Scientists declared the 5-week-old BP spill in the Gulf of Mexico to be the worst in U.S. history on Thursday, while federal and oil industry officials capped a day of confusion by announcing they had suspended and then restarted their mud-pumping "top kill."
BP's chief operating officer disclosed that engineers had not pumped any mud into the runaway oil and gas spill since the night before. On Thursday night, the Coast Guard announced that BP had resumed pumping mud in an effort to plug the leak. A 10-hour burst of 15,000 barrels of mud on Wednesday slowed the spill, said BP's Doug Suttles. But engineers suspended it to replenish the mud back to its 50,000 barrel capability and review their procedures.
Thursday night's resumption might follow with a "junk shot'' of "plating materials'' and "dense rubber balls'' to plug the leak.
The news came on a day of grim news and conflicting reports about the latest effort to end the catastrophic oil spill in its 38th day.
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Coast Guard Adm. Thad Allen stirred confusion in a series of remarks that reported ‘‘the mud was suppressing the hydrocarbons," meaning the oil and gas leak, but failed to mention that the so-called top kill was suspended.
Then U.S. Geological Survey Director Marcia McNutt disclosed a new series of studies that found the leak was a magnitude of two to five times larger than initial estimates -- and far worse than the 1989 Exxon Valdez spill off Alaska.
One team estimated the rate of release at between 12,000 and 19,000 barrels per day. Another team using different methods found the range could have been up to 25,000, she said.
Still, McNutt defended the federal performance in the disaster, saying that the U.S. government "resources and tactics in response to the oil spill have been based on a worst case, catastrophic scenario."
Environmentalists responded in a fury. "It's as if two Exxon Valdez tankers have already run aground and more are on the way if they don't get this hole plugged," warned Jeremy Symons, senior vice president of the National Wildlife Federation. "Now we know the true scale of the monster we are fighting in the Gulf. BP has unleashed an unstoppable force of appalling proportions."
More possible bad news came from the University of South Florida College of Marine Science in St. Petersburg, which said a research vessel in the Gulf of Mexico had detected a disturbing find: A massive new plume in the deep recesses of the gulf spreading northeast toward the continental shelf. More tests would determine if it was contamination from the oil spill heading in a new direction -- toward Mobile Bay, Ala.
A secondary plume, uncovered by the college's Weatherbird II, "could eventually become a threat to marine life and habitats nonetheless."
President Barack Obama addressed the nation at midday, saying there were no guarantees of success in the latest effort to stem the leak "a mile under the surface where no human being can go."
But he vowed both deeper reforms of oil industry oversight and to protect American small businesses damaged by the disaster.
"We will help them recover and we will help them rebuild," the president said, noting that all but three Gulf beaches in Louisiana were still open to bathers.
Meantime, the Obama administration said Elizabeth Birnbaum, head of the U.S. Minerals Management Service inside the Interior Department, had resigned after days of blistering criticism over the federal government's lax oversight of BP and the rest of the offshore oil industry.
Obama said his administration had inherited a Minerals Management Service "that had been plagued by corruption for years." Investigators, he said, had uncovered a ‘‘scandalously close relationship'' between federal regulators and the oil industry.
To combat that, he said, the government would separate those who issue the permits in government from those responsible for regulating safety measures.
Also, the administration was suspending some planned exploration of Alaska's coast and would suspend the issuing of drill permits for the next six months.
The president emphasized that, while BP was responsible for stopping the leak and mitigating the damage, it were under federal supervision.
McClatchy correspondents Erika Bolstad and Clark reported from Washington, D.C. Goodman reported from Venice, La. Rosenberg reported from Miami.