Natural attenuation of mine drainage-borne zinc in shallow subsurface soils over permafrost, central Yukon, Canada

摘要

Zinc-bearing mine effluent of pH～6 discharges from an inactive underground silver mine on a hillside in central Yukon, Canada, near the northern limit of the discontinuous permafrost zone. The effluent percolates through shallow soils overlying permafrost and discharges to small stream in the valley below. Water sampling undertaken during summer 2000 shows progressive removal of zinc from drainage waters in the downslope direction; typical effluent zinc concentrations of 150 mg/1 at the adit mouth are reduced to <2 mg/1 where the drainage discharges to the creek. Investigation of the shallow subsurface revealed a poorly decomposed organic horizon overlying a poorly sorted fine grained mineral soil. These two soil types were sampled at numerous locations across the study area and subsequently subjected to batch adsorption tests as a measure of the natural attenuation capacity of the organic and mineral soils in contact with the mine drainage.