2018-05-11_REVISION - M1977493 (2)

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Water Quality Monitoring Plan Climax Molybdenum Company Version. R4 Permit No. M-1977-493 water quality trends. As indicated in the 2013 and 2014 reports for the Robinson seep investigation, no increases were observed in concentrations of other TR-18 indicator parameters cadmium, copper, lead, molybdenum or zinc. Nevertheless, with the exception of lead, all of these parameters will remain on the Climax indicator parameter list. Lead has not been observed at concentrations above the most stringent CBSG table value standard (0.05 mg/L) in the available data from collected mine waters around the site (EPP Table T-E-6) and nearly all of the observed concentrations of lead in internal monitoring wells, in all three basins, are at least an order of magnitude below the CBSG value. Therefore lead was removed from the TR-18 indicator parameter list. Molybdenum will remain on the indicator parameter list because it has been observed at concentrations above the CBSG table value (0.210 mg/L) at internal monitoring well locations and is a constituent of process waters and collected mine waters throughout the site. In the case of cadmium, copper, and zinc; although data from the internal monitoring well network in each of the three watersheds do not indicate a significant presence or particular concern related to the observed concentrations of these parameters, data from the collected mine water sources (EPP Table T-E-6) do indicate elevated levels of these metals, and therefore they will be retained as indicator parameters. Baseline monitoring data also were evaluated to determine if any other parameters should be added to the indicator parameter list. The results of this evaluation are as follows: ■ Calcium, magnesium, potassium, sodium, bicarbonate (HCO3), total alkalinity, and total organic carbon (TOC): No standards have been established in the CBSG for these inorganic and general chemistry parameters. Although concentrations of calcium and magnesium showed an apparent increase, similar to sulfate and TDS, in monitoring well EVMW-1S in early 2013, inclusion of these parameters will not provide a solid indicator to identify impacts from site-wide, mine-related sources. The data collected during the extended baseline monitoring program for all of these parameters are generally consistent within each well and are considered representative of the general chemistry of groundwater at each location. A suitable baseline data record has therefore been established, which can be used as a point of comparison if expanded monitoring or analyses are performed in the future. ■ Cyanide, chromium, mercury, arsenic, and silver: While CBSG standards are established for these metals, a review of data from collected mine water sources (EPP Table T-E-6) do not indicate any concentrations in excess of CBSG standards. In addition, with the exception of one observed arsenic concentration,the concentrations of these parameters in internal and POC wells are consistently well below their respective CBSG values. Since these metals are not associated with mine-related sources throughout the site and have only been observed at low concentrations throughout the monitoring network, they are not considered to be appropriate indicator parameters at Climax. Although arsenic was measured once at a reported concentration equal to the CBSG value (0.01 mg/L) in deep POC monitoring well TM-MW-002D in March 2015, the lack of an obvious upgradient source and a mean concentration of 0.004 mg/L at this location do not warrant the inclusion of arsenic as an indicator parameter. ■ Selenium, thallium, and vanadium: Although no data are available for these metals from collected mine water sources, the baseline monitoring data indicate that more than 96% of the samples analyzed for these parameters have been reported with concentrations below the method detection limits. Therefore they are not appropriate indicator parameters. EPP—Appendix C May 2018 14