2011-08-08_REVISION - M1977493 (33)

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• • Technical Revision (TR -18) Climax Molybdenum Company Environmental Protection Plan Permit No. M- 1977 -493 subject to extensive placer and lode mining, milling, and smelting operations since the discovery of placer gold in the 1860s (reference for historic information: Dempsey, S. and J.E. Fell, Jr. 1986; Mining the Summit. University of Oklahoma Press). At one time, the Tenmile Creek Valley within the present boundaries of Climax supported four incorporated towns: Carbonateville, Robinson, Kokomo, and Recen. At the peak of historic mining development in the 1880s, more than 10,000 people resided in the valley during the snow -free period. A number of mills and several smelters processed lead /silver, gold, copper, and (later) zinc ores extracted from the numerous mines in the area. Thus, Tenmile Creek Watershed from the top of Fremont Pass to well downstream of the Climax property line was impacted prior to the discovery and development of the Climax molybdenum ore body. Indeed, operations at Climax since the early 1970s have stabilized and dramatically improved environmental conditions in the watershed downstream of the property. Such improvements are evidenced by the documented recovery of the aquatic ecosystem in Tenmile Creek from its virtually sterile condition prior to 1970. Within the Tenmile Creek Watershed certain impacted waters are collected and routed to the SDP, for initial treatment and discharged to the Tenmile TSF. The SDP was incorporated into the mine's water treatment/management system in 2007 (AM -05) to improve both water treatment efficiency and sludge management and has a capacity of approximately 6,900 gpm. Employing lime neutralization, precipitation /settling, and sludge thickening steps, the SDP significantly reduces the water content of solids placed in the Tenmile TSF, thereby making more efficient use of the facility's solids storage capacity. The SDP produces a sludge that is deposited in a constructed cell on Tenmile TSF. Evaporation and freeze /thaw cycles increase sludge density. Water treatment, following the SDP, is currently accomplished using the water pools of the Tenmile and Mayflower TSFs for first and second stage treatment, respectively. In the first stage treatment, discharges from the SDP and impacted waters that exceed the SDP's treatment capacity of 6,900 gpm are treated by lime addition and settling in the water pool of the Tenmile TSF. In the second stage, treated water is decanted from the Tenmile TSF and flows by gravity into the Mayflower TSF where pH is again adjusted upward with lime addition to further precipitate metals and enhance settling. Water decanted from the Mayflower TSF is neutralized with sulfuric acid before merging with flow from the Interceptor System and is discharged at Outfall 001. When mineral extraction and production resumes, water treatment during Phase 1 Deposition (the period with active tailing deposition on the Tenmile TSF) will be similar to current operations, except that the tailing slurry would be deposited in the Tenmile TSF, and excess water would be reclaimed for use in the mill. Consistent with current water treatment practices, the SDP will provide first stage treatment of a significant portion of the primary impacted water sources, and first and second stage treatment would be accomplished by lime addition and settling in the water pools of the Tenmile and Mayflower TSFs. The Mayflower TSF will continue to provide second stage treatment before treated water is decanted from the pool, adjusted to a target pH of 6.5 to 9.0 with sulfuric acid, merged with waters from the Interceptor System, and discharged to Tenmile Creek downstream of 5 Dam. Treated water is discharged under the CDPS Permit as discussed in Section T -2.2 and as detailed in the schematic drawings in Permit Amendment AM -06 Exhibit G. During Phase II Deposition, tailing will be delivered to the Mayflower TSF (5 Dam) through a combination of new and rehabilitated tailing delivery pipelines (TDLs). The tailing slurry will be deposited in the Mayflower TSF utilizing the upstream deposition method by operation of a header and spigot system along the crest of 5 Dam. The mill water reclaim system will continue to operate generally as described above. The additional facility required during Phase II Deposition is the Mayflower Barge and reclaim water pipeline. This barge is to be located in the Mayflower TSF water pool and will deliver water from the pool to the north portal of the Tenmile Tunnel. As in Phase I Deposition, the first priority water to be delivered to the mill will be the water decanted from the water pool on Tenmile TSF. Supernatant from the Mayflower TSF water pool will be delivered to Robinson Lake at times when the upstream sources are inadequate to satisfy the mill water demand or when there is storage space available in Robinson Lake. During Phase II Deposition, the SDP will provide first stage treatment of impacted water for use at the mill, with the sludge pumped into the tailing delivery line. However, first stage treatment of other impacted water will take place in the Mayflower TSF water pool. The discharge of circumneutral tailing slurry into EPP: Revision R1 T -22 July 2011