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SMALL AREA EXEMPTION <br />CLEAN WATER DIVERSION t DIS'T'URBANCE AREA <br />' 1.0 INTRODUCTION <br />In an effort to eliminate minor erosion in Clean Water Diversion 1 (CWD-1), EFCI has <br />realigned a small portion of the diversion. In the process of realigning CWD-1, EFCI disturbed <br />- a small area north of the diversion which will not drain naturally to Sediment Pond 1. The <br />disturbed area has been regraded, seeded, and mulched. The total regraded area is approximately <br />0.2 acres u shown on Mine Site Water System and Refuse Map (Map 12). Runoff from the site <br />will be controlled by straw bales located along the south side of the disturbance Brea u shown <br />on this map. <br />2.0 HYDROLOGY DESIGNS <br />Runoff peak discharge calculations were performed utilizing the SEDCAD+ computer model <br />consistent with the methodology previously discussed in this permit document. The sediment <br />fence is designed to safely pass the peak discharge from a 10-year, 24 hour storm event. <br />2.1 Hydrology Inputs <br />All hydrology inputs are shown on the SEDCAD+ computer printouts (see attached). <br />The curve number (CN) used wu obtained from Procedures for Determining Pea.( Flows in <br />• Colorado and Techttica! Release No.55 (C/SDA•SCS, 1980J. Based on soil type and vegetation <br />cover, the CN was determined using Table 2-2d, USDA-SCS TR-55, for the following <br />conditions: <br />Disturbed (Mulched) <br />Soil Type: C <br />Ground Cover: Poor <br />Cover Type: Herbaceous <br />CN: 87 <br />2.2 Results <br />Peak Discharge <br />10-year, 24-hour event: 0.8 cfs ~ <br />2.3 Straw Bale Requirements <br />Given the peak discharge and permi[tivity of the sediment fence, the amount of straw bale <br />surface area required to safely pass the peak discharge from a 10-year, 24-hour event was <br />determined as follows: <br />Straw Bale Permi[tivi[y: 17 gal/min/ft' or 0.038 cfs/ft= (Bradfield, 1985) <br />• Required Surface Area: 0.8 cfs/0.038 cfs/ft7 - 21 ft= <br />Gk~~Rawn~SAEDOC <br />