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

Abstract

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, K diss a i , and NAPL/water total specific interfacial area, a i . K diss a 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 diss a 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 diss a 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 diss a 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.