Quantification of the Mechanisms Controlling the Removal Rate of Volatile Contaminants by Air Sparging

Air sparging is a technology for removing dissolved and volatile phase chemicals (VOCs) from the saturated zone. It is used in conjunction with soil vapor extraction (SVE) and sometimes pump and treat systems. The air sparging process involves the injection of air at some depth below the water table; as the air rises, VOCs transfer to the vapor phase and discharge to the unsaturated zone. In almost all applications, SVE is used to capture the sparging gas as well as to clean up the unsaturated zone. Several researchers have investigated air flow patterns, but relatively little ongoing research is being done to define the mass transfer rates that govern the performance of air sparging. This paper presents a model to quantify the removal mechanisms during air sparging. The model simulation is compared to an analytical solution and the dimensionless groups are analyzed to determine the dominant mass transfer processes. The model shows that mass transfer is dominated by gaseous dispersion and advection, and liquid diffusion.