MODELING OF MULTICOMPONENT REACTIVE TRANSPORT IN GROUNDWATER .2. METAL MOBILITY IN AQUIFERS IMPACTED BY ACIDIC MINE TAILINGS DISCHARGE

The mobility of potentially toxic dissolved metals discharged from a m ine tailings source into an aquifer is investigated by using the multi component reactive transport model MINTRAN. A generic aquifer resembli ng a site in northern Ontario is used as a basis, and a scenario analy sis is performed to determine the effect of terminating the source inp ut of acidity and dissolved metals after a finite time. It is found th at for most metals the buffering reactions in the carbonate aquifer lo wer the dissolved metal concentrations substantially, often by several orders of magnitude. In the case of a 12-year source duration, most m etals are effectively immobilized by precipitation, and the concentrat ions of metals remaining in solution are well below drinking water lim its. The risk of contamination of water resources by toxic metals can thus be controlled.