This paper examines the feasibility of the natural soil and sewage sludge ash (SSA) mixtures, which satisfy the criteria to be used as landfill liners. The effect of SSA content on hydraulic conductivity and strength characteristics of natural soil and SSA mixtures has been investigated through a series of laboratory tests. The results demonstrate that mixtures exhibit an increase in both hydrodynamic diffusion coefficient and strength with the increasing SSA content. With the content of SSA from 0% to 5%, the values of the hydrodynamic diffusi...