A valve at the Pacheco Conduit inlet in California lets workers drain the conduit without draining the 5.3-mile-long tunnel that feeds it. During tests after construction in 1986, however, Bureau of Reclamation engineers found a 125-gallon-per-minute leak at the concrete valve structure expansion joint. Although a waterstop had been installed at the joint, inadequate concrete consolidation was permitting water to bypass the waterstop.

Removing and replacing the valve structure concrete would have been too costly. Repair by epoxy injection was rejected because liquid epoxy would penetrate the sponge rubber filler in the expansion joint, gluing the faces together. Then the repaired section wouldn't be able to accommodate seasonal temperature change movements between the tunnel portal and valve structure. The leak needed to be plugged while still allowing movement at the joint.

On several other projects, the Bureau of Reclamation had successfully repaired smaller leaks using hydrophilic polyurethane resin, injected like an epoxy. The urethane resin reacts with water to form an expansive foam that cures to a tough, flexible, cellular rubber.