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• <br />The SEDCAD 4 calculations presented on the following pages demonstrate a silt fence 20-feet <br />long will treat the run-off from a 0.5 acre generic site so the peak setteable solids concentration <br />in the run-off are less than 0.5 ml/I. The following table presents data that indicates the <br />drainage area from the generic overburden stockpile area is larger than the South Fan <br />Overburden Stockpile Nos. 10 and 11, the 2 West Overburden Stockpile No. 13 and the 2 West <br />Portal Substation drainage areas. Therefore, a 20-foot long silt fence will be utilized for <br />sedimentation control at the following reclaimed areas. <br />Overburden Stockpiles <br />Overburden Stock files <br /> Area -Acres Run-off Acre-ft <br />South Fan Overburden Stockpile No. 10 <br />= 135' x 45' CN 89 1.4" Storm 0.14 0.006 <br />South Fan Overburden Stockpile No. 11 <br />= 70' X 150' CN 89 1.4" Storm 0.24 0.012 <br />Data From A endix 13-3 <br />2 West Overburden Stock file No. 13 0.202 0.009 <br />2 West Portal Substation 0.18 0.008 <br /> <br />Overburden Stock files -Generic 0.5 0.023 <br />• <br />• <br />Notes for SEDCAD Calculation <br />1. 10-year 24-hour storm event 1.4°. <br />2. The Lazear soil type, hydrologic soil group "D" was utilized to remain consistent with <br />Appendix 13-3. <br />3. A curve number of 89 for the disturbed areas is derived from Table 2-2a Run-off curve <br />numbers for urban areas -Dirt (including right-of-way), <br />4. Soil K factor of 0.24 represents a sandy loam and fine sandy loam soil. <br />5. A "C" factor of 0.52 for the disturbed (reclaimed) run-off areas indicates 1/4 tons of <br />straw mulch per acre, Figure 8 "C" Values for Quantities of Mulch, SCS Technical Notes <br />#50, January 1977. <br />6. Drainage areas are relatively small. Areas are calculated utilizing maps SL-16-009 and <br />Exhibit 58 and verified with field measurements where required. <br />7. Silt fences will be constructed on the contour down gradient of all run-off. The peak <br />stage for the silt fence is 0.38-feet. Therefore 1.5' high berms will be utilized to collect <br />and direct run-off to the silt fences. <br />The SEDCAD calculations and information presented on pages 14-6-45 through 14-6-52 were <br />prepared by me during the month of August 2000, and the information presented is true and <br />correct to the best of my knowledge and belief. <br />James E. Stover, P.E. <br />Registered Professional Engineer <br />State of Colorado No. 19230 <br />14-6-44 <br />Date <br />New 8/00 <br />