An experimental research program was carried out to evaluate the environmental impacts of embankments constructed with steel slag on groundwater. A series of sequential water leach tests and sequential column leach tests were performed to study the leaching of aluminum, copper, and zinc into groundwater due to the flow of percolating rainwater through treated steel slag. The results indicated that treating steel slag prior to use by mixing with an alum-based water treatment residual resulted in lower effluent pH and metal concentrations. Metal leaching was greatly affected by the effluent pH and total metal content, as well as the natural pH and buffering capacity of the subgrade. The results of the employed numerical model showed that the field metal concentrations were expected to be considerably lower than those measured in laboratory column leach tests due to dispersion within the vadose zone.