INFLUENCE OF VISCOUS AND BUOYANCY FORCES ON THE MOBILIZATION OF RESIDUAL TETRACHLOROETHYLENE DURING SURFACTANT FLUSHING

The potential for nonaqueous phase liquid (NAPL) mobilization is one o f the most important considerations in the development and implementat ion of surfactant-based remediation technologies. Column experiments w ere performed to investigate the onset and extent of tetrachloroethyle ne (PCE) mobilization during surfactant flushing. To induce mobilizati on, the interfacial tension between residual PCE and the aqueous phase was reduced from 47.8 to 0.09 dyn/cm by flushing with different surfa ctant solutions. The resulting PCE desaturation curves are expressed i n terms of a total trapping number (N-T), which relates viscous and bu oyancy forces to the capillary forces acting to retain organic liquids within a porous medium. The critical value of N-T required to initiat e PCE mobilization fell within the range of 2 x 10(-5) to 5 x 10(-5), while complete displacement of PCE was observed as NT approached 1 x 1 0(-3). The interplay of viscous and buoyancy forces during PCE mobiliz ation is illustrated in horizontal column experiments, in which angled banks of PCE were displaced through the columns. These results demons trate the potential contribution of buoyancy forces to PCE mobilizatio n and provide a novel approach for predicting NAPL displacement during surfactant flushing.