Numerical simulation of air sparging for remediation of NAPL contamination

A numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite-difference, multiphase-Bow, contaminant transport code. The code is used to model two-dimensional air sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field-scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and air sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the sparging-induced gas pressure increase, or ''positive pressure,'' measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the sparging radius of influence.