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7.0 CONCLUSIONS AND RECOMMENDATIONS <br />Limiting equilibrium stability analyses were conducted for a proposed new gob pile at Bowie <br />Resources No. 2 mine near Paonia, Colorado. Both drained and undrained analyses were <br />conducted for static loading conditions. The evaluations were based on wastepile geometry <br />provided by J.E. Stover and Associates, foundation characterization conducted by Lambert and <br />Associates (200 1) along the railway south of the proposed site, and previous strength testing on <br />gob materials produced at Bowie by Buckhorn (2006). In order to verify the assumed foundation <br />conditions, a subsurface investigation should be conducted. Additionally, we recommend on- <br />going strength testing of compacted gob material and continued moisture /density testing of the <br />placed gob material. <br />Three cross - sections were evaluated for the proposed new gob wastepile. The evaluations <br />considered a maximum slope of 3H:1 V and maximum vertical wastepile heights of 70 and 90 <br />feet. The critical factor of safety determined from the analyses ranged from approximately 1.7 to <br />3.2. These factors of safety are considered to be adequate for the proposed construction. <br />However, stability of the wastepile will be contingent on careful and proper fill placement; <br />inspection, in -situ density testing, and laboratory testing of gob material, as appropriate; and <br />proper management of surface water drainage on and around the wastepile. <br />It must be emphasized that pore pressures are a crucial component of the stability of the gob <br />stockpile. The undrained shear strength of gob material is largely a function of moisture content. <br />Therefore, it is critical that gob materials are not placed wet of the optimum moisture content. <br />Consequently, at times it may be necessary to allow gob to dry prior to compaction. Once at a <br />suitable moisture content, gob should be sealed (by compaction) to minimize infiltration from <br />precipitation and should be graded to shed water per the drainage plan. <br />8.0 REFERENCES <br />Buckhorn Geotech, Inc. (2006). Geotechnical Report, Stability Evaluation of Coal Waste <br />Disposal Area, Bowie No. 2 Mine, Delta County, Colorado, February 15, 2006. <br />Dunrud, C. Richard (1989). Geologic Map and Coal Stratigraphic Framework of the Paonia <br />Area, Delta and Gunnison Counties, Colorado, United States Geological Survey, Map C- <br />115,1989. <br />Lambert and Associates (2001). Geotechnical Engineering Study, Unit Train Load Out Track <br />Alignment, Bowie Number 2 Mine, Gob Pile, Paonia, Colorado, December 6, 2001. <br />Lambert and Associates (2003). Geotechnical Engineering Study, Bowie # 2 Mine, Gob Pile, <br />Paonia, Colorado, November 10, 2003. <br />Rocscience (2004). Slide 2D limit equilibrium slope stability for soil and rock slopes, version <br />5.027, Rocscience, Inc., 2004. <br />Bowie No 2 South Gob Pile preliminary stability evaluation <br />Project #05- 126- GEO -08 <br />Page 9 of 10 <br />