2011-03-14_REVISION - M1977493 (57)

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Permit Amendment (AM-06) - Climax Mine CM0000496 T-6.1 Background and Program The groundwater program at the Climax Mine entailed drilling four monitoring wells and conducting sampling and analysis of those wells. The first two wells (GW#1 and GW#2) were completed in 1984 in the Tenmile Creek valley below the Mayflower TSF. The third well, located in the Eagle River watershed (Eagle Valley MW, EVMW) between the Robinson Dam and Eagle Park Reservoir, was installed in late 1993. Likewise, the fourth well was drilled and completed in late 1993 in the Arkansas River watershed (ARwell) at the southwest corner of the reclaimed Arkansas gravel pit. Groundwater has been monitored in the Eagle River and Arkansas River watersheds since late 1993. The schedule for groundwater monitoring is still under evaluation by DRMS at this time. Climax continues to monitor groundwater as proposed in the monitoring plan submitted in TR-08 in 1995. Per Rule 3.1.7(2)(a), the following sections present a discussion of the hyrogeologic conditions and practice-based controls which are specific to the three drainages at the Climax mine site. T-6.1.1 Tenmile Creek Valley Groundwater in the Tenmile Creek valley primarily occurs in a veneer of alluvium glacial till which overlay bedrock consisting of Paleozoic sedimentary and Tertiary quartz monzonite formations. Data from seismic refraction surveys and monitoring well logs indicate that the alluvium and glacial till range in thickness form 0 to over 90 feet. The alluvium consists of deposits ranging in size from clays and silts to boulders. Groundwater level data indicate that groundwater occurs between 10 and 30 feet below ground surface with a seasonal flux in elevation. The direction of groundwater flow in the Tenmile Creek valley is controlled by the bedrock topography and outcroppings. Previously collected hydraulic conductivity test data indicate that the alluvium and glacial till in the Tenmile drainage are significantly more permeable than the bedrock units. By comparison, the bedrock units are of relatively low permeability. Therefore, the bedrock units are not capable of transporting significant quantities of groundwater. In 1987, two groundwater monitoring wells, GW #1 and GW #2 were installed in the Tenmile Creek drainage downgradient of the Mayflower Tailing Dam (Figure AM-06-G-01, Exhibit G). The purpose of these wells was to determine the depth to bedrock and groundwater elevations in the drainage, as well as provide groundwater quality monitoring. T-6.1.2 Arkansas River Valley The Arkansas River Valley is located south of the mine and on the East side of the Continental Divide. Within the drainage, groundwater occurs very close to the ground surface within layers of alluvial sands and gravels, and glacially derived silts and clays. These units overlay the Paleozoic sedimentary deposits (west of the Mosquito Fault) and the Precambrian Silver Plume Granite (east of the Mosquito Fault). The thickness of the alluvial and glacial soils ranges between 10 to 20 feet in the Arkansas drainage. Hydraulic properties of the bedrock and soils in the drainage have not been measured, however, the results of the 1994 hydrogeologic evaluation on the flooding of the underground workings determined that the bedrock on the east-side of the Mosquito Fault is of low permeability and not capable of transmitting significant quantities of groundwater. This evaluation also determined that the Mosquito Fault creates a hydraulic barrier to east-west groundwater flow within the bedrock. Mine water associated with the underground workings at Climax is currently handled and monitored at the 5-Shaft Pump Station where it is pumped over the Continental Divide and into the Climax Water Treatment System. The 5-Shaft pump station is an EPF as identified in Section T-5.1.2. The 5-Shaft Pump Station serves to maintain the water level in the underground workings at an elevation that does not threaten the flow of impacted water to the Arkansas River Valley. Groundwater levels in a piezometer located approximately 60 feet downgradient from the shaft are monitored for changes on a monthly basis. There are no current active mining facilities located within the Arkansas River Valley. Inactive mining facilities are currently being reclaimed. 0 Exhibit T T-24 May 2010