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Demonstration of Compliance Climax Molybdenum Company With Regulation 41 Permit M-1977-493 Robinson TSF drainage north down the Tenmile Creek basin. Prior to 2005, drainage that collected on the surface of Robinson TSF was conveyed to Robinson Lake in the Eagle River basin through the West Gravity Line. The West Gravity Line was subsequently abandoned and plugged with concrete. This project eliminated a significant source of impacted water inflow to the Eagle River basin. ■ In 2008, in accordance with information provided in TR-15, Climax conducted a sludge removal project in the east end of Robinson Lake to optimize the capacity of the facility for future production. Sludge and sediment removal was again conducted in 2010 and early 2011, and approximately one million cubic yards of material were removed. This work significantly reduced the amount of material that could potentially leach contaminants. Thus, no new or increased sources of contamination were initiated in the Eagle River Watershed subsequent to January 31, 1994. Rather, several projects have eliminated and mitigated historical sources in the area. An increasing trend of certain water quality parameters in monitoring well EVMW-1 S was observed beginning in late 2012 to early 2013. Following the procedures of the WQMP to protect downgradient water resources, the DRMS and Eagle Park Reservoir Company were notified and a program that included increased monitoring frequency, field investigation and data evaluation was conducted. The results of these efforts have been reported to DRMS and Eagle Park Reservoir Company (Tetra Tech, 2013 and Tetra Tech, 2014). As presented in the 2014 Status Report; Robinson Seep Investigation (Tetra Tech, 2014), a review of the data collected over 2013 and 2014 indicate that the previously observed, and short-lived, increasing trends observed for primary indicators have reversed, and an overall decreasing trend has been observed since the summer of 2013. These data suggest that the cause of the increasing trends observed in 2013 was likely related to the filling of Robinson Lake in 2011 to prepare for the resumption of Climax milling operations in 2012. The Robinson Lake water level had been maintained at a lower elevation typically not exceeding 10,850 feet for a ten year period from 2000— 2010. Following the completion of the sludge removal project(described above) in 2010, the reservoir was refilled between April and July 2011, from a water surface elevation of 10,830 feet to 10,875 feet, an elevation typical of water storage at Climax in the mid-to late- 1990s. When viewed in the context of conditions relative to January 31, 1994,this event is not indicative of a new or increased source of groundwater contamination. Rather, it is reflective of historical conditions in the upper Eagle River Basin at this particular facility. Most importantly, as observed in the data described in the following section, groundwater quality in this basin has remained within the historical range of constituent concentrations. 4.2 Data Evaluation Groundwater monitoring well EVMW, constructed in September 1993, below the Robinson Lake Seepage Collection System Cut-Off Wall, was replaced by a similar shallow monitoring well, EVMW-1 S, in October 2011. These monitoring locations provide a combined period of record from 1993 through the third quarter of 2016. Similar to well ARwell in the Arkansas River Watershed, monitoring at EVMW began with four consecutive quarters of sampling from September 1993 through September 1994. Monitoring was suspended following the initial year December 2016 13