Frequently asked questions about the dry-stack tailings-storage facility (TDF) at Greens Creek
A: Tailings are the minerals left over after the economic minerals have been removed from the ore.
A: Tailings at Greens Creek are first run through a filter press to remove most of the water, then trucked to the TDF, where they are spread and compacted and eventually reclaimed to a natural state. The water that is removed is reused in the milling process.
A: Yes. The expanded TDF has been designed to provide the same or better environmental protection as the two prior TDF expansions. The area will be protected by a synthetic liner, and all water that comes in contact with the tailings is collected through a gravity-drainage system and temporarily stored in ponds until treated to Alaska Department of Environmental Conservation (APDES) permit standards and released.
A: The dry-stack method of tailings disposal used at Greens Creek eliminates the need for an embankment (dam) and slurry pond and reduces the tailings footprint by 80%.
- No dam
- Significantly smaller footprint
- Tailings can be reclaimed in stages
A: Greens Creek uses sound engineering, tailings-placement methods and water-control procedures to operate the TDF in a safe, environmentally responsible manner:
- Divert surface runoff from undisturbed areas around the TDF
- Collect and route direct runoff on the TDF via ditching and piping into water-management ponds for water treatment and discharge in compliance with the mine’s APDES permit
- Minimize tailings contact with groundwater by installing sub-drains, slurry walls, liners and finger and blanket drains beneath the tailings
A: No. About half are mixed with a binder, usually cement, then pumped underground to fill voids and help support the underground operation.
A: Yes. The mine asked to expand the TDF in 2001 and 2010. Approval was received in 2003 and 2014 following issuance of Final Environmental Impact Statements (EIS) and Records of Decision. In all cases, the Forest Service analyzed alternative TDF sites and determined that the existing site was the most appropriate and environmentally preferred for the expansion.
A: Yes. In the original 1983 environmental impact statement (EIS) for the mine and the two subsequent EISs, in 2003 and 2014.