Ž . Journal of Contaminant Hydrology 41 2000 385–402 www.elsevier.comrlocaterjconhyd Modeling of air sparging of VOC-contaminated soil columns Washington Braida, Say Kee Ong ) Department of CiÕil and Construction Engineering, 490 Town Engineering Building, Iowa State UniÕersity, Ames, IA 50011, USA Received 28 October 1998; received in revised form 28 July 1999; accepted 18 August 1999 Abstract Air sparging is a remediation technology currently being applied for the restoration of sites Ž . contaminated with volatile organic compounds VOCs . Attempts have been made by various researchers to model the fate of VOCs in the gas and liquid phase during air sparging. In this study, a radial diffusion model with an air–water mass transfer boundary condition was developed and applied for the prediction of VOC volatilization from air sparging of contaminated soil columns. The approach taken was to use various parameters such as mass transfer coefficients and tortuosity factors determined previously in separate experiments using a single air channel apparatus and applying these parameters to a complex system with many air channels. Incorpo- Ž . rated in the model, is the concept of mass transfer zone MTZ where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the air–water interface but with negligible impact outside the zone. The model predicted fairly well the change in the VOC concentrations in the exhaust air, the final average aqueous VOC concentration, and the total mass removed. The predicted mass removal was within 1% to 20% of the actual experimental mass removed. The results of the model seemed to suggest that air-sparged soil columns may be modeled as a composite of individual air channels surrounded by a MTZ. For a given air flow rate and air saturation, the VOC removal was found to be inversely proportional to the radius of the air channel. The approach taken provided conceptual insights on mass transfer processes during air sparging operations. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Air sparging; Volatile organic compounds; Remediation; Modeling ) Corresponding author. Tel.: q1-515-294-3927; fax: q1-515-294-8216; e-mail: skong@iastate.edu 0169-7722r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-7722 99 00075-3