2022-04-05_REVISION - M1977342 - Laserfiche WebLink

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Climax Molybdenum Company Permit No.1977-342 Technical Revision (TR-35) 2. PROJECT DESCRIPTION The project scope includes the construction and operation of a 600 gpm WTP at the Henderson Mill.The proposed WTP will be located northeast of the mill building in a previously disturbed area within the Mill Complex and current Affected Land Boundary. Figure 1 presents an overall site plan for the Henderson Mill facility, with an inset showing the proposed location for the WTP, and the location of the outfall at the Williams Fork River. The WTP will treat surplus process water from the mill for discharge to the WFR. The main objectives for the WTP are to facilitate flexible site-wide water management under varying climatic conditions, maintain operational flexibility of the mill, increase the efficient use and re-use of water and achieve and maintain compliance with the effluent limits to be established underthe Colorado Discharge Permit System(CDPS)administered by the Water Quality Control Division (WQCD). The mill recirculates, stores, recycles and reuses process water between the TSF, EBR, and the mill. Process water from the mill is conveyed to the TSF with the tailing slurry for storage. Process water is then recycled from the TSF to the mill by pumping water from the TSF decant pond into the EBR and subsequently to the mill for use. Although water treatment has always been part of the long-term life-of-mine plan, the mill facility has operated as a zero-discharge facility since Henderson began operations in 1976; meaning that all water within the system has been recirculated for use within the milling circuit. The WTP treatment process will consist of a lime-based, single-stage high-density sludge (HDS) process capable of treating surplus water at a design flow rate of 600 gpm, which is 1.3 cfs or 0.86 MGD, year-round. The HDS process recirculates sludge to increase the neutralization potential of the added lime, improve coagulation and settling, and reduce reagent use. As the pH is raised to alkaline conditions, metals are precipitated. The resulting precipitate, or sludge, is thickened and removed from the HDS effluent using a clarifier. Ultimately, waste sludge will be conveyed to the TSF for disposal using existing pipelines. Clarifier overflow, or effluent, is filtered and undergoes pH neutralization using carbon dioxide. Finally, an existing pipeline will convey treated water from the WTP to the discharge location on the WFR at the existing Williams Fork pump station. The Henderson Mill holds an active CDPS permit which allows for the discharge of process water under certain conditions, although, as stated above, the Henderson Mill has operated as a zero-discharge facility. This current permit was issued in 2007 and has been administratively extended. A CDPS permit renewal application for the Henderson Mill was submitted to the WQCD on April 14, 2020,with modifications to encompass the WTP project. The WQCD will process the application and issue a permit establishing discharge limits, based on the applicable water quality standards in the receiving stream to protect its classified uses. The construction of the WTP is the subject of this Technical Revision. Key project elements are summarized below, and additional detail is provided in subsequent sections: The WTP will be located northeast of the mill building in a previously disturbed area within the Mill Complex; Plant capacity is rated at 600 gpm; The plant is designed as a High Density Sludge (HDS) process and includes polymer-enhanced flocculation, clarification, and gravity filtration; Sludge will be re-circulated to increase the neutralization potential of the added lime and improve coagulation and settling; Carbon dioxide will be dissolved in the water to neutralize the pH prior to discharge; Chemicals to be used for water treatment will include hydrated lime, flocculent polymer, and carbon dioxide; The WTP has been designed with sumps to catch overflows and spills. These sumps will return captured water to treatment; The WTP building will be a pre-engineered steel building with concrete floor and foundation; April 2022