Analysis of Facilitated Air Intrusion during Surfactant-enhanced Air Sparging Using Surface Tension-reducing Chemicals: Surfactants and Alcohols

The effect of lowered groundwater surface tension using alcohols and surfactants, and increased viscosity using a thickener on the performance of the air sparging (AS) process was investigated, and the mechanism of facilitated air intrusion into the saturated zone during surfactant-enhanced air sparging (SEAS) was proposed.When aqueous solutions of alcohols (e.g., ethyl alcohol) displaced the resident water in a sand-packed column, the air saturation slightly decreased during AS, whereas the addition of surfactants increased air saturation. During the AS process, a significant difference in the air pressure measurements was observed, depending on the chemicals (alcohols and surfactants). Significantly higher air pressure was measured during SEAS than AS process with alcohol solutions. In this study, it is proposed that the foam formation and displacement through the soil interstices during the SEAS process increases air pressure. And this additional air pressure is responsible for the additional air intrusion into the smaller pores at lowered surface tension. Increased hydraulic pressure or water viscosity showed no significant effect on the air saturation during alcohol-applied AS. However, during SEAS, the increased viscosity using a thickener increased the viscosity of the foam inducing high air pressure, resulting in further enhanced air saturation.