Association of Hanford origin radionuclides with Columbia River sediment

Results are reported from measurements of present radionuclide concentrations in Columbia River sediments. A description of the rates and mechanisms governing the decrease in radioactivity levels in the river sediments between 1971 and 1976; a characterization of the areal and depth distribution of fine grain, silty sediments in the McNary Reservoir mode by sub-bottom seismic surveying; and analysis of deep piston cores which penetrate the entire thickness of sediment deposits at selected sites in McNary Reservoir to provide radionuclide data for estimating the inventories of radionuclides in the sediment deposits in the McNary Reservoir are included. The results of these studies showed that the short- and intermediate-lived radionuclides have now decayed to insignificant levels, and only a few long-lived radionuclides (i.e., 54Mn, 55Fe, 60Co, 137Cs, 152-154Eu, 238Pu, 239-240Pu, and 241Am) at trace concentrations remain buried in the sediment deposits. The surface sediments in the McNary Reservoir contain much lower radionuclide concentrations than deeper sediments because of the build-up of 40 to 80 cm of fresh, relatively uncontaminated new sediment deposits since 1971