Chromatographic Alteration of a Nonionic Surfactant Mixture During Transport in Dense Nonaqueous Phase Liquid Contaminated Sediment

Chromatographic alteration of a nonionic surfactant mixture during transport 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 mixture, which is a concern when the surfactant mixture is applied for the purpose of DNAPL solubilization. This study examined a nonionic surfactant mixture, which was characterized in terms of oligomer distribution within the mixture and the ability of the mixture to solubilize residual DNAPL. Three sediment-packed columns were connected in series to represent up-gradient, residual, and down-gradient zones, respectively, of a DNAPL-contaminated site. In the up-gradient column, greater retardation of high ethoxylate (EO) content oligomers was observed relative to low EO content oligomers, due to preferential sorption of high EO content oligomers by the sediment. In the residual-zone column, much greater retardation of low EO content oligomers relative to high EO content oligomers occurred, due to preferential sorption of low EO content oligomers to residual DNAPL. In the down-gradient column, 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 surfactant mixture. Increased solution flow rate decreased surfactant sorption but resulted in an overall decrease in the mass of DNAPL solubilized due to kinetic limitations in DNAPL solubilization.