Officials from Pleasant Grove, Lindon and Orem spent several hours Tuesday trying to learn how a highly combustible substance got into the sewer system.

Police and fire officials responded to Wok Right In, 70 N. State, Lindon, about noon Tuesday to investigate the report of a gas leak, said Pleasant Grove fire marshal Dave Vickers. Officials determined the strong odor was coming from the sewer system.Gas detectors measured "a significant quantity" of a high-level combustible vapor in the sewer near the restaurant and at several nearby locations, Vickers said. Orem sewer officials tested the substance at a Pleasant Grove lab and determined it was toluene, a hydrocarbon used as a solvent.

"We never were able to track down the source or whether it was an illegal dumping," Vickers said. "After about three hours, the levels had gone down to the point where there was no danger of an explosion."

Pleasant Grove police are investigating the situation because toluene is a substance that can be used to manufacture illegal drugs, Vickers said.