Which of the following best defines a change in service for an underground storage tank?

• A. Replacing the aging tank with a newer model.
• B. Moving the UST to a different site.
• C. Placing a UST out-of-service by using it to store a non-regulated substance instead of a regulated substance.
• D. Ending operation of the tank entirely.

Answer: (C)

A change in service means altering what the tank stores, not where it is or whether it’s kept running. If a tank that previously held regulated petroleum products is now used to store a non-regulated substance, its service has changed. This situation fits the definition because it changes the regulatory status tied to the tank’s contents, which can change the applicable requirements. The other options describe replacing equipment, relocating the tank, or shutting it down—none of these reflect a change in what the tank stores, so they don’t define a change in service.