Issue
Date: August
23, 1999
ASTTest
Services, Inc.
ASTTest
Mass Balance Leak Detection System
BULK UNDERGROUND
STORAGE TANK LEAK DETECTION METHOD (50,000 gallons or greater)
Certification
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Leak
rate is proportional to product surface area (PSA).
For tank with PSA of 5,575 ft², leak rate is 0.88 gph
with PD = 95% and PFA = 5%.
For other tank sizes, leak rate equals [(PSA in ft² ÷
5,575 ft²) x 0.88 gph].
Example: For a tank with PSA = 10,000 ft²; leak rate =
[(10,000 ft² ÷ 5,575 ft²) x 0.88 gph] = 1.578 gph.
Leak rate may not be scaled below 0.2 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 5,575 ft², leak threshold is 0.44
gph.
For other tank sizes, leak threshold equals [(PSA in ft²
÷ 5,575 ft²) x 0.44 gph].
Example: For a tank with PSA = 10,000 ft²; leak threshold
= [(10,000 ft² ÷ 5,575 ft²) x 0.44 gph] = 0.789 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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Diesel,
aviation fuel, fuel oil, kerosene.
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 larger
than 50,000 gallons.
Maximum product surface area (PSA) is 13,938 ft² (approximately
133 ft diameter).
Performance not sensitive to product level.
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Waiting
Time
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Minimum
of 48 hours after delivery or dispensing.
Valve leaks and pump drain-back may mask a leak.
Allow sufficient waiting time to minimize these effects.
There must be no dispensing or delivery during waiting
time.
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Test
Period
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Minimum
of 48 hours.
There must be no dispensing or delivery during test.
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Temperature
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Average
for product is determined by a minimum of 10 thermistors.
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Water
Sensor
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None.
Water leaks are measured as changes in level inside tank.
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Calibration
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Level
and temperature sensors must be checked regularly and,
if necessary, calibrated 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 2,000,000 gallon, vertical aboveground
tank with product surface area (PSA) of 5,575 ft².
Tests conducted in a vertical wall underground tank may
achieve better results.
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ASTTest
Services, Inc.
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Evaluator: Albert Machlin, P.E.
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2336
Hamlet Drive
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Tel: (212) 675-5868
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Melbourne,
FL 32934
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Date
of Evaluation: 11/98
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Tel: (407) 242-1474
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