From 1988 through 2004, samples of upper-layer sediments from the Columbia River and Snake River were collected under the Hanford Site Surface Environmental Surveillance Project to document concentrations and trends of radionuclides. Low concentrations of potassium-40, cesium-137, uranium isotopes, and plutonium isotopes were detected consistently in sediment samples over the entire sampling period. The concentrations of most radionuclides were similar to values measured upstream of the Hanford Site behind Priest Rapids Dam. For all locations, the concentrations of radionuclides in sediment samples from the Columbia and Snake rivers were below concentrations that would result in a 1-mrem effective dose equivalent to a hypothetical exposed individual using a shoreline exposure scenario (i.e., 500 hr/yr of external dose). The DOE limit for public exposure is 100 mrem/yr.
Revised: November 2, 2007 |
Published: October 1, 2007