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GROUNDWATER
Groundwater
• What happens to precipitation once it
reaches the ground
– infiltration
– percolation
• Water filling pore space, cracks &
crevices in rocks- Porosity
• Aquifer- Geologic unit that can store,
transmit and yield appreciable amounts
of water
Porosity and Permeability
• Porosity
–
–
% of rock or sediment that is open (void
spaces)
ability to hold water
• Permeability- ability to transmit water
Movement of ground water
• Moves in response to differences in water
pressure & elevation
• Velocity influenced by
–
–
Slope of water table
Permeability
Aquifers
• Geologic unit that can store, transmit
and yield appreciable amounts of water
• Highly permeable & saturated with water
–
Good aquifers
• Aquitards- impermeable
• Unconfined aquifer
– open to atmosphere
• Confined aquifer
– under pressure
– artesian- flows w/o being pumped
Groundwater Movement
• Darcy’s Law
– Q= KA (h1-h2)/(l)
– Where Q is discharge; A= BxW
– K is hydraulic conductivity
– (h1-h2)/(l) is hydraulic gradient
Wells
• Penetrate aquifer within the saturated
zone
• Water table rises and falls during seasons
–
Recharge
• Cone of depression
–
Drawdown
• Artesian well- no need to pump
–
Artesian aquifer
Cone of Depression
After pumping in a well stops, the water level slowly recovers its
previous level and the cone of depression disappears
Springs and Streams
• Spring
– Water table intersecting hillside
• Gaining stream= Effluent Stream
• Losing stream= Influent Stream
Springs and Streams
• Spring
– Water table intersecting hillside
• Gaining stream= Effluent Stream
• Losing stream= Influent Stream
WT
WT
Pollution of Ground Water
• Pollutants
– Chemicals
• Gasoline
• Pesticides & herbicides
• Fertilizers
• Heavy metals
–
–
–
–
Bacteria, viruses, parasites- Sewage
Acid mine drainage
Radioactive waste
Natural pollution
Balancing Withdrawal &
Discharge
• Overpumping results in:
–
–
Falling water table
Ground subsidence
• Artificial recharge
Subsidence of land
caused by extraction
of groundwater in the
San Juaquin Valley, CA
The land sank 9m or
30 ft in 52 years
Effects of Groundwater Action
• Karst topography-Caves
–
–
Rock usually limestone
Dissolves by weakly acidic water
–
–
Dripstone- Speleothem
•
•
–
rainwater pH 5.5 and carbonic acid from humus
stalagtite
stalagmite
Flowstone
– Sinkholes
GUILIN DISTRICT, CHINA
Hot Water Underground
• Hot springs
–
–
Near magma or cooling igneous rocks
Deep-circulating groundwater or
• Geyser
• Precipitation of dissolved ions
–
–
Travertine- calcite
Sinter- silica
• Mudpot
• Geothermal Energy
Hot Water Underground
• Hot springs
–
–
Near magma or cooling igneous rocks
Deep-circulating groundwater or
• Geyser
• Precipitation of dissolved ions
–
–
Travertine- calcite
Sinter- silica
• Mudpot
• Geothermal Energy