Agenda - Public Works Committee - 10/19/2021

Home

Chapter 4 — Regional Surface Water Treatment Plant (Approach 1) 4.1 Overview Several Minnesota communities have the Mississippi River as their source of drinking water, including St. Cloud, St. Paul Regional Water Services (SPRWS), and Minneapolis. An advantage to using the Mississippi River is that a large quantity of water can be accessed from one spot (versus numerous wells). 4.2 Surface WTP Locations Two locations are being considered for a potential surface water treatment plant, including a location in Ramsey and a location in Dayton. These WTP locations are meant to serve as examples only and specific parcels and/or property owners were not identified. Figure 4-1 identifies the potential WTP locations. The City of Ramsey is in the feasibility stage of constructing a water treatment plant to remove manganese (See Section 5.3a). The proposed location of the Ramsey water treatment plant is the same location shown on Figure 4-1. 4.3 River Withdrawal Options Two options were considered for withdrawal from the river including collector wells and a direct withdrawal from the river through an intake structure. 4.3a Collector Wells Collector wells are large capacity horizontal wells that take water from a a shallow sand layer in the vicinity of the river. Because the water from a collector well has travelled through the surrounding sand, the water quality is often better than water taken directly from a surface water source. This requires a significant thickness of sand and gravel with limited clay or - silt. A previous MCES report (Regional Water Supply, Enhanced Groundwater Recharge, and Stormwater Capture and Reuse Study, Northwest Metro Area, MCES, 2016) reviewed the geology along the Mississippi River in Dayton and Ramsey. It was determined that relatively few locations in the area would be suitable for horizontal collector wells. It is assumed that horizontal collector wells are not a suitable option for this study. 4.3b Direct River Withdrawal Location 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 Appendix A). 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. Page—21 1 METROPOLITAN COUNCIL