Analytical Model for Volatile Organic Compound Transport in the Coupled Vadose Zone–Groundwater System
Publication: Journal of Hydrologic Engineering
Volume 26, Issue 1
Abstract
A 3D mathematical model that describes transport of volatile organic compounds in a coupled vadose-saturated zone system is proposed. The subsurface processes incorporated in the model include advection, dispersion, interphase mass transfer, and diffusive mass exchange between two horizontal porous media formations, as well as the time-dependent mass loading from a source zone. The analytical solutions are derived subject to the specific initial and boundary conditions. The solutions are evaluated by numerical Laplace inverse transform. The model solutions can be used to study the fate and transport in subsurface formations composed of a vadose zone and a water table aquifer, where the volatile organic compound is released from entrapped nonaqueous phase liquid in the vadose zone, or the dissolved volatile organic compound transports with groundwater accompanied by diffusive mass transfer into the overlying soil formations. Mass transfer between two layers is demonstrated to have back-diffusion characteristics, which results in secondary contamination and retains low levels of contaminant concentrations over a prolonged period of time. The model solutions are specifically useful in assessing the vapor intrusion process in a contaminated site where a vadose zone is underlain by a water table aquifer contaminated with volatile organic compounds.
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Data Availability Statement
MATLAB codes used to create figures in this paper are available from the corresponding author upon request.
Acknowledgments
The United States Environmental Protection Agency (USEPA), through its Office of Research and Development, funded and conducted this research. The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of USEPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The author wishes to acknowledge and thank Dr. Richard Wilkin and Dr. Jeffrey Yang of Center for Environmental Solutions and Emergency Response, USEPA, for their review and commentary on this paper. The author is grateful for the constructive comments from the Editors and two anonymous reviewers.
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Journal of Hydrologic Engineering
Volume 26 • Issue 1 • January 2021
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© 2020 Published by American Society of Civil Engineers.
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Received: Mar 7, 2019
Accepted: Aug 20, 2020
Published online: Nov 13, 2020
Published in print: Jan 1, 2021
Discussion open until: Apr 13, 2021
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