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Issue
Date: August 23, 1999
Mass
Technology Corp.
Precision
Mass Measurement System (24 hour test)
BULK
UNDERGROUND STORAGE TANK LEAK DETECTION METHOD (50,000 gallons
or greater)
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Certification
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Leak
rate is proportional to product surface area (PSA).
For tanks with PSA of 1,257 ft² or less, leak rate is
0.1 gph with PD = 97.9% and PFA = 2.1%.
For tanks with larger PSA, leak rate equals [(PSA in ft²
÷ 1,257 ft²) x 0.1 gph].
Example:
For a tank with PSA = 2,000 ft²; leak rate = [(2,000 ft²
÷ 1,257 ft²) x 0.1 gph] = 0.16 gph.
Calculated minimum detectable leak rate is 0.078 gph with
PD = 95% and PFA = 5%.
Leak rate may not be scaled below 0.1 gph.
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Leak
Threshold
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Leak
threshold is proportional to product surface area (PSA).
For tanks with PSA of 1,257 ft² or less, leak threshold
is 0.05 gph.
For tanks with larger PSA, leak threshold equals [(PSA
in ft² ÷ 1,257 ft²) x 0.05 gph].
Example:
For a tank with PSA = 2,000 ft²; leak threshold = [(2,000
ft² ÷ 1,257 ft²) x 0.05 gph] = 0.08 gph.
A tank system should not be declared tight if the test
result indicates a loss or gain that equals or exceeds
the calculated leak threshold.
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Applicability
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Gasoline,
diesel, aviation fuel, fuel oil #4.
Other liquids may be tested after consultation with the
manufacturer.
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Tank
Capacity
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Use
limited to single field-constructed vertical tanks.
Maximum product surface area (PSA) is 3,143 ft² (approximately
63 ft diameter).
Performance not sensitive to product level.
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Waiting
Time
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Minimum
of 1 hour, 6 minutes after delivery or dispensing.
Valve leaks and pump drain-back may mask a leak.
Allow sufficient waiting time to minimize these effects.
Waiting times during evaluation ranged from 62 minutes
to 31 hours.
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Test
Period
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Minimum
of 24 hours.
There must be no dispensing or delivery during test.
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Temperature
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Measurement
not required by this system.
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Water
Sensor
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None.
Water leaks are measured as increase in mass inside tank.
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Calibration
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Differential
pressure sensor must be checked regularly in accordance
with manufacturer's instructions.
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Comments
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Tests
only portion of tank containing product.
As product level is lowered, leak rate in a leaking tank
decreases (due to lower head pressure).
Consistent testing at low levels could allow a leak to
remain undetected.
Evaluated in a nominal 120,000 gallon, vertical underground
tank with product surface area (PSA) of 1,257 ft².
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Mass
Technology Corp.
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Evaluator: Ken Wilcox Associates
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7
Cox Drive
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Tel: (816) 443-2494
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Kilgore,
TX 75662
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Date
of Evaluation: 03/25/98
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Tel: (903) 986-3564
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