Risk assessment procedure for the performance-based design of landfill lining systems and cutoff walls

The performance-based design of pollutant containment systems, such as landfill bottom liners and cutoff walls, requires the impact of pollutant migration on groundwater quality to be assessed. The effectiveness of pollutant containment systems is indeed demonstrated through the verification that the risk for human health and the environment due to the pollutant migration is limited to an acceptable level. This risk is quantified through the calculation of the pollutant concentration in the groundwater, which is expected to remain less than some prescribed level at a compliance point. The paper describes analytical and numerical solutions to pollutant transport, which allow the pollutant concentration in the groundwater to be calculated under different boundary conditions. Based on the results obtained from these solutions, the role played, not only by the hydraulic and diffusive properties of the containment barriers, but also by the hydrogeological features of the site (e.g. the groundwater velocity and the mechanical dispersion within the aquifer) is pointed out.