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From the GMA Techline
Subject: Geomembrane thickness— We have been designing an ash pond for a thermal- electric plant, where we intend to use an HDPE geomembrane for the lining system. Can you recommend what thickness we should use for safety reasons, as our project is located near Halong Bay [in northeast Vietnam]? Do you have any U.S. standard to recommend the minimum thickness for this application?
In addition, a GCL is also one of our options for a lining system, and based on installation manuals from GCL manufacturers, there is no need to test the seaming of the GCL, as bentonite will seal the overlap by itself. Do you have any paper or standard regarding this? (M. Nguyen, Hanoi)
Reply: Regarding HDPE geomembranes, the minimum thickness required by the U.S. Environmental Protection Agency is 1.5mm. However, in Germany it is 2.0mm. That said, thinner HDPE material has been installed, but I do not recommend thinner than 1.0mm under any circumstances. And below 1.5mm, the workmanship becomes critical as far as welding of the sheets together.
Regarding GCL seams, you are correct in that there is no physical seam, per se, and it is simply an overlap. While some manufacturers claim that 150mm is adequate, I prefer 300mm overlaps. Also, depending on the product used, you might have to extrude a continuous bentonite paste in the overlap area.
We do not have a standard or technical paper on these issues. Best wishes on your project.