Other motorists noticed a leak at approximately 4:45 p.m. Friday and pulled the tanker over at the Tinicum exit.
"It was leaking for about five or ten minutes after they pulled him over and then it stopped by itself," said Tinicum Assistant Fire Chief Jonathan Buschmeier, who was among the first to arrive on the scene and made the decision to close the roadways.
According to Delaware County Emergency Services Executive Director Ed Truitt, the tanker truck is owned by New Jersey-based Dana Transport, Inc, and was bound for St. Louis with 44,000 pounds of acetic anhydride.
Officials report that the leak has been capped, but the roads remained closed for several hours while a decontamination unit can assessed the damage and Dana representatives offloaded the tanker.
Firefighters evacuated dozens of residents from Colonial Park West to Interboro High School.
There were concerns about wind shifts and the chemical reacting with the rainwater.
"It worries me, you know, when you have three kids and you have to think about how they're going to be and make sure they're safe, because your kids are your first concern before yourself, and you have to make sure they're safe," said Chrissy Welsh.
I-95 has reopened and those evacuation have been allowed to go back into their homes.
Acetic anhydride, used by companies for the coating of photographic film, can be corrosive and noxious.
Truitt said the Pennsylvania Emergency Management Agency is aware of the incident and a Department of Environmental Protection representative has been dispatched to the scene.
"The EPA has also been contacted because of the close proximity to the wildlife preserve," Truitt said.
"We sent our mobile command post down there at his request," Truitt said. "It doesn't seem to be a whole lot of product (on the road). The truck is still on its wheels. It sounds like it could be a valve malfunction."
The operator of the tanker did not appear to be injured.
"The driver is okay, to the best of our knowledge," Truitt said, adding that a ConocoPhillips decontamination trailer was being brought in as a precautionary measure.
The Tinicum Township Fire Company says that hazmat was able to cap the leak around 8:30pm, and they were able to begin the cleanup.
I-95 was closed for about five hours.
The incident snarled rush hour traffic in both directions and caused backups from Philadelphia into the state of Delaware.
Northbound motorists on I-95 were forced to exit at Stewart Avenue in Ridley Park and drivers heading south had to get off at Island Avenue.