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Mr. Peter Hays <br />TR -29— 3 Dam Buttress Stage 1 <br />January 26, 2018 <br />• Stage 2: crest elevation at 8887 ft (estimated year 2021) <br />• Stage 3: crest elevation at 8893 ft (estimated year 2025) <br />• Stage 4: crest elevation at 8900 ft (estimated year 2029) <br />Staae 1 Buttress Desian <br />Henderson will undertake Stage 1 construction activities throughout 2018 and 2019 with engineering <br />oversite by AECOM, the EOR for the tailings facility. Stage 1 of the buttress will involve placing an <br />estimated 108,200 cubic yards of buttress material and 17,800 cubic yards of filter Material. The material <br />will be graded to a 3:1 slope. Based on material availability and proximity, material for the buttress will be <br />borrowed from excess tailing material on the benches of 1 Dam. Engineering analysis has demonstrated <br />the excess material on 1 Dam does not offer any structural support to 1 Dam, making it an optimal borrow <br />source. A chimney drain and blanket drain will be installed to collect seepage at the interface of the <br />buttress and the original dam and stepback. In addition, benches will be constructed with a slight <br />downstream slope to provide a proper drainage path for surface water runoff. The seepage canal will be <br />realigned to allow for construction and proper drainage. An estimated 4,400 cubic yards of material will be <br />excavated for the drainage channel. <br />In addition, horizontal and foundation drains will be extended in order keep them functional during <br />operation, maintaining a lower phreatic surface. Some of the instrumentation on the dam will be impacted <br />by the buttress, therefore additional instrumentation will be installed in the impacted areas and monitored <br />through construction. Existing piezometers that will be impacted, will be extended to keep them functional <br />through all phases of the buttress construction. <br />Construction will begin in the summer of 2018 with installation of infrastructure including the filter blanket, <br />relocation of the existing seepage collection channel, drain extensions, and instrumentation. A portion of <br />the buttress fill will be constructed in 2018 with the remainder being constructed in 2019. A design report <br />and associated design drawings for this project are included in attachments 1 and 2. Engineer's <br />certification and as -built drawings will be submitted upon project completion. <br />A check in the amount of $1,006.00 is included with this submittal to cover fees for this Technical <br />Revision. If you have any comments, questions, or concerns regarding this project, please contact me at <br />720-942-3480 or Miguel Hamarat at 720-942-3255. <br />Sincerely, <br />OUJ440.17a_'_� <br />Amber Parmet <br />Senior Environmental Engineer <br />Climax Molybdenum Company <br />Henderson Operations <br />Attachments: <br />1. Design Letter Report <br />2. Design Drawings <br />3. Check # 0000890561 in the amount of $1,006.00 <br />cc: Miguel Hamarat, CMC <br />Tim Haynes, CMC <br />Wally Erickson, DRMS <br />Pile <br />