A Review of In-Situ Air Sparging for the Remediation of VOC-Contaminated Saturated Soils and Groundwater

In-situ air sparging is a developing remediation technique that has significant potential for use in VOC-contaminated saturated soils and groundwater. This technique consists of injecting air below the contaminated area to partition the dissolved, sorbed and free phase VOCs into the gas phase and to enhance the aerobic biodegradation of the VOCs. Because of the buoyancy effect, the VOCs in the gas phase are transported by air to the vadose zone where they are removed and subsequently treated by a soil vapor extraction system. Currently, the design, operation, and monitoring of air sparging systems is based mainly on an empirical approach with limited field experience. Extreme care must be exercised in designing and implementing the air sparging system so that the contaminants are removed efficiently and without adverse effects on the subsurface environment, particularly the spread of the contaminants to the clean areas. The current state of knowledge is inadequate for the design of effective air sparging systems which also prevent the spreading of contaminants into the clean areas. This paper first outlines the fundamentals of air sparging and then presents an overview of previous air sparging field and laboratory investigations. The paper then details a critical assessment of modeling studies which predict contaminant transport during the air sparging process. Finally, the paper outlines an on-going comprehensive research program that involves developing the most efficient and economical air sparging systems. This research program, which is being conducted at the University of Illinois at Chicago (UIC), includes performing laboratory aquifer simulation tests to characterize the basic mechanisms of air sparging, developing a contaminant transport model to optimize the different design variables in a typical air sparging system, and conducting a field demonstration of the optimal air sparging system.