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[t is also important to keep in mind that in order Ibr a glacial sediment aquifer to be usable, it not <br />only has to have permeable deposits <br />(sand and gravel) of a large aerial <br />extent. it also must he thick (typically at <br />least 30 feet thick) and it must be <br />saturated or have a substantial saturated <br />thickness. A sand and gravel unit that is <br />only saturated [o about 10 feet is not a <br />good candidate For a water supply. <br />The Metropolitan Conncil (2007h) <br />ranked the availability of groundwater <br />water supplies in the seven-county <br />metropolitan area using criteria such as <br />number and productivity of aquifers, <br />presence of known contamination, <br />population growth, well-interference <br />effects, and presence of nearby natural <br />~ -~ <br />I I <br />it Poronlial AquNer Yield _ _,_i ~' <br />Ras mRW ~ ~ ~ <br />M o: ~. ~~~~~ _ i <br />Hg~ MOGAOIe -~r-F ~ Y( <br />®~~ F ~ }~ <br /> <br />Figure 8 Relative Aquifer Yield (from Metropolitan <br />Council, 2007b) <br />for <br />resources that are sensitive to groundwater withdrawals. Their map (included here as Figure K) shows <br />areas of relative aquifer yield. The areas of highest aquifer yield are in eastern Hennepin, Ramsey, <br />and Dakota Counties, where the Prairie du Chien-Jordan Aquifer System is available. Northwestern <br />Hennepin County and western Anoka County area are shown as having only "moderate° to high <br />moderate" potential ayuifer yield. <br />2.4 Regional Groundwater Contamination and Water fluality <br />Contamination of groundwater impacts water-supply availability in some parts of the metropolitan <br />area. Nompoint source pollutants, such as nitrate, pesticides, and herbicides have impacted <br />groundwater quality in agricultural (or formerly agricultural) areas of llakota, Scott, and Washington <br />Counties, although no wells have been taken out of service due to these contaminants. Nitrate, for <br />example, can be removed from wafer using reverse osmosis (RO) treatment. Pesticide and herbicide <br />levels are generally relatively tow and higher levels are typically isolated and impact domestic wells. <br />The MPCA has identified many leaky underground storage tank (LUST) sites in the region. <br />Typically, these sites are not causes of contamination to community water supply wells. Other <br />potential sources of contamination (e.g., dump sites, etc.) are in various stages of investigation and <br />P:ANlpls\23 N'VV IA'2371 Its Writer Supply NtemeG ve Study\hin~IDeliv erable+AAlte~'nalhe Rtport fin - Ldoc ~ 5 <br />