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Technical Revision (TR-28) Climax Molybdenum Company <br /> Environmental Protection Plan Permit No. M-1977-493 <br /> ■ 4 Dam Seepage Collection and Pump System; <br /> ■ Chalk Mountain Interceptor; and <br /> ■ Robinson Lake Pumping System. <br /> Climax EPFs in the upper Eagle River Watershed are described in detail below. Where appropriate, the <br /> descriptions include the rationale for each EPF, the level of protection afforded Eagle Park Reservoir and <br /> East Fork Eagle River, and the contingencies for worst-case storm or other events to preclude discharge <br /> of impacted water. <br /> Robinson TSF and 1 Dam: 1 Dam, along with 2 Dam, contain tailing material and an approximate 60 <br /> acre water pool within the Robinson TSF. The Robinson TSF is also discussed in the Tenmile Creek <br /> watershed section. 1 Dam forms the divide between the Tenmile Creek and Eagle River basins. <br /> 1 Dam was upgraded and reconfigured in a project that was initiated in 1989 and completed in 1992. <br /> Briefly, this project entailed construction of a large diameter toe drain collection and discharge system, <br /> flattening of the slope of the dam from approximately 2H:1V to approximately 4H:1V, and armoring the <br /> face of the dam with rock cover material. The dam was revegetated at the end of this project. <br /> Prior to 2005, drainage that collected on the surface of Robinson TSF was conveyed to the Eagle River <br /> basin through the West Gravity Line. As part of a reclamation project in 2005, the East Side Channel and <br /> a spillway for the TSF through 2 Dam were constructed and now convey Robinson TSF drainage north <br /> down the Tenmile Creek basin. The West Gravity Line was subsequently abandoned and plugged with <br /> concrete. This project eliminated a significant source of impacted water inflow to the Eagle River basin. <br /> A collection system along the toe of 1 Dam collects seepage from 1 Dam and routes it to Warren's Pump <br /> Station (within the Robinson Lake footprint) for delivery to the water treatment system in the Tenmile <br /> Creek basin. Warren's Pump Station is itself considered an EPF during periods when the Robinson Lake <br /> Pump Station is not in operation and is discussed further in following sections. <br /> Another component of the 1 Dam/Robinson TSF EPF is the capping and reclamation program. As <br /> discussed earlier, 1 Dam was graded and capped in the early 1990s. Portions of 1 Dam were covered <br /> with topsoil and revegetated successfully from 2004 to 2009. The majority of the remainder of the TSF <br /> was capped with rock material from a portion of the E and F Dumps, the open pit cirque area, and other <br /> areas. This cap reduces infiltration of surface water into the tailing material and reduces available oxygen <br /> (particularly during the winter months) necessary for acid production. The vegetation also consumes <br /> water that would otherwise infiltrate into the tailing material and become impacted. Revegetation work <br /> began in 1997 and is ongoing. <br /> The size of the water pool on the TSF is maintained as small as practical to reduce infiltration into and <br /> through the tailing material. This is expected to reduce the volume of seepage emanating from the toe of <br /> 1 Dam. <br /> Climax also has developed a comprehensive water quality monitoring plan (Section T-8) to detect <br /> potential changes in water quality downgradient of mine facilities such as Robinson TSF and 1 Dam to <br /> enable implementation of measures that may be needed to protect off site water resources such as Eagle <br /> Park Reservoir and East Fork Eagle River, including the addition of new EPFs if necessary. The water <br /> quality monitoring plan is included as Appendix T-C. <br /> Robinson Lake and Dam: The Robinson Lake system including the reservoir proper and Robinson Dam <br /> is considered an EPF. Robinson Lake is designed and operated as a zero discharge facility to preclude <br /> overflow to Eagle Park Reservoir and East Fork of Eagle River. The Robinson Lake Pump Station <br /> located directly below the dam, Warren's Pump Station, and the seepage collection and return system are <br /> each considered EPFs and are discussed individually. The purpose of Robinson Lake is to store process <br /> water, which is routed into Robinson Lake through the Tenmile Tunnel and delivered by the Robinson <br /> Lake Pump Station back to the mill facilities. Robinson Lake also receives seepwater pumped from the <br /> Robinson Dam and 4 Dam seepwater collection systems. <br /> EPP: Version R4 T-21 August 2018 <br />