Chapter 10
Groundwater
  •  H2O stored in the ground
  •  Next to glaciers in fresh H2O content
  •  Gets into ground by infiltration from precipitation
  •  Infiltration through pores of permeable rocks


    • Position of H2O in the Ground

    Zone of aeration (or unsaturated zone)

  •  Top layer of soil with air and water


    • Zone of saturation (Saturated zone)

  •  Lower layer, below water table - all space (pores) occupied by H2O


    • Water table: Top of saturated zone not necessarily flat, follow topography
    (Figure here)

    Aquifer: Porous, permeable water-bearing layer of rock, capable of supplying water for use

    Porosity: Ability to store water
    Permeability: Ability to transmit aquifer must have both
    e.g. sand, limes-tones, fractured igneous, metamorphic rocks etc., fractured shale.

    Aquitard: impermeable body of rock (opposite to aquifer)
    - Clay, shale, igneous and metamorphic rocks, etc.

    Confined Aquifer: An aquifer trapped by two aquitards (usually under pressure)

  •  If intersected by borehole, can form:

    • (a)Artesian Well (b) Flowing Artesian Well

     Figure here.

    Unconfined Aquifer: exposed at surface (not under pressure)
    Recharge Areas: where H2O gets into aquifer (usually high elevation)
    Discharge Areas: where H2O gets out of aquifer (usually low elevation, valleys)

  • Aquifers get contaminated more in recharge areas than in discharge areas??

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  • Aquifers contain large volumes of H2O

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  • In the US, Ground H2O within 1 km is more than 30 times the volume of all H2O in lakes, rivers & reservoirs on the surface


    • Withdrawal: is in liters/s, gallons/s or m3/s or min, etc.

    Aquifer problems

     Water Balance: Aquifer use should maintain water balance

     Inflow = Outflow

     Figure here.

  • Often, balance is not maintained
  • Could be natural or artificial (human induced)


    • Natural: Less recharge than discharge

    Human induced: Too much pumping

  • Can cause problems
  •  Dry wells, pollution (Salt water intrusion)


    •  Eg. Aquifer: Ogallala Aquifer:

  • World’s largest freshwater body
  •  Underlies 8 states in HIGH PLAINS REGION
  •  In the past had 16 times H2O than all lakes, streams, rivers & marshes on earth
  •  H2O recharged from glacial melt H2O about 15000 years ago
  •  Used mainly for agriculture & domestic
  • Currently problems:
    1. Farming products will be reduced
    2.  Domestic use will stop, etc.
  • Depth of water in 1930 was 20 m, BUT now (1987) about 3m
    •  WHY? Cone of depressioin


     Groundwater Movement:

     Direction: From high hydraulic head to low hydraulic head
    Quantity: According to Darcy’s Law:
     
     

  • Will be taught in lab!!!


    • Water Pollution:

  • Urbanization pollutes surface & groundwater
  •  Pollution: any change in water quality that affects: (a) living organisms (b) makes H2O unsuitable for uses


    • Contamination: Concentration of pollutant just above EPA standard Pollution: Much above standard

  •  Change can be physical, chemical, biological
  •  Any change that uses up oxygen at the expense of fish, other living organisms
  •  Can be POINT or NON-POINT sources


    • Point Sources: Factories, power plants, sewage treatment plants, coal mines, oil well, etc.
    (All discharge through specific locations.)

    NON-POINT: Scattered/diffuse sources
    Runoff from farm fields, gardens etc. (seasonal)

    Treatment of Pollution (Sewage)

    Human sewage is treated in stages -

    1.  PRIMARY TREATMENT - First stage in treatment, & it removes solids raw polluted source.
    2.  SECONDARY TREATMENT - Remaining solid is removed & decomposed using bacteria
    3.  TERTIARY TREATMENT - Removes inorganic minerals & plant nutrients


    (Tertiary treatment produces water that is usable for drinking.)

    e.g., polluted water can also be disposed off in deep water wells.

    Some Effects of Water Pollution

  •  Water pollution can cause health hazards.


    • The most likely pollutants that cause health hazards are PATHOGENS (i.e., disease causing organisms), bacteria and viruses

  • It is very difficult to detect pathogens, therefore, water is usually analyzed for COLIFORM BACTERIA that live in human intestine & those of other animals
  •  When found colifom bacteria indicate the presence of FECES.


    • Others:

  •  Table salt: is a pollutant & can kill if taken in high enough quantity.
  •  Warm water: is considered as a pollutant & make life difficult for some living organism.
  •  Ocean water: is pollutant & has bad effects on organisms & humans.
  •  Oil spills: are pollutants that are very difficult to remove from environment once there.
  •  River Sediments: are pollutants that can be both harmful & beneficial
  •  Municipal sewage: is a pollutant BUT can be a good source of useful metals.

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