The transport and fate of Fe, Mn, Cu, Zn, Cd, Pb and SO4 in a groundwater plume and in downstream surface waters in the Coeur d'Alene Mining District, Idaho, U.S.A

A plot of calcium versus sulphur demonstrated that a plume of acidic contaminated groundwater flowing below a flotation mill was diluted by infiltration of rainwater and creek water and by ambient deep groundwater. Concentrations of iron decreased from 2.1 mg per litre as concentrations of dissolved lead increased to 0.37 mg per litre and concentrations of up to 16 mg zinc per litre, 6.2 mg aluminium per litre, 2.1 mg copper per litre and 0.077 mg cadmium per litre in shallow groundwater were conserved until the plume emerged in a seep area. Groundwater was then diluted with creek water by factors of 11-50 and pH became neutral. Metal removal over a 20 m stream reach was in the order iron-aluminium-lead-copper-manganese and zinc and cadmium. Lead and copper removal continued as the creek reached a tailings dam while zinc concentrations increased. The contaminated creek water (zinc concentration 400-800 mg per litre) was then diluted by 2 water masses and 2 tracers (dissolved silicon and sulphur) were required to distinguish between mixing and geochemical reaction. Lead concentrations decreased below detection limits while copper and manganese were removed to a lesser extent during low flow conditions. Less than 10 per cent of plume zinc and cadmium were lost from solution over a 5 km distance downstream. There are 30 references.