Underground Storage Tank (UST) Program

Underground storage tank system illustration

What is a Leaking UST?

An underground storage tank (UST) that has had a release of a regulated substance (typically petroleum) is called a leaking UST.  This designation does not mean that the UST system continues to leak; it means that a release occurred. Even with upgrade requirements and improvements in leak prevention, some UST systems will have a release. There are regulatory requirements for how an owner and operator must respond to a suspected and confirmed release from their UST system.

Environmental Concerns

Leaking USTs may present safety and environmental risks. Millions of gallons of petroleum products and hazardous substances are stored in USTs in the United States, and leaking USTs have been identified as a major source of soil and groundwater contamination. Leaks from USTs may create a risk to soil, groundwater and surface water (drinking water resources) and air (through vapor intrusion). Contamination from the release may require extensive and expensive cleanup efforts (which is why UST owners and operators are required meet Financial Responsibility requirements).

Learn more about Financial Responsibility requirements | Learn More >

How are Releases Addressed?

Federal and state regulations are designed to reduce the risk of and address releases to minimize environmental harm and keep the costs of major cleanups down. When a release is discovered, the owner or operator must report the release to ADEQ, mitigate immediate threats, investigate the extent of contamination and implement a plan of corrective action to address the risks.

In addition to inspections to ensure facilities are in compliance with regulations, ADEQ’s UST program provides financial assistance to eligible UST owners, operators and property owners and resources to conduct both proactive leak prevention measures and corrective actions.

Learn more about ADEQ's UST programs | Learn More >
Learn more about compliance | Learn More >
Learn about environmentally responsible remediation practices | Learn More >


The cleanup of UST releases is required by both the federal government and the state of Arizona. Federal requirements are set forth in the Code of Federal Regulations and the state requirements are contained in Arizona Revised Statutes1and Arizona Administrative Code.2

If a confirmed leak from USTs is not addressed by the owner or operators in the time frames required by federal regulations and states rules and laws, the non-compliant UST facilities are referred for enforcement.

Enforcement actions are conducted pursuant to the ADEQ Compliance and Enforcement Handbook. The actions range from the issuance of a Notice of Violation to administrative orders and ultimately to a civil lawsuit in the Superior Court of Arizona if compliance cannot be achieved informally.

View ADEQ Compliance and Enforcement Handbook | View >

Consult the Arizona Revised Statutes for more information about enforcement | View >

What leaking USTs are in my community? | View Map >