DETERMINATION OF A RADON RISK BOUNDARY ON THE PALOS VERDES PENINSULA, CALIFORNIA

Because radon gas is ultimately derived from soil uranium, knowledge of surface uranium concentrations is the most important factor in determining areas that may be at risk for elevated indoor radon. Our past studies, aimed at the delineation of high and low risk radon neighborhoods, have found that the direct measurement of surface uranium concentrations by gamma ray spectrometry is the most reliable method of detecting rapid changes in radon source strength and the attendant radon risk.

In January 2005 the California Department of Health Services released an indoor radon potential map of Southern Los Angeles County, which assigned a moderate radon risk potential to the entire Palos Verdes Peninsula. However, previous efforts to map the soil uranium concentrations of school sites on the peninsula indicated that many of the sites on the west side supported high soil uranium levels, whereas those on the east side consistently displayed lower than average levels. These results suggest that an approximate north-south boundary could exist separating areas of high and low radon potential, and that the determination of this boundary could justify a revision of the radon potential map of Palos Verdes for greater accuracy and utility.

In order to locate this transition, surface potassium, uranium, and thorium concentrations were measured in east-west traverses across the Palos Verdes Peninsula using a gamma ray spectrometer. The results are plotted on a Dibblee geologic map to compare the measured values against the mapped geologic units, and to visually locate any obvious west-east concentration changes. In addition, comparisons with other known high radon potential areas in southern California are discussed in order to estimate the difference in radon levels that could occur in homes of the west and east sides of the Palos Verdes Peninsula.