A liner system is constructed in a landfill for the purpose of preventing an outflow of contaminant and an inflow of underground water. In order to confirm the compatibility of the liner system, a contaminant migration analysis through a liner is indispensably necessary. In the analysis, the advection-dispersion equation govern the contaminant transport mechanism. It is also generally assumed that the liner condition is fully saturated during the design life time. However, the results of landfill investigation revealed that most of landfills are unsaturated, and hence we should employ the unsaturated condition in analyzing the contaminant transport. That is, it could be a decisive factor in the movement of solute through a liner. Therefore a simulation process was performed using two liner conditions, of which one considers a fully saturated condition and the other considers an unsaturated condition. In the later, velocity variation with infiltration is described by Richards equation and Darcy's law. The unsaturated model was assumed to have a homogeneous degree of saturation and the result was compared with that for fully saturated condition. It was found that if infiltration is so slow that an unsaturated condition could be maintained, the consideration of the unsaturated condition results in the decrease of contaminant movement, compared with that for a fully saturated condition. In the case which we apply a decreasing boundary condition for considering a reality, the same result is obtained. Consequently, the reflection of an unsaturated condition provides with a more effective liner design scheme.
