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15 Cards in this Set

  • Front
  • Back
Groundwater use
involves extraction or the pumping of water from the ground. This requires the drilling or digging of wells to intersect the groundwater table. Once a well is installed, the area of the well that intersects the aquifer will have a variety of impacts on the groundwater
impacts related to groundwater usage
Environmental impacts due to
groundwater use

-Lowering of the water table
•Reversing the flow direction of groundwater
•Saltwater intrusion
•Land subsidence
Lowering of the Water Table
immediate effect of pumping
groundwater is the lowering of the
groundwater table around the well. As
water is pumped out of the aquifer, the
water level near the well will begin to form
a cone shaped depression. The extent that
this cone of depression forms is known as
the drawdown for the well. When pumping
ceases, then the ideal result is that the
groundwater will flow back into the cone
of depression, and the groundwater table
will recover.
Lowering of the groundwater table cause
the well for the single family home to go dry, while the
farm can continue to pump groundwater to irrigate the fields. Although the home owner may feel
that the farm is the reason for the loss of groundwater during the summer, the reality is that the
well is just not deep enough. The solution to this problem is for the home owner to deepen the
existing well, or drill a second, but deeper well. Although it may be cost prohibitive, the home
owner really has no choice but to invest in a deeper well. Otherwise, the home can not be
occupied during the dry season.
Reversal of Groundwater Flow Direction
the location of a high volume well for irrigation forms a very large cone of
depression, resulting in the local reversal of groundwater flow direction. Note that the waste
water from the septic system also flows toward the irrigation well, but is intersected by the well
for the home. This is a real problem and results in contaminated water supply. The only way to
correct this problem would be to regulate the irrigation well, filter and treat the contaminated
water, drill a new well in an area beyond the large cone of depression, deepen the existing home
well much below the level of the cone of depression, introduce municipal water (city water lines),
or move the location of the leach field.
Saltwater Incursion
Salt water is more dense than
fresh groundwater, so at the coast the salty groundwater will reside below the fresh groundwater. As coastal regions are develop and groundwater is used to supply homes, the deep salty water will migrate upward.
In effect, the amount of salty groundwater increases as the amount of fresh groundwater is pumped from the ground to supply the coastal communities.
Land Subsidence
Aquifers in unconsolidated sediment will
compact if the groundwater is extracted at a
rate that exceeds recharge. The removal of
groundwater allows the sediments to settle
and compact. At the scale of a few grains of
sand, this type of compaction may not seem
important, however, at the scale of 10’s or
100’s of kilometers, this process has resulted
in serious environmental problems.
Point Source or a Regional Source
Pollution in the groundwater.An example of a
point source would be the septic tank or salt pile, where a general regional pollutant
would be fertilizer that is spread over large fields.
Contaminant Plumes
Once a pollutant enters the groundwater system, it then will migrate with the water in
the form of a plume. The plume has the highest concentration of contaminants near the
source.. One of the major problems with
groundwater pollution is that it migrates away from the source to cause problems over
larger areas.
SOLUBLE
completely dissolved in the water
LEACHATE
The final “juice” that exists the bottom of the landfill.In most landfills, the
leachate is contained by an impermeable barrier that is emplaced prior to the development of
the landfill. This barrier can be clay or plastic liners. However, if there is a leachate break -out, the leachate will migrate to the groundwater system and create a pollution plume.
Insoluble Plumes
If contaminants are INSOLUBLE (do
not dissolve in water), then they will
either float on the groundwater, or sink
to the bottom of the aquifer. Gasoline
is less dense than water. If gasoline
leaks into the ground, then it will
reside on top of the groundwater and
move in the direction of the
groundwater flow.
dense non-aqueous phase liquid.
if a toxic chemical is more
dense than water, then it will seek the
lowest level within the groundwater
system and may even flow in the
opposite direction of the regional
groundwater flow.
Contaminant Plumes
The slow migration of water in the sandstone allows for sufficient time for the liquid sewage to
purify and have not adverse impact on the well. But, the fracture aquifer allows the liquid sewage to flow
rapidly, and may result in contamination of a water well that is at a considerable distance.
If contaminants are SOLUBLE
then
they
move with the
local groundwater flow. Imagine the rain water that seeps into a municipal landfill. As it
migrates through the landfill, the water leaches chemicals that exist in the trash.