Radionuclides in groundwaters: contaminants and tracers

As groundwaters serve for drinking-water purposes, radionuclides in groundwater are generally considered as contaminants. Some of the radionuclides contributing to natural radioactivity in groundwater and some of the manmade atmospheric radionuclides, however, have become good tracers for the assessment of residence times (groundwater age) and mixing. Controlled experiments with artificial radionuclides, on the other hand, are restricted to a few special cases, e.g. the single-borehole dilution method, or two-borehole injection-withdrawal experiments.