Which of the following stored substances must owners and operators demonstrate compatibility for?

The requirement for owners and operators to demonstrate compatibility specifically pertains to E15, which is a blend of gasoline containing 15% ethanol. As ethanol is known to have different chemical properties compared to pure gasoline, it can interact with various materials used in underground storage tanks (USTs) and their associated systems.

Demonstrating compatibility is essential because certain materials could degrade or fail when exposed to higher concentrations of ethanol, leading to potential leaks or failures in the storage system. The importance of this demonstration is rooted in regulatory compliance, environmental safety, and ensuring the integrity of the storage system.

The other substances listed, such as B50, C10, and R100, do not have the same broad regulatory emphasis on compatibility as E15 does. In particular, while they may also need to be assessed for compatibility, they do not carry the same level of scrutiny or concern from regulators as E15, primarily due to the recognized impact that ethanol has on storage materials and the subsequent need for stricter oversight.