IMPROVEMENT IN THE ACCURACY OF RADON POTENTIAL MAPS USING LOCALIZED GROUND GAMMA RAY SPECTROMETRY

Radon is a colorless, odorless gas that is generated from the decay of naturally occurring uranium present in most soils. It is the second leading cause of lung cancer in the United States, resulting in approximately 21,000 deaths each year. In order to help the public address this health hazard, the US EPA and USGS have published state and overall county radon risk maps. A combination of data from indoor radon testing and equivalent uranium (eU) measurements from aerial radiometric surveys is used to determine the radon risk potential of different geologic subunits.

However due to airspace restrictions, most major metropolitan areas have no flight line data whatsoever, and estimates for the uranium content of the underlying soils can have large uncertainties that have been documented in our past studies. The uranium concentrations of identically labeled rock units were found to vary widely, even within a county, and hence their radon potential cannot be assumed to be consistent. In addition, there is often only sparse indoor radon data due to low homeowner awareness in California, and hence the true risk levels associated with these subunits can be difficult to ascertain.

Because of these uncertainties, definitive eU results obtained by ground gamma ray spectrometry can help assess the radon potential of targeted soils without the need for assumptions or extrapolations. Furthermore, ground measurements can be particularly useful in delineating high risk neighborhoods in metropolitan areas that lack the eU data typically derived from aerial surveys. The present paper will discuss specific examples of risk areas in California that could benefit from this approach.