An evaluation of model parameters for clogging of coarse drainage material in landfill leachate collection systems

Leachate collection systems are an engineered component of most modern landfills and may consist of a network of perforated collection pipes within a drainage layer. The system is designed to control the leachate head acting on the landfill base, limiting the advective flow of contaminants through the barrier system by collecting and transporting leachate out of a landfill, thus reducing the potential for groundwater contamination in the surrounding environment. Field and laboratory studies have indicated that "clog" material can build up within the collection pipes and on the drainage material and disrupt the design function of the leachate collection system. McIsaac and Rowe (2005) conducted controlled laboratory column experiments to assess the clogging of coarse gravel and tire shreds permeated with Keele Valley Landfill leachate. This thesis uses a numerical clogging model (BioClog) to calculate the measured removal of volatile fatty acid concentration in the leachate and measured decrease in drainage material porosity along the length of the McIsaac and Rowe columns with time and compares the calculated and experimental results. It is suggested that the difference in pore structure between the gravel and tire shreds was a major factor in influencing the different rate of clogging of the two media. Another key parameter was found to be the change in dispersivity during clogging. The dispersivity for clean gravel and tire shreds was calculated to be 4 mm and 45 mm respectively, after conducting laboratory tracer tests and corresponding modeling. Both experimental observation and numerical modeling indicates that some of the suspended solids in the inlet section of the coarse gravel column was lost from the system due to sedimentation. Using the calibrated parameters, BioClog provided results that were in reasonable agreement with the measured data.