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I Huddleston•Berry <br />In order to evaluate the impacts of changes in the piezometric surface on the <br />stability, HBET conducted sensitivity analyses. HBET increased the elevation of the <br />piezometric surface by 15 feet and 30 feet at BG06 -06. At BG06 -02, the piezometric <br />surface was increased to the ground surface elevation. The results of the sensitivity <br />analyses indicate that a piezometric surface elevation increase of 15 feet at the location of <br />BG06 -06 will not reduce the factor -of- safety below 1.5. However an increase in the <br />piezometric surface elevation of 30 feet at the location of B006 -06 will reduce the factor - <br />of- safety below 1.5. The results of the sensitivity analyses are included in Appendix C. <br />With regard to sensitivity of the shear strength of the gob, as discussed <br />previously, HBET believes that the drained friction angle of 30° used in the analyses is <br />conservative. HBET does not believe that a friction angle of less than 30° will be <br />appropriate for the gob material. Therefore, sensitivity analyses using friction angles of <br />less than 30° were not completed for gob pile #3. <br />4.6 Conclusions <br />As discussed previously, the analyses indicated that the proposed gob pile #3 will <br />be stable. However, changes in pore water pressures may impact the stability of the gob <br />pile over time. As a result, it is recommended that vibrating wire piezometers be <br />installed at gob pile #3 to evaluate any increases in pore pressures associated with the gob <br />placement. <br />5.0 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 />Huddleston -Berry Engineering and Testing, LLC is pleased to be of service to <br />your project. Please contact us if you have any questions or comments regarding the <br />contents of this report. <br />Respectfully Submitted: <br />Huddleston - )3erl Engineering and Testing, LLC <br />39.010 <br />�'0'Ai.'��" <br />Michael A. Berry, E. <br />Vice President of Engineering <br />X:12008 ALL PROJECTS`00489 • JE Storer Associates Ine'00489-0003 Do4sie Mine4200 - Geo'Gob Mevision T004M0003 8052114 R2 doc 5 <br />