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• The watershed area of the topsoil piles was assumed to be the largest area, which would contribute to runoff <br />volume. The SEDCAD computer program was run to obtain runoff volumes for the topsoil stockpile <br />watershed areas. <br />Size Determination <br />Once the existing size in acres of a topsoil pile location is determined, a required catchment basin capacity <br />can be determined by utilizing SEDCAD. The capacities shown on Figure 13-8-1 are minimum required <br />capacities and must be increased to allow for adequate freeboard. For a well vegetated topsoil stockpile (CN <br />= 61), there is no runoff to contain until the watershed area of the stockpile is greater than 3.5 acres. See <br />Addendum 1 for the SEDCAD input and output. Since there is no runoff from a 10-year, 24hour stone event <br />from these well vegetated stockpiles, a catchment sump is not required. Topsoil Stockpiles A, C, D, E, F, G, <br />J, TWS, BB, TT, XX, and AAA require no catchment sumps however upon removal catchment dtches <br />and sumps will be constructed. Topsoil Stockpiles PP, OO, RR, and CCC require catchment sumps and <br />dRches. Addendum 2 contains the SEDCAD inputs and outputs for these stockpiles. <br />Construction <br />The catchment basins will be field located based on existing topography to ensure that all runoff will be <br />incepted and contained. All side slopes will be th:ty or flatter and the minimum depth shall be 3.0 feet. <br />• Figure 13-8-1 shows a typical topsoil pile catchment basin. After construction, catchment sumps will be <br />certified to ensure adequate cepacty. Table 13-8-2 shows the design and acual capacity of the constructed <br />catchment sumps. The as-built construction certification of the sumps for Topsoil Stockpiles PP, OO, and RR <br />are depicted an ExhibRs 13-BPP, 13$Op, and 13-BRR, respectively <br />Catchment Ditches <br />Catchment ditches may be utilized to contain runoff from SAE stockpiles to catchment sumps for <br />containment. Ditches will be designed as an erodible, v-ditch channel with side slopes of 1 h:1v, and 0.3 feet <br />of freeboard. Table 13-8-3 lists the catchment ditch design parameters. The catchment ditches w711 be <br />routinely inspected for erosion and maintained to ensure adequate capacity. <br />TAHR Stockoiles <br />Alf existing TAHR topsoil stockpiles (A, C, D, E, F, and G) and temporary waste stockpile (TWS) have been <br />approved as small area exemptions in TR-8. Catchment berms were constructed around the perimeter of the <br />stockpiles to divert runoff to catchment sump locations. These catchment sumps were field located to <br />contain the runoff from the stockpiles. Since these structures are no longer required, they will be regraded to <br />ensure that no water is impounded. <br />• <br />TR-50 1&8-2 Revised 10/05 <br />