Which federal agency is responsible for regulating UST systems?

The Environmental Protection Agency (EPA) is the federal agency tasked with regulating Underground Storage Tank (UST) systems. This responsibility arises from the federal legislation known as the Resource Conservation and Recovery Act (RCRA), which governs the management of hazardous waste, including the regulations concerning USTs. The EPA's regulations aim to prevent leaks and spills that can contaminate soil and groundwater, ensuring environmental protection and public health.

In addition to establishing guidelines for the installation, operation, and maintenance of USTs, the EPA provides oversight and enforcement of compliance with these regulations. This includes requirements for spill detection, correction of leaks, and periodic inspections, which are crucial for safeguarding environmental quality.

Other agencies listed, while important in different contexts, do not have responsibilities specific to the regulation of UST systems. OSHA focuses on workplace safety and health, the Department of Transportation deals with transportation regulations, and the FBI addresses national security and criminal investigations. Thus, the EPA stands out as the correct answer due to its direct regulatory role concerning UST systems.