Agenda - Council - 07/28/2015 - Laserfiche WebLink

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Figure 15. Geologic cross-section of aquifers service the metro area, from east to west across the northern metro. WEST WturrigM CE)iiniy FliYr'Irloiairl COUrIty ST PAUL EAST Ramsey County Wasiiingtorl Couiily L C LIAIFHNAriy A04 lii-E-42 WATER REf ANG, E UT ONLY MINOR AMOUNTS PRAIRIE DU C -iIENJ JORDAN A UIFER M 1 UNNF1 {:y I Y-wN3-Woc. AQ1.-111-3-1-91 11.1 MT. SIMON -HINCKLEY AQUIFER - 1:-ONrPNIN4c LAYER 1 i1u rt r� 1 m,:nr. The amount of groundwater that can be sustainably withdrawn depends on the amount of recharge available, the rock properties that control how easily water moves through the aquifer, and human - imposed limits that have been established to protect public health, maintain ecosystem services, and reduce water use conflicts. Recharge - the ultimate sources of water to the groundwater system - has been estimated by the Metropolitan Council, U.S. Geological Survey and Minnesota Pollution Control Agency. The range of these estimates suggest that 900 to 1,200 million gallons per day is the upper limit on the amount of groundwater available for all needs including baseflow to surface waters, drinking water, and to support industry and commerce (Metropolitan Council, 2014d). To understand what portion of potential recharge may be sustainably available from the groundwater system, regional groundwater flow modeling can also be used to explore approximately the limit (as an estimated range) on how much groundwater can be pumped without causing unacceptable conditions (Appendix 4). These conditions were incorporated into a regional groundwater model scenario that tests the sustainable capacity of aquifers in areas where high capacity wells already exist, under the assumptions that: • Sustainable groundwater pumping should maintain aquifer levels consistent with safe yield conditions defined in Minnesota Statutes • Sustainable groundwater pumping should maintain surface water by limiting withdrawals, including diversions of groundwater that supports them, to maintain protected flows and elevations • Sustainable groundwater pumping should minimize impacts to groundwater flow directions in areas where groundwater contamination has, or may, result in risks to the public health Results suggest that the region might sustainably withdraw approximately 400-500 million gallons of groundwater per day in areas where high capacity wells currently exist (Appendix 4). However, even when groundwater withdrawals are less than that, local limitations may still exist due to proximity of sensitive local features such as neighboring wells or a trout stream. This calculation is an estimate of sustainable withdrawals, and can be used as a guide to regional water supply management. Additional data produced by expanded monitoring and aquifer analysis can be used to refine this estimate. The result is most sensitive to the factors used to define sustainable conditions. This type of modeling approach may be a useful tool to evaluate how WATER SUPPLY MASTER PLAN- Draft June 2015 35