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Gulf oil spill update: What's known now about cause and effects

Amid hearings on the cause of the Deepwater Horizon disaster, government scientists, academics, and those most affected by the Gulf oil spill are at odds over the extent of its effects.

By Staff writer / November 9, 2010

A raccoon walked in an oil-impacted area of marsh grass near the Louisiana coast late last month. A recent estimate said 93 miles of coastline had moderate to heavy oil.

Patrick Semansky/AP

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New Orleans

The well responsible for the Gulf oil spill was permanently sealed on Sept. 19. Since then, little else regarding an event many consider the worst environmental disaster in American history has been so categorical.

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The presidential commission investigating the accident is searching for what caused the explosion, but is not yet assessing blame. Government scientists are offering relatively positive observations about state of the Gulf, which are being vociferously questioned by some independent scientists and fishermen. The government also differs with oil industry economists on how much the now-ended moratorium on deep-water drilling hurt the Gulf economy.

The effects of the spill are so complex that they may not be fully known for years. But they are emerging.

IN PICTURES: Destructive oil spills

What is known about the cause?

Investigators know that a huge bubble of flammable methane gas escaped the well and ignited after shooting up the drill pipe, past several seals that were meant to suppress it. How and why the gas escaped is one focus of the presidential commission looking into the accident and its implications for offshore drilling.

The commission's final report is due Jan. 12. A second report, by the US Coast Guard and the Bureau of Ocean Energy Management, Regulation and Enforcement, will be available March 27.

So far, the three companies involved – Transocean (owner of the Deepwater Horizon rig), BP (holder of the lease for the well), and Halliburton (a contractor) – are engaged in a mutual blame game.

A BP report published in September suggests the explosion was the result of an interlinked series of missteps, including mechanical failures and human errors, among all partners. Transocean called the report "self-serving" and called BP's well design flawed. Halliburton said the report had "substantial omissions and inaccuracies."

Halliburton received its own share of blame in late October when the investigator for the presidential commission issued a report saying that the company had used a cement mixture it knew was unstable. The commission did not blame the accident on Halliburton's cementing job, though.

A lead investigator on the presidential commission reported this week that BP does not share sole responsibility for the accident, indicating that it was likely due to several missteps among all the partners. One example is the decision by BP and Transocean to operate the well after a pressure test suggested that it was not stable enough to handle the explosive gas and oil mixture.

Is the oil cleaned up?

The cleanup efforts – paid for by BP, directed by the US Coast Guard – continue in the Gulf, with about 9,200 workers and 200 local vessels. At the height of the crisis, more than 48,000 workers and 3,200 vessels were involved.

Oil is still being discovered along the shorelines of all four coastal states, even appearing in areas that were once cleaned, a frustrating situation caused by unpredictable tidal patterns.

In an Oct. 27 briefing, the oil spill response command said 93 miles of coastline had moderate to heavy oil. Two months earlier, on Aug. 24, that number was 135 miles.

There is no determination yet on how to define when the job will be finished. Officials say beach cleanup efforts will likely end by early 2011. But critics say that despite the cosmetic cleaning being performed by work crews, oil will continue to smear shorelines for the foreseeable future.

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