performance objectives. The point of compliance for the tanks was selected by DOE and the South Carolina DHEC for the tank closure assessments for Tanks 17 and 20.

Similarly, the exposure scenario is crucial to the calculated dose results. The U.S. Environmental Protection Agency (EPA) approach to protecting human health and the environment from such contaminants differs from that used by the USNRC. The EPA uses a lifetime cancer risk criterion to determine acceptable levels of residual soil contamination, whereas the USNRC and most states use an annual dose criterion. The two criteria cannot be compared in a meaningful way without also examining each agency’s entire system for the protection of public health and the environment, including methods of site characterization, assumptions about future land use, and methods assessing dose and risk, as well as uncertainties in determining levels of residual contamination and uncertainties in dose and risk assessments (NCRP, 2004).

Selection of an intruder scenario and the point of compliance involve policy and technical choices. A number of different intruder scenarios and points of compliance have been used in performance assessments and accepted by regulatory authorities. However, good risk management practice requires that the intruder doses and the rest of the spectrum of risks and trade-offs associated with future scenarios be considered with other assumptions in the context of the entire decision-making process, not in isolation. The committee is exploring what it can say further on these matters in its final report.

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