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ti ~ • • <br />design because an examination of the highwalls as they have been exposed have provided <br />the basis to steepen the highwall. The catch bench height will be reduced to 75 feet (from <br />80 feet), the interbench angle will be steepened to 79 degrees (from 72 degrees), the <br />interbench offset will be eliminated and the overall slope angle will be increased to 60 <br />degrees. <br />Stability of the overall slope was evaluated using an effective friction angle of 40 degrees, <br />a cohesion factor of 0 - 10,000 psi and a groundwater pressure of 0 psi. The resulting <br />factors of safety were 0.5,1.75, 7.0 and 60.0 for various percentages of intact rock within the <br />potential failure pathway. The operator contends that approximately 10% of the critical <br />potential failure pathway will pass through intact rock so, accordingly, the FOS for the 60 <br />degree slope is computed to be 7.0. As further evidence of stability, the operator states that <br />"several areas well within the Mine boundary have been mined at the 60 degree slope as a <br />test of the stability of this configuration" and that "these areas are standing well". <br />Overall slope angles, interbench angles, etc., are not a big concern to the Division during <br />mining operations. However, the Division does have a concern about highwall stability after <br />mining ceases (during and after reclamation). The operator should have sufficient data, <br />prior to initiating reclamation, to determine whether or not the mined highwalls will remain <br />stable for the long-term at the 60 degree overall slope angle just in case a revision to the <br />permit is necessary to incorporate the revised mine wall design. <br />I concur with Mr. Hardaway's statement that CC&VG has satisfied the information <br />requirement it committed to with respect to the strength of the Cresson ore. <br />If you need anything else let me know. <br />M: \oss\kmg\ 1126JD I.1D I <br />