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ASC0M AECOM 303-694 2770 tel <br /> 6200 S Quebec St 303 694 3946 fax <br /> Greenwood Village,CO 80111 <br /> www.aecom.com <br /> February 14, 2020 <br /> Ms. Diana Kelts <br /> Climax Molybdenum Company-Climax Mine <br /> Highway 91 —Fremont Pass <br /> Climax, CO 80429 <br /> Subject: REV 0—Mayflower Tailings Storage Facility, Phase II Tower Design, Climax Mine, <br /> Permit No. M-1977-493 <br /> Dear Ms. Kelts: <br /> AECOM, through its legacy company URS Corporation, serves as the Engineer of Record (EOR)for <br /> the Mayflower Tailings Storage Facility(TSF) at the Climax Mine, located near Fremont Pass <br /> Colorado. It is our understand that Climax and DRMS has requested a letter from the FOR providing <br /> support of the proposed design modifications of the Mayflower flood bypass system changing from a <br /> side hill intake control structure used during Stage 1 to a vertical intake tower proposed from Stage 2. <br /> The tower design is depicted in drawings titled Mayflower Flood Bypass Tunnel Phase 11 Vertical <br /> Intake Structure- Vertical Intake Tower and Access Bridge dated February 2020 that were submitted <br /> for DRMS review. These drawings were prepared under the direction of and stamped by Mr. John <br /> Sikora with AECOM. <br /> Mayflower Vertical Intake Review <br /> As EOR, I have partipated in key meetings throughout the design process with Climax personnel and <br /> stakeholders including a Semi-Qualitative Risk Assessment(SQRA) meeting where the decision to <br /> go forward with the tower design was selected in part due to foundation conditions located in the <br /> Stage 2 area. A summary of the Mayflower tunnel system proposed for the Mayflower Tailings facility <br /> restart is provided in the Mayflower Tailings Storage Facility and 5 Dam Operations and Maintenance <br /> Manual(O&M), Revision 1.1 dated May 2014. Within this O&M it is noted that additional inlet <br /> structures will be needed as the dam height is raised. The vertical inlet tower proposed for the <br /> second stage is in accordance with this approach. <br /> General information and Closing <br /> AECOM represents that our services are performed within the limits prescribed by the Client in a <br /> manner consistent with the level and skill ordinarily exercised by other consultants under similar <br /> circumstances. No representation to the Client, expressed or implied, and no other warranty or <br /> guarantee is included or intended. <br /> C:\USERS\KELLY.BURKEI\DESKTOP\2020 MAYFLOWER PHASE 11 TOWER FOR REV A.DOCX <br />