Landfill caps should be designed using appropriate materials and with stability in mind, according to Agru America, manufacturer of MicroSpike Liner. While geomembranes, predominately linear low-density polyethylene, have been used for landfill caps for decades and have generally performed well, there are now four commonly used material options:
- Geomembrane and soil composites. Technically feasible in all climates, geomembrane and soil composites require soil depths suitable to the selected vegetative community used to hold the topsoil system together. Their stability is based on veneer interface strengths.
- Synthetic turf cover. Synthetic turf replaces the soil protection and vegetative cover layers and protects the underlying membrane from UV degradation. Stability is less of a concern and cost savings can be significant.
- Exposed geomembrane cover. This is the least expensive geosynthetic option. While stability is less of a concern, because these covers are subject to UV degradation and wind uplift, their use has been limited to temporary covers.
- Monosoil, water-based or evapotranspirative covers. Technically feasible for climates with 19 inches or less of annual precipitation, these covers require an appropriate fine-grain soil and long-rooted vegetative community. Their stability is based on the soil’s internal shear strength and erosion resistance.
To prevent liners and caps from sliding down slopes, they are often textured or structured to enhance friction with the underlying soil or non-woven geotextile on geosynthetic clay liners and geocomposites. Texturing is the process utilized during the blown film manufacturing process while structured profiles are created using the advanced flat die extrusion calendaring manufacturing process.
A well-designed capping system can help prevent slope failure on landfill closure projects.
Agru America provided an overview of leachate treatment options in a recent blog post.
Photo: landfill waste site via Shutterstock.