Buoyant Advection of Gases in Unsaturated Soil
Publication: Journal of Environmental Engineering
Volume 120, Issue 5
Abstract
In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two‐dimensional, homogeneous sand pack with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady‐state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser‐than‐air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil.
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Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 120 • Issue 5 • September 1994
Pages: 1230 - 1247
Copyright
Copyright © 1994 American Society of Civil Engineers.
History
Received: Dec 29, 1992
Published online: Sep 1, 1994
Published in print: Sep 1994
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