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 • Robinson TSF and 1 Dam; • Robinson Lake and Dam; • Warren's Pump System; • Robinson Lake Seepage Pump System; • 4 Dam Seepage Collection and Pump System; • Chalk Mountain Interceptor, and • Robinson Lake Pumping System. Climax EPFs in the upper Eagle River Watershed are described in detail below. Where appropriate, the descriptions include the rationale for each EPF, the level of protection afforded Eagle Park Reservoir and East Fork Eagle River, and the contingencies for worst -case storm or other events to preclude discharge of impacted water. Robinson TSF and 1 Dam: 1 Dam, along with 2 Dam, contain tailing material and an approximate 60 acre water pool within the Robinson TSF. The Robinson TSF is also discussed in the Tenmile Creek watershed section. 1 Dam forms the divide between the Tenmile Creek and Eagle River basins. 1 Dam was upgraded and reconfigured in a project that was initiated in 1989 and completed in 1992. Briefly, this project entailed construction of a large diameter toe drain collection and discharge system, flattening of the slope of the dam from approximately 2H:1V to approximately 4H:1V, and armoring the face of the dam with rock cover material. The dam was revegetated at the end of this project. Prior to 2005, drainage that collected on the surface of Robinson TSF was conveyed to the Eagle River basin through the West Gravity Line. As part of a reclamation project in 2005, the East Side Channel and a spillway for the TSF through 2 Dam were constructed and now convey Robinson TSF drainage north down the Tenmile Creek basin. The West Gravity Line was subsequently abandoned and plugged with concrete. This project eliminated a significant source of impacted water inflow to the Eagle River basin. A collection system along the toe of 1 Dam collects seepage from 1 Dam and routes it to Warren's Pump Station (within the Robinson Lake footprint) for delivery to the water treatment system in the Tenmile Creek basin. Warren's Pump Station is itself considered an EPF during periods when the Robinson Lake Pump Station is not in operation and is discussed further in following sections. Another component of the 1 Dam /Robinson TSF EPF is the capping and reclamation program. As discussed earlier, 1 Dam was graded and capped in the early 1990s. Portions of 1 Dam were covered with topsoil and revegetated successfully from 2004 to 2009. The majority of the remainder of the TSF was capped with rock material from a portion of the E and F Dumps, the open pit cirque area, and other areas. This cap reduces infiltration of surface water into the tailing material and reduces available oxygen (particularly during the winter months) necessary for acid production. The vegetation also consumes water that would otherwise infiltrate into the tailing material and become impacted. Revegetation work began in 1997 and is ongoing. The size of the water pool on the TSF is maintained as small as practical to reduce infiltration into and through the tailing material. This is expected to reduce the volume of seepage emanating from the toe of 1 Dam. Climax also has developed a comprehensive water quality monitoring plan (Section T -8) to detect potential changes in water quality downgradient of mine facilities such as Robinson TSF and 1 Dam to enable implementation of measures that may be needed to protect off site water resources such as Eagle Park Reservoir and East Fork Eagle River, including the addition of new EPFs if necessary. The water quality monitoring plan is included as Appendix T -C. Robinson Lake and Dam: The Robinson Lake system including the reservoir proper and Robinson Dam is considered an EPF. Robinson Lake is designed and operated as a zero discharge facility to preclude overflow to Eagle Park Reservoir and East Fork of Eagle River. The Robinson Lake Pump Station EPP: Version R2 T -20 December 2011