The design and maintenance of landfills for waste disposal has received great attention over the last few decades due to the increasing interest and attention paid to environment protection issues, such as ground and ground water protection. Over the years, landfill liner construction has seen innovative new practices such as addition of engineered clays, synthetic lining material and designing of more sophisticated leachate collection systems. The main objective of such practices is to enhance the landfill liner performance as a hydraulic barrier and to minimise or prevent the migration of landfill leachate into the surrounding hydro-geological system. The compacted clay liners (CCLs) are among the most widely used hydraulic barrier system in modern waste containment systems.

When a waste containment system is in operation, leachate is generated at different concentrations and characteristics over a considerably long period of time. The subsequent clay–leachate interaction processes influence the mineralogical stability and physical properties of the clay. Understanding of the possible effects of leachate over a considerably long period of time is therefore of a significant importance in effective designing of clayey barrier systems for sustainable waste containment facilities.

This chapter provides the results of a study aimed at investigating the effects of landfill leachate on the performance of a compacted basaltic clay soil, over a period of time. For this purpose, a typical Melbourne basaltic clay with varying percentages of montmorillonite clay was selected and a synthetic leachate was developed based on the composition of typical municipal waste landfill leachate reported in the literature. The clay–leachate interactions were allowed to take place under controlled anaerobic 330laboratory conditions. Samples were then tested for the effect of leachate over different time periods to identify the variations in grain size distribution (GSD) and hydraulic conductivity characteristics.

The analyses of test results suggest that the long-term behaviour of a CCL could be significantly affected by the clay–leachate interactions, due to the possible alterations in the physical and mineralogical properties of the clay.