Soil-gas entry into an experimental basement driven by atmospheric pressure fluctuations—Measurements, spectral analysis, and model comparison

Abstract

To study the effects of atmospheric pressure fluctuations on the entry of radon and soil-gas contaminants into houses, we have simultaneously measured the changes in atmospheric pressure and the gas flow rate between the interior of an experimental basement structure and the underlying soil. Atmospheric pressure fluctuations draw soil gas into the experimental basement without the indoor-outdoor pressure differences commonly associated with advective entry of soil-gas contaminants. The soil-gas flow rate induced by a change in atmospheric pressure depends on both the characteristic response time of the soil and the time-rate-of-change of the atmospheric pressure fluctuation. Spectral analysis indicates that relatively low-frequency fluctuations in atmospheric pressure are the most important for driving soil-gas into and out the of the experimental structure; more than 60% of the total power of the soil-gas flow spectrum occurs at frequencies less than 100 d −1. A transient finite-element model based on Darcy's law correctly predicts both the dynamics and the magnitude of the observed gas flow. Atmospheric pressure fluctuations may increase the long-term radon entry rate into the experimental structure by as much as 0.2 Bq s −1, which is more than twice the measured diffusive entry rate into the structure and comparable to the radon entry rate driven by a − 0.4 Pa, steady indoor-outdoor pressure difference.