Field observations of clogging in a landfill leachate collection system

The findings from a rare opportunity to exhume, examine, and sample a granular underdrain leachate collection system at a large municipal landfill site are reported. The "clear stone" drainage blanket was constructed from uniform, coarse gravel (with a nominal 50 mm particle size) obtained by crushing dolomitic limestone. After exposure to municipal landfill leachate for 1-4 years, the drainage stone was found to contain a considerable mass and volume of clog and slime materials. These were composed of mineral precipitates, fine granular particulate, and biofilm, growing under the ambient anaerobic conditions prevalent below the landfilled waste. The spatial distribution, physical and hydraulic properties, and chemical and microbiological composition of this material were examined and compared with similar material recovered from a laboratory mesocosm. The findings suggest a theoretical framework for a model of clogging behaviour of leachate collection drains at municipal solid waste landfill sites.