ANCHORAGE - The cleanup continued Thursday on the North Slope, where a pipeline carrying a mixture of oil, gas and water was discovered leaking onto tundra four days ago.
The spill was discovered Sunday, but officials do not have an estimate of how much material leaked because a mixture of residual matter was carried in the 18-inch pipeline operated by oil giant BP.
"This is a line that carries three: gas, oil and water. Knowing the exact ratio among those three elements presents a challenge," said Matt Carr, the Environmental Protection Agency's on-scene coordinator.
About 80 cubic yards of contaminated snow has been removed, said Randy Selman, BP's incident commander.
According to BP officials, more than 100 people are involved in the cleanup, as well as state and federal agencies with onsite representatives.
Crews were working to depressurize the pipe, which is plugged with ice at both ends. Workers must remain outside a 20-foot diameter safety zone established around the leak.
Once crews can get next to the pipe, the congealed oil and water will be removed and the tundra cleaned up. Plans called for eventually melting, measuring and recycling the spilled materials.
Spill responders said the leak has stopped and that the cold weather is helping keep contaminants from spreading.
The flow line was built in the mid-1980s and last inspected in 2008. It carried about 11,000 barrels a day from the Lisburne field, just north of the Prudhoe Bay oil field, until it was taken out of service several weeks ago because of ice plugs.
A pipeline next to the one that leaked is making up for the lost capacity. Production at Prudhoe, North America's largest oil field, is not being affected, officials said.
The trans-Alaska pipeline carries an average 670,385 barrels of oil a day.