EVALUATION OF THE SATURATED-UNSATURATED GROUNDWATER CONDITIONS OF A THICKENED TAILINGS DEPOSIT

The method of thickened tailings disposal has been in use at an active copper-zinc mine near Timmins, Ontario, for approximately 25 years. T he thickened tailings deposit that has been formed was investigated. F ield and laboratory tests were conducted to determine particle-size di stribution at Various horizontal locations, in situ values of hydrauli c conductivity, moisture-retention characteristics, groundwater levels , and in situ water contents. The results of the investigation show th at the thickened tailings deposit is relatively homogeneous. Shallow g roundwater levels were also observed to follow the gently sloping topo graphy of the tailings surface. Upward-seepage analyses were conducted for various steady-state evaporative fluxes. The analyses showed the tailings tend to maintain saturated conditions for the highest potenti al rate of evaporation observed. The ability of the tailings to mainta in saturation is attributed to the shallow groundwater levels and the high air-entry value of the tailings. The tendency to saturated condit ions at the tailings surface is a positive result. Saturated condition s in the tailings minimize the diffusion of atmospheric oxygen into th e tailings. This aids in the prevention of acid generation in these ta ilings, which have the potential to oxidize and produce acid drainage.