Estimating Persistent Mass Flux of Volatile Contaminants from the Vadose Zone to Ground Water

Contaminants may persist for long time periods within low permeability portions of the vadose zone where they cannot be effectively treated and are a potential continuing source of contamination to ground water. Setting appropriate vadose zone remediation goals typically requires evaluating these pe...

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Bibliographic Details
Published in:Ground water monitoring & remediation 2009-05, Vol.29 (2), p.63-72
Main Authors: Truex, M.J., Oostrom, M., Brusseau, M.L.
Format: Article
Language:English
Subjects:
CARBON TETRACHLORIDE
case studies
ENVIRONMENTAL SCIENCES
ENVIRONMENTAL TRANSPORT
estimation
GROUND WATER
groundwater contamination
groundwater recharge
hydrologic models
mass flux
remediation
simulation models
SOILS
THREE-DIMENSIONAL CALCULATIONS
TWO-DIMENSIONAL CALCULATIONS
vadose zone
volatile compounds
volatile contaminants
VOLATILE MATTER
water table
WATER TABLES
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Summary:Contaminants may persist for long time periods within low permeability portions of the vadose zone where they cannot be effectively treated and are a potential continuing source of contamination to ground water. Setting appropriate vadose zone remediation goals typically requires evaluating these persistent sources in terms of their impact on meeting ground water remediation goals. Estimating the impact on ground water can be challenging at sites with low aqueous recharge rates where vapor-phase movement is the dominant transport process in the vadose zone. Existing one-dimensional approaches for simulating transport of volatile contaminants in the vadose zone are considered and compared to a new flux-continuity-based assessment of vapor-phase contaminant movement from the vadose zone to the ground water. The flux-continuity-based assessment demonstrates that the ability of the ground water to move contaminant away from the water table controls the vapor-phase mass flux from the vadose zone across the water table. Limitations of these approaches are then discussed with respect to the required assumptions and the need to incorporate three-dimensional processes when evaluating vapor-phase transport from the vadose zone to the ground water. The carbon tetrachloride plume at the U.S. Department of Energy Hanford Site is used as the example site where persistent vadose zone contamination needs to be considered in the context of ground water remediation.
ISSN:1069-3629
1745-6592
DOI:10.1111/j.1745-6592.2009.01236.x