Evaluation of the Effect of Geological Heterogeneity on the Surfactant Transport by Performing Push-Pull Test in a Physical Aquifer Model (PAM)

A surfactant flushing process is commonly used to remove light non-aqueous phase liquids (LNAPLs) such as benzene, toluene, ethylbenzene, and xylene (BTEX) by enhancing solubility of the contaminants. Since the surfactant flushing process is significantly affected by the degree of geological heterogeneity, push-pull tests in a physical aquifer model (PAM) was performed to evaluate the surfactant transport and toluene removal efficiency in a lab-scale three layered aquifer. Push-pull tests showed that maximum bromide concentration detected at a sampling port located 15 cm downgradient from an injection port was approximately 95% of average injected bromide concentration in two permeable layers (0.22±0.02 cm/min of hydraulic conductivity) and only 40% in lower permeable layers (0.05±0.02 cm/min of hydraulic conductivity). Through the push-pull tests, we also found the different mass recovery of bromide (58%), toluene (47%) and surfactant (17%) in the PAM, confirming higher absorption characteristics of the surfactant on the soil particle than other solutes. Interestingly, toluene mass recovery in the presence of excessive surfactant decreased, possibly because of adsorption of toluene mass on the surfactant attached to soil particle. Through this work, we proved soil permeability, adsorption rate of surfactant, and amount of injected surfactant should be considered to remove the LNAPL contaminants efficiently by surfactant flushing process from the heterogeneous aquifer.