Containment of Organic Contaminants Using Geosynthetics
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The use of geosynthetics to contain volatile organic compounds (VOCs) and polychlorinated biphenyls (PCBs) in composite liner systems is evaluated through laboratory and field experiments. Diffusive parameters for benzene, toluene, ethylbenzene, and xylenes (BTEX) and PCBs through geomembranes are evaluated. Diffusion of BTEX is also evaluated through vapour barriers, as well as diffusion of PCBs through a compacted clay liner (CCL) and a GCL. The permeation coefficient (Pg) for BTEX diffusion was lowest for high density polyethylene (HDPE) geomembrane, followed by chlorosulphonated polyethylene (CSPE), linear low density polyethylene (LLDPE), two ethylene interpolymer alloy (EIA) coated polyester products, four different PE based vapour barriers, and then polyvinyl chloride (PVC). In applications such as landfill covers or under-slab vapour barriers to mitigate VOC migration into buildings, these differences in Pg between products may have a significant effect on performance. PCBs were found to have very high partitioning coefficients to HDPE geomembranes (Sgf = 150,000) and low Dg (1.0 × 10-14 m2/s), suggesting geomembranes can act as a sink to capture and store contaminants and not just as a diffusive barrier. In a typical municipal solid waste landfill (MSW) with good construction quality assurance (CQA), PCBs are unlikely to give rise to environmental concern. However, if CQA allows significant leakage, the environmental impacts from PCBs would need to be carefully evaluated on a case by case basis by modelling. Containment using geosynthetics in remote Arctic environments for PCB contaminants is also evaluated. Geosynthetics are found to not have performance issues specific to climate, but instead with respect to subsurface angularity of soil, suggesting that normal design precautions should be maintained in polar environments. Evaluation of core samples exhumed from pond liners after nine years showed that with respect to PCBs, EIA geomembranes were similar to HDPE, with low Dg, and high Sgf. Laboratory and field experiments were conducted to examine the hydration of GCL liners used to contain hydrocarbon-contaminated soil in Antarctica. Results indicate that hydration is achievable in Antarctica, but is heavily dependent on subsoil grain size and hydrology.