SummaryThe permeability of glacial till soils having mainly montmorillonite in the clay fraction was negligible when the exchangeable sodium percentage (ESP) exceeded 15 to 20. Relatively higher permeability values were obtained in soils containing gypsum, but water transmission through such soils was negligible above ESP of 30 to 35. The relative decrease in permeability with increase in exchangeable sodium depends not only on the ESP and electrolyte concentration in the soil solution but is affected by the types of clay minerals.