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

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5 5.1.2 By the year 2040, Ramsey will need 10.3 rviGD in firm capacity. To provide this capacity without using Wells 1 and 2, an additional 3 wells will be needed by 2040 (assuming 850 gpm per well). Groundwater Availability The City of Ramsey currently utilizes groundwater as ils exclusive source of drinking water. For planning purposes, the City needs to understand whether groundwater can continue to provide existing and future water demands. Description of the Hydrogeological Setting The following sections describe the hydrogeology (groundwater) in Ramsey. Surficial Hydrogeological Setting The surficial geology in the region is primarily associated with erosional and depositional glacial events during the Quaternary Period. Surficial aquifers throughout this region have highly variable aquifer properties. The Metropolitan Council classifies these as having a moderate to high water yield for potable use: however, il is often challenging to identify the locations for the most productive units with some areas providing little or no yield for water supply. Depending on the location, the presence of finer grained units that can act as confining layer will affect water recharge rates to these aquifers and limit the quantity of water these aquifers can supply. Surficial aquifers are often the first aquifer to be recharged and thus can be more vulnerable to contamination, Therefore, the overall water quantity and quality is described by the Metropolitan Council as variable. Bedrock Hydrogeologic Setting The bedrock underlying the City of Ramsey and surrounding areas consists of Precambrian to Ordovician age Paleozoic sedimentary strata overlying Precambrian age basement rock. While variation and extent of bedrock aquifers occur, in general five regional aquifers are described and support much of the potable water for the Twin Cities region, from oldest to youngest: (1) Mt Simon-Flinckley (2) Tunnel City-Wonewoc (3) Prairie du Chien -Jordan (4) St. Peter, and (5) Quaternary aquifers. These aquifers are hydrologically disconnected by a variety of interbedded confining layers. Regional aquifers can also be subdivided further; for example, the Tunnel City- Wonewoc Aquifer maybe be hydraulically disconnected if the Lone Rock Formation (of the Tunnel City Group) acts as a confining unit. Primary lithology, and hydrogeologic designations are summarized in the table below, from oldest to youngest, for the area. Regionally other bedrock aquifers exist that are not listed above, the following are aquifers present within the City of Ramsey area. These aquifers are discussed in detail in the following sections. Throughout the City of Ramsey, The Tunnel City group is the uppermost Bedrock unit meaning the St Lawrence and Jordan Sandstone is only sparsely present. Above these Bedrock units are unconsolidated sediment discussed in sections above. FEASIBILITY STUDY -DRAFT RAMSY 154354 Page 13