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r 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Nalu ral Resources ~~oF~co~~ Ns 1313 Sherman St., Room 215 Denver, CO 80203 Phone: (303 866-3567 ~ • /evc • FAX: 1303) 832-8106 Roy Romer Governor Michael B. Long November 24, 1993 Division D~rectar Ms. Kathleen Welt Mountain Coal Company P.O. Box 591 Somerset, CO 81434 RE: Adequacy Review; Technical Revision No. 66; West Elk Mine; File No. C-80-007 Dear Ms. Welt; The Division has reviewed Mountain Coal Company's response to our adequacy review of your application for Technical Revision No. 66, which proposes a minor reconfiguration of the west facing slope of the refuse pile in order to repair a slump and buttress the spring which initiated the slump. The Division has the following additional concerns: 1. As drawing 2.oA, Proposed Landslide Remediation, will be inserted into Exhibit 51, MCC should provide an updated table of contents for this exhibit. The Division finds the schedule to monitor the new survey monuments on a quarterly basis acceptable. The results of the survey should be submitted along with the survey results for the north face monuments. The Division would recommend the surveys begin during the first quarter of 1994. The Division continues to believe the installation of a piezometer is appropriate. If properly installed, the piezometer should not allow the communication of fluid pressure. A properly installed piezometer, like a monitoring well, should be isolated to contact only the zone of interest. In this case the piezometer should be installed perhaps five feet outside the gravel french drain to determine whether the refuse is saturated above the elevation of the french drain, which the french drain is intended to prevent. The piezometer should be cased with plastic pipe, perforated for the lowermost five feet, and then gravel packed through the perforated interval. Finally, it should be sealed with bentonite to prevent the communication of fluids.