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

The removal of denser than water nonaqueous phase liquids (DNAPLs) tra pped at residual saturation is an important problem at many contaminat ed ground-water sites. Because pump-and-treat technologies have been i neffective in removing DNAPLs, alternative strategies have been sugges ted, one of which is enhancing the mobilization and dissolution of DNA PLs by flushing with a cosolvent. Tetrachloroethylene (PCE)/methanol/w ater systems were studied to evaluate the effect of methanol an the re mediation of PCE-contaminated porous media. Experimental measurements of interfacial tension, equilibrium phase composition, and phase densi ty at various methanol/water fractions were combined with other publis hed properties to characterize these systems. In methanol flushing exp eriments, PCE mobilization, nonequilibrium PCE dissolution, and Row by passing were allobserved. The results demonstrate that (a) small-scale heterogeneities may lead to locally high residual DNAPL saturations t hat are more easily mobilized than DNAPL residuals in homogeneous medi a; (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 by passing, due to nonuniform distributions of DNAPL residual or dissolut ion fingering, can occur in even small-scale experiments.