Karst geology, radon fluctuations, and implications for measurement and mitigation

Results of an investigation into factors contributing to elevated indoor radon concentrations insupposedly mitigated homes suggest that, in areas of extensive karst geological development,fluctuations in indoor radon concentrations may be extraordinary in magnitude, duration and seasonaloccurrence. Long-term monitoring of radon concentrations and other building and environmentalparameters indicate that the dominant factor producing these variations is the temperature differencebetween the ground and ambient air, acting with elevation gradients to cause movement of radonbearingsoil gas through the karst formation. The extreme nature of these variations may necessitatealternative measurement strategies and mitigation procedures to reduce 'false negatives' and 'falsepositives' and to enable effective reduction of indoor levels.Intensive diagnostic investigations of the study houses were carried out, and procedures weredeveloped to predict and simulate mitigation system mechanical performance. The investigationcontinues with efforts to evaluate various measurement strategies.