Workers are still trying to stem the flow of 5,000 barrels a day from the well that was beneath the Deepwater Horizon oil rig when it exploded and sank. Oil from the well has fouled a large area of the gulf and threatens miles of environmentally sensitive U.S. coastline.
The containment dome is part of a multipronged attack, which also includes using robotic submarines to shut off the well and additional drilling to cut the source of the flow. Oil has been leaking since the April 20 blast on the platform. Eleven rig workers are missing and presumed dead.
BP, the company that operated the rig, said Thursday, a valve on a broken drill pipe had been closed, but that wasn't expected to lessen the flow of escaping oil. The relief well, which was begun Sunday, is estimated to take three months to complete. The 13,440-cubic-foot, 100-ton containment dome was to be lowered to the seafloor -- 5,000 feet below the surface -- Thursday.
The hope is that the device will trap about 85 percent of the leaking oil and workers will be able to siphon it from the dome to surface tankers.
The oil company also said it continued dropping dispersant on the oil slick and, to date, more than 100 miles of booms, meant to keep oil from the shore, had been deployed. Officials also burned off some of the surface oil.