Development of Radon Enrichment in Soil Gas over Quartz-Mica Schist in Virginia

Abstract

A major portion of northern Virginia is underlain by a quartz-muscovite soil, on average about 10 meters thick, that has developed on a bedrock of polymetamoirphic schist. The schist formed from an ancient clay-rich sediment eventually recrystallized several times, as the modem Appalachian rocks were heated deep in the Earth and subsequently exposed by erosion. The total gamma radioactivity and the permeability of the schist are higher than average, and combine to generate a radon-rich soil-gas that can be brought into homes by the pressure differential normally present in local homes that commonly are well insulated and have basements. More than half of the homes, based on three-month measurements, exceed the U.S. Environmental Protection Agency recommended maximum for indoor radon of 4 pCi/L. Fortunately, while the area is experiencing a rapid increase in new home construction, it is possible to avoid types of home construction susceptible to, and areas of, high soil-gas radon and high permeability.