Parameters of contaminant transport of compacted clay liners with fractures

The service period of landfill liners is reduced because of the fractures in compacted clay liners (CCL), which shorten the breakthrough time of contaminants passing through the barrier. It is very important to predict the breakthrough time of the leachate for CCL with fractures when the parameters of contaminant transport of fractures are acquired. The experiment is carried out to obtain the coefficient of molecular diffusion and dispersion for chloridion in the fractures simulated by the sands with different porosities. The results show that the coefficient of molecular diffusion for chloridion is consistent when the chloridion passes through fractures with the width more than or equal to 15 mm and water, while the coefficient of molecular diffusion is reduced exponentially in the fractures with the width less than 15 mm. The coefficient of dispersion is approximately three orders of the magnitude more than that of molecular diffusion. Based on different hydraulic gradients, the dispersion coefficient of fractures with width more than or equal to 10 mm is essentially constant and almost equal to that acquired from the sand column experiment. While the hydraulic gradient is more than or equal to 0.2, the variation of dispersion coefficient is steady and not influenced by the width of the fractures.