ANCHORAGE (AP) -- An estimated 450 barrels of drilling mud and cuttings spilled Tuesday at BP's Northstar drilling pad on Seal Island in Prudhoe Bay.
According to a Department of Environmental Conservation situation report, the spill occurred at 1 p.m. and DEC was notified four hours later.
''It's not in the water. It's controlled. It's contained,'' said DEC Deputy Commissioner Kurt Fredrikkson.
DEC officials said a containment cell gave way and released the 18,900 gallons of drilling mud and cuttings.
Fredrikkson described the containment cell as a crib constructed of 12-by-12 wood beams, spiked together and lined, that acts as a temporary container.
Drilling muds are made up mostly of water, ground-up clay and a polymer. The mud lubricates the drill bit, carries cuttings to the surface and helps seal the side of the drill hole. The polymer makes the mud thicker and heavier to assist in sealing the hole.
DEC said no oil contamination was released in the spill. The drilling mud and cuttings were from rock above the oil-bearing zone.
BP contained the spill with a 150-foot by 200-food temporary snow berm.
According to the department, the drilling mud has solidified and is being pushed back into the containment cell with heavy equipment.
Drilling was suspended until the cleanup can be completed.
Fredrikkson said the cause of the spill has not been determined.
DEC said the spilled mud eventually will be loaded onto trucks and stored on the island until it can be safely transported over sea ice to a disposal site. The ice road to the island has not been completed.
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