ABSTRACT
It is becoming increasingly more common to install a layer of highly permeable granular material beneath the primary liner in a landfill. Most commonly, the layer is intended to allow detection and collection of leachate which escapes through the primary liner. The separation between the aquifer and the landfill would be as large as possible for a design involving a secondary leachate collection system. However, in many practical situations the actual thickness may be quite thin. The role of advection for allowing the migration of contaminants from waste disposal facilities is well recognized. More research is required to determine relevant parameters; however, it is evident that diffusive transport through geomembranes and secondary leachate collection systems is an important consideration in the design of these facilities. The processes involved in contaminant migration for hydraulic control systems are better understood than the processes of migration for systems that use the granular layer as a secondary leachate collection system.
