Certification

Leak rate is proportional to product surface area (PSA). 
For tanks with PSA of 11,786 ft², leak rate is 3.00 gph with PD = 95.3% and PFA = 4.7%
For other tank sizes, leak rate equals [(PSA in ft² ÷ 11,786 ft²) x 3.00 gph]. 
Example:
For a tank with PSA = 10,000 ft²; leak rate = [(10,000 ft² ÷ 11,786 ft²) x 3.00 gph] = 2.54 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 11,786 ft², leak threshold is 1.50 gph.
For other tank sizes, leak threshold equals [(PSA in ft² ÷ 11,786 ft²) x 1.50 gph]. 
Example:
For a tank with PSA = 10,000 ft²; leak threshold = [(10,000 ft² ÷ 11,786 ft²) x 1.50 gph] = 1.27 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

Gasoline, diesel, aviation fuel. 

Tank Capacity

Use limited to single, field-constructed, vertical-walled tanks 50,000 gallons to 2,100,000 gallons. 
Maximum product surface area (PSA) is 11,786 ft².
Tank must be at least 44% full.

Waiting Time

None.
Testing may be initiated immediately following a delivery provided a minimum of 72 hours of quality data are collected and analyzed.

Test Period

Minimum of 72 hours. 
There must be no dispensing or delivery during test.

Temperature

Measurement not required by this system.
System is self-compensating for product temperature changes.
Buoyancy of float changes with product density in response to temperature changes.

Water Sensor

None.
Water ingress leaks are measured as an increase in product level inside the tank.

Calibration

Servo product level measurements must be verified annually and, if necessary, calibrated in accordance with manufacturer's instructions.

Comments

Not evaluated using manifolded tank systems.
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 2,100,000 gallon vertical underground tank with diameter of 122.5 ft., height of 23.4 ft., and PSA of 11,786 ft².
System is a volumetric measurement test method.