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  Newsletters > September 07

Chapman Engineering
September 2007 Newsletter

Leak Detection Methods for Underground Storage Tank Systems

To Our Valued Customers:

We have calls regularly from customers, tank owners, and – more and more – City and other government officials.  A question often asked is, “What options do I have for leak detection on my tank system?”

The options are the same now as they were from about 1993 forward.  And the allowable methods are still just five, in terms of definitions:

• Vapor monitoring
• Ground-water surface monitoring
• Interstitial monitoring
• Automatic tank gauges (ATG’s)
• Statistical inventory reconciliation (SIR)

We tend to see ground-water surface monitoring – that method where you check a water surface in observation wells once a month for any signs of a product thickenss – used down along the Coast, where ground water is really shallow.  It’s either “fine” or “fail” in terms of results.

There are many vapor monitoring methods out there, that vary in sophistication and cost over a VERY wide range.

Interstitial monitoring is done when you have double-walled tanks and piping.  You simply monitor for product showing up in what should be a dry space between the inner shell and the outer shell.  There are other variations, but double-walled equipment is a great safety factor.

ATG’s are valuable tools for managing fuel inventory.  For leak detection, they only give results for the tanks.  Lines have to be tested separately.  And the more inventory moves through a tank system per month, the less reliable ATG’s may be for good leak detection performance.

SIR was not approved as a UST leak detection method by EPA until 1993.  It requires you to get good inventory control data and submit that to an outside vendor.  That vendor puts the data into a complex computer program and looks at trends that might indicate fuel loss.  The SIR vendors do their work very inexpensively, which is attractive.  But we have seen very inconsistent results from this method, according to many, many clients as well as some large “institutional” users.  If you go to SIR, be prepared to spend a lot of money trying to confirm or deny problems indicated by the SIR results.