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 Low porosityHigh 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 over- pressured 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 surface- level 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