Concentration-driven leakage

Another important leakage mechanism is a concentration-driven diffusive flux in contrast with the pressure-driven hydrodynamic flux considered previously. The flux of species A relative to the average molar velocity of all components is given by Fick s first law. 

Leakage through a synthetic liner is controlled by Fick s first law, which applies to the process of liquid diffusion through the liner membrane. The diffusion process is similar to flow governed by Darcy s law except that it is driven by concentration gradients and not by hydraulic head. Diffusion rates in membranes are very low in comparison with hydraulic flow rates even in clays. In synthetic liners, therefore, the factor that most influences liner performance is penetrations. Synthetic liners may have imperfect seams or pinholes, which can greatly increase the amount of leachate that leaks out of the landfill. 

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