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Hydrologic Soil Group—Snohomish County Area,Washington <br /> Hydrologic Soil Group <br /> Hydrologic Soil Group—Summary by Map Unit—Snohomish County Area,Washington(WA661) <br /> Map unit symbol Map unit name Rating Acres in AO1 Percent of AOI <br /> 5 Alderwood-Urban land B 4.0 100.0% <br /> complex,2 to 8 <br /> percent slopes <br /> Totals for Area of Interest 4.0 100.0% <br /> Description <br /> Hydrologic soil groups are based on estimates of runoff potential. Soils are <br /> assigned to one of four groups according to the rate of water infiltration when the <br /> soils are not protected by vegetation, are thoroughly wet, and receive <br /> precipitation from long-duration storms. <br /> The soils in the United States are assigned to four groups (A, B, C, and D) and <br /> three dual classes (A/D, B/D, and C/D). The groups are defined as follows: <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 /> If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is <br /> for drained areas and the second is for undrained areas. Only the soils that in <br /> their natural condition are in group D are assigned to dual classes. <br /> Rating Options <br /> Aggregation Method: Dominant Condition <br /> 1:,i>A Natural Resources Web Soil Survey 3/1/2017 <br /> Conservation Service National Cooperative Soil Survey Page 3 of 4 <br />