Performance of Geosynthetics for Remediation of Hydrocarbons and Emerging Contaminants

Abstract

Diffusion of volatile organic contaminants through a thin (0.508 mm) seven-layer geomembrane including EVOH was evaluated using laboratory diffusion tests and compared to traditional polyethylene geomembranes. Using the laboratory tests, diffusion (Dg), partitioning (Sgf) and permeation (Pg) coefficients were developed for the EVOH layer and the complete liner. The seven-layer membrane resulted in a decrease in steady-state flux by a factor of 19.2-64.4 compared to 1.5 mm HDPE. Transport of TCE and PCE through geomembranes, including two geomembranes coextruded with EVOH, was assessed through laboratory testing. Dg, Sgf, and Pg values were developed for the individual materials, and single layer Dg, Sgf, and Pg values were developed for the coextruded geomembranes using the harmonic mean of the Pg values and the weighted average of Sgf values in relation to the layer thicknesses. Vapour intrusion models were used to compare the vapour intrusion of TCE and PCE into a warehouse with a constant source of contaminant. Modelled concentrations were significantly reduced where coextruded geoemembranes are present by more than a factor of 10, compared to single material geomembranes of similar thicknesses. Laboratory testing of PFOA and PFOS diffusion through four geomembranes at multiple temperatures was examined. Laboratory testing of 0.1 mm LLDPE and LLDPE coextruded with EVOH showed extremely low (<8 μg/L) concentrations of PFOA and PFOS after over 400 days of testing. Elevated temperature testing of 0.75 mm LLDPE and LLDPE coextruded with EVOH showed similarly low receptor concentrations after over 350 days. Estimated permeation coefficients for PFOA and PFOS through LLDPE are less than 5.2x10-15 m2/s. Laboratory testing of exhumed GCLs from an Antarctic site examined performance properties of GCLs post-exposure. Small changes in hydraulic conductivity and swell index were observed, however these values were not significantly different than virgin values. A field scale hydration test plot was constructed to assess the impact of subgrade on GCL performance. GCLs overlying sieved soils (<50 mm) had more consistent hydration throughout the field season and smaller indentations, indicating better long-term performance. Inclusion of a geotextile in the subgrade resulted in lower hydration due to the geotextile acting as a capillary break