Recently, the demand for suitable clay as an impermeable barrier in waste disposal sites has been growing because it is a readily available natural material of low permeability. The Torbali Neogene clay deposit is a significant clay source used as the basement layer for waste disposal sites in Izmir, Turkey. In this study, the effects of different leachates taken from the Torbali region on the geotechnical properties of the clay including various clay minerals were investigated. Geotechnical analyses of clay samples treated with different leachates were carried out in terms of index properties, compressibility, and hydraulic conductivity based on Atterberg limit tests and one-dimensional consolidation tests. The results indicated that the liquid limit values of the samples were unaffected by the increase in cation concentration when the plastic limit values affected. As a result of high cation concentration, the initial void ratio, compressibility, and the settlement behavior (C-C/I+e(0)) of clay-groundwater, clay-waste water, clay-surface water, and clay-distilled water increased in that order. Although the hydraulic conductivity of the clay-ground water sample had the highest value, it was not found a linear relation between the cation concentration and the hydraulic conductivity of the samples. The results indicated that the influence of leachate on the hydraulic conductivity under high pressures was negligible. It was concluded that the Torbali Neogene clay could be used as landfill liner material in Torbali and the Izmir region.