[en] The Savannah River Plant has maintained thermoluminescent dosimeters both inside and outside of public buildings at 57 cities and towns within a 50-mile radius of the plant since 1980. The dosimeters, which are replaced and processed quarterly, have provided backgound gamma radiation levels at these locations. In the event of a nuclear incident, the dosimeters would be collected and processed to determine the integrated dose to individuals in these areas. The data show that dose rates inside buildings ranged from 51 to 212 mR/y, while those outside the buildings ranged from 55 to 146 mR/y. Measurements at individual locations have been consistent over this time period. Differences between inside and outside measuements are attributed primarily to radioactivity in construction materials with a possible contribution from the buildup of radon and thoron that occurs in well-insulated, airtight buildings. 3 references, 3 figures, 1 table