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KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL <br />(2) CN values can be area weighted when they apply to pervious areas of similar CN's (within 20 <br />CN points). However, high CN areas should not be combined with low CN areas (unless the <br />low CN areas are less than 15% of the subbasin). In this case, separate hydrographs shoved be <br />generated and summed to form one hydrograph. <br />FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS INKING COUNTY <br />SOIL GROUP <br />HYDROLOGIC <br />GROUP' <br />SOIL GROUP <br />HYDROLOGIC <br />GROUP* <br />AI erwo <br />© <br />Orcas Peat <br />D <br />Arenas, Alderwood Material <br />C <br />Oridia <br />D <br />Arents, Everett Material <br />B <br />Ovall <br />C <br />Beausite <br />C <br />Pilchuck <br />C <br />Bellingham <br />D <br />Puget <br />D <br />Briscot <br />D <br />Puyallup <br />B <br />Buckley <br />D <br />Ragnar <br />B <br />Coastal Beaches <br />Variable <br />Renton <br />D <br />Earlmonl Silt Loam <br />D <br />Riverwash <br />Variable <br />Edgewick <br />C <br />Sala[ <br />C <br />Everett <br />A/B <br />`Sammamish <br />D <br />Indianola <br />A <br />Seattle <br />D <br />Kitsap <br />C <br />Shacar <br />D <br />Klaus <br />C <br />Si Sill <br />C <br />Mixed Alluvial Land <br />Variable <br />Snohomish <br />D <br />Neilton <br />A <br />Sultan <br />C <br />Newberg <br />B <br />Tukwila <br />D <br />Nooksark <br />C <br />Urban <br />Variable ) <br />Normal Sandy Loam <br />D <br />Woodinville <br />D i <br />HYDROLOGIC SOIL GROUP CLASSIFICATIONS <br />A. (Low runoff potential). <br />Soils having high infiltration rates, even when thoroughly wetted, and consisting <br />chiefly of deep, well -to <br />-excessively drained sands or gravels. These soils have a high rate of water <br />transmission. <br />B. (Moderately low runoff <br />potential). Soils having moderate infiltration rates when thoroughly wetted, and <br />consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of <br />water transmission. <br />C. (Moderately high rum.0 potential). Soils having slow Infiltration rates when thoroughly wetted, and <br />consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately <br />fine to fine textures. These <br />soils have a slow rate of water transmission. <br />D. (High runoff potential). <br />Soils having very slow infiltration rates when thoroughly wetted and consisting <br />chiefly of clay soils with <br />a high swelling potential, soils with a permanent high water table, soils with a <br />hardpan or clay layer at or near the surface, and shallow soils over nearly Impervious material. These soils <br />have a very slow rate of water transmission. <br />From SCS, TR-55, Second Edition, June 1986, Exhibit A-1. Revisions made from SCS, Soil Interpretation <br />Record, Form ft5, September 1988. <br />3.5.2-2 11/92 <br />