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2007-11-28 CC Packet
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2007-11-28 CC Packet
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<br />According to the Bedrock Geology and Structure Map of the Seven-County Twin Cities Metropolitan <br />Area (Mossier and Tipping, Minnesota Geologic Survey, 2000) for the project area, the uppermost <br />bedrock units with the project area are the St. Peter Sandstone over much of the project area, with the <br />Prairie du Chien Dolomite present as the first bedrock unit over the northern and western edges of the <br />project area. The Prairie du Chien is present over the entire project area, but is overlain by the St. Peter <br />over much of the project. <br /> <br />Where the Prairie du Chien is present as the first bedrock unit, it is generally found at the depth <br />between 50-100 feet, classifying the area as being a "transition karst" area, as opposed to an "active <br />karst" area where depth to carbonate bedrock is less than 50 feet deep. In general, areas of transition <br />karst do not typically experience hazards such as sinkholes unless changes are made to local <br />topography to reduce depth-to-bedrock. However, a minor risk for karst features developing in the <br />project area does exist simply due to the nature and depth of the bedrock in the area. <br /> <br />Soils <br />According to Anoka County soils information, the soil types listed in the following table are identified <br />in the project area. <br /> <br />SOIL TYPES <br /> <br />Hydrologic <br />Symbol Soil Name Special Significance * Soil Group * * <br />(HSG) <br /> <br />Alluvial land, mixed, fre uentl <br /> <br />Blomford loam fine sand <br /> <br />Cut and fill land <br /> <br />Dundas loam <br /> <br />Ha den fine sand loam, 2-6% slo es <br /> <br />Hayden fine sandy loam, <br /> <br />6-12% slo es, eroded <br /> <br />NeA Nessel fine sand loam, 1-4% slo es B <br /> <br />Wb Webster loam BID <br /> <br />Af Alluvial land, mixed, fre uentl flooded H dric D <br /> <br />" Hydric soils, prime farmland soils and other important farmland soils were identified using the USDA NRCS online Soil Data <br />Mart tool for Anoka County, Minnesota. Prime farmland, as defined by the USDA, is land that has the best combination of <br />physical and chemical characteristics for producing food, feed, forage, fiber, and oilseed crops and is available for use in these <br />areas. The designation is not meant to include land that is urban or built up. Soils designated as farmland of statewide <br />importance are not considered prime but are still considered of value for agricultural use. <br />""The hydrologic soil group refers to soils grouped according to their runoff-producing characteristics. The chief consideration is <br />the inherent capacity of the soil bare of vegetation to permit infiltration. The slope and kind of plant cover are not considered <br />but are separate factors in predicting runoff. Soils are assigned to four groups. In Group A are soils having a high infiltration <br />rate when thoroughly wet and having a low runoff potential. They are mainly deep, well drained, and sandy or gravelly. In <br />Group D, at the other extreme are soils having a slow infiltration rate and thus a high runoff potential. They have a c1aypan or <br />clay layer at or near the surface, have a permanent high water table, or are shallow over nearly impervious bedrock or other <br />material. A soil is assi ned to two h drolo ic rou s if art of the acrea e is artificiall drained and art is undrained. <br /> <br />Af <br />Bm <br />Cu <br />Du <br />HdB <br />HdC2 <br /> <br /> <br />D <br />BID <br /> <br /> <br />BID <br />B <br />B <br /> <br />In general, water moves through coarse textured soils at a faster rate than through medium or fine <br />textured soils. Therefore, potential impacts to ground water from spilled chemicals would be expected <br />to be greater in areas with coarse textured soils. However, many factors in addition to soil granularity <br />can affect infiltration and percolation rates in soils. Some of these factors include: soil water content, <br />soil frost, the temperature of soil and water, surface roughness, the nature of the soil pore openings, <br />vegetative ground cover, and the degree of soil compaction. <br /> <br />Centerville <br />Downtown Redevelopment <br /> <br />Page 25 <br />
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