California State Water Board Requiring Permanent Closure of Single-Walled Underground Storage Tanks (USTs)

September 2023

The California State Water Resources Control Board’s (Water Board) deadline for permanently closing all single-walled USTs is fast approaching. Under California law, tanks and connected piping must have approved secondary containment and continuous leak detection systems. Cal. H&S Code, § 25291(a)(1)-(6). Under the terms of Senate Bill 445, signed in 2014, UST owners and operators had ten years to permanently close their single-wall tanks and piping systems. Now, with the law about to sunset on December 31, 2025, the Water Board has estimated approximately 2,000 UST systems require closure or modification to prevent enforcement actions.

What are USTs?

The law defines a UST 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.” Cal. H&S Code, § 25281(y). These tanks are most often found at current or historic gas and service stations, although they can also be present at airports, hospitals, automotive repair shops, and industrial plants, among others.

As the name indicates, single-walled USTs have only one thickness of wall material, unlike double-walled USTs, which have an inner and outer wall. Single-walled USTs are more susceptible to leaks from corrosion, poor installation, earthquake damage, and other events. When a UST leaks, it can contaminate soil and groundwater with petroleum products, hazardous chemicals, or other pollutants. Recognizing the risk of leaks from single-walled USTs, California lawmakers passed the Underground Storage Tank Cleanup Fund to protect California’s drinking water and environment.

How does single-walled UST closure affect California businesses?

Single-walled USTs that have not been permanently closed by the regulatory due date are out of compliance, cannot be operated, and could be red-tagged by the Unified Program Agency (UPA) or the State Water Board. If a UST owner/operator is red-tagged, they may not be able to deposit, deliver, or dispense fuel and incur daily penalties of up to $5,000. Even for USTs that are not single-walled, property owners may face liability for removal and potential cleanup of unused or abandoned UST contamination.

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