ANCHORAGE (AP) -- BP had cleaned up about 75 percent of spilled drilling material Thursday at the Northstar development site.
BP spokesman Paul Laird said he expected the job to be completed Friday.
About 18,900 gallons drilling muds spilled Tuesday afternoon when a wooden containment barrier collapsed. The mud spilled across a portion of the gravel drill pad at the site.
Northstar is a 149 million-barrel oil development about six miles off the Arctic coast.
Drilling muds are injected down wells to lubricate the bit and flush out rock, sand and other debris. Used drilling muds are typically disposed of by injection back into the ground.
BP does not yet have permits to use its Northstar injection well, forcing the company to store the muds in the surface containment pen.
Laird said the company does not know why the containment pen collapsed.
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