5.4. SR 09-07-2004 - Laserfiche WebLink

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a. Approximate depth (in feet) to groundwater: (approximate water elevation 944) Existing conditions: 0 minimum; 20 maximum; approximately 5 average Operating Conditions: minus 45 minimum; 20 maximum (deepest base of mining elevation 900) Restored Conditions: minus 45 minimum: 6 maximum (restored elevation will range from approximately 950 to 900) Depth to bedrock: (top of bedrock elevation approximately 825) Existing conditions: 125 minimum; 140 average Operating Conditions: 75 minimum; 120 average (deepest base of mining elevation 900) Restored Conditions: 75 minimum: 120 average (restored elevation will range from approximately 944 to 900) 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. Sinkholes or other karst conditions, or shallow limestone formations do not exist in the area of the Site. The general geologic and hydrogeologic conditions in the vicinity of the Site were described in the Environmental Impact Statement (EIS) prepared for the Elk River Gravel Mining District, Elk River, Minnesota, prepared by Maier Stewart and Associates, Inc (MSA), dated May 1994 (the 1994 EIS). As the mining district surrounds the property on three sides, the conditions described in the EIS are applicable to the site. The following discussion is a summary of the geology and hydrogeology of the Elk River Gravel Mining District, copied from the 1994 EIS. "The mining district is situated on the northwestem edge of a major regional structural feature termed the Twin Cities Basin. The general geology of the mining district and vicinity consists of a sequence of glacio-fluvial deposits overlying an erosional surface of Paleozoic sedimentary bedrock units. Bedrock formations in the area dip southeastward, towards the center of the basin." "The surficial deposits and topography result from at least two major glacial events. The glacial depositional event responsible for many of the larger landforms in the region, occurred as a result of advance of the St. Croix phase of the Superior Lobe (Helgeson, Ericson and Lindholm, 1975). This glacial advance occurred from the northeast and deposited a sandy till that is characteristically red in color. The terminal moraine, formed by stagnation of the St. Croix lobe, trends northwest-southeast through the region and forms the core of many of the regions larger geomorphic features. The Grantsburg Sublobe of the Des Moines Lobe subsequently advanced through the region from the northwest and deposited a characteristic calcareous grey till with shale fragments. The Grantsburg till was the last major glacial depositional event in the region. Typically, the St. Croix glacial features are reworked with, and overlain by, a relatively thin veneer of Des Moines Lobe outwash sands and till. The Anoka sand plain is situated east of the mining district and was formed during 12