Abstract
This work developed a model for predicting the volatilization flux from the unsaturated soil contaminated by volatile chemical substances (VCSs) such as mercury and benzene. The model considers a series of phenomena under the unsaturated condition such as multi-phase flow consisting of a non-aqueous phase liquid, water, and gases together with the permeation of rainfall into the surface soil, the volatilization/condensation of VCSs, and the adsorption/desorption of VCSs. On this basis, this work clarified a mechanism for the generation of a volatilization flux at the ground surface. In addition, the effects of various transport phenomena in the surface soil on the magnitude and seasonal changes in this flux due to variations in weather factors such as rainfall level, temperature, and air pressure were quantitatively evaluated. This newly developed prediction model can be utilized to estimate dynamic variations in the flux under real-environmental conditions.
Highlights
In recent years, there have been numerous reports concerning the contamination of soil and groundwater derived from volatile chemical substances (VCSs) such as mercury (Hg) and benzene (C6H6) as a result of leakage from factories and illegal dumping
The accurate prediction of volatilization flux from the ground surface based on detailed mathematical modeling of the advection and dispersion behaviors of VCSs under unsaturated condition is necessary for the quantitative evaluation of the risks derived from these compounds
We developed the prediction model of volatilization flux from unsaturated soil contaminated by VCSs, based on mathematical modeling of a series of phenomena under unsaturated conditions
Summary
There have been numerous reports concerning the contamination of soil and groundwater derived from volatile chemical substances (VCSs) such as mercury (Hg) and benzene (C6H6) as a result of leakage from factories and illegal dumping. These compounds tend to permeate into the pore space in the surface soil (in the region defined as the unsaturated zone) as a result of advection and dispersion and can subsequently transfer to either groundwater or the ambient atmosphere with the changes of mass and composition based on several phenomena These include the elution of undiluted VCSs into pore water and precipitation from the aqueous phase, volatilization into gas phase and condensation into liquid phase, and partitioning between pore water and soil particle as the solid phase due to adsorption/desorption. This paper describes in detail the newly developed predictive model and the results obtained from this approach, based on a numerical analysis
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