SOIL-GAS ENTRY INTO AN EXPERIMENTAL BASEMENT DRIVEN BY ATMOSPHERIC-PRESSURE FLUCTUATIONS - MEASUREMENTS, SPECTRAL-ANALYSIS, AND MODEL COMPARISON

To study the effects of atmospheric pressure fluctuations on the entry of radon and soil-gas contaminants into houses, we have simultaneousl y measured the changes in atmospheric pressure and the gas flow rate b etween the interior of an experimental basement structure and the unde rlying 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 Bow rate induced by a change in atmospheric pressure depends on both the characteristic response time of the soil and the time-rat e-of-change of the atmospheric pressure fluctuation. Spectral analysis indicates that relatively low-frequency fluctuations in atmospheric p ressure are the most important for driving soil-gas into and out the o f the experimental structure; more than 60% of the total power of the soil-gas Bow spectrum occurs at frequencies less than 100 d(-1). A tra nsient finite-element model based on Darcy's law correctly predicts bo th the dynamics and the magnitude of the observed gas flow. Atmospheri c pressure fluctuations may increase the long-term radon entry rate in to the experimental structure by as much as 0.2 Bq s(-1), which is mor e 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. (C) 1997 Elsevier Science Ltd.