Chlorine, Free Available Residual. That portion of the total residual chlorine remaining
in water at the end of a specified contact period, which will react chemically and
biologically as hypochlorous acid, HOCl, or hypochlorite ion, (OCl-).
Chlorine Ice. A solid hydrate of chlorine sometimes formed at the diffuser or in the bell
jar of a chlorinator, where the gas comes in contact with the cold water.
Chlorine Residual. The total amount of chlorine (combined and free available chlorine)
remaining in water at the end of a specified contact period following chlorination.
Clarification. Process of subsidence and deposition by gravity of suspended matter
carried by water or other liquids. Also called settling, it is usually accomplished by
reducing the velocity of flow of the liquid below the point where it can transport the
Coagulant. A chemical or material which when added to water will combine with added
or naturally present chemicals to form a precipitate, called a floc, which will settle and
aid in the removal of suspended matter in the liquid.
Coagulation. The destabilization and initial aggregation of colloidal and finely divided
suspended matter by the addition of a floc-forming chemical.
Coagulation Basin. A basin employed for the coagulation of suspended or colloidal
matter, with or without addition of a coagulant, in which the liquor is mixed gently to
induce coagulation, flocculation, and agglomeration, in preparation for subsequent
Coefficient. A numerical quantity or factor, determined by experimental methods, put
into a formula, which expresses the relationship between two or more variables,
commonly used to adjust the theoretical relation to that found in actual practice.
Coefficient, Discharge. The factor or number by which the theoretical discharge of
fluids through orifices, nozzles, tubes, weirs, etc., must be multiplied to obtain the
Coefficient, Roughness. A factor, in the Kutter, Manning, and other formulas for
computing the average velocity of the flow of water in a conduit. It represents the effect
of roughness of the confining material of the channel or conduit upon the energy losses
in the flowing water.
Coefficient, Uniformity. The degree of variation in the size of the grains that constitute
a granular material. It is the ratio of: (1) the diameter of a grain of a size that is too
large to pass through a sieve which allows 60 percent of the material (by weight) to
pass through, to (2) the diameter of a grain of a size that is too large to pass through a
sieve which allows 10 percent of the material (by weight) to pass through. The