Attenuation of landfill leachate by clay liner materials in laboratory columns,1. Experimental procedures and behaviour of organic contaminants

The chemical attenuation of natural organic matter and 13 organic micropollutants (BTEX, aromatic hydrocarbons, pesticides, chloro-aromatic and -aliphatic compounds) in methanogenic landfill leachate by two UK clay liner materials was compared in laboratory columns over 15 months. Organic contaminant behaviour was evaluated using a first order decay transport model. Sorption of organic micropollutants by the clay liners was greater (by up to a factor of four) than expected. The organic micropollutants were degraded under different redox conditions and solute half lives varied from 4 to 112 days. Degradation of many organic micropollutants was complex and influenced by the sequential transformation of preferred substrates in the leachate. This cannot be predicted, although the results show that degradation in fieldscale liners will be extensive. Benzene was recalcitrant under the conditions and timespan (> 280 days) of the experiments. Natural organic matter (COD) behaved conservatively in the experiments. Attenuated organic contaminants were not released from the clay liners during flushing with freshwater suggesting that organic micropollutants are permanently sorbed or only slowly desorbed within the experiment. A conceptual model of liner performance is presented. Chemical attenuation of organic pollutants can be included in containment liner design to produce a dual reactive-passive barrier for landfills.