Evaluation of transient dissolution of slightly water-soluble compounds from a light nonaqueous phase liquid pool

A transient two-dimensional mathematical model was developed using an advection-dispersion equation to describe the dissolution and transport of slightly water-soluble compounds (SWSCs) from a pool of light nonaqueous phase liquid (LNAPL) into an aquifer. The LNAPL pool is located in a capillary fringe, and the bottom of the pool is in direct contact with the aquifer. In the LNAPL pool, SWSCs are assumed to move by liquid diffusion, and within the aquifer by mass flow under the influence of steady horizontal groundwater flow. The dissolution process along the LNAPL/water interface assumed a local phase equilibrium relation. A formal analytical solution to the mathematical model was first derived in the Laplace transform domain and inverted numerically by means of the Bellman algorithm. This solution was used to calculate the dissolution of a SWSC from an LNAPL pool to groundwater and to identify physicochemical factors that could significantly affect this transient mass transfer process. Results show that within the range of parameters we used in the study, the SWSC flux, which is represented by the modified Damkohler number <(Da(t))over bar>, can be related to the Fourier number F-o the transverse hydrodynamic Peclet number Pe(T), and the ratio of nonaqueous diffusion Peclet number Pe(N) to Pe(T) (or D-T/D-N) through a simple power law relationship.