What type of tanks fall under UST financial responsibility requirements?

The correct choice involves understanding the specific regulations that govern financial responsibility for underground storage tanks (USTs). UST financial responsibility requirements typically pertain to tanks that store petroleum products and hazardous substances underground, ensuring that owners can cover costs related to leaks and environmental damage.

In this context, 600-gallon used oil tanks are classified under regulated USTs if they are used for storing certain substances. These tanks fall under scrutiny because they pose environmental risks if they leak, and thus financial responsibility requirements apply to ensure proper management and remediation if necessary.

The other options consist of storage tanks that generally do not meet the criteria for UST financial responsibility. For instance, aboveground petroleum tanks are not regulated under the same financial responsibility requirements as USTs. Residential heating oil tanks, typically smaller and often exempt from stringent regulations, also do not share the same requirements. Similarly, portable fuel tanks are not considered permanent underground installations and do not fall under the UST financial criteria. This makes the 600-gallon used oil tanks the correct focus for financial responsibility in the context of underground storage tank regulations.