Depending on its physical, chemical, and biological properties, a contaminant
may move within an aquifer in the same ways that ground water
moves. (Some contaminants, however, do not follow ground water
flow). It is possible to predict, to some degree, the transport
within an aquifer of those substances that move along with ground
water flow. For instance, both water and certain contaminants
flow from recharge areas to discharge areas. Soils that are porous
and permeable tend to transmit water and certain types of contaminants
with relative ease to an aquifer below.
Just as ground water generally moves slowly, so do contaminants in ground water.
Because of this slow movement, contaminants usually remain concentrated
in the form of a plume that often flows along the same
path as the ground water. The size and speed of the plume depend
on the amount and type of contaminant, its solubility and density,
and the velocity of the surrounding ground water.
Degradation or Destruction of the Water Supply
The consequences of a contaminated water supply often are serious. In some cases,
contamination of ground water is so severe that the water supply
must be abandoned as a source of drinking water. (For example,
less than 1 gallon of gasoline can render 1 million gallons of
ground water nonpotable.)
Costs of Cleaning Up Contaminated Groundwater
Because ground water generally moves slowly, contamination often remains undetected
for long periods of time. This makes cleanup of a contaminated
water supply difficult, if not impossible. If a cleanup is undertaken,
it can cost millions of dollars.
