Download Groundwater

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