Evaluation of Anomalous Solute Transport in a Large Heterogeneous Soil Column with Mobile-Immobile Model
Publication: Journal of Hydrologic Engineering
Volume 14, Issue 9
Abstract
This study uses the mobile-immobile model (MIM) and the traditional convection-dispersion equation (CDE) to analyze the observed breakthrough curves (BTCs) at different distances in a 1,250-cm-long saturated and highly heterogeneous soil column. It provides a simple method to determine the mobile water fraction independently as the ratio of effective porosity over total porosity of the packed soil materials. The effective porosity is calculated a priori as the ratio of measured flow rate and estimated pore-water velocity. It is found that there is a significant amount of immobile water in the soil column, resulting in the anomalous early breakthrough and tailing behaviors of the measured BTCs. Comparing to the CDE, the measured asymmetric BTCs at various scales can be better described by the MIM, especially their early arrival and long tailing parts. The degree of anomalous transport behavior in this large heterogeneous soil column is reduced with transport scale due to the increased mobile water fraction and associated greater solute mixing, and the MIM can detect this evolution adequately. The solute mass transfer timescales at various distances are compared to the advection timescales and longitudinal interaction timescales, respectively. It is found that the latter is better correlated with the timescales of solute mass transfer, which implies that the mass transfer rate in the heterogeneous soil column is predominantly subjected to the local velocity variation.
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Acknowledgments
This research was partially supported by the Major State Basic Research Development Program of China (Grant No. UNSPECIFIED2006CB403406), the National Natural Science Foundation of China (Grant No. NNSFC50779066), and Program for Changjiang Scholars and Innovative Research Team in University (Grant No. UNSPECIFIEDIRT0657). We are grateful to Dr. Renduo Zhang for providing us the experimental data of the heterogeneous long soil column and Dr. Rien van Genuchten for providing us the CXTFIT2.1 software. We thank the two anonymous reviewers for their constructive comments.
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Information
Published In
Journal of Hydrologic Engineering
Volume 14 • Issue 9 • September 2009
Pages: 966 - 974
Copyright
© 2009 ASCE.
History
Received: Feb 28, 2008
Accepted: Jan 13, 2009
Published online: Jun 13, 2009
Published in print: Sep 2009
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