Comparison of multimedia model predictions for a contaminant plume migration scenario

Predictions of four risk assessment models — RESRAD, PRESTO, MMSOILS, and MEPAS — for a test scenario involving the migration of a single, rapidly transforming radionuclide, 90Sr, and a persistent, long radionuclide chain, 234U and its progeny, in groundwater are compared. All four models make comparable predictions for the plume centerline concentrations of the primary contaminants in the aquifer for a distance of up to about 300 m from the source. MEPAS, MMSOILS, and RESRAD make similar predictions for the transverse concentration profiles in the aquifer. The four models make considerably different predictions for the temporal concentration profiles of the progeny in the aquifer. The profiles differ in shape, magnitude of the peak, and in width. The differences are a result of the simplifying assumptions underlying each of the models.