Where are interstitial monitoring sensors located in double-wall tanks?

• A. On the outer surface of the tank
• B. In the product storage area
• C. In the ventilation duct
• D. In the space between primary and secondary barriers

Answer: (D)

The key idea is that interstitial monitoring aims to detect leaks in the barrier between the inner tank and the outer containment. Placing sensors in the space between the primary (inner) barrier and the secondary (outer) barrier lets the system sense any liquid or vapor that penetrates the inner tank and enters the interstitial space. This early warning helps prevent releases to the environment. Placing sensors on the outer surface, in the product storage area, or in a ventilation duct wouldn’t monitor the barrier gap effectively, so the correct location is the space between the primary and secondary barriers.