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Transport of volatile organic compounds across the capillary fringe (1993)
| Venue: | Water Resour. Res |
| Citations: | 6 - 0 self |
BibTeX
@ARTICLE{Mccarthy93transportof,
author = {Kathleen A. Mccarthy and Richard and L. Johnson},
title = {Transport of volatile organic compounds across the capillary fringe},
journal = {Water Resour. Res},
year = {1993},
pages = {1675--1683}
}
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Abstract
Physical experiments were conducted to investigate the transport of a dissolved volatile organic compound (trichloroethylene, TCE) from shallow groundwater to the unsaturated zone under a variety of conditions including changes in the soil moisture profile and water table position. Experimental data indicated that at moderate groundwater velocities (0.1 m/d), vertical mechanical dispersion was negligible and molecular diffusion was the dominant vertical transport mechanism. Under these conditions, TCE concentrations decreased nearly 3 orders of magnitude across the capillary fringe and soil gas concentrations remained low relative to those of underlying groundwater. Data collected during a water table drop showed a short-term increase in concentrations throughout most of the unsaturated zone, but these concentrations quickly declined and approached initial values after the water table was returned to its original evel. In the deep part of the unsaturated zone, the water table drop resulted in a long-term decrease in concentrations, illustrating the effects of hysteresis in the soil moisture profile. A two-dimensional random walk advection-diffusion model was developed to simulate the experimental conditions, and numerical simulations agreed well with experimental data. A simpler, one-dimensional finite-difference diffusion-dispersion model was also developed. One-dimensional simulations based on molecular diffusion also agreed well with experimental data. Simulations which incorporated mechanical dispersion tended to overestimate flux across the capillary fringe. Good agreement between the one- and two-dimensional models suggested that a simple, one-dimensional approximation of vertical transport across the capillary fringe can be useful when conditions are appropriate.
Keyphrases
capillary fringe volatile organic compound unsaturated zone experimental data water table drop molecular diffusion soil moisture profile short-term increase one-dimensional simulation water table position experimental condition good agreement deep part vertical transport vertical mechanical dispersion long-term decrease two-dimensional model original evel dominant vertical transport mechanism one-dimensional approximation mechanical dispersion water table moderate groundwater velocity numerical simulation low relative advection-diffusion model initial value one-dimensional finite-difference diffusion-dispersion model two-dimensional random soil gas concentration underlying groundwater shallow groundwater physical experiment tce concentration
