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generally coarse sand with pebbles. As mentioned above, the Anoka • <br />Sand Plain extends into the northwest part of the District. In the north <br />central and northeast portion of the watershed are deposits of till, <br />consisting of loamy sand and clay. <br />Figure II-2 in the CRWD Plan shows the bedrock for the District. <br />Bedrock geology in the City of Falcon Heights consists of Decorah <br />Shale, which acts as a confining layer. The Decorah Shale is green <br />calcareous shale with thin limestone interbeds. <br />The Platteville and Glenwood Formations underlie the Decorah Shale. <br />The Platteville consists offine-grained dolostone and limestone. The <br />Glenwood consists of thin green sandy shale (3-5.5 feet thick). <br />4.3.4 Soils <br />The soils of the City of Falcon Heights are found in Figure 10 on the <br />following page. The main soil classification groups are based on <br />hydrologic features of the soils. Hydrologic soils groups are used to <br />estimate runoff from precipitation. Vegetation, soils composition, and <br />slope area are all used to determine the soils runoff potential. There are <br />four hydrologic groups, Table 5, below, provides a summary of the four <br />hydrologic soil groups. <br />Table 5 -Soil Classification <br /> }~ ,~ . <br /> Soils having high infiltration rates when thoroughly wet (low <br />A runoff potential). Deep, well drained to excessively drained <br /> sand or gravelley sand. <br /> Soils having a moderate infiltration rate when thoroughly <br />B wet. Moderately deep or deep, moderately well drained or <br /> well drained with moderately to moderately coarse texture. <br /> Soils having a slow infiltration rate when thoroughly wet. <br />C Soils that have a layer that impedes the downward movement <br /> of water or soils of moderately fine texture or fine texture. <br /> Soils having very slow rates of infiltration when thoroughly <br /> wet (high runoff potential). Soils consists of clays with high <br /> shrink-swell potential, soils that have a permanent high water <br />D table, soils that have a claypan or clay layer at or near the <br /> surface and soils that are shallow over nearly impervious <br /> materials. <br />Urban Areas of development that are covered by asphalt, concrete, <br />Land and buildings. <br />Data from SCS. 1977. <br />TComprehensive Plan UpdateT <br />Ciry of Falcon Heights <br />AFAL000701.00 <br />Page 22 <br /> <br />r, <br />~J <br />