Gas diffusion coefficients

From the GMA Techline

Subject: Gas diffusion coefficients— I am in the process of evaluating the mass flux of a gas moving through a 30-mil PVC geomembrane. I am working with volatile organic compounds in soils.

What I need are typical values based on unsaturated soil vapors. I have found information on aqueous liquids but not on unsaturated soil vapors.

Can you provide any assistance in finding typical gas diffusion coefficients through geomembranes? (David, Illinois)

Reply: Henry Haxo of Metrocon evaluated solvent vapor diffusion—as opposed to water vapor diffusion— many years ago. His data is in my book, “Designing with Geosynthetics.” The test is ASTM E96, which is difficult to perform using thick polymer geomembranes but is nonetheless doable. The French have a more elaborate “pouch test” but it is very tedious and expensive to run.

Regarding unsaturated soil vapors, there is nothing. I suspect that you could commission a lab to do the tests, but I have never seen such data.

Bob Koerner | GMA Techline