Identification and assessment of a small, geologically localized radon hot spot

Abstract A small, geologically localized radon hot spot known as the Rincon Shale Formation has been identified in Santa Barbara, California. Surveys which sample randomly chosen homes at the county level have failed to identify this hot spot. Stratified sampling according to geologic province identified the high radon potential region. Detailed analysis of aerial photographs show that approximately 5% of the homes in the county are affected by the hot spot. Because the outcroppings of the formation do not conform with administrative boundaries, such as county, city or postal code, identification by random sampling of the hot spot is difficult. More than 70% of homes on the hot spot are predicted to exceed 4 p Ci/L(150 Bq/m 3 ) in standardized screening tests. The indoor radon concentrations for homes on the hot spot (geometric mean 8.4 pCi/L = 310 Bq/m 3 ) are an order of magnitude greater than California levels (geometric mean 0.7 pCi/L = 26 Bq/m 3 ). Indoor radon data which diverge from the usual lognormal pattern at high magnitudes may indicate the presence of a radon-prone subpopulation. Of standard statistical measures, the geometric standard deviation is the most sensitive to the presence of a radon hot spot.