Science of Water : Concepts and Applications

404 The Science of Water: Concepts and Applications
Chlordane Octachlor-4,7-methanotetrahydroindane. An organochlorine insecticide no longer
registered for use in the United States. Technical chlordane is a mixture in which the primary
components are cis- and trans-chlordane, cis- and trans-nonachlor, and heptachlor.
Chlorinated solvent A volatile organic compound containing chlorine. Some common solvents
are trichloroethylene, tetrachloroethylene, and carbon tetrachloride.
Chlorofl uorocarbons A class of volatile compounds consisting of carbon, chlorine, and fl uorine.
Commonly called freons, they have been used in refrigeration mechanisms, as
blowing agents in the fabrication of fl exible and rigid foams, and, until banned from use
several years ago, as propellants in spray cans.
Chlorination The process of adding chlorine to water to kill disease-causing organisms or to
act as an oxidizing agent.
Chlorine demand A measure of the amount of chlorine that will combine with impurities, and
is therefore unavailable to act as a disinfectant.
Cienaga A marshy area where the ground is wet due to the presence of seepage of springs.
Clean Water Act (CWA) Federal law dating to 1972 (with several amendments) with the objective
to restore and maintain the chemical, physical, and biological integrity of the nation’s
waters. Its long-range goal is to eliminate the discharge of pollutants into navigable waters
and to make national waters fi shable and swimmable.
Climate The sum total of the meteorological elements that characterize the average and extreme
conditions of the atmosphere over a long period of time at any one place or region of the
Earth’s surface.
Coagulants Chemicals that cause small particles to stick together to form larger particles.
Coagulation A chemical water treatment method that causes very small suspended particles to
attract one another and form larger particles. This is accomplished by the addition of a coagulant
that neutralizes the electrostatic charges that cause particles to repel one another.
Coliform bacteria A group of bacteria predominantly inhabiting the intestines of humans or
animals, but also occasionally found elsewhere. Presence of the bacteria in water is used
as an indication of fecal contamination (contamination by animal or human wastes).
Color A physical characteristic of water. Color is most commonly tan or brown from oxidized
iron, but contaminants may cause other colors, such as green or blue. Color differs from
turbidity, which is water’s cloudiness.
Combined sewer overfl ow A discharge of untreated sewage and stormwater to a stream when
the capacity of a combined storm/sanitary sewer system is exceeded by storm runoff.
Communicable diseases Usually caused by microbes—microscopic organisms including bacteria,
protozoa, and viruses. Most microbes are essential components of our environment
and do not cause disease. Those that do are called pathogenic organisms, or simply
pathogens.
Community In ecology, the species that interact in a common area.
Community water system A public water system that serves at least 15 service connections
used by year-round residents or that regularly serves at least 25 year-round residents.
Composite sample A series of individual or grab samples taken at different times from the
same sampling point and mixed together.
Concentration The ratio of the quantity of any substance present in a sample of a given volume
or a given weight compared to the volume or weight of the sample.
Cone of depression The depression of heads around a pumping well caused by withdrawal of
water.
Confi ned aquifer (artesian aquifer) An aquifer that is completely fi lled with water under pressure
and that is overlain by material that restricts the movement of water.
Confi ning layer A body of impermeable or distinctly less permeable material stratigraphically
adjacent to one or more aquifers that restricts the movement of water into and out of the
aquifers.