Deterministic and Probabilistic Assessment of Compacted Clay Liners in Municipal Solid Waste Landfills

Modern engineered municipal solid waste (MSW) landfills generally have a low permeability liner at the base of landfills to minimize contaminants within landfills migrating into groundwater and surface water. The Chinese national standard for MSW landfills permits the use of a compacted clay liner (CCL) with a thickness ≥ 2 m and a hydraulic conductivity ≤ 10–9 m/s. A commonly adopted index to assess the performance of landfill liners is the time (i.e., the service life) when the contaminant concentration in the aquifer below the liner exceeds the acceptable level. The calculation of service life of landfill liners is generally based on a deterministic approach using a single value for each parameter associated with contaminant transport through the liner. The probabilistic approach using Monte-Carlo simulations has been increasingly used in geotechnical and geoenvironmental engineering by taking the inherent uncertainty of material properties into consideration. This paper examined the performance of CCLs in MSW landfills using both deterministic and probabilistic approaches. The results show that the probabilistic approach provides not just the service life of the CCL but also the probability of failure, and thus is more informative over the deterministic approach (with a single quantitative service life). The use of the probabilistic approach yields a more informed design decision for CCLs in MSW landfills.