Agenda - Public Works Committee - 10/19/2021

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Mississippi River Water Quality Summary March 12, 2020 Page 3 Multiple Site Water Quality Comparison Sites upstream and downstream of the confluence of the Crow River with the Mississippi River were evaluated to assess the optimum location for a northwest metro area regional surface water treatment plant(WTP) intake. This preliminary assessment is based on limited data from the MDH databases and additional evaluation is necessary to fully assess water quality variations along the river. The preliminary assessment compared conventional constituents at the four sites including: total organic carbon, alkalinity, suspended solids, and turbidity. The following Figures 2 through Figure 5 demonstrate the results of these water quality constituents compared between monitoring sites. The selection of a river withdrawal location will depend on several factors, including: type of withdrawal system, river profile and geology, and proximity of known dischargers to the withdrawal location. The river depths along a portion of the study area is generally 9 feet to 12 feet deep. This stretch of the river in the study area has no permitted dischargers, but there are several WWTPs on the Crow River and upstream on the Mississippi River(refer to Figure A in the Appendix). The water quality was compared for sites upstream and downstream of the Crow River confluence. The preliminary analysis did not identify significant differences to suggest locating the intake upstream of the Crow River. However,with the ever growing concern for emerging contaminants that are not routinely tested or not yet identified, there may be merit in further evaluation of an intake location. E. Gap Analysis For future water supply characterization, additional historic data can be reviewed to better assess the optimum location for a water supply intake. The impact of the Crow River on the water supply intake location could be evaluated more closely by analyzing the water quality of the Mississippi River in a location more directly upstream of the Crow River confluence than the St. Cloud monitoring station. Pathogens of interest in planning a drinking water supply that are not monitored in the MCES program are Cryptosporidium and Giardia. Since these our routinely monitored for the WTPs treating Mississippi River water and are readily available in the MDH database, future data reviews should coordinate use of both databases.Additional information on the sample collection and analysis methods for the different monitoring programs is recommended and should be considered when comparing and utilizing multiple databases. For the purposes of this concept level study, this effort was not expended. F. Conclusion The water quality of the Mississippi River as a source for a northwest metro area regional WTP was characterized using the MCES Anoka site. The MCES database provided sampling data over a wide period of time and a large range of constituents, making it very comprehensive. The data for several constituents related to drinking water quality were analyzed statistically and, in some cases, compared with data from other monitoring sites. The analysis characterized water quality constituents of interest in determining treatment requirements and adherence to regulatory requirements. With the more than 45,800 samples analyzed, constituents with concentrations exceeding SDWA limits were limited to those that are removed through conventional treatment processes. Additional assessment is needed to better define the optimum intake location for a WTP, but general indications are that conventional constituents are not expected to have statistically significant variation along that reach of the Mississippi River, assuming best practices are used in the location of a site and method of water withdrawal from the river.