2024-05-17_REVISION - M1977493 (4)

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G-4 Groundwater Groundwater in the vicinity of the Climax mine site is generally present within a thin veneer of alluvium and glacial till overlaying the bedrock, and ranges from near ground surface to a few tens of feet below ground surface. Groundwater occurrence within the bedrock is limited to the upper fractured portion of the bedrock units. A hydrogeologic study of the underground workings conducted in 1994 indicated that the bulk permeability of the bedrock is relatively low and that the bedrock is not capable of transporting significant quantities of groundwater. Additionally, it was shown that the presence of the Mosquito Fault provides a hydraulic barrier to lateral flow of groundwater flow in the bedrock. The direction of groundwater flow is controlled by bedrock topography, but is coincidentwith the surface water drainages, where groundwater discharges into streams and creeks. The following sections present a discussion of the hydrogeologic conditions and controls which are specificto the three drainages at the Climax mine site. G-4.1 Tenmile Creek Valley Groundwater in the Tenmile Creek valley primarily occurs in a veneer of alluvium and 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 drainage, downgradient of the Mayflower Tailing Dam(Figure G-01).The purpose of these wells was to determine the depth to bedrock and groundwater elevations in the drainage, as well as to provide for groundwater quality monitoring. G-4.2 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 soils overlay the Paleozoic Minturn Formation (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 environmental protection facility identified in the Climax Environmental Protection Plan. 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 waterto 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 Exhibit G G-17 May 2024