Underground Storage Tanks (UST)

Underground Storage Tanks (UST)

An underground storage tank (UST) is defined by law 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" (certain exceptions apply). UST Owners/Operators are required to understand and comply with all UST regulations. Any deviation from regulations may result in fines and/or permit revocation.

Assessing Underground Storage Tanks for Earthquake Damage

In light of the August 24, 2014 earthquake in Napa, the State Water Board has prepared the following document for guidance on assessing underground storage tanks for earthquake damage.

UST Earthquake Assessment 2014

UST Installations:

All newly installed underground storage tanks must be double walled with the capability of monitoring the interstitial space. The piping must also provide double containment, which includes a line leak detection system, and be able to monitor the entire secondary containment system.

The following information must be submitted for the installation of UST(s):

  1. UST Permit Application. (PDF: 132 kB)
  2. Two copies of the installation plans (blueprints).
  3. A cut sheet indicating the items to be installed along with a UL type approval.
  4. State Form A (PDF: 66 kB) and State Form B (PDF: 35 kB) (a separate Form B is required for each tank).
  5. State Form Certification of Installation / Modification (PDF: 48kB).
  6. Site Safety Plan
  7. Monitoring Plan (PDF: 120 kB).
  8. Response Plan (PDF: 50 kB).
  9. Appropriate fee.
  10. Certificate of Financial Responsibility (PDF: 44 kB).
  11. Any other documentation requested by the Sonoma County Fire and Emergency Services Department.

UST Removals:

  1. UST Permit Application. (PDF: 132 kB)
  2. State Form A (PDF: 66 kB) and State Form B (PDF: 35 kB) (a separate Form B is required for each tank).
  3. Site safety plan.
  4. Plot map of the site indicating location of UST and other information necessary for the tank removal.
  5. Current contractor's license with the expiration date (this information may be on the contractor's list).
  6. Current workers compensation policy (this may be on the contractor's list).
  7. Appropriate fee.
  8. Any other documentation requested by Sonoma County Fire and Emergency Services Department.


Biodiesel can be used, either as a pure fuel or blended with conventional petroleum-based diesel fuel, to power diesel engines and has become an increasingly popular alternative fuel choice. UST Owners/Operators must remain aware of regulations regarding the storage of biodiesel. Blends of greater than 20% biodiesel have not yet been approved by the State Water Regional Control Board (SWRCB) for storage in underground tanks. Any UST Owner/Operator found to be storing a non-approved biodiesel blend in an underground storage tank will be required to remove the biodiesel product or be subject to enforcement actions and fines.

UST Owners/Operators that currently store or would like to store biodiesel in an underground tank must complete and submit a Sonoma CountyNotice of Intent to Store Biodiesel form(PDF: 74 kB) to our office.

Enhanced Vapor Recovery (EVR) Upgrades:

Enhanced Vapor Recovery (EVR) is required for gasoline dispensing facilities with underground storage tanks that are already required to have a vapor recovery system. Air districts that are in attainment with the state ozone standard are exempt from most EVR requirements. Air districts that have recently been designated as non-attainment areas,may have different EVR deadlines than those provided here. Check with the Bay Area Air Quality Management District or the Northern Sonoma Air Pollution Control District to determine the vapor recovery requirements for your facility.

The State deadline for EVR Phase-II upgrades was April 1, 2009. All UST Owners/Operators are required to comply with this State mandate. Those who do not meet this deadline are subject to fines and/or UST closure.

EVR upgrades require permitting from Sonoma County's Permit and Resource Management Department (PRMD) and may require a permit from Sonoma County Fire and Emergency Services Department Hazardous Materials Division. Check with our office, 707-565-1152, prior to beginning work to determine if a permit is required for installation of EVR.


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