An underground storage tank (UST) is defined by law as "any one or combination of tanks, including pipes connected thereto, that is used for the storage of hazardous substances and that is substantially or totally beneath the surface of the ground" (certain exceptions apply).

The statewide UST Program works to protect public health and safety and the environment from releases of petroleum and other hazardous substances from USTs through four elements: the Leak Prevention Program, Office of Tank Tester Licensing, cleanup of petroleum releases from UST systems and Low Threat Closure, and enforcement.