2021-06-02_HYDROLOGY - M1977342 (2)

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t CMC—Henderson Operations DRMS 2020 Annual Water Monitoring Report May 2021 Executive Summary This report provides a summary of the 2020 water monitoring data collected pursuant to the Climax Molybdenum Company(CMC)—Henderson Operations(Henderson)Technical Revision 16(TR- 16) to Permit M-1977-342 Groundwater Management Plan (GWMP). The Division of Reclamation,Mining and Safety(DRMS)approved the Henderson GWMP in July 2012.The focus of this report is 2020 data;however,historical data is also included from the 2015-2019 monitoring periods to allow for the assessment of trends over time. All sampling was conducted at the required locations in accordance with the GWMP and each sample was analyzed for the required parameters. In a memorandum dated April 14,2015,the DRMS preliminarily accepted new proposed Numeric Protection Limits (NPLs) for indicator parameters at Mill Point of Compliance (POC) locations. Given that the NPLs were only preliminarily accepted, the 2020 report will again be using the original NPLs of pH 6.5 to 8.5 until the new limits are formally accepted. Proposed POC wells MLGW-15 and MLGW-17 are also being monitored and results presented in this report. Mine Water Monitoring Henderson observed pH values during 2020 that were below the NPL limits at POC location MNGW-1.No deviations or anomalies were observed at non-POC locations at the Mine. Mine water monitoring data for POC well MNGW-1 and non-POC long-term surface water locations BG-20, CC-10 and CC-30 are included in this report and presented both in a table and trend evaluation graphs. Mill Water Monitoring No deviations or anomalies from established NPLs were observed at Mill POC wells. Mill water monitoring data for POC wells MLGW-ACR and MLGW-7, proposed POC wells MLGW-15 and MLGW-17, and non-POC long-term surface water monitoring locations WFR-20 and WFR-40 are included in this report and presented both in a table and trend evaluation graphs. 1 of 5