Environmental Engineering Reference
In-Depth Information
removes valuable vegetation such as the saguaro cactus (which requires years to grow),
contributes to degrading the entire ecosystem, and can result in dust-bowl conditions.
A dendritic drainage pattern should be maintained to direct flows away from develop-
ments, and care should be taken to control floods and minimize erosion. Solutions to sim-
ilar conditions in Albuquerque, New Mexico, are described by Bishop (1978).
Salinization
Salinization is associated with a desert or low-rainfall environment. It is caused by irriga-
tion or by natural runoff migrating downslope, carrying large amounts of salts that are
deposited in the valley trough to accumulate and result in nonfertile areas.
Surface drainage to eliminate the ponding of water affords some control. Subsurface col-
lector drains in irrigated valleys carry away the saline waters to larger drains and canals
for discharge in some location environmentally acceptable.
8.5.2
Groundwater Pollution Control
Pollution
Sources
Forms of pollutants include liquid wastes moving directly into the groundwater system or
leachates from liquid or solid wastes flowing or percolating into the groundwater system.
Liquid waste
pollutes by percolation or direct contact, and originates from:
Domestic sources disposed into septic tanks, with or without leaching fields,
which produce biological contaminants
●
Industrial sources disposed into shallow unlined pits or reservoirs, or by deep-
well injection, which produce chemical contaminants
●
Spills from chemical plants or other industrial sources
●
Solid waste
produces leachates from groundwater or rainwater percolating through:
Domestic sources disposed of in garbage, rubbish dumps, or sanitary land fills,
producing biological and chemical contaminants
●
Industrial waste dumps that produce chemical contaminants. Solid wastes result
from such industries as coal and phosphate mining, power generation (fly ash
and nuclear wastes), pulp and paper manufacturing, etc.
●
Occurrence
Pollution occurs when the liquid waste or leachate moves away from the disposal area.
Pollution potential depends on the mobility of the contaminant, its accessibility to the
groundwater system, the reservoir characteristics, and climate.
Permeable soils permit relatively rapid movement, but depending upon the rate of
movement, biological contaminants may be partially or effectively filtered by movement.
Chemical constituents, however, are generally free to move rapidly when they enter the
groundwater flow system and can travel relatively large distances. Cavernous or highly
fractured rock will directly and rapidly transmit all pollutants for great distances where
running water is present. Impervious materials retard movement, or restrict leachates to
the local vicinity of the waste disposal site, and pollution of underlying aquifers is negli-
gible as long as the impervious stratum is adequately thick.
