Analysts typically incorporate into groundwater pathway models for low-level radioactive waste a simplified approach for the buildup and decay of radioactive progeny during environmental transport. The inventory is transported to the exposure point, with doses calculated there for the parent and progeny based on predicted concentrations of the parent radionuclides. This approach generally provides conservative values because maximum combined doses are larger than they would be if transport of parent and progeny were based on differing travel times. For some radionuclides, however, the approach causes underestimation of doses. Because of buildup of radiologically significant progeny, the dose at the exposure point may be higher at later arrival times than at the parent's arrival time. Also, if a parent radionuclide is shorter-lived and less mobile than one of its progeny, the parent may reach maximum dose before the progeny. We developed an alternate approach that provides conservative doses for these radionuclides. ¿ 1998 American Geophysical Union