13.04 What is vacuum monitoring for tanks, sumps, and piping?

The State of California requires continuous active monitoring of underground fuel systems including tanks, sumps, and piping. The concern was that dry interstitial spaces at atmospheric pressure could fail without recognition, and that a leak could escape from the containment prior to flowing to a sensor and being detected.

The regulation allowed pressure, vacuum, and hydrostatic methods of monitoring fuel containment secondary spaces. The hydrostatic method had been used for many years successfully in underground fiberglass tanks. The same method was extended to fiberglass sumps and double wall fiberglass piping. Pressure based systems have not been widely adopted.

The vacuum system has been widely adopted in California for a several reasons:

• The leading tank monitor developed systems to generate and monitor vacuum systems
• The vacuum generating device is the submersible fuel pump already present in most UST systems
• The vacuum method works for either fiberglass of flexible plastic piping system
• The vacuum method works for steel or fiberglass tanks and sumps

The vacuum monitoring system works essentially as follows:

• The Veeder Root monitor activates the submersible pump which is detailed to draw a vacuum on the interstitial spaces of tanks, sumps, and piping
• A Veeder Root vacuum sensor measures the vacuum and the vacuum decay rate.
• The control monitor determines if the vacuum decay rate is within the test pass parameters or not
• The tank monitor indicates a pass or fail result for the test.