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hha_jan10 - January 10 Where does water flow underground...

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12/6/2010 1 January 10 •Today: Occurrence of Water Underground •Jan 12: Geology and Groundwater; Florida Groundwater Reading on web (links will be provided on web site) http://water.usgs.gov/ogw/aquiferbasics/ Quiz 1 (will cover Jan 5 and today’s material) Where does water flow underground? Spaces Fractures Caves between grains (pores) Porosity (n): Percentage of a rock or soil that is open n = V v /V x 100 where V v is the volume of voids and V is the total volume Effective porosity,n e , is the % of interconnected porosity, available for fluid flow Sediments can be >50% porosity Well sorted sediments have higher porosity than poorly sorted sediments. well-sorted sand or gravel 25 to 50 mixed sand and gravel 20 to 35 POROSITY glacial till 10 to 20 silt 35 to >60 clay 35 to >60 Porosity decreases during burial due to compaction
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12/6/2010 2 Porosity decreases as minerals fill pore space (cementation) Primary porosity is very low in crystalline rocks, such as intrusive igneous rocks, metamorphic rocks, some chemical sedimentary rocks.
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