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A Dictionary of Technical and Legal Terms
Related to Drinking Water
Go to the concise consumer-friendly glossary.
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).
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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.
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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 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 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 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. 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 radio-logical
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.
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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-p-phenylene-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.
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E
eductor (e-DUCK-ter). A hydraulic device used to create a negative
pressure (suction) by forcing a liquid through a restriction, such as a
Venturi. An eductor or aspirator (the hydraulic device) may be used in the
laboratory in place of a vacuum pump. As an injector, it is used to produce
vacuum for chlorinators.
effective corrosion Inhibitor residual. A concentration of
corrosion inhibitor sufficient to form a protective coating on the interior
walls of a pipe, reducing its corrosion.
effective range. That portion of the design range (usually upper
90 percent) in which an instrument has acceptable accuracy. Also see range
and span
effective size (E.S.). The diameter of the particles in a granular
sample (filter media) for which 10 percent of the total grains are smaller
and 90 percent larger on a weight basis. Effective size is obtained by
passing granular material through sieves with varying dimensions of mesh and
weighing the material retained by each sieve. The effective size is also
approximately the average size of the grains.
effluent (EF-loo-ent). Water or some other liquid-raw, partially
or completely treated-flowing from a reservoir, basin, treatment process or
treatment plant.
ejector. A device used to disperse a chemical solution into water
being treated.
electrochemical reaction. Chemical changes produced by electricity
(electrolysis) or the production of electricity by chemical changes
(galvanic action). In corrosion, a chemical re-action is accompanied by
the flow of electrons through a metallic path. The electron flow may come
from. an external force and cause the reaction, such as electrolysis caused
by a D.C. (direct current) electric railway or the electron flow may be
caused by a chemical reaction as in the galvanic action of a flashlight dry
cell.
electrochemical sries. A list of metals with the standard
electrode potentials given in volts. The size and sip of the electrode
potential indicates how easily these elements will take on or give up
electrons, or corrode. Hydrogen is conventionally assigned a value of zero.
electrolysis (ee-leck-TRAWL-us-sis). The decomposition of material
by an outside electrical current.
electrolyte (ee.-LECK-tro-LIGHT). A substance which dissociates
(separates) into two or more ions when it is dissolved in water.
electrolytic cell (ee-LECK-tro-LIT-ick). A device in which the
chemical decomposition of material causes an electric current to flow. Also,
a device in which a chemical reaction occurs as a result of the flow of
electric current. Chlorine and caustic (NaOH) are made from salt (NACl in
electrolytic cells.
electromotive force (E.M.F.). The electrical pressure available to
cause a flow of current (amperage) when an electrical circuit is closed. See
voltage
electromotive series. A list of metals and alloys presented in the
order of their tendency to con-ode (or go into solution). Also called the
Galvanic Series. This is a practical application of the theoretical
ELECTROCHEMICAL SERIES.
electron. An extremely small, negatively charged particle; the
part of an atom that determines its chemical properties.
element. A substance which cannot be separated into its
constituent parts and still retain its chemical identity. For example,
sodium (Na) is an element.
end bells. Devices used to hold the rotor and stator of a motor in
position.
end point. Samples are titrated to the end point. This means that
a chemical is added, drop by drop, to a sample until a certain color change
(blue to clear, for example) occurs. This is called the END POINT of the
titration. In addition to a color change, an end point may be reached by the
formation of a precipitate or the reaching of a specified pH. An end point
may be detected by the use of an electronic device such as a pH meter.
endangerment assessment. A site-specific risk assessment of the
actual or potential danger to human health or welfare and the environment
from the release of hazardous substances or waste. The endangerment
assessment document is prepared in support of enforcement actions under
CERCLA or RCRA.
endemic (en-DEM-ick). Something peculiar to a particular people or
locality, such as a disease which is always present in the population.
endrin (EN-drin). A pesticide toxic to freshwater and marine
aquatic life that produces adverse health effects in domestic water
supplies.
energy grade line (E.G.L.). A line that represents the elevation
of energy head of water flowing in a pipe, conduit or channel. The line is
drawn above the hydraulic grade line (gradient) a distance equal to the
velocity head (V2/2g) of the water flowing at each section or point along
the pipe or channel. Also see hydraulic gradeline.
enteric. Of intestinal origin, especially applied to wastes or
bacteria.
entrain. To trap bubbles in water either mechanically through
turbulence or chemically through a reaction.
enzymes (EN-zimes). Organic substances (produced by living
organisms) which cause or speed up chemical reactions. Organic catalysts
and/or biochemical catalysts.
EPA United States Environmental Protection Agency.
epidemic. Widespread outbreak of a disease, or a large number of
cases of a disease in a single community or relatively small area. Disease
may spread from person to person, and/or by the exposure of many persons to
a single source, such as a water supply.
epidemiologic study. Study of human populations to identify causes
of disease. Such studies often compare the health status of a group of
persons who have been exposed to a suspect agent with that of a comparable
non-exposed group.
epidemiology (EP-uh-DE-me-ALL-o-gee). A branch of medicine which
studies epidemics (diseases which affect significant numbers of people
during the same time period in the same locality). The objective of
epidemiology is to determine the factors that cause epidemic diseases and
how to prevent them.
epilimnion (EP-ub-LIM-knee-on). The upper layer of water in a
thermally stratified lake or reservoir. This layer consists of the warmest
water and has a fairly uniform (constant) temperature. The layer is readily
mixed by wind action.
erosion. Wearing away of soil by timing water, wind, or ice;
erosion is the process by which the earth's surface is shaped and occurs
even in remote, uninhabited areas at a slow rate (geologic erosion); of more
concern is accelerated erosion caused by people's activities.
ester. A compound formed by the reaction between an acid and an
alcohol with the elimination of a molecule of water.
eutrophic (you-TRO-fick). Reservoirs and lakes which are rich in
nutrients and very productive in terms of aquatic animal and plant life.
eutrophication (you-TRO-fi-KAY-shun). The increase in the nutrient
levels of a lake or other body of water; this usually causes an increase in
the growth of aquatic animal and plant life.
evaporation. The process by which water or other liquid becomes a
gas (water vapor or ammonia vapor). Water from land areas, bodies of water,
and all other moist surfaces is absorbed into the atmosphere as a vapor.
evapotranspiration (ee-VAP-o-TRANS-purr-A-shun). The combined
processes of evaporation and transpiration. It can be defined as the sum of
water used by vegetation and water lost by evaporation.
exemption. A State with primacy may relieve a public water system
from a requirement respecting an MCL,treatment technique or both, by
granting an exemption if certain conditions exist. These are: 1) the system
cannot comply with a MCL or treatment technique due to compelling factors
which may include economic factors; 2) the system was in operation on the
effective date of the MCL or treatment technique requirement; and 3) the
exemption will not result in an unreasonable public health risk. Also see
variance.
exposure. Contact with a chemical or physical agent.
exposure assessment. The determination or estimation (qualitative
or quantitative) of the magnitude, frequency, duration, route, and extent
(number of people) of exposure to a chemical.
exposure coefficient. Term which combines information on the
frequency, mode, and magnitude of contact with contaminated medium to yield
a quantitative value of the amount of contaminated medium contacted per day.
exposure level (chemical). The amount (concentration) of a
chemical at the absorptive surfaces of an organism.
exposure scenario. A set of conditions or assumptions about
sources, exposure pathways, concentrations of toxic chemicals and
populations (numbers, characteristics and habits) which aid the investigator
in evaluating and quantifying exposure in a given situation.
extrapolation. Estimation of unknown values by extending or
projecting from known values.
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F
facultative (FACK-ul-TAY-tive). Facultative bacteria can use
either molecular (dissolved) oxygen or oxygen obtained from food material
such as sulfate or nitrate ions. In other words, facultative bacteria can
live under aerobic or anaerobic conditions.
fecal coliform bacteria. Bacteria found in the intestinal tracts
of animals. Their presence in water or sludge is an indicator of pollution
and possible contamination by pathogens.
feedback The circulating action between a sensor measuring a
process variable and the controller which controls or adjusts the process
variable .
filtration. A process for removing particulate matter from water
by passage through porous media.
finished water. Water that has passed through a water treatment
plant; all the treatment processes are completed or "finished". This water
is ready to be delivered to consumers. Also called PRODUCT WATER.
first draw. The water that immediately comes out when a tap is
first opened. This water is likely to have the highest level of lead
contamination from plumbing materials.
first draw sample. A one-liter sample of tap water, collected in
accordance with CFR Section 141.86(b)(2), that has been standing in plumbing
pipes at least 6 hours and is collected without flushing the tap.
fix, sample. A sample is fixed in the field by adding chemicals
that prevent the water quality indicators of interest in the sample from
changing before final measurements are performed later in the lab.
flagellates (FLAJ-el-LATES). Microorganisms that move by the
action of tail-like projections.
flame polished. Melted by a flame to smooth out irregularities.
Sharp or broken edges of glass (such as the end of a glass tube) are rotated
in aflame until the edge melts slightly and becomes smooth.
floc. Clumps of bacteria and particulate impurities that have come
together and formed a cluster. Found in flocculation tanks and settling or
sedimentation basins.
flocculation. The gathering together of fine particles in water by
gentle mixing after the addition of coagulant chemicals to form larger
particles.
floodplain. The flat or nearly flat land on the floor of a steam
valley or tidal area that is covered by water during floods.
fluidized (FLEW-id-i-zd). A mass of solid particles that is made
to flow like a liquid by injection of water or gas is said to have been
fluidized. In water treatment, a bed of filter media is fluidized by
backwashing water through the filter.
fluoridation (FLOOR-uh-DAY-shun).The addition of a chemical to
increase the concentration of fluoride ions in drinking water to a
predetermined optimum limit to reduce the incidence (number) of dental
caries (tooth decay) in children. Defluoridation is the removal of excess
fluoride in drinking water to prevent the mottling (brown stains) of teeth.
fluorosis. An abnormal condition caused by excessive intake of
fluorine, characterized chiefly by mottling of the teeth.
flush. I)To open a cold-water tap to clear out all the water which
may have been sitting for a long time in the pipes. m new homes, to flush a
system means to send large volumes of water gushing through the unused pipes
to remove loose particles of solder and flux. 2) To force large amounts of
water through liquid to clean out piping or tubing. storage or process
tanks.
flushing. A method used to clean water distribution lines.
Hydrants are opened and water with a high velocity flows through the pipes,
removes deposits from the pipes, and flows out the hydrants.
flux. A flowing or flow.
foot valve. A special type of check valve located at the bottom
end of the suction pipe on a pump. This valve opens when the pump operates
to allow water to enter the suction pipe but closes when the pump shuts off
to prevent water from flowing out of the suction pipe.
formation. A group of similar consolidation (that is, relatively
solid) rocks of unconsolidated (that is, relatively loose) minerals.
free available residual chlorine. That portion of the total
available residual chlorine composed of dissolved chlorine gas cl2),
hypochlorous acid (HOCl), and/or hypochlorite ion (OCl-) remaining in water
after chlorination. This does not include chlorine that has combined with
ammonia, nitrogen, or other compounds.
free residual chlorination. The application of chlorine to water
to produce a free available chlorine residual equal to at least 80 percent
of the total residual chlorine (sum of free and combined available chlorine
residual).
freeboard. 1) The vertical distance from the normal water surface
to the top of the confining wall. 2) The vertical distance from the sand
surface to the underside of a trough in a sand filter. This distance is also
called AVAILABLE EXPANSION
friction losses. The head, pressure or energy (they are the same)
lost by water flowing in a pipe or channel as a result of turbulence caused
by the velocity of the flowing water and the roughness of the pipe. channel
walls, and restrictions caused by fittings. Water flowing in a pipe loses
pressure or energy as a result of friction losses. Also see head loss.
fresh water. Water that generally contains less than 1,000
milligrams-per-liter of dissolved solids
fungi (FUN-ji). Mushrooms, molds, mildews, rusts, and smuts that
are small non-chlorophyll-bearing plants lacking roots, stems and leaves.
They occur in natural waters and grow best in the absence of light. Their
decomposition may cause objectionable tastes and odors in water.
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G
gage pressure. The pressure within a closed container or pipe as
measured with a gage. In contrast, absolute pressure is the sum of
atmospheric pressure (14.7 lbs/sq in) PLUS pressure within a vessel (as
measured by a gage). Most pressure gages read in gage pressure or psig
(pounds per square inch gage pressure).
galvnic call. An electrolytic cell capable of producing electrical
energy by electrochemical action. The decomposition of materials in the
cell causes an electric (electron) current to flow from cathode to anode.
galvanic series. A list of metals and alloys presented in the
order of their tendency to corrode (or go into solution). Also called the
ELECTROMOTIVE SERIES. This is a practical application of the theoretical
ELECTROCHEMICAL SERIES.
galvanize. To coat a metal (especially iron or steel) with zinc.
Galvanization is the process of coating a metal with zinc.
garnet (GAR-nit). A group of hard, reddish, glassy, mineral sands
made up of silicates of base metals (calcium, magnesium, iron and
manganese). Garnet has a higher density than sand.
gastroenteritis. An inflammation of the stomach and intestine
resulting in diarrhea, with vomiting and cramps when irritation is
excessive. When caused by an infectious agent, it is often associated with
fever.
gauge, pipe. A number that defines the thickness of the sheet used
to make steel pipe. The larger the number, the thinner the pipe wall.
gavage. Type of exposure in which a substance is administered to
an animal through a stomach tube.
geological log. A detailed description of all underground features
discovered during the drilling of a well (depth, thickness and type of
formations).
geophysical log. A record of the structure and composition of the
earth encountered when drilling a well or similar type of test hole or
boring.
germicide (GERM-uh-SIDE). A substance formulated to kill germs or
microorganisms. The germicidal properties of chlorine make it an effective
disinfectant.
Giardia lamblia. Flagellate protozoan which is shed during its
cyst stage into the feces of man and animals. When water containing these
cysts is ingested, the protozoan causes a severe gastrointestinal disease
called giardiasis.
giardiasis (gee-are-DYE-us-sis). Intestinal disease caused by an infestation
of Giardia flagellates.
glass, pipe and fittings. The working pressure rating of a
specific pipe for use in water distribution systems which includes
allowances for surges. This term is used for cast iron, ductile iron,
asbestos cement and some plastic pipe.
gooseneck A portion of a service connection between the
distribution system water main and a meter. Sometimes called a pigtail.
grab sample. A single sample collected at a particular time and
place which represents the composition of the water only at that time and
place.
grade. 1) The elevation of the invert of the bottom of a pipeline.
canal, culvert or similar conduit. 2) The inclination or slope of a
pipeline, conduit, stream channel, or natural ground surface; usually
expressed in terms of the ratio or percentage of number of units of vertical
rise or fall per unit of horizontal distance. A 0.5 percent grade would be a
drop of one-half foot per hundred feet of pipe.
gram. A unit of mass equivalent to one milliliter of water at 4
degrees Celsius. 1/454 of a pound.
gravimetric. A means of measuring unknown concentrations of water
quality indicators in a sample by WEIGHING a precipitate or residue of the
sample.
grey water. Wastewater other than sewage, such as sink drainage or
washing machine discharge.
ground water. The supply of fresh water found beneath the Earth's
surface. usually in aquifers. which is often used for supplying wells and
springs. Because ground water is a major source of drinking water there is
growing concern over areas where leaching agricultural or industrial pollutants or substances from leaking underground storage tanks are contaminating
ground water.
ground water under the direct influence (UDI) of surface water.
Any water beneath the surface of the ground with: 1) significant
occurrence of Insects or other macroorganisms algae. or large-diameter
pathogens such as Giardia lamblia or, 2) significant and relatively rapid
shifts in water characteristics such as turbidity, temperature,
conductivity, or pH which closely correlate to climatological or surface
water conditions. Direct influence must be determined for individual sources
in accordance with criteria established by the State. The State
determination of direct influence may be based on site-specific measurements
of water quality and/or documentation of well construction characteristics
and geology with field evaluation.
gross alpha particle activity. The total radioactivity due to
alpha particle emission as inferred from measurements on a dry sample.
gross beta particle activity. The total radioactivity due to beta
particle emission as inferred from measurements on a dry sample.
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H
half-life. The length of time required for the mass, concentration, or activity of a chemical or physical agent to be reduced by one-half.
halogen. One of the chemical elements chlorine, bromine, or
iodine.
hard water. Alkaline water containing dissolved salts that
interfere with some industrial processes and prevent soap from lathering.
Water may be considered hard if it has a hardness greater than the typical
hardness of water from the region. Some textbooks define hard water as water
with a hardness of more than 100 mgAL as calcium carbonate.
hardness, water. A characteristic of water caused mainly by the
salts of calcium and magnesium, such as bicarbonate, carbonate, sulfate,
chloride and nitrate. Excessive hardness in water is undesirable because it
causes the formation of soap curds, increased use of soap, deposition of
scale in boilers, damage in some industrial processes, and sometimes
causes objectionable tastes in drinking water.
hazard evaluation. A component of risk assessment that involves
gathering and evaluating data on the types of health injury or disease
(e.g., cancer) that may be produced by a chemical and on the conditions of
exposure under which injury or disease is produced.
head. The vertical distance (in feet) equal to the pressure (in
psi) at a specific point. The pressure head is equal to the pressure in psi
times 2.31 ft/psi.
head loss. The head, pressure or energy (they are the same) lost
by water flowing in a pipe or channel as a result of turbulence caused by
the velocity of the flowing water and the roughness of the pipe, channel
walls or restrictions caused by fittings. Water flowing in a pipe loses
head, pressure or energy as a result of friction losses. Also see friction
losses.
header. A large pipe to which a series of smaller pipes are
connected. Also called a MANIFOLD.
heat sensor. A device that opens and closes a switch in response
to changes in the temperature. This device might be a metal contact, or a
thermocouple which generates a minute electrical current proportional to the
difference in heat, or a variable resistor whose value changes in response
to changes in temperature. Also called a TEMPERATURE SENSOR.
heavy metals. Metallic elements with high atomic weights, e.g.,
mercury, chromium, cadmium, arsenic, and lead. They can damage living things
at low concentrations and tend to accumulate in the food chain.
hectare (HECK-tar). A measure of area in the metric system similar
to an acre. One hectare is equal to 10,000 square meters and 2.4711 acres.
hematopoiesis. The production of blood and blood cells;
hemopoiesis.
hepatic. Pertaining to the liver.
hepatitis (HEP-uh-TIE-this). Hepatitis is an inflammation of the
liver usually caused by an acute viral infection. Yellow jaundice is one
symptom of hepatitis.
hepatoma. A malignant tumor occurring in the liver.
herbicide (HERB-uh-SIDE). A compound, usually a man-made organic
chemical, used to kill or control plant growth.
hertz. The number of complete electromagnetic cycles or waves in
one second of an electrical or electronic circuit. Also called the frequency
of the current. Abbreviated Hz.
heterotrophic microorganisms. Bacteria and other microorganisms
that use organic matter synthesized by other organisms for energy and
growth.
heterotrophic plate count (HPC). The number of colonies of
heterotrophic bacteria grown on selected solid media at a given temperature
and incubation period, usually expressed in number of bacteria per
milliliter of sample.
high-line jumpers. Pipes or hoses connected to fire hydrants and
laid on top of the ground to provide emergency water service for an isolated
portion of a distribution system.
high-to-low-dose extrapolation. The process of prediction of low
exposure risks to rodents from the measured high exposure-high risk data.
histology. The study of the structure of cells and tissues;
usually involves microscopic examination of tissue slices.
hose bib. Faucet. A location in a water line where a hose is
connected.
HTH (pronounce as separate letters). High Test Hypochlorite.
Calcium hypochlorite or Ca(OCl)2
human equivalent dose. A dose which, when administered to humans,
produces an effect equal to that produced by a dose in animals.
human exposure evaluation. A component of risk assessment that
involves describing the nature and size of the population exposed to a
substance and the magnitude and duration of their exposure. The evaluation
could concern past exposures, current exposures, or anticipated exposures.
human health risk. The likelihood (or probability) that a given
exposure or series of exposures may have or will damage the health of
individuals experiencing the exposures.
humus. Organic portion of the soil remaining after prolonged
microbial decomposition.
hydrated lime. Limestone that has been burned and treated with
water under controlled conditions until the calcium oxide portion has been
converted to calcium hydroxide (Ca(OH)2). Hydrated lime is quicklime
combined with water. CaO + H20 --> Ca(OH)2. Also see quicklime.
hydraulic grade line. The surface or profile of water flowing of
hydraulic gradient The slope of the hydraulic grade line. is under pressure,
the hydraulic grade line is at the level water would rise to in a small
vertical tube connected to the pipe. Also see energy grade line
hydraulic gradient. The slope of the hydraulic grade line This is
the slope of the water surface in an open channel, the slope of the water
surface of the groundwater table, or the slope of the water pressure for
pipes under pressure.
hydrogeologic conditions. Conditions stemming from the interaction
of ground water and the surrounding soil and rock.
hydrogeologic cycle. The natural process recycling water from the
atmosphere down to (and through) the earth and back to the atmosphere again.
hydrogeology. The geology of ground water, with particular
emphasis on the chemistry and movement of water.
hydrogeologist (HI-dro-gee-ALL-uh-gist). A person who studies and
works with groundwater.
hydrograph. A graph of the rate of runoff plotted against time for
a point on a channel.
hydrologic cycle (HI-dro-LOJ-ick). Movement or exchange of water
between the atmosphere and the earth.
hydrology. The study of the occurrence, distribution and
circulation of the natural waters of the earth.
hydrolysis (hi-DROLL-uh-sis). A chemical reaction in which a
compound is converted into another compound by taking up water.
hydrophilic (Hi-dro-FILL-ick). Having a strong affinity (liking)
for water. The opposite of hydrophobic.
hydrophobic (Hi-dro-FOE-bick). Having a strong aversion (dislike)
for water. The opposite of hydrophilic.
hydropneumatic (Hi-dro-new-MAT-ick). A water system, usually
small, in which a water pump is automatically controlled (started and
stopped) by the air pressure in a compressed-air tank.
hydrostatic pressure (Hi-dro-STAT-ick). 1) The pressure at a
specific elevation exerted by a body of water at rest or, 2) In the case of
groundwater, the pressure at a specific elevation due to the weight of water
at higher levels in the same zone of saturation.
hydrochlorination (Hi-poe-KLOR-uh-NAY-shun). The application of
hypochlorite compounds to water for the purpose of disinfection.
hydrochlorinators (Hi-poe-KLOR-uh-NAY-tors). Chlorine pumps,
chemical feed pumps or devices used to dispense chlorine solutions made from
hypochlorites such as bleach (sodium hypochlorite) or calcium hypochlorite
into the water being treated.
hypochlorite (Hi-poe-KLOR-ite). Chemical compounds containing
available chlorine; used for disinfection. They are available as liquids
(bleach) or solids (powder, granules and pellets). Salts of hypochlorous
acid.
hypolimnion (Hi-poe-LIM-knee-on). The lowest layer in a thermally
stratified lake or reservoir. This layer consists of colder, more dense
water, has a constant temperature and no mixing occurs.
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I
imhoff cone. A clear. cone-shaped container marked with
graduations. The cone is used to measure the volume of settleable solids in
a specific volume (usually one liter) of water.
impeller. A rotating set of vanes in a pump designed to pump or
lift water.
impermeable (im-PURR-me-uh-BULL). Not easily penetrated. The
property of a material or soil that des not allow, or allows only with great
difficulty, the movement or passage of water.
incidence of tumors. Percentage of animals with tumors.
indicator (chemical). A substance that gives a visible change,
usually of color, at a desired point in a chemical reaction, generally at a
specified end point.
indicator (instrument). A device which indicates the result of a
measurement. Most indicators in the water utility field use either a fixed
scale and movable indicator (pointer) such as a pressure gage or a movable
scale and movable indicator like those used on a circular-flow recording
chart. Also called a RECEIVER.
infiltration. 1) The gradual flow or movement of water into and
through (to percolate or pass through) the pores of the soil. Also see
percolation. 2) the penetration of water from the soil into sewer or other
pipes through defective joints, connections or manhole walls.
infiltration gallery. A subsurface groundwater collection system,
typically shallow in depth, constructed with open-jointed or perforated
pipes that discharge collected water . into a water-tight chamber. From this
chamber the water is pumped to treatment facilities and into the
distribution system. Infiltration galleries are usually located close to
streams or ponds and may be under the direct influence of surface water.
infiltration rate. Quantity of water (usually measured in inches)
that will enter a particular type of soil per unit time (usually one hour).
influent (IN-flu-ent). Water or other liquid-raw or partially
flowing INTO a reservoir, basin, treatment process or treatment plant.
ingestion. Type of exposure through the mouth.
inhalation. Type of exposure through the lungs.
initial compliance period. The first full three-year compliance
period which begins at least 18 months after promulgation.
in-line filtration. The addition of chemical coagulants directly
to the filter inlet pipe. The chemicals are mixed by the flowing water.
Flocculation and sedimentation facilities are eliminated. This pretreatment
method is commonly used in pressure filter installations.
Also see conventional filtration and direct filtration.
inorganic. Material such as sand, salt, iron, calcium salts and
other mineral materials. Inorganic substances are of mineral origin, whereas
organic substances are usually of animal or plant origin. Also see organic.
input horsepower. The total power used in operating a pump and
motor. Input HP = (Brake HP)(100%)Motor Efficiency, %)
insecticide. Any substance or chemical formulated to kill or
control insects.
in situ. In place, the original location, in the natural environment.
instream uses. Water uses that can be carried out without removing
the water from its source, as in navigation and recreation.
integrated exposure assessment. A summation over time, in all
media, of the magnitude of exposure to a toxic chemical.
integrator. A device or meter that continuously measures and
calculates (adds) total flows in gallons, or million cubic feet. or some
other unit of volume measurement. Also called a TOTALIZER.
interface. The common boundary layer between two substances such
as water and a solid (metal); or between two fluids such as water and a gas
(air); or between a liquid (water) and another liquid (oil).
interflow. Lateral movement of water in the upper layer of soil.
interlock An electrical switch, usually magnetically operated.
Used to interrupt all (local) power to a panel or device when the door is
opened or the circuit exposed to service.
Internal friction. Friction within a fluid (water) due to cohesive
forces.
interspecies extrapolation model. Model used to extrapolate from
results observed in laboratory animals to humans.
Interstate carrier. Any vehicle or transport which conveys
passengers in interstate commerce.
interstice (in-TUR-stuhz). A very small open space in a rock or
granular material. Also called a void or void space. Also see pore.
invert The lowest point of the channel inside a pipe, conduit, or
canal.
in vitro. In glass; a laboratory experiment performed in a test
tube or other vessel.
in vitro studies. Studies of-chemical effects conducted in
tissues, cells or subcellular extracts from an organism (i.e., not in the
living organism).
in vivo. With in a living organism; a laboratory experiment
performed in which the substance under study is inserted into a living
organism.
in vivo studies. Studies of chemical effects conducted in intact
living organisms.
ion. An electrically charged atom, radical (such as SO42-), or
molecule formed by the loss or gain of one or more electrons.
ionic concentration. The concentration of any ion in solution,
usually expressed in moles per liter.
ionization (EYE-on-uh-ZAY-shun). The splitting or dissociation
(separation) of molecules into negatively and positively charged ions.
irreversible effect. Effect characterized by the inability of the
body to partially or fully repair injury caused by a toxic agent.
J
jar test A laboratory procedure that simulates a water treatment
plant's coagulation/flocculation units with differing chemical doses and
also energy of rapid mix, energy of slow mix, and settling time. The purpose
of this procedure is to ESTIMATE the minimum or ideal coagulant dose
required to achieve certain water quality goals. Samples of water to be
treated are commonly placed in six jars. Various amounts of chemicals are
added to each jar, and the settling of solids is observed. The dose of
chemicals that provides satisfactory settling removal of turbidity and/or
color is the dose used to treat the water being taken into the plant at that
time. When evaluating the results of a jar test, the operator should also
consider the floc quality in the flocculation area and the floc loading on
the filter.
jogging. The frequent starting and stopping of an electric motor.
joule (jewel). A measure of energy, work or quantity of heat. One
joule is the work done when a force of one newton is displaced a distance of
one meter in the direction of force.
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K
kilo. 1) Kilogram. 2) Kilometer. 3) A prefix meaning "thousand"
used in the metric system and other scientific systems of measurement.
kinetic energy. Energy possessed by a moving body of matter, such
as water, as a result of its motion.
kjeldahl nitrogen (KELL-doll). Nitrogen in the form of organic
proteins or their decomposition product ammonia, as measured by the Kjeldahl
Method.
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L
landfill Facility in which solid waste from municipal and/or
industrial sources is disposed; sanitary landfills are those that are
operated in accordance with environmental protection standards.
Langelier index (L.I.). An index reflecting the equilibrium pH of
a water with respect to calcium and alkalinity. This index is used in
stabilizing water to control both corrosion and the deposition of scale.
Langelier index = pH - pHs where pH = actual pH of the water, and pHs= pH at
which the water having the same alkalinity and calcium content is just
saturated with calcium carbonate.
large water system. A water system that serves more than 50,000
persons
latency. Time from the first exposure to a chemical until the
appearance of a toxic effect.
laundering weir (LAWN-der-ing weer). Sedimentation basin overflow
weir. A plate with V-notches along the top to assure a uniform flow rate and
avoid short-circuiting.
launders (LAWN-ders). Sedimentation basin and filter discharge
channels, consisting of overflow weir plates (in sedimentation basins) and
conveying troughs.
LC50. The concentration of a chemical in air or water which is
expected to cause death in 50% of test animals living in that air or water.
LD50. The dose of a chemical taken by mouth or absorbed by the
skin which is expected to cause death in 50% of the test animals so treated.
leachate. A liquid that results from water collecting contaminants as it trickles through wastes, agricultural pesticides or fertilizers.
Leaching may occur in farming areas, feedlots, and landfills, and may result
in hazardous substances entering surface water, ground water, or soil.
leaching. The process by which soluble substances are dissolved
and transported down through the soil by recharge.
lead(Pb). A heavy metal that is hazardous to health if breathed or
swallowed.
Its use in gasoline. paints, and plumbing compounds has been
sharply restricted or eliminated by federal laws and regulations. See heavy
metals.
lead service line. A service line made of lead which connects the
water main to the building inlet and any lead pigtail, gooseneck or other
fitting which is connected to such lead line.
legionella. A genus of bacteria, some species of which have caused
a type of pneumonia called Legionnaires Disease.
lesion. A pathological or traumatic discontinuity of tissue or
loss of function of a part.
lethal. Deadly; fatal.
level controls. A float device (or pressure switch) which senses
changes in a measured variable and opens or closes a switch in response to
that change. In its simplest form, this control might be a floating ball
connected mechanically to a switch or valve such as is used to stop water
flow into a toilet when the tank is full.
lifetime exposure. Total amount of exposure to a substance that a
human would receive in a lifetime (usually assumed to be 70 years).
lindane (LYNN-dane). A pesticide that causes adverse health
effects in domestic water supplies and also is toxic to freshwater and
marine aquatic life.
linearity (LYNN-ee-AIR-it-ee). How closely an instrument measures
actual values of a variable through its effective range; a measure used to
determine the accuracy of an instrument.
linearized multistage model. Derivation of the multistage model,
where the data are assumed to be linear at low doses.
littoral zone (LIT-or-al). 1)That portion of a body of fresh water
extending from the shoreline lakeward to the limit of occupancy of rooted
plants. 2) The strip of land along the shoreline between the high and low
water levels.
loading. The quantity of a substance entering the environment
(soil, water, or air).
LOAEL Lowest-observed-adverse-effect level; the lowest dose in an
experiment which produced an observable adverse effect.
logarithm (LOG-a-rith-m). The exponent that indicates the power to
which a number must be raised to produce a given number. For example: if B2
= N, the 2 is the logarithm of N (to the base B), or 102 =100 and log10 100
= 2. Also abbreviated to "log."
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M
macroscopic organisms (MACK-row-SKAWP-ick). Organisms big enough
to be seen by the eye without the aid of a microscope.
malignant Very dangerous or virulent, causing or likely to cause
death.
managerial controls Methods of nonpoint source pollution control
that are derived from managerial decisions, such as changes in application
times or rates for agrochemicals.
manifold. A large pipe to which a series of smaller pipes are
connected. Also called a HEADER.
man-made beta particle and photon emitting All radionuclides
emitting beta particles and/or photons listed in Maximum Permissible Body
Burdens and Maximum Permissible Concentration of Radionuclides in Air or
Water for Occupational Exposure, NBS Handbook 69, except the daughter
products of thorium-232, uranium-235 and uranium-238.
manometer (man-NAH-mut-ter). An instrument for measuring pressure.
Usually, a manometer is a glass tube filled with a liquid that is used to
measure the difference in pressure across a flow-measuring device such as an
orifice or Venturi meter. The instrument used to measure blood pressure is a
type of manometer.
margin of safety (MOS). Maximum amount of exposure producing no
measurable effect in animals (or studied humans) divided by the actual
amount of human exposure in a population.
mathematical model. Model used during risk assessment to perform
extrapolations.
maximum contaminant level (MCL). The maximum permissible level of
a contaminant in water which is delivered to the free flowing outlet of the
ultimate user of a public water system, except in the case of turbidity
where the maximum permissible level is measured at the point of entry to the
distribution system. Contaminants added to the water under circumstances
controlled by the user are excluded from this definition, except those
contaminants resulting from the corrosion of piping and plumbing caused by
water quality.
maximum contaminant level goal (MCLG). The maximum level of a
contaminant in drinking water at which no known or anticipated adverse
effect on the health of persons would occur, and which allows an adequate
margin of safety. Maximum contaminant level goals are non-enforceable health
goals .
maximum total trihalomethane potential (MTTP). The maximum
concentration of total trihalomethanes produced in a given water containing
a disinfectant residual, after 7 days at 25 degrees C or above.
MBAS. Methylene - Blue - Active Substances. These substances are
used in surfactants or detergents.
MCL See maximum contaminant level.
measured variable. A characteristic or component part that is
sensed and quantified (reduced to a reading of some kind) by a primary
element or sensor.
Mechanical joint A flexible device that joins pipes or fittings
together by the use of lugs and bolts.
medium-size water system. A water system that serves greater than
3,300 and less than or equal to 50,000 person.
meg. A procedure used for checking the insulation resistance on
motors, feeders, buss bar systems, grounds, and branch circuit wiring. Also
see megger.
megger (from megohm). An instrument used for checking the
insulation resistance on motors, feeders, buss bar systems, grounds, and
branch circuit wiring. Also see MEG.
megohm. Meg means one million, so 5 megohms means 5 million ohms.
A megger reads in millions of ohms.
meniscus (meh-NIS-cuss). The curved top of a column of liquid
(water, oil, mercury) in a small tube. When the liquid wets the sides of the
container (as with water), the curve forms a valley. When the confining
sides are not wetted (as with mercury), the curve forms a hill or upward
bulge.
mesh. One of the openings or spaces in a screen or woven fabric.
The value of the mesh is usually given as the number openings per inch. This
value does not consider the diameter of the wire or fabric; therefore, the
mesh number does not always have a definite relationship to the size of the
hole.
mesotrophic (MESS-o-TRO-rick). Reservoirs and lakes which contain
moderate quantities of nutrients and are moderately productive in terms of
aquatic animal and plant life.
metabolism (meh-TAB-uh-LIZ-um). The sum of the chemical reactions
occurring within a cell or a whole organism; includes the energy-releasing
breakdown of molecules (catabolism) and the synthesis of new molecules
(anabolism).
metabolite. Any product of metabolism, especially a transformed
chemical.
metalimnion (MET-uh-LIM-knee-on). The middle layer in a thermally
stratified lake or reservoir. In this layer there is a rapid decrease in
temperature with depth. Also called the THERMOCLINE.
metastatic. Pertaining to the transfer of disease from one organ
or part to another not directly connected with it.
methoxychlor (meth-OXY-klor). A pesticide which causes adverse
health effects in domestic water supplies and is also toxic to freshwater
and marine aquatic life. The chemical name for methoxychlor is 2,2-bis
(P-methoxyphenol)- 1, 1, I - trichloroethane.
methyl orange alkalinity. A measure of the total alkalinity in a
water sample. The alkalinity is measured by the amount of standard sulfuric
acid required to lower the pH of the water to a pH level of 4.5, as
indicated by the change in color of methyl orange from orange to pink.
Methyl orange alkalinity is expressed as milligrams per liter equivalent
calcium carbonate.
mg/L. See milligrams per liter.
microbial growth (my-KROW-bee-ul). The activity and growth of
microorganisms such as bacteria, algae, diatoms, plankton and fungi.
microgram (pg). One-millionth of a gram (3.5 x 10-8 oz.
0.000000035 oz.).
micrograms per liter (mg/L) One microgram of a substance dissolved
in each liter of water. This unit is equal to parts per billion (ppb) since
one liter of water is equal in weight to one billion micrograms.
micron (MY-kron). A unit of length. One millionth of a meter or
one thousandth of a millimeter. One micron equals 0.00004 of an inch.
microorganisms (MY-crow-OR-gan-IS-zums). Living organisms that can
be seen individually only with the aid of a microscope.
mil A unit of length equal to 0.001 of an inch. The diameter of
wires and tubing is measured in mils, as is the thickness of plastic
sheeting .
milligram (mg). One-thousandth of a grain (3.5 x 10-1 oz. 0.000035
oz.).
milligrams per liter (mg/L). A measure of concentration of a
dissolved substance. A concentration of one mg/L means that one milligram of
a substance is dissolved in each liter of water. For practical purposes,
this unit is equal to parts per million (ppm) since one liter of w | 
