Which of the following is a key feature of double-walled UST systems?

The key feature of double-walled UST systems is that they include a monitoring system for external leaks. These systems are designed with two walls: an inner tank that holds the stored product and an outer tank that serves as a secondary containment structure. This design enhances the safety and environmental protection of underground storage tanks by providing a barrier that prevents leaks from reaching the surrounding soil and groundwater.

The external monitoring system is crucial because it allows for the detection of any leaks that may occur in the inner tank. This proactive approach enables operators to respond quickly to any leaks, thus minimizing potential environmental contamination and ensuring compliance with regulatory requirements. By continuously monitoring the space between the inner and outer walls, facility operators can identify issues before they escalate into more significant problems.

Other options, such as a single layer of protection, increased capacity for storage, or lower construction costs, do not accurately represent the advantages or features of double-walled UST systems. In fact, having a single layer would not provide the necessary safeguards, and while double-walled tanks may sometimes have similar storage capacities or involve higher initial investment due to additional materials and construction complexities, their primary goal remains leak prevention and environmental safeguarding.