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UST Program - Available Local Guidance (LG) Letters

UST Program - Local Guidance (LG) 125-1


MAY 19, 1994

To: Local Agencies

The California Underground Storage Tank Regulations, Title 23, Chapter 16 have been amended and the new regulations are effective as of May 5, 1994. Section 2643.1 of the regulations specify the new product level requirement for tank testing.

Previous regulations required that tank testing be conducted "after tank filling." This statement was clarified and explained in detail in LG-125, October 23, 1992 (now obsolete), requiring that tank testing must be conducted with the tank filled to the highest routine operating level.

Under the newly amended regulations for non-volumetric tank testing methods there is no regulatory minimum product level requirement but the test method must be capable of detecting leaks from the entire tank. For volumetric test methods the regulatory minimum product level requirement is 65 percent and the portion of the tank which does not contain product must also be tested using an ullage test method.

It is important not to confuse the minimum regulatory requirement and any technical limitations set for the test equipment/method. Each tank test method is third-party certified based on a minimum product level for the test method. The minimum product level specification is listed in the State Water Board LG-113 series. The enclosure gives some examples to help clarify the minimum acceptable product level for tank testing.

It is this agency's recommendation that tank tests be conducted under conditions which more closely represent actual operating conditions of the tank. There are many factors that could interfere with field performance and accuracy of the test method. The third-party certification does not evaluate a test method against all these factors

It is also important to note that Section 2643.1 of the amended regulations require tank test methods take into account the presence of water in the tank backf'ill. That is, all tank testers must determine if water is present in the backfill and report the height of the water table above the bottom of the tank in the test report. Volumetric test methods should compensate for the hydrostatic pressure of the water outside in the backfill by raising the product level in the tank (in accordance with the calculations specified in the test protocol). Ullage test methods and non-volumetric tests methods compensate for this effect by increasing the ullage pressure and/or extending the test time. The leak detection equipment list (LG-113 series) specifies how each test method compensates for the external water pressure on the tank. Specific information provided by the equipment manufacturer for each test method should be consulted for details on water compensation procedures.

If you have any questions regarding this letter, please contact Shahla Farahnak at (916) 227-4350 or David Holtry at (916) 227-4332. To obtain additional copies of this letter, fax a request to Virginia Lopez at 916-227-4349 or call 916-227-4303.


[Original Signed by:]
James George Giannopoulos
Supervising Engineer




Minimum Product Level Requirement For Various Tank Testing Categories

1. Overfilled Volumetric Tank, Tightness Test Method:

Product level in the tank is raised above grade level, in accordance with the test protocol, and the certified tightness test is conducted.

Presence of water in the backfill is taken into account in the calculations to determine product level above grade level.

2. Underfilled Volumetric Tank Tightness Test Method:
a. Product level in the tank is raised to the overfill prevention device set point (level above which no product can be added to the tank) or the tightness test method certification level (as listed in LG- 1 13 series), whichever is higher. and the certified tightness test is conducted.

Presence of the water in the backfill may require the product level to be higher than the above specified level.

b. Product level in the tank is raised to the 65 percent regulatory level or the test equipment certification level (as listed in LG-113 series), whichever is higher, and the certified volumetric tightness test is conducted. This test should be followed by an ullage test method, which is third-party certified (listed in LG-113 series), to detect leaks from portion of the tank which does not contain liquid product.

Presence of the water in the backfill may require the product level to be higher than the above stated levels.

3. Non-Volumetric Tank Tightness Method
Product level in the tank is raised to the listed in LG-ll3 series for the specific tightness test method and a certified tightness test is conducted.

Presence of water table above the backfill will require modifications as stated in the LG-113 series.

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