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-54- <br />prepared in conformance with the current state-of-the-art of <br />geotechnical science. The report does propose one variance from normal <br />waste pile practice. The variance requested within the report is the <br />deletion of a specific underdrain system beneath the initial waste rock <br />pile. The consultant bases this request upon the impermeable nature of <br />the upper most 50 feet of foundational subsoil beneath the proposed <br />waste pile, the relatively small volume of the waste pile, and the <br />proposed impermeable 4.0 feet of cover material. The Division agrees <br />with the consultants recommendations and waives the underdrain <br />requirement. <br />West Elk Coal Company applied for a permit revision to allow the <br />construction of an upper waste rock pile in October of 1984. The <br />operator had noted its intention to construct an upper waste pile in <br />the original permit application. The permit revision application <br />represented the submission of a detailed engineering plan for that <br />structure, for which a general plan had earlier been submitted. <br />West Elk Coal proposes, within the amended permit revision application, <br />to construct a five million ton coal processing waste pile. The refuse <br />will consist of coarse coal reject and development waste rock. The <br />mine projects waste production at a rate of 150,000 tons for the first <br />year and 100,000 tons per year thereafter. The completed waste pile <br />structure will cover approximately 40 acres,. and attain a maximum <br />thickness of 160 feet. <br />The waste pile will have 2.5 H: 1V (horizontal to vertical) facial <br />slopes with 30 foot wide benches at 50 foot vertical intervals. The <br />overall final facial slope will be approximately 3 H:1V (horizontal to <br />vertical slope of approximately 18.2 degrees) in order to facilitate <br />reclamation. Samples of currently produced waste were collected and <br />tested, in order to provide material properties for a mathematical <br />stability analysis. Samples were also collected and tested of subgrade <br />colluvium and bedrock for the same purpose. The stability analysis <br />projected a minimum static slope.safety factor of 1.64 for an overall <br />facial slope of 2.5 H:1V, steeper then the requested configuration. <br />At the request of the Division, West Elk Coal Company also completed an <br />analysis of the potential stability affects upon the F-Seam, from the <br />placement of a five million ton surcharge load upon the existing <br />workings within the mine. The plan calls for approximately the eastern <br />half of the waste pile to be undermined. In completing this analysis, <br />the operator assumed: <br />1. An ultimate configuration of the waste pile reaching <br />elevation 6,880 feet above sea level: <br />2. No secondary extraction beneath the pile. <br />No barrier pillars, even though one is planned. <br />,l <br />