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recharge but if the storm water is routed by sewer systems to the rivers, recharge could be reduced. 4. Further regulatory limitations on use of the Mt. Simon-Hinckley Aquifer in response to regional lowering of water levels in the Mt. Simon-Hinckley Aquifer. 5. Unforeseen contamination of the aquifer. An example of unforeseen contamination of an aquifer is the Woodbury-Cottage Grove area where a previously unknown contaminant (poly- fluoro compounds) was discovered to be widespread in occurrence. Elk River Municipal Utilities currently does not have aback-up water supply (neither do many other communities). Interconnections with adjacent communities are highly encouraged by the Minnesota DNR to provide emergency water in case of unforeseen circumstances. Elk River is less vulnerable in this regard than, for example, Minneapolis, which relies on a single intake for their water supply - Elk River has seven wells and it is unlikely that all seven would experience a simultaneous failure or contamination. The surficial aquifer could provide aback-up water supply via wells, although additional study would be necessary to determine the viability of the surficial aquifer in the Elk River area. Depending on the permeability of the Eau Claire Aquitard in this area, it may be possible to pair surficial aqufier wells with Mt. Simon-Hinckley Aquifer wells without inducing significant well- interference effects. Well Sites #5, #6 and #11-#12 appear to be the most promising and well yields over 1,000 gallons per minute might be realized from these wells. Additional testing would need to be performed to verify these estimates. The surficial aquifer is more susceptible to contamination and to drought conditions than the Mt. Simon-Hinckley Aquifer. Any use of surface water requires a level of treatment that is substantially more expensive than treatment of groundwater. It is unlikely that Elk River Municipal Utilities could support the construction and operation of a surface-water treatment plant and intake structure with its existing customer base. The economics of a surface-water source might become viable if additional customers could be added (e.g., by selling treated water to neighboring communities) or by partnership with other communities in a jointly owned and operated plant. Purchasing water from other parties to meet future demand may also be viable. It is unlikely that nearby communities will have excess groundwater to sell to Elk River because communities in this area are already experiencing limits on groundwater availability. Therefore, any purchased source P:\Mpls\23 MN\71\2371105 Water Supply Alternative Study\FinalDeliverables\Alternatives_Report_final.doc 44