water supply or other source of contamination. For example, if you have a pump moving nonpotable water and hook into the g water system to supply water for the pump seal, a cross-connection or mixing between the two water systems can occur. This mixing may lead to contamination of the drinking water. Also see backsiphonage and backflow.
CT or CTcalc. The product of "residual disinfectant concentration" (C) in mg/l determined before or at the first customer, and the corresponding "disinfectant contact time" (T) in minutes, i.e., "C" x "T". If a public water system applies disinfectants at more than one point prior to the first customer, it must determine the CT of each disinfectant sequence before or at the first customer to determine the total percent inactivation or "total inactivation ratio".In determining the total inactivation ratio, the public water system must determine the residual disinfectant concentration of each disinfection sequence and corresponding contact time before any subsequent disinfection application point(s). "CT99.9" is the CT value required for 99.9 Percent (3-log) inactivation of Giardia lamblia cysts. CT99.9 a variety of disinfectants and conditions appear in Tables 1. l- 1.6, 2.1, and 3.1 of section 141.74(b)(3) in the code of Federal Regulations. CT99.9 is the inactivation ratio. The sum of the inactivation ratios, or total inactivation ratio shown as E = (CT calc) / (CT99.9) is calculated by adding together the inactivation ratio for each disinfection sequence. A total inactivation ratio equal to or greater than 1.0 is assumed to provide a 3-log inactivation of Giardia lamblia cysts.
cumulative exposure. The summation of exposures of an organism to a chemical over a period of time.
curb stop. A water service shutoff valve located in a water service pipe near the curb and between the water main and the building. This valve is usually operated by a wrench or valve key and is used to start or stop flows in the water service line to a building. Also called a "curb cock."
curie. A measure of radioactivity. One Curie of radioactivity is equivalent to 3.7 x 1010 or 37,000,000,000 nuclear disintegrations per second.
current. A movement or flow of electricity. Water flowing in a pipe is measured in gallons per second past a certain point, not by the number of water molecules going past a point. Electric current is measured by the number of coulombs per second flowing past a certain point in a conductor. A coulomb is equal to about 6.25 x 1018 electrons (6,250,000,000,000,000,000 electrons). A flow of one coulomb per second is called one ampere, the unit of the rate of flow of current.

D

dateometer (day-TOM-uh-ter). A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed.
day tank. A tank used to store a chemical solution of known concentration for feed to a chemical feeder. A day tank usually stores sufficient chemical solution to properly treat the water being treated for at least one day. Also called an AGE TANK.
dead end. The end of a water main which is not connected to other parts of the distribution system by means of a connecting loop of pipe
decant To draw off the upper layer of liquid (water) after the heavier material (a solid or another liquid) has settled.
dechlorination (dee-KLOR-uh-NAY-shun). The deliberate removal of chlorine from water. The partial or complete reduction of residual chlorine by any chemical or physical process.
decibel (
DES-uh-bull). A unit for expressing the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 130 for the average level at which sound causes pain to humans.
decomposition. The conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.
defluoridation (de-FLOOR-uh-DAY-shun). The removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.
degasification (DEE-GAS-if-uh-KAY-shun). A water treatment process which removes dissolved gases from the water. The gases may be removed by either mechanical or chemical treatment methods or a combination of both.
degradation. Chemical or biological breakdown of a complex compound into simpler compounds.
demineralization (DEE-MIN-er-al-uh-ZAY-shun). A treatment process which removes dissolved minerals (salts) from water.
denitrification. The biochemical conversion of nitrate; and nitrite nitrogen in the soil dissolved in water to gaseous nitrogen.
density (DEN-sit-tee). A measure of how heavy a substance (solid, liquid or gas) is for its size. Density is expressed in terms of weight per unit volume, that is, grams per cubic centimeter or pounds per cubic foot. The density of water is 1.0 gram per cubic centimeter or about 62.4 pounds per cubic foot.
dermal exposure. Contact between a chemical and the skin.
desalinization (DEE-SAY-leen-uh-ZAY-shun). The removal of dissolved salts (such as sodium chloride, NACI) from water by natural means (leaching) or by specific water treatment processes.
desiccant (DESS-uh-kant). A drying agent which is capable of removing or absorbing moisture from the atmosphere in a small enclosure.
desiccation (DESS-uh-KAY-shun). A process used to thoroughly dry air; to remove virtually all moisture from air.
desiccator (DESS-uh-KAY-tor). A closed container into which heated weighing or drying dishes are placed to coot in a dry environment. The dishes may be empty or they may contain a sample. Desiccators contain a substance, such as anhydrous calcium chloride, which absorbs moisture and keeps the relative humidity near zero so that the dish or sample will not gain weight from absorbed moisture.
destratification (de-STRAT-uh-fuh-KAY-shun).The development of vertical mixing within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life. This vertical mixing can be caused by mechanical means (pumps) or through the use of forced air diffusers which release air into the lower layers of the reservoir.
detention lag. The time period between the moment a change is made and the moment when such a change is finally sensed by the associated measuring instrument.
detention time. 1) The theoretical (calculated) time required for a small amount of water to pass through a tank at a given rate of flow. 2) The actual time in hours, minutes or seconds that a small amount of water is in a settling basin, flocculating basin or rapid-mix chamber. In storage reservoirs, detention time is the length of time entering water will be held before being drafted for use (several weeks to years, several months being typical). Detention Time (hr) = Basin Volume (gal.)(24 hr/day)t Flow (gal/day)
dew point. The temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the vapor in the air. d
ewater. 1) To remove or separate a portion of the water present in a sludge or slurry. To dry sludge so it can be handled and disposed. 2) To remove or drain the water from a tank or a trench.
diatomaceous earth. A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms, a type of free-floating, microscopic plant found in the ocean.
diatomaceous earth filtration (DE filtration). A filtration method resulting in substantial particulate removal, that uses a process in which: 1) a "precoat" cake of diatomaceous earth filter media is deposited on a support membrane (septum), and 2) while the water is filtered by passing through the cake on the septum, additional filter media, known as "body feed," is continuously added to the feed water to maintain the permeability of the filter cake.
diffusion. The movement of suspended or dissolved particles from a more concentrated to a less concentrated region as a result of the random movement of individual particles; the process tends to distribute them uniformly throughout the available volume.
digital readout Use of numbers to indicate the value or measurement of a variable. The readout of an instrument by a direct, numerical reading of the measured value.
dilute solution. A solution that has been made weaker usually by the addition of water.
dimictic (die-MICK-tick). Lakes and reservoirs which freeze over and normally go through two stratification and two mixing cycles within a year.
direct current (D.C.). Electrical current flowing in one direction only and essentially free from pulsation.
direct filtration. A filtration method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. The flocculation facilities may be omitted, but the physical- chemical reactions will occur to some extent. The sedimentation process is omitted. Also see conventional filtration and in-line filtration.
direct runoff. Water that flows over the ground surface or through the ground directly into streams, rivers, or lakes.
discharge head. The pressure (in pounds per square inch or psi) measured at the centerline of a pump discharge and very close to the discharge flange, converted into feet.
disinfectant. Any oxidant, including but not limited to chlorine, chlorine dioxide, chloramines, and ozone, that is added to water in any part of the treatment or distribution process and is intended to kill or inactivate pathogenic microorganisms.
disinfectant contact time ("T" in CT calculations). The time in minutes that it takes for water to move from the point of disinfectant application or the previous point of disinfectant residual measurement to a point before or at the point where residual disinfectant concentration (C) Is measured. Where only one C is measured. T is the time in minutes that it takes for water to move from the point of disinfectant application to a point before or at where residual disinfectant concentration (C) is measured. Where more than one C is measured, T is (a) for the first measurement of C, the time in minutes that it takes for water to move from the first or only point of disinfectant application to a point before or at the point where the first C+ is measured and (b) for subsequent measurements of C, the time in minutes that it takes for water to move from the previous C measurement point to the C measurement point for which the particular T is being calculated- Disinfectant contact time in pipelines must be calculated based on plug flow by dividing the internal volume of the pipe by the maximum hourly flow rate through that pipe. Disinfectant contact time within mixing basins and storage reservoirs must be determined by tracer studies or an equivalent demonstration.
disinfection. The process designed to kill most microorganisms in water, including essentially all pathogenic (disease- causing) bacteria. There are several ways to disinfect, with chlorine being most frequently used in water treatment. Compare with sterilization.
disinfection by-product A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.
dissolved oxygen (DO). Measure of water quality indicating free oxygen dissolved in water.
distillate (DIS-tuh-late). In the distillation of a sample, a portion is evaporated; the part that is condensed afterwards is the distillate.
divalent (die-VAY-lent). Having a valence of two, such as the ferrous ion, Fe2+.
diversion. 1) Use of part of a stream flow as a water supply. 2) A structural conveyance (or ditch) constructed across a slope to intercept runoff flowing down a hillside, and divert it to some convenient discharge point.
Domestic or Other Non-distribution System Plumbing Problem. A coliform contamination problem in a public water system with more than one service connection that is limited to the specific service connection from which the coliform positive sample was taken.
dosage. The quantity of a chemical administered to an organism.-
dose. The actual quantity of a chemical to which an organism is exposed. See absorbed dose.
dose equivalent. The product of the absorbed dose from ionizing radiation and such factors as account for differences In biological effectiveness due to the " of radiation and is distribution in the body as specified by the International Commission on Radiological Units and Measurements (ICRU).
dose-response. A quantitative relationship between the dose of a chemical and an effect caused by the chemical.
dose-response curve. A graphical presentation of the relationship between degree of exposure to a chemical (dose) and observed biological effect or response. -
dose-response evaluation. A component of risk assessment that describes the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease.
dose-response relationship. The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury produced.
downgradients The direction that ground water flows; similar in concept to: downstream for surface water, such as a river.
DPD (pronounce as separate letters). A method of measuring the chlorine residual in water. The residual may be determined by either titrating or comparing a developed color with color standards. DPD stands for N,N-diethyl-pphenylene-diamine.
draft 1) The act of drawing or removing water from a tank or reservoir. 2) The water which is drawn or removed from a tank or reservoir.
drainage. A technique to improve the productivity of some agricultural land by removing excess water from the soil; surface drainage is accomplished with open ditches; subsurface drainage uses porous conduits (drain tile) buried beneath the soil surface.
drainage basin. The area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel. Also see watershed.
drawdown. 1) The drop in the water table or level of water in the ground when water is being pumped from a well. 2) The amount of water used from a tank or reservoir. 3) The drop in the water level of a tank or reservoir.
DWEL (Drinking Water Equivalent Level). Estimated exposure (in mg/L) which is interpreted to be protective for non carcinogenic endpoints of toxicity over a lifetime of exposure. DWEL was developed for chemicals that have a significant carcinogenic potential (Group B). Provides risk manager with evaluation on non-cancer endpoints, but infers that carcinogenicity should be considered the toxic effect of greatest concern.
dynamic pressure. When a pump is operating, the vertical distance (in feet) from a reference point (such as a pump centerline) to the hydraulic grade line is the dynamic head.

References

Water Treatment Plant Operation. California State University, Sacramento, School of Engineering, Applied Research and Design Center. 1988. Surface Water Treatment: The New Rules. Harry von Huben. American Water Works Association. 1991. Safe Drinking Water Act Amendments, Regulations and Standards. Calabrese, EJ; Gilbert, CE and Pastides, H. Eds. Lewis Publishers. Chelsea Michigan. 1988. Water Resources Planning. Dzurik, AA. Rowman & Littlefield, Savage, MD. 1990. Code of Federal Regulations, Title 40, Chapter I, Section 141.2.July 1, 1991 Federal Register 56 FR 26547, June 7, 1991 (Lead and Copper) 56 FR 3578, January 30, 1991 (Phase 11)

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