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 from new fill areas. This water will be directed by gravity to the Camp Area or Open Pit. Demonstration of the Mosquito Fault as a hydraulic barrier to potential process water impacts to the Arkansas was discussed with DRMS during a site inspection and in verbal and written correspondence in the fall of 1994. Subsequent geophysical evaluations were performed to establish the criteria to maintain water levels 19 feet below the apex of the Mosquito Fault. The Mosquito Fault is located approximately 350 ft west of the 5 -Shaft. A pumping station installed in 5 -Shaft maintains the water level at a target elevation of 11,080 feet that does not allow the flow of impacted water to the Arkansas River Valley. The level of water in 5 -Shaft is kept below the apex of the Mosquito Fault to prevent mine water from potentially impacting the Arkansas River. Climax also monitors a piezometer located approximately 60 feet from the 5 -shaft for changes in water level, on the same side of the Mosquito Fault as the 5 -Shaft. The effectiveness of 5 Shaft pumping is verified by the water level in the piezometer adjacent to the shaft that shows a hydraulic gradient towards the shaft. As the mining of the open pit advances in depth, the 5 Shaft Pump Station will become obsolete and water levels will be controlled by other means. The continued operation of the Storke Wastewater Pump Station and the Ceresco Ridge collection system will be dependent upon final reclamation activities in the area, but will continue indefinitely until water quality conditions are demonstrated to no longer require collection. T - 5.4.2 Eagle River Watershed As with the EPFs throughout the Climax Mine site, those in the upper Eagle River Watershed have been highly effective in containing and controlling the release of potential contaminants during the recent history of the mine. The primary EPFs in the watershed are Robinson Lake (and dam), the Robinson Lake Pump Station, and the associated seep collection and return systems below Robinson Lake. As described in Section T- 5.2.2, the capacities of the collection and pumping systems in -place are more than adequate to provide protection of water resources in the Eagle River Watershed. Multiple improvements to the EPFs in the Eagle River Watershed have been made over the last 15 to 20 years, and include: The installation of Tim's Pond and improvements to Warren's Pump Station to capture the majority of seepage from 1 Dam and Tenmile Tunnel and pumping this water to the SDP before it enters Robinson Lake; Upgrading the Robinson Lake Seepage Collection System including the application of an impermeable coating on the upstream side of the cut -off wall and construction of a collection pond upgradient of the wall to provide increased storage capacity. The effectiveness of the system of EPFs in -place in the Eagle River Watershed is demonstrated by the improvements in water quality observed at monitoring well EVMW. Additional water quality monitoring locations, as described in the Water Quality Monitoring Plan (Appendix T -C) will further enhance the ability to identify and react to potential adverse changes in water quality above Eagle Park Reservoir. Robinson Lake functions as a process water and seepage containment, storage and return system. The Robinson Lake Pump Station will return process waters directly to the process water tank for the mill. Because the integrity of this collection and return system is essential to production of molybdenum concentrates, close observation of its operation and maintenance of the systems is a priority. The development of the Robinson Lake Operating Plan (Appendix T -D) is intended to provide additional operational safeguards to prevent an overflow condition from Robinson Lake. The 4 Dam and Robinson Dam seepage collection and pump systems will remain in place and fully functional until such time as seepage from the dam meets water quality standards for this segment of the Eagle River. The seepage collected in the 4 Dam Seepage Collection System averages only approximately 10 gallons per minute, and the system has a redundant design to provide secondary containment, as described in Section T- 5.2.2. The effectiveness of this system, has been provided through the previous demonstrations of water quality in the East Fork Eagle River (performed as part of the remediation and surety reduction demonstrations for the Eagle Park Reservoir). The 1 Dam EPF has been effective in controlling the release of tailing material from the TSF. The regrading, capping, and reclamation of this dam (Section T- 5.2.2) have increased its present and future effectiveness. EPP: Version R2 T -30 December 2011