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Henderson Mill — Permit No. M-1977-342 <br /> Technical Revision No. 29 <br /> 3 Dam Buttress—Stage 1 <br /> The 3 Dam Buttress-Stage 1 Project was approved as Technical Revision No. 29 to Mill Permit No. <br /> M-1977-342 on April 4th,2018. The project is located at Climax Molybdenum Company's Henderson <br /> Mill in Grand County. The project involved constructing a separate north and south toe buttresses <br /> on the original 3 Dam plus a multi-tiered buttress on Stepback 3 Dam. The buttress was <br /> constructed from tailings material borrowed from 1 Dam by removing an interim non- <br /> instrumentation bench. The completed crest elevations for the three Stage 1 buttress areas are <br /> Elevation 8799 ft for the north toe buttress, Elevation 8780 ft for the south toe buttress,and <br /> Elevation 8825 to 8841 ft for the multi-tiered stepback buttress. Overall constructed slopes range <br /> from 3:1 horizontal to 4:1 horizontal. <br /> Henderson Mill completed construction over the 2018 and 2019 seasons(June to October 2018 and <br /> May to September 2019). The project was designed by AECOM. Modifications to the initial design <br /> have been reflected in the construction record drawings signed and dated October 25,2019. <br /> AECOM provided full-time construction oversight of the buttress placement and instrument <br /> installation activities for Stage 1 with construction by Henderson Mill. The project was completed in <br /> general conformance with the approved design as submitted to the Division of Reclamation,Mining, <br /> and Safety. The statement is based in part on information provided by others. <br /> Lisa R.Yenne, P.E —'00 RE i <br /> • <br /> AECOM ;per•.•. E 1F,y P Date: January 7,2020 <br /> Colorado PE No.35847 = <br /> 35= • <br /> S/ONAL L� <br /> ‘% = <br />