2011-08-08_REVISION - M1977493 (33)

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• Technical Revision (TR -18) Climax Molybdenum Company Environmental Protection Plan Permit No. M- 1977 -493 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 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. T - 5.4.3 Tenmile Creek Watershed EPFs in the critical Tenmile Creek Watershed have been, and continue to be, extremely effective in containing and controlling contaminants and preventing contaminant release into the environment. As the EPFs essentially function in series from the top of the watershed, the effectiveness of the system is increased through the redundancy or secondary containment afforded by this arrangement. Each EPF serves as a protective layer for up- gradient EPFs. However, it must again be emphasized that the upper Tenmile Creek Watershed has been significantly impacted by historic placer and lode mining, milling and smelting activities, which peaked in the 1880s. Prior to construction of the Mayflower TSF and the Interceptor System, impacted waters and significant loads of contaminated sediments from these non - Climax historic operations entered Tenmile Creek and were transported downstream. The Climax water treatment and discharge system, which treats large volumes of water, has an exemplary track record. The treated discharge at Outfall 001 has met effluent limitations contained in the permit and has passed Whole Effluent Toxicity (WET) tests. Unlike other more complex and technically complicated water treatment processes, utilizing the first and second stage treatment processes of the SDP and the TSFs for lime precipitation is a simple and effective means of treatment. The decant system on the Mayflower TSF can be managed to increase retention time, thus allowing time to ensure treatment process and control discharge. The sulfuric acid tank is 120 percent contained within a series of sumps, and both primary and secondary containment. The EPFs that control and contain the water treatment chemicals, as with the process water and tailing circuit, have a proven track record for effectiveness at the Climax Mine. As discussed in Section T- 5.3.2, water treatment chemicals have primary and secondary containment. The ETDL generally has a good record for effectiveness. However, leaks have occurred in the past. When these leaks have occurred, repairs to the line have been made promptly and as stated above, other EPFs downgradient of the ETDL serve to contain water that may escape, preventing a release outside of EPP: Revision R1 T -28 July 2011