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capacity, dual HSGs are usually considered as D soils. The most current soils data within the watershed are <br />based on the Soil Survey Geographic dataset (SSURGO) from the NRCS and are presented in Figure 2-5. <br />Portions of the watershed are not rated with respect to HSG. The "Not Rated/Not Available" classification <br />is typically assigned to areas where development has altered the existing soil, or data were unavailable <br />prior to development. Development may increase the potential for high volumes of runoff. As land is <br />developed for urban use, much of the soil is covered with impervious surfaces, and soils in the remaining <br />areas are significantly disturbed and altered. Development often results in consolidation of the soil and <br />tends to reduce infiltration capacity of otherwise permeable soils, resulting in significantly greater <br />amounts of runoff. Grading, plantings, and tended lawns tend to dominate the pervious landscape in <br />urbanized areas and may become more important factors in runoff generation than the original soil type. <br />Figure 2-5 provides general guidance about the infiltration capacity of soils. Site specific data such as <br />geologic borings, piezometers, and other engineering studies are necessary to evaluate soil infiltration <br />capacity for individual project sites. <br />2-1 1 <br />