Using Double Liners in Landfill Design and Operation

Abstract

Experience with double liners at solid waste landfills in eastern states of the U.S.A. dates back to the late 1970s. Regulatory agencies at both Federal and State levels are now mandating that landfills have primary and secondary liner systems designed to prevent migration of pollutants into adjacent soil or ground and surface waters during their active lives and before the end of the landfill post closure monitoring period. Primary liners should be at least 0.76 mm (30 mil) thick flexible synthetic membranes protected by 30 cm (12 in) minimum sand layers both above and below the liner. The lower sand layer should contain a perforated discharge pipe to serve as a leak detection system. Secondary liners at the bottom of the landfill are preferably two component systems: a flexible synthetic membrane 0.76 mm (30 mil) thick over top of 90 cm (36 in) of a low permeability soil which must achieve a hydraulic conductivity of 1 × 10^-7 cm s^-1 or less. Liner material selection is based upon compatibility with, or resistance to, the waste stream contained and, the configuration of the landfill and critical locational factors such as soil stability and groundwater table elevations. Quality assurance/quality control during construction are essential to insure that the liner system performs up to its design specifications. Performance of double liner systems has been successful at those landfills where adequate quality assurance/quality control were known to have been exercised.