Contaminant transport resulting from multicomponent nonaqueous phase liquid pool dissolution in three-dimensional subsurface formations

A semi-analytical method for simulating transient contaminant transport originating from the dissolution of multicomponent nonaqueous phase liquid (NAPL) pools in three-dimensional, saturated, homogeneous porous media is presented. Each dissolved component may undergo first-order decay and may sorb under local equilibrium conditions. The NAPL pool dissolution process is envisioned to occur in a series of consecutive short intervals (pulses), The mole fraction, nonaqueous phase activity coefficient and aqueous solubility of every pool constituent are estimated before the initiation of each pulse, and they are assumed to remain constant for the duration of each interval. Individual component aqueous phase concentrations resulting from each dissolution interval are estimated by existing analytical solutions applicable to single component NAPL pools, and total concentration distributions of the same component are obtained by direct superposition. The semi-analytical method is more efficient and less computationally demanding than a finite-difference approximation. Furthermore, it is shown that neglecting the changes in nonaqueous phase activity coefficients that occur during multicomponent NAPL pool dissolution may result in erroneous predictions. The model presented in this work is useful for the design and interpretation of experiments in laboratory bench scale aquifers, certain homogeneous subsurface formations, and for the verification of complex numerical codes. (C) 1998 Elsevier Science B.V.