Understanding Secondary Containment Systems
Written by: Brian Pottebaum, Director of Training Services
This is part one of our two part series on secondary containment systems. To read part two about the inspection and testing requirements for secondary containment systems, click here: Inspecting and Testing Secondary Containment Sumps - PMMIC
Secondary containment is the only method of leak detection that can detect a “leak” without allowing a “release” to the environment. It is the best method available to protect against spills and leaks to the environment. However, if not operated and maintained properly, secondary containment systems are ineffective, or worse, become inoperable and you may not know about the problem until a release to the environment has occurred.
Double walled tanks These tanks have two layers with an “interstice” space in-between, in other words, it is a tank inside of another tank. In most double walled tanks, the interstitial space (i.e., space between the inner and outer tank walls) is monitored with a liquid sensor, but some tanks do allow for manual monitoring with a vacuum gauge or “sticking” process. The tank walls must be tight and liquid sensors (if installed) must be programmed and function properly. Make sure that tank interstice caps are always installed properly to prevent surface water from entering the interstice. If monthly monitoring is properly conducted, a periodic tightness test of the tank interstice is not required. However, if there is a problem suspected, a tightness test may be required. The contractor must provide specifics on what type of system is being tested and how the test was conducted. The test results and any repairs or adjustments need to be reported as well.
Double walled piping This is piping with at least two layers and an interstitial space in which a leak in either layer would allow liquid to travel to the monitoring area. The piping walls must be tight and liquid sensors (if installed) must be programmed and function properly. The entire run of double wall piping must be monitored, therefore the piping interstice should be continuous from one end to the other, unless multiple monitoring areas are used. If the monitoring is done at a sump, the double wall piping interstice must drain freely between dispenser sumps and piping sumps (i.e., piping test boots are open). Monitoring should be conducted as is recommended by the piping manufacturer, but if monthly monitoring is properly conducted and no problems are suspected, periodic tightness tests of the piping primary and interstice are not required.
Piping containment sump These containment sumps are located at piping termination or connection points at tank-top or intermediate locations (splice, junction, or transition sumps). The containment must be liquid-tight and liquid sensors (if installed) must be programmed and functioning properly. The sumps can be monitored with a liquid sensor or by physically checking the condition of the sump. Remember that all containment sumps must be monitored (tank-top, intermediate, and dispenser). This method of leak detection requires that the containments be liquid-tight, meaning all entry boots, conduits, and walls are intact. Also, ensure that the entire run of piping interstice can flow freely into the sumps being monitored. When the containment system is inspected and the integrity is in question, then a hydrostatic tightness test (or another approved test) must be conducted to determine if repairs need to be made. The contractor must provide specifics on what type of system is being tested and how the test was conducted. Test results and any repairs or adjustments must be reported.
Under dispenser containment (UDC) Like the piping containment sump, under dispenser containment is part of the required containment inspection and testing protocol. The containment must be liquid-tight and liquid sensors (if installed) must be programmed and functioning properly. The sumps can be monitored with a liquid sensor or by physically checking the condition of the sump. This method of leak detection requires that the containment be liquid-tight, meaning all entry boots, conduits, and walls are not damaged and are intact. Ensure that the entire run of piping interstice can flow freely between dispenser sumps and into the piping sump being monitored.
Spill basin/sump Spill basins, sometimes referred to as spill buckets, are liquid-tight containers placed around the fill pipe designed to capture small spills that occur during a fuel delivery into the tank. They must be kept clean, and all liquid and debris should be removed regularly. Although spill buckets are not usually part of the piping system, they are a form of containment and must be inspected and tested according to regulatory requirements. When the spill basin is inspected and the integrity is in question, then a hydrostatic tightness test (or another approved test) must be conducted to determine if replacement or repairs need to be made. The contractor must provide specifics on the basins being tested and how the test was conducted. All testing, repairs, and installations must be done according to manufacturer’s specifications. Test results and any repairs or adjustments must be reported accordingly.