Chromatographic alteration of a nonionic surfactant mixture during transport in dense nonaqueous phase liquid contaminated sediment

Chromatographic alteration of a nonionic surfactant mixture during transpor t through DNAPL-contaminated aquifer sediment may occur due to differential loss of oligomers to sediment and to dense nonaqueous phase liquid (DNAPL) . These losses may significantly alter the solubilizing properties of the m ixture, which is a concern when the surfactant mixture is applied for the p urpose of DNAPL solubilization. This study examined a nonionic surfactant m ixture, which was characterized in terms of oligomer distribution within th e mixture and the ability of the mixture to solubilize residual DNAPL. Thre e sediment-packed columns were connected in series to represent upgradient, residual, and down-gradient zones, respectively, of a DNAPL-contaminated s ite. In the up-gradient column, greater retardation of high ethoxylate (EO) content oligomers was observed relative to low EO content oligomers, due t o preferential sorption of high EO content oligomers by the sediment. In th e residual-zone column, much greater retardation of low EO content oligomer s relative to high EO content oligomers occurred, due to preferential sorpt ion of low EO content oligomers to residual DNAPL. In the downgradient colu mn, retardation of only the high EO content oligomers was observed, due to lack of sorption of low EO content oligomers to sediment. Surfactant losses to sediment and DNAPL delayed the solubilization of DNAPL due to reduction of surfactant concentration and overall increased polarity of the surfacta nt mixture. Increased solution flow rate decreased surfactant sorption but resulted in an overall decrease in the mass of DNAPL solubilized due to kin etic limitations in DNAPL solubilization.