Geomembranes may function best under a ballast of soil, but this is not always necessary, due to their high UV resistance and durability. PVC is particularly susceptible to UV degradation, and will need at least 6 inches of soil above it to prevent solar damage. Other kinds of geomembranes, like RPE's, are rated for direct sun-exposure. Geomembranes used as pond liners will often be covered in a layer of soil in order to provide room for aquatic life to grow and feed.
If the geomembrane liner is exposed, and not placed underground, an anchor trench or shelf is used in order to prevent the material from uplifting or moving. The size of the trench will be determined by the particular project's demands, but a standard minimum for a small pond is typically 6 inches deep. For larger applications, like dams or reservoirs, an industry standard usually specifies a minimum of 2 feet. Other times, the liner may be connected and anchored by concrete beams, or another heavy material.
