A functional relation for field-scale nonaqueous phase liquid dissolution developed using a pore network model

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K_dissa_i, and NAPL/water total specific interfacial area, a_i. K_dissa_i was computed as a function of modified Peclet number(Pe′) for various NAPL saturations (S_N) and a_i during drainage and imbibition and during dissolution without displacement. The largest contributor to a_i was the interfacial area in the water-filled corners of chambers and tubes containing NAPL. When K_dissa_i was divided by a_i, the resulting curves of dissolution coefficient, K_diss versus Pe′ suggested that an approximate value of K_diss could be obtained as a weak function of hysteresis or S_N. Spatially and temporally variable maps of K_dissa_i calculated using the network model were used in field-scale simulations of NAPL dissolution. These simulations were compared to simulations using a constant value of K_dissa_i and the empirical correlation of Powers et al. [Water Resour. Res. 30(2) (1994b) 321]. Overall, a methodology was developed for incorporating pore-scale processes into field-scale prediction of NAPL dissolution.