Impact of Vapor Sorption on the Subsurface Transport of Volatile Organic Compounds: A Numerical Model and Analysis

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Abstract
A flexible finite element transport model, which includes the impact of vapor sorption, is developed to simulate the movement of volatile organic compounds (VOCs) in variably saturated porous media. The two‐dimensional numerical model predicts contaminant transport by aqueous advection, aqueous dispersion, aqueous and vapor diffusion, and surface volatilization. For a soil with increasing water contents with depth, one‐dimensional simulations demonstrate that strong vapor sorption may reduce the total amount of VOC that volatilizes in 100 days from 84.6% of the initial mass volatilized without vapor sorption to 73.2%. Yet, for a soil with low water contents at depth, such as in an area with limited recharge, vapor sorption enhanced the rate of volatilization in 100 days from 72.4% without vapor sorption to a peak of 90.3%. When low soil moisture was combined with a soil type that has strong vapor sorption characteristics, VOC transport was significantly retarded.