MIDDLEBURY, Vt. (AP) – A defective rail apparently caused a train derailment that spilled gasoline into a river and forced about 500 people from their homes, officials said Tuesday.

The evacuation order was lifted. Work crews, meanwhile, began transferring gasoline from the rail cars to a tractor-trailer for removal and a specially equipped bulldozer was brought in to begin righting the cars that tipped on their sides.

The 25-car freight train carrying gasoline and salt was headed from Albany, N.Y., to Burlington on Monday when its weight apparently compromised a defective rail, prompting one car to derail and 18 others to follow suit, according to David Wulfson, president of Vermont Rail System, which operates on the state-owned rail line.

It was traveling about 10 miles per hour at the time, in accordance with the posted limit.

That section of track had been visually inspected about 15 minutes before the derailment by a Vermont Rail System patrolman, but the defect was invisible. As it happens, the track was scheduled for a routine ultrasound test – looking for defects – on Wednesday, two days after the derailment occurred, he said.

“(There was) nothing wrong when he looked at it. It happens quite often … if there is a defect in there, it can break under the weight of the next train,” said Wulfson, who compared the stress to that experienced by a coat hanger bent back and forth until it weakens.

Gasoline leaked from some of the cars into Otter Creek and into the ground alongside the tracks, but officials called it a small amount. They said Tuesday the amount still hadn’t been determined.

The leak has been contained.

Justin Johnson, the state’s environmental conservation commissioner, said no long-term impact on wildlife was expected.

Four local streets remained blocked off by police Tuesday.

The evacuated people – who included residents, Middlebury College workers and students and business owners – were cleared to return at 5:30 a.m. Tuesday, said Middlebury Fire Chief Richard Cole.

Gasoline from the derailed cars was being pumped into trucks to be transported. A bulldozer using a side boom was employed to lift the cars, which weigh about 125 tons when loaded and about 35 tons when empty, according to Wulfson.

The derailed cars are expected to be removed from the site by Wednesday, he said.

No dollar damage estimate was available Tuesday.

The Federal Rail Administration and U.S. Environmental Protection Agency had representatives on site to assist in the investigation of the derailment.

AP-ES-10-23-07 1638EDT