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