VALIDATION OF THE DERIVATIVE RADON-RISK MAP OF WILLIAMSBURG, VIRGINIA

A derivative radon-risk map based on a geologic map shows low, moderate, and high risk areas. Recent research has shown a correlation between unsafely high radon gas levels in homes in Williamsburg, VA to homes built in and slightly above sediments of the Pliocene Yorktown Formation. The purpose of this study was to validate the radon risk map of Williamsburg by administering radon detection tests in homes throughout Williamsburg in each of these areas. During Radon Awareness Week, we publicized this opportunity for homeowners to have their homes tested via the local newspaper and a campus announcement. Radon detection kits, donated by the Virginia Department of Health, were provided to 27 Williamsburg homeowners. After the 48 hour test, the detectors were returned to Alpha Energy Laboratories for results. Corentium Pro long term detectors were placed in two of the homes to verify the accuracy of the short term detectors. The results generally matched the expected risk. In a few cases, measured radon was lower than expected, likely due to home construction. However, one home that was expected to be at low risk had an activity of 11.5 pCi/L, the highest of the 27 tested homes. Subsequent auger samples around the home contain abundant heavy minerals. Analysis of the minerals shows uranium and thorium concentrations ten times the crustal average and radium activity twenty times the crustal average. More research needs to be done to determine the extent of these mineralized sands. Overall, the radon risk map was validated at most locations. We found that the use of a derivative geologic map is a reliable way to predict radon risk within the boundaries of the City of Williamsburg.