Assessment of the contributions of volatilization and biodegradation to in situ air sparging performance

In situ air sparging refers to a process in which clean air is injected directly into an aquifer formation to treat contaminant source zones, remediate dissolved contaminant plumes, or provide barriers to dissolved contaminant plume migration. This paper presents a theoretical analysis of the mechanisms and factors contributing to the overall performance of in situ air sparging systems. By examining processes occurring at the microscale, the significance of volatilization, biodegradation, bulk water flow, chemical concentrations, partitioning parameters, and air distribution are assessed. The analysis indicates that (a) if aerobic biodegradation occurs, it only enhances performance relative to the case of volatilization when dissolved contaminant concentrations are <1 mg/L, independent of other chemical parameters; (b) bulk water movement induced by water evaporation has the potential to significantly improve performance if a water velocity >2 cm/d toward the air channels occurs; (c) performance is expected to be significantly better for dissolved plumes than in sources containing immiscible phase contaminants; (d) the chemical property most affecting performance in source zones is solubility; and (e) in situ air sparging has significant potential for remediating spills of very soluble, but slowly degrading fuel oxygenates, such as MTBE.