Agenda - Environmental Policy Board - 10/15/2018

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19. Geologic Hazards and Soil Conditions 19a. Approximate depth (in feet) to ground water: 4 minimum, 10 average Approximate depth (in feet) to bedrock: 120 minimum, 160 average Describe any of the following geologic site hazards to groundwater and also identify them on the site map: sinkholes, shallow limestone formations or karst conditions. Describe measure to avoid or minimize environmental problems due to any of these hazards 19b. Describe the soils on the site, giving NRCS (SCS) classifications, if known. Discuss soil granularity and potential for groundwater contamination from wastes or chemicals spread or spilled onto the soils. Discuss any mitigation measures to prevent such contamination. For an AUAR, a map should also be included to show any groundwater hazards identified. A standard soils map for the area should be included. 19a. The regional water table is four feet from the surface in low areas of the site, but average depth to groundwater is ten feet (Figure 19.1). The easily accessible water table provides a readily available source of groundwater. Bedrock units below surficial materials provide additional groundwater sources. The City of Ramsey drinking water is currently supplied by five wells. Three of these well are in, and adjacent to, the Town Center and pump water from the Franconia -Ironton -Galesville (FIG) aquifer. Details of this system are provided in Item 13. Groundwater flows at low gradients to the south- southeast towards the Mississippi River in the FIG aquifer. Surficial sediments consist of Quaternary glacial outwash composed primarily of sand and gravel (Figure 19.2). The majority of the site lies within the Langdon Terrace. The northeast edge of the site consists of the Richfield Terrace. Both Terraces are deposits of the historic Mississippi River and consist of sand layers of varying thickness overlaying till or bedrock. Boulder lags and scarps are typically found at the contact between the two Terraces. Clay layers of varying thickness are found at typical depths of 50 feet. Thickness varies and the layers do not appear to be continuous. These clay layers inhibit the downward flow of groundwater to lower bedrock units. The clay is typically mixed with sand or gravel, or has pockets of sand and gravel. Silt, clay, and hydric soils can be found at or near the surface in some areas. These materials are hydraulic barriers retaining surface water where surface water features are not reflections of groundwater. Beneath the Town Center, minimum depth to bedrock is 120 feet and average depth is approximately 160 feet (Figure 19.3). The uppermost bedrock unit below the Town Center is the Franconia Formation (Figure 19.3). The Upper Franconia is fine- to coarse - grained dolomite cemented sandstone with thin beds of shale. The Lower Franconia units are glauconitic and feldspathic well -cemented sandstone inter -bedded with thin shale layers. The two are separated by a thicker shale bed, which is far less able to transmit water, further slowing the downward flow of water to deeper aquifers. Below the 19-1