Developing a pilot groundwater contaminant transport model involved intensive data and simulation model evaluation, and included re-calibrating an existing groundwater flow model for the Chillon River aquifer. Flow model re-calibration significantly improved head-matching statistics for the 1985-1997 era. Equilibrium-concentration and backtracking-augmented approaches guided sulfate contaminant transport model calibration. Because the flow-related data were known with more certainty than the transport-related data, the newly developed flow model parameters were not varied during transport model calibration. Transport model calibration optimization identified seepage water sulfate concentrations, that best match field measurements of 1993-1997. Project circumstances dictated the brevity of the history-matching era. Both the flow model and the transport model are as accurate as the data upon which they are based. They can be improved by enhanced positioning of pumping wells within the model grid, and increased horizontal and vertical discretization.