Volatile organic compound and methane transport through composite barriers with co-extruded geomembrane containing ethylene vinyl-alcohol

A co-extruded geomembrane (GM) with a layer of ethylene vinyl-alcohol (EVOH) is being introduced in environmental containment applications to take advantage of the hydrophobic properties of polyethylene as a barrier to contaminant flux; specifically, the potential to substantially reduce the diffusion of non-polar volatile organic compounds (VOCs) and methane. This research effort involved the experimental measurement of the relative migration of five common VOCs through composite landfill liners constructed with two types of co-extruded EVOH GM overlying either a compacted clay liner (CCL) or a geosynthetic clay liner (GCL). VOC breakthrough in composite liners employing high-density polyethylene (HDPE) GMs was more than two to four times faster than the composite liners composed of a co-extruded EVOH GM with a linear low density polyethylene (LLDPE) or HDPE outer layer where breakthrough occurred at 70 and 150 d, respectively, with significantly higher VOC concentrations. Numerical modeling (i.e., finite difference method) of VOC migration through a composite liner with CCL with a co-extruded EVOH GM indicated that contaminant transport was significantly lower at 100 years in comparison to the equivalent HDPE composite liner. Overall, the diffusion coefficient of co-extruded GM evaluated with a series of batch tests was approximately 20 times smaller than that of HDPE GM. An equivalent diffusion coefficient was derived analytically based on sorptive and diffusive behavior through the co-extruded GM (i.e., non-homogeneous layers in series). The relative rates of transport of methane through an interim cover constructed with a co-extruded GM that contains a layer of EVOH were evaluated and compared to conventional GMs including polyethylene (PE), LLDPE, and polyvinyl chloride (PVC). Soil type minimally influenced diffusive behavior of methane through the interim cover in comparison to GM type. The LLDPE and PVC GMs produced five times more rapid breakthrough (≈ 20 d) of methane and higher flux in comparison to the EVOH GM (≈ 100 d). Further, the co-extruded EVOH GM had measured diffusion coefficients that were more than 170-250 times smaller compared to conventional single-composition GMs. Thus, co-extruded EVOH GMs can act as an effective barrier to VOC and methane migration in landfill liners and interim covers.