The past few decades of advancements in developing new drainage media have led to the use of geocomposites as the primary drainage layer above the bottom lining system geomembrane. However, you need to be watchful for the free flow of leachate through the thin layer of geocomposite under high gas pressures near the bottom lining system.
Short of investigations and clear guidelines for addressing high gas pressure near the bottom lining system, you can use a gas pressure relief system near the bottom in future new disposal cells. The pressure relief system can simply include a few perforated high-density polyethylene pipes laid in parallel directly above the soil layer placed above the bottom lining system drainage layer, as shown in the schematic.
About the author: Dr. Ali Khatami