Methane gas geomembrane permeability

Q: What is the least permeable geomembrane to methane gas? Regarding the permeability of geomembranes to methane gas, could you send me some technical guidelines?

A: High-density polyethylene (HDPE) geomembranes are denser (more crystalline) than linear low-density polyethylene (LLDPE) geomembranes and less permeable. The water vapor, solvent and methane transmission (diffusion) of an HDPE barrier is better (less) than an LLDPE. However, sometimes it still may be too high to be suitable as a barrier for some applications. In such cases, ethylene vinyl alcohol (EVOH) is used as a layer sandwiched between polyethylene layers (plies) in the geomembrane cross section to give even lower gas permeability.

Refer to the Los Angeles County Department of Public Works (2020) geomembrane specification for additional technical guidelines and a prescribed testing protocol. Stark and Choi (2005) is also useful in this regard.

Los Angeles County Department of Public Works. (2020). “Gas hazard mitigation policy and standard.” Feb. 3.

https://dpw.lacounty.gov/epd/swims/docs/pdf/methane/methane%20packet.pdf

Stark, T. D., and Choi, H. (2005). “Methane gas migration through geomembranes.” Geosynthetics International, 12(2), 120–26.