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Page 17 <br /> <br /> <br />11. Geology, Soils, and Topography/Landforms: <br /> <br />a) Geology - Describe the geology underlying the project area and identify and map any <br />susceptible geologic features such as sinkholes, shallow limestone formations, <br />unconfined/shallow aquifers, or karst conditions. Discuss any limitations of these features <br />for the project and any effects the project could have on these features. Identify any <br />project designs or mitigation measures to address effects to geologic features. <br /> <br />Per the Sherburne County Local Water Management Plan, “the County is comprised of primarily <br />sandy soils; quaternary glacial till, lacustrine sand, various outwash deposits, and floodplain <br />alluvium, which were deposited during the last glacial stage of the Pleistocene epoch (Wisconsin <br />stage). The County lies almost completely within the Anoka Sand Plains, a broad area that was a <br />former lake. Sand dudes, kettle lakes, and tunnel valleys are prominent features” (4). The <br />geology of the project area is expected to be similar to that of the County. <br /> <br />Surficial Geology <br />The surficial geology across Sherburne County primarily consists of sands and gravel deposited <br />during the final stages of glacial retreat (18). The surficial geology identified on the Minnesota <br />Geologic Atlas within the project area is of the Holocene and Pleistocene era. Full unit <br />descriptions are included in Appendix C. <br /> Qtu – Upper terrace <br />o Surface ranges in elevation from approximately 880 feet in the County's <br />southeast corner (18). <br /> Qa – Sand, sandy loam to silt loam <br />o Generally, coarse-grained sediment (sand and gravel) in the channels and <br />finer-grained sediment (fine-grained sand and silt) on floodplains coarsens <br />with depth. <br />o Along the Mississippi River, the unit consists of generally less than 6 feet (2 <br />meters) of silt loam to loamy sand overlaying sand, gravelly sand, or cobbly <br />gravel, with scattered wood and shell fragments (18). <br /> Qtl – Lower terrace <br />o Surface ranges in elevation from approximately 870 feet in the County's <br />southeast corner (18). <br /> <br />Bedrock Geology <br />“Sherburne County is almost completely covered by Quaternary glacial till, lacustrine sand, <br />outwash deposits, terrace deposits, swamp deposits (peat), and floodplain alluvium” (18). The <br />bedrock geology identified on the Minnesota Geologic Atlas within the project area is <br />summarized below. Full unit descriptions are included in Appendix C. <br /> Ctc – Tunnel City Group (Upper Cambrian) <br />o Ranges from less than 135 to approximately 180 feet in thickness in the map <br />area and is missing because of erosion over much of the County. <br />o Divided into two formations: the upper Mazomanie Formation, and the lower <br />Lone Rock Formation.” <br />o Most of the Lone Rock Formation in Sherburne County consists of the