A representative of the Houston-based oil refinery and chemical company said the amount of leaked gas likely was less than initially reported, although no alternate figure was offered. The initial estimate came from a report submitted by the company to the government's National Response Center.
Federal and tribal officials and the company worked Friday to determine what caused the break in the 8-inch underground line. It occurred about 15 miles southwest of Lodge Grass, a town of about 430 people near the Wyoming border. The same line has seen at least three spills over the past two decades.
The latest spill was not expected to enter any surface water supplies, and no public health problems were anticipated, the company said. It was discovered late Tuesday by operators in the company's Bartlesville, Okla., pipeline control center, who noticed a pressure drop along the line, according to federal officials and Phillips 66 Co. spokesman Dennis Nuss.
It's uncertain how long the line had been leaking or whether any of the gasoline can be recovered.
"We're still assessing the area," Nuss said. "The line has been excavated in order to be able to be repaired."
The closest residence is about 2 miles from the spill site, said Curtis Kimbel with the Environmental Protection Agency. He confirmed that no streams or lakes were in the immediate area but did not know if any underground aquifers were present.
Kimbel said about 60 workers contractors for Phillips 66 were involved in the response effort.
The Seminoe pipeline carries gasoline, diesel and other refined petroleum products from Phillips 66's Billings refinery to Wyoming, Utah and Colorado. It has a maximum daily capacity of 46,000 barrels, equivalent to more than 1.9 million gallons.
Nuss said the line was shut down within five minutes of the pressure drop. It was not reported to the federal response center until Wednesday morning, after company workers reached the site and confirmed the spill, Nuss said.
Gasoline is highly toxic. But unlike oil, it can evaporate, making the cleanup on the reservation potentially more straightforward as long as no water bodies are tainted by the fuel.
"That's not saying it won't have an effect on the environment, but it's not like oil which seeps into the ground and sticks around," said Damon Hill, a spokesman for the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration.
The same pipeline broke twice in a week in 1997, spilling a combined 2,300 barrels of gasoline near Lodge Grass and Banner, Wyo.
The spill near Lodge Grass was estimated at 1,612 barrels of gasoline, while 704 barrels of gasoline spilled near the Wyoming community.
Conoco Pipe Line Co. reached a $465,000 settlement with federal prosecutors over Clean Water Act violations related to those spills and another pipeline break near Conrad, Mont., in 2001 that spilled 30 barrels of crude oil.
The latest incident near Lodge Grass comes almost two years to the day after a major crude oil spill into Montana's Yellowstone River. That 63,000-gallon spill from an Exxon Mobil line cost the company more than $135 million in cleanup and repair costs.
Nuss said it was too early to come up with a cost estimate for the Seminoe spill, and it's unclear when the pipeline could resume operations.
"Obviously we want to make sure the line's safe and there's no further problems," Nuss said.
Associated Press writer Matt Volz in Helena contributed to this report.
Copyright 2013 The Associated Press.
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