The impact of environmental radioactivity at the INL Site on nonhuman biota is assessed using the U.S. Department of Energy (DOE) technical standard entitled A Graded Approach for Evaluating Radiation Doses to Aquatic and Terrestrial Biota and associated software, RESRAD-Biota (https://www.standards.doe.gov/standards-documents/1100/1153-astd-2019). The Graded Approach is used to meet the requirements of DOE Order 458.1 “Radiation Protection of the Public and the Environment" (https://www.energy.gov/ehss/services/environment/radiation-protection-public-and-environment). DOE facilities are required to demonstrate in their Annual Site Environmental Reports that routine radioactive releases from their sites are protective of non-human receptors. Sites are encouraged to use the Graded Approach for this purpose.
The first step in the graded approach uses conservative default assumptions and maximum values for all currently available data. For example, for the INL Site evaluation maximum concentrations of radionuclides in soils and effluent ponds are used for the general screening level. The general screening level (Level 1 in RESRAD-Biota) provides generic limiting concentrations of radionuclides in environmental media, termed Biota Concentration Guides (BCGs). Each BCG is the environmental concentration of a given radionuclide in soil or water that, under assumptions of the model, would results in a dose rate less than 1 rad/d (10 mGy/d) to aquatic animals or terrestrial plants or 0.1 rad/d (10 mGy/d) to terrestrial animals. If the sum of the measured maximum environmental concentrations divided by the BCGs (the combined sum of the fractions) is less than one, no negative impact to plant or animal populations is expected. If the sum of fractions is greater than one, more realistic, site-specific parameters are used in the model. The INL Site assessment have never exceeded the fraction of one using soil and water measurements.
A site-specific analysis employing a kinetic modeling tool is provided in RESRAD-Biota (Level 3). Multiple parameters that represent contributions to the organism internal dose can be modified to represent site- and organism-specific characteristics. Concentrations of radionuclides measured in the tissue of an organism can be input into RESRAD-Biota to estimate the dose to the organism. At the INL Site, waterfowl collected near effluent ponds have measureable concentrations of radionuclides associated with the effluent. Level 3 assessments using maximum radionuclide concentrations measured in waterfowl tissue are performed for the Annual Site Environmental Report. The assessment shows that doses received by waterfowl are less than the limit of 0.1 rad/d (10 mGy/d).
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