Interstitial monitoring in UST systems means which of the following?

• A. The space between the primary tank and secondary containment is monitored for leaks
• B. The system uses external monitoring
• C. It indicates no risk of leaks
• D. The tank is above ground

Answer: (D)

Interstitial monitoring checks the space between the inner storage tank and its secondary containment. In a double-walled UST, any leaked product would first collect in that interstitial space, and sensors or monitoring systems watch that gap for changes—like liquid presence or pressure differences—to alert you before a release reaches surrounding soil or groundwater. This setup is about early detection, not guaranteeing there is no leak or implying the tank’s location above ground. External monitoring and other interpretations are separate concepts; interstitial monitoring specifically targets the gap between walls to spot leaks.