Plans to isolate radioactive waste raise more questions than can be answered within the lifetime of today's researchers. The existence of a multitude of unanswered questions, however, is not a unique phenomenon related to waste isolation, but is a general characteristic of all science. Although most questions related to the isolation of radioactive waste are interesting scientifically, answers to only a small but critical fraction of the questions are vital to the practical aspects of the problem. Almost all hydrogeologic evaluations of repository sites convey an excessively negative view with respect to geologic processes. Repositories do not necessarily become more hazardous with time. Many slow, normal geologic processes will seal and cover repository sites, making radionuclide migration less likely in the future than at present. Furthermore, several more rapid geologic processes, which are viewed with great apprehension, will not always have negative effects. Faulting could block ground-water circulation near the repository and consequently slow the outward migration of radionuclides; volcanism could cover repository sites, with only a slight chance of a volcanic vent contracting the radioactive waste; and in most of the northern part of the Midwest, future glacial activity would probably plaster the ground surface with layers of till, thus helping to isolate and protect any potential deep repository. Safety of waste repositories will depend on multiple barriers to migration of radionuclides. Further research focused on each barrier, however, is required before repository safety is assured. Davis,-S.N. (Univ. of Arizona, Tucson)
