Optimal Configuration of a Double Liner System Including a Geomembrane Liner and a Composite Liner

A number of landfills are designed with a double liner system that includes a geomembrane liner and a composite liner. The design engineer must select which of these two liners should be the primary liner. A comparative study is presented in this paper to help determine which configuration is preferable. The comparative study consists of comparing the rate of leachate migration through two double liner systems having the following inverse configurations: (i) a double liner system where the primary liner is a geomembrane liner and the secondary liner is a composite liner; and (ii) a double liner system where the primary liner is a composite liner and the secondary liner is a geomembrane liner. The composite liner considered in the study consists of a geomembrane on a geosynthetic clay liner (GCL). The comparison between the two liner systems is based only on advective flow through geomembrane defects (i.e. defects in the geomembrane liner as well as defects in the geomembrane component of the composite liner). Other factors that may have an impact on the selection of a liner configuration, such as diffusive flux and construction issues, are not considered in the comparison. The study shows that, from the viewpoint of minimizing the advective flow of leachate through geomembrane defects, it is preferable to use the configuration where the primary liner is a composite liner.