Modeling dissolution and volatilization of LNAPL sources migrating on the groundwater table

A mathematical model was developed to describe LNAPL migration in the subsurface and contaminant transport in soil gas and in groundwater. The governing equations were obtained by vertically averaging the system. The NAPL phase equation accounted for the mass loss due to residual NAPL, dissolution, and volatilization and was coupled with the dissolved and volatilized contaminant transport equations by mass transfer terms. Instantaneous mass balance equations were used to handle the residual NAPL captured by capillary forces, and kinetic and constant mass transfer terms were employed to assess dissolution and volatilization.; Simulation results on LNAPL migration showed that ambient groundwater velocity had major effects on both LNAPL mound formation and LNAPL mound migration. The degree of residual saturation affected only LNAPL mound migration. Model results provided distributions of NAPL phase and contaminated soil. Simulations of LNAPL dissolution indicated that LNAPL transport was not affected to a significant degree by dissolution and that both the mass transfer and the LNAPL mobility were equally important when assessing contamination of groundwater and soils. Sensitivity analysis indicated that groundwater contamination was largely affected by ambient groundwater flow velocity and capillary fringe thickness when kinetic dissolution was used. The study on dissolution and volatilization of LNAPL showed that LNAPL migration was greatly affected by volatilization and that the evaporative mass loss to the atmosphere was sensitive to the NAPL volatility and to the vadose zone depths.; It was concluded that the model and its solution method developed in this study could be used as a screening tool to assess the impact of the subsurface contamination by moving LNAPL that is inert, soluble, and/or volatile.