A railroad tank car that leaked hazardous chemicals, forcing thousands of people from their homes, had been loaded with a dangerous cocktail of corrosive acids that it was not designed to resist, authorities said Monday.

Hazardous materials crews and rail officials were angered by an alleged lack of information from the company that leased the rail car.

Sunday's leak produced a cloud of orange fumes that spread over several blocks of South Salt Lake, chasing some 6,000 people from their homes and closing several roads and highways, including a stretch of Interstate 15. By midmorning Monday, evacuees were allowed home and the roads were reopened.

Samples tested by hazmat crews showed the tank car had been filled with a mixture of acetic, hydrofluoric, phosphoric and sulphuric acids, which easily corroded the car's lining, officials said. The evacuations had been ordered Sunday after part of the tanker started to soften.

"That combination attacked the integrity of the rail car," said Louie Cononelos, a spokesman for Kennecott Utah Copper (search) of Magna, Utah, which had leased the car to Phillips Services.

"The rail cars are used for the transportation of sulphuric acid. That's what they're designed for," Cononelos said. "For whatever reason, they were shipping something that was not sulphuric acid."

Phillips Services also leased two other tankers from Kennecott. Both were traced to a rail yard in Ohio, where local authorities embargoed them at Kennecott's request.

Officials of Phillips Services did not immediately return calls seeking comment Monday.

Union Pacific (search) spokesman John Bromley said the corroded rail car would likely be scrapped. "It's too badly damaged," he said.

South Salt Lake Fire Chief Steve Foote said Monday there was a possibility of a criminal investigation.

"They're not being straight with us," Foote had said late Sunday.

Officials had spent all day Sunday trying to learn the tank car's contents from Phillips.

The manifest said it contained sulfuric and hydrofluoric acids, but the company told local officials it was hydrochloric, hydrofluoric, nitric and sulfuric acids. Late Sunday, the officials said, the company corrected itself, saying it was a mixture of phosphoric, acetic, sulfuric and hydrofluoric acids and ammonia — all at a concentration of only 10 percent.

Foote said the waste appeared to be of a much higher concentration.

The car originally carried 13,000 gallons of 94 percent nitric acid, shipped by Kennecott Utah Copper from one of its facilities in Utah to a company operation at Darwin, Nev., Foote said. He said the car was loaded at Darwin with the mixture of waste and the train arrived at the Roper Rail Yard shortly after 6 a.m. Sunday.

It was supposed to be taken to a site in Ohio for disposal, but the tanker was found to be leaking.

As the leak worsened and the tanker wall began to soften, specialized equipment was brought in that enabled crews to remotely puncture the tank car so the waste could be pumped into portable tanks.

Officials said 6,000 gallons of liquid was pumped out and it was believed about 6,500 gallons more had leaked and soaked into the ground. Contaminated soil will have to be neutralized with lime, dug up and taken away, they said.