A review of aqueous-phase VOC transport in modern landfill liners.

Leachates from municipal solid waste (MSW) and hazardous waste landfills contain a wide range of volatile organic compounds (VOCs) in addition to inorganic compounds. VOCs have been shown to migrate and contaminate the surrounding environment and impair the use of groundwater. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs is of concern. Most modern landfills employ a composite liner consisting of a geomembrane overlying a compacted clay liner or a geosynthetic clay liner. The geomembrane is often believed to be the primary barrier to contaminant transport. However, for VOCs, the clay component usually controls the rate of transport since VOCs are shown to diffuse through geomembrane at appreciable rates. Additionally, analyses have shown that transport of volatile organic compounds (VOCs) generally is more critical than transport of inorganic compounds (e.g., toxic heavy metals), even though VOCs are often found at lower concentrations in leachates. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs and transport of VOCs through clay liners and modeling of transport through composite liners merit scrutiny. This paper presents a review of recent research by the author and others on these topics. A systematic and comprehensive approach to determine mass transport parameters for transport of VOCs in liquid phase through compacted clay liners, geosynthetic clay liners (GCLs), and geomembranes has enabled to develop realistic models to predict mass flux of VOCs through modern composite liners and provide a quantitative basis to evaluate potential for transport of dissolved VOCs and the equivalency of different composite liners.