I had the good fortune of having lunch with Larry Gregory yesterday, a retired engineer with Exxon Mobile who’s visited gas stations all over the globe and who probably knows more about designing and building UST systems than anyone I know. We had just met when we found ourselves driving by a convenience store with a cordoned off dispenser, a large pile of dirt and a contractor looking into the pit. Being UST geeks that we are, we stopped by to investigate.
What we saw was an open pit with exposed flexible plastic piping connecting an under dispenser containment sump and a tank top sump. So pressurized, double-walled pipes with sump sensors and a mechanical line leak detector. The soil didn’t appear stained and the sump looked clean and dry. I drove by the same site a few months ago and remember one of the tanks was being relined. So my curiosity was piqued. The contractor was friendly and enthusiastic that someone would take an in interest in his work and explained the following:
There appeared to be a failure of the inner wall of the flexible plastic double wall piping a few inches upstream from where the pipe entered the tank top sump. Unfortunately the interstitial boot was sealed at the bottom (and the top, it was later discovered) so the fuel, once leaked out, just backed up in the interstice and sat there for an unknown time. At some point the seal at the lower end of the interstice failed, the sump filled up with fuel, the sump sensor alarm went off and the mechanical leak detector went into slow flow. (Although the exact order of how all this happened is unclear.) The contractor cut back the flex pipe and removed the structurally unsound pipe, shortening the pipe run and reattached it, then opened the interstices top and bottom.
The good news: no apparent release to the environment; the sump sensor and mechanical LLD seemed to work and the operator (trained not by us, alas) had the wherewithal to call someone to investigate.
The bad news: Another flex pipe story. We are not big fans of flexible piping and would have voted since the whole pipe run was exposed to replace with double wall fiberglass piping. I’m not convinced the pipe might not fail again down the road; the problem seems in part to be faulty equipment and poor installation, something the Class A/B operator has little control or knowledge over. Also Larry wasn’t sure how the contractor knew the remaining pipe was structurally sound other than through visual inspection. The biggest impediment to rapid detection appears to be the failure of the installer to keep the interstice open, plus the UST state inspector not noticing the interstice plugged. Of course period testing of the interstitial system as proposed by EPA might have found this flaw sooner.
Bottom line: UST systems that are leak free happen because all aspects of its life cycle are done correctly, from design to manufacturing to shipping to installation to testing, then finally operation and maintenance. UST operator training can help in the last stages of this cycle but operators are at the mercy of all the previous steps being done correctly.
Suggestions: Pay close attention to the condition of your flexible plastic piping, verify the interstice is open and the sump sensors adequately positioned, test your leak detectors annually, and train your staff what slow flow and sump sensors alarms mean. And if your flex piping fails, just consider replacing the whole length instead of just cutting off the failed section.