California UST System Operator Practice Test

Compatibility is not required for every blend of biodiesel fuel used in underground storage tank (UST) systems because the requirements can vary depending on the specific blend percentages and the existing materials used in the UST. Some components such as seals, gaskets, and hoses may be compatible with certain biodiesel blends but not with others.

Blends that are lower in biodiesel content often maintain compatibility with traditional petroleum materials and are less likely to result in issues such as swelling or degradation of these materials. However, as the biodiesel content increases, the risk of material incompatibility also increases. Therefore, it is essential to assess compatibility on a case-by-case basis, particularly for higher concentration blends which may necessitate specific compatibility checks.

The question's premise suggests understanding the varying requirements applicable to the use of biodiesel blends in UST systems, indicating a more nuanced approach rather than a blanket requirement for all blends.