424CHRONIC: A stimulus that lingers or continues for a relatively long period of time, often one-tenth
of the life span or more. Chronic should be considered a relative term depending on the life span
of an organism. The measurement of chronic effect can be reduced growth, reduced
reproduction, etc., in addition to lethality.
Circulation: The continual flow of drilling fluid from injection to recovery and recirculation at the
surface.
CLEAR WELL: A large underground storage facility sometimes made of concrete. A clear well or
a plant storage reservoir is usually filled when demand is low. The final step in the conventional
filtration process, the clearwell provides temporary storage for the treated water. The two main
purposes for this storage are to have filtered water available for backwashing the filter and to
provide detention time (or contact time) for the chlorine (or other disinfectant) to kill any
microorganisms that may remain in the water.
ClO2: The molecular formula of Chlorine dioxide.
COAGULATION: The best pH range for coagulation is between 5 and 7. Mixing is an important
part of the coagulation process you want to complete the coagulation process as quickly as
possible.
COLIFORM TESTING: The effectiveness of disinfection is usually determined by Coliform
bacteria testing. A positive sample is a bad thing and indicates that you have bacteria
contamination.
COLIFORM: Bacteria normally found in the intestines of warm-blooded animals. Coliform
bacteria are present in high numbers in animal feces. They are an indicator of potential
contamination of water. Adequate and appropriate disinfection effectively destroys coliform
bacteria. Public water systems are required to deliver safe and reliable drinking water to their
customers 24 hours a day, 365 days a year. If the water supply becomes contaminated,
consumers can become seriously ill. Fortunately, public water systems take many steps to ensure
that the public has safe, reliable drinking water. One of the most important steps is to regularly
test the water for coliform bacteria. Coliform bacteria are organisms that are present in the
environment and in the feces of all warm-blooded animals and humans. Coliform bacteria will not
likely cause illness. However, their presence in drinking water indicates that disease-causing
organisms (pathogens) could be in the water system. Most pathogens that can contaminate water
supplies come from the feces of humans or animals. Testing drinking water for all possible
pathogens is complex, time-consuming, and expensive. It is relatively easy and inexpensive to
test for coliform bacteria. If coliform bacteria are found in a water sample, water system operators
work to find the source of contamination and restore safe drinking water. There are three different
groups of coliform bacteria; each has a different level of risk.
COLLIOD: Mixture of evenly dispersed substances, such as many milks.
COLLOIDAL SUSPENSIONS: Because both iron and manganese react with dissolved oxygen to
form insoluble compounds, they are not found in high concentrations in waters containing
dissolved oxygen except as colloidal suspensions of the oxide.
COLORIMETRIC MEASUREMENT: A means of measuring an unknown chemical concentration
in water by measuring a sample's color intensity.
COMBINED CHLORINE: The reaction product of chlorine with ammonia or other pollutants, also
known as chloramines.
COMBUSTION: An exothermic reaction between an oxidant and fuel with heat and often light
COMMUNITY WATER SYSTEM: A water system which supplies drinking water to 25 or more of
the same people year-round in their residences.
COMPLIANCE CYCLE: A 9-calendar year time-frame during which a public water system is
required to monitor. Each compliance cycle consists of 3 compliance periods.
COMPLIANCE PERIOD: A 3-calendar year time-frame within a compliance cycle.
COMPOSITE SAMPLE: A water sample that is a combination of a group of samples collected at
various intervals during the day.
COMPOUND: A substance that is made up of two or more chemically bonded elements.
CONDENSATION: The phase change from gas to liquid. The process that changes water vapor
to tiny droplets or ice crystals.
CONDENSATION: The process that changes water vapor to tiny droplets or ice crystals.
CONDUCTOR: Material that allows electric flow more freely.