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t ~II ~I~~I~~I~~~~~~I~ 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Depanmenl o! Natural Resources 1717 Sherman 51., Room 215 Denver, Colorado 80203 Phone: 13031 866-3567 FAX: ()0)1832-8106 .March 30, 1994 Mr. Ralph Lopez Environmental Engineer Basin Resources, Inc. 14300 Highway 12 Weston, CO 81091 Re: Refuse Disposal Area, New FJk Mine, Permit No. C-81-012 Basin Resources,lnc. Dear Mr. Lopez: I~~ DEPARTMENT OF NATURAL..., RESOURCES Roy Rorner Governor Ken Salazar Eaecmrve Dueaor Michael g. Long Diviswn Di,eUa In reviewing the 1991 and 1993 geotechnical analyses conducted by CTLlfhompson, Inc., on the New EIk refuse disposal area, the Division has a concern with the moisture content of the refuse. In the April 29, 1991 report by CTL/Thompson, 'Density and Stability Study, Refuse Disposal Area, New Elk Coal Mine,' the consultants', on page 10, conclusions numbers 2 and 3, expressed a concern about a wet zone within the refuse pile. CTL/Thompson stated that measures should be taken to reduce the moisture content of the refuse at the time of place- ment. On page 9 of this same report, it is stated that if drier refuse is placed on the pile in the future, then the computed safety factor would be 1.(i. A factor of safety of .8 was computed for the condition of continued placement of wet refuse without other precautions being taken. In the May 3, 1993 letter from CTL/Thompson to Basin Resources, it was stated that the consultants believed that the moisture content had been reduced from 25 to 30 percent down to 15 to 18 percent, and that this reduction in moisture occurred before disposal. Further, the consultants recommended that the refuse coming off of the refuse belt be sampled for material properties because, at that time, no refuse was coming off of the belt for them to sample. In the May 20, 1993 report from CTLlfhompson, it was stated that Basin Resources had implemented the actions as outlined in the May 3, 1993 letter, to lower the moisture content of the refuse. In a letter to the Division dated March 17, 1994 and received at the Division on March 21, 1994, Basin Resources stated that the moisture content of the refuse coming off of the belt was 25 to 30 percent. The Division has a concern with this, in that the wet material is being allowed to stand at the temporary stockpile and at temporary windrow sites until the refuse is workable for grading and compaction. This excess moisture may be draining downward into the refuse pile, potentially decreasing the factor of safety for the refuse pile as a whole or for portions of the refuse pile, such as the temporary stockpile area and the windrow area. As CTLlThompson stated in the May 20, 1993 letter, on page 3, the stability of the refuse pile is relatively insensitive to compaction. Therefore, the Proctor test results that have been obtained to date cannot be used alone to assure slope stability.