Date: August 23, 1999
ASTTest Services, Inc.
ASTTest Mass Balance Leak
BULK UNDERGROUND STORAGE TANK
LEAK DETECTION METHOD (50,000 gallons or greater)
||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
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 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
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.
||Diesel, aviation fuel, fuel oil, kerosene.
||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
Performance not sensitive to product level.
||Minimum of 48 hours after delivery or
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.
||Minimum of 48 hours.
There must be no dispensing or delivery during test.
||Average for product is determined by a
minimum of 10 thermistors.
Water leaks are measured as changes in level inside tank.
||Level and temperature sensors must be
checked regularly and, if necessary, calibrated in accordance with
||Tests only portion of tank containing
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
Albert Machlin, P.E.
Tel: (212) 675-5868
of Evaluation: 11/98
Tel: (407) 242-1474