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C-1981-019 TR-81 14 July 2010 AR#2 - mlt Page 5 of 6 the bedrock toe buttress had been incorporated into the S& W design. If so, then it would be important that the physical dimensions of the buttress not be inadvertently altered in the field by earth-moving activities. Please review the assumptions made for Section D-D' in the S&W study, and provide the details (if any) of minimum bedrock toe buttress dimensions. 28(l) In the process of conducting the TR-81 adequacy review, the Division revisited the earlier S&W Study and Addenda Nos. 1 and 2. We note a discrepancy in the transcription and utilization of data, as follows: Table B-1 in Appendix B presents a "Summary of Laboratory Test Results by Boring". Data in the Direct Shear "Cohesion" and "Friction Angle" columns, for Borings CO-3 and LW-1, appears to have been incorrectly transcribed from Figures B-4 and B-5, the original reports prepared by Knight-Piesold Consulting. Corrected friction angles for CO-3 and LW-1 would be 24 and 33 degrees, respectively. Similarly, the tabulated cohesion values for these two samples should actually have been 370 and 40 psf. The incorrect numbers shown in Table B-1 appear to have been used in the development of the Average Friction Angle and Cohesion values reported in Table C-1 for "Soil", which parameters were in turn used for input into the Slope/W program. Inclusion of these erroneous values may have resulted in Factors of Safety that were inaccurate (too high). Please review the information presented in Appendices B and C of the original Study, and revise as appropriate, including any conclusions or recommendations that may change as a result of the review. (We note that corrected friction angle and cohesion values from Boring CO-3 appear to have been used in the S&W study submitted with TR-81) Colowyo responds that the new S& W Addendum No. 3 effectively supersedes all previous geotechnical studies, including tabulated material strengths and computer based slope stability analyses. While this may be true, the tabulated data should be accurate to the extent possible. The Division withdraws its request to re-run the Slope/W models, but reiterates the requirement to update the data in Tables B-1 and C-1. Please review the information presented in Tables B-1 and C-1 and revise as appropriate. 29(2) The overall footprint of the Excess Spoil fill areas does not appear to have been revised between the July 2006 Study and the first two Addenda. Significant changes are proposed, however, with Addendum No. 3, dated October 21, 2009. The spoil configuration has been revised, and outslopes have been steepened, to allow sizable temporary spoil fills to be placed over the permanent spoil fills. Additional laboratory testing has been performed on spoil and clay soil overburden, and on the Carbonaceous Mudstone (CMS) layer exposed on the floor of the pit. New Figures 1 thru 6 are presented, along with a new Appendix A. There is potential for future confusion with respect to the new "Addendum". Addendum No. 1 and Addendum No. 2 consisted of minor modifications to the original S&W Study, and updated specific Figures or Tables while maintaining the original order. Addendum No. 3 includes a new set of Figures (1 thru 6) that do not correlate with Figures 1 thru 9 of the July 2006 Study. A new "Appendix A" has been provided, which does not appear to be designed to replace the current Appendix A. If you wish to name the October 2009 study "Addendum No. 3", we suggest renumbering the accompanying Figures beginning at "10" and changing the Appendix from "A" to "D". Alternatively, it may be simpler to eliminate the "Addendum" reference and give the current study its own title. Please revise the contents of the October 2009 S&W study to correlate with the existing Exh. 21, Item I Study, or eliminate the "Addendum " tie to the previous Study.