SURFACTANT ENHANCED REMOVAL OF PCE IN A NOMINALLY 2-DIMENSIONAL, SATURATED, STRATIFIED POROUS-MEDIUM

Although surfactant enhanced remediation of nonaqueous phase liquids ( NAPLs) by pump-and-treat technology has been studied extensively in th e laboratory with one-dimensional columns, very few multi-dimensional investigations have been reported. In this study we focus on the remov al of perchloroethylene (PCE) from a two-dimensional, saturated porous medium containing a low permeability sand layer situated in an otherw ise high permeability sand. A PCE spill was applied at the surface of the porous medium and allowed to redistribute until static equilibrium was achieved. The porous medium was then flushed with various surfact ant and co-solvent formulations injected at the PCE source location an d extracted at the bottom of the porous medium using a configuration s imilar to that of Abdul and Ang [Abdul, S.A., Ang, C.C., 1994. In situ surfactant washing of polychlorinated biphenyls and oils from a conta minated field site: Phase II. Pilot study. Ground Water 32, 727-734], Effluent samples were analyzed for dissolved PCE concentrations. Volum etric water and PCE content values were determined at a number of loca tions by means of dual-energy gamma radiation measurements. Once surfa ctant flushing had started, PCE moved as a distinct separate phase ahe ad of the surfactant front. Most of this downward moving PCE accumulat ed on top of the low permeability sand layer. Some PCE, however, passe d quickly through this layer and subsequently through the high permeab ility sand below it. Movement of some of the PCE into and through the low permeability sand layer was attributed to local heterogeneities co mbined with reduced interfacial tensions associated with the surfactan t formulation. Clean-up of PCE in most of the high permeability sand w as considered to be effective. PCE accumulated on top of the fine laye r, however, posed a significant challenge to remediation and required several pumping configurations and surfactant/co-solvent formulations before most of it was removed. (C) 1998 Elsevier Science B.V. All righ ts reserved.