Agenda - Public Works Committee - 10/19/2021

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groups and 12 microbiological contaminants. The list includes chemicals used in commerce, pesticides, biological toxins, disinfection byproducts, and waterborne pathogens. The contaminants on the list are not currently regulated by existing Primary drinking water standards. The CCL should be reviewed when considering a surface water source for drinking water. 2.1d Water Quantity The Mississippi River flow in the Northwest Metro study area averages 7,000 cfs and typically ranges between 4,800 cubic feet per second (cfs) and 8,700 cfs. The average WTP flow in 2040 is 12 cfs (7.8 MGD) and 45 cfs (29 MGD) at ultimate buildout. The proposed withdrawals for a regional surface WTP would be less than 1% of the seasonal flow. DNR begins to restrict water usage from the Mississippi River at 2,000 cfs near Ramsey. 2.2 Groundwater The Northwest Metro communities currently gets the majority of its drinking water from 17 wells drilled in the Tunnel City-Wonewoc (TCW) aquifer. The remainder of the water is purchased from the City of Maple Grove. 2.2a Regional Aquifers Several groundwater aquifers exist in the Northwest Metro study area including from shallowest to deepest; Quaternary aquifers, St. Peter, Prairie du Chien-Jordan, Tunnel City-Wonewoc, and the Mt. Simon-Hinckley. Only the TCW and Mt. Simon-Hinckley aquifers exist over the majority of the Northwest Metro area and can relied upon for municipal scale drinking water wells. The Mt. Simon- Hinckley aquifer is a protected resource in the Metro area and new high capacity wells are generally not permitted by Minnesota Law. If a communities does not have other viable options, a variance can be granted by the Minnesota Department of Natural Resources for Mt. Simon-Hinckley wells. New wells in this report are assumed to be drilled in the TCW aquifer because it is the aquifer that is consistently available and legally allowed. 2.2b Regional Groundwater Supply In 2016, the Metropolitan Council along with the support of HDR completed a study on the groundwater supply within the Northwest Metro regional area (Regional Water Supply, Enhanced Groundwater Recharge, and Stormwater Capture and Reuse Study(Northwest Metro Study Area) Report, December 2016). The study was one of several studies to support an update to the Twin Cities Metropolitan Area Master Water Supply Plan (Minn. Stat., Sec. 473.1565) and other activities identified by the 2005 Minnesota Legislature to address water supply needs of the seven-county metro area. As part of these activities, the Metropolitan Council modeled the existing source water aquifers to evaluate current and future drawdown of the aquifers and discussed the potential for using alternative water sources or increasing water recharge to the source water aquifers. The 2016 study concluded that the existing source water aquifers are expected to see an increase in drawdown at existing municipal well sites under the predicted 2040 water demand. Areas within the Northwest Metro area could see drawdown in their bedrock aquifers between 10 - 40 feet. To compensate for the excessive drawdown, the report discusses the use of alternative water supplies such as surface water, stormwater reuse, and the potential for enhanced groundwater recharge. Page—10 1 METROPOLITAN COUNCIL