Action Level (AL)
the concentration of a contaminant which, if exceeded, triggers treatment or
other requirements which a water system must follow
Chlorine Residual
the amount of chlorine in water available for disinfection
Disinfection By-product (DBP)
Chemical compounds that result from the addition of chlorine to water
containing organic substances
HAA (haloacetic acids)
the combined concentration of the following five contaminants: dibromo-
dichloro-, monobromo-, monochloro-, and trichloro- acetic acids
Inorganic Contaminant
chemical substances of mineral origin, such as iron or manganese
Maximum Contaminant Level (MCL)
the highest level of a contaminant that is allowed in drinking water. MCLs are
set as close to the MCLGs as possible.
Maximum Contaminant Level Goal (MCLG)
the level of a contaminant in drinking water below which there is no known or
expected risk to health. MCLGs allow for a margin of safety.
mg/L
(milligrams per liter) corresponds to one part of liquid in one million parts of liquid (parts per million - ppm)
Microbiological contaminant
Very small organisms, such as bacteria
MRDL
Maximum Residual Disinfectant Level, the maximum amount of chlorine allowed
NA
not applicable
ND
not detected at testing limits
NTU
Nephelometric Turbidity Unit - a measurement of particles in water
Organics
substances containing the element carbon. These can be naturally occurring or
man-made and can include pesticides, solvents, and by-products of disinfection.
pCi/L
picocuries per liter; units of concentration of radioactive substances
ppb
parts per billion; a concentration equal to 1 microgram of a substance in one
liter of water, µg/L
ppm
parts per million, a concentration equal to 1 milligram of a substance in one
liter of water, mg/L
Radionuclides
Contaminants giving off ionizing radiation
TTHM (total trihalomethanes)
the combined concentration of the following four contaminants:
bromodichloromethane, bromoform, chloroform, and dibromochloromethane
TON (threshold odor number)
The greatest number of dilutions of a sample with "odor-free" water yielding a
definitely perceptible odor
Treatment Technique (TT)
A required process intended to reduce the level of a contaminant in drinking water
W (waiver)
variances and exemptions—state permission not to meet an MCL, treatment
technique, or monitoring requirement under certain conditions
µg/L
(micrograms per liter) corresponds to one part of liquid in one billion parts
of liquid (parts per billion, ppb)
