Hydraulic Properties of Geosynthetic Clay Liners

The long-term quality of groundwater resources requires careful waste management. One vulnerability results from the percolation of rainwater through various types of landfills; the resulting leachate may contaminate groundwater. Modern landfill design employs composite lining systems along the base and along the top cover after closure to mitigate potential environmental damage. Multiple layers of different materials, including geosynthetics, work together at the base to collect leachate and to prevent it from leaving the landfill. Geosynthetic clay liners (GCLs) are composite materials which utilize the swelling ability of bentonite clay to slow seepage by restricting the hydraulic conductivity. GCLs are deployed in top and bottom liner systems, and studies of GCLs in laboratory and field conditions show that GCLs may maintain long-term hydraulic conductivities <10-10 m/s to a variety of solutions.
The strengths and susceptibilities of GCL products must be considered during the design and installation of liner systems to ensure long-term performance as adequate hydraulic barriers. The goal of the research herein is to promote the understanding of the hydraulic behavior of GCL deployed in the field. The primary study analyzes the effects of an extended atmospheric exposure upon the hydraulic properties of GCL in a composite landfill liner system (geomembrane overlying GCL). Properties of the GCL varied between favorable and severely degraded, depending on location along the slope length. Measured hydraulic conductivities of exhumed GCL ranged between 10-11-10-6 m/s. Evidence of down-slope bentonite erosion was observed at mid-slope and slope-bottom locations.
During the secondary study herein, research was conducted to improve the characterization of polymer content in bentonite-polymer mixtures. These mixtures provide GCLs with increased chemical resistance to certain highly concentrated waste leachates. Accurately and precisely quantifying the distribution of polymer in these mixtures is necessary to achieve reliable and consistent mixture properties for use in bentonite-polymer GCL products.