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Status Report, Robinson Seep Investigation Climax Molybdenum Company <br />6.0 EVALUATION OF THE EFFECTIVENESS OF MONTHLY <br />MONITORING <br />Monthly monitoring was initiated in March 2013 and has continued for 19 consecutive months. <br />With the exception of iron, all other constituent concentrations have been within a well- defined <br />range and generally within historical ranges for well EVMW /EVMW -1 S pairing. Concentrations <br />of constituents are generally much lower below the Robinson Lake seep collection system than <br />above it with the following exceptions: <br />• There is a general seasonal fluctuation observed within Robinson Lake Seep, with <br />lower concentrations observed in the late spring associated with snowmelt runoff. <br />Iron still continues to fluctuate within EVMW -1 S. As discussed in Section 3.0, this <br />fluctuation can be attributed to a dynamic geochemical condition associated with the <br />interaction of dissolved iron from Robinson Lake and subtle changes in redox <br />associated with saturated soils immediately downgradient. As shown in Figure 2, <br />dissolved iron does not extend far downgradient of EVMW -1 S in either the sediments <br />or fractured bedrock (Figure 2) with the geochemical conditions conducive to the <br />precipitation of dissolved iron as Fe (OH)s. While it is anticipated the dissolved iron <br />will continue to fluctuate with the shifting redox boundary, the attenuation of iron <br />through precipitation within the downgradient groundwater will be protective of Eagle <br />Park Reservoir. The fluctuations are believed to be the result of the iron chemistry <br />rather than a direct impact of Robinson Lake. <br />Based on the available monthly data, the conclusions drawn would be the same as that of <br />quarterly data: <br />• Robinson Lake Seep fluctuates seasonally based on snowmelt in the spring; <br />• The decrease in concentrations downgradient of the Robinson Lake seep collection <br />system compared with above the Robinson Lake seep collection system confirms the <br />effectiveness of this system; <br />• Residual constituents migrating below the Robinson Lake seep collection system are <br />quickly attenuated; and <br />• Dissolved iron fluctuations within EVMW -1 S above historical data obtained from <br />EVMW can be attributed to natural iron chemistry. <br />Tetra Tech November 2014 10 <br />