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Technical Revision (TR -28) Climax Molybdenum Company Environmental Protection Plan Permit No. M-1977-493 As described in Exhibit E — Reclamation Plan to 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 site. 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 covers are anticipated to develop into a sustainable mosaic of mesic, wet meadow, and emergent marsh habitats that will support a variety of wildlife and waterfowl species. In addition, the infrastructure at the TSFs, will allow the ponds to be utilized for detention storage capacity at closure. Final reclamation of the OSFs, also described in 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 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. 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. The EPFs discussed throughout this EPP are shown on Figures AM -06-T-01 through AM -06-T-06. In addition to these EPFs, a number of internal systems also exist to provide additional control. The internal systems are classified separately to identify those systems that while serving an important function at the Site, are not absolutely necessary for the control, and prevention of a release, of acid mine drainage, or toxic or acid-forming materials. The EPFs and internal controls are listed in Table T-3 and detailed EPP: Version R4 T-16 August 2018