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South Fan Borrow Area <br />The SEDCAD 4 calculations presented on the following pages demonstrate a silt fence 50-feet <br />long will treat the run-off from this 1.32 acre site so the peak setteable solids concentration in <br />the run-otf are less than 0.5 ml/I. As shown in the following table, the drainage area at the <br />South Fan borrow area is larger than the 2 West South Portal, 2 West North Portal and <br />South Fan drainage areas. Therefore, the same 50-foot long silt fence will be utilized for <br />sedimentation control at the following reclaimed areas. <br />South Fan Borrow Area <br /> Area -Acres Run-off Acre-ft <br />Data From A endix 13-3 <br />South Fan -Bench and To soil Stock ile 0.455 0.018 <br />2 West Portal -North Portal 0.119 0.004 <br />2 West Portal -South Portal 0.244 0.009 <br /> <br />South Fan Borrow Area - Ma SL-16-009 1.32 0.05 <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 85 for the undisturbed areas represents sage brush with grass <br />understory in poor condition. <br />4. 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 />5. Soil K factor of 0.24 represents a sandy loam and fine sandy loam soil. <br />6. A "C" factor of 0.45 for the undisturbed run-off areas indicates 0% ground cover and no <br />appreciable canopy from Figure 7 "C" Factors for Permanent Pasture and Rangeland, <br />SCS Technical Notes #50, January 1977. <br />7. 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 />S. 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 />9. Silt fences will be constructed on the contour down gradient of all run-off. The peak <br />stage for the silt fence is 0.36-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 14-6-36 through 14-6-43 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. Date <br />Registered Professional Engineer <br />State of Colorado No. 19230 <br />14-6-35 New 8/00 <br />