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Status Report; Robinson Seep Investigation Climax Molybdenum Company <br />7.0 CONCLUSIONS AND RECOMMENDATIONS <br />The following conclusions and recommendations are presented based on the evaluation of results <br />from the 2013 and 2014 fieldwork programs and the water quality results from monthly monitoring <br />of the Eagle Basin sampling locations: <br />• Field observations of electrical conductivity (EC) in water samples collected from <br />shallow fractured bedrock in 2014 were comparable to samples collected in 2013. <br />EC continues to be a good indicator of seepage /sulfate migrating from Robinson <br />Lake. <br />• Field observations of EC, and subsequent dissolved iron analyses, indicate that <br />dissolved iron originating from Robinson Lake attenuates downgradient of the <br />Robinson Lake seep collection system. <br />• The presence of total iron within groundwater samples collected from sediments <br />downgradient of the EVMW -1 S are likely natural given the presence of hydric soils. <br />• The fluctuation in dissolved iron concentrations within EVMW -1 S is likely due to <br />fluctuating redox conditions within the alluvial sediments combined with the seepage <br />migrating from Robinson Lake. <br />• Slug test data from monitoring well EVMW -1 S shows a hydraulic conductivity of <br />4x10-4 cm /s, typical of unconsolidated sediments. <br />• A review of the last two years of data indicate that the previously observed <br />increasing trends observed for primary indicators sulfate and TDS have reversed, <br />and an overall decreasing trend has been observed since the summer of 2013. Iron <br />concentrations appear to also have returned to within the limits of long -term trends. <br />These data suggest that the cause of the increasing trends observed in 2013 were <br />likely from a slug of poor quality water that was mobilized due to the filling of <br />Robinson Lake when Climax resumed operations. The plume of poor quality water <br />has steadily been attenuating over time. <br />• An evaluation of monthly data indicates that no differences in trends or additional <br />information were observed when compared with quarterly sampling data. <br />Based on these findings, it is recommended that routine monitoring of the previously identified <br />monthly and quarterly sampling locations be reduced in frequency back to routine sampling every <br />quarter without risk to Eagle Park Reservoir. Water quality along with field parameters can <br />continually be monitored every quarter, ensuring that any unusual fluctuations in chemistry are <br />identified so that subsequent action can be taken. <br />Tetra Tech November 2014 11 <br />