2018-05-11_REVISION - M1977493 (2)

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Water Quality Monitoring Plan Climax Molybdenum Company Version:R4 Permit No. M-1977-493 ■ Antimony, barium, beryllium, chloride, cobalt, nickel, and total nitrate + nitrite as N: In general, no data are available for these parameters from collected mine water sources. Observed concentrations of these constituents at internal monitoring well locations are consistently well below the most stringent CBSG table values, typically at least an order of magnitude lower, indicating that these are not constituents of mine-related sources. Antimony concentrations, slightly above the CBSG value (0.006 mg/L), have been reported on two occasions in deep POC monitoring well TM-MW-002D. However, antimony has been reported as non-detect in approximately 92% of samples collected from every other groundwater monitoring well throughout the site, supporting the conclusion that antimony is not an appropriate indicator parameter. Antimony has not been detected in any samples from the shallow wells in the Tenmile Creek basin (GW#1 and GW#2) above the detection limit of 0.0004 mg/L, and the average and maximum observed concentrations in the upgradient deep well (TM-MW-001 D) are 0.0007 mg/L and 0.0032 mg/L, respectively. Ongoing monitoring of these parameters is not necessary for detecting potential mine-related effects. ■ Aluminum:As indicated in EPP Table T-E-6, aluminum has been observed in samples of collected mine water sources at concentrations above the CBSG value (5 mg/L — agricultural standard). For this reason, consideration was given to adding this metal to the indicator parameter list. Aluminum was reported as non-detect in approximately 90% of the groundwater samples in the Eagle River Watershed; with a maximum observed concentration of 0.21 mg/L in well EVMW-3D. In the Tenmile Creek Watershed, aluminum was reported as non-detect in approximately 88% of the samples in wells TM- MW-001 D, GW#2, and TM-MW-002D, with a maximum observed concentration for the watershed of 0.13 mg/L in shallow internal monitoring well GW#1. Similarly, in the Arkansas River Watershed, aluminum is detected in deep internal monitoring well AR- MW-002D, with a mean concentration of 0.24 mg/L and a maximum observed concentration of 1.25 mg/L. Aluminum in the other three wells in the Arkansas River Watershed was reported as non-detect in approximately 83% of the samples, with a maximum observed concentration of 0.05 mg/L in POC wells ARwell and ARK-MW-001 D. Based on a review of these data, although aluminum is observed in collected mine water sources, it does not appear to be a useful addition to the indicator parameter list, in comparison to iron, manganese, sulfate, and TDS. ■ Fluoride: Fluoride is observed in most of the wells within the monitoring network (with the exception of shallow POC well GW#2 in Tenmile, and EVMW-2 and EVMW-3S in the Eagle River Watershed). Higher concentrations are typically observed in the deep bedrock wells in the Arkansas and Tenmile Creek watersheds. A brief statistical summary of the fluoride data from the monitoring well network, using valid data collected through the fourth quarter of 20171, are presented in the tables below(for reference, the most stringent CBSG table value standard is the 2 mg/L agricultural standard and domestic water supply—human health standard is 4 mg/L): ' Some of the fluoride results from sampling performed in 2017 were determined to be invalid through the data validation process Non-standard laboratory procedures caused the unnecessary dilution of samples prior to fluoride analysis, resulting in reporting of estimated values or non-detect results at elevated method detection limits This issue was specific to fluoride analyses during several sampling events in 2017 and has since been corrected. EPP—Appendix C May 2018 15