Vertical barrier walls are often constructed to prevent contamination of ground water and soils by landfill leachate. The leachate water levels in landfills in southern China are generally high. Contaminants in such landfills may migrate through the vertical barrier walls and give rise to environmental problems. Qizishan landfill in Suzhou, China was taken as an example to investigate contaminant migration through the vertical barrier walls. Advection, diffusive and adsorption processes were considered in the analysis. Influences of permeability and depth of the barrier wall on contaminant migration were analyzed. The results show that it will be 13.5 years before breakthrough at 0.1% of the source concentration and 20.5 years before breakthrough at 10% of the source concentration. By and large, the contaminant has not passed through the barrier wall at present, and the contaminated zone is mainly located in the sandy clay layer near the earth dam, which is validated by testing on sampled soils. Hydraulic conductivity and depth of the barrier wall are critical to contaminant migration. Special attention need to be paid on them when building such a barrier wall. If bottom of the barrier wall is keyed into the aquitard and the hydraulic conductivity reaches 10(-9) m/s, the time before breakthrough will be long enough to allow stabilization of the landfill. Pollution of the surroundings will be avoided, and therefore the requirement for contaminant control will be attained.
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