5.2. ERMUSR 02-12-2008 - Laserfiche WebLink

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Franconia-Ironton-Galesville agtaifer water has allowed the City to forgo the construction of additional treatment facilities. 6. Future appropriations from the drift aquifer are likely to be met more favorably by the DNR because this aquifer is quickly recharged by infiltrating precipitation and pumping effects are localized rather than regional. 7. As gravel mining operations in the area diminish, water availability from the drift will likely become more plentiful. There are two main disadvantages to the paired well approach. Drift aquifers, because they are shallow, will be more susceptible to long-term drought conditions. Drift aquifers are also more vulnerable to contamination from land-use activities, including leaky underground storage tanks, urban runoff, and non-point source contamination form agricultural activities. In southern Washington County, applications of anhydrous ammonia fertilizers from decades past have resulted in elevated nitrate levels in the shallow groundwater. 5.1 Thickness of the Eau Claire Formation Paired wells should only be considered where the Eau Claire Formation is relatively thick in order to minimize well interference effects caused by leakage through the Eau Claire Formation. It is not possible in this evaluation to determine precisely what the minimum thickness should be, but as a guideline, the Eau Claire Formation should be at least 25 feet thick and preferably greater than 50 feet thick. The thickness of the Eau Claire Formation in the vicinity of the existing and proposed Mt. Simon-Hinckley wells is shown on Figure 203. Based on existing information, the thickness of the Eau Claire Formation is greater than 25 feet at all well locations except Existing Well #4. 5.2 Thickness of Unconsolidated Deposits In order for an drift aquifer well to be productive, the unconsolidated deposits must be relatively thick (although there are other considerations, such as saturated thickness and permeability). The thickness of unconsolidated deposits is shown on Figure 21. The thickness of unconsolidated deposits is generally over lU0 feet at each well location. 3 The locations of proposed wells were provided by Elk River Municipal Utilities. P:\Mpls\23 MN\7l\2371105 Water Supply Alternative Study\FinalDeliverables\Alternatives_Report_final.doc 37