2018-05-11_REVISION - M1977493 (2)

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Water Quality Monitoring Plan Climax Molybdenum Company Version:R4 Permit No. M-1977-493 4.1.4 Surface Water Monitoring Baseline Data Evaluation Analytical data collected from the internal surface water monitoring locations CC-SW1, and EI-SW1 during the extended baseline monitoring period is presented in Appendix B-4. Tables included in Appendix B-5, present available surface water data from the East Fort Arkansas River, East Fork Eagle River and the EPR outlet. Monitoring using the full baseline parameter list began in the fourth quarter of 2011 for the Eagle River and EPR Outlet locations, and the first quarter of 2012 for the Arkansas River locations. The data for each location are presented in individual tables. The data in these tables have been summarized with descriptive statistics, including the calculation of the minimum, maximum, and mean concentrations, the standard deviation, the number of data records, or analyses for each analyte, and the number of observations below the method detection limit. In accordance with the approach described in TR-18, river and EPR Outlet data are presented along with applicable surface water standards for the East Fork Arkansas and East Fork Eagle Rivers. As described in Section 3.1.6, Arkansas River monitoring location Arkansas#1 is upstream of former and present mine facilities in the upper reach of the Arkansas River basin. Arkansas River monitoring location Arkansas#2 is located at the property boundary on the south side of Highway 91. In evaluating the full period of record at these locations, concentrations of several water quality constituents have decreased since monitoring began in 1993, most notably are decreases in manganese and zinc, although there is a seasonal pattern with higher concentrations typically observed in the early spring. Consistent with the groundwater monitoring program, cadmium, copper, iron, manganese, molybdenum, zinc, pH, sulfate, and TDS are included in the indicator parameter list for long term surface water monitoring. Lead is not included due to its absence in collected mine water sources, the predominance of results below the detection limit, and the fact that recent data indicate concentrations well below surface water standards at all monitored locations. Because standards are in place for both dissolved and total recoverable iron, total recoverable iron will be added to the indicator parameter list. Similarly, although dissolved molybdenum has been monitored through the baseline period, total recoverable molybdenum has been added to the indicator parameter list since the surface water standard is expressed as total recoverable. Aluminum, calcium, and magnesium are not included as indicator parameters for the long-term monitoring at surface water monitoring locations. There are no surface water standards for these three parameters in any of the stream segments identified in Section 3 for the three river basins. Aluminum is not included as an appropriate indicator parameter, based primarily on recent data that are typically reported as non-detect. Calcium and magnesium are excluded because they are not considered indicators for the identification of impacts from mine-related sources. Hardness is retained in the indicator parameter list since it is a useful parameter for monitoring the East Fork Eagle and Arkansas Rivers, since many surface water standards are hardness based. Of the remaining additional baseline monitoring parameters, only arsenic and silver warrant significant discussion. Both dissolved arsenic and silver are reported as non-detect in nearly all of the samples obtained from the river and EPR surface water monitoring locations and, as discussed in the groundwater data evaluation (Section 4.1.1.1), neither arsenic nor silver are associated with mine-related sources at Climax. Therefore, arsenic and silver are not included in the indicator parameter list. The data collected at the internal surface water monitoring locations (CC-SW1 and EI-SW1, located above Clinton Reservoir), represent natural, un-impacted conditions. To simplify the monitoring program the same surface water indicator parameter list is recommended. For consistency, relevant surface water standards are also presented for comparison purposes with the data for the internal surface water monitoring location data in Appendix B-4. EPP—Appendix C May 2018 20