Various methods used to confirm the integrity of an underground storage tank.
The most widely used method for testing the integrity of a tank was originally the standpipe method. The tank to be tested was filled to the top with product. Then a transparent cylinder (the standpipe) was fitted into the fill opening at the top of the tank. More product was dispensed into this standpipe, and it was possible to visually observe the liquid level inside. Over a period of hours, the level was monitored. During this period, temperature readings were also taken at various levels in the tank below, so allowance could be made for contraction or expansion of the liquid caused by temperature changes. The test also included procedures that compensated for tank-end deflection.
Another tightness testing method involves use of acoustical sensing. A vacuum is created in the tank and sensitive instruments “listen” for the sound made by air bubbling in through tiny holes in the tank.
Some tank-tightness test methods do not require that the tank be completely filled while the test is in progress.
Electronic in-tank gauging devices, when set in a leak detection mode, are also capable of detecting tank leaks.