Simulation of Natural and Engineered Hydraulic Trap Systems in a Landfill, Using one- dimensional Three-Layer Laboratory Models

The role of unsaturated drainage layer and hydraulic control systems in sanitary-engineered solidwaste landfills were simulated using three-layer one-dimensional laboratory models. In the models,from top to bottom, a sodium chloride solution as a contaminant source reservoir, a first compacted siltlayer as a primary liner, a coarse sand layer as a secondary leachate collection system or a hydrauliccontrol layer, a second compacted silt layer as a secondary liner, and a bottom water reservoir as agroundwater aquifer, were used. In the first two tests, the model simulated the secondary leachatecollection system and natural hydraulic trap system (upward flow through the second clayey siltlayer). In this case, the contaminant transport mechanisms through the first silt layer were downwardadvection and diffusion, and through the second silt layer, diffusion was downward and advection wasupward. The results showed that the implementation of the natural hydraulic control system couldeffectively reduce the contaminant transport to the underlying groundwater reservoir. In the third test,the natural and engineered hydraulic trap systems were simulated (upward flow from the bottomreservoir to the upper reservoir). In the fourth test, the model simulated the engineered hydraulic trapsystem (downward flow through the first silt layer and upward flow through the second silt layer). Theresults showed that natural and engineered hydraulic trap systems have important effects on reducingthe contaminant transport toward the underlying aquifer. In all experiments the chloride concentrationin silt and coarse sand layers and top and bottom reservoirs were measured and the observedconcentrations were compared with theoretical concentrations calculated by computer code POLLUTEV6. The results showed that there is good agreement between theoretical and observed data.