| Abstract
| - Introduction of surfactant mixtures to the subsurface forthe purpose of surfactant-enhanced aquifer remediationrequires consideration of the effects of surfactant sorptionto sediment and nonaqueous phase liquids. Theseeffects include alteration of the solubilizing properties ofthe surfactant mixture and alteration of the sorption propertiesof the stationary phase. Sorption of octylphenol ethoxylate(EO) surfactant oligomers to a low organic carboncontent (foc) aquifer sediment and to dense nonaqueousphase liquid (DNAPL) consisting of tetrachloroethene (PCE)was examined in batch experiments. At aqueous surfactantconcentrations far below the critical micelle concentration(CMC) of the mixture, sorption to sediment was characterizedby an initial steep isotherm for both high and low EOcontent oligomers, with somewhat greater uptake of highEO content oligomers. This stage of sorption resulted inmild increases in the equilibrium constant, Kd,PCE, fordistribution of PCE between solution (including surfactant)and sediment (including sorbed surfactant). As theaqueous surfactant concentration increased, surfaceaggregation of low EO content oligomers on the sedimentcommenced, and a dramatic increase in Kd,PCE wasobserved. At aqueous surfactant concentrations increasingabove the CMC, the formation of solution micellescaused the sorbed surfactant concentrations to plateauand then decrease. This decrease in sorbed surfactant,along with competition by micelles for contaminant, likelycontributed to the observed rapid decrease in Kd,PCEtoward zero. Surfactant sorption to PCE DNAPL was greaterrelative to sediment by 1−2 orders of magnitude, withmuch greater uptake of the low EO content oligomers.Sorption of all but the lowest EO content oligomers to thePCE DNAPL was terminated by micellization.
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