One of the most important regulatory requirements on landfill bottom lining system drainage layer is that the maximum head of leachate over the liner should not exceed 1 ft. When this requirement was developed, the consensus was that the drainage layer consisted of granular materials. Later, when geonets and geocomposites entered the market, the unwritten consensus among solid waste engineers and regulators was that the maximum head of leachate at the base should not exceed the thickness of the geonet or geocomposite drainage layer.
With that in mind, the reduction in hydraulic transmissivity of geocomposite laid over steeper slopes can adversely affect the maximum leachate head over the liner. When hydraulic transmissivity value reduces due to steeper slope at the base, the hydraulic conductivity reduces in turn as well. Reducing hydraulic conductivity results in an increase in the maximum head of leachate passing through the geocomposite.
Read Dr. Ali Khatami’s design advice for cell base slopes under these circumstances to maximize hydraulic transmissivity; recently published in the winter edition of Talking Trash.