Challenges in developing estimates of exposure rate near the Nevada Test Site

As one of several dose reconstruction projects, the Off-site Radiation Exposure Review Project needed to develop models that reflect processes and lifestyles of the past and obtain accurate and adequate historical data to drive the models. One of the critical pieces, ultimately used to estimate the potential dose to people in the area surrounding the Nevada Test Site, was the development of exposure rate estimates used as input to the external and internal dose models. The historical data available for making these estimates were collected in manners and for purposes not necessarily consistent with the needs of this task. The Town Data Base is the culmination of the effort to develop those estimates for the Project's Phase I region (or for locations near the Nevada Test Site that were primarily covered by ground monitoring at the time of the nuclear tests). It includes estimates of discernible exposure rate at 353 populated locations in Arizona, California, Nevada, and Utah and for 74 nuclear tests at the Nevada Test Site. Each dose reconstruction effort has similarities with, and variations from, others. This paper describes some of the challenges encountered in creating the Town Data Base and the approaches used to address them. These challenges included collecting historical data, incorporating net exposure rate values of zero into the estimates, defining a discernible fallout level, handling the lack of measurements at some locations and creating dispersion estimates. The approaches were developed to create "best" estimates and to use actual data (as opposed to assumed values) as the primary source where such data were available. A summary of the spatial distribution of these estimates and a comparison of relative levels of fallout by location are also included.