Development and validation of practical membrane efficiency models for landfill liner systems

Contaminant transport in landfills affects groundwater quality. As a result, compacted clay liners and bentonite-based clays are used as barriers in landfills due to their membrane behavior and low hydraulic conductivity. Membrane behavior is the restriction ability of clays owing to the overlap of the diffuse double layers of clay particles. This physico-chemical characteristic is quantified as the membrane efficiency coefficient. Membrane behavior impacts rates of contaminant transport through clay liners; therefore, the main goal of this study is to develop practical membrane efficiency models for salt-contaminated clays that can be used to design barriers. To show the reliability of models, experimental test results for membrane efficiency were adopted from the literature and used in this study. Afterward, two different modeling approaches were presented, both of which defined the membrane behavior as a function of void ratio and salt concentration. The first model is purely empirical and needs four material constants for each type of clay to be determined. The other one is a semi-analytical model being developed based on the combination of microscopic approach modeling for bentonite and experimental test results. The second model needs three constants. Although some discrepancies seem inevitable, both models show good agreements with the experimental data points. However, the results revealed that the first model is more applicable in dilute solute concentration. Finally, constants were presented for several types of clay reported in the experimental database of the current literature.