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• When topsoil stockpiles are not associated with structures identfied in Rule 4.05.2(4), where routing topsoil <br />stockpile runoff to a sedimentation pond for treatment is not feasible, and where the topsoil stockpile is not <br />within a drainage controlled by a sedimentation pond, a small area exemption (SAE) will be utilized. <br />Catchment sumps will be constructed to completely contain the runoff from topsoil stockpiles. Where no <br />runoff volume is calculated, a catchment sump will not be constructed. The location of the existing small area <br />exemption stockpiles and associated catchment sumps are shown on <br />Exhibits 13-2, 13-2A, and 133. <br />Stockpile area J, TT, XX and AAA will have ditches and sumps constructed to contain potential runoff <br />sediment once topsoil is removed from the stockpile area and will be maintained until the areas are <br />revegetated. The SEDCAD results for the four (4) areas are included in Addendum 3. Table 13-8-1, 2 <br />and 3 contain summaries of the SEDCAD results. <br />Design Analysis <br />General. Catchment basins and ditches are designed to completely contain the runoff from the 10-year, 24 <br />• hour storm event without experiencing any discharge. This will demonstrate that the disturbed area of The <br />topsoil stockpiles meet the requirements of Rule 4.05.2(3)(a). <br />Hydrology. The hydrology of the watershed of the topsoil pile was analyzed utilizing the SEDCAD computer <br />program. Tab 13, Attachment 13-1 contains a description of the design methods and a listing of the SEDCAD <br />input variables. <br />Input consists of precipitation amount (inches), watershed area (acres), time of concentration (hours), and <br />runoff curve number (CN). <br />The precipitation depth fora 10-year, 24hour storm event was 1.6 inches. The time of concentration was <br />assumed to be between 0.02 and 0.04 hours. Since this tc is less than 0.125 hours, SEDCAD assumes an <br />instantaneous hydrogreph. <br />The curve number ranged from 86 for new topsoil piles to 61 for a well vegetated stockpile. For the TAHR <br />topsoil stockpiles, a curve number of 61 was assumed, based on vegetation cover data. <br />• <br />TR-50 13-6-1 Revised 10/05 <br />