EXECUTIVE SUMMARY
This report is prepared by the National Research Council (NRC) Committee on an Assessment of CDC Radiation Studies. It reviews the draft report, Task 4. EnvironmentalPathways–Models and Validation, submitted in 1993 by the Radiation Assessment Corporation (RAC) to the Centers for Disease Control and Prevention (CDC). The RAC's report describes the methods RAC plans to apply in a dose reconstruction project at the Feed Materials Production Center (FMPC) at Fernald, Ohio. The facility, which is northwest of Cincinnati, operated from 1951 to 1989. During that time, there were discharges of uranium compounds and small amounts of other radionuclides to the atmosphere and to groundwater and surface water. The goal of Task 4 of the project is to develop a method that can be used to translate the release estimates into actual concentrations of radioactive materials in the environment surrounding the facility and to predict the radiation exposures to human populations living in these environments.
The methods RAC used to assess environmental transport are similar to those used at other locations and for environmental impact studies, although other dose reconstructions have often been able to rely on actual environmental data, rather than trying to reconstruct a source term from very few measurements. In this committee's review, special attention was given to the examination of the models used and to RAC's validation methods and uncertainty estimates. There does not seem to be adequate validation of models by comparison with measurements in all cases nor an adequate discussion of why the RAC 's estimate of the total uranium released differs significantly from the estimate of Stevenson and Hardy (1993). Short-term, “episodic releases” require more detailed attention.
The study's environmental models focus on the principal environmental pathways –atmospheric dispersion, air-to-ground deposition, ground-to-air resuspension, and runoff and leaching of radionuclides from soil and storage sites to surface water, groundwater, food, and forage. The National Research Council committee paid particular attention to the description of particle-size distribution and to the assessment of radon releases from storage silos. The influence of the chemical form of the effluents on the dose coefficients to be used must still be addressed.
With respect to the uncertainties associated with the dose estimates, there is no indication of how the uncertainties in the source terms and environmental pathways will be propagated. The data used to define the size and demographic characteristics of the surrounding population during the period are appropriate and their use is reasonable.
The committee finds that the conceptual approach that RAC proposed for modeling environmental pathways is sound. Much work has been done by RAC in preparation for performing the actual dose calculations but it is not yet clear to the committee if sufficient effort to uncover data has been invested by RAC. It is difficult to judge the study as a whole because many decisions about methodology cannot be made until the first comprehensive assessment is complete.
