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Groundwater and karst topography

Groundwater and karst topography. #1 factor in geoenvironmental problems of the Nittany Valley. Karst topography: dissolution of limestone along fractures. CO 2 + H 2 O = H 2 CO 3 (acid) H 2 CO 3 + CaCO 3 = Ca 2+ + 2 HCO 3 -

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Groundwater and karst topography

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  1. Groundwater and karst topography #1 factor in geoenvironmental problems of the Nittany Valley

  2. Karst topography: dissolution of limestone along fractures • CO2 + H2O = H2CO3 (acid) • H2CO3 + CaCO3 = Ca2+ + 2 HCO3- • Produces 50-100 mg/L Ca & HCO3 ions dissolved in groundwater; these are carried away, perpetuating the dissolution. • Collapse of land surface above caverns forms a KARST topography

  3. Nittany Valley karst features

  4. Small-scale cavity formation in the Salona Formation

  5. Two possible scenarios of sinkhole subsidence • (a) collapse above caves • (b) washout of plugs above chimneys to cave systems • Almost always, sinkhole collapse is NOT a problem if the underground caverns are below the water table or if groundwater flow is not downward. And in all cases, the caves are preexisting.

  6. Sinkhole: cavity overlain by bedrock roof

  7. Tussey Sink

  8. Former Beaver Stadium sinkhole

  9. Nittany Mall sinkholes

  10. Sinkhole: cavity connected to the near-surface by a chimney

  11. Flow of groundwater can be predicted from hydrogeologic measurements in wells and some math

  12. k is permeability (ability to transport water). Note last column, and relatively rapid transport in karst limestone

  13. Accelerated transport & therefore solution in zones of fractures

  14. A fracture trace: Big Hollow

  15. Example of an environmental problem: Pb from a TV tube factory

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