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1 <br />J <br />STATE OF <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanment of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FAX: (303)832-8106 <br />DATE: September 3, 1994 <br />TO: Erica Crosby <br />.~- <br />FROM: Jim Pendleton <br />RE: Roadside/ ame e, Technical Revision No. 18 <br />Stability ysis of Waste Pile CRDA #1 <br />[Permit No: C-81-041] <br /> <br />J <br />DEPARTMEN-T OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />lames 5 Lochhead <br />Eneculive Director <br />Michael B. tong <br />Division Director <br />Powderhorn Coal Company suspended use of Waste Pile CRDA #1 at the <br />Roadside/Cameo Mine in 1986. Seeps had been noted on the face of <br />the pile and the Division and OSM had questioned the pile's <br />stability. Coincidentally, market conditions for coal had worsened <br />and the Mine effectively entered temporary cessation, rendering it <br />unnecessary to continue deposition of waste material on the pile. <br />Powderhorn Coal requested permission to defer the completion of a <br />reanalysis of the pile's stability until such time as it proposed <br />to commence deposition of waste on the pile. <br />Powderhorn is now requesting permission to commence the deposition <br />of waste material on waste pile CRDA #1. The operator contracted <br />Western Engineers of Grand Junction to complete an appropriate <br />reanalysis of the waste pile's stability in order to satisfy the <br />conditions placed upon its use by the Division in 1986. <br />In response to your request I have completed a review of Phases 1 <br />and 2 of the CRDA #1 stability analysis. Candidly, Western <br />Engineers has summarized one of the most complete hydrologic field <br />investigations and most comprehensive embankment stability analyses <br />I have encountered in my 27 year professional career. <br />The field hydrologic investigation, including extensive analysis of <br />the 30 isolated zonal piezometers installed in 5 newly installed <br />monitoring bores, has characterized a extremely complex series of <br />perched aquifers, connected by an intricate network of transient <br />flow paths. This fits the method of material placement. Perhaps <br />more importantly, Western has applied that understanding to the <br />completion of comprehensively modeled stability analyses of two <br />critical cross-sections within the structure. They have also <br />completed "sensitivity-style" analyses to investigate what <br />