Airport hydrant systems are large underground pressurized piping systems. Typically, these systems operate with a pressure of about 150 psi and range in diameter from 6 in. to 16 in.. Systems vary in their design, but typically have trunk lines and laterals that end in hydrant pits. These systems are orders of magnitude larger than piping systems found at retail fuel outlets. The lines themselves may contain 250 000 to 500 000 gal of product. Since they are large and operate at high pressure, the potential for environmental damage in the event of a leak is correspondingly increased.
Airport hydrant systems are currently deferred from the leak detection requirements of the federal EPA regulations covering underground storage tanks. However, several states, eg. Texas, have neither exempted nor deferred these systems. These states are regulating hydrant systems on a case by case basis. There is a clear need for leak detection methods for such systems.
A number of approaches to leak detection for hydrant systems have been proposed. These include double wall piping with interstitial monitoring, external monitoring methods for vapor or liquid product on the water table, tracer methods, pressure-step methods, and inventory methods. This paper describes several approaches to leak detection for hydrant systems. It also provides estimates of the performance that may be expected from each method. It relates these performance estimates to the EPA standards for nonexempt/nondeferred systems. The approximate cost to install and operate the methods is discussed.