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EXECUTIVE SUMMARY <br />Buckhorn Geotech has conducted a stability evaluation of a proposed new coal wastepile, <br />designated Gob Pile No. 3, for Bowie Mine No. 2, near Paonia, Colorado. The proposed site is <br />located in the North Fork valley bottom, approximately one-third mile southwest of the existing <br />Gob Pile No. 2. <br />A geotechnical site investigation was conducted to characterize the subsurface conditions at the <br />proposed footprint for the gob pile. Seven boreholes were drilled to depths of 40 to 90 feet. <br />Foundation soils encountered consisted of damp to moist, stiff to hard, silty clay with variable <br />gravel and cobble content to clayey gravel and cobbles. Open standpipe piezometers installed in <br />each borehole indicated depths to groundwater of approximately 19 to 58 feet during December <br />2006 and January 2007. A laboratory testing program was conducted to determine index <br />properties for the foundation soils and strength parameters of the gob and foundation soils. <br />Previous strength testing conducted on placed gob from the existing Gob Pile No. 2 is <br />referenced. <br />Conventional two-dimensional static limiting equilibrium stability analyses were conducted to <br />evaluate the proposed Gob Pile No. 3. Both total and effective stress analyses were conducted <br />and both circular and block-type failure surfaces were evaluated for three cross-sections. The <br />gob slopes and ultimate wastepile height were optimized to achieve minimum factors of safety <br />with respect to stability of 1.50, Several gob pile configurations are presented that have a critical <br />• factor of safety of at least 1.50. Recommendations are provided to ensure an adequate stability <br />margin for the gob pile during and following construction. <br />r~ <br />LJ <br />Bowie Gob Pile No. 3 stability report <br />Project#06-481-002 <br />Page 3 of 17 <br />