2022-02-23_PERMIT FILE - M2021059 (13)

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To: Mr. f'etcr flays Date: FcbMar�, 21, 2022 Page 15 Slide-2D. We can provide the modeling files to DRMS upon request. The analysis utilized the characterization from over 35 boreholes that show the materials are at sandy gravels and gravely sands. Telesto used the minimum shear strength (with no cohesion) from literature values for those materials. Thus, the analysis meets the "worst-case scenario" request indicated in Comment 34 (although the regulations do not require worst-case scenarios). Comment 35 The Geotechnical Stability cover letter states the analysis shows that LRM can excavate the pits wet using a large excavator, but that the excavator will require a working platform roughly 16'x20'to distribute the load. The platform requirement is not discussed in Exhibit D — Mining Plan. Please revise Exhibit D to incorporate the requirements of the geotechnical stability report. Response 35 Attachment 13 updates Exhibit D. Updates in Sections 6.1.2 and 6.2 specify that LRM mine at slopes and with appurtenances indicated by the slope stability analyses presented in Appendix B 1 (Attachment 12). Comment 36 The Applicant selected a required factor of safety (FOS) of 1.3 from Table I — Recommended Minimum Factors of Safety for Slope Stability Analyses for Operations and Reclamation. The selected FOS is for strength measurements resulting from multiple tests. The Division does not agree the Applicant's utilization of the results of particle-size distributions and boring logs qualifies as tests. The Division will require the Applicant to meet a factor of safety of 1.5, unless laboratory strength tests were performed on soils at the site. Response 36 It is our experience that laboratory testing will produce strength parameter results weaker than the lowest literature values for the identified materials, and that identifying the types of materials present is extremely important. Regardless,we have re-calculated the stability analysis utilizing a FOS of 1.5. As infrastructure is designed for construction(e.g.,bridge abutments, access roads)and mining commences, LRM will collect samples for laboratory strength tests. They will update the slope stability analysis based on those results and submit a technical revision at that time to use a FOS of 1.3 and update safe mining slopes. Comment 37 In the Conclusions section of the stability report, the Applicant states it is safe for DRMS's reclamation slope of 2H.•1 V, and can be steepened to 1.78H.•I V during mining as long as 20220209_1045_DRMS_Adequacy_Revietiv_Response_MASTE Rdocx TELEST®