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Issue
Date: August 23, 1999
Vista
Research, Inc. and Naval Facilities Engineering Service Center
LRDP-48
(V1.1)
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 6,082 ft², leak rate is 0.749 gph
with PD = 95% and PFA = 0.012%.
For other tank sizes, leak rate equals [(PSA in ft² ÷
6,082 ft²) x 0.749 gph].
Example:
For a tank with PSA = 10,000 ft²; leak rate = [(10,000
ft² ÷ 6,082 ft²) x 0.749 gph] = 1.232 gph.
Calculated minimum detectable leak rate is 0.376 gph with
PD = 95% and PFA = 5%.
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 6,082 ft², leak threshold is 0.563
gph.
For other tank sizes, leak threshold equals [(PSA in ft²
÷ 6,082 ft²) x 0.563 gph].
Example:
For a tank with PSA = 10,000 ft²; leak threshold = [(10,000
ft² ÷ 6,082 ft²) x 0.563 gph] = 0.926 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.
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 15,205 ft² (approximately
139 ft diameter).
Performance not sensitive to product level.
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Waiting
Time
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Minimum
of 24 hours 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 16.08 to 115.8
hours.
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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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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 600,000 gallon, vertical underground
tank with product surface area (PSA) of 6,082 ft².
Not evaluated as a stand alone system.
Significant bias of 0.078 gph was detected during the
evaluation.
Evaluator believes this bias was the result of product
inflow into the tank from valve leaks and product drain
back from the pump return line and thus evaluator did
not use this bias in calculating above results.
Performance of the system can be improved by combining
results of 2 or more tests.
If this option is used, it is important to determine the
number of tests, their timing and the number of passing
results necessary to confirm a tank is tight.
The LRDP-24-5 (V1.1) combines the results of 5 tests and
is one evaluated option to improve the performance of
this system.
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Vista
Research, Inc.
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Evaluator:
Ken Wilcox Associates
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755
North Mary Ave.
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Tel:
(816) 443-2494
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Sunnyvale,
CA 94085
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Date
of Evaluation: 01/29/99
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Tel:
(408) 830-3300
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