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Demonstration of Compliance Climax Molybdenum Company
<br /> With Regulation 41 Permit M-1977-493
<br /> of sampling, but resumed again in February 1997, and continued generally on a quarterly basis
<br /> through 2011. Although, not a POC location, the data from this location are useful to evaluate
<br /> conditions and identify long-term trends in the watershed from 1993 to present. Figure 4-1 is a
<br /> series of temporal water quality concentration graphs representing the entire period of record at
<br /> EVMW and EVMW-1 S (1993 -2015). The first two graphs present concentrations of the primary
<br /> indicator parameters sulfate and TDS, and the second two graphs present dissolved manganese,
<br /> iron, and molybdenum. These graphs illustrate the overall decreasing trend in concentrations of
<br /> sulfate,TDS, and molybdenum at this location, despite the relatively short-term increase in sulfate
<br /> and TDS concentrations observed in 2012 and 2013. Although the increases in manganese and,
<br /> in particular, dissolved iron observed in 2012 and 2013 were greater, relative to historical
<br /> concentrations, than the short-term increases in sulfate and TDS, the current concentrations are
<br /> within the historical range observed in the January 1994 time frame. As indicated in the Robinson
<br /> Seep investigation status reports, dissolved manganese and, in particular, dissolved iron, are
<br /> subject to greater variability due to influences from relatively small shifts in pH and redox potential
<br /> (Eh). This is supported by the observation that the dissolved iron concentrations in groundwater
<br /> at well EVMW-1 S, located below the cut-off wall, were higher than concentrations in Robinson
<br /> Lake seepage above the cut-off wall. A review of data for other indicator parameters (cadmium,
<br /> copper, and zinc) at this location also indicate that the majority of the data observations are at, or
<br /> near, the detection limits, and no increases were observed in the 2012 to 2013 time frame.
<br /> The evaluation of the increased monitoring effort in response to the observations of trends at
<br /> EVMW-1 S, indicated that the cut-off wall and Robinson Lake seepage collection system is
<br /> effective in limiting the migration of chemical constituents downgradient of the cut-off wall, and
<br /> that similar increasing trends were not observed, particularly considering primary indicators
<br /> sulfate and TDS, in any of the other monitoring well locations. These findings support the
<br /> conclusion that the short-term, water quality trends associated with the controlled re-filling of
<br /> Robinson Lake were limited to the shallow aquifer immediately downgradient of Robinson Lake.
<br /> The data record, therefore, is considered in its entirety to demonstrate that the overall
<br /> groundwater quality has improved relative to the January 1994 time frame.
<br /> Water quality data for POC monitoring wells EVMW-3S, EVMW-3D, and EV-MW-004 are
<br /> presented graphically in Figures 4-2 and 4-3, attached to this appendix. Figure 4-2 presents
<br /> graphs of sulfate and TDS, as well as dissolved manganese and iron, for EVMW-3S and EVMW-
<br /> 3D, over the period of record for these wells from November 2011 through September 2016.
<br /> Figure 4-3 presents that same data for EV-MW-004 over its period of record from December 2012
<br /> through September 2016. These graphics illustrate, that while TDS concentrations show some
<br /> variability over time, there are no discernable trends in observed concentrations of either TDS or
<br /> sulfate, which are considered the most reliable indicator parameters for mine-related waters. The
<br /> graphs of dissolved manganese and iron concentrations show greater variability in
<br /> concentrations, particularly for manganese. In the absence of similar variability in sulfate, TDS or
<br /> other parameters, these data suggest that the variability of manganese and iron is due to natural
<br /> physio-geochemical changes within an otherwise stable system.
<br /> The 2012-2013 event described above relates to short term increases associated with relatively
<br /> small changes in water chemistry and not the introduction of a new or increased source, relative
<br /> to conditions prior to January 31, 1994. Data generated subsequent to January 31, 1994 and
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