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GROUNDWATER

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					GROUNDWATER
         GROUNDWATER
Ø Groundwater is subsurface water that fully
  saturate pore spaces of bedrock
Ø The rate of movement of groundwater is
  gravity driven, varying between 0.6 inches
  per day (in sandstones) to several inches
  per year (in granitics)
Ø The source of groundwater is rain and
  melt water infiltrating and percolating
  through fractures/pores in soil and bedrock
GROUNDWATER MOVEMENT
     AND SOURCES
    How much groundwater is there?
Ø   Estimates of up to 4 million km3 for groundwater
Ø   Surface water – 160,000 km3
Ø   Extraction of groundwater measured in ‘acre-
    feet’ (the amount of water that covers one acre
    of land, one foot deep)
Ø   California extracts 17-20 million acre-feet (maf)
    per year
Ø   The Ogallala Aquifer in central United States
    produces 110 maf per year (317 billion gallons of
    water per year)
GROUNDWATER USAGE
WHO USES GROUNDWATER?
Ø Almost all humans will use groundwater –
 either directly pumping it into their own
 cistern or through major metropolitan
 water transportation systems.
Where is Groundwater Stored?
Ø   Groundwater is stored in rock bodies called
    aquifers.
    l   A good aquifer provides both storage and transmittal
        of groundwater
Ø   Characteristics of aquifers:
    l   Porosity
         • The number and size of pore spaces, fractures, joints, in
           bedrock
         • Provides Storage for groundwater
    l   Permeability
         • The connectedness of pore spaces, fractures, joints in
           bedrock
         • Provides Transmittal for groundwater
      What Bedrock makes a Good
               Aquifer?
Ø Any bedrock with both good porosity and
 good permeability
  l   Unconsolidated sedimentary rock
  l   Sandstones
  l   Fractured igneous rocks (basalt) or jointed
      limestone
POROSITY and PERMEABILITY
                POROSITY




     PERMEABILITY
      What if bedrock only has good
      porosity or only permeability?
Ø Bedrock with good porosity but poor
  permeability are call aquicludes or
  aquitards
Ø These types of bedrock may store water,
  but cannot transmit it.
  l   Unfractured igneous rock
  l   Metamorphic rock
  l   Bedrock with high amounts of clay
       • Shales, claystones, mudstones, siltstones
What Is An Unconfined Aquifer?
Ø   An unconfined aquifer has little to no overlying
    sedimentary layers.
    l   There is no confining layer of clay or other
        impermeable sedimentary layers
Ø   The largest unconfined aquifer in the United
    States is the Ogallala Aquifer which extends
    from Texas through Oklahoma, Kansas,
    Nebraska and North Dakota, plus parts of
    Wyoming, Colorado and New Mexico.
UNCONFINED AQUIFER
OGALLALA AQUIFER
   What is a Confined Aquifer?
Ø Confined Aquifers are usually sandwiched
  between two non-permeable layers.
Ø The confining layers provide pressure on
  the aquifer, allowing the groundwater to
  rise to the surface under its own energy –
  no pumping required: Artesian Wells
Ø Largest Artesian well in United States is
  the Big Spring in Missouri
  l   Produces 300-400 million gallons of water/day
CONFINED AQUIFER
ARTESIAN WELLS
Decorative Waterwheel
placed over original Artesian
Wells in SFV (Sportsman’s
Lodge)
Historic springs exist many
places along Ventura
Boulevard.
This is why the Spaniards
established California's first
highway, El Camino Real,
along this long used pathway.




Photo in Archives of The
Museum of the San
Fernando Valley -2008 -
Photo by Gerald Fecht
Big Spring, Missouri
                 AQUIFER ZONES
Ø   The Vadose Zone: Zone of Aeration
    l   This is the upper zone of an aquifer
    l   Between each pore space and within each joint or fracture, both
        air and water can be stored
Ø   The Phreatic Zone: Zone of Saturation
    l   This is the lower zone of an aquifer
    l   Between each pore space and within each joint or fracture, only
        water is stored.
    l   Represents the zone within the aquifer designated as ‘true
        groundwater’
Ø   Water Table
    l   This is the upper limit of the Phreatic Zone within an aquifer
    l   This is the boundary between the Vadose and Phreatic Zone
    l   Depth of water table determined by wells – they will fill to the
        level of the water table
    l   Lakes, springs, streams are ‘surface expressions’ of the water
        table
VADOSE AND PHREATIC
      ZONES




  Phreatic zone
DIAGRAM OF AN AQUIFER
Ø California
Statewide Aquifers
LOS ANGELES GROUNDWATER BASINS
 San Fernando Valley/San
Gabriel Valley Groundwater
San Francisco Area
   Groundwater
Ventura County Groundwater
GROUNDWATER MANAGEMENT
      CHALLENGES
Ø Laws
Ø Water Table Depletion
Ø Ground Subsidence
Ø Contamination
    Laws on Groundwater Usage
Ø   Only two states of USA have no laws regarding
    the use of groundwater: Texas and California
Ø   The only requirement for the water to be of
    “beneficial use”
Ø   Recent attempts in California’s Legislature to
    regulate groundwater have been met with strong
    resistance from many groups: farmers,
    municipalities included
    l   Most recent ‘water bill’ passed has some restrictions,
        but groundwater still not regulated
GROUNDWATER WITHDRAWALS
  WATER TABLE DEPLETION
Ø Water table depletion can be the result of
  natural droughts as well as human activity
Ø Over-pumping wells can result in
  temporary and permanent lowering of the
  water table
NORMAL CONDITIONS FOR
    WATER TABLE
CONDITIONS FOR WATER
  TABLE DEPLETION
 DRAWDOWN EFFECT AND
CONE OF DEPRESSION WITH
       RECOVERY
DRAWDOWN – NO RECOVERY




    lowered
    GROUND SUBSIDENCE
Ø Over pumping groundwater can result in
  the sinking of overlying layers.
Ø Groundwater acts to ‘buoy’ up overlying
  sedimentary layers – remove the water
  and all the pore spaces, fractures, and
  joints can collapse
        SUBSIDENCE
Picture from the San Joaquin Valley
showing the amount of land
subsidence since 1925 due to
aggressive groundwater pumping
SUBSIDENCE IN CALIFORNIA
SUBSIDENCE IN CALIFORNIA
SUBSIDENCE IN TEXAS
            CONTAMINATION
Ø Groundwater contamination comes in
 several ways
  l   Landfills and septic tanks
  l   Agriculture
  l   Industrial
  l   Urban
  l   Toxic wastes
  l   Salt water intrusion
SOURCES OF CONTAMINATION
LANDFILL CONTAMINATION
GAS TANK CONTAMINATION
Septic Tank Contamination
AGRICULTURE CONTAMINATION
Ø Pesticides
Ø Insecticides
Ø Herbicides
Ø Fertilizers
Ø Animal Waste
AGRICULTURAL
CONTAMINATION
INDUSTRIAL CONTAMINATION
San Fernando Valley/San Gabriel
Valley Groundwater contamination
San Francisco Area Groundwater
     Basin Contamination
SALT WATER INTRUSION

				
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posted:11/21/2013
language:English
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