Diffusive transport of organic vapors in the unsaturated zone with kinetically-controlled volatilization and dissolution: analytical model and analysis

Kinetically-controlled volatilization and dissolution of nonaqueous-phase liquids (NAPLʹs) in the unsaturated (vadose) zone are a more general model as compared to the usually used local equilibrium model of mass transfer. This paper presents a one-dimensional vertical model of kinetically-controlled diffusive transport of organic vapors pertinent to pollution caused by a relatively long, ground surface-originating, mainly horizontally-spread leak of NAPL, the volatile compound of which undergoes sorption and degradation in the soil. Analytical solutions of this model are applicable to homogeneous soils with ground surface fully open to the atmosphere. Application of the solutions to several examples demonstrates the role of kinetically-controlled volatilization and dissolution at both early and advanced stages of the transport process. Asymptotic analysis of the outlined solutions is employed in order to examine the depletion of the contaminant source.