UST Programs - LG 113

Issue Date: November 14, 1997
Revision Date: December 6, 2002

Tanknology - NDE

Quick Test (Underfill Test)

NON-VOLUMETRIC TANK TIGHTNESS TEST METHOD (VACUUM)

Certification	Leak rate of 0.1 gph with PD = 100% and PFA = 0%.
Leak Threshold	A tank system should not be declared tight when the acoustic signal detected is different from the baseline. Baseline is the acoustic signal before tank is evacuated.
Applicability	Gasoline, diesel, aviation fuel, fuel oil #4, waste oil. Other liquids may be tested after consultation with the manufacturer.
Tank Capacity	Maximum product volume of 30,000 gallons. Tank product level must be between 7 and 86 inches.
Waiting Time	None between delivery and testing
Test Period	A few minutes to determine background noise and a leak. Depends on background noise at the site and on size of leak. There must be no dispensing or delivery during test.
Test Pressure	Vacuum of 0.5 psi beyond the vacuum required to overcome the tank bottom pressure must be maintained in ullage by a vacuum blower. Net vacuum applied = 0.5 psi + [inches of product level x the specific gravity of product x 0.036].
Temperature	Acoustic signal is independent of product temperature.
Groundwater	Per California regulations, depth to groundwater in tank excavation backfill must be determined. If groundwater is above the tank bottom, this system may not be used.
Comments	Not evaluated using manifolded tank systems. Evaluated using diesel. Tests only portion of tank containing product. Ullage portion of tank must be tested with an ullage test method. Microphone was 25 feet away from the leak source during evaluation. If background noise is too high, test is inconclusive. Noise signals are tape recorded (not digitally recorded). Vacuum test method may not be effective in some tank excavation backfill (such as clay) because it may plug holes in tank. If soil is saturated with product, air or water ingress may not be declared by vacuum test. A well point in tank excavation backfill may help identify presence of this condition.

Tanknology - NDE	Evaluator : Ken Wilcox Associates
8900 Shoal Creek Blvd. , Building 200	Tel: (816) 443-2494
Austin , TX 78757	Date of Evaluation: 06/25/96
Tel: (800) 800-4633

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