Agenda - Public Works Committee - 10/19/2021

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Chapter 2 — Water Supply Quality and Quantity The regional water supply approaches evaluate two sources of water: the Mississippi River and groundwater, focusing on the Tunnel City-Wonewoc aquifer. This section provides information about the water quality and quantity of each supply in the study area vicinity of relevance to designing a drinking water system. 2.1 Mississippi River The following sections discuss Mississippi River water quality, constituents of concern, and regulated constituents. 2.1a Water Quality In the Twin Cities metro area, the Mississippi River serves as the primary drinking water source for Minneapolis and St. Paul and the communities they serve with wholesale or retail water. These long- serving drinking water systems provide a historic record of water quality and treatment practices as a reference to define system components for a Northwest Metro area regional surface water treatment system. It is common practice to treat Mississippi River water using a lime softening process with various filtration methods. The closest water quality monitoring site to a potential intake for a new regional water treatment plant is located in Anoka, less than 2 miles downstream of the Dayton/Ramsey border. MCES has been collecting field and laboratory analyzed samples at this site for over 45 years. The Anoka monitoring site is the primary reference source for water quality characterization in this study. Other data sources reviewed include data maintained by the Minnesota Department of Health (MDH) at Fridley, MCES' monitoring at Fridley and MDH data for St. Cloud, to provide a reference point upstream of the Crow River confluence. This study focused on a subset of constituents important when considering surface water as a source for drinking water. Constituents of interest in planning for conventional drinking water treatment processes are categorized in this study as primary constituents of interest. This list is expanded to summarize the full list of constituents regulated for public drinking water supplies. Historic data is also reviewed for other monitored constituents not currently regulated for drinking water supplies to identify any constituents that may have been detected. Appendix A provides information on the data sources, monitoring site locations, data analysis methods, and a more comprehensive compilation of water quality data. Surface water sources, including the Mississippi River, have a wider range of potential contaminants than groundwater due to intentional and unintentional discharges to the river. This could include runoff, wastewater treatment discharges, and accidental releases. A discussion of regulated contaminants and potential future regulations is presented in Section 2.1 c. 2.1 b Primary Constituents of Interest Historic data for constituents of interest in selecting and designing drinking water treatment processes are listed in Table 2-1. The average concentrations and variability are generally similar to what is observed for other surface WTPs along this upper stretch of the Mississippi River. Conventional treatment processes with accepted best practices are able to treat these constituent concentration ranges. Page—7 1 METROPOLITAN COUNCIL