2021-08-17_REVISION - M1977342 (4)

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TR-34 to Permit M-1977-342 Environmental Protection Plan 7.2. Mill Environmental Protection Facilities EPFs at the Henderson Mill site involve three main areas/categories: • Process Water and Tailing Circuit; • Designated Chemical Storage Facilities; and • Stormwater Diversion System. The EPFs in these areas are defined and evaluated in Sections 7.2.1, 7.2.2 and 7.2.3, respectively. Figures 3 and 4 identify the locations of the EPFs at the Mill site. Leaks, spills, or any other accidental or unauthorized releases are immediately addressed and reported as described in the Henderson Mill IRM (Appendix B). In addition, Henderson has contracted with a contractor to provide third party emergency services who is available to assist in the event of an accidental release. 7.2.1. Process Water and Tailing Circuit Currently, the Henderson Mill employs a zero-discharge process water circuit. There is no active discharge of process waters, although a CDPS permit for Henderson Mill allows for the discharge of process waters if needed. Design of the Mill WTP is in progress and construction is anticipated between 2022 and 2024, depending on climatic conditions and site water balance. The water management system at the Mill includes the following components: Mill-EPF 1.1- East Branch Reservoir System: This EPF includes the reservoir, dam, pump station below the dam, and the process water line between the East Branch pump station and the Mill process water tanks. The EBR is the principal storage area for mill process water. Its capacity is 2,000 acre-feet stored behind an earthen dam with a spillway which was constructed in 1970- 71 from local cut and fill material and certified by W.W. Wheeler and Associates, Inc.The outlet pipe from the reservoir runs to the pump house located just below the dam. Water from the reservoir is pumped from this station to the Mill process water tanks, and from there to the Mill on an as needed basis. Effectiveness: The reservoir is located such that any water escaping during a catastrophic failure would drain toward the tailing system storage where it would be contained. Monitoring: The EBR dam is regulated by the Division of Water Resources (DWR), and all monitoring and maintenance is performed according to requirements by the DWR. The reservoir is routinely inspected by Mill personnel to assess effectiveness and integrity. Maintenance and/or updates to facilities, systems, equipment, or procedures are performed as needed to be protective of the environment and to prevent releases. Mill EPF 1.2- Mill Process Water Storage Tanks:This EPF includes two (2) 1.5 million gallon steel tanks that are located east of and upgradient of the Mill buildings. Water from these tanks is gravity fed to the Mill system and 500,000 gallons in each tank is reserved for firefighting purposes. Effectiveness: The tanks are located such that any water escaping during a catastrophic failure would drain toward the EBR or to the TSF, where it would be contained. Climax Molybdenum Company August,2021 Henderson Operations Page 20 of 45