The containment of high ionic strength leachates by bentonite-polyacrylate composites is presented. Sodium bentonite (Na-bentonite) was modified to control flow and contaminant migration in containment applications where natural Na-bentonite barriers, such as geosynthetic clay liners (GCLs), will not adequately control flow and contaminant migration. Polyacrylate was combined with Na-bentonite by in situ polymerization of acrylic acid within bentonite slurry to create a bentonite-polymer nanocomposite (BPN). BPN swells more than two times more than Na-bentonite from a GCL (73 vs. 30.5 mL/2 g), but in high strength CaCl₂ solutions, has a swell similar to calcium bentonite (< 10 mL/2 g). Thin layers of BPN and Na-bentonite simulating GCLs were directly permeated with 50, 200, and 500 mM CaCl₂. BPN maintained low hydraulic conductivity (<8×10⁻¹¹ m/s) to hydraulic and chemical equilibrium termination criteria, while Na-bentonite had hydraulic conductivities at least three orders-of-magnitude higher. The mechanisms underlying these behaviors are also discussed.