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Engineering Properties--Weld County,Colorado, Northern Part Koskie Pit 2020 Amendment <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 <br /> similar storm and cover conditions. The criteria for determining Hydrologic soil <br /> group is found in the National Engineering Handbook, Chapter 7 issued May <br /> 2007(http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx? <br /> content=1 7757.wba). Listing HSGs by soil map unit component and not by soil <br /> series is a new concept for the engineers. Past engineering references contained <br /> lists of HSGs by soil series. Soil series are continually being defined and <br /> redefined, and the list of soil series names changes so frequently as to make the <br /> task of maintaining a single national list virtually impossible. Therefore, the <br /> criteria is now used to calculate the HSG using the component soil properties <br /> and no such national series lists will be maintained.All such references are <br /> obsolete and their use should be discontinued. Soil properties that influence <br /> runoff potential are those that influence the minimum rate of infiltration for a bare <br /> soil after prolonged wetting and when not frozen. These properties are depth to a <br /> seasonal high water table, saturated hydraulic conductivity after prolonged <br /> wetting, and depth to a layer with a very slow water transmission rate. Changes <br /> in soil properties caused by land management or climate changes also cause the <br /> hydrologic soil group to change. The influence of ground cover is treated <br /> independently. There are four hydrologic soil groups, A, B, C, and D, and three <br /> dual groups, A/D, B/D, and C/D. In the dual groups, the first letter is for drained <br /> 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 <br /> thoroughly wet. These consist mainly of deep, well drained to excessively <br /> drained sands or gravelly sands. These soils have a high rate of water <br /> 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 <br /> drained soils that have moderately fine texture to moderately coarse texture. <br /> These soils 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 <br /> water 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 <br /> layer at or near the surface, and soils that are shallow over nearly impervious <br /> material. These soils have a very slow rate of water transmission. <br /> Depth to the upper and lower boundaries of each layer is indicated. <br /> USDA Natural Resources Web Soil Survey 3/24/2020 <br /> Conservation Service National Cooperative Soil Survey Page 1 of 6 <br />