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Colowyo has responded that, because the toe buttress is part of the existing ground and not <br />a designed buttress, no change has been made as a result of the Division's question. The <br />Division's question was whether certain dimensions of the existing bedrock toe buttress had <br />been incorporated into the Shannon and Wilson design. If so, then it would be important <br />that the physical dimensions of the buttress not be inadvertently altered in the field by earth- <br />moving activities. Please review the assumptions made for Section D-D' in the S&W study, <br />and provide the details (if any) of the minimum bedrock toe buttress dimensions that will be <br />part of the fill. <br />Response: Although the material is described as bedrock, it can be observed on the actual slope <br />stability plot in the report that the strength parameters assigned to this stratum for <br />stability analysis were conservatively set as less than those set for the spoil. In fact <br />the rock material would be expected to be considerably stronger than the spoil. The <br />analysis run in this manner does not require it to be any stronger than the spoil, and <br />therefore the presence or absence of the rock material at the toe (Stratus 3) become <br />moot. The safety factor for the analysis is therefore the same as if the rock buttress <br />was not there and the spoil feathers to zero thickness at the toe. <br />Rule 4.14 - Backfilling and Grading <br />26. Response Accepted. Colowyo has changed the post-mining topography based on the <br />questions contained in the Division's preliminary adequacy letter. These changes have <br />adequately addressed this question. <br />27. Response Accepted. Colowyo's changes to the post-mining topography have <br />adequately addressed this question. Please note that the Division still has concerns <br />regarding the swell factor, as detailed in question 2 above. <br />Response: Colowyo is confident that the response given in question 2 will minimize the <br />Division's concerns regarding the swell factor. <br />Comments Regarding Shannon and Wilson Report <br />28. The Division's original adequacy question is as follows: In the process of conducting <br />the TR-81 adequacy review, the Division revisited the earlier Shannon and Wilson Study <br />and Addenda Nos. 1 and 2. A discrepancy was noted in the transcription and utilization of <br />data, as follows: Table B-1 in Appendix B presents a "Summary of Laboratory Test Results <br />by Boring". Data in the Direct Shear "Cohesion" and "Friction Angle" columns, for Borings <br />CO-3 and LW-1, appears to have been incorrectly transcribed from Figures B-4 and B-5, <br />the original reports prepared by Knight-Piesold Consulting. Corrected friction angles for <br />CO-3 and LW-1 would be 24 and 33 degrees, respectively. Similarly, the tabulated <br />cohesion values for these two samples should actually have been 370 and 40 psf. The <br />incorrect numbers shown in Table B-1 appear to have been used in the development of the <br />Average Friction Angle and Cohesion values reported in Table C-1 for "Soil", which <br />parameters were in turn used for input into the Slope/W program. Inclusion of these <br />erroneous values may have resulted in Factors of Safety that were inaccurate (too high). <br />Please review the information presented in Appendices B and C of the original Study, and <br />revise as appropriate, including any conclusions or recommendations that may change as a <br />result of the review. (We note that corrected friction angle and cohesion values from Boring <br />CO-3 appear to have been used in the Shannon and Wilson study submitted with TR-81.)