This study presents numerical simulations of contaminants transport through a composite geomembrane geosynthetic clay liner (GMB-GCL) li nings system. Organic contaminants have been studied (TCE, P-cresol). GCLs properties are considered after cation exchange and wet dry cycles to take into account the alteration of the GCL by their environment. To study the durability of these ged GCLs, results are compared with contaminant transfers through composite liners involving virgin GCLs. Typical published values for the diffusion coefficient for both virgin and aged GCL used in this study are shown to give good predictions of contaminants migration and effluent concen-tration with time. Indeed, obtained relative concentrations evolutions with time agree well with the theoretical break-through curve. Indeed, Simulated contaminant concentrations through GCLs showed that alteration by the environment of GCLs seems not to affect significantly the diffusion of organic contaminant examined in this study.