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