SOUTH SALT LAKE — Up to 8,000 people were evacuated and thousands of motorists diverted off I-15 Sunday, after a rail tanker car began leaking acid — material that might be extremely toxic.

South Salt Lake police said the site of the leak, first discovered about 6 a.m., was about 2270 S. 600 West.

With the rail car's structure compromised, workers dared not climb its ladder to attach a hose and pump out acids. Instead, about 9:30 p.m. they used a specialized machine to puncture the wall of the tank, insert a hose, and begin pumping the acid into holding tanks.

First reports said that operation was going smoothly, but it would take two or three hours to complete the job.

Gov. Jon Huntsman Jr. was at the scene Sunday night consulting with safety experts. At one point, at least 100 police, fire and emergency personnel were helping control the spill, evacuate the neighborhood, direct traffic or were standing by in case of disaster.

By then, an estimated 5,500 gallons had leaked from the car, which originally contained 13,500 gallons. According to Steve Foote, South Salt Lake fire chief, early reports said the car's contents included hydrochloric acid, hydrofluoric acid, nitric acid and sulfuric acid.

Later, word came that what was in the tank was phosphoric acid, sulfuric acid, acetic acid, hydrofluoric acid and ammonia, with the acid at only 10 percent concentration.

"We're still concerned" about what's on board, Foote said, "due to the fact that we have had complete disintegration of the tank." He said he wants to get to the bottom of the situation.

At the scene, Huntsman cited the conflicting messages about the tank's contents. That troubles him, he said. "We're going to find out exactly why there was a miscommunication," he said. "You have to know what's inside in order to formulate a response."

Depending on the type of acid and concentration of fumes inhaled, the material could severely damage a person's lungs.

"It's waste acid," Foote said Sunday afternoon. "It was used in a manufacturing process, and now that rail car's leaking."

He described the tank's leaks as looking like "big white softballs that are all along the rail car. . . . It's just bubbling like big blisters along the side of that tank.

"And these are not blisters caused by paint. It's not the paint blistering. It's the actual metal itself."

Foote said apparently a protective liner inside the tank failed. When the acid touched the metal, it caused a corrosive reaction. The reaction may have released a lot of heat, and officials were afraid that if they put water on it, it could explode.