Effects of heterogeneity on the surfactant-enhanced remediation of aquifer contaminated with nonaqueous phase liquids

Abstract

"Surfactant-enhanced aquifer remediation (SEAR) is an innovative technology for the removal of nonaqueous phase liquids (NAPLs) in the aquifer. Heterogeneity in aquifer permeability constitutes one of the greatest challenges to remediation process because removal of NAPLs can occur only at the contacted formation by injected surfactant solution. A three-dimensional, multiphase, multicomponent compositional simulator is employed to simulate the solubilization and mobilization of NAPL during the remediation in spatiallycorrelated heterogeneous fields. Aquifer heterogeneity was accounted for by considering the permeability as a spatial random variable and a geostatistical method was used to generate random distributions of the permeability. Spatial distributions of NAPL saturations in the aquifer and temporal changes of organic recovery, effluent concentrations of organics and surfactant, and pressure drop at the injection well were compared with those in homogeneous aquifer and related to heterogeneity. Variations in permeability fields have a pronounced effect on the organic recovery efficiency due to the long-term persistence of nonaqueous phase liquid in bypassed portion of aquifer and additional dispersion. Higher heterogeneity also results in tailing of effluent organic concentrations and significant loss in injectivity over the remediation life. For a small slug, surfactant-enhanced remediation had a relatively small improvement on the recovery of NAPL, especially in highly heterogeneous aquifers. Migration of the high concentration organic plumes to the other layer by crossflow is also found to have a significant influence on SEAR behavior.