Issue Date: November 22, 1995
Revision Date: September 22, 2009


U3 Ullage Test (Vacuum or Pressure Test)


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 pressurized or evacuated.
Applicability Gasoline, diesel, aviation fuel, fuel oil #4, waste oil.
Tank Capacity Maximum ullage volume is 16,500 gallons.
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 the size of the leak. 
After the desired pressure has been reached, the tank should be allowed to settle for 10 minutes.
There must be no dispensing or delivery during test.
Test Pressure Vacuum of 1 psi must be maintained in ullage by a vacuum blower, or total pressure at bottom of tank of 4 psi must be maintained using nitrogen.
Temperature Acoustic signal is independent of product temperature.
Groundwater Depth to groundwater in tank excavation backfill must be determined. 
If groundwater is above product level, vacuum test should not be used. 
Pressure test may only be used if net pressure can be maintained at a minimum 1 psi throughout ullage during test. 
If this requires more than 5 psi total pressure at tank bottom, the ullage test must not be used.
Comments Not evaluated using manifolded tank systems. 
Evaluated using diesel. 
Tests only ullage portion of the tank. 
Product-filled portion of tank must be tested with an underfill 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.



Evaluator:  Ken Wilcox Associates

11000 North MoPac Expressway, Suite 500

Tel:  (816) 443-2494

Austin, TX 78759

Date of Evaluation:  01/15/93

Tel: (800) 800-4633



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