Factors Affecting Bank Formation during Surfactant-Enhanced Mobilization of Residual NAPL

Two-dimensional flow cell experiments were used to
investigate the flow dynamics and factors affecting
tetrachloroethylene (PCE) mobilization and bank formation
in an otherwise water-saturated porous medium. Aqueous
phase injection rates and flow cell angles were varied to
control both buoyancy and viscous forces, and both
macroscopic- and pore-scale images were captured and
analyzed to determine the effects of these forces on PCE
transport characteristics. Results were interpreted in
terms of a nondimensional bank number, NBa, which relates
the forces on the trapped nonaqueous phase liquid
(NAPL) ganglia parallel to the flow direction to those
forces perpendicular to the flow. NBa, was found to predict
bank formation well except for NBa ≈ 1, where other
characteristics may have been important, such 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 process.