TRANSPORT IN POROUS-MEDIA CONTAINING RESIDUAL HYDROCARBON .1. MODEL

When liquid hydrocarbons or nonaqueous phase liquids (NAPLs) become entrapped below the water table, flowing ground waters carry soluble NAPL components away from the spill zone. Transport of dissolved NAPL components is controlled by several processes including advection, dispersion, sorption onto aquifer materials, and liquid-liquid partitioning. A model is developed to predict solute movement through heterogeneous porous media containing residual NAPL. Governing equations describe both instantaneous and time-dependent processes including: (1) Exchange between mobile and immobile waters; (2) exchange between residual NAPL and water; and (3) exchange between aquifer solids and water. A one-dimensional analytical Laplace-space solution to governing equations is presented. The resulting transport model handles combinations of solute exchange activities that cannot be investigated with other analytical or numerical formulations. The model is tested during an investigation of several hypothetical systems. The investigation shows rate-limited processes causing early solute arrival, a delay in total breakthrough, and asymmetric breakthrough curves.