The federal underground storage tank (UST) regulations apply to tanks that contain a regulated substance (petroleum products or hazardous substances) and tanks that have at least 10% of volume (including piping) underground. Regulated substances can be found under Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). (See 40 Code of Federal Regulations (CFR) 302, Section 302.4.)

Federal rules exclude the following UST systems from the definition of a UST:

• Any UST system holding hazardous wastes listed or identified under Subtitle C of the Solid Waste Disposal Act or a mixture of such hazardous waste and other regulated substances;
• Any wastewater treatment tank system that is part of a wastewater treatment facility regulated under Section 402 or 307(b) of the Clean Water Act;
• Equipment or machinery that contains regulated substances for operational purposes, such as hydraulic lift tanks and electrical equipment tanks;
• Any UST system whose capacity is 110 gallons (gal) or less;
• Any UST system that contains a de minimis concentration of regulated substances;
• Any emergency spill or overflow containment UST system that is expeditiously emptied after use;
• Farm and residential tanks of 1,100 gal or less capacity holding motor fuel used for noncommercial purposes;
• Tanks storing heating oil used on the premises where it is stored;
• Tanks on or above the floor of underground areas, such as basements or tunnels;
• Septic tanks and systems for collecting stormwater and wastewater; and
• Flow-through process tanks.

Governing laws and regulations:
40 CFR 280.10 to 280.12