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Custom Soil Resource Report <br />Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned <br />to one of four groups according to the rate of water infiltration when the soils are not <br />protected by vegetation, are thoroughly wet, and receive precipitation from long- <br />duration storms. <br />The four hydrologic soil groups are: <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 consist <br />chiefly of moderately deep or deep, moderately well drained or well drained soils that <br />have moderately fine texture to moderately coarse texture. These soils have a <br />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 soils <br />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 potential, <br />soils that have a high water table, soils that have a claypan or clay layer at or near the <br />surface, and soils that are shallow over nearly impervious material. These soils have <br />a very slow rate of water transmission. <br />If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for <br />drained areas and the second is for undrained areas. <br />Surface runoff refers to the loss of water from an area by flow over the land surface. <br />Surface runoff classes are based on slope, climate, and vegetative cover. The concept <br />indicates relative runoff for very specific conditions. It is assumed that the surface of <br />the soil is bare and that the retention of surface water resulting from irregularities in <br />the ground surface is minimal. The classes are negligible, very low, low, medium, high, <br />and very high. <br />The months in the table indicate the portion of the year in which a water table, ponding, <br />and/or flooding is most likely to be a concern. <br />Water table refers to a saturated zone in the soil. The water features table indicates, <br />by month, depth to the top (upper limit) and base (lower limit) of the saturated zone in <br />most years. Estimates of the upper and lower limits are based mainly on observations <br />of the water table at selected sites and on evidence of a saturated zone, namely <br />grayish colors or mottles (redoximorphic features) in the soil. A saturated zone that <br />lasts for less than a month is not considered a water table. <br />Ponding is standing water in a closed depression. Unless a drainage system is <br />installed, the water is removed only by percolation, transpiration, or evaporation. The <br />table indicates surface water depth and the duration and frequency of ponding. <br />Duration is expressed as very brief if less than 2 days, brief if 2 to 7 days, long if 7 to <br />30 days, and very long if more than 30 days. Frequency is expressed as none, rare, <br />occasional, and frequent. None means that ponding is not probable; rare that it is <br />unlikely but possible under unusual weather conditions (the chance of ponding is <br />nearly 0 percent to 5 percent in any year); occasional that it occurs, on the average, <br />once or less in 2 years (the chance of ponding is 5 to 50 percent in any year); and <br />frequent that it occurs, on the average, more than once in 2 years (the chance of <br />ponding is more than 50 percent in any year). <br />29