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15 Cards in this Set
- Front
- Back
Groundwater use
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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
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impacts related to groundwater usage
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Environmental impacts due to
groundwater use • -Lowering of the water table •Reversing the flow direction of groundwater •Saltwater intrusion •Land subsidence |
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Lowering of the Water Table
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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. |
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Lowering of the groundwater table cause
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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. |
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Reversal of Groundwater Flow Direction
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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. |
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Saltwater Incursion
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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. |
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Land Subsidence
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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. |
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Point Source or a Regional Source
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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. |
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Contaminant Plumes
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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. |
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SOLUBLE
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completely dissolved in the water
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LEACHATE
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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. |
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Insoluble Plumes
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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. |
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dense non-aqueous phase liquid.
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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. |
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Contaminant Plumes
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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. |
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If contaminants are SOLUBLE
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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. |