More than half of the affected area was coated by a sprayed mist from an 18-inch flow line, a pipeline that carries raw oil, water and gas to the center for separation, according to officials with BP Exploration (Alaska) Inc., the company that runs most North Slope oil fields.
Late Tuesday it remained unclear how much oil had spilled or why the pipeline leaked.
Leaks from North Slope fields -- especially the older ones like Prudhoe Bay and Kuparuk River -- have been problematic for the industry in recent years.
Two years ago, a federal judge put BP on probation for three years and ordered it to pay $20 million in criminal penalties for a 201,000-gallon Prudhoe Bay oil spill in 2006, the largest spill ever in the North Slope fields. BP entered a guilty plea to a misdemeanor count of violating the Clean Water Act.
Later in 2006, another corrosion-caused pipeline spill resulted in the temporary closure of part of Prudhoe Bay, the nation's largest oil field.
Since then, the state and federal governments have sued BP in civil courts over its spills.
The new spill was discovered Sunday afternoon. Cleanup of contaminated snow began late Monday, with 12 workers removing 40 cubic yards of contaminated snow with hand tools, according to officials involved in the cleanup.
Crews had not yet begun clearing the more heavily affected remainder of the spill area nearest the pipe, which will first require building an ice pad to support them and their equipment.
Concern about ice blockages in the line, which can build pressure inside, have prompted officials to establish a 10-foot safety zone around the pipe. Until they get a closer look, officials won't know what caused the leak, BP Alaska spokesman Steve Rinehart said.
The pipeline was not in operation when the leak was discovered, though product remained inside, Rinehart said. Production suffered a slight dip Sunday but was back up Monday as a parallel line made up the difference, he said.
The cause of the spill remained under investigation.
Find James Halpin online at adn.com/contact/jhalpin or call 257-4589.
Important warning about e-mails purporting to be from the adn.com staff.