Which of the following is NOT a cause of underground storage system failures?

The correct answer highlights that scheduling issues are not a direct cause of underground storage system failures. Failures in underground storage tanks (UST) are primarily attributed to factors that physically impact the system's integrity and functionality.

Corrosion is a significant concern; it can lead to leaks and other mechanical failures. Tanks made of material susceptible to corrosion can deteriorate over time, especially when exposed to environmental factors and stored liquids.

Debris can also contribute to failures by obstructing drainage systems or creating conditions conducive to corrosion and blockages, thus compromising the storage system's integrity.

Temperature fluctuations can affect the materials used in USTs, possibly leading to expansion, contraction, and changes in the viscosity of stored products. Such fluctuations may cause stress on the structural components of the tank and associated piping, potentially resulting in failures.

In contrast, while scheduling issues may impact maintenance or operations, they do not directly cause a failure in how the tank functions or its physical integrity. Therefore, it is recognized as a management or operational aspect rather than a technical cause of failure in the underground storage system.