Factors affecting bank formation during surfactant-enhanced mobilization of residual NAPL

Two-dimensional flow cell experiments were used to investigate the flow dyn amics and factors affecting tetrachloroethylene (PCE) mobilization and bank formation in an otherwise water-saturated porous medium. Aqueous phase inj ection rates and flow cell angles were varied to control both buoyancy and viscous forces, and both macroscopic- and pore-scale images were captured a nd analyzed to determine the effects of these forces on PCE transport chara cteristics. Results were interpreted in terms of a nondimensional bank numb er, N-Ba, which relates the Forces on the trapped nonaqueous phase liquid ( NAPL) ganglia parallel to the flow direction to those forces perpendicular to the flow. N-Ba, was found to predict bank formation well except for N-Ba approximate to 1, where other characteristics may have been important, suc h as droplet coalescence. Pore-scale observations showed that the mobilized PCE moved through the porous medium as noncoalesced droplets and that some of the trapped NAPL was mobilized through a dissolution/mobilization proce ss.