2011-12-15_REVISION - M1977493 (2)

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Technical Revision (TR -18) Climax Molybdenum Company Environmental Protection Plan Permit No. M- 1977 -493 acknowledges that surface water from Climax must meet effluent limitations prior to discharge. As described in Exhibit E — Reclamation Plan to Permit Amendment AM -06, both Tenmile and Mayflower TSFs will be reclaimed with a combination of dry and wet covers. Due to concerns regarding water treatment, flood control, constructability, and dam safety, a wet cap is needed for the Climax Mine site. The flow rate of impacted water requiring treatment at Climax currently ranges from about 3,000 gpm during the winter to about 40,000 gpm during the peak of the snowmelt period. Climax manages water to reduce the volume and flow rate of water requiring treatment. This management includes the use of interceptor canals, diversion ditches, surface treatments, and reclamation of formerly impacted land. The seepage from TSF dams and water pumped from the open pit or underground mine workings, however, will continue to require treatment well into the future. These future sources of impacted water are expected to follow a similar pattern of significant seasonal variability. The use of a wet cap reclamation scenario provides detention storage capacity that allows for seasonal attenuation during the peak flow periods and promotes a more constant flow rate for water treatment. This detention storage dampens the peaks of the impacted water hydrograph and reduces the required capacity of the treatment system. In addition, an active reservoir to store impacted water provides flexibility in the timing and rate of water treatment and therefore reduces the risk of releasing impacted water during an upset scenario in the water treatment system or under unusual hydrologic conditions. Hydrologic flood studies indicate that peak flow rates onto the TSFs are generally in the thousands of cfs during a PMP event. If there is no detention storage capacity within the TSF to attenuate these flows, which would be the case in a dry cover scenario, then very large and heavily armored channels would be required to convey the flood flows safely beyond the site. The detention storage capacity provided by the wet cover configuration allows for much lower capacity flood conveyance facilities. The detention concept is less sensitive to peak flood flow estimation and results in lower risk from erosion, channel failure, and potential dam breach. The wet cap configuration also is consistent with that presented to DRMS and approved in Technical Revision TR -13. The wet cover already established on the Robinson TSF is currently developing into a sustainable mosaic of mesic, wet meadow, and emergent marsh habitats which support a variety of wildlife and waterfowl species. In addition, previously constructed infrastructure at the Robinson TSF, including the existing East Side Channel and 2 Dam Spillway will allow the established pond on the Robinson TSF to be utilized for detention storage capacity at closure. Final reclamation of the OSFs, also described in Permit Amendment AM -06 Exhibit E — Reclamation Plan, will involve regrading of the overburden material to the final closure grades as determined through the ongoing geotechnical stability evaluations and placement of a soil cover and revegetation. T -5 Climax Mine Environmental Protection Facilities An "Environmental Protection Facility" (EPF) is defined in Section 1.1(15) of the Rules as "...a structure which is identified in the "Environmental Protection Plan" as designed, constructed and operated for control or containment of designated chemicals..., acid mine drainage, or toxic or acid - forming materials that will be exposed or disturbed as a result of mining or reclamation operations." Except where noted, the EPFs as defined are present and operational at Climax. Some of the EPFs identified and described herein are under construction or planned for future construction. Because of Climax's unique geographic position affecting both sides of the Continental Divide and three distinct and major watersheds (Arkansas River, Eagle River, and Tenmile Creek), the following discussion of EPFs and controls is organized by watershed. Within the three watersheds, defined EPFs involve (in no particular order): • Control of run -off that contacts potentially contaminated material; • The process water circuit, which includes process water reclaimed from the TSFs for use in the mill process, the TSFs and seepwater control systems; • Mine water drainage and control systems; • Storage and containment facilities for designated chemicals used in the milling process; and • Facilities associated with the water management and treatment system. EPP: Version R2 T -15 December 2011