Environmental Engineering Reference
In-Depth Information
Community water system:
A public water system that serves at least 15 ser-
vice connections used by year-round residents or 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 sam-
ple 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.
Confined aquifer (artesian aquifer):
An aquifer that is completely filled with
water under pressure and that is overlain by material that restricts
the movement of water.
Confining layer:
A body of impermeable or distinctly less permeable mate-
rial located stratigraphically adjacent to one or more aquifers; this
layer restricts the movement of water into and out of the aquifers.
Confluence:
The flowing together of two or more streams; the place where a
tributary joins the main stream.
Conglomerate:
A coarse-grained sedimentary rock composed of fragments
larger than 2 millimeters in diameter.
Constituent:
A chemical or biological substance in water, sediment, or biota
that can be measured by an analytical method.
Consumptive use:
The quantity of water that is not available for immediate
rescue because it has been evaporated, transpired, or incorporated
into products, plant tissue, or animal tissue.
Contact recreation:
Recreational activities, such as swimming and kayak-
ing, in which contact with water is prolonged or intimate and in
which there is a likelihood of ingesting water.
Contaminant:
Toxic material found as unwanted residue in or on a substance.
Contamination:
Degradation of water quality compared to original or natu-
ral conditions due to human activity.
Contributing area:
The area in a drainage basin that contributes water to
streamflow or recharge to an aquifer.
Core sample:
A sample of rock, soil, or other material obtained by driving a
hollow tube into the undisturbed medium and withdrawing it with
its contained sample.
Criterion:
A standard rule or test on which a judgment or decision can be
based.
Cross connection:
Any connection between safe drinking water and a non-
potable water or fluid.
C
×
T
value:
The product of the residual disinfectant concentration (
C
), in mil-
ligrams per liter, and the corresponding disinfectant contact time
(
T
), in minutes. Minimum
C
×
T
values are specified by the Surface
Water Treatment Rule, as a means of ensuring adequate kill or inac-
tivation of pathogenic microorganisms in water.