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3.4 Results <br />Based upon DRMS Rule 4.10.4(2), a minimum Factor -of -Safety (FS) of 1.5 is <br />required for the analyses to indicate a stable condition. <br />below. <br />The results of the analyses are included in Appendix B and are summarized <br />• Circular Failure — minimum FS = 1.649 <br />• Block Failure — minimum FS = 1.794 <br />3.5 Discussion <br />As indicated above, the results of the analyses yielded factors -of -safety for the <br />existing slopes along gob pile #1 above 1.5. It is important to note that the observed <br />factors -of -safety are based upon the assumptions above regarding shear strength and <br />piezometric surface. In order to evaluate the impacts of changes in these parameters on <br />the stability, HBET conducted sensitivity analyses. The results of the sensitivity analyses <br />are included in Appendix C and are summarized in the following sections. <br />Friction Angle of Gob <br />As discussed above, HBET believes that a friction angle of 36° is appropriate for <br />the coal mine waste at gob #1. However, for conservatism, HBET conducted sensitivity <br />analyses considering a friction angle of 34°. The results indicate that gob pile #1 will still <br />have a factor -of -safety above 1.5. <br />Pore Pressures <br />Again, HBET believes that considering the piezometric surface at the original <br />base grade is conservative. However, HBET conducted sensitivity analyses by increasing <br />the elevation of the piezometric surface. An increase in the piezometric surface of 6 feet <br />would be necessary to reduce the F.S. to less than 1.5. <br />3.6 Conclusions <br />As indicated previously, the analyses indicated that the existing slopes on gob pile <br />#1 are stable. However, changes in the pore water pressures could affect the stability. <br />Currently there are no piezometers in gob pile #1. However, considering that placement <br />of coal waste at gob pile #I was completed 10 years ago, pore water pressures have likely <br />normalized such that excess pore pressures do not exist in the gob. <br />4.0 GENERAL <br />This conclusions, results, etc. in this report is based upon the information in the <br />referenced documents, current analyses, and on our experience with similar projects. The <br />conclusions are valid only for the subject project. <br />X:\2008 ALL PROJECTS\01349 -Bowie Resources, LLC\01349-0001 Bowie Mine\200 - Geo\Gob 1\01349-0001 RI 12114.doc 4 <br />