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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.aecorn corn <br /> April 18, 2019 <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 Leadoff Clarification, 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 understanding that DRMS has requested clarification on the number of leadoffs <br /> required following a submittal by Climax showing the proposed 5 Dam crest raise configuration <br /> prepared by W. W. Wheeler&Associates, Inc. (Wheeler). On this drawing it showed increasing the <br /> number of leadoffs from three to four. <br /> Leadoff Clarification <br /> The Mayflower Tailings Storage Facility and 5 Dam Operations and Maintenance Manual(O&M), <br /> Revision 1.1 plan dated May 2014 discusses leadoffs and the use of leadoffs several times <br /> throughout the O&M manual. Leadoffs are used for winter deposition to fill in storage created during <br /> the summer months. One reference in the O&M manual under Section 4.5.2 discusses and shows in <br /> Figure 3-2 three leadoffs for the Mayflower TSF at startup. <br /> The three leadoffs referenced in the O&M manual depicts conditions at startup and was not meant to <br /> imply only three leadoffs should be used throughout the life of the TSF. As the dam is raised, the <br /> crest length will continue to increase and the number of leadoffs (plus location)will need to be <br /> adjusted to effectively fill the storage developed through the spigot season. The plan developed by <br /> Wheeler titled "2019 5 Dam Crest Line Raise, General Arrangement" dated 12/18 has increased the <br /> number of leadoffs to four leadoffs 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\AMY PHARO\APPDATA\LOCAL\MICROSOFT\WINDOWS\TEMPORARY INTERNET FILES\CONTENT OUTLOOK\XPKUBVUJ\2019 MAYFLOWER <br /> LEADOFF REVIEW REV 0 DOCX <br />