2021-08-17_REVISION - M1977342 (4)

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TR-34 to Permit M-1977-342 Environmental Protection Plan total of approximately 134 acre-feet of storage capacity exists in the areas which feed the Ute Park pump station (as discussed in EPF 1.5). This is comprised of 78 acre-feet in the 1-Dam Primary Seepage Detention area and 56 acre-feet in the 3-Dam Primary Seepage Detention area. The storage capacity of these combined areas based on a conservative maximum rate of 3,000 gpm (during the wet spring runoff period) and a nominal seepage rate of 1,000 gpm would provide between approximately 10-30 days of storage; sufficient time to place backup pumps into operation. Effectiveness: If the pump and alarm systems lose power,there is a solar and battery powered fail-safe system that closes the seep water feed channels to the pump house. An emergency diesel pump is located in the seepage detention area which is capable of pumping seepage water directly from the 1-Dam detention area back into the TSF. Monitoring: The Ute Park pumping system includes numerous instruments and control equipment, including a programmable logic controller, display screen for instrumentation monitoring and control, and radio telemetry system that includes provisions for, among other things, pump rates, high level alarms and pump power failures. 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 1.8 — Mill Water Treatment Plant: The Mill facility has operated as a zero-discharge facility since the beginning of operations in 1976, however, under forecasted operating and climate conditions, a water scenario is possible which results in surplus water that must be stored in the TSF or EBR. The new Mill WTP will provide treatment of excess process water to provide operational flexibility and allow appropriate management of stored water volumes under a variety of conditions. The treatment process to be used at the WTP will consist of a lime-based single-stage HDS process capable of treating surplus water at a design flow rate of 600 GPM (0.86 MGD) year- round. The HDS process recirculates sludge to improve coagulation and settling, and minimize reagent use. As the pH is raised to alkaline conditions, metals are oxidized and precipitated. A flocculant is added to promote precipitation. The resulting precipitate or sludge is thickened and removed from the HDS effluent using a clarifier. Ultimately, waste sludge will be pumped to the TSF for disposal using existing pipelines. Clarifier overflow, or effluent, will be filtered and undergo pH neutralization using carbon dioxide. This treated water will be conveyed through an existing pipeline that runs between the Mill complex and the Williams Fork Pump Station. Treated water will be discharged through the existing Williams Fork Pump Station outlet structure to the Williams Fork River. The WTP will consist of a metal building with concrete floor and foundation to house the process area tanks, piping, pumps, control equipment, and chemical storage, as well as a control room, lab, break room, restrooms, electrical, maintenance, and mechanical rooms. The plant will be constructed with a sealed concrete floor sloped to a central trench drain system that flows to sumps for collection of spills and water from floor cleaning in the process area such that all spills will be collected within this system and recycled to the HDS reactor tanks. Effectiveness: As stated in Sections 2.2 and 15.2,the Mill WTP is currently in the design stage, with construction anticipated to commence between 2022 and 2024. The treated effluent will Climax Molybdenum Company August,2021 Henderson Operations Page 24 of 45