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Groundwater
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GoalTo understand why groundwater is important,
where it comes from, and some complications with its use.
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Importance of groundwaterGroundwater: Water that comes from the ground—
pumped out of wells or from springs• In U.S., 50% of drinking water and 40% of irrigation
water comes from groundwater• Pumping water over two highest mountain ranges
in Lower 48 to supply Denver and L.A.
California
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Groundwater source
Infiltration: Surface water soaking into ground—source of all ground water
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Groundwater sourceWater table: Uppermost surface of zone in Earth that
is saturated with water• Surface to 10-meters depth in Maine—Meets
surface at base of Mayflower Hill• 500 meters or more below surface in desert
locations
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Groundwater sourcePorosity: Amount of open space in rocks and
sediment that can hold water• Can be as high as 30% of rock volume
Low porosityHigh porosity
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Groundwater sourcePermeability: Ability for fluids to flow in rock or
sediment• Some rocks a very permeable, called aquifers• Others almost completely block ground water flow,
called aquitards
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Groundwater sourceConfined aquifer: Aquifer that is bounded by
aquitards so that groundwater flow is confined and can become over-pressured
Potentiometric surface: Level to which over-pressured water will rise
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Issues with groundwater useOveruse can lead to depletion of aquifer—Like your
bank account, recharge has to balance withdraw, otherwise there is a problem
Decline of High Plains Aquifer in western Kansas 1996–2006
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Issues with groundwater useCone of depression: Area around a well where water
table is locally depressed due to withdraws• If cone of depression large enough, can lead
neighboring wells to go dry
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Formation of a Cone of Depression
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Issues with groundwater useSubsidence: Ground surface-
level drops due to groundwater withdraws
• 26 ft. in the Great Valley of California, contributes to New Orleans subsidence
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Issues with groundwater useSaltwater intrusion: In coastal areas large withdraws
of fresh groundwater can allow saltwater to flow into aquifer
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Groundwater qualitySources of groundwater pollution• Landfills: typically 100-yr life on liner, many already
leak• Industrial spills and waste disposal: regulations on
industrial dumping only came about in the 60’s and 70’s
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Groundwater qualitySources of groundwater pollution• Agricultural runoff: Animal waste, pesticides, and
chemical fertilizers can all contaminate groundwater
• Sewage leaks and septic tanks: septic tanks are engineered sewage dispersal
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Groundwater qualitySources of groundwater pollution• Leaking storage tanks: Leaking fuel storage tanks
are one of the biggest sources of ground water contamination
• Non-point-source contamination: used motor oil, left over paint, spilled gas
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Groundwater qualityMitigation: how we can deal with the problem• Isolation: If nobody is using the groundwater and
pollution can’t get out, then regulating agencies won’t require a cleanup, just monitoring
Monitoring well
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Groundwater qualityMitigation: how we can deal with the problem• Filtration, dilution, and decomposition: As
groundwater flows, chemical reactions and microbes naturally breakdown contaminants
Wetlands play a major role
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Groundwater qualityMitigation: how we can deal with the problem• Pump and treat: Aquifer is purposely pumped down
and water is treated to remove contamination
Steam injection to enhance natural chemical removal of groundwater contaminants
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Groundwater qualityMitigation: how we can deal with the problem• Excavation: Contaminated soil is literally dug out
and treated