Agenda Packets - 2021/07/06 - Laserfiche WebLink

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In one period of retreat during the Superior lobe glaciation, melt waters deposited a thick layer of glacial outwash made up of sand and gravel over a widespread area including Mounds View. Another layer of till subsequently covered this outwash. This period of glacial activity lasted from about 30,000 to about 20,000 years ago. The more recent Grantsburg sublobe glaciation took place between 20,000 and 10,000 years ago. The Grantsburg sublobe, in addition to moving and redepositing materials from the Superior lobe, deposited new materials over the area. As the Grantsburg sublobe retreated and melted, these changes formed large streams that carried significant amounts of sands. These streams deposited broad level plains of sand and gravel that are referred to as the Anoka Sandplain. 2.5 GROUNDWATER In Ramsey County, there are four main drinking water aquifers present. In order of depth from shallow to deep, they are: The Quaternary Drift aquifer: found in sand and gravel glacial deposits. Yields from the drift aquifer can vary widely based on the permeability of the sediments. The Prairie du Chien -Jordan (PDCJ) aquifer: comprised of both dolomite bedrock and underlying sandstone bedrock. Yields can range from 1000-2000 gpm (gallons per minute) for most large diameter municipal wells completed in this aquifer in areas where the full thickness of the aquifer is present and fully saturated. This aquifer is the most widely used aquifer in portions of the Twin Cities area where it is present for municipal water supply systems. The Franconia -Ironton -Galesville (FIG) or Tunnel City-Wonewoc (TCW) sandstone aquifer: three bedrock units with layers of moderate to highly permeable sandstone. Yields can range between 300- 1000gpm for large diameter wells in this portion of the Twin Cities area. Current nomenclature refers to the FIG as the TCW, however FIG is still often used. The Mount Simon -Hinckley aquifer: located beneath the Eau Claire bedrock formation, a siltstone, shale, and silty sandstone -confining layer that is between this aquifer and the Franconia -Ironton -Galesville aquifer. Yields typically range between 500-1000gpm for large diameter municipal wells. The City of Mounds View currently operates five municipal wells. Well Number 1 is a multi -aquifer well open to both the FIG aquifer and the Mount Simon -Hinckley aquifer. Well Number 2 is a single -aquifer well open to the Mount Simon -Hinckley aquifer. Well Number 3 is a single -aquifer well open to the PDCJ aquifer. Well Number 5 is open to the PDCJ aquifer. Well Number 6 is a multi -aquifer well open to the PDCJ, FIG, and Mt. Simon aquifers. At present, the Minnesota Department of Natural Resources (MnDNR) has restricted cities in the Twin Cities area from drilling any additional Mt. Simon -Hinckley aquifer wells unless no viable options remain for those cities. They are restricting this use to limit the usage of this aquifer in order to ensure that aquifer withdrawals do not exceed the recharge that naturally replenishes the aquifer. The MnDNR will allow cities like Mounds View that already have existing Mt. Simon -Hinckley wells to continue to use them at their currently permitted discharge rates. Any future wells that Mounds View may need to install will most likely be required to be completed in one of the other three aquifer units, most likely the PDCJ or FIG aquifers. Figure 2.3 shows Drinking Water Supply Management Areas (DWSMAs) within the City. Note that some of these DWSMAs are protecting groundwater sources in neighboring communities. DWSMA boundaries are City of Mounds View 6 Local Surface Water Management Plan Stantec Project No. 193804166 5 5tantec