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!'~ <br />HYDROLOGIC DOCI7MENTATION <br />SMALL AREA EXEMPTION <br />NORTH SAE <br />The following calculations demonstrate the amount of sediment fence or straw <br />bales surface area required to adequately handle the runoff from the D-Seam <br />Portal Pad north outslope. <br />Runoff volume and peak discharge calculations were performed utilizing the <br />SEDCAD 4 computer model consistent with the methodology previously discussed in <br />this Exhibit. The sediment control structure was designed to handle the peak <br />discharge from a 10-year, 24-hour storm event. <br />1 Hydrology Inputs <br />All hydrology inputs are shown on the SEDCAD 4 computer printouts. <br />The CN numbers used for the SAE watershed were obtained from Procedures <br />for Determining Peak Flows in Colorado and Technical Release No. 55 <br />(USDA-SCS, 1980)and consistent with previously approved hydrology <br />reports. Based on soil type and vegetation cover, curve numbers were <br />determined using Table 2-2a and 2-2d, USDA-SCS TR-55, for the following <br />conditions: <br />Disturbed <br />Soil Type: C and large & small boulders <br />Ground Cover: NA <br />Cover Type: NA <br />CN: 90 <br />Area: 0.25 ac <br />2 Hydrology Results <br />Peak Discharge In <br />10-year, 24-hour event <br />Peak Discharge Out - Silt Fence <br />10-year, 24-hour event <br />Peak Discharge Out - Straw Bales <br />10-year, 24-hour event <br />0.24 cfs <br />0.24 cfs <br />0.24 cfs <br />- 3. Sediment -Fence-Requirements' <br />Sediment Fence Permissivity <br />Required Surface Area: <br />10 gal/min/ftz or 0.022 cfs/ftZ <br />0.24 cfs / 0.022 cfs/ftZ = 11 ft2 <br />The silt fence should be installed in accordance with the manufactures <br />recommendations. Design assumes regular inspections and maintenance. <br />4. Straw Bale Requirements <br />Straw bale Permissivity: 14 gal/min/ftZ or 0.031 cfs/ftZ <br />Required Surface Area: 0.24 cfs / 0.031 cfs/ftZ = 8 ft2 <br />MR-(~¢ <br />Gov ~ ZDD2 <br />