The need to consider the service life of all components of a modern MSW landfill liner system.

The long-term performance of a geosynthetic clay liner (GCL) above a drainage layer and a geocomposite drain (GCD) are investigated. Full-scale tests are used to: (i) assess the integrity of GCL and GCD in a double composite liner below a defect in the primary geomembrane with ageing, and (ii) establish the head at which there was internal erosion in GCL without a carrier geotextile (GTX) such that the bentonite is in direct contact with the underlying gravel drainage. Six years after contact with simulated landfill leachate at 85 °C through an intentional defect on the geomembrane, the GCL resting on the GCD had failed due to degradation of the GTX between the bentonite and the core of the GCD and subsequent erosion of the bentonite into the core structure of the GCD was observed. In addition to complete degradation of its GTX at some locations, the GCD had also experienced extensive stress cracking and rib rollover. The second test demonstrates that if a suitable gravel drainage layer had been used instead of the GCD, the GTX component of the GCL would not have been required for acceptable long-term performance under normal design conditions and indeed could withstand a head of up to 15 m before problems became evident. The findings serve as a warning landfill designers and regulators that more attention must be paid to the service life of all components of double liner systems used in Municipal Solid Waste (MSW) landfills.