Certification

Leak rate is proportional to product surface area (PSA). 
For tanks with PSA of 11,786 ft², leak rate is 4.50 gph with PD = 96.3% and PFA = 3.7%
For other tank sizes, leak rate equals [(PSA in ft² ÷ 11,786 ft²) x 4.50 gph]. 
Example:
For a tank with PSA = 10,000 ft²; leak rate = [(10,000 ft² ÷ 11,786 ft²) x 4.50 gph] = 3.80 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 2.25 gph.
For other tank sizes, leak threshold equals [(PSA in ft² ÷ 11,786 ft²) x 2.25 gph]. 
Example:
For a tank with PSA = 10,000 ft²; leak threshold = [(10,000 ft² ÷ 11,786 ft²) x 2.25 gph] = 1.91 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 having a capacity of 50,000 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

Average for product is determined by resistance temperature detectors (RTDs) located at 18 inch increments from the bottom of the tank.

Water Sensor

Must be used to detect water ingress.
Minimum detectable water level in the tank is based on the length of the probe as follows:
<25 feet = 3.0 inches
<40 feet = 3.8 inches
<60 feet = 4.7 inches
The water sensor “inactive zone” can be countered by installing the probe over the tank sump.
Minimum detectable change in water level is 0.015 inch.
Water ingress sensing is continuous and independent of leak detection testing.

Calibration

No scheduled maintenance or recalibration is required.
The sensor pipe should be checked annually for build up of process material.
Floats should move freely along the sensor pipe.  If they do not, routine cleaning should be performed.

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.