Which of the following is NOT a common material used for UST liners?

Concrete is not commonly used for UST liners due to its porous nature, which can allow for the permeation of contaminants and result in environmental hazards. UST liners are essential for preventing leakage and protecting the surrounding environment from pollutants.

High-density polyethylene (HDPE), fiberglass-reinforced plastics, and carbon fiber are materials specifically designed for use in UST systems. HDPE is valued for its chemical resistance and flexibility, making it an excellent choice for preventing leaks. Fiberglass-reinforced plastics offer strength and durability, ensuring that the liner can withstand various environmental conditions. Carbon fiber is known for its lightweight properties and high strength, which can enhance resistance to structural changes and leaks over time. Each of these materials has been engineered to provide robust containment solutions, while concrete does not possess the properties needed to effectively prevent leaks in underground storage applications.