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Particular attention should be paid to the ground water <br /> and surface water hydrology of the site, pursuant to <br /> Rule 4 . 10 . 3 . Thorough material shear strength and <br /> density results should be determined through appro- <br /> priate laboratory and field testing techniques. The <br /> stability analysis should be prepared to properly model <br /> the actual site-specific Coal Basin waste pile situation. <br /> In accordance with Rule 2 . 05 . 3 (6) (c) (v) , <br /> any stability analysis " . . .shall be accompanied by a <br /> description of all engineering design assumptions and <br /> calculations and the alternatives considered in selecting <br /> the specific design specifications and methods. " <br /> As described within the text of the permanent program <br /> permit application, and shown in Exhibit II-B-8 , portions <br /> of the coal processing waste bank existed prior to the <br /> permanent program inception. In accordance with Rule <br /> 2 . 05. 3 (3) (b) (ii) , the permit application must include <br /> a compliance plan which demonstrates how the existing <br /> portions of the waste pile will be brought into <br /> conformance with the performance standards of Rule 4 . 09, <br /> 4 . 10, and 4 . 11. <br /> Reply The existing coal processing waste pile at <br /> Coal Basin has not experienced an episode of significant <br /> slope instability. The episode of April 8 , 1979 was <br /> due to the cosmetic application of some refuse and soil <br /> in a reclamation program that occured late (Nov. ) in <br /> 1978. The area in question was adjacent to the refuse <br /> belt conveyor and facing the office, bathhouse complex. <br /> It was the company' s desire to revegetate this area in <br /> the fall in order that it would have an opportunity to <br /> utilize the winter moisture for growth in the spring. <br /> The area was quickly done (in fact finished in a snow <br /> storm) . The drainage system was not completed properly <br /> which in the spring allowed all of the drainage to go to <br /> this area and collect rather than into the normal drainage <br /> pattern of the pile. The result was a saturation of <br /> this loose material that had been placed the previous <br /> fall and a slump occured. This area has a slope of <br /> approximately 3 to 1 or flatter than any part of the <br /> refuse pile. No structural failure has ever occured in <br /> the main formation of the refuse pile. <br /> Vol . 1, Chap. II, Sec. B-9-b (Add explanation on <br /> Page 71. 1) . <br /> Geotechnical analysis has been accomplished in a study <br /> by Morrison-Knudsen which is attached. <br /> 13 <br /> Vol . 2 , (Add Appendix II-B er, Refuse Disposal <br /> Study by Morrison-Knudsen, Co. ) <br />