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Mountain Coal Company West Elk Mlne Post 01fke Banc 591 Somerset, Coloreeo 91434 Tekptgne 9708?9-5075 Faz 970 9?&5595 JAN 21 1997 January 14, 1997 Mr. Michael Boulay Colorado Division of Minerals and Geology 1313 Sherman Street, Room 215 Denver, CO 80203 Divi~inn nt rv~inyr~y~g ti G.,r?p~nQy RE: Minor Revision No. 206; Rest ;Elk Mine; Permit No. C-80-007 Dear Mr. Boulay: III IIIIIIIIIII~IIII sss ~` Mountain Coal Company (MCC) is providing this minor revision application to clarify the record in regard to the correspondence between the Colorado Division of Minerals and Geology (CDMG) and MCC on the stability analysis performed on the redesigned Lower Refuse Pile (LRP) per Technical Revision No. 78 (TR#78). The correspondence occurred following the approval of the redesigned LRP, which was approved by CDMG on May 20, ] 996. The design presented in TR#78, and all subsequent analyses of the design, was completed by Harding Lawson Associates (I-II,A). During the final review of the technical revision application, CDMG requested a color plot of the gradation of the various refuse samples tested for sheaz strength pazameters and an explanation from the laboratory testing firm explaining the labeling of the percentages of the fines for the tests. MCC provided the requested information in a letter dated July 11, 1996. In a letter dated June 20, 1996, CDMG forwarded a memorandum from Jim Pendleton outlining concerns regarding the LRP reconfiguration. The concerns were related to the Phase V slope stability analysis and that the analyses did not address the presence of a perched ground water table within the refuse pile. Dr. Pendleton stated that he beheved the stability analyses, which assumed non-saturation of the refuse, was inwrect. MCC provided a response to Dr. Pendleton's concerns in a letter dated August 12, 1996. The response included a revised slope stability analyses for the LRP using a slope stability program called GEO-SLOPE. The revised analyses showed the minimum factor of safety with a perched ] 0-feet water table and 10 percent coal fines was 1.45. It was HLA's opinion, based on their long-term working and monitoring experience with the LRP, that the 1.45 factor of safety is within the margins of tolerance for non- failure of the LRP slopes. The 10-feet thick perched water table was an assumed worst-case situation. On November 12, 1996, a letter was written by CDMG summarizing their review of the revised stability analyses. CDMG agreed that the methodology and modeled distributions were