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Water Quality Monitoring Plan Climax Molybdenum Company Version R4 Permit No M-1977-493 3.3 Tenmile Creek Watershed The open pit mine, mill facilities, overburden storage facilities (OSFs), and the Robinson, Tenmile and Mayflower TSFs are all located within the Tenmile Creek Watershed,west of the Continental Divide(Figure 1).The land adjacent to the Climax property is primarily National Forest Land managed for various uses by the U.S. Forest Service (USFS). 3.3.1 Existing and Potential Future Uses of Groundwater Groundwater in the Tenmile Creek Valley within the Climax Mine property boundary occurs adjacent to and downstream of the TSFs. The WQCC has not adopted classifications or site-specific groundwater standards in the Tenmile Creek Watershed in the vicinity of the Climax Mine. Climax maintains wells on- site in the McNulty and PDWTP areas for industrial and potable supplies, as needed, but further development of groundwater in these areas would not be likely given the site location and climate conditions. The majority of groundwater use within the lower property boundary of Climax is recharge of Tenmile Creek, which is classified for aquatic life, recreation, and agricultural uses. 3.3.2 Location and Description of Classified Stream Segments Blue River basin, Segment 13, contains the main stem of Tenmile Creek from the Climax Parshall Flume (Climax CDPS Permit Outfall 001A)to the point immediately above the confluence of West Tenmile Creek. Also included are all tributaries and wetlands from the source of Tenmile Creek to the point immediately above the confluence with West Tenmile Creek. Exceptions include: Segment 15,the main stem of Clinton Creek from the source to the confluence with Tenmile Creek. Segment 13 of the Blue River basin is classified as Aquatic Life Cold 1, Recreation P, and Agriculture (although there is no documented agricultural use). Segment 15 is classified as Agriculture, Aquatic Life Cold 1, Recreation E, and Water Supply. 3.3.3 Potential Contamination Sources and EPFs The majority of the site, including most of the mine's water management and treatment activities occur within the Tenmile Creek drainage area, including the release of water at the permitted outfall to Tenmile Creek. Potential contaminant sources and established environmental protection facilities(EPFs)within this portion of the site are identified and described in Section T-5.3 of the EPP. In addition, a more detailed discussion of contaminant sources, EPFs, and reclamation activities performed within the Tenmile Creek Watershed are presented in Section 5.1 of the Regulation 41 Compliance Demonstration Report (Tetra Tech, 2016). 3.3.4 Hydrogeology 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 (Climax Molybdenum Co., 1984) indicate that the alluvium and glacial till range in thickness from 0 to over 90 feet. The alluvium consists of deposits ranging in size from clays and silts to boulders. Depth to water data collected in monitoring wells GW#1 and GW#2 (identified in the previous WQMPs as GWM-1 and GWM-2, respectively) indicate that groundwater occurs between 10 and 30 feet below ground surface with a seasonal flux in elevation. EPP—Appendix C March 2018 9