Certification

Leak rate of 1.717 gph with PD = 95% and PFA = 5%.
The US EPA has not set a minimum detectable leak rate for aboveground storage tank systems at the time of this evaluation.

Leak Threshold

0.859 gph.
A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds this threshold.

Applicability

Gasoline, diesel, jet fuel, fuel oil up to #6.

Tank Capacity

AST’s with surface areas from 7,854 to 30,172 sq. ft. and diameter’s from 100 to 196 feet.
Tank must be 20% full.

Waiting Time

Minimum of 20 minutes.

Test Period

Minimum of 20 hours.
There must be no delivery, transfer, or dispensing during test.

Temperature

One Resistance Temperature Detector (RTD) attached to the bubbler unit.

System Features

This system uses nitrogen under pressure conveyed to the bottom of the tank via a hose to generate (bubbler unit) and release small bubbles at the tank bottom.
The pressure required to produce the bubbles is equal to the hydrostatic head pressure produced by the fluid in the tank plus one atmosphere.  This pressure is measured by a pressure transducer.
The measured differential pressure is a direct measurement of the mass of the fluid in the tank.

Calibration

The differential pressure transducer is benchmark calibrated by the manufacturer.
Annual calibration is performed by the CBU/SIM unit and returned to the manufacturer if results fall outside the benchmark calibration values.
RTDs are calibrated annually.
Barometer is replaced every five years.

Comments

Data set is filtered to extract only night time data to eliminate the effects of radiant solar heating.
The CBU/SIM control unit is not rated for installation in areas where an explosive ignition risk may exist.
Method may be applied to steel, concrete, aluminum, or fiberglass tanks with either fixed or floating roofs.
Bubbler test pressure must not exceed 18 psig.