Part of the environmental permitting effort for PolyMet’s proposed copper-nickel and precious-metal mine included tailings-basin closure planning. Barr evaluated both wet and dry closure approaches for the basin. A “wet closure” approach would consist of a large pond surrounded by wetland and meadow areas to cover the basin, limit oxygen intrusion into the tailings, minimize water-quality impacts, and accommodate wetland mitigation at the time of basin closure. A “dry closure” approach would include surface contouring to shed surface water, a hydraulic barrier to limit water infiltration, and a vegetated soil cover. We studied water-quality impacts for both of the closure options, as well as constructability, long-term maintenance, and slope-stability factors of safety for the basin.
Vice President Senior Hydrogeologist
Vice President Senior Geotechnical Engineer