Environmental Problems of Groundwater

1
Environmental Problems of Groundwater
Three main environmental problems prevail
1) Groundwater Overuse -- Threatens water supply
Reference Tarbuck and Lutgens Pages 113 - 115
2) Groundwater Withdrawal -- Causes land
subsidence
3) Groundwater Contamination -- Contaminates
drinking water
2
Groundwater Overuse

• Groundwater appears to be an endless renewable
  resource, for it is replenished by rain and
  melting snow.

• But in some regions, groundwater has been
  treated as a non-renewable resource. Not having
  enough time to replenish itself.

• Where this is the case the amount of water
  available to recharge the aquifer is
  significantly less than the amount being
  withdrawn.

3
Groundwater Overuse

• In agriculture areas, irrigation practices for
  extended periods of time result in groundwater
  depletion. It can be said that, groundwater is
  literally being mined.

• It could take tens to hundreds of years for the
  groundwater to be replenished.

4
Groundwater Withdrawal

• Can lead to land subsidence (sinking).

• Water is removed (pumped) from the land faster
  than it can naturally recharge.

• This effect is evident in areas where layers of
  loose sediments is present.

• As water is withdrawn, the weight packs the
  sediment grains tightly together and the ground
  sinks.

5
Groundwater Contamination

• Groundwater contamination is a serious problem,
  particularly where aquifers supply areas with
  drinking water and fresh water ponds.

Types of contamination that threaten groundwater
include
1) Sewage from septic tanks and broken sewer
lines.
2) Pollutants from landfills and industrial
waste.
3) Chemicals from highway salt, pesticides and
fertilizers.
6
Contamination by Septic Tanks

• Sewage seeps from drain pipes of septic tanks.
  If sediment has high porosity and is extremely
  permeable, the contaminants reach the zone of
  saturation and contaminate the groundwater
  supply.

7
Contamination by Landfills

• As rain water percolates through the soil, it
  can carry pollutants down to the water table
  where it mixes with and contaminates
  groundwater.
• These contaminants are then carried to ponds,
  rivers, wells, etc.

8
Contamination by Other Sources

• Other pollutants and chemicals that . . seep
  into the ground and contaminate . groundwater
  include
• 1) Highway Salt
• 2) Industrial Waste (leaking tanks)
• 3) Fertilizers (lawns and farms)
• 4) Pesticides (agriculture chemicals)

9
Groundwater Purification

• For purification to occur, the aquifer must be
  of the correct composition. Permeable aquifers
  has large porosity and contaminated water
  travels great distances without being purified.

• The best aquifer for purification is sand or
  sandstone. Contaminated water can sometimes be
  purified after traveling only tens of meters
  through it.

10
Sample Problem
Explain how contaminated ground water can be
purified by passing through Earths materials.
Answer As ground water percolates slowly through
sediment or rock of relatively low permeability
and porosity (sand or sandstone) the contaminants
are filtered from the water. The filtering of
groundwater occurs when contaminants is trapped
in the pore spaces and on the surface of the
grains within sediment and sedimentary rock.