KALISPELL, Montana (Reuters) - Montana Governor Brian Schweitzer on Sunday questioned Exxon Mobil Corp's contention that its oil pipeline spill into the Yellowstone River was concentrated within a 10-mile area.
Exxon said the spill, which occurred early Saturday near Billings, Montana, released into the river between 750 and 1,000 barrels of oil, which equals up to 42,000 gallons.
The company also has said the spill appeared to be concentrated within a 10-mile stretch of the river between Billings and the nearby town of Laurel.
But Schweitzer said the oil's spread in the Yellowstone -- which is the longest undammed river in the United States -- could be more extensive.
"This is a lot of wild country, and they haven't any idea whether it's 5 miles, 50 miles or 100 miles, they're guessing," Schweitzer, a Democrat, told Reuters in a telephone interview.
A full assessment of the oil's spread will not be possible until small boats can be deployed in the river, he said.
An Exxon official said earlier on Sunday that the river's turbulence made it unsafe to use boats, but that the company sent aircraft flights over the river to view the spill.
Schweitzer said he wanted "every foot" of the Yellowstone's banks to be examined for oil, and he said that he expects Exxon and any other responsible parties to clean up the spill.
"(President) Reagan used to say, 'Trust but verify.' Well we're not even going to trust, we're just going to verify," Schweitzer said.
Exxon discovered the leak early Saturday when a loss of pressure was detected on the pipeline, and within six minutes the line was shut off, company officials said.
Some residents were briefly evacuated as a precaution, but they were allowed to return home later that morning.
CONCERN FOR FARM FIELDS, WILDLIFE
Exxon said it would have about 100 people working on the oil spill by the end of Sunday. It has deployed oil-absorbent pads and boom to aid in cleanup efforts.
The cause of the leak, which happened on a pipeline that dates from 1991, remains unclear.
Alan Jeffers, an Exxon spokesman, said in response to Schweitzer's comments that the company made its assessment that the oil spill appeared to be confined to within a 10-mile area of the Yellowstone River, based on what it had observed and what was reported to it.
"The bulk of it appears to be in that area, but we're continuing to look for oil along the river," he said.
Schweitzer said he was concerned about damage from the spill to farm fields recently flooded when the Yellowstone overflowed its banks, and to the state's prized trout fishing industry.
"To say that there's no harm to wildlife, that would be silly, otherwise we would just allow rivers to have oil in them all the time," Schweitzer said.
Air monitoring has detected no threat to residents from the spill, Gary Pruessing, president of Exxon Mobil Pipeline Company, told reporters on Sunday. Municipal water systems also have shown no signs of infiltration by the oil, he said.
And Pruessing said that he expects some of the oil to dissolve and evaporate.
"The turbulence of the river is going to break (the oil) apart and move it in a lot of different directions," he said.
Pruessing said the pipeline had been shut in May as a precaution as the river approached a high-water point, but that it was judged to be safe and turned back on.
The spill occurred on a pipeline that runs only in Montana, from Silver Tip to Billings, the state's largest city and where the crude is refined.
The U.S. Environmental Protection Agency and the Montana Department of Environmental Quality were among the agencies dealing with the leak.
"We will stay with the cleanup until it is complete, and we sincerely apologize to the people of Montana for any inconvenience the incident is creating," Pruessing said.
(Reporting by Emilie Ritter, Alex Dobuzinskis, Ben Berkowitz and Laura Zuckerman: Editing by David Bailey)