Shale as a Sorbent Additive to Increase Containment Barrier Efficiency

Abstract: A variety of sorbents have been suggested for use as additives to soil containment barriers to reduce transport of organic chemicals from hazardous waste sites to the outside environment. This study investigated sorption capacities and mechanisms for a natural shale rock and four synthetic organoclays, along with the effects of addition of these sorbents on soil-bentonite barrier diffusive transport and hydraulic conductivity. Transport model simulations combined these factors to generate estimates of contaminant breakthrough. Shale exhibited substantial sorption capacity for a variety of organic contaminants, and proved to be an exceptionally cost-effective sorbent. In addition, the shale and a short-chain organoclay had no adverse impacts on soil-bentonite barrier hydraulic conductivity. In contrast, addition of 5% (w/w) hydrophobic long-chain organoclay sorbents increased hydraulic conductivity by up to an order of magnitude. Sorbent addition had little effect on barrier tortuosity, and diffusion coefficients were not significantly affected. Overall, shale was shown to have tremendous promise as a sorbent additive as a result of its high sorption capacity, lack of adverse effects on soil-bentonite barrier hydraulic conductivity or diffusive transport, inherent long-term viability, ability to be pulverized to allow for good mixing with backfill soil, and availability in man