Assessment of Ecological Risks and Impacts of Remedial Activities at the Department of Energy's Hanford Site. C. S. Duke, CommonSense Environmental, 9569 Humphrey Road, Cincinnati, Ohio 45242; and L. Dean and K. CadweIl, Advanced Sciences, Inc., 1777 Terminal Drive, Richland, Washington 99352
The U.S. Department of Energy's Hanford Site, near Richland, Washington, covers about 148,000 ha, including one of the last undisturbed tracts of native sagebrush steppe habitat in the state of Washington. Plans are currently being formulated for the remediation of over 1,100 past practice waste sites at the facility. Potential remedial activities being evaluated include dredging of riverine sediments, capping of waste sites, and large scale excavation of buried wastes. Exposure to radionuclides and chemicals present in the wastes could have adverse effects on ecological receptors at the site. Conversely, the physical impacts on ecological resources of remedial activities such as large scale excavation and dredging may be extensive. Evaluation of both the potential ecological risks of exposure to wastes and of the potential impacts of remedial activities is therefore a critical step in the selection of remedial actions. Baseline ecological risks and potential remediation impacts were assessed for an environmental impact statement at the facility. Source terms were estimated from waste inventory data aggregated within cells (1 kM2 each) of a matrix plotted on a Geographic Information System (GIS) map of the facility. Radiation doses and chemical hazard quotients were estimated using a screening-level model which included a generic plant, the Great Basin pocket mouse, and two predators, the coyote and the red-tailed hawk. Physical impacts were evaluated by mapping areas likely to be disturbed during remediation over maps of habitats and sensitive species distributions. The results indicate that potential ecological hazards exist in the Central Plateau region and adjacent to the reactors along the Columbia River, with estimated radiation doses exceeding the current DOE benchmark of one rad per day and chemical hazard quotients exceeding 1.0 for receptors exposed to the maximum estimated radionuclide and chemical concentrations in soils. No attempt was made to quantify uncertainties, but they are likely to be high. Field studies suggest that current exposures are limited and hazards low. Conversely, the physical impacts which would result from remediation are extensive and are likely to have much lower uncertainty. These results illustrate the significant tradeoffs which must be made if remediation of potential radiological and chemical hazards is to proceed in areas with important ecological resources.