Long-term barrier performance of modified bentonite materials against sodium and calcium permeant solutions

The results of long-term hydraulic conductivity test results on two modified bentonite materials, a multiswellable bentonite (MSB) and a dense-prehydrated geosynthetic clay liner (DPH-GCL), permeated with electrolytic chemical solutions are reported. In addition, their chemical compatibilities are discussed in order to investigate the applicability of these compounds as barrier materials at waste containment facilities. Hydraulic conductivity tests with inorganic chemical solutions of NaCl and/or CaCl2 were conducted for a maximum of 7 years. The hydraulic conductivities of MSBs with NaCl solutions, which had a molar concentration of ⩽1.0 M, were k≅1.0×10−11 m/s. However, when the molar concentration of the NaCl solution was 2.0 M the hydraulic conductivity of the MSB was nearly identical to that of natural bentonite. The hydraulic conductivities of DPH-GCLs with CaCl2 solutions, which had a molar concentration of ⩽1.0 M, were k≅1.0×10−12 m/s, regardless of the concentration of the solution tested. Hence, both MSBs and DPH-GCLs exhibit remarkable swelling and chemical resistances, respectively, to electrolytic solutions of NaCl and CaCl2 with a molar concentration of ⩽1.0 M.