INFLUENCE OF SEASONAL PRECIPITATION ON INDOOR RADON

Measurements of indoor radon are generally thought to be greatest during the winter, because home occupants tend to keep their windows closed to conserve heat, as is done in our northern Virginia study area. Rainfall is generally thought to temporarily increase indoor radon concentrations, because a home becomes surrounded by water-saturated impermeable soil preventing radon from escaping. Studies have shown that during a rainstorm, and for several hours after the storm ends, the soil-gas radon concentration increases, allowing more to be drawn into the home. We have found in a two year study that the season with the greatest total rainfall had the highest average indoor radon. In a study of seasonal (three month) measurements using alpha-track monitors in over 1000 homes, one summer had higher total rainfall than all the other seasons and had higher indoor radon, as was demonstrated using subsets delineated by geological units, home construction and type of heating. Comparisons of the two winters also showed positive correlations using these subsets between total precipitation and average indoor radon.