K- permeability (ability to hold) of aquifer H- differences in height L- flow distance • When mining groundwater removes water faster than it recharges o The water table is lowered which creates a Cone of Depression If there are many wells there may be a regional lowering of the water table Can be mitigated by artificial discharge, but slow
o Land Subsidence- if water is withdrawn, mineral grains are unsupported by water ad collapse o Saltwater intrusion- occurs in coastal areas, or areas of salt dome dissolution Salt water flows into pores to replace fresh water Fresh water is less dense and floats on salt water Excessive pumping of freshwater will cause salt contamination In times of low flow rates of Mississippi river, sale has been known to reach up to New Orleans Major aquifers- commonly the main source of water • US Great Plains • Ogallala aquifer (only a few years of supply left) 4. Water resources from major aquifers Major aquifers- commonly the main source of water 5. Erosion by groundwater Dissolution- the chemical process of minerals going directly into solution • Important in carbonate rocks • Carbonates are highly soluble in weak carbonic acid • Little residue is left • Relatively fast process Carbonate Caves- dissolution • Rate of cave formation increases with quantity of acid passing (flow velocity) • Wide range of sizes of caves Cave deposits- created from dripping of flowing water rich in solutes; dripstones and flowstones • Stalactite- long spike of carbonate growing from ceiling • Stalagmite- long spike of carbonate growing toward ceiling • Indicator of past climate Sinkholes- large dissolution chambers open to sky; collapse occurs rapidly Karst- area underlain by carbonates where significant solution and collapse occur 6. Water Quality- depends on groundwater chemistry- kinds and amounts of materials dissolved in water- total dissolved solids (TDS) Hard water- significant Ca, Mg, and HCO3- (generally pass through carbonate rocks) Soft water- few dissolved ions Potable water- ~150 ppm TDS Distilled water has <1 ppm TDS Some elements must be very low (EPA level of arsenic <.05 ppm Some elements make the water taste (iron) Sewage pollution (wells, springs) • Most common source of groundwater pollution
• Septic tanks in rural areas with high water tables Purification- sand as a cleansing agent • Mechanical filtration of bacteria
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