Pony mill site closure: Healing a black eye of the mining industry

摘要

In late 1994, low concentrations of cyanide were detected in a domestic wel in the town of Pony, Montana, and at a nearby spring. The cyanide is believed to have leaked through the liner of a tailings impoundment at the site of the Pony Custom Gold Mill. The Montana Department of Environmental Quality has responsibility for the site and has begun reclamation efforts by removing hazardous chemicals from the site and dewatering the tailings pond. Further reclamation of the site required engineering design involving the dam, pond, and the surrounding slopes. Of particular interest is the manner in which the cyanide-processed tailings will be handled. The tailings will be encapsulated inside the current pond liner and will be buried under several feet of soil. Successful completion of the encapsulation includes: minimization of leachate escaping from the liner, minimization of differential settling, and minimization of ponding water on the liner.