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Certification
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Leak
rate of 0.1 gph with PD = 100% and PFA = 1.6%.
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Leak
Threshold
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A
tank system should not be declared tight when the acoustic
signal detected is different from the baseline signal
before a vacuum is placed on the tank, or when water ingress
is detected by the water sensor.
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Applicability
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Gasoline,
diesel, aviation fuel, fuel oil #4, waste oil.
Other liquids may be tested after consultation with the
manufacturer.
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Tank
Capacity
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Maximum
of 30,000 gallons.
Ullage volume must exceed the greater of 1% of tank volume
or 50 gallons.
Maximum of 30,000 gallons per tank for manifolded tank
systems with microphone, water sensor and pressure monitoring
gauges in each tank.
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Waiting
Time
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None
between delivery and testing.
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Test
Period
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When
groundwater level in tank excavation backfill is below
bottom of tank:
A few minutes to determine background noise and about
2 minutes to run the test after desired vacuum is reached.
When groundwater level in tank excavation backfill is
above bottom of tank or when the groundwater level in
the tank excavation backfill has not been determined:
The time it takes for water ingress to increase the water
level in the tank to allow the water sensor to detect
the "minimum detectable change in water level"
(see "Water Sensor" section below).
Test period based on water ingress is dependent on tank
size. For example, the test period is 36 minutes for a
10,000 gallon (96" dia x324" lg) tank.
Before starting test, water sensor must be calibrated
to "minimum detectable water level" (see "Water
Sensor" section below) according to manufacturer's
instructions.
There must be no dispensing or delivery during test.
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Test
Pressure
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Pressure
differential across tank wall at bottom of tank must be
at least 0.5 psig.
Pressure differential across tank wall is equal to the
absolute value of vacuum applied to tank, plus pressure
of tank excavation backfill on tank, plus groundwater
pressure on tank, minus pressure of liquid in tank.
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Temperature
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Acoustic
signal is independent of product temperature.
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Water
Sensor
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Conductivity
water sensor must be used to detect water ingress and
must be calibrated for every test when groundwater level
in tank excavation backfill is above bottom of tank or
when the groundwater level in the tank excavation backfill
has not been determined.
Minimum detectable water level is 0.014 inch.
Minimum detectable change in water level is 0.0095 inch.
Minimum water level in tank must be adjusted to at least
0.014 inch (sensor's minimum detectable water level) before
calibrating sensor and starting test.
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Groundwater
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Per
California regulations, depth to groundwater in tank excavation
backfill must be determined.
If groundwater level in tank excavation backfill is above
bottom of tank or the groundwater level in the tank excavation
backfill has not been determined, water sensor must be
used and test time extended to ensure water ingress detection
during test.
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Comments
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Microphone
was 25 ft away from leak source during evaluation.
Although not tested on empty tanks, a third party acoustics
specialist has certified the device is equally effective
when tanks are empty as when tanks contain product.
Test may be inconclusive if there is high background noise.
Vacuum test method may not be effective in some tank excavation
backfill (such as clay) because it may plug holes in tank.
If free product is present in tank excavation backfill,
a leak in the free product zone may not be detected by
a vacuum test method.
An observation well or soil probe in tank excavation backfill
may help determine backfill material, water level in tank
excavation backfill, and free product. Manufacturer must
certify operator at least every 2 years.
More than 4 psi pressure differential across the tank
wall at any location in the tank could damage tank.
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