Abstract: In order to evaluate the antifouling performance of the composite cut-off wall composed of geomembrane and soil- bentonite to the organic pollutants, a one-dimensional transient diffusion model was established to describe the diffusion behavior of pollutants through the composite cut-off wall when the pollutants were degraded in the source region. The solution of the analytical model was calculated by the Laplace transform and the Talbot numerical inversion. When the effects of pollutant diffusion and degradation were considered under the 3rd type inlet boundary condition, the 100-year breakthrough concentration of the type I (geomembrane/soil-bentonite) and type II (soil-bentonite/geomembrane/soil-bentonite) composite cut-off walls decreased by 59% and 53% than that under the 1st type inlet boundary condition, respectively. Since the permeability coefficient of geomembrane was assumed to be higher than 10–12 m/s, the convection of pollutants in the composite cut-off wall cannot be ignored. Thus, the type II composite cut-off wall enabled the soil-bentonite to play a dominant role in isolating the organic pollutants better. By reducing the permeability coefficient of geomembrane from 10–10 m/s to 10–16 m/s, the breakthrough time of type I composite cut-off wall was increased from 26 years to 188 years, and that of type II composite cut-off wall was increased from 32 years to 81 years, correspondingly. The antifouling performance of the composite cut-off wall can be effectively increased by adopting the methods, such as adjusting the negative head loss inside and outside the wall by a pumping well, and increasing the degradation capacity of pollutants in the source region.

Key words: degradable organic pollutant, inlet boundary condition, geomembrane, composite cut-off wall, numerical inversion;