SIMPLIFIED CALCULATION METHOD FOR CONTAMINANT TRANSPORT IN COMPACTED CLAY LINER CONSIDERING THERMAL DIFFUSION

Taking compacted clay liner(CCL)as the object, thermal diffusion under the effect of temperature gradient is added to traditional convection dispersion equation. The analytical solution in a semi-infinite domain is obtained. The results show that relative concentration and flux at the base of CCL obtained from the analytical solution considering thermal diffusion are greater than those obtained from traditional convection dispersion equation. The stable flux at S_T=0.5 K^-1 is 2.5 times larger than that at S_T=0. Thermal diffusion flux is -AS_TD/v times the convection dispersion, and both increase with service time. With the increasing of time, molecular diffusion flux increases to a peak, then approaches zero. Taken the effects of temperature on migration parameters and thermal diffusion into account, temperature increase leads to the increase of relative concentration, the advance of breakdown time, and the significant increase of flux. When the temperature increases from 30℃ to 70℃, the breakdown time changes from 8.5 to 5.1 years, and the steady flux increases by 1.7 times. Pollution risk may be higher when the effect of temperature on contaminant transport is eliminated in design of CCL.