2011-03-14_REVISION - M1977493 (48)

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Permit Amendment (AM-06) - Climax Mine CM0000087 alluvial groundwater conditions in the valley. The groundwater in the Arkansas River valley is forced to the surface and reports to the Arkansas River downgradient of ARWell. G-6.3 Eagle River Valley The groundwater in the Eagle River valley also primarily occurs in the shallow alluvium above the bedrock. The alluvium overlays bedrock consisting of the Minturn Formation and Tertiary-aged quartz monzonite intrusives. As in the other drainages at Climax, the bedrock topography controls the direction of groundwater flow. Groundwater flow in the valley is also influenced by the presence of three surface water bodies; Chalk Mountain Reservoir, Robinson Lake, and Eagle Park Reservoir. Each of these reservoirs was constructed by excavating and building an engineered dam to impound water. Construction records for each dam indicate that a low permeability cut-off wall was excavated into the underlying bedrock to control groundwater. Cut-off walls under each dam present a physical barrier to groundwater flow. Therefore, significant and continuous groundwater flow in the alluvium and bedrock throughout the valley is unlikely as groundwater flow is intercepted by the reservoirs. Eagle Park Reservoir is located above the East Fork of the Eagle River. Groundwater exiting the drainage and the Climax property is intercepted by the Eagle Park Dam (4 Dam). Site observations indicate that very little groundwater exits below 4 Dam. Groundwater which does seep below 4 Dam is collected in seepage collection system keyed into bedrock with secondary containment. This seepage is pumped back to Robinson Lake. The average, intermittent pumping rate for the 4 Dam Seepage Collection and Pump System is approximately 10 gpm which reflects the low rate of groundwater seepage. Groundwater quality within the Eagle River valley is monitored quarterly at the EVMW monitoring well, which was installed in September, 1993. EVMW is located upgradient of Eagle Park Reservoir, as indicated on Figure AM-06-G-01. Robinson Lake Seepage Pump System, a cut-off wall below the Robinson Dam outlet area has been installed and keyed to bedrock to contain seepage from the upstream Robinson Lake reservoir. Captured seepage is collected and pumped back to Robinson Lake. This cut-off component restricts seepage from entering Eagle Park Reservoir. G-6.4 Groundwater Quality The groundwater monitoring program at Climax involves the measurement of water levels and the collection of water quality samples from the four monitoring wells described in the preceding sections. The location of these wells is presented on Figure AM-06-G-01. Climax continues to monitor groundwater in general accordance with the proposed Groundwater Monitoring Plan submitted to the DRMS under TR-08 in 1995. A summary of the analytical sampling results and depth to water measurements in each of the wells from 2000 to 2009 is presented in Exhibit T - Appendix D. G-7 PMP Flood Control A critical component in the operation of the Climax facilities is flood protection. Climax has dedicated significant resources to the protection of these facilities from extreme flood events. The flood control systems at Climax generally consist of two levels of protection. The first level involves the interception and diversion of flows resulting from snowmelt runoff and normal rainfall events. This diversion is provided by the freshwater bypass and interceptor systems previously described. The second level of protection at the site relates to the capacity of the system to safely withstand the effects of extreme precipitation events such as the PMP. PMP flood control is the subject of this section of this exhibit. G-7.1 Background In 2005, W. W. Wheeler and Associates (Wheeler) completed a site-wide hydrological assessment of the Climax Mine and evaluated its ability to safely handle the flood generated by the PMP event (Wheeler, 2005). As part of that study, Applied Weather Associates performed a hydro-meteorological analysis and developed a Exhibit G G-14 May 2010