Environmental Engineering Reference
In-Depth Information
Concentration of dissolved solids (mg/L)
Slightly saline 1000-3,000
Moderately saline 3000-10,000
Very saline 10,000-35,000
Brine More than 35,000
Saturated zone:
A subsurface zone in which all the interstices or voids are
filled with water under pressure greater than that of the atmosphere.
Screening:
A pretreatment method that uses coarse screens to remove large
debris from the water to prevent clogging of pipes or channels to the
treatment plant.
Secondary Drinking Water Standards:
Regulations developed under the
Safe Drinking Water Act that established maximum levels of sub-
stances affecting the aesthetic characteristics (taste, color, or odor) of
drinking water.
Secondary maximum contaminant level (SMCL):
The maximum level of
a contaminant or undesirable constituent in public water systems
that, in the judgment of the U.S. Environmental Protection Agency,
is required to protect the public welfare. SMCLs are secondary (non-
enforceable) drinking water regulations established by the USEPA
for contaminants that may adversely affect the odor or appearance
of such water.
Secondary treatment:
The second step of treatment at a municipal waste-
water treatment plant. This step uses growing numbers of microor-
ganisms to digest organic matter and reduce the amount of organic
waste. Water leaving this process is chlorinated to destroy any dis-
ease-causing microorganisms before its release.
Sedimentation:
A physical treatment method that involves reducing the
velocity of water in basins so the suspended material can settle out
by g rav it y.
Seep:
A small area where water percolates slowly to the land surface.
Seiche:
A sudden oscillation, caused by the wind, of a moderate-size body
of water.
Sinuosity:
The ratio of the channel length between two points on a channel
to the straight-line distance between the same two points; a measure
of meandering.
Soil horizon:
A layer of soil that is distinguishable from adjacent layers by
characteristic physical and chemical properties.
Soil moisture:
Water occurring in the pore spaces between the soil particles
in the unsaturated zone from which water is discharged by the tran-
spiration of plants or by evaporation from the soil.
Solution:
Formed when a solid, gas, or another liquid in contact with a liq-
uid becomes dispersed homogeneously throughout the liquid. The
substance that dissolves is called a
solute
, and the liquid in which it
dissolves is called the
solvent
.
