The objectives of this technical note are to review the gas transport mechanisms through flexible geomembranes, and to measure the methane gas transmission rate, permeance, and permeability coefficient of PVC, LLDPE, and HDPE geomembranes by performing the standard gas transport test (ASTM D1434). The measured methane gas permeability coefficient through a PVC geomembrane is 7.55 3 10 ml(STP).m...