Underground Storage Tank Single-Walled Systems

On or before December 31, 2025, UST owners or operators must permanently close an underground storage tank (UST) if it was designed and constructed either before January 1, 1984 and does not meet the secondary containment and continuous monitoring requirements of Health and Safety Code (HSC), chapter 6.7, section 25291(a)(1)-(6), or if it was designed and constructed before January 1, 1997 with single-walled components (hybrid system), in accordance with HSC, section 25291(a)(7).

Currently, over 2,000 single-walled UST systems remain in operation statewide. Since the permanent closure deadline is rapidly approaching, the State Water Resources Control Board (State Water Board) will focus on single-walled UST systems during the Certified Unified Program Agency (CUPA) Performance Evaluation. During the evaluation, State Water Board staff (staff) will review California Environmental Reporting System data, facility files, and conduct oversight inspections at single-walled UST facilities within the CUPA’s jurisdiction. To assist CUPAs with the evaluation process, the State Water Board is providing guidance documents that discuss the criteria used to evaluate single-walled UST systems during the evaluation. Staff will continue to provide outreach and update guidance documents for the CUPAs to encourage owners and/or operators to permanently close single-walled USTs prior to the December 31, 2025 deadline.

Single-Walled Guidance Documents and Web Sites