Abstract
Both diurnal and weather-system-induced atmospheric pressure changes can cause air pressure gradients to form in the unsaturated zone. As the subsurface pressure re-establishes equilibrium with the changing surface pressure, gas is “breathed” in and out of the unsaturated zone. This movement of gas and subsequent advection of organic vapors present above a contaminated aquifer may provide a significant mechanism of ground-water contaminant mass loss through the unsaturated zone to the atmosphere. Previous research into the nature and effects of barometric pumping are presented. Studies involving field measurements and modeling of subsurface airflow and vapor fluxes at land surface are reviewed. This research indicates that, under certain circumstances, gas-phase contaminant transport in the unsaturated zone is influenced by atmospheric pressure changes at land surface. New data and modeling results involving unsaturated-zone pressure gradients and airflow are also presented. Air pressure, moisture content, and water table elevation were measured as functions of depth and time in the unsaturated zone at Picatinny Arsenal, New Jersey during dry periods in August and October, 1996. Significant air-pressure gradients between the subsurface and the atmosphere were observed, while little variation in air pressure was measured at depths between 0.5 and 1.7 m. Changing subsurface air pressures in response to varying atmospheric pressure were successfully simulated using a simplified, 1-dimensional, finite-difference model. Further model results indicated non-zero subsurface air velocity during most of the simulation period. Based on these results, it was concluded that airflow is occurring in the unsaturated zone and that this airflow can be explained by one-dimensional (vertical) pressure gradients driven by atmospheric-pressure variations.
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© 2002 Kluwer Academic Publishers
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Tillman, F.D., Choi, JW., Katchmark, W., Smith, J.A., Wood, H.G. (2002). Unsaturated-zone Airflow: Implications for Natural Remediation of Groundwater by Contaminant Transport through the Subsurface. In: Smith, J.A., Burns, S.E. (eds) Physicochemical Groundwater Remediation. Springer, Boston, MA. https://doi.org/10.1007/0-306-46928-6_14
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DOI: https://doi.org/10.1007/0-306-46928-6_14
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