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Memo to Bill York-Feirn 2 Januax•y 14, 1994 frequency, continuity, and water conditions of rock mass features. The results of the mapping program should be included in the annual report in the form of histograms, rose diagrams, stereographic projections, etc. to present the structural data, as well as a map showing locations of fracture mapping stations, and analysis of the data in terms of its impact on the pit wall criterion pr~asented in the above table. Essentially, Mobile Premix has committed to bench face angles less than or equal to the dip of adversely oriented, continuous structures - annual reporting will allow the Division to track compliance with this commitment. The 1981 and 1994 Merrill reports raise several questions that should be addressed prior to approval of TR-001. 1. What is the location of the east-west trending Jackson Gulch Fault relative to the Spec-Ag Quarry? 2. What is the maximum height of the overburden fill placed, or to be placed, on catch benches relative to catch bench width? It is the Division's stance that if the bench back-fill is to be placed in prisms with out-slopes steeper than 2:1, that compaction, incorporation of geo-grid, or some other sort of stabilization will be necessary. The operator should provide the Division with a plan outlining the methods for !back-fill stabilization, and assess the impact that compaction, etc. will have on reclamation costs. It is imperative i:hat fill placed on the benches be stable in the long term, because by completely filling the benches you lose the safet}~ benefit provided by catch benches to catch rock fall and rav~:lling or sloughing material from higher on the slope. 3. The 1981 Merrill report states that "the rock is hard and strong with the exception of the weathered and dE~composed material near the undisturbed surface". This statement should be quantified through a Rock Quality Determination. The Divisions position is that the stability of the pit walls in terms of a deep-seated failure is dependent on the quality of the rock mass, as well as the lack of large structures (faults, brecciation, etc.) behind the pit walls. Conclusions The operator's procedure for assuring pit wall stability is to quarry in such a way that adversely oriented, continuous structures are not exposed (day-lighted) in the pit walls. This is acceptable to the Division, but requires that the data base for structural geology at the pit be continually updated. The Division will also require that there be enforceable pit slope parameters in place for the quarry that are based on minimum annual geologic mapping and reporting.