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STATE OF COLORADO RiCHnRD D Govcinni ItI ~II~II~II~fiII III <br />DEPARTMENT OF NATURAL RESOURCES 999 <br />D. Monte Pascoe, Executive Director <br />MIlVED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />M E M O R A N D U M <br />~.AM <br />David C. Shelton <br />Director <br />11 Decmeber 1981 <br />TO: Mike Long <br />FROM: Jim Pendleton <br />RE: Western Fvel's eque to Steepen the Facial Slopes of the <br />Waste Di o it es at the Deserado Mine <br />To document our discussion this morning concerning Deserado's request <br />to construct the waste pile with a 3h:ly facial slope, I forward the <br />following comment. As the findings document relates, the waste piles were <br />approved with an overall facial slope of Sh:ly. The stability analysis <br />submitted by Western Fuels considered a range of facial slopes from Sh:ly <br />to 3h:Iv. The analysis assumes material strengths for the materials <br />involved because the waste was not available at the time. The analysis <br />demonstrated that static slope safety factors well in excess of 2.0 would <br />be achieved at a facial slope of Sh:ly at a total height of 100 feet. <br />(Figure 7, "Geotechnical Investigation, Deserado Coal Mine, Coal Waste Banks", <br />by Chen 6 Associates, Inc., January 5, 1981) Based upon this conservative <br />factoring the operator was given the option of building at the lower slope <br />angle or verifying the assumed properties through laboratory material strength <br />testing. <br />The operator is now requesting permission to revise the waste piles <br />configuration to the least conservative facial slope of 3h:ly. This revision <br />can be formally considered. However, I feel it appropriate to require <br />discrete verification of the actual waste material shear strength properties. <br />Please advise Western Fuels to submit an appropriate revision accompanied <br />by material strength laboratory data verifying the material strength assumption <br />of density of 95 pounds per cubic foot, internal angle of friction of 22 degrees <br />and a cohesion of 200 pounds per square foot, the properties assumed in the <br />analysis. If appropriate analyses show these properties to be correct or <br />conservative I will approve the revision. If, on the other hand, these <br />tests determine that the properties assumed were inappropriately high the <br />applicant will be required to prepare an amended stability analysis of <br />the actual configuration proposed using the actual material strength <br />determined during the laboratory testing. <br />cc: Ed Bischoff <br />