1998-02-25_HYDROLOGY - M1977493 - Laserfiche WebLink

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the head of the East Fork of the Eagle River west of the Project Construction primary tailings disposal facilities in the Tenmile drainage. In the two years of operation of the Molyoxide plant, 917M in The preferred option using removal by hydraulic of tailing were deposited in this facility known as the "Oxide monitoring and pumping began in 1993. This initial method Pond". proved untenable due high plasticity of the material and inadequate tailing density in the slurry being pumped under Project Development high head. A truck and shovel operation was initiated in early 1995 to remove the tailing from the Eagle River basin to the In 1989 a clear understanding of the water asset Tenmile Creek basin, a distance of approximately 4.8 km. value of the property and a desire to reduce care and Truck and shovel operations continued through the summer of maintenance costs led to the assessment of alternatives for to 1996. site footprint reduction and reclamation. Review of the oxide pond,from which over 370M in (300 acre-feet)of water had Management of the tailing and dewatering activity been annually pumped to the Tenmile water treatment proved to be the largest challenges of the construction project. facilities for the 30 years following curtailment of the The initial assessment of the tailing revealed that the material Molyoxide processing,determined that removal of the tailing was predominantly composed of silt-sized particles with in the reservoir was feasible (Woodward-Clyde Consultants, liquid limits ranging between 32 and 40 and plasticity indices 1998). ranging from 1 to 6. Moisture content of the material ranged from 35 to 49 percent indicating that the moisture content of The Climax Mine Reclamation Permit, held with the oxide tailing was above the liquid limit. Materials were the Colorado Division of Minerals and Geology, calls for considered to be of very low strength, and large settlements reclamation of the Oxide Pond and several other mine were anticipated under small loads (Woodward-Clyde facilities to a post-mining beneficial land use of Developed Consultants, 1998). During excavation, the material did Water Resources. The methods by which Climax would behave as a heavy liquid,requiring short loading of trucks and obtain this designated post-mining land use are not the installation of special tailgates to hold liquefied tailing specifically outlined in the permit. Climax evaluated long- during the haul. term management of tailing in the pond and considered tailing removal using dredge and pump systems, truck and shovel An equally important aspect of the removal removal, or capping and fix-in-place alternatives to retire the operation was the management of water during the period of facility. Both physical and chemical characteristics of the excavation and hauling. Water management was an important materials were reviewed in the pre-feasibility evaluation. task in allowing equipment access and egress. In addition, thirty years of tailing storage in the impoundment had The study found that cost effectiveness, long-term contaminated dam foundation materials as water seeped maintenance costs, and the most favorable environmental through the dam to a seepage return system at the dam's toe. protections were best obtained through tailing removal This seepage and all water in the reservoir throughout the (Woodward-Clyde Consultants, 1998). The driver for this removal project required pumping to the Climax Water project ultimately became the regional recognition of the Treatment System in the Tenmile Creek basin. Climax treats potential beneficial use of stored water at the headwaters of all mine water under a National Pollution Discharge the Eagle River. Elimination System (NPDES) permit in an active lime neutralization process to a discharge point in Tenmile Creek. The Eagle Valley of Colorado is host to recreation and residential development activities in support of a thriving Additional pollution protections and infrastructure ski industry. Water use in the Eagle Valley increases during construction occurred through 1998. A concrete cutoff wall winter low flow months for snowmaking and municipal water was constructed to a bedrock foundation in the drainage treatment during the winter tourist season. Stream depletions between upgradient process water facilities and the reservoir. in the Eagle Valley are not replenished until the Eagle River Climax managed seepwater at the toe of the dam through and the Colorado River converge well downstream of water pump upgrades and pipeline improvements. Because the use. Upstream replenishment of in-stream depletions was Oxide Pond was designed to prevent the release of water therefore a desire of Eagle Valley water users, the Colorado down the Eagle Valley, outlet works in the Class 1 dam, Water Conservation Board, and other stakeholders for water reconstruction of the emergency spillway, and installation of use in the valley. The location of the Oxide Pond,on private conveyance and flow measurement devices were required. land at the headwaters of the Eagle River, coupled with the These dam improvements were subject to review by the presence of an earthen core impoundment capable of storing Colorado Office of the State Engineer. fresh water rather than tailing, provided the site for basin water storage. Capacity of the new facility would be 3.9MM Since reservoir capacity was to be maximized, m3 (3,148 acre-feet) with a live yield of 2.5MM m3 (2,016 additional excavation occurred after identification of growth acre-feet) (W.W. Wheeler& Assoc., 1994). In 1993, Climax media(topsoil)residing beneath the tailing. During the fall of and Vail Associates entered a cooperative agreement to 1996, 41M m3(33 acre-feet) of growth media were hauled 6 perform tailing removal and tailing pond reclamation using km to temporary stockpiles for reclamation of overburden the preferred removal options outlined in the pre-feasibility wastes near the Climax milling complex. This activity process. provided badly needed materials for successful high-altitude