Environmental Engineering Reference
In-Depth Information
Reference dose (RfD): An estimate of the amount of a chemical that a per-
son can be exposed to on a daily basis that is not anticipated to cause
adverse systemic health effects over the person's lifetime.
Representative sample: A sample containing all the constituents present in
the water from which it was taken.
Return flow: That part of irrigation water that is not consumed by evapo-
transpiration and that returns to its source or to another body of
water.
Reverse osmosis (Ro): Solutions of differing ion concentration are sepa-
rated by a semipermeable membrane. Typically, water flows from
the chamber with lesser ion concentration into the chamber with the
greater ion concentration, resulting in hydrostatic or osmotic pres-
sure. In RO, enough external pressure is applied to overcome this
hydrostatic pressure, thus reversing the flow of water. This results in
the water on the other side of the membrane becoming depleted in
ions and demineralized.
Riffle: A shallow part of the stream where water flows swiftly over com-
pletely or partially submerged obstructions to produce surface
agitation.
Riparian: Pertaining to or situated on the bank of a natural body of flowing
water.
Riparian rights: A concept of water law under which authorization to use
water in a stream is based on ownership of the land adjacent to the
stream.
Runoff: That part of precipitation or snowmelt that appears in streams or
surface water bodies.
Rural withdrawals: Water used in suburban or farm areas for domestic and
livestock needs. The water generally is self-supplied and includes
domestic use, drinking water for livestock, and other uses such as
dairy sanitation, evaporation from stock-watering ponds, and clean-
ing and waste disposal.
S
Safe Drinking Water Act (SDWA): A federal law that was passed in 1974
with the goal of establishing federal standards for drinking water
quality, protecting underground sources of water, and setting up a
system of state and federal cooperation to ensure compliance with
t he l law.
Saline water: Water that is considered unsuitable for human consumption
or for irrigation because of its high content of dissolved solids (gen-
erally expressed as mg/L of dissolved solids); seawater is generally
considered to contain more than 35,000 mg/L of dissolved solids. A
general salinity scale is
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