The mobility of potentially toxic deissolved metals discharged from a mine tailings source into an aquifer is investigated by using the multicomponent reactive transport model MINTRAN. A generic aquifer resembling a site in northern Ontario is used as a basis, and a scenario analysis is performed to determine the effect of terminating the source inputy of acidity and dissolved metals after a finite time. It is found that for most metals the buffering reactions in the carbonate aquifer lower the dissolved metal concentrations substantially, often by several orders of magnitude. In the case of a 12-year source duration, most metals are effectively immobilized by precipitation, and the concentrations of metals remaining in solution are well below drinking water limits. The risk of contamination of water resources by toxic metals can thus be controlled. ¿ American Geophysical Union 1994