1. (a) A tank containing normal butane, isobutane, propane, or butylene (including isomers) or mixtures composed predominantly thereof in a liquid or gaseous state having a vapor pressure in excess of 40 pounds per square inch absolute at a temperature of 100 degrees Fahrenheit.
2. (b) A tank containing steam-refined asphalt that is not liquid at standard temperature and pressure, which means at 60 degrees Fahrenheit and 14.7 pounds per square inch absolute.
3. (c) A septic tank designed and used to receive and process or store biological waste.
4. (d) A tank designed to treat influent wastewater through physical, chemical, or biological methods and which is located at a public or private facility that treats wastewater and is regulated under section 402 or 307(b) of the Clean Water Act (33 U.S.C. section 1251 et seq.). These tanks include untreated wastewater holding tanks, oil-water separators, clarifiers, sludge holding tanks, filtration tanks, and clarified water tanks that do not continuously contain hazardous substances.
5. (e) A depression in the ground which lacks independent structural integrity and depends on surrounding earthen material for structural support of fluid containment.
6. (f) Piping, pumps, conduits, and any other equipment necessary to collect and transport the flow of surface water run-off resulting from precipitation, or domestic, commercial, or industrial wastewater to and from retention areas or any areas where treatment is designated to occur. The collection of storm water and wastewater does not include treatment except when incidental to conveyance.
7. (g) A tank containing radioactive material, such as a spent fuel pool, radioactive waste storage tank, and similar tanks under the Atomic Energy Act of 1954 (42 U.S.C section 2011 et seq.).
8. (h) An emergency containment tank kept empty to receive accidental spills that has been approved for such use by the Unified Program Agency.
9. (i) A drum, or other portable container, located in a basement or other below-grade structure, that contains 55 gallons or less of a hazardous substance.
10. (j) A tank containing hazardous waste as defined in section 25117 of the Health and Safety Code if the Department of Toxic Substances Control has either issued a hazardous waste facilities permit for the tank pursuant to section 25200 of the Health and Safety Code or granted the tank interim status under section 25200.5 of the Health and Safety Code.
11. (k) A tank and associated piping located in a vault, basement, or other below-grade structure that meets the requirements of section 25283.5 of the Health and Safety Code.
12. (l) A tank in an underground area which meets the requirements of section 25270.2(o) of the Health and Safety Code. For purposes of this chapter, other than containment sumps attached to an underground storage tank, a tank in an underground area includes any portion of petroleum supply or return piping extending beyond the underground storage tank's tank top fittings, including associated pumps and components, dedicated solely to connecting the underground storage tank to one or more tanks in an underground area.
13. (m) A pipeline located in a refinery or in an oil field unless the pipeline is connected to an underground storage tank.
14. (n) Unburied fuel delivery piping at marinas if the owner or operator conducts daily visual inspections of the piping and maintains a log of inspection results for review by the Unified Program Agency.
15. (o) Unburied fuel piping connected to an emergency tank system if the owner or operator conducts visual inspections of the hazardous substance primary containment piping each time the tank system is operated, but no less than monthly, and maintains a log of inspection results for review by the Unified Program Agency.
16. (p) A tank or combination of manifolded tanks located on a farm that holds no more than 1,100 gallons of petroleum which is used for fueling motor vehicles used primarily for agricultural purposes and is not for resale.
17. (q) A tank located on a farm or at a personal residence that holds no more than 1,100 gallons of home heating oil solely for consumptive use at the premises where the tank is located.
18. (r) A tank containing hydraulic fluid for a closed loop mechanical system that uses compressed air or hydraulic fluid to operate lifts, elevators, and other similar devices.
19. (s) Underground storage tanks that are part of an emergency generator system at nuclear power generator facilities licensed by the Nuclear Regulatory Commission pursuant to appendix A of section 50 of the Code of Federal Regulations.
20. (t) Any other tank or structure not listed above that is excluded from the definition of an “underground storage tank” in section 25281 of the Health and Safety Code or exempt from the requirements of this chapter pursuant to the Health and Safety Code.

The following are not subject to the requirements of this chapter because they are excluded from the definition of an “underground storage tank” in section 25281 of the Health and Safety Code or they are exempt from the requirements of this chapter pursuant to the Health and Safety Code:

Note: Authority cited: Sections 25299.3 and 25299.7, Health and Safety Code. Reference: Sections 25117, 25200, 25200.5, 25270.2, 25281, 25281.5 and 25283.5, Health and Safety Code; and 40 CFR Sections 280.10 and 280.12.

History

1. New section filed 10-28-2025; operative 1-1-2026 (Register 2025, No. 44).