23
KARST GEOLOGY, RADON FLUCTUATIONS, AND IMPLICATIONS
FOR MEASUREMENT AND MITIGATION

Jack R. Hughes, Brad Turk, Robby Cardwell, Patsy Brooks, Gene Fisher,
Marsha White, Francis Fitzgerald, David Wilson, James O. Bryant, Jr.
Southern Regional Radon Training Center
Engineering Extension Service
217 Ramsay Hall
Auburn University, AL 36849

Results of an investigation into factors contributing to elevated indoor radon concentrations in
supposedly mitigated homes suggest that, in areas of extensive karst geological development,
fluctuations in indoor radon concentrations may be extraordinary in magnitude, duration and seasonal
occurrence. Long-term monitoring of radon concentrations and other building and environmental
parameters indicate that the dominant factor producing these variations is the temperature difference
between the ground and ambient air, acting with elevation gradients to cause movement of radon-bearing
soil gas through the karst formation. The extreme nature of these variations may necessitate
alternative measurement strategies and mitigation procedures to reduce 'false negatives' and 'false
positives' and to enable effective reduction of indoor levels.
Intensive diagnostic investigations of the study houses were carried out, and procedures were
developed to predict and simulate mitigation system mechanical performance. The investigation
continues with efforts to evaluate various measurement strategies.

Key words: radon, Rn, karst, measurement, mitigation, seasonal, variations