A fundamental component of the hydrological cycle

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Groundwater
A fundamental component of the hydrological cycle
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Groundwater
among our most precious natural resources

• Is groundwater important? According to U.S.
  estimates, groundwater provides
• 22 of all freshwater withdrawals
• 34 of agricultural use (mostly for
  irrigation)
• 40 of the public water supply withdrawals
• 53 of all drinking water for the total
  population
• 97 of drinking water for the rural population

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Consumption

• A human can survive with about 2 liters of water
  per day.
• In the US, per capita use (all purposes) is about
  6000 liters per day.
• Per capita domestic use in the US is 2-4x greater
  than in western Europe (where users pay up to
  350 more for their water).

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The water table

• Material
• saturated with
• water lies below
• the water table.
• - Materials that conduct water (are porous and
  permeable) are aquifers.
• - Materials that do not conduct water (are
  well-cemented, unfractured, etc.) are aquicludes
  or confining layers.

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The water table wetlands
Wetlands areas of low topographic relief where
the water table intersects the Earths surface.
They are classified based on characteristic soil,
organisms and water coverage during the nominal
growing season.
Importance - water quality - flood control -
coastal storms - fire buffers - carbon storage
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Mines and quarries typically work below the water
table
The water table Mines and Quarries
Below-surface mines and quarries have to be
actively pumped. If not, they fill up with water
to the height of the water table.
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The water table Perched aquifers
porous sediment lt 40 porosity hard rock lt1
Perched aquifer
Aquiclude layer
Perched aquifers are common the geology of
the near-surface can be fairly complex. Perching
may be a result of slight variations in the clay
content of sediment layers. Clay-rich sediment
and shale tend to be impermeable.
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Springs
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Springs in cross section
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Springs along Rock-type boundaries
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Movement of Groundwater
Water entering the ground is recharge.
Groundwater flowing out from the ground is
discharge..
When groundwater flows into streams they are
called effluent. When the water table drops,
streams become influent, and water leaks from the
stream bed into the ground.
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Movement of GroundwaterConfined and unconfined
aquifers
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Movement of Groundwater Artesian Flow
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Movement of Groundwater Effect of pumping

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Movement of Groundwater Salt water intrusion
A consequence of overpumping in coastal
regions Influx of saline seawater into fresh
aquifers.
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Subsidence from groundwater withdrawal

• Long-term overpumping, and slow recharge
  subsidence
• (a major problem).
• - Water acts as support. Withdraw causes
  large-scale compaction of material on the
  aquifer.
• Areas
• oil fields, mines, agriculture.

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Water quality
The EPA estimates that 15 of all underground
fuel storage tanks are leaking.
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Groundwater contamination
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Differential contaminate behavior
Different types of contaminates will have
different physical properties, such as density,
water solubility, volatility, reactivity.
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Natural attenuation of contaminated groundwater
One means of eliminating contaminates in
groundwater is by leaving them in the ground
intentionally. The process of water-rock (or
soil) reaction often naturally removes
(attenuates) the undesired substances from the
water.
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Fracture flow is fast flow
Groundwater flows faster through a network of
fractures than through a complex path of tiny
pores. As a result, natural attenuation
may not work in this setting, since the
attenuation requires time.
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Solution of rock by groundwater karst features
Carbonate rocks are subject to chemical
weathering, especially if water is
abundant. Karst features produced by
dissolution and reprecipitation of carbonate
rocks. What is required? Caves are the
result. stalagtites stalagmites.
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Karst topography
Typifies much of Florida and eastern Kentucky,
among others.
Limestone dissolution causes characteristic
landforms, known as karst topography.
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A fine sinkhole
among the largest US sinkholes 130 meters long,
100 meters wide, 45 meters deep
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Sinkholes mass wasting, karst style
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Formation of geodes and other concretions
rhythmic precipitation of microcrystalline quartz
(agate)
macroscopic quartz crystals
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Hot springs and geysers
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Sedimentary deposition from hot springs
The minerals that form here are essentially the
same as what forms in karst environments
carbonates.
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10 ways of protecting / conserving groundwater
1. Dispose of chemicals properly. 2. Recycle used
motor oil (recycling center). 3. Limit the amount
of fertilizer used on plants. 4. Take shorter /
less showers take baths. 5. Shut off water
while brushing your teeth, or the teeth of
others. 6. Run full loads of dishes and
laundry. 7. Repair leaking faucets. 8. Water
plants only when necessary. 9. Keep a pitcher of
drinking water in the refrigerator. 10. Get
involved in water education.