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(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 he 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 fut. incorporating pore-scale processes into field-scale prediction of NAPL dissolution. (C) 2001 Published by Elsevier Science B.V.