GROUNDWATER

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GROUNDWATER

• Groundwater is water stored inside the Earth's
  soil and rock layers.

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Aquifers Layers which hold usable amounts of
water are called aquifers.
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Porosity and Permeability

• Two important factors help determine how good an
  aquifer is
• 1. PorosityThe percentage of the volume of a
  rock layer which is empty space (called pore
  space) and thus can hold water. Some rock layers
  are highly porous, with up to 40 of their volume
  made of pore space others have low porosities of
  less than 1. However, even in the least porous
  rock, there can be water..

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Porosity
http//www.dpiwe.tas.gov.au/inter.nsf/Images/LBUN-
4YJ7UA/File/water_sedimentarylarge.jpg
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Permeability

• 2. PermeabilityMore or less, how easy it is for
  water to flow through a rock layer. Permeability
  is partially controlled by porosity and partially
  by how the pores are connected and such.
• Essentially, the higher the porosity, the more
  water the rock layer can hold, and the higher the
  permeability, the easier it is to extract that
  water. Good aquifers will have high porosity and
  permeability.

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Permeability
http//www.mhhe.com/earthsci/geology/mcconnell/ima
ges/anim_permeability.gif
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Unsaturated VS Saturated

• Typically, the pore space in the shallow soil
  beneath our feet is not full of water, but
  contains some air. This shallow part is called
  the unsaturated zone. Beneath the unsaturated
  zone, the pore space is full of water, and this
  zone is called the saturated zone.

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• Groundwater begins as precipitation that is
  absorbed into the ground. A lot of it is taken up
  by plant roots and evapotranspired. What makes it
  beyond to root zone is pulled down by gravity
  until it reaches the water table. Below the water
  table all the pore space in the soil is filled
  with water. This is the saturated zone.

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Groundwater Table

• The boundary between the unsaturated and
  saturated zones is called the groundwater table
  or water table. Clearly, if you are going to
  drill a well for water, you want to get well
  below the water table into the saturated zone.

• http//geology.er.usgs.gov/eespteam/brass/ground/a
  rt/fig10_6.gif

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White residual clay pit southeast of Cold
Spring, Augusta County.

• Some layers are highly porous and permeable
  (aquifers), but others are very impermeable -
  water does not penetrate or flow through these
  layers, which are often made of clay or shale.
  These layers are called aquicludes or aquitards.

http//www.mme.state.va.us/Dmr/GALLERY/HISTORIC/cl
ay/bwclay20_2a.html
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Unconfined Aquifers

• Some aquifers have an aquiclude beneath them but
  not above them these are called unconfined
  aquifers and are easily filled with infiltrating
  rainwater.

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Confined Aquifers

• Other aquifers are sandwiched between aquicludes
  (confined) the water in such aquifers is often
  pressurized, and if a well is drilled into one,
  the well will flow freely with no pumping. Such
  wells are called artesian.

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Recharge/Discharge

• Recharge is adding water to an aquifer and
  discharge is removing water from an aquifer. If
  recharge exceeds discharge, the aquifer will
  slowly fill with water. If discharge exceeds
  recharge, the aquifer will slowly drain of water.

http//www.umaine.edu/WaterResearch/outreach/image
s/gw3_for_web.gif
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Cone of Depression.

• If you pump water from an aquifer at a rate which
  exceeds the rate of recharge, you will lower the
  water table near your well this region of
  lowered water table is called a cone of
  depression.
• If you pump water too quickly for too long, your
  well's cone of depression may deepen to the
  bottom of the well, and your well will run dry.
  You will either have to stop pumping and wait for
  recharge or drill a deeper well.

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Cone of Depression
http//www.epa.state.il.us/water/groundwater/image
s/cone-of-depression.gif
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SUBSIDENCE

• Overpumping can cause problems at the surface, as
  well. If you drain the water from an aquifer, the
  pore space may collapse, causing the material to
  shrink and the surface to become depressed. This
  surface depression is called subsidence, and is a
  major problem for some parts of the world.

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SUBSIDENCE

• In many areas of the arid Southwest, earth
  fissures are associated with land subsidence.
  Earth fissures can be more than 100 feet deep and
  several hundred feet in length. One extraordinary
  fissure in central Arizona is 10 miles long.
  These features start out as narrow cracks, an
  inch or less in width. They intercept surface
  drainage and can erode to widths of tens of feet
  at the surface.

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Sinking Venice

• Venice is slowly subsiding into the northern
  Adriatic Sea because of over pumping of
  groundwater Mexico City is sinking into the
  former lake bed on which it is built. In some
  areas of the world, the Earth's surface is
  subsiding at a rate of one foot per year as a
  result of over pumping.

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Groundwater Contamination Clearly, if
groundwater flows that slowly, anything which
contaminates the water will be there for a long
time. Among the sources for groundwater
contamination are

• Leaking gasoline storage tanksA new law was
  recently put into effect requiring gas stations
  to upgrade from single-walled underground storage
  tanks to double-walled tanks, to try to reduce
  gas leakage into groundwater. (This is why many
  gas stations have been either torn down or
  temporarily closed recently.)
• http//bcn.boulder.co.us/basin/waterworks/lust-ana
  t2.htm
• Poorly-maintained septic tanks
• Oh, the stench of it all!

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Groundwater Contamination

• Unlined landfillsIf you dump trash and toxic
  materials into a landfill, gunk will eventually
  make its way into groundwater. However, if you
  build a clay or rubber liner under your landfill,
  you can slow or stop this process.
• AgriculturePesticides and other agricultural
  contaminants can enter groundwater over time.

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Groundwater Contamination

• Mining wasteOften as mines were dug (and still
  are in some places), big piles of leftover rock
  and debris were left behind. Lots of heavy metals
  are present in these tailings, and rainwater can
  also leach acids out of them. Neither heavy
  metals nor acids are stuff I want in my drinking
  water.

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Water and tin mining waste - a noxious mixture
http//news.bbc.co.uk/olmedia/320000/images/_32210
7_mine.jpg
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Industrial Waste

• Superfund Sites / Toxic Waste

Virginias 30 Superfund cleanup sites increase
the risk of soil, groundwater, and surface water
contamination, especially in areas with multiple
listings such as York County and the city of
Portsmouth
.  
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Virginia

• Water QualityPollution and development have
  compromised the Old Dominions water sources
  Virginia ranks sixth highest in the nation for
  amount of developmental toxins released into the
  states waters. The problems affect people as
  well as natural ecosystems 81 percent of
  Virginias coastal waters and 30 percent of
  rivers, streams, and creeks are under fish
  consumption advisories due to chemical
  contamination, and half of the states 55
  watersheds are at high risk for loss of wetland
  and aquatic species.

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Radioactive Waste

• Radioactive wasteWe generate lots of high-level
  nuclear waste in bomb-making and reactors. While
  nuclear power is a good way to generate
  electricity, the waste must be dealt with. One
  proposal is to drill a series of giant tunnels
  and caverns into Yucca Mountain in the
  south/central Nevada desert and entomb the waste
  for 10,000 years. Of course, you have to worry
  about the water table and contamination, and
  billions of dollars have been spent on this
  project. What will ultimately happen is still not
  clear.

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Radioactive Waste

• In USA high-level civil wastes all remain as
  spent fuel stored at the reactor sites. It is
  planned to encapsulate these fuel assemblies and
  dispose of them in an underground engineered
  repository about 2010, at Yucca Mountain, Nevada.

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Summary

• What you need to know
• 1.What is an aquifer?
• 2. Define Porosity and Permeability.
• 3. What is the an unsaturated zone verses a
  saturated zone?
• 4. What is a groundwater table?
• 5. What is an aquicludes or aquitards?
• 6. Explain the differences between a confined
  aquifer and an unconfined aquifer.
• 7. What does recharge and discharge mean?
• 8. What is the Cone of Depression?
• 9. What is subsidence? And how does it occur?
• 10.Understand how contaminates can affect our
  water supply?

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CITED

• http//pasadena.wr.usgs.gov/office/ganderson/es10/
  lectures/lnotes.html
• http//www.internationalwaterlaw.org/Articles/IGW-
  Models/Aquifers.jpg
• http//www.dpiwe.tas.gov.au/inter.nsf/Images/LBUN
  -4YJ7UA/File/water_sedimentarylarge.jpg
• http//geochange.er.usgs.gov/sw/changes/anthropoge
  nic/subside/
• http//kylereed.com/Pictures/ForeignTravel/Europe2
  /VeniceSinking.jpg
• http//www.orcbs.msu.edu/environ/programs_guidelin
  es/wellhead/glossary_faq/where_groundwater_comes_f
  rom.htm
• http//www.mhhe.com/earthsci/geology/mcconnell/ima
  ges/anim_permeability.gif
• http//www.mhhe.com/earthsci/geology/mcconnell/dem
  o/prop.htm
• http//geology.er.usgs.gov/eespteam/brass/ground/a
  rt/fig10_6.gif
• http//www.mme.state.va.us/Dmr/GALLERY/HISTORIC/cl
  ay/bwclay20_2a.html
• http//www.sepa.org.uk/groundwater/images/confined
  -unconfined-aquifer.gif
• http//www.umaine.edu/WaterResearch/outreach/image
  s/gw3_for_web.gif
• http//www.epa.state.il.us/water/groundwater/image
  s/cone-of-depression.gif
• http//www.nicholas.duke.edu/crossroads/virginia.h
  tml
• http//news.bbc.co.uk/olmedia/320000/images/_32210
  7_mine.jpg