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Groundwater Goal To understand why groundwater is important, where it comes from, and some complications with its use. Importance of groundwater Groundwater: 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 source Water 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 source Porosity: Amount of open space in rocks and sediment that can hold water • Can be as high as 30% of rock volume High porosity Low porosity Groundwater source Permeability: 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 source Confined aquifer: Aquifer that is bounded by aquitards so that groundwater flow is confined and can become over-pressured Potentiometric surface: Level to which overpressured water will rise Issues with groundwater use Overuse 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 use Cone 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 use Subsidence: Ground surfacelevel drops due to groundwater withdraws • 26 ft. in the Great Valley of California, contributes to New Orleans subsidence Issues with groundwater use Saltwater intrusion: In coastal areas large withdraws of fresh groundwater can allow saltwater to flow into aquifer Groundwater quality Sources 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 quality Sources 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 quality Sources 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 quality Mitigation: 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 quality Mitigation: 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 quality Mitigation: 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 quality Mitigation: how we can deal with the problem • Excavation: Contaminated soil is literally dug out and treated