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• POWDERHORN COAL COMPANY GRDA <br />SMALL AREA EXEMPTION <br />STOCKPILE 5 (5E) <br />570CKPILE 6 (NW) <br />Cameo Refuse Disposal Area Number 1, shown on Powderhorn Coal Company Map 9B, contains 2 <br />areas where Small Area Exemptions (5AE's) will be evaluated. The first SAE is on the <br />Northwest corner of the pile, referenced as Stockpile 6, the second SAE is on the Southeast <br />corner, referenced as Stockpile 5. Both areas were examined using SEDCAD 4 to show that a <br />grass filter will effectively treat the site so that the peak settleable solids concentration in the <br />runofF are less than 0.5 ml/I. <br />Notes for SEDCAD 4 Calculation: <br />1. 10-year 24-hour storm event 1.4" <br />2. Exhibit 23, Soils map, shows the area as Type 15 "Cameo". There is no defined soil group <br />associated with the "Cameo" soil, but generally soil samples for this area and other disturbance <br />areas classifies the soil to be sandy to silty loam (Tab Section 9, Appendix 9-5) which equates <br />to a "B" soil group. <br />• 3. The roughness coefficient, .02, was used. <br />4. An infiltration rate of .15 was recommended by the Author of SEDCAD for a Soil Group "B" <br />(sandy loam). <br />5. A stiffness factor of 2 was used. <br />6. Time of concentration, Tc, was calculated in the SEDCAD 4 program based on site area and <br />gradient. <br />7. A curve number of 72 represents the Desert Shrub, Soil group B, in fair condition. <br />8. A "K" factor of .24 represents a loam, and fine sandy loam. <br />9. A "C" factor of .35 represents brush. <br />ER'S CERTIFICATION <br />The SEDCAD calculation, ~c~presented on pages 14-6-86 through 14-6-102 were <br />prepared by me or und~l~y' e s ~41S9c~n during the month of May 2001, and the <br />information presented ~r~sand correct-`tp'the best of my knowledge and belief. <br />~g ^ <br />:*~G 23 ~ *! 5~i/oL <br />~o,iame Sto~ut~ .E. ate <br />R a~~Prp(e~s~al Engineer <br />• Sta ~es" 0.19230 <br />14-6 -86 New 5/01 <br />