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Water Quality Monitoring Plan Climax Molybdenum Company Version R4 Permit No M-1977-493 described in Section T-5.2 of the EPP. In addition, a more detailed discussion of contaminant sources, EPFs, and reclamation activities performed within the Eagle River Watershed are presented in Section 4.1 of the Regulation 41 Compliance Demonstration Report(Tetra Tech, 2016). 3.2.4 Hydrogeology The groundwater in the upper Eagle River Watershed occurs primarily in the shallow alluvium above the bedrock. Data from test pits(Kumar and Assoc., 1993)and additional field investigations performed in 2013 and 2014 (Tetra Tech, 2013 & 2014) northwest of Robinson Lake indicated that groundwater is present close to the ground surface and that alluvium in the valley consists primarily of silts, sands, and gravels. The alluvium overlays bedrock consisting of the Minturn Formation and Tertiary-aged quartz monzonite intrusives. A hydraulic conductivity(K)value of 1.15 feet per day(ft/day)was calculated from a slug test performed in the EVMW-1 S well, screened through the saturated alluvium and into the uppermost part of the weathered bedrock, in August of 2014 (Tetra Tech, 2014). Recovery tests performed in two temporary drive points installed to respective depths of 6 feet and 3 feet in the alluvium downstream from EVMW-1S, indicated hydraulic conductivity values of 0.19 and 0.08 feet/day for the alluvium. Bedrock beneath the alluvium consists of Minturn Formation,typically shale with minor sandstone and dolomite, interbedded with younger igneous rocks, typically quartz monzonite porphyry or granodiorite. Permeability in the bedrock is limited to fractures. Results of permeability testing in the Minturn Formation and igneous rock at relatively shallow depths in the Tenmile and Eagle valleys provide a median hydraulic conductivity value of 0.17 feet/day (Climax Molybdenum Company, 1984; Climax Molybdenum Company, 1985; Kumar, 1994; Titan Environmental, 1995; Wells, 1996; Arcadis, 2012). Fracture density typically decreases with depth. 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 reservoir 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 trenches 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 privately owned and is located above the East Fork of the Eagle River and below Climax facilities (Figure 1). Seepage emanating from the toe of No.4 Dam is collected in a collection sump keyed into bedrock and pumped back to Robinson Lake. The average, intermittent pumping rate for the sump is approximately 10 gpm which reflects the low rate of groundwater flow in this area. 3.2.5 Groundwater Monitoring Sites 3.2.5.I POC Groundwater Monitoring Site A shallow/deep pair of POC monitoring wells (EVMW-3S (alluvium) and EVMW-3D (bedrock)) were constructed near the East Fork Pumping Station at the Climax property boundary above the East Fork of the Eagle River and downgradient of 4 Dam (a.k.a. Eagle Park Reservoir Dam). Climax also established an additional POC groundwater monitoring well site above Eagle Park Reservoir (EV-MW-004). The locations of the wells are indicated on Figure 3 and well logs are included in Appendix A. Section 4 of this WQMP describes the monitoring parameters and schedule. Sections 5 and 6 describe the numeric protection levels and data evaluation procedures for the property boundary POC location, and the POC EPP—Appendix C March 2018 7