Assessment Advances from the Hanford Environmental Dose Reconstruction. B. A. Napier and W. T. Farris, Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland Washington 99352
Radiation doses to individual members of the public resulting from releases of radionuclides from plutonium production operations of the DOE’s Hanford Site in eastern Washington were estimated by the Hanford Environmental Dose Reconstruction (HEDR) Project. The HEDR Project was directed by an independent Technical Steering Panel and involved members of the public, regional States, and local Native American tribes. The technical approach taken was to reconstruct releases of radioactive materials based on facility operating information; develop and/or adapt transport, pathway, exposure, and dose models and computer codes; reconstruct environmental, meteorological, and hydrological monitoring information; reconstruct demographic, agricultural, and lifestyle characteristics; apply statistical methods to all forms of uncertainty in the information, parameters, and models; attempt to validate results where possible; and perform scientific investigations that were technically feasible. The project made extensive use of screening approaches, expert elicitation, technical and public reviews, and active solicitation of public input. Efforts included massive searches for data through over 40,000 boxes of records, and establishment of declassification procedures to allow release and use of the information, and methods of making the information directly available to interested members of the public. The results are applicable to a domain of over 200,000 km2 for a time period extending from the year 1944 to the present. Three major transport pathways were considered: the atmosphere, the Columbia River, and groundwater. The radionuclide of most concern for the atmospheric pathway was iodine-131. The median dose for the maximally exposed individual was 2.3 Gy (230 rad) to the thyroid, with a 90% subjective confidence interval of 0.54 to 87 Gy (54 to 870 rad). The Columbia River was studied from Priest Rapids Dam, upstream of the Hanford Site, to the mouth of the river and nearby bays in the Pacific Ocean. Radionuclides of interest for the river pathway were sodium-24, phosphorus-32, zinc-65, arsenic-76, and neptunium-239. The median dose from the river pathway for the maximally exposed individual was 0.015 Sv (1.5 rem). Doses from the groundwater pathway were determined to be below levels of interest for the project. The results are currently being used in both a major epidemiological investigation and a public outreach program.