COSOLVENT ENHANCED REMEDIATION OF RESIDUAL REUSE NONAQUEOUS PHASE LIQUIDS - EXPERIMENTAL INVESTIGATION

The removal of denser than water nonaqueous phase liquids (DNAPLs) trapped at residual saturation is an important problem at many contaminated ground-water sites. Because pump-and-treat technologies have been ineffective in removing DNAPLs, alternative strategies have been suggested, one of which is enhancing the mobilization and dissolution of DNAPLs by flushing with a cosolvent. Tetrachloroethylene (PCE)/methanol/water systems were studied to evaluate the effect of methanol an the remediation of PCE-contaminated porous media. Experimental measurements of interfacial tension, equilibrium phase composition, and phase density at various methanol/water fractions were combined with other published properties to characterize these systems. In methanol flushing experiments, PCE mobilization, nonequilibrium PCE dissolution, and Row bypassing were allobserved. The results demonstrate that (a) small-scale heterogeneities may lead to locally high residual DNAPL saturations that are more easily mobilized than DNAPL residuals in homogeneous media; (b) mass transfer rate coefficients for PCE/methanol/water systems can be predicted to within 30% using an existing correlation developed for systems with similar NAPL emplacement procedures; and (c) flow bypassing, due to nonuniform distributions of DNAPL residual or dissolution fingering, can occur in even small-scale experiments.