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ICOLORADO <br /> Division of Reclamation, <br /> Mining and Safety <br /> Depa Urr,_rit rf i`laa,riI Resou, <br /> 1313 Sherman Street, Room 215 <br /> Denver,Colorado 80203 <br /> June 8,2017 <br /> Climax Mine <br /> Attn: Mr.Ray Lazuk <br /> Highway 91 <br /> Climax,CO 80429 <br /> RE: File M 1977-493; Climax Mine; Technical Revision 25 (TR25)—North 40 and McNulty Overburden <br /> Storage Facility Design Adequacy Review <br /> Mr. Lazuk: <br /> The Division of Reclamation, Mining and Safety received Technical Revision 25—North 40 and McNulty <br /> Overburden Storage Facility Design Report on May 19, 2017. The decision date for this revision is currently set <br /> at June 19, 2017. Please be advised that if you are unable to satisfactorily address any concerns identified in this <br /> review before the decision date, it will be your responsibility to request an extension of the review period. If there <br /> are outstanding issues that have not been adequately addressed prior to the end of the review period, and no <br /> extension has been requested,the Division must deny this revision. <br /> DRMS has completed the initial adequacy review of TR25. As with most revisions of this scope and complexity, <br /> there are items that will require clarification of the existing information or submittal of additional information. <br /> In the submitted design report,the post-closure seismic factor of safety(FOS)for section C as depicted on the <br /> submitted figures is reported to be 1.0. The design report states that it was prepared using the assumption that a <br /> post-closure minimum seismic FOS of>1.0 would be acceptable when calculated utilizing the maximum design <br /> earthquake event(PGA of 0.14G) and the methods and assumptions stated in the geotechnical stability analysis <br /> included as Appendix C. <br /> The"standard" DRMS minimum acceptable pseudo-static FOS for a critical structure is 1.15 when data from <br /> multiple material strength measurements is utilized. McNulty OSF would be considered a critical structure, as <br /> well as an Environmental Protection Facility(EPF) due to its size, environmental impact, and proximity to <br /> Highway 91 and the associated utility corridor. <br /> The long term stability of the McNulty overburden storage facility is a primary concern, and the currently <br /> provided seismic FOS for section C is below the minimum FOS recommended by DRMS standard practice <br /> guidance. However,the DRMS FOS guidelines are based on general best-practices, and do not consider all <br /> possible site-specific factors and considerations. Therefore, DBMS is requesting additional discussion or <br /> information regarding the submitted post-closure seismic (pseudo-static) factor of safety for Section C to <br /> demonstrate that the provided post closure FOS of 1.0 is appropriate and acceptable. DRMS would also like to <br /> know what, if any, modifications to the proposed design could be made to increase the post-closure seismic FOS <br /> to a level of 1.15 or higher for all cross sections presented in the design report. <br /> 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mimng.state.co.us I 1�7 90, <br /> John W. Hickentooper, Governor I Robert W. Randall, Executive Director I Virginia Brannon, Director R .* <br /> 1876 <br />