Which of the following is a violation of UST closure requirements?

A violation of UST closure requirements occurs when essential steps necessary for safe, compliant, and effective closure of an underground storage tank (UST) are not followed. Cleaning and removing the UST is a critical component of the closure process, as residual contaminants can pose a significant environmental risk. Proper closure requires that the tank be emptied, cleaned, and removed according to the established regulations to prevent leaks or hazards.

The other options might seem significant but do not inherently violate UST closure requirements on their own. For instance, removing all fuel from the UST is actually a required step in the closure process. Notifying local authorities is also a necessary action that must be taken in compliance with regulations. While filing the closure report late can lead to administrative issues and potential penalties, it does not directly impact the physical closure process itself. Thus, failing to clean and remove the UST represents a clear violation of the requirements designed to ensure safety and environmental protection during the closure of USTs.