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<br /> <br />~II ~~~~I~~I~~~~~ ~~~ <br />STATE OFCOLORADO RiCHARDD LAMM Governor 999 <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Director <br />MINED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 866-3567 <br />David C. Shelton <br />Director <br />December 28, I98I <br />TO: Tom Gillis <br />FROM: Jim Pendleton " <br />RE: Review of E ibit .9.A, submitted by ARCO Coal Company in <br />Conformance Stipulation No. 14, Permit No. C-007-80 (OSM <br />Permit Stipulation No. 31) <br />Pursuant to your request, I have reviewed Exhibit 3.2.9.8, entitled "Preliminary <br />Stability Evaluation, Upper Waste Rock Pile, Mt. Gunnison Coal Mine, for ARCO <br />Coal Company", prepared by Geo-Nydro Consulting, Inc. This report represents <br />a comprehensive but preliminary analysis. As such, it assumes ground water <br />and material strength parameters in completing a "sensitivity-type" analysis. <br />This analysis finds that the upper bench above the Mt. Gunnison No. 1 mine <br />portals can be utilized to deposit wastes if certain recommendations are <br />followed: <br />(1) Any future waste pile should be carefully designed prior to construction. <br />(2) Based upon the results of the preliminary analysis, the toe of the waste <br />pile should be inset at least 150 feet from the crest of the upper bench. <br />(3) No waste material should be deposited directly above underlying mine <br />entries. <br />(4) Subsidence effects will have to be evaluated once the mining method <br />below the pile is determined. <br />(5) The operator should investigate actual ground water conditions beneath <br />the bench and evaluate their impact upon stability during and following <br />cessation of mining. <br />(6) Dewatering of the bench area should be accomplished. <br />(7) It will be necessary to install an appropriate surface drainage system <br />above the proposed waste pile. <br />(8) Prior to the driving of any mine entries beneath the proposed area of <br />the upper waste pile, an appropriate surface monitoring system should be <br />installed to detect any deformation of the upper bench or the slope between the <br />crest of the bench and the portal entries. <br />~ - r <br />