2011-03-08_REVISION - M1977493 - Laserfiche WebLink

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I . Potential impacts from movement and quality of ground water tributary to Eagle Park Reservoir: The Reservoir Company and Eagle Entities have expressed concern that CMC's plan to eventually raise the No. 3 Dam on the Tenmile Tailings Storage Facility (TSF) by approximately 28 feet could cause a change in flow direction of the ground water, potentially allowing seepage from Tenmile TSF to enter the Eagle River drainage and to affect water quality in the Eagle Park Reservoir. CMC Response: Existing systems are in place to collect seepage from No. 1 Dam, on the south side of the Tenmile TSF, and direct collected water to the water management and treatment system. Existing monitoring and collection systems are in place, including a Water Quality Monitoring Plan submitted as part of TR-08. CMC recognizes that refinement of the Groundwater Monitoring Program will be addressed in a future submittal for review and approval by DRMS before full-scale mining and milling operations resume. Although no impacts are expected to Eagle Park Reservoir, CMC will examine the hydrologic conditions in the area of concern and will incorporate into the refined Groundwater Monitoring Program submittal to DRMS any additional monitoring measures deemed necessary by CMC to provide further protection of surface water. 2. Potential impacts from additional storage of process water in Robinson Lake and potential failure of the Robinson Reclaim Pipeline: The Reservoir Company and the Eagle Entities expressed concern that the current Robinson Lake Seepage Pump Station may not be adequate to collect increased seepage associated with the planned increase in storage in Robinson Lake, and that water quality in the Eagle Park Reservoir could be negatively impacted from this seepage or if the planned Robinson Lake Reclaim Pipeline were to fail. CMC Response: During the completion of the Eagle Park Reservoir reclamation work in 1997, a cutoff wall was installed between Robinson Lake and the Eagle Park Reservoir. The Robinson Lake Seepage Pump System also is currently in place at the toe of the Robinson Dam at the cutoff wall. The Robinson Lake Seepage Pump System consists of a seepage collection system, pump station and pipeline that convey seepage water to Robinson Lake. This facility is an identified Environmental Protection Facility approved by DRMS in the Climax Environmental Protection Plan in CMC's permit, and is regulated and inspected by the DRMS as such. The Robinson Lake operating level may increase by up to four feet when operations resume. Although some increase in seepage could occur from the increase in hydraulic gradient, the seepage collection pump system is sized with sufficient capacity to capture any increased seepage (by over a factor of 10) resulting from the increase in water stored in Robinson Lake. Also, ground water quality has been measured at the Robinson Lake Seepage Pump System and from a monitoring well located downgradient from the cutoff wall, and water quality at the pump system has improved substantially since the installation of the cutoff wall in 1997 and continues on this trend based on monitoring from the well. With regards to potential failure of the Robinson Lake Reclaim Pipeline, if that were to occur, CMC engineered systems include containment and other measures to provide notice of possible leakage. A failure of the pipeline above the point where it passes the Robinson Dam Spillway (approximately 19,000 feet of pipeline) would be contained in Robinson Lake, or other process water facilities if the failure happens further up the line (e.g. Robinson TSF). There is an approximately 1,180 foot long section of the pipeline between the new pump station and the point where it crosses Robinson Dam Spillway. A failure in this section would report to the Robinson Lake seepage collection system. This seepage pump system has enough capacity to contain a large leak in this section of the pipeline. Instrumentation and alarms also would be triggered if there is a high level in the seepage collection pond, indicating a pipeline leak. 2