Assessment of HDPE geomembrane performance in a municipal waste landfill double liner system after eight years of service

In the late 1970s and early 1980s, environmental regulations were upgraded in a general national movement to effect secure management of our municipal and residual solid wastes. The new regulations required varying combinations of natural and/or synthetic barrier and drainage layers to prevent the unrestricted release of contaminants. The acceptable barrier materials included synthetic flexible membrane liners (FMLs) of various types. One of those most commonly used has been high-density polyethylene (HDPE) geomembrane. HDPE has been selected because of its good chemical resistance characteristics, among others. Background compatibility testing has shown the HDPE geomembrane to be extremely resistant to the leachates that are generated by municipal and residual solid waste landfills. The background testing for design has generally been based on relatively short-term tests that are conducted under extreme conditions to ‘forecast’ service life. Recently, a municipal solid waste landfill double liner system that was constructed in 1988 was exhumed. The HDPE geomembranes of this liner system had been exposed to varying degrees of leachate since 1989. Samples of the HDPE were extracted from the in-place liner system and were laboratory-tested for physical, mechanical and endurance properties. The selected suite of tests duplicated the test protocol conducted in 1988 as part of the liner system construction quality assurance (CQA) program. The results of this testing show that the HDPE properties are still within the range of data generated by the original testing in 1988. No degradation in properties was indicated by this testing program. The HDPE had been exposed to the leachate, methane, and static and dynamic stresses for approximately 8 years. The results of this test program support the design selection of HDPE as the synthetic barrier component of this landfill liner system.