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The glacial drift represents another aquifer that may he useable as a municipal water supply. The <br />glacial drift is typically very permeable sand and gravel in the Elk River area (a westward portion of <br />the Anoka Sand Plain). Recharge rases to this aquifer are likely higher than in many other parts of the <br />metro area because of the more permeable surficial soils. The Elk River and the Mississippi River are <br />in direct hydraulic connection with the glacial drift aquifer, providing a stable discharge zone and <br />controlling the minimum groundwater levels. Like other shallow sand and gravel aquifers, glacial <br />drift aquifers 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 metropolitan area (including St. Cloud and Elk River) used <br />approximate 13l-billion gallons of groundwater. The distribution of groundwater pumping is shown <br />on Figure 9. This is an <br />increase of approximately <br />34billion gallons of <br />annual use since 1990, or <br />an increase of 26%. <br />Figure LO 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 />largely occurred as a result <br />of [he 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:AMpls\23 MYV71A2371105 Wmec Supply Nterna[Ive Study\FinulDelive~ables'AAlteuietives_.Repod Jfnal.doc l9 <br />Figure 11 Locations of High-Capacity Wells Put Into Service Since 1990 <br />