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~ ~ <br />LJ <br />1.0 INTRODUCTION <br />The Bowie Mine No. 2 is a subsurface coal mine owned and operated by Bowie Resources LLC <br />(Bowie). The Bowie Mine No. 2 is located north of Bowie Road, approximately 3.5 miles <br />northeast of Paonia, Colorado. The mine produces approximately 5 million tons of coal per <br />year. Coal waste from the preparation plant as well as some high ash coal is disposed at a coal <br />mine waste bank located immediately north of Colorado State Highway 1336. Buckhorn <br />Geotech, Inc. (BGI) has been retained by Bowie to evaluate stability of the Coal Waste Disposal <br />Area No. 2 (CWDA No. 2). Our initial stability evaluation is documented by a 2006 report (BGI, <br />2006). This report presents an updated stability evaluation based on monitoring of vibrating- <br />wire piezometers and inclinometers carried out over the past three years. <br />2.0 PROJECT BACKGROUND <br />The Bowie CWDA No. 2 is located immediately north of Bowie Road near the bottom of an <br />unnamed drainage designated `~D-Gulch" in the permit documents. Placement of coal mine <br />waste commenced in 2004. Foundation preparation included construction of two underdrains <br />with laterals as well as upland surface water diversion channels. The coal mine waste primarily <br />consists of waste from the preparation plant and some high ash coal. Native soils have been <br />blended with the coal waste during construction to improve workability and compaction. <br />A summary of the geotechnical work performed to date for CWDA No. 2 follows. As <br />construction of the waste pile has progressed, we have gathered valuable data that allow for <br />better characterization of the waste at this site which allows us to refine our stability evaluation. <br />Lambert and Associates (2003) performed the original geotechnical evaluation of the CWDA <br />stability. That study included a geotechnical drilling investigation of the foundation materials, <br />shear strength testing on remolded samples of unprocessed coal waste, and a preliminary <br />stability evaluation. The CWDA No. 2 was permitted in March 2004. Placement of coal waste <br />commenced in July 2004. <br />Lambert (2005) present a stability evaluation of the waste pile with 2H: iV toe slope from 0 to <br />50 feet. The slope above was varied for the analyses. A 5.5H:iV upper slope was found to <br />result in a factor of safety of 1.50 or greater. The model parameters for this study were based <br />on unconsolidated-undrained (UU) triaxial shear tests on remolded samples. No pore pressures <br />were reported from these tests. <br />BGI was retained by Bowie in 2005 to provide another evaluation of the stability of the CWDA <br />No. 2. Another geotechnical drilling investigation was conducted with several objectives: (i) <br />better characterize strength of the coal mine waste (placement of coal mine waste had <br />commenced at this point); (ii) install vibrating wire piezometers to monitor actual pore <br />pressures, (iii) install inclinometers to monitor deformation of the waste material; and (iv) to <br />provide a stability evaluation the CWDA. Consolidated-undrained (CU) triaxial shear tests were <br />conducted on both remolded and thin-walled (Shelby) tube samples of placed coal mine waste. <br />Total stress and effective stress analyses were conducted to evaluate undrained (end of <br />construction) and drained (long-term) conditions. The undrained analyses indicated an upper <br />Bowie No 2 2008 Reevalution of Coal Mine Waste Stability.doc <br />Project #OS-126-GEO <br />Page 3 of 15 <br />