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• POWDEKHORN COAL COMPANY CRDA <br />SMALL AREA EXEMPTION <br />STOCKPILE 5 (5E) <br />STOCKPILE 0 (NW) <br />Cameo Refuse Disposal Area Number 1, shown on Powderhorn Coal Company Map 913, contains 2 <br />areas where Small Area Exemptions (5AE'5) will be evaluated. The first 5AE 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 5EDCAD 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 5E1)CAD 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 />is 3. The roughness coefficient, .02, was used. <br />4. An infiltration rate of .15 was recommended by the Author of 5EDCAD 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 5EDCAD 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 />The SEDCAD calculation resented on pages 14 -6 -86 through 14 -6 -102 were <br />prepared by me or unde) a sgtgn during the month of May 2001, and the <br />information presented irjWsand correct- `tp'the best of my knowledge and belief. <br />Sto�u��.E. <br />R a��Prpjesal Engineer <br />• Sta jes" 0.19230 <br />14-6-86 New 5/01 <br />