A relatively small rural landfill was designed with a PVC/GCL composite liner system overlain by 300 mm of gravel. One end of the project contained a slope having an inclination at 4(H):1(V) for a length of approximately 58 m. Three months after construction the PVC liner had ripped along the crest of the slope, and the gravel and PVC had slid on top of the GCL along the entire slope length. The GCL was exposed about half way down the slope. The failing interface was clearly between the PVC and the GCL. The lessons learned from this project were (a) to conduct slope stability testing and analyses for interim and construction conditions in addition to final fill conditions, and (b) interface direct shear testing should have interfaces sprayed with water during the setup, and not just count on flooded conditions to allow water to travel to the interface. Neither of these lessons is particularly new to the industry, showing the value of having a project peer-reviewed by designers experienced with the nuances of geosynthetics design and construction.