ANCHORAGE (AP) -- Corrosion in a pipe apparently caused what may be one of the largest spills on the North Slope over the past five years -- 92,400 gallons of saltwater and crude oil that leaked late Sunday.
The spill saturated nearly an acre of snow- and ice-covered tundra, said Ed Meggert, head of oil spill response with the state Department of Environmental Conservation in Fairbanks.
''It looks like erosion or corrosion to the pipe is the cause,'' Meggett said, adding that the incident was under investigation.
The spill was discovered at 11:30 p.m. Sunday and the line was shut down within 12 minutes, the agency said. The water is fluid removed from crude oil and contains up to 3 percent crude oil. The fluid escaped at a temperature of more than 100 degrees Fahrenheit.
It was the fourth major spill on the North Slope this winter and the second believed caused by erosion or corrosion.
By midday Monday, Phillips Alaska, which operates the Kuparuk oil field, North America's second largest, said it had cleaned up most of the spill, or around 92,000 gallons.
Much of that may have been snow and ice melted by the hot crude and water mixture.
Corrosion from water and erosion from abrasive such materials as sand are a growing problem on the North Slope.
As Kuparuk and Prudhoe Bay age, the oil companies are grappling with internal pipe corrosion from water running through lines and external corrosion from water seeping between pipe insulation and hot steel pipe walls, where it eats at the metal.
The timing of the accident is bad for Alaska's big oil companies -- Phillips, BP and Exxon Mobil -- and policymakers who are trying to put a positive spin on the oil industry's environmental record in an effort to open the Arctic National Wildlife Refuge to drilling.
The refuge sits about 90 miles east of existing oil fields and may hold the largest undeveloped oil reserves in the nation, government geologists have said.
While the DEC's Meggert said oil content in the water was low, or about 1 percent, the huge spill size means that independent of the saltwater, nearly 1,000 gallons of crude oil hit the tundra.
That crude spill would be one of the 10 largest spills on the North Slope in the past five years, according to state records. The high temperature as it left the pipe may mean the mixture penetrated the ground.
Meggert said the saltwater may be more damaging to the tundra than oil. ''It's just as toxic as diesel,'' he told the Anchorage Daily News. ''The plants that normally grow die. The crude will only coat but the saltwater penetrates.''
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