Conditions on the swollen Yellowstone have hampered efforts to find the cause of Friday's break in the 12-inch Exxon Mobil pipeline that spilled an estimated 1,000 barrels of crude oil.
The river has been flowing too swiftly for crews to reach some oiled areas, and forecasters said mountain snowmelt was adding to high water levels. Officials speculated that the surge may push oil into areas that haven't yet been damaged.
Much of the riverbank also is covered with dense underbrush, making it difficult to walk the shoreline. Most observations have been made through aerial flights.
Sweat-drenched workers in hazmat suits and life-preservers slogged through the riverside vegetation under a blistering sun. Some raked oily muck into trash bags; others dabbed at blackened grass with absorbent pads.
Booms to collect the oil bobbed in water, and plastic kiddie pools were set up for workers to wash off their boots once they left the water.
A few miles downriver from the broken pipe, homeowner Robert Castleberry said he had been out of his house since Saturday because of dangerous fumes from oil that the river pushed across his yard and into the crawlspace beneath his house.
Castleberry's wife suffers from heart disease and the fumes gave her difficulty breathing, he said. While he appreciated the company promising to cover the couple's immediate expenses, the retired fuel truck driver was doubtful workers would be able to clean up the black, gooey film that laced through the underbrush along the river.
"Exxon's been nothing but 100 percent with us," he said. "But when you get into brush that thick, that's going to be virtually impossible to clean."
Company and federal officials said they have only seen oil about 25 miles downstream from the site of the break near Laurel. But Gov. Brian Schweitzer said he believes some has traveled hundreds of miles to North Dakota.
"At seven miles per hour, some oil is already in North Dakota. That's a given," Schweitzer said. "I'm asking everyone to get out there and report what you see on the river."
Representatives of Exxon Mobil and the Environmental Protection Agency said they had no reports of oil beyond the town of Huntley.
The Department of Transportation said Tuesday that oil was observed as far downstream as 240 miles in Terry, Mont. The agency said that information was provided by Exxon Mobil, but company spokesman Alan Jeffers said he was not aware of any such sighting.
Company officials said they were concentrating cleanup in the Laurel area, but have acknowledged the scope of the leak could extend beyond the 10-mile stretch that they initially said was the most affected area. Sherman Glass, Exxon's president of refining and supply, said crews have identified 10 places where oil has pooled in the heaviest amounts between Laurel and Huntley.
Exxon Mobil Pipeline Co. President Gary Pruessing has said the company is not limiting the scope of the cleanup to the immediate site. Exxon planned to test the river's conditions with a jet boat, with eight more on standby if the launch is successful, Glass said.
Water-quality tests downstream of the spill site began Monday, with more planned, according to EPA spokesman David Ostrander.
The Silvertip pipeline is buried just under the bottom of Yellowstone River, delivering 40,000 barrels of oil a day to a refinery in Billings. Pruessing said it took a half-hour to shut down and seal off the ruptured pipe after workers spotted a dip in pressure.
But documents released by the Department of Transportation showed it took 56 minutes to fully seal the pipeline. The longer time was based on information provided to the federal agency by Exxon Mobil, Jeffers said.
He added that the discrepancy may have resulted from Pruessing speaking without notes in front of him. "Clearly our communication with the regulator (DOT) is the one that we've got precision on," Jeffers said.
Federal regulators have ordered Exxon to make safety improvements to the 20-year-old pipeline. Among them was an order to re-bury the line to protect against external damage and assess risk where it crosses a waterway.
Company officials said they were considering burying the line deeper when it is repaired.
The company also will have to submit a restart plan to the Department of Transportation before crude can again flow through the line, which delivers oil to a refinery in Billings and other customers.
"When companies are not living up to our safety standards, we will take action," Transportation Secretary Ray LaHood said in a statement.
Schweitzer also ordered a review of pipelines that cross major and minor rivers in the state. Officials will look at the pipes' age, location of shut-off valves and whether they are similar to the ruptured pipe. He said the state has 88 such crossings.
Modern pipelines can be buried as much as 25 feet beneath bodies of water; Exxon Mobil's Silvertip line was 5 to 8 feet below the bottom of the Yellowstone.
The line was temporarily shut down in May after Laurel officials raised concerns that it could be at risk as the Yellowstone started to rise. The company restarted the line after a day, following a review of its safety record.
The cause of the rupture has not been determined, but company and government officials speculated that high waters in recent weeks may have scoured the river bottom and exposed the pipeline to damaging debris.
The site is downstream of Yellowstone National Park, which is about 110 miles away and not under threat. But the stretch of the river where the spill occurred is home to sauger, bass catfish, goldeye, trout and, farther downstream below Miles City, native pallid sturgeon.
Schweitzer said he noticed that oil was pooling in areas near banks with slower-moving water, close to islands and cottonwood stands that support the microbes and insects that bring life to the river.
"Those riparian areas are a biological treasure trove. That's the health and wealth of the river," he said.