Coprecipitation, the precipitation of trace metals in solids mostly composed of other major constituents, is an important process that controls the fate and transport of contaminants associated with mining wastes. Typically, acidic drainage water has high concentrations of aluminum and iron. Sharp reductions in the concentrations of hazardous metals occur concurrently with the precipitation of aluminum and iron hydroxides, which are commonly attributed to coprecipitation. However, coprecipitation has not been incorporated into currently available transport models. In order to better simulate contaminant transport in groundwater where coprecipitation plays a significant role, we are developing a coupled reactive transport model that is capable of simulating advection, dispersion, coprecipitation along with aqueous speciation, ion-exchange, and surface adsorption. We believe that the coupled code with coprecipitation reactions will better simulate the transport of metal contaminants in chemically heterogenous groundwater systems typical of acidic mine tailings environments.