Two separate coupling effects are evaluated with respect to steady-state potassium chloride (KCI) diffusion through a bentonite-based geosynthetic clay liner(GCL)that behaves as a semipermeable membrane. Both of the coupling effects are correlated with measured chemico-osmotic efficiency coefficients, ω, that range from 0.14 to 0.63 for the GCL The first coupling effect is an explicit (theoretical) salt-sieving effect expressed as a coupled effective salt diffusion coefficient, D{sub}ω*, that is lower than the true (uncoupled) effective salt diffusion coefficient, D{sub}s*, because of the observed membrane behavior. However, the maximum difference between D{sub}ω* and D{sub}s* based on measured chloride concentrations is relatively small (i.e., = 10), and the difference decreases with decreasing a; (i.e., D{sub}ω* →D{sub}s* as ω → 0). The second coupling effect is implicit (empirical) and is characterized by the measurement of concentration-dependent effective salt diffusion coefficients that results in an ～ 300 decrease in D{sub}s* as a; increases from 0.14 to 0.63. The decrease in D{sub}s* resulting from implicit coupling is attributed to solute exclusion described in terms of a restrictive tortuosity factor.
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