Which component is critical for accurately detecting leakage in double-walled UST systems?

Interstitial monitoring systems are critical for accurately detecting leakage in double-walled underground storage tank (UST) systems because they are specifically designed to monitor the space between the inner and outer walls of the tank. This interstitial space can act as a containment area, allowing any potential leaks from the inner tank to accumulate in a controlled environment. The monitoring systems can detect the presence of liquids or vapors in this space, providing an early warning of leakage before it can escape into the surrounding environment.

This functionality is essential in preventing environmental contamination and ensuring regulatory compliance. Unlike the other options, which serve different purposes within UST operations, interstitial monitoring directly addresses the need for leak detection in double-walled systems. For instance, while fuel vapor recovery systems are focused on reducing emissions during fuel dispensing, or pressure relief valves regulating pressure, they do not play a role in leak detection within the tank structure itself. Thus, interstitial monitoring stands out as the key component for leakage detection in this context.