WEST MIDDLESEX — An explosives contractor spent about five hours searching for dynamite believed to be buried near the West Middlesex viaduct Thursday, but all workers found were mounds of slag.

After digs at two sites, excavation of a third spot near the state Route 318 bridge was scrapped minutes before a severe thunderstorm rolled through the borough.

“This is done for now,” said Brian Yedinak, a PennDOT design services engineer.

But a mystery remains, because Yedinak said he still considers credible the story of an 87-year-old man who remembers finding the dynamite as a boy when buildings were being demolished to make way for the viaduct that stands today.

“I personally believe it’s out there somewhere,” Yedinak said. “It may not be in the vicinity of this bridge.”

Edward G. Anderson told PennDOT that in 1936 when he was 11 he and his brother helped their dad dismantle four buildings along the Shenango River. They found five crates of dynamite, along with a case of nitroglycerine caps, while clearing the site.

At the time, Anderson’s father and borough officials decided the best way to dispose of the dynamite was to bury it. They placed the crates in an empty cellar nearby, secured the cellar door with cast iron seats removed from a theater and put a heavy lock on the door, Anderson said. Within two days the area was completely covered with dirt and what the Andersons found was lost to history.

For decades this was merely a childhood memory. But when PennDOT said it was going to replace the nine-span bridge, Anderson wrote the agency a letter to alert officials of what he considered a danger – explosives that might be set off by the construction.

Anderson’s letter, and the many details he provided in subsequent conversations, prompted PennDOT to take action. They hired a company to search the soil on the north side of the bridge with both metal detectors and radar. And on Thursday another contractor, Reactive Explosive Materials Training Corp. of New Jersey, excavated two of the three spots the metal and radar detectors had pinpointed.

Kevin Pi is an unexploded cqordnance technician with the company. He said every dig is different – the firm often searches for un-detonated items on military bases – and before starting at the West Middlesex viaduct the key was “we go incredibly slow.”

Excavation began shortly after 9 a.m., and crews didn’t finish digging out the first 10-foot-deep hole until after noon. They spent another two hours excavating the second location. At the end of it, Pi said he had dug down “basically to the river bottom,” and “where (the dynamite) is supposed to be, it wasn’t.”

Pi was confident that a search of the third site wouldn’t have yielded anything different. They never hit the stone wall of the cellar Anderson described.

West Middlesex resident and historian Bob Lark doubted crews would find anything.

Though no one was allowed near the dig site, Lark and a few other residents milled around Main Street under the hot sun as the work went on. Lark carried historic photos of West Middlesex in the 1920s that showed some of the buildings that were removed to build the viaduct, which was dedicated in 1941.

“It’s possible. I don’t think it’s probable that it’s there,” Lark said of the dynamite as the search continued. It might have been dug up years ago, he said.

Anderson has steered clear of most media requests for interviews, though he did tell his story to The Herald last week, and talked to the newspaper again Thursday after the search was called off.

He and his son had tried to find a spot near the viaduct to watch the work, but were moved back – like everyone else – for safety reasons. He ended up spending much of the day at a command post set up inside the West Middlesex borough office and fire station.

From there he got an up-close view of some of the search work. Cameras flashed images on computer screens, he said.

And though no one found the dynamite Anderson so-clearly remembers finding and burying near the viaduct, he said Thursday he didn’t regret telling his story or alerting PennDOT.

“I’m a little anxious to tell you the truth,” Anderson said. “I hope they don’t find it.”

Construction of the $12.1 million bridge is expected to begin in 2016. PennDOT said the dynamite search ended up costing at least $17,000, far less than the maximum $100,000 the agency estimated earlier. That higher cost included removal and detonation expenses for any dynamite that might have been found.