Agenda - Council Work Session - 10/20/2020 - Special

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5.2 Root Mean Squared of 5.0 percent. It is noted that this error is less than the calibration target of 15 percent (Anderson et al., 2015). Groundwater Modeling Conclusions The Source water aquifer that the City of Ramsey currently utilizes is a deep -confined aquifer comprised of two geologic units, the Tunnel City and Wonewoc Aquifers. Throughout the region, numerous other unconsolidated and bedrock aquifers exist along with substantial surface water bodies such as the Mississippi River. Overall the area surrounding the Twin Cities has substantial surface and groundwater resources to support present and Fong term portable water. At present, there is no reason to assume that the current source water aquifer for the City of Rarnsey will not be able to supply potable water for the foreseeable future, The City of Rarnsey's source water aquifer and wells are able lo meet present day demand and appear to have a noticeable but temporary radius of influence on the surrounding aquifer. The wells are able to support high pumping rates with specific capacity showing acceptable drawdown alongside the aquifer's ability to recharge to static levels within a day of pumping. The City of Rarnsey will need to balance water demand with drawdown to meet Minnesota Department of Natural Resources drawdown thresholds described in MN Rule 6115.0630 Definitions Subps.15 and 16. Two thresholds are in place and regulate that wells must not drawdown MnONR assigned static water levels to within 50% and 25°AD to the top of aquifer. These threshold values are sel by a MnDNR observation well and would typically be enforced if long term issues are observed. Thresholds for the City of Ramsey could become a concern if there is extending pumping within a single well or pumping by multiple wells in close proximity. In summary, the source water aquifer for the City of Ramsey should continue to produce potable water to meet present and foreseeable future demands; however, the City of Ramsey should plan additional well sites to ensure static water levels remain sufficiently above top of aquifers to meet MnDNR thresholds. Single well pumping for the City of Ramsey, as depicted by Ramsey Well 5 in May, 2019 saw approximately 90 to 100 feet of temporary drawdown, This observed drawdown nears the MnDINIR 50% threshold; however, the pumping extended multiple days and recharged within the same time period back to static levels. This supports the ability of the wells to supply continued water and ability to stay within prescribed State Statute. A single well also creates a radius of influence drawing down adjacent water levels. The zone of influence for a single well was observed and modeled to be approximately two to three thousand feet, meaning that a single well pumping at approximately 800 feet will not cause a significant drawdown in another well. When multiple well are being utilized such as under heavy day demand or under 2040 conditions the modeled and observed drawdown in nearby wells sees a substantial drop in static water levels from that of a single well pumping. Modeled drawdown during present heavy day conditions depict 30-40 feet of drawdown approximately 1,500 feet around the wellfield. After pumping stops, the aquifer will recharge to static levels within one or two days. In general, it appears new well sites should be spaced at least 1,500 to 2,000 feet away from existing wells to ensure a pumping scheme that gives the aquifer sufficient time to recharge. Future well sites should attempt to balance the City's current economics. well spacing, and take into account the underlying geology. The City of Ramsey should continue to utilize the current FEASIBILITY STUDY -DRAFT RAMSY 154354 Page 23