In this term to consider a natural saturated clay liner of waste landfill overlaying an
aquifer that the mechanical dispersion can be negligible in this process of contaminant and
using of diffusion process as diffusive equation. Because effects of mechanical dispersion
and molecular diffusion are of the same order of magnitude, and the spreading is caused by
mainly mechanical dispersion, mechanical dispersion predominates in the range of validity of
Darcy’s law, except of a factor governing the transversal dispersion, pure mechanical
dispersion, but beyond the range of Darcy's law. Moreover, Effect of inertia and turbulence
can be no longer neglected. But this process of contaminant does not turbulence, so the
mechanical dispersion can be negligible in the process of contaminant.