The migration of salt solutions (NaCl) through remoulded, compacted clay in a laboratory physical model is compared with field migration through a similar but undisturbed clay located below a domestic waste landfill. In both the laboratory and field systems, the salt profiles indicated that migration was dominated by diffusion.After 12 years of leachate exposure at the landfill site, both Na+ and Cl− had migrated about 1.5 m from the soil/refuse interface compared to an estimated advance of the seepage front of only 3–4 cm. The pore water Na+ and Cl− values versus depth exhibited considerable scatter, requiring data from three boreholes to delineate the concentration boundaries of the vertical migration.Diffusion coefficients, D, were obtained using an analytical solution to the one-dimensional dispersion–convection equation. Laboratory values of D, corrected to the estimated field temperature, were similar to field values. The D values of 3 to 6 × 10−6 cm2/s for Cl− and 2.5 × 10−6 cm2/s for Na+ appear suitable for preliminary design in nonfractured clays. Key words: salt migration, diffusion, domestic landfill, pollution.