ABSTRACT
The geochemical factors which control the groundwater distribution of each radionuclide are discussed in Hess et al. Groundwater derived from silicic igneous rocks, primarily granites, routinely has elevated levels of all the radionuclides investigated in this study. The Ogallala Formation of the High Plains region produces groundwater with a wide range of radionuclide concentrations, including some of the highest uranium values in the country. While these granites are generally as high in radionuclide content as the granites of the Rocky, Appalachian, and Sierra Nevada ranges, these Canadian Shield granites locally produce elevated concentrations of radionuclides in groundwater. Elevated uranium levels occur in groundwater derived from the Dakota Sandstone and its stratigraphic equivalents in portions of the Great Plains region. Northern Washington and Idaho are underlain by igneous and metamorphic rocks, including granites, which contain groundwater with elevated radionuclide levels. Groundwater is primarily derived from alluvial deposits in Alaska and generally displays low radionuclide concentrations.
