The effect of surface defects on the durability of high density polyethylene geomembrane as a liquid barrier in waste containment system was examined by comparing the mechanical properties and chemical resistance of virgin gieomembranes with made on the surface of geomembranes by a specially designed scratching apparatus. The number of scratches applied at the shear rate of scratch induced mechanism, 100 mm/min. The tensile and bursting strength decreased but the tensile strain increased with the above conditions. In chemical resistance of defective geomembranes, the tensile strength was decreased but the tensile strain was increased with longer immersion period and higher temperature of chemical treatment, under the same scratching conditions.