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Status Report; Robinson Seep Investigation Climax Molybdenum Company <br />3.0 GROUNDWATER QUALITY <br />Measured field parameters for all sample locations are presented in Table 1 and Figure 1, <br />and analytical results are presented in Table 2, including groundwater monthly sampling data <br />collected in August 2014. The following observations are made from the field investigations and <br />data evaluation: <br />EC values obtained from bedrock samples during the August 2014 field sampling <br />generally follow observations from the 2013 drilling (Tetra Tech, 2013). Additional <br />EC data collected from bedrock locations downgradient of the Robinson Lake seep <br />collection system were all below 1,000 pS /cm and decreased downgradient. As a <br />result, no apparent change in the movement of the EC plume is observed between <br />2013 and 2014. <br />• Additional data collected within saturated sediments downgradient of the Robinson <br />Lake seep collection system show EC values between 300 and 775 pS /cm extending <br />downgradient, towards Eagle Park Reservoir. <br />• Dissolved iron concentrations (Figure 2) greater than 1.0 mg /L are restricted within <br />the 1,000 pS /cm EC plume and indicate that Robinson Lake is a potential source of <br />iron identified within monitoring well EVMW -1 S. Observed iron concentrations <br />support the conceptual model that Robinson Lake is a source of iron. <br />Elevated total iron concentrations are also identified to the west of Robinson Lake <br />seep collection system (EV -28) and downgradient of Robinson Lake seep collection <br />system (EV -31, EV -32, EV -33). The redox conditions support the precipitation of <br />iron rather than persisting in the dissolved phase (Figure 3). Concentrations of <br />dissolved iron and total iron for samples collected from EVMW -1 S suggest that this <br />well is subjected to water quality conditions indicative of both dissolved iron migrating <br />from Robinson Lake and saturated sediments immediately downgradient of the well. <br />The hydrogeochemical conditions suggest that dissolved iron migrating from <br />Robinson Lake will quickly precipitate once it enters the sediments, providing <br />geochemical attenuation before entering Eagle Park Reservoir. The temporal <br />fluctuation of dissolved iron concentrations within EVMW -1 S is likely due to the <br />interaction of differing redox conditions between the source (Robinson <br />Lake /Robinson Lake Seep) and the downgradient sediments. <br />Chemical data from the August 2014 field investigation were plotted on a Piper <br />Diagram (Figure 4a and 4b). Sample points attributed to Robinson Lake, Robinson <br />Lake Seep, EVS -006, and the two piezometers contain the highest concentrations of <br />sulfate (dominant anion). Although, a decreasing concentration trend is observed <br />with distance from Robinson Lake, illustrating the effectiveness of the cutoff wall and <br />natural attenuation of water moving downgradient towards Eagle Park Reservoir. <br />Likewise, downgradient attenuation is observed by the TDS concentration circles that <br />show decreasing concentrations (radii) with distance from Robinson Lake (Figure <br />4b). Additionally, cation concentrations are similar between all waters regardless of <br />proximity to Robinson Lake (Figure 4a and 4b). <br />Tetra Tech November 2014 <br />