Numerical modeling of diffusion for volatile organic compounds through composite landfill liner systems

Mass flux of solute exiting a landfill liner system is a valuable indicator for evaluating the performance of the Municipal Solid Waste (MSW) landfill liner systems. For the volatile organic compounds, such as toluene, the diffusion occurring inevitably in the intact landfill liner systems can transport toluene through the liner system and finally contaminate the outer groundwater. The diffusion of toluene, through four different municipal solid waste landfill liner systems, i.e., Subtitle D composite liner system, composite liner system with a Geosynthetic Clay Liner (GCL) instead of low permeability compacted soil, Wisconsin NR500 liner system, and a proposed four-component composite liner system that is a combination of the GCL composite liner system and the Subtitle D liner (with a 61 cm (2 feet) or 91.5 cm (3 feet) thick compacted clay liner), were evaluated in terms of mass flux. A one-dimensional block-centered numerical model of the diffusive transport through the four intact liner systems was developed for this purpose. The comparison of mass flux shows that the proposed four-component composite liner system outperforms the other liner systems based on mass flux and can be a preferable alternative for a MSW composite liner system.