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COLORADO OPERATIONS <br /> ® Climax Molybdenum Henderson Mine <br /> A Freeport-McMoRan Company 1746 CR 202 <br /> Empire, CO 80438 <br /> Phone (303)569-3221 <br /> April 7, 2021 RECEIVED <br /> APR 13 2021 <br /> Via Email and UPS Tracking #: 1Z 804 847 03 4597 0430 <br /> D1VMON <br /> IN';NG AND SSA S <br /> Mr. Peter Hays <br /> Division of Reclamation, Mining and Safety <br /> 1313 Sherman St., Rm. 215 <br /> Denver, CO 80203 <br /> Re: Henderson Mine Point of Compliance Well MNGW-1 Low pH Status Update, Climax <br /> Molybdenum Company, Henderson Operations Permit No. M-1977-342 <br /> Mr. Hays: <br /> Climax Molybdenum Company, Henderson Operations (Henderson) is providing this status update <br /> regarding low pH measurements and additional water quality monitoring completed in relation to the <br /> Henderson Mine point of compliance (POC) groundwater well MNGW-1. Routine monitoring of MNGW-1 <br /> in accordance with the Henderson Groundwater Monitoring Plan (GWMP), submitted as Technical Revision <br /> 16 (TR-16) identified low pH levels beginning in early 2012, at which time Henderson initiated additional <br /> water quality monitoring and investigations. <br /> As communicated in a July 11, 2013 letter to DRMS, Henderson increased monitoring frequency at MNGW- <br /> 1 to monthly to better evaluate pH trends and underlying water chemistry. The results of this monitoring <br /> were detailed in a letter to DRMS on December 30, 2013. It was then determined that further investigation <br /> was necessary which included monthly monitoring at MNGW-1 through 2014 for a short list of indicator <br /> parameters. This investigation also involved the drilling and installation of two other wells in the surrounding <br /> area: MNGW-3 and MNGW-4. <br /> After all monthly monitoring had been conducted through 2014 Henderson, in a letter to DRMS on April 6, <br /> 2015, described plans to continue investigations into the low pH observed at MNGW-1. These plans <br /> included additional monitoring at MNGW-1, MNGW-3, MNGW-4 and No Name Gulch (when flowing). <br /> The attached memorandum prepared by Ajax and Clear Creek Associates provides an assessment of <br /> hydrogeology and water quality in the area. This evaluation concludes that the naturally low pH water <br /> conveyed by No Name Gulch off of Red Mountain is likely contributing or directly causing the low pH <br /> conditions observed in MNGW-1. Based on the vast extent of the current water level and water chemistry <br /> dataset, which now includes over five years of monthly monitoring data, and given the consistency and <br /> repeatability of monitoring results, monthly monitoring activities are no longer recommended. <br /> Therefore, Henderson intends to return to triannual monitoring at MNGW-1 as required in the GWMP <br /> beginning in April, 2021. Additionally, where future pH measurements are below the 6.5 s.u. NPL and are <br /> consistent with prior monitoring results, confirmatory sampling requirements are not considered necessary, <br /> and the initial reading will be assumed valid and utilized for required reporting. <br /> Page 1 <br />