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 strict regulatory requirements for how an owner and operator must respond to a suspected and confirmed release from their UST system.

Must all UST leaks be investigated and cleaned up?

All leaks are required to be investigated to determine the extent and degree of contamination. If the level of contamination is considered a risk, the owner and operator are required to conduct corrective actions to address this risk.

Leaking USTs may present safety and environmental risks, for 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. Federal EPA and state UST regulations are designed to reduce the risk of and address underground leaks to minimize environmental harm and keep the costs of major cleanups down.

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).

When a leak 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.


The cleanup of releases of petroleum products from underground storage tanks is required by both the federal government and the state of Arizona. The federal requirements are set forth in the Code of Federal Regulations and the state requirements are contained in the Arizona Revised Statutes under A.R.S.§ 49-1005 1and the Arizona Administrative Code under A.A.C. R18-12-250 through R18-12-264 2.

If a confirmed leak from USTs is not addressed by the owner or operators in the time frames required by the 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.

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