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GEOTECHNICAL ADEQUACY COMMENTS Mt. Gunnison No. 1 -- Upper Waste Pile West Elk Coal Company has proposed the construction of a 9 million ton upper coal processing waste pile at their Mt. Gunnison No. 1 underground coal mine, located near Somerset, Colorado. This structure is proposed to be located on a topographic bench situated above the existing portals of that mine with a toe elevation of approximately 6660' above mean sea level. The completed pile would reach a maximum thickness of approximately 200' with a maximum facial slope of 2:1 (horizontal to vertical gradient). Facial slope configuration would include 30' wide terrace benches at 50' vertical intervals. The pile is proposed as a life of mine facility. A 2,500' length of 30' wide haul road is proposed to transport waste to the pile site for placement. This waste structure was addressed as a general plan in the original approved permit for the Mt. Gunnison No. 1 mine. The application includes extensive material testing data regarding the current underground development waste produced at the mine. The applicant commits, on page 13 of the application, to performance of additional materials testing on eventual coal processing plant waste when it is produced, in order to verify the design values used in the engineered design and stability analyses. However, the application fails to state that these results will be submitted to the Division. It will be necessary for the Division to require submittal of all testing results, in order for the Division to complete a determination of whether or not redesign or reanalysis is necessary. The permit revision application presents the results of extensive and prudent sensitivity-type analyses of the slope stability of the proposed pile's configuration. The Division finds these analyses to be acceptable for the purpose of demonstrating the structure's internal integrity, assuming foundation on a stable base. The Division is concerned, however, regarding the potential effect of placing a 9 million ton surcharge load above the partially extracted F-seam. The waste pile location overlies the area of the main entries of the Mt. Gunnison No. 1 mine. The application states that the pile foundation is separated vertically from the F-seam mine workings by between 110' to 550' of overburden. In relation to this overburden thickness, the Division suspects that the average 160' thickness of coal processing waste may represent a significant additional load. The immediate bedrock orientation represents an approximately 5o dip downslope into the adjoining val]ey of the North Fork of the Gunnison River. As the application observes, the area of the surface facilities has experienced recent surficial landslide movement. Observations within the existing mine workings, beneath the proposed location of the upper waste pile, have determined that a problematic floor clay exists beneath the F-seam and that unique differential consolidation related phenomena have resulted in the development of open penetrating roof cracks in areas of the mine underlying the proposed waste piie site. For all of these reasons, the Division believes it is appropriate to require the operator to complete an analytical determination of the effect of the proposed waste pile's construction upon lateral stability of the F-seam.