Performance-based design of contaminant barriers for sustainable landfilling and site remediation

A sustainable approach to the design of contaminant barriers should balance the two conflicting needs of maximising the protection of the groundwater quality and minimising the environmental impact related to the construction of the barrier. In front of this challenge, the most helpful technological innovation is represented by geosynthetic products, such as geomembranes and geosynthetic clay liners, which allow reaching performances equivalent to those of mineral barriers while reducing the consumption of natural resources and emission of greenhouse gases. A second crucial innovation is represented by the transition from a prescriptive-based design approach to a performance-based design approach, which provides a quantification of the risk to human health and the environment due to pollutant migration through the barrier system. The performance-based design guarantees to protect the groundwater resource, avoiding recourse to oversized barrier systems, with relevant economic and environmental savings, and, moreover, encourages adopting the most advanced technologies through a comparison of their performances with respect to traditional systems. This paper focuses on the performance-based design of pollutant containment systems, such as landfill bottom liners and cutoff walls. The effectiveness of pollutant containment systems is demonstrated by calculating 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.