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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
