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35715 HIGHWAY 40 <br /> 1%6,X BUILDING B, SUITE 120 <br /> A L B E R T F R E T & SONS EVERGREEN, CO 80439 <br /> MAIN (303) 289-1837 <br /> vtu <br /> September 30, 2021 <br /> OCT Q 5 202, <br /> Email to Peter.haysCa-),state.co.its <br /> Reclamation, Mining and Safety , <br /> c/o Peter Hays <br /> 131 erman Street, Room 215 <br /> Denver, CO 80203 <br /> Re: AFS Response to Walstrum AM-09 Geotech Adequacy Review #3 <br /> Dear Peter: <br /> Enclosed please find the AFS response to the Geotech Review#3 comments by Zach Trujillo <br /> dated September 26, 2021. <br /> DRMS Geotech Review#1 August 31, 2021 Comments: <br /> When comparing the Division's slope profile to that of the provided profiles with the <br /> supplemental information, it appears that the angle of slope used for the low strength rock do not <br /> match. Using a 45-degree angle for the low strength rock, the Division's slope profile appears to <br /> be angled steeper than that which was provided with the supplemental information. When <br /> measuring the provided slope angles within AutoCAD, the maximum angle discovered was 40 <br /> degrees. This difference in a higher angle would result in the lower factor of safety as observed <br /> with the Division's results for the sensitivity analysis. This leads the Division to believe that <br /> perhaps there is a typo in Table 5 within the Exhibit and a lesser angle of slope was used for the <br /> sensitivity analysis to result in a factor of safety of 1.15 under pseudo-static conditions. <br /> • Please have Walstrum confirm the angle used for the low strength rock in the sensitivity <br /> analyses that result in the factors of safety provided in Table 5 of the Exhibit. <br /> AFS Response September 14, 2021: The Division correctly identified an error in Table 5, which <br /> also occurs in Appendix I. Using a hypothetical material with slope of 35 degrees in the <br /> sensitivity analysis, the resulting Factors of Safety are 1.15 for 10-ft-thick Xb and 0.95 for 20-ft- <br /> thick Xb. See Attachment 5 for the updated page 31 of 35 with corrected Table 5 (Geotechnical <br /> Stability Exhibit). See Attachment 6 for the updated page 4 of 8 with corrected Figures 7 and 8 <br /> (Geotechnical Stability Exhibit, Appendix I). <br /> Pagel of 3 <br />