2018-05-11_REVISION - M1977493 (2)

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Water Quality Monitoring Plan Climax Molybdenum Company Version:R4 Permit No M-1977-493 3.1.4 Hydrogeology Within the Arkansas River Watershed, groundwater occurs 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 range between 10 and 40 feet in the Arkansas drainage. Hydraulic properties of the bedrock and soils in the drainage have not been measured, however, the results of a hydrogeological evaluation on the flooding of the underground workings (Titan, 1994) 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 seams of clay and fault gouge associated with the Mosquito Fault create a hydraulic barrier to east-west groundwater flow between the bedrock units. Demonstration of the Mosquito Fault as a hydraulic barrier to potential process water impacts to the Arkansas was discussed with DRMS during a site inspection and in verbal and written correspondence in the fall of 1994. Subsequent geophysical evaluations were performed to establish the criteria to maintain water levels below the apex of the Mosquito Fault. The Mosquito Fault is located approximately 350 feet west of 5 Shaft. A pumping station installed in 5 Shaft maintains the water level at an elevation below the apex of the Mosquito Fault to prevent mine water from potentially impacting the Arkansas River. A well located approximately 60 feet from 5 Shaft can be used when needed to verify groundwater levels adjacent to 5 Shaft. Groundwater flow direction in the Arkansas River Watershed is generally westward, paralleling the flow of the Arkansas River. As in the other drainages at Climax, the groundwater flow is controlled by the bedrock topography. 3.1.5 Groundwater Monitoring Sites 3.1.5.1 POC Monitoring Site The groundwater quality in the Arkansas River Valley has historically been monitored by well ARwell located downgradient of the Arkansas Pond (Figure 2).ARwell was constructed in September of 1993, and the well log is included in Appendix A. ARwell was completed in alluvium and is therefore being used as a POC well for alluvial groundwater in the valley below Climax facilities. Climax constructed a deeper, bedrock POC well (ARK-MW-001 D)adjacent to ARwell in 2012 so that both shallow and deeper hydro-stratigraphic units are monitored. Section 4 of this WQMP describes the monitoring parameters and schedule and Section 5 describes the numeric protection levels and data evaluation procedures. Well logs are in Appendix A and a compilation of water quality monitoring data which have been submitted in Annual Reports to DRMS are included in Appendix B-1. 3.1.5.2 Internal Groundwater Monitoring Site Climax established additional groundwater monitoring sites in the Arkansas River Watershed between the ARwell POC location and the Mosquito Fault to monitor groundwater conditions closer to mine facilities. The paired wells, ARK-MW-002S (alluvium) and ARK-MW-002D (bedrock), are identified on Figure 2 and well logs are in Appendix A. Section 4 of this WQMP describes the monitoring parameters and schedule and Section 5 describes the data evaluation procedures. Water quality monitoring data which have been submitted in Annual Reports to DRMS are included in Appendix B-1. EPP—Appendix C May 2018 5