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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 |
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. |
| Leak
Threshold |
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. |
| Applicability |
Diesel, aviation fuel, fuel oil, kerosene.
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| Tank
Capacity |
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. |
| Waiting
Time |
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. |
| Test
Period |
Minimum of 48 hours.
There must be no dispensing or delivery during test. |
| Temperature |
Average for product is determined by a
minimum of 10 thermistors. |
| Water
Sensor |
None.
Water leaks are measured as changes in level inside tank. |
| Calibration |
Level and temperature sensors must be
checked regularly and, if necessary, calibrated in accordance with
manufacturer's instructions. |
| Comments |
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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