NUMERICAL MODELING OF 3-DIMENSIONAL CONTAMINANT MIGRATION FROM DISSOLUTION OF MULTICOMPONENT NAPL POOLS IN SATURATED POROUS-MEDIA

A three-dimensional model for contaminant transport resulting from the dissolution of multicomponent nonaqueous phase liquid (NAPL) pools in three-dimensional saturated subsurface formations is developed. The s olution is obtained numerically by a finite-difference scheme, and it is suitable for homogeneous porous media with unidirectional interstit ial velocity. Each dissolved component may undergo first-order decay a nd may sorb under local equilibrium conditions. It is also assumed tha t the dissolution process is mass transfer limited. The nonaqueous pha se activity coefficients of the NAPL pool components are evaluated at each time step. The model behavior is illustrated through a synthetic example with a NAPL pool consisting of a mixture of TCA (1,1,2-trichlo roethane) and TCE (trichloroethylene). The numerical solution presente d in this work is in good agreement with a recently developed analytic al solution for the special case of a single component NAPL pool. The results indicate the importance of accounting for the necessary change s in the organic phase activity which significantly affects the equili brium aqueous solubility.