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What is ground water? The Hydrologic Cycle (emphasizing ground water flow) Why is ground water important? 50% of drinking water in U.S. is ground water 27% of drinking water in NC is ground water 90% of drinking water in the NC Coastal Plain is ground water In addition, it is used for irrigation and industry What’s an Aquifer? A geologic unit capable of storing and transmitting water in sufficient quantities to supply wells. Land Surface Water Table Unsaturated zone Unconfined Saturated zone Aquifer Confining Beds Confined Aquifers Aquifers (white) and confining layers (gray) in the Coastal Plain of North Carolina www.ncwater.org/ For water to infiltrate to form aquifers, the soil/rocks must have….. Porosity Permeability Porosity and Permeability of Different Aquifer Types Type of Aquifer Porosity Permeability Gravel Coarse- to fine sand Fine-grained sand & silt Sandstone, mod. cemented Fractured Shale Metamorphic Rocks Unfractured Shale Very High High Moderate Mod - Low Low Low Very Low Very High High Mod - Low Low Low Very Low Very Low Press, et.al, Understanding Earth, 4th edition Drill rig equipped with core barrels, drill stems and mud reservoirs USGS Elizabethtown, NC 2003 Drill bits are designed to cut through different materials. This one will go through both sand and clay at depth USGS Elizabethtown, NC 2003 Continuous cores of the rock are collected through the drill bit in a wireline core rig USGS Elizabethtown, NC 2003 Preparing to set the monitoring well casing in the drill hole USGS Elizabethtown, NC 2003 View of unlocked monitoring well with its pressure cap USGS Elizabethtown, NC 2003 How deep do you have to go to find ground water? Potentiometric surface: The “head”, or the level to which water will rise in a well For unconfined aquifers: Potentiometric surface = water table For confined aquifers Potentiometric surface relates to pressure Potentiometric Surface What is a “flowing well”? Ground water comes up out of the well without pumping Also known as an artesian well Typical for confined aquifers but not unconfined aquifers Occurs because potentiometric surface (head) is above top of the well Springs Press, et.al, Understanding Earth, 4th edition Where does ground water flow? In general, from high elevation to low elevation From high pressure to low pressure Ground Water Flow 2002 Potentiometric Surface of the Upper Cape Fear Aquifer (contour elevations in feet above or below mean sea level, contour interval = 10 feet) Ground water Problems List problems you can think of related to ground water Depletion due to over-pumping Contamination Salt-water Intrusion Depletion Relates to cone of depression developed around a well that is pumped Example: Kinston, NC 1920’s – artesian well flowing under own pressure Today – pumping by industry, public water and farms has dropped the water level 150 feet Why is depletion in deep (vs shallow) aquifers especially a problem? It takes thousands of years for deep aquifers to recharge with ground water Ground Water Recharge