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The glacial drift represents another aquifer that may be useable as a municipal water supply., The <br />gla~-ial drift is typically very permeable sand and gravel in the F.lk River area (a westward portion of <br />the Anoka Sand Plain i. Recharge rates to this aquifer are likely higher than in many other parts of the <br />metro area t~ecause of the more permeable surficial soils. The Elk River and the Mississippi. River are <br />in direct hyc.rauli:; connection with the glacial drift aquifer, providing a stable discharge zone and <br />controlling +.he minimum groundwater levels, Like other shallow sand and gravel aquifers, glacial <br />drift aquifer, are susceptible to contamination from land use activities -particularly non-point <br />agricultural source pollutants such as nitrate and pesticide/herbicides. Treatment to remove nitrate <br />typically involves reverse osmosis or nano-filtration methods., which are expensive. <br />2.6 Regional Groundwater Use <br />In 2005 the greater Twin Cities m?tropolit~n area (including St. Cloud and Elk River) used <br />approximate 131-billion gallons of groundv~ titer. 'The distribution of groundwater pumping is :,hewn <br />on Figure 9. This is an <br />increase of approximately <br />34-billion gallons of <br />annual use since 1990, or <br />an increase of 26%. <br />Figure 10 illustrates where <br />the increased <br />appropriations have taken <br />place. In the outer-ring <br />suburbs of the Twin <br />Cities, increases have <br />largelg occurred as a result. <br />of the installation of new <br />wells, whereas increased <br />annual pumping of <br />existing wells accounts for <br />the increases in the inner- <br />ring suburbs, The <br />Interstate-94 corridor. <br />running northwest from <br />P:\Mpis\23 MN\7Z\23%1105 Water Supply ,~lie~native Study\FinalDeliverableslAlternatives_Repoct_final.doc 19 <br />Figure 11 Locations of High-Capacity Wells Put Int•i Service Since 1990 <br />