Modeling Cationic Surfactant Transport in Porous Media

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Abstract
Laboratory and field experiments have shown that cationic surfactants can be used to modify aquifer materials, and thereby form zones of enhanced sorption for hydrophobic organic contaminants (HOC's) migrating in ground water. Coupled to a contaminant degradation or removal process, this concept has potential as a remediation technology. In order to apply enhanced sorption in a remediation scheme, an ability to predict the transport and partitioning behavior of cationic surfactants in the subsurface is necessary. In this paper we present the results of a numerical modeling study in which the transport and partitioning behavior of the cationic surfactant hexadecyltrimethylammonium chloride (HDTMA) in porous media is investigated. Modeling of previously published batch and column HDTMA sorption experimental results for Columbus Air Force Base aquifer material indicates that, under certain conditions, kinetic effects will dominate the transport process with slow desorption of HDTMA being the likely rate‐controlling step. The results suggest that a significant departure from equilibrium will exist under natural gradient conditions for the Columbus aquifer material. Low aqueous surfactant concentrations can be expected to persist within a surfactant‐enhanced sorption zone, even after considerable flushing with surfactant‐free ground water. The low aqueous concentration may have implications in terms oftoxicityto microorganisms.