George Nilson, 69, said the fumes from oil that washed through his neighbor's property had been overwhelming.
"I've been in it for five days now, and the only way I can breathe is to have all the windows open," he said.
Health officials say symptoms residents have reported, such as nausea, dizziness and shortness of breath, are likely to ease as the chemicals in the oil evaporate or break down.
Steve Merritt of the EPA said Thursday that contractors for the agency and for Exxon Mobil Corp. will collect the air samples. The Texas-based company operated the pipeline that spilled an estimated 1,000 barrels of oil into the river.
Laboratory results from the air testing are expected to take about a week. Merritt says Exxon Mobil's contractors will collect duplicate samples so their results can be verified by government scientists.
The cause of Friday night's pipeline rupture beneath the riverbed in Montana remains under investigation, but the prevailing theory among officials and the company is that the raging Yellowstone caused erosion and exposed the line to damaging rocks or debris.
There is still no definitive word on how far downriver the spill could spread.
Oil has fouled miles of the waterway that flows from the famed Yellowstone National Park, upriver from the spill, and across farmlands and prized fishing grounds, to North Dakota. There have been confirmed reports of oil as far as 80 miles downstream, although most appears to be concentrated in the first 25 miles.
Officials in Laurel, near the site of the spill, raised questions last year about erosion along the riverbank threatening the Exxon Mobil line. The company in December surveyed the pipe's depth and said it was at least 5 to 8 feet beneath the riverbed.
The line was temporarily shut down in May after Laurel officials again 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 company said in a June 1 email -- just a month before the spill -- that the line was buried at least 12 feet beneath the riverbed, according to the U.S. Department of Transportation, which oversees pipelines.
Exxon Mobil spokesman Al Jeffers said Thursday that the agency's claim was wrong, and that the 12-foot figure in the email referred to the pipeline's depth on shore. Jeffers added that the company provided transportation officials with the survey that showed the 5- to 8-foot depth beneath the riverbed.
The documents also contained additional details that raised new questions about the company's response.
Exxon Mobil took almost an hour to fully seal the pipeline after the accident -- nearly twice as long as it had publicly disclosed. The company said that did not change its estimate of how much crude entered the river.
"The best thing they could do at this point is be completely honest," said Montana Gov. Brian Schweitzer. "It is clear that their veracity has not been 100 percent to this point."
Company representatives initially said the spill lasted "at most" 30 minutes, and then later said workers began shutting down the line within six minutes of the break. On Tuesday, Exxon Mobil Pipeline Co. President Gary Pruessing said in response to a question from Schweitzer that it took 30 minutes to seal off all the valves needed to stop the flow of crude into the river.
DOT records indicate the pipeline was not fully shut down for 56 minutes after the break at 10:40 p.m. local time. Emergency responders at the National Response Center were notified of the spill at 12:19 a.m.
Brigham McCown is a former federal pipeline safety official who now advises pipeline companies at a Dallas firm. He said the federal Pipeline and Hazardous Materials Safety Administration, where he was an acting administrator, will look at Exxon Mobil's records to make sure they were adequately prepared for a spill.
Federal regulations require that pipelines be buried more than 4 feet beneath the riverbed at stream crossings. McCown said he believes most pipelines are buried at about that depth, although there are some exceptions.
In normal weather conditions, about 4 feet below ground is a safe depth, but pipeline companies should be paying close attention to the safety of their networks given this year's unusual weather and record floods, he said.
Pipelines carrying oil and liquid fuels are often buried beneath rivers because the industry considers that safer than suspending them above waterways, where they could be vulnerable to lightning, tornados or other external threats.
"It's a fact of life that when we connect consumers to the supply that we will have to go under some rivers," said Andy Black, CEO of the Association of Oil Pipe Lines, a Washington-based industry group whose members include Exxon Mobil.
Pipeline operators sometimes place extra protection over lines running underneath rivers, or use thicker pipe to ward off potential hazards, said Richard Kuprewicz, a Redmond, Wash., pipeline engineer and consultant.
While government regulations require that pipeline companies file emergency response plans, including how they would cope with a worst-case scenario spill -- that information is hard for the public to obtain, he added.
"If I lived on the Yellowstone, I'd want to know if Exxon really has addressed the worst case -- and if they are prepared to deal with it," he said.
The spill and safety concerns about pipelines running beneath waterways will be discussed in a hearing before the U.S. House Committee on Energy and Commerce later this month, said Charlotte Baker, a committee spokeswoman.
An Exxon Mobil spokesman said the longer time span was based on information provided to the agency by the company and the discrepancy might have come about because Pruessing spoke without any notes when he talked with Schweitzer.
It was not the first time the company offered clarification over its handling of the spill.
A day earlier, the company acknowledged under political pressure that the leak's impact could extend far beyond a 10-mile stretch of the river it initially said was the most affected area.
The company earlier downplayed government officials' assertions that damage was spread over dozens of miles.
Transportation officials said Wednesday 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.
Federal regulators have ordered Exxon Mobil to make safety improvements before re-starting the 20-year-old pipeline.
Among them was an order to re-bury the line as much as 25 to 30 feet deep to protect against external damage and assess risk where it crosses a waterway. The company intends to comply, Jeffers said.
