Quantification of Volatile Organic Compounds Diffusion for Virgin Geosynthetic Clay Liners and for a GCL after Contact with a Synthetic Leachate

The effects on the nature of bentonite, natural sodium, and calcium activated, and of the cation exchange on the diffusive properties of two geosynthetic clay liners (GCLs) were examined. Diffusion laboratory tests were conducted to estimate the diffusion coefficients of 1, 2-dichloroethane (DCA), dichloromethane (DCM), thrichloroethylene (TCE), toluene, and benzene. Both GCLs were needle-punched and came from the same manufacturer. The nature of the bentonite contained in both GCLs was different because a natural sodium bentonite and a calcium activated sodium bentonite were tested. Furthermore, one of the GCLs experienced cation exchange from contact with a synthetic leachate used to generate an increase in its hydraulic conductivity by a factor of 8.5. The objective of this process was to evaluate if an increase in the hydraulic conductivity by cation exchange in a GCL would result in a significant increase in the diffusion coefficients of volatile organic compounds (VOCs). The results obtained for both virgin GCLs were very close to one another. No effect on the nature of the bentonite was observed. An increase in the diffusion coefficient was noticed for the case in which the GCL experienced cation exchange while in contact with a synthetic leachate for DCM, DCA, and TCE at a given bulk GCL void ratio. The largest increase, a factor of 2.6, was observed for TCE. However, this increase in the diffusion coefficient could have been balanced by the decrease in the bulk GCL void ratio from 3.9 to 3. The increase in the diffusion coefficient of VOCs, thus, does not seem to be of concern for the range of GCL hydraulic conductivities generated by cation exchange in this study.