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"Mining"groundwater is another method that has kaeen and can be used in the US. and across the globe to alleviate shortages of renewab..le freshwater. resources. A.certain amount of rain and snow falling on the earth percolates to and recharges underground aqu ifers.. I n the Li,S., groundwater is the source of drinking water for about half of our total population and nearly all our rural population, and it provides. over 50 billion gallons per day for agriculturaI needs.16 When the amourit of groundwater pumped out for these purposes is equal to or less than the amount of precipitation percolating into the groundwater, the use.is sustainable,. this amount of groundwater is generally included when calculating available..renewable.freshwater resources. But when groundwater is pumped.at rates exceeding the natural precipitation recharge, it. diminishes water levels that mayhave..taken centuries. to: bull d up, and will take centuries to recharge; Used in this manner, groundwater is essentially a.nonrenewable resource, like oil or minerals —hence the term. "groundwater mining." The. Earth's Future report noted that groundwater mining has been.frequently used to supplement renewable freshwater resources in the {past and could he used to help cover the anticipated freshwater shortfalls in the 21 st. century,17 But the approach is fundamentally problematic, to say the. Least, given the already depleted. state of many aquifers,. and could "hastenEj the arrivaI of the day when groundwater mining is no longer econonnically viable" Groundwater mining it) the Ogallala Aquifer demonstrates the magnitude of the problem. The aquifer underlies approximately 175,000 square miles of land in parts of eight states, :including Colorado, Kansas, Nebraska, New Mexico, Oklahoma,.5outh Dakota, Texas; and Wyoming, and provides 30 percent of the nation's irrigation grou.ndwater.js As.of 1960--before the.a.dvent of large-scale groundwater -pumping agricultural irrigation systems in the region=only 3.percent of the aqulfer's water had been tapped.19 By 2010, an estimated 30 percent of the Ogailala aquifer had been depleted; based on existing trends, an additional 39 percent. will be gone by 2060.20 Once groundwater in the Ogallala aquifer is sucked dry; It:would take between 500 and 1,300 years to.refiil. Given these challenges to find ing. a d eq uate supplies of fresh water, it is perhaps not surprising that the eyes of water -starved parts of the U.S. have occasianal,ly turned. north to the world's must magnificent repository of fresh water: the Great Lakes. The Great Lakes: vast but finite As the wind slips over your waters., Sing to me. sweetly Superior, Sing me a Chippewa story, Under the quarter moon -Carla Sciaky; Under the Quarter Moon The Great Lakes —Superior, M lchigan,.. Huron, Erie, and qn#ari4—came into being during the last ice age, when the weight of the mile -thick Laurentide ice sheet carved. gia.nt depressions in the earth, As the climate warmed approximately 20,000 years. ago, the ice melted., filling these depressions<a.nd farming the .Great: Lakes. 6ecatise of this geologic.history; Great Lakes water is essentially a non-renewable resource. Only.1 percent.of the Great Lakes' water moves through the system:each year; the remaining 99 percent is original glacial water.22 Once that water is removed. from .the Great Lakes Basin—i.e..; the. lakes themseives plus adjacent land areas where surface water and.groundwater flow hack toward the lakes -it is basically gone for.good.