Pressurized Layer Reduces Transport through Compacted Clay Liners
Compacted clay liners are often used in hazardous waste surface impoundments and landfills to provide a physical barrier to the flow of leachate. If a liner develops cracks or regions of high conductivity, convective fluxes can lead to increased chemical transport through the liner. In this study, we investigate the use of a pressurized layer of coarse material sandwiched between two compacted clayey soil layers to eliminate the hydraulic gradient across the upper layer. Our hypothesis is that such a system would limit convective transport through cracks or regions of high conductivity. Miscible displacement experiments were conducted using compaction permeameters filled with layered and unlayered soil materials. Experiments were carried out with and without a “worst case” hole penetrating the soil columns vertically. The experimental results show that, by using the pressurized interlayer in the presence of a worst case hole, both mean solute travel times and times to first breakthrough were significantly greater than when no interlayer was used. Travel times and time to first breakthrough were also increased when the pressurized interlayer was introduced in a column not containing a hole. The experimental results also serve to demonstrate the devastating effect of a small crack or hole on solute transport.
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