In unsaturated composite liners, the heterogeneous distribution of water content and capillarity are common phenomena with remarkable influence on the transport parameters. This study presents an analytical solution to assess the effect of unsaturation-dependent retardation and capillarity on the organic contaminant diffusion through an unsaturated composite liner. The solution is obtained by the generalized integral transform technique and is verified against other analytical and numerical solutions. Particular attention is paid to the potential errors in predicting organic contaminant transport caused by unsaturationindependent retardation factor assumption. The results show that neglecting saturation-dependent retardation may cause considerable errors. The considerations of capillary fringe and degradation also have significant effects on the errors. In addition, a simplified solution based on a new averaged retardation factor is proposed and its performance is evaluated.

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