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Technical Revision (TR -18) Climax Molybdenum Company
<br />Environmental Protection Plan Permit No. M- 1977 -493
<br />T -5.3 Tenmile Creek Watershed
<br />T -5.3.1 Potential Sources of Contamination
<br />The open pit mine, mill facilities, overburden storage facilities (OSFs), and the Robinson, Tenmile and
<br />Mayflower TSFs are all located within the Tenmile Creek Watershed (Figure AM- 06- T -01). Most of the
<br />mine's water treatment/management activity occurs within the Tenmile Creek drainage area and must
<br />address: (1) a component of water that is pumped from the Eagle and Arkansas River drainages to the
<br />Tenmile drainage; (2) a large component of minimally impacted runoff from areas above the interceptor
<br />channels within the Tenmile drainage; and (3) wastewater from the mill circuit and water which has had
<br />direct contact with mine tailing, overburden, or other disturbed areas.
<br />Water from the Arkansas River drainage introduced to the Tenmile drainage includes water from the
<br />underground mine workings (5 -Shaft) and water from the Arkansas Well used for domestic supply at the
<br />mill. Water introduced from the Eagle River drainage includes dam seepage (1 and 4 Dam), and runoff
<br />collected in Robinson Lake that may enter the Tenmile drainage area as makeup to the mill water circuit.
<br />All other waters managed by Climax originate as snow or rainfall within the Tenmile Creek drainage on
<br />the mine site or on land above the interceptor canals.
<br />The upper Tenmile Creek Watershed, including its tributary drainages of McNulty Gulch, Kokomo Gulch,
<br />Searle Gulch, Rose Gulch, Tucker Gulch, Humbug Creek, Mayflower Creek, and Clinton Creek, has been
<br />subject to extensive placer and lode mining, milling, and smelting operations since the discovery of placer
<br />gold in the 1860s (reference for historic information: Dempsey, S. and J.E. Fell, Jr. 1986; Minim the
<br />Summit. University of Oklahoma Press). At one time, the Tenmile Creek Valley within the present
<br />boundaries of Climax supported four incorporated towns: Carbonateville, Robinson, Kokomo, and Recen.
<br />At the peak of historic mining development in the 1880s, more than 10,000 people resided in the valley
<br />during the snow -free period. A number of mills and several smelters processed lead /silver, gold, copper,
<br />and (later) zinc ores extracted from the numerous mines in the area. Thus, Tenmile Creek Watershed
<br />from the top of Fremont Pass to well downstream of the Climax property line was impacted prior to the
<br />discovery and development of the Climax molybdenum ore body. Indeed, operations at Climax since the
<br />early 1970s have stabilized and dramatically improved environmental conditions in the watershed
<br />downstream of the property. Such improvements are evidenced by the documented recovery of the
<br />aquatic ecosystem in Tenmile Creek from its virtually sterile condition prior to 1970.
<br />Within the Tenmile Creek Watershed certain impacted waters are collected and routed to the SDP, for
<br />initial treatment and discharged to the Tenmile TSF. The SDP was incorporated into the mine's water
<br />treatment/management system in 2007 (AM -05) to improve both water treatment efficiency and sludge
<br />management and has a capacity of approximately 6,900 gpm. Employing lime neutralization,
<br />precipitation/settling, and sludge thickening steps, the SDP significantly reduces the water content of
<br />solids placed in the Tenmile TSF, thereby making more efficient use of the facility's solids storage
<br />capacity. The SDP produces a sludge that is deposited in a constructed cell on Tenmile TSF.
<br />Evaporation and freeze/thaw cycles increase sludge density.
<br />Water treatment, following the SDP, is currently accomplished using the water pools of the Tenmile and
<br />Mayflower TSFs for first and second stage treatment, respectively. In the first stage treatment,
<br />discharges from the SDP and impacted waters that exceed the SDP's treatment capacity of 6,900 gpm
<br />are treated by lime addition and settling in the water pool of the Tenmile TSF. In the second stage,
<br />treated water is decanted from the Tenmile TSF and flows by gravity into the Mayflower TSF where pH is
<br />again adjusted upward with lime addition to further precipitate metals and enhance settling. Water
<br />decanted from the Mayflower TSF is neutralized with sulfuric acid before merging with flow from the
<br />Interceptor System and is discharged at Outfall 001.
<br />When mineral extraction and production resumes, water treatment during Phase 1 Deposition (the period
<br />with active tailing deposition on the Tenmile TSF) will be similar to current operations, except that the
<br />tailing slurry would be deposited in the Tenmile TSF, and excess water would be reclaimed for use in the
<br />mill. Consistent with current water treatment practices, the SDP will provide first stage treatment of a
<br />significant portion of the primary impacted water sources, and first and second stage treatment would be
<br />accomplished by lime addition and settling in the water pools of the Tenmile and Mayflower TSFs. The
<br />EPP: Version R2
<br />T -24 December 2011
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