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Colowyo Coal Company, L.P. <br />Attn.: Mr. Juan Garcia <br />January 4, 2013 <br />Page 5 of 7 <br />SHANNON &WILSON, INC. <br />spoil and clay with failure surface exiting through the rock slope. The remaining cases, using <br />mean shear strength values from laboratory test results, indicated FS values of 1.8 to 2.2. <br />CONCLUSIONS AND RECOMMENDATIONS <br />In our opinion, the minimum FS of 1.3, calculated when using low -bound strength estimates, is <br />acceptable for the planned temporary excess spoil fill. Using the mean shear strength for the <br />spoil, based on laboratory testing, results in FS values in excess of 1.8. The permanent portion <br />of this fill, after re- grading to the PMT, will be considerably flatter with resulting higher FS. <br />These flatter slopes were analyzed in our study for the permanent excess spoil fill (Shannon & <br />Wilson, 2006) and meet the minimum FS of 1.5 for permanent excess spoil fills (Colorado <br />Division of Minerals and Geology, 2005, Rule 4.09.2 (1). <br />The temporary fill slope surface could direct surface water towards the South Taylor northern <br />end wall. We recommend that a surface water collection and diversion ditch be incorporated into <br />planning. The ditch should be located between the toe of the southern portion of the fill and the <br />crest of the northern end wall of the South Taylor pit. <br />CLOSURE <br />Our services were provided in accordance with our Master Service Agreement, M366. The <br />opinions and recommendations presented in this report were prepared in accordance with <br />generally accepted professional geotechnical engineering principles and practice in this area at <br />the time we prepared this report. We make no other warranty, either express or implied. If you <br />have any questions or require further information, please contact me at 303 - 825 -3800. <br />23 -1- 01105 -600 <br />