Owners and operators must demonstrate compatibility for which of the following stored substances?

The compatibility of stored substances in underground storage tanks (USTs) is crucial to ensure safety and compliance with environmental regulations. Among the options provided, B50 pertains to a blend of biofuels that contains 50% biodiesel and 50% conventional diesel. Demonstrating compatibility for such a blend is essential because it can have different chemical properties compared to standard diesel fuels.

When tanks are used to store blended fuels like B50, it is critical that the tank materials, piping, seals, and other components are compatible with the specific chemical makeup of the fuel. The potential for corrosion, degradation, or other physical failures can increase if materials in the UST are not suitable for the stored substance. This aligns with regulatory requirements to prevent leaks and spills, which could pose environmental hazards.

In examining other choices, E15 is a blend of 15% ethanol and 85% gasoline that requires compatibility considerations, while T50 and A50 designations do not represent widely recognized fuel blends or components at the same level of regulatory scrutiny regarding compatibility with storage materials. Therefore, B50 represents a blend that requires official demonstration of compatibility to ensure UST infrastructure integrity and safety.