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Issue Date: November 14, 1997
Revised: September 22, 2009
Tanknology
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.
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| 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 |
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. |
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Tanknology
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Evaluator : Ken Wilcox
Associates
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11000 North MoPac Expressway, Suite 500
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Tel:
(816) 443-2494
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Austin, TX 78759
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Date of Evaluation:
06/25/96
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Tel: (800) 800-4633
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