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Benefits of designing for closure in Nevada

Before a tailings facility can be constructed in Nevada, detailed engineering design must be approved at state level, including plans describing process fluid operating protocols and methods and costs for disposing of process fluids and stabilising process materials. A reclamation plan must be prepared and approved by state and government regulators with a bond posted for these costs (“reclamation bond”), often funded by cash on hand. SRK recently permitted a new disposal system for flotation tailings in Nevada.

The conceptual design envisioned traditional grading, embankment construction, managed deposition into a synthetically-lined impoundment with an above-liner drainage collection system that directs fluids to a recycling system. In addition, the conceptual design incorporated a diversion channel for upstream stormwater to control 1-in-100 year, 24-hour peak flows. Initial bond cost estimates for post-closure fluid management were similar in magnitude to the project’s capital costs. Therefore, the design was modified to reduce the long-term water management liabilities. The tailings facility was double-lined with a gravity-draining leakage collection and recovery system (LCRS). This LCRS flow is the only water source requiring management under post-closure conditions, and the maximum-flowrate expected is extremely low, less than 150 gallons per day.

In addition, the site grading was designed to limit the rates of rise of the tailings surface to generally less than 10 feet per annum. The drainage system was reconfigured to flow to an internal sump and the water either discharged back onto the tailings surface or recycled to the plant. If operations suddenly cease, the tailings impoundment would experience a net negative water balance and any surface water remaining at closure would evaporate within the first closure year.

The design was also modified by excavating and stockpiling borrow material upstream of the impoundment to divert peak flows and provide a short-haul borrow for the final closure cover.

While capital costs increased by about 20 percent, reclamation costs decreased by about 70 percent, resulting in a net 25 percent reduction in short-term capital layout for construction and reclamation bond payment for the tailings impoundment. 

Dave Bentel:
Breese Burnley:

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