[en] One of the major factors involved in evaluating the suitability of the Columbia River basalts for the siting of a nuclear waste repository is the assessment of the ability of the basalt geohydrologic system to retard the transport of radionuclides to the accessible environment. Solubility limited release of radionuclides and sorption of radionuclides on basalt and its associated secondary minerals are two of the dominant mechanisms for retardation of radionuclide transport in the groundwater-basalt system. A simple one-dimensional transport model, incorporating the available radionuclide solubility constraints and sorption behavior imposed by the basalt geohydrologic system, has been employed to evaluate the ability of the basalt system to retard the migration of radionuclides to the accessible environment. A comparison of the resultant predicted radionuclide transport behavior with proposed US environmental regulations has been used to evaluate preliminary performance requirements for a waste package in the basaltic repository. 18 refs., 5 tabs