| Summary: | An adit on the United Keno Hill property discharges water at 1-10 L/sec with 20-30 mg/L (ppm) zinc. This paper describes how a wetland treatment system was developed to passively treat this discharge. Adit water was supplied to a 180 m2 pilot-scale wetland at a rate of 18 L/min. The wetland reduced zinc concentrations from 25 ppm to approximately 3 pprn. However, water in parts of the wetland had 0.3 ppm zinc. Microcosms established within the wetland reduced zinc concentrations to <0.2 ppm. Cobalt, iron, manganese, and nickel were also removed in the wetland and the microcosms. Finally, a natural wetland receiving water with 3 ppm zinc produced a discharge of 0.3 ppm zinc. Taken together, these results suggest that a constructed wetland can, in principle, reduce zinc below the permitted discharge limit of 0.5 ppm. Zinc appeared to be retained in the pilot wetland by reacting with hydrogen sulphide, generated in sediments by sulphate-reducing bacteria. Metals accumulating in natural wetlands receiving mine-impacted water were primarily retained with iron and/or manganese oxides, or as sulphides. These metals were not taken up by wetland plants.
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