Groundwater. Goal To understand why groundwater is important, where it comes from, and some...
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Transcript of Groundwater. Goal To understand why groundwater is important, where it comes from, and some...
Groundwater
GoalTo understand why groundwater is important,
where it comes from, and some complications with its use.
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
Groundwater source
Infiltration: Surface water soaking into ground—source of all ground water
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
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
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
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
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
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
Formation of a Cone of Depression
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
Issues with groundwater useSaltwater intrusion: In coastal areas large withdraws
of fresh groundwater can allow saltwater to flow into aquifer
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
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
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
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
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
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
Groundwater qualityMitigation: how we can deal with the problem• Excavation: Contaminated soil is literally dug out
and treated