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The Hanford Environmental Dose Reconstruction Project was initiated because of public interest in the historical releases of radioactive materials from the Hanford Site, located in southcentral Washington State. By 1986, over 38,000 pages of environmental monitoring documentation from the early years of Hanford operations had been released. Special committees reviewing the documents recommended initiation of the Hanford Environmental Dose Reconstruction Project, which began in October 1987, and is conducted by Battelle, Pacific Northwest Laboratories. The technical approach taken was to reconstruct releases of radioactive materials based on facility operating information; develop and/or adapt transport, pathway, 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; and perform scientific investigations that were technically defensible. The geographic area for the study includes approximately 2 x 10(5) km2 (75,000 mi2) in eastern Washington, western Idaho, and northeastern Oregon (essentially the Mid-Columbia Basin of the Pacific Northwest). Three exposure pathways were considered: the atmosphere, the Columbia River, and ground water. the radionuclide of interest for atmospheric pathway doses was 131I. The median dose for the maximally exposed individual was approximately 2.3 Gy (230 rad) to the thyroid over the period from 1944 to 1972 with a 90% subjective confidence interval of 0.54 to 8.4 Gy (54 to 840 rad). The Columbia River was studied from Priest Rapids Dam, upstream of the Hanford Site, to the mouth of the river and nearby bays. Radionuclides of interest for river pathway doses were 24Na, 32P, 65Zn, 76As, and 239Np. The median dose from the river pathway for the maximally exposed individual was approximately 0.0015 Sv (0.15 rem) effective dose equivalent in the period of maximum exposure (1950-1970). Doses from the groundwater pathway were determined to be below levels of interest for the project.

Radiation doses to individuals were estimated for the years 1944-1992 as part of the Hanford Dose Reconstruction Project (HEDR). The dose estimates were based on the radioactive releases to the atmosphere and Columbia River from the Hanford Site in southcentral Washington State. Conceptual models, computer codes, and previously published dose estimates were used to reconstruct doses. The most significant exposure pathway was found to be the consumption of cow's milk containing 131I. The median cumulative dose estimates to the thyroid of children ranged from < 0.7 mGy to 2.3 Gy throughout the study area, depending upon residence location. The highest estimated cumulative dose to a child ranged from 0.6-8.4 Gy (5th and 95th percentiles) with a median of 2.3 Gy based on 100 Monte Carlo realizations. The geographic distribution of the dose levels was directly related to the pattern of 131I deposition and was affected by the distribution of commercial milk and leafy vegetables. For the atmospheric pathway, the highest cumulative effective dose equivalent to an adult was estimated to be 12 mSv at Ringold, Washington, for the period 1944-1992. For the Columbia River pathway, cumulative effective dose equivalent estimates ranged from < 5 mSv to 15 mSv cumulative dose to maximally exposed adults downriver from the Hanford Site for the years 1944-1992. The most significant river exposure pathway was consumption of resident fish containing 32P and 65Zn.

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