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