Underground Storage Tank

An Underground Storage Tank endorsement is required for owners of storage tanks with all of the following:

• Capacity greater than 110 gallons.
• At least 10% of volume (including piping) below the surface of the ground.
• Contain petroleum or other hazardous substances.

Note: Some tanks may be exempt.

Licensing requirements and additional supporting documents

• Business License Application (PDF).
• Underground Storage Tank Addendum (PDF).
• Weighing and Measuring Devices Addendum (PDF).
• Closure and Site Assessment Notice (required for temporary and permanent tank closures and change in service.)
• Tank Owner/Operator Training Requirements.
• The owner must file an application within 30 days after a new installation is complete, or upon modification or purchase of existing tanks.
• A notice of intent to install (PDF) must also be filed directly with the Department of Ecology at least 30 days before new installation work begins.
• All owners of regulated UST's, other than state or federal government agencies, must provide proof of ability to pay costs of a release from their tanks at the liability minimums set in WAC 173-360A 1000 through 1015.

Note: If using insurance, attach the complete insurance policy from the provider, which includes the certificate as set forth in WAC 173-360A-1083. The certificate holder should be:

If you are not using liability insurance, attach a Certificate of Financial Responsibility as set forth in WAC 173-360A-1096.

See also the Underground Storage Tanks – Business Bulletin (PDF).