Environmental Engineering Reference
In-Depth Information
D
Datum plane:
A horizontal plane to which ground elevations or water sur-
face elevations are referenced.
Deepwater habitat:
Permanently flooded lands lying below the deepwater
boundary of wetlands.
Degradation products:
Compounds resulting from transformation of an
organic substance through chemical, photochemical, and/or bio-
chemical reactions.
Denitrification:
A process by which oxidized forms of nitrogen such as
nitrate are reduced to form nitrites, nitrogen oxides, ammonia, or
free nitrogen; commonly brought about by the action of denitrifying
bacteria and usually resulting in the escape of nitrogen to the air.
Detection limit:
The concentration of a constituent or analyte below which a
particular analytical method cannot determine, with a high degree
of certainty, the concentration.
Diatoms:
Single-celled, colonial, or filamentous algae with siliceous cell
walls constructed of two overlapping parts.
Direct runoff:
Runoff entering stream channels after rainfall or snowmelt.
Discharge:
The volume of fluid passing a point per unit of time, commonly
expressed in cubic feet per second, million gallons per day, gallons
per minute, or seconds per minute per day.
Discharge area (groundwater):
Area where subsurface water is discharged
to the land surface, to surface water, or to the atmosphere.
Disinfectants and disinfection byproducts (DBPs):
A term used in con-
nection with state and federal regulations designed to protect pub-
lic health by limiting the concentration of either disinfectants or the
byproducts formed by the reaction of disinfectants with other sub-
stances in the water (such as trihalomethanes, or THMs).
Disinfection:
A chemical treatment method involving the addition of a sub-
stance (e.g., chlorine, ozone, hydrogen peroxide) that destroys or
inactivates harmful microorganisms or inhibits their activity.
Dispersion:
The extent to which a liquid substance introduced into a ground-
water system spreads as it moves through the system.
Dissociate:
The process of ion separation that occurs when an ionic solid is
dissolved in water.
Dissolved constituent:
Operationally defined as a constituent that passes
through a 0.45-micrometer filter.
Dissolved oxygen (Do):
The oxygen dissolved in water, usually expressed
in milligrams per liter, parts per million, or percent of saturation.
Dissolved solids:
Any material that can dissolve in water and be recovered
by evaporating the water after filtering the suspended material.
Diversion:
A turning aside or alteration of the natural course of a flow of
water, normally considered to be the water physically leaving the
natural channel. In some areas, this can be consumptive use direct
