ANCHORAGE - Crews on Wednesday were continuing to remove snow contaminated with oil from an area around a well house where a pipe broke in the Prudhoe Bay oil field.
Tom DeRuyter, the state's on-scene spill coordinator, said the area around the well house is misted with oil. He said 72 cubic yards of contaminated snow - most of it from the well house's gravel pad - have been removed but there is more to go.
The spill was discovered Monday morning by a BP oil field operator doing a routine inspection. The break in the 6-inch line occurred where the production line left the well house.
The cause of the break is not yet known, DeRuyter said.
"The case is going to be under investigation as to why the line parted," he said.
BP spokesman Steve Rinehart said the well line broke at a weld and released an estimated 3 gallons of oil and 131 gallons of water. The estimation was reached by considering how much oil and water the pipe normally carried and how quickly the automatic shut-off valve worked, he said.
Rinehart said the pipe carried 98 percent water. A test in mid-December showed it took the valve 30 seconds to close, he said.
Spill responders have delineated the spill area and marked it with stakes in the event it becomes covered in snow, DeRuyter said.
The area of the spill appears to cover about five acres with the heaviest coating of oil closer to the well house and a gravel pad, where an estimated 14,000 square feet was contaminated. The other areas of contamination are about 50,000 square feet in a reserve pit and about 158,000 square feet of snow-covered tundra.
The line that broke carried a mixture of crude oil, produced water and gas. DeRuyter said the contamination appears to be oil.
"It is all misted oil," he said.
DeRuyter said when oil is released under pressure it forms an aerosol and is carried by the wind. The outer edges of the contaminated area are a very faint gray, he said.
Front loaders were being used Wednesday to scoop up the contaminated snow and take it to a facility for disposal.
"The clean up is well under way," Rinehart said.
BP operates the Prudhoe Bay oil field - North America's largest oil field.
Last month, one of the North Slope's biggest spills - 46,000 gallons of oil, water and natural gas - was reported at the Lisburne oil field, another BP-operated site. That spill occurred when an 18-inch line split on Nov. 29. The cause of that spill is believed to be ice buildup in the line.
Lois Epstein, an Anchorage consultant on pipeline safety, said the recent spills highlight a long-standing problem on the North Slope in certain pipelines that carry oil, gas and water. For decades those lines, unlike transit lines that carry oil after processing, have been unregulated by the federal government, she said. The flow lines were placed under state regulation only recently.