The role of chemico-osmosis in the performance assessment of bentonite-based contaminant barriers

Although conservative estimates of the containment performance of bentonite-based barriers can be obtained from the classical advective-diffusive transport theory, the semipermeable properties of the bentonite component can determine a significant reduction in the migration rate of contaminants at low salt concentrations (< 100 mM). After introducing the transport equations for a semipermeable porous medium, the paper presents the laboratory testing apparatuses and procedures that allow the chemico-osmotic efficiency coefficient, ω, and the osmotic effective diffusion coefficient, D ^* _ω, of bentonites to be experimentally assessed. Finally, the advantages that derive from the ability to model the semipermeable behaviour of bentonites in the design of geoenvironmental barriers are discussed with the aid of a calculation example, which considers the use of geosynthetic clay liners for the bottom lining of waste disposal facilities. (paper)