Abstract: The retardance of organic contaminants in acetigenic and methanogenic lanfill leachate by different vadose zone lithology was studied in laboratory columns. Experimental results demonstrated that the organic content of clay and fine sand in the vadose zones was increased from 0.70% and 0.87% to above 0.80% and 1.00% contaminated by young leachate and decreased to below 0.70% and 0.50% polluted by old leachate. In the vadose zone the organic matter content rose when contaminated by young leachate, however decreased when polluted by old leachate. Silt as the vadose material was more easily impacted by leachate than clay. It means that the property of landfill leachate influences the organic matter content in the vadose zone; furthermore silt would more likely exaggerate the effects more than clay.

Key words: landfill leachate, landfill age, organic materials, vadose zone