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Demonstration of Compliance Climax Molybdenum Company <br /> With Regulation 41 Permit M-1977-493 <br /> used by Climax to determine ambient quality at POC locations are representative of existing <br /> quality as of January 31, 1994, in accordance with the CBSG Interim Narrative Standard <br /> (41.5(C)(6)(b)(iii)). <br /> Consistent with the methodology approved by DRMS in Section 5.1 of the WQMP, the use of the <br /> mean concentration plus two standard deviations of the baseline data set were used to compare <br /> against monitoring data as the basis to demonstrate compliance with Regulation 41. <br /> 4.2.1 Analysis of Available Information to Determine or Estimate Ambient Quality <br /> In accordance with the Interim Narrative Standard of the CBSG, data collected subsequent to <br /> January 31, 1994 can be used to determine or estimate ambient quality as of January 31, 1994. <br /> In all instances, DRMS is to exercise its best professional judgment as to what constitutes <br /> adequate information to determine or estimate existing ambient quality, taking into account the <br /> location, sampling date, and quality of all available data. In the situation where the available <br /> information indicates that there have been no new or increased sources of groundwater <br /> contamination initiated in the areas in question subsequent to that date, data generated <br /> subsequent to January 31, 1994 shall be presumed to be representative of existing quality as of <br /> January 31, 1994. <br /> Although the EVMW/EVMW-lS location is not a POC location, it is in an area in close proximity <br /> to POC well EV-MW-004 and has a long period of record representative of the watershed <br /> downgradient of Robinson Lake. Therefore, it provides an opportunity to evaluate the historical <br /> range of data representative of existing quality as of January 31, 1994 relative to more recent <br /> water quality data. As discussed above, the graphical presentation of data at this location <br /> indicates that current water quality is generally the same or has improved at this location since <br /> January 31, 1994. <br /> Data used to determine ambient quality for the POC wells EVMW-3S, EVMW-3D, and EV-MW- <br /> 004, are the data collected over the full period of record for these locations (from November 2011 <br /> for EVMW-3S/3D wells, and from December 2012 for EV-MW-004). All data collected at these <br /> locations has been subject to the quality control and quality assurance procedures identified in <br /> the current WQMP and are deemed suitable to fully characterize baseline conditions at the POC <br /> locations. As described above, the data for these locations depict generally stable water quality, <br /> with manganese exhibiting the greatest variability of any monitored parameter,which as has been <br /> previously discussed, is determined to be normal fluctuation. Therefore, considering the overall <br /> trend of water quality in the shallow aquifer upgradient of these locations and the history of <br /> reclamation and EPF facility construction and maintenance in the areas upgradient of both POC <br /> locations, groundwater quality over this time period is believed to have improved since January <br /> 31, 1994. These data are deemed appropriate to determine, ambient quality representative of <br /> existing quality as of January 31, 1994. <br /> The following sections describe the evaluation of data from the POC well locations (from 2011 <br /> through the second quarter of 2016) in establishing ambient-based values for manganese <br /> representative of existing quality as of January 31, 1994. <br /> December 2016 15 <br />