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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
WTWT
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 landcaused by extraction of groundwater in theSan Juaquin Valley, CAThe land sank 9m or30 ft in 52 years
Effects of Groundwater Action
• Karst topography-Caves– Rock usually limestone– Dissolves by weakly acidic water
– rainwater pH 5.5 and carbonic acid from humus
– Dripstone- Speleothem• 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