BISMARCK, N.D. (AP) -- BNSF Railway resumed shipments Friday along a track in North Dakota two days after an oil train derailed and caught fire, and cleanup continued on crude that spilled into nearby wetlands.

The 109-car train was hauling crude from the Bakken oil patch in western North Dakota when the cars filled with about 180,000 gallons of oil went off the tracks and caught fire about 7:30 a.m. Wednesday.

The mainline through the small town of Heimdal was reopened after the six derailed tank cars were removed and a section of track that was damaged during the accident was repaired and inspected, BNSF Vice President Mike Trevino said.

The section of track where the derailment occurred was last inspected by BNSF on May 4, and by federal officials on Feb. 2, said Federal Railroad Administration spokesman Kevin Thompson.

The inspections found no defects or violations of federal regulations, Thompson said.

Trevino said the railroad was "absolutely confident" the track was safe to put back into service.

An estimated 34,000 gallons of oil burned in the fire and 60,000 gallons spilled from the tankers, state Health Department Environmental Health Chief Dave Glatt said.

No one was hurt, but residents of Heimdal were forced from their homes for about a day.

The U.S. Environmental Protection Agency said oil entered wetlands near the derailment site. It was not known how much of the oil ended up on the ground or in a nearby waterway, Big Slough, that connects with the James Rivers about 15 miles downstream, Glatt said.

Railroad crews were removing contaminated dirt and set up booms to keep the oil from traveling down the slough.

"We're not seeing the James River or downstream interests being adversely impacted from this spill," Glatt said.

The slough is not used for drinking water and is home to only small aquatic life such as frogs. There were no immediate signs of harm to wild birds, Glatt said.

Glatt added that it might take a week or two to get an answer on whether any groundwater was contaminated. Heimdal residents receive water from a pipeline that was not affected by the derailment.

The cause remained under investigation, said Keith Holloway with the National Transportation Safety Board. Pieces of a broken wheel from one of the derailed cars were recovered from the scene Thursday.

After a defective wheel emerged as the suspected cause of a fiery oil train derailment in March in Illinois, federal railroad regulators issued an advisory April 17 for railroads to take extra precautions to prevent a repeat of that scenario.

The Department of Transportation recommended that only the most skilled personnel conduct pre-departure inspections of the cars. It also advised railroads to lower their threshold for taking action on tank cars that show early indications of problems.

Trevino could not immediately say if those recommendations were being followed. But he said that on April 1, BNSF had tightened its oversight of tank cars and reduced its tolerance for when potential wheel defects would lead the company to pull a car out of service.

The railroad still was evaluating the April advisory to determine who would qualify to conduct the pre-departure inspections. It was not immediately clear if those inspections were the responsibility of the railroad or the company shipping the fuel, in this case the Hess Corporation.

Wednesday's derailment followed a string of fiery train wrecks in the U.S. and Canada in the past few years involving tank cars known to be susceptible to failure since the early 1990s. With oil from North Dakota now shipped to refineries across North America, federal officials have pushed railroads to make details on the trains' cargoes quickly accessible to first responders.

Local authorities who responded in Heimdal said they received a shipping manifest from the train's engineers on the crude that was being transported within 15 minutes of arriving on the scene. Firefighters on the scene had trained specifically for an oil train accident. U.S. Sen. Heidi Heitkamp said that should be done across the nation.

"Those firefighters felt prepared for what they were walking into. We'd like to see every fire service along the tracks trained the same," the North Dakota Democrat said Friday after visiting the scene of the fire.