Innovative Waste Containment Barriers for Subsurface Pollution Control

Bentonite modified by cationic surfactants has been the focus of attention for engineering applications such as in horizontal cut-offs, grout mixes, cut-off slurries, soil motars, and landfill liners because of its high organic removal capacity. In this study, the feasibility of using modified clays in conjunction with conventional soil-bentonite admixtures as a waste containment barrier with the combined abilities of acting as a sealant and effectively retaining dissolved organic contaminants was investigated by a series of experimental tests. The sorption isotherms of total organic carbon, a gross organic term, by five types of soil admixtures are nonlinear. The soil specimen with more modified clays exhibits higher organic sorption capacity and a larger retardation factor. The specimens with 20% of pure bentonite by dry weight have a higher optimum water content and plasticity. With the addition of bentonite in the soil material consisting of natural soils and modified clays, the hydraulic conductivity to leachate decreases from about 10-7 to 10-8 cm/s. No incompatibility between landfill leachate and soil specimens is found. The curve fitting technique was applied to determine the effective porosity and hydrodynamic dispersions of both Cl and total organic carbon. The 1D contaminant transport model was used to develop design charts for the determination of liner thickness. Results show that the presence of modified clays in the soil containing 20% bentonite largely reduces the required liner thickness.