Abstract: It is assumed that voids are uniformly distributed in the substance space occupied by soils and the sorption of soil skeleton onto the contaminants behaves equilibrium and linear feature. Based on the analysis of basic interrelationship between volume and mass, an empirical formula is presented for evaluating the change of the porosity induced by sorption of soil skeleton. Under the condition of variable porosity, the governing equation for describing one-dimensional contaminant migration is established; and the initial conditions and boundary conditions are formulated for actual conditions including landfill profile, waste degradation and compacted clay liner (CCL) of finite depth in practice. The resulting initial boundary-values issue is numerically solved. Through parametric computations and comparative analyses, it is shown that the reduction of soil porosity induced by sorption of soil skeleton will decrease the breakthrough potential of contaminants into compacted clay liners. Compared with the case of constant porosity, the peak of concentration of contaminant transport in CCL will be reduced 10 % when the variable porosity due to sorption is considered. When the variable effect of soil porosity is taken into account, dispersion mechanism play a controlling role in the contaminant transport and the effect of the distribution coefficient in the sorption equation on contaminant migration is appreciable.

Key words: approximate formula of sorption-induced porosity reduction, compacted clay liner(CCL), aquifer, contaminant, breakthrough capacity