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 (h 1 -h 2 )/(l) –Where Q is discharge; A= BxW –K is hydraulic conductivity –(h 1 -h 2 )/(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

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 – 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