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Custom Soil Resource Report <br /> Engineering Properties <br /> This table gives the engineering classifications and the range of engineering <br /> properties for the layers of each soil in the survey area. <br /> Hydrologic soil group is a group of soils having similar runoff potential under similar <br /> storm and cover conditions. The criteria for determining Hydrologic soil group is <br /> found in the National Engineering Handbook, Chapter 7 issued May 2007(http:// <br /> directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17757.wba). <br /> Listing HSGs by soil map unit component and not by soil series is a new concept for <br /> the engineers. Past engineering references contained lists of HSGs by soil series. <br /> Soil series are continually being defined and redefined, and the list of soil series <br /> names changes so frequently as to make the task of maintaining a single national <br /> list virtually impossible. Therefore, the criteria is now used to calculate the HSG <br /> using the component soil properties and no such national series lists will be <br /> maintained. All such references are obsolete and their use should be discontinued. <br /> Soil properties that influence runoff potential are those that influence the minimum <br /> rate of infiltration for a bare soil after prolonged wetting and when not frozen. These <br /> properties are depth to a seasonal high water table, saturated hydraulic conductivity <br /> after prolonged wetting, and depth to a layer with a very slow water transmission <br /> rate. Changes in soil properties caused by land management or climate changes <br /> also cause the hydrologic soil group to change. The influence of ground cover is <br /> treated independently. There are four hydrologic soil groups, A, B, C, and D, and <br /> three dual groups, A/D, B/D, and C/D. In the dual groups, the first letter is for <br /> drained areas and the second letter is for undrained areas. <br /> The four hydrologic soil groups are described in the following paragraphs: <br /> Group A. Soils having a high infiltration rate (low runoff potential)when thoroughly <br /> wet. These consist mainly of deep, well drained to excessively drained sands or <br /> gravelly sands. These soils have a high rate of water transmission. <br /> Group B. Soils having a moderate infiltration rate when thoroughly wet. These <br /> consist chiefly of moderately deep or deep, moderately well drained or well drained <br /> soils that have moderately fine texture to moderately coarse texture. These soils <br /> have a moderate rate of water transmission. <br /> Group C. Soils having a slow infiltration rate when thoroughly wet. These consist <br /> chiefly of soils having a layer that impedes the downward movement of water or <br /> soils of moderately fine texture or fine texture. These soils have a slow rate of water <br /> transmission. <br /> Group D. Soils having a very slow infiltration rate (high runoff potential)when <br /> thoroughly wet. These consist chiefly of clays that have a high shrink-swell <br /> potential, soils that have a high water table, soils that have a claypan or clay layer at <br /> or near the surface, and soils that are shallow over nearly impervious material. <br /> These soils have a very slow rate of water transmission. <br /> Depth to the upper and lower boundaries of each layer is indicated. <br /> Texture is given in the standard terms used by the U.S. Department of Agriculture. <br /> These terms are defined according to percentages of sand, silt, and clay in the <br /> fraction of the soil that is less than 2 millimeters in diameter. "Loam,"for example, is <br /> soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent sand. <br /> If the content of particles coarser than sand is 15 percent or more, an appropriate <br /> modifier is added, for example, "gravelly." <br /> 26 <br />