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