Deepwater Horizon oil spill

"2010 oil spill" and "BP oil spill" redirect here. For other oil spills in 2010, see 2010 Port Arthur oil spill. For the 2006 oil spill involving BP, see Prudhoe Bay oil spill. For other uses, see Deepwater Horizon explosion.

Deepwater Horizon oil spill
The oil slick as seen from space by NASA's Terra satellite on 24 May 2010
Location	Gulf of Mexico near Mississippi River Delta, United States
Coordinates	28°44′17.30″N 88°21′57.40″W
Date	Spill date: 20 April – 15 July 2010 Well officially sealed: 19 September 2010
Cause
Cause	Wellhead blowout
Casualties	11 dead
Operator	Transocean under contract for BP
Spill characteristics
Volume	up to 4.9 million barrels (210,000,000 U.S. gallons; 780,000 cubic meters)
Area	2,500 to 68,000 sq mi (6,500 to 176,100 km2)

The Deepwater Horizon oil spill (also referred to as the BP oil spill, the BP oil disaster, the Gulf of Mexico oil spill, and the Macondo blowout) is an oil spill in the Gulf of Mexico which flowed unabated for three months in 2010, and may be continuing to leak. Named the largest accidental marine oil spill in the history of the petroleum industry, its source was a sea-floor oil gusher resulting from the 20 April 2010 Deepwater Horizon explosion which claimed 11 lives. The Deepwater Horizon drilled on the BP-operated Macondo Prospect, block 252. The gushing wellhead was capped after 87 days, on 15 July 2010. An estimated 53,000 barrels per day (8,400 m³/d), or 2.2 million gallons, of crude oil spewed into the Gulf. The total discharge is estimated at 4.9 million barrels (210 million US gal; 780,000 m³). The well was declared sealed on 19 September 2010.

The response plan to protect beaches, wetlands, and estuaries from the spreading oil employed various methods including skimmer ships, floating boom, controlled burns, and an estimated 2 million US gallons (7,600 m³) of Corexit oil dispersant. The spill and its clean up caused human health problems as well as extensive damage to marine and wildlife habitats and the Gulf's fishing and tourism industries. In the summer of 2010, scientists reported immense underwater plumes of dissolved oil in addition to an 80-square-mile (210 km²) "kill zone" surrounding the blown well. By July 2011, roughly 491 miles (790 km) of coastline in Louisiana, Mississippi, Alabama and Florida remained contaminated by oil. Tar balls continued to wash up along the Gulf coast two years after the spill began. Researchers found that oil on the bottom of the seafloor does not seem to be degrading and that as much as one-third of the released oil may remain in gulf. NOAA stated that dolphins and whales were dying at twice the normal rate in 2011. Scientists in 2012 reported finding "alarming numbers" of mutated crab, shrimp and fish resulting from chemicals released during the spill. Corexit made the oil 52 times more toxic and allowed polycyclic aromatic hydrocarbons (PAHs) to more deeply penetrate beaches and possibly groundwater, according to a 2012 study.

In January 2011 the White House oil spill commission released its final report on the causes of the spill. They blamed BP and its partners for making a series of cost-cutting decisions and the lack of a system to ensure well safety. They also concluded that the spill was not an isolated incident caused by "rogue industry or government officials", but that "The root causes are systemic and, absent significant reform in both industry practices and government policies, might well recur". After its own internal probe, BP admitted that it made mistakes which led to the spill. In June 2010 BP set up a $20 billion fund to compensate victims of the spill.

In September 2011, the U.S. government published its final investigative report on the accident. In essence, that report states that the main cause was the defective cement job, and put most of the fault for the spill with BP, also faulting Deepwater Horizon operator Transocean and contractor Halliburton. The first spill-related arrest was in April 2012; an engineer was charged with obstruction of justice for allegedly deleting 300 text messages showing BP knew the flow rate was three times higher than initial claims by the company, and knew that "Top Kill" was unlikely to succeed, but claimed otherwise. Charges have been filed also against three other BP employees for obstruction of justice, lying to federal investigators, withholding information from Congress, ignoring abnormally high pressure readings and manslaughter. On 14 November 2012, BP agreed to plead guilty and pay a record breaking $4.525 billion in fines and other payments for a criminal settlement. It also plead guilty to 11 counts of seaman's manslaughter related to the Deepwater explosion and fire. BP faces payouts to thousands of fishermen, businesses and others harmed by the spill as well as fines under the Clean Water Act, which could reach $21 billion. Estimates of the total amount of penalties that BP may be required to pay have reached as high as $90 billion. In November 2012 the EPA announced that BP will be temporarily banned from seeking new contracts with the US government because of the company's "lack of business integrity" during the disaster.

Background

Deepwater Horizon drilling rig

Main article: Deepwater Horizon

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Location of the Deepwater Horizon on 20 April 2010

Deepwater Horizon prior to explosion. Parts of the rig providing buoyancy are not visible below the waterline in this picture.

The Deepwater Horizon was a 9-year-old semi-submersible mobile offshore drilling unit, a massive floating, dynamically positioned drilling rig that could operate in waters up to 10,000 feet (3,000 m) deep. Built by South Korean company Hyundai Heavy Industries and owned by Transocean, the rig operated under the Marshallese flag of convenience, and was under lease to BP from March 2008 to September 2013. At the time of the explosion, it was drilling a 35,050 feet (10,680 m) deep exploratory well at a water depth of approximately 5,100 feet (1,600 m). The well is situated in the Macondo Prospect, which is located in the Mississippi Canyon Block 252 (MC252) of the Gulf of Mexico, in the United States exclusive economic zone. The Macondo well is located roughly 41 miles (66 km) off the Louisiana coast. BP was the operator and principal developer of the Macondo Prospect with a 65% share, while 25% was owned by Anadarko Petroleum Corporation, and 10% by MOEX Offshore 2007, a unit of Mitsui.

Explosion

Main article: Deepwater Horizon explosion

Supply boats continued to battle the fire, viewed from a Coast Guard helicopter

At approximately 9:45 pm CDT, on 20 April 2010, high-pressure methane gas from the well expanded into the drilling riser and was released onto the drilling rig, where it ignited and exploded, engulfing the rig. At the time, 126 crew members were on board: seven employees of BP, 79 of Transocean, and employees of various other companies involved in the operation of the rig. Eleven workers were never found despite a three-day Coast Guard (USCG) search operation, and are believed to have died in the explosion. Ninety-four crew were rescued by lifeboat or helicopter, 17 of whom were treated for injuries.

Volume and extent of oil spill

See also: Timeline of the Deepwater Horizon oil spill

An oil leak was discovered on the afternoon of 22 April when a large oil slick began to spread at the former rig site. According to the Flow Rate Technical Group, the leak amounted to about 4.9 million barrels (210,000,000 US gal; 780,000 m³) of oil, exceeding the 1989 Exxon Valdez oil spill as the largest ever to originate in U.S.-controlled waters and the 1979 Ixtoc I oil spill as the largest spill in the Gulf of Mexico. BP has challenged this calculation saying that it is overestimated as it includes over 810,000 barrels (34,000,000 US gal; 129,000 m³) of oil which was collected before it could enter the Gulf waters.

Spill flow rate

In its permit to drill the well, BP estimated the worst case flow at 162,000 barrels per day (25,800 m³/d). Immediately after the explosion the USCG did not estimate any oil leaking from the sunken rig or from the well. On 24 April, USCG Rear Admiral Mary Landry announced that a damaged wellhead was indeed leaking. She stated that "the leak was a new discovery but could have begun when the offshore platform sank . . . two days after the initial explosion." Initial estimates by USCG and BP officials, based on remotely operated vehicles as well as the oil slick size, indicated the leak was as much as 1,000 barrels per day (160 m³/d). Outside scientists quickly produced higher estimates, which presaged later increases in official numbers. Official estimates increased from 1,000 to 5,000 barrels per day (160 to 790 m³/d) on 29 April, to 12,000 to 19,000 barrels per day (1,900 to 3,000 m³/d) on 27 May, to 25,000 to 30,000 barrels per day (4,000 to 4,800 m³/d) on 10 June, and to between 35,000 and 60,000 barrels per day (5,600 and 9,500 m³/d), on 15 June. Internal BP documents, released by Congress, estimated the flow could be as much as 100,000 barrels per day (16,000 m³/d), if the blowout preventer and wellhead were removed and if restrictions were incorrectly modeled.

Progression of oil spill flow rate estimates

Source	Date	Barrels per day	Gallons per day	Cubic metres per day
BP estimate of hypothetical worst case scenario (assumes no blowout preventer)	Permit	162,000	6,800,000	25,800
United States Coast Guard	23 April (after sinking)	0	0	0
BP and United States Coast Guard	24 April	1,000	42,000	160
Official estimates	29 April	1,000 to 5,000	42,000 to 210,000	790
Official estimates	27 May	12,000 to 19,000	500,000 to 800,000	1,900 to 3,000
Official estimates	10 June	25,000 to 30,000	1,100,000 to 1,300,000	4,000 to 4,800
Flow Rate Technical Group	19 June	35,000 to 60,000	1,500,000 to 2,500,000	5,600 to 9,500
Internal BP documents hypothetical worst case (assumes no blowout preventer)	20 June	up to 100,000	up to 4,200,000	up to 16,000
Official estimates	2 August	62,000	2,604,000	9,857

Official estimates were provided by the Flow Rate Technical Group—scientists from the National Oceanic Atmospheric Administration (NOAA), United States Geological Survey (USGS), Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), U.S. Department of Energy (DOE), and outside academics, led by USGS director Marcia McNutt. The later estimates were believed to be more accurate because it was no longer necessary to measure multiple leaks, and because detailed pressure measurements and high-resolution video had become available. According to BP, estimating the oil flow was very difficult as there was no underwater metering at the wellhead and because of the natural gas in the outflow. The company had initially refused to allow scientists to perform more accurate, independent measurements, saying that it was not relevant to the response and that such efforts might distract from efforts to stem the flow. Former EPA Administrator Carol Browner and Congressman Ed Markey (D-MA) both accused BP of having a vested financial interest in downplaying the size of the leak in part due to the fine they will have to pay based on the amount of leaked oil.

The final estimate reported that 53,000 barrels per day (8,400 m³/d) were escaping from the well just before it was capped on 15 July. It is believed that the daily flow rate diminished over time, starting at about 62,000 barrels per day (9,900 m³/d) and decreasing as the reservoir of hydrocarbons feeding the gusher was gradually depleted.

In a 3 December 2010, statement, BP claimed the government overestimated the size of the spill by between 20% and 50%. A document submitted by BP to the commission, NOAA, and The Justice Department says that "they rely on incomplete or inaccurate information, rest in large part on assumptions that have not been validated, and are subject to far greater uncertainties than have been acknowledged. Representative Edward Markey, a member of the House energy panel that is investigating the spill, said in a statement that BP has done whatever it could to avoid revealing the true flow rate of the spill. "With billions of dollars at stake, it is no surprise that they are now litigating the very numbers which they sought to impede." A BP spokesperson said that BP "fully intends to present its own estimate as soon as the information is available to get the science right."

Spill area and thickness

Oil slicks surround the Chandeleur Islands, Louisiana, in this aerial photo.

The oil's spread was initially increased by strong southerly winds caused by an impending cold front. By 25 April 2010, the spill covered 580 square miles (1,500 km²) and was only 31 miles (50 km) from the ecologically sensitive Chandeleur Islands. An 30 April 2010, estimate placed the total spread of the oil at 3,850 square miles (10,000 km²). The spill quickly approached the Delta National Wildlife Refuge and Breton National Wildlife Refuge. On 19 May 2010, both NOAA and other scientists monitoring the spill with the European Space Agency Envisat radar satellite stated that oil had reached the Loop Current, which flows clockwise around the Gulf of Mexico towards Florida and then joins the Gulf Stream along the U.S. east coast. On 29 June 2010, NOAA determined that the oil slick was no longer a threat to the loop current and stopped tracking offshore oil predictions that include the loop currents region. The omission is noted prominently on the ongoing nearshore surface oil forecasts that are posted daily on NOAA's website.

On 14 May 2010, the Automated Data Inquiry for Oil Spills model indicated that about 35% of a hypothetical 114,000-barrel (18,100 m³) spill of light Louisiana crude oil released in conditions similar to those found in the Gulf would evaporate, that 50% to 60% of the oil would remain in or on the water, and the rest would be dispersed in the ocean.

The wellhead was capped on 15 July 2010, and by 30 July, the surface oil appeared to have dissipated more rapidly than expected. Some scientists believe that the rapid dissipation of the surface oil may have been due to a combination of factors that included the natural capacity of the region to break down oil (petroleum normally leaks from the ocean floor by way of thousands of natural seeps and certain bacteria can consume it.); winds from storms appeared to have aided in rapidly dispersing the oil, and the cleanup response by BP and the government helped control surface slicks. As much as 40% of the oil may have simply evaporated at the ocean surface, and an unknown amount remains below the surface.

However, many scientists dispute the report's methodology and figures. Scientists said much oil was still underwater and could not be detected. According to the NOAA report released on 4 August 2010, about half of the oil leaked into the Gulf remains on or below the Gulf's surface. Some scientists are calling the NOAA estimates "ludicrous." According to USF chemical oceanographer David Hollander, while 25% of the oil can be accounted for by burning, skimming, etc., 75% is still unaccounted for. The federal calculations are based on direct measurements for only 430,000 barrels (68,000 m³) of the oil spilled – the oil burned and skimmed. According to Bill Lehr, an author of the NOAA report, the other numbers are "educated scientific guesses," because "it is impossible to measure oil that is dispersed". FSU oceanography professor Ian MacDonald called it "a shaky report" and is unsatisfied with the thoroughness of the presentation and "sweeping assumptions" involved. John Kessler of Texas A&M, who led a National Science Foundation on-site study of the spill, said the report that 75% of the oil is gone is "just not true" and that 50% to 75% of the material that came out of the well remains in the water in a "dissolved or dispersed form". On 16 August 2010, UGA scientists said their analysis of federal estimates show that 80% of the oil the government said was gone from the Gulf of Mexico is still there. The Georgia team said "it is a misinterpretation of data to claim that oil that is dissolved is actually gone".

Oil sightings

Oil began washing up on the beaches of Gulf Islands National Seashore on 1 June 2010. By 4 June 2010, the spill had landed on 125 miles (201 km) of Louisiana's coast, had washed up along Mississippi and Alabama barrier islands, and was found for the first time on a Florida barrier island at Pensacola Beach. On 9 June 2010, oil sludge began entering the Intracoastal Waterway through Perdido Pass after floating booms across the opening of the pass failed to stop the oil. On 23 June 2010, oil appeared on Pensacola Beach and in Gulf Islands National Seashore, and officials warned against swimming for 33 miles (53 km) east of the Alabama line. On 27 June 2010, tar balls and small areas of oil reached Gulf Park Estates, the first appearance of oil in Mississippi. Early in July 2010, tar balls reached Grand Isle, but 800 volunteers were cleaning them up. On 3 and 4 July 2010, tar balls and other isolated oil residue began washing ashore at beaches in Bolivar and Galveston, though it was believed a ship transported them there, and no further oil was found 5 July. On 5 July 2010, strings of oil were found in the Rigolets in Louisiana, and the next day tar balls reached the shore of Lake Pontchartrain. The amount of Louisiana shoreline affected by oil grew from 287 miles (462 km) in July to 320 miles (510 km) in late November 2010.

On 10 September 2010, it was reported that a new wave of oil suddenly coated 16 miles (26 km) of Louisiana coastline and marshes west of the Mississippi River in Plaquemines Parish. The Louisiana Department of Wildlife and Fisheries confirmed the sightings. On 23 October 2010, it was reported that miles-long stretches of weathered oil had been sighted in West Bay, Texas between Southwest Pass, the main shipping channel of the Mississippi River, and Tiger Pass near Venice, Louisiana. The sightings were confirmed by Matthew Hinton of The Times-Picayune.

At the end of October 2010, two research vessels studying the spill's effect on sea life found substantial amounts of oil on the seafloor. Kevin Yeager, a USM assistant professor of marine sciences found oil in samples dug up from the seafloor in a 140-mile (230 km) radius around the site of the Macondo well. The oil ranged from light degraded oil to thick raw crude. The sheer abundance of oil and its proximity to the well site, though, makes it "highly likely" that the oil is from the Macondo well. A second research team turned up traces of oil in sediment samples as well as evidence of chemical dispersants in blue crab larvae and long plumes of oxygen-depleted water emanating from the well site 50 miles (80 km) off Louisiana's coast.

In late November 2010, Plaquemine Parish, Louisiana coastal zone director P.J. Hahn reported that more than 32,000 US gallons (120 m³) of oil had been sucked out of nearby marshes in the previous 10 day period. In Barataria Bay, Louisiana, photos and firsthand accounts show oil still reaching high into the marshes, baby crabs and adult shrimp covered by crude and oil slicks on the surface of the water.

In January 2011, a spill commissioner reported that tar balls continue to wash up, oil sheen trails are seen in the wake of fishing boats, wetlands marsh grass remains fouled and dying, and crude oil lies offshore in deep water and in fine silts and sands onshore. On 26 May 2011, the Louisiana Department of Environmental Quality extended the state of emergency related to the spill. In April 2012, oil was found dotting 200 miles (320 km) of Louisiana's coast.

Underwater oil plumes

On 15 May 2010, researchers from the National Institute for Undersea Science and Technology, aboard the research vessel RV Pelican, identified oil plumes in the deep waters of the Gulf of Mexico, including one as large as 10 miles (16 km) long, 3 miles (4.8 km) wide and 300 feet (91 m) thick in spots. The shallowest oil plume the group detected was at about 2,300 feet (700 m), while the deepest was near the seafloor at about 4,593 feet (1,400 m)4,593. Other researchers from the UGA found that the oil may have occupied multiple layers.

By 27 May 2010, marine scientists from the USF had discovered a second oil plume, stretching 22 miles (35 km) from the leaking wellhead toward Mobile Bay, Alabama. The oil had dissolved into the water and was no longer visible. Undersea plumes may have been the result of the use of wellhead chemical dispersants. NOAA conducted an independent analysis of the water samples provided from the 22–28 May 2010, research mission of the USF's Weatherbird II vessel. The samples from all undersea plumes were in very low concentrations, less than 0.5 parts per million. NOAA indicated that one of the plumes was unrelated to the BP wellhead leak, while the other plume samples were in concentrations too low or too highly fractionated to determine their origin. In a report released on 8 June 2010, NOAA stated that one plume was consistent with the oil from the leak, one was not consistent, and that they were unable to determine the origin of two samples.

On 23 June 2010, NOAA released a report which confirmed deepwater oil plumes in the Gulf and that they did originate from BP's well, stating, "The preponderance of evidence based on careful examination of the results from these four different cruises leads us to conclude that DWH-MC252 oil exists in subsurface waters near the well site in addition to the oil observed at the sea surface and that this oil appears to be chemically dispersed. While no chemical "fingerprinting" of samples was conducted to conclusively determine origin, the proximity to the well site and the following analysis support this conclusion". Reporting on a study that ended on 28 June 2010, scientists published conclusive evidence of a deep plume 22 miles (35 km) long linked directly to the Deepwater Horizon well. They reported that it did not appear to be degrading quickly and that it may pose a long-lasting threat for marine life deep in the ocean. On 23 July 2010, USF researchers and NOAA released two separate studies confirming subsea plumes of oil resulting from the Deepwater Horizon well.

Researchers from NOAA and Princeton University concluded that the deep plumes of dissolved oil and gas would likely remain confined to the northern Gulf of Mexico and that the peak impact on dissolved oxygen would be delayed (several months) and long lasting (years). David Valentine of UCSB believes that the oil plumes had been diluted in the ocean faster than they had biodegraded, suggesting that the LBNL researchers had overestimated the rate of biodegration. In October 2010, scientists reported a continuous plume of over 22 miles (35 km) in length at a depth of about 3,600 ft (1,100 m). That plume persisted for several months without substantial degradation.

NOAA's research vessels later found evidence of the multiple undersea plumes, and Lubchenco subsequently warned that these plumes might be the source of some of the 'most significant impacts' due to the effect on juvenile Bluefin Tuna and other fish.

Suppression of science

When scientists initially reported the discovery of undersea oil plumes, BP stated its sampling showed no evidence that oil was massing and spreading in the gulf water column. NOAA chief Jane Lubchenco urged caution, calling the reports "misleading, premature and, in some cases, inaccurate." Scientists from the USF and the USM said that when they brought the evidence of deep sea plumes to NOAA and the USCG, the government tried to suppress their findings. According to Vernon Asper, oceanographer at USG, "We expected that NOAA would be pleased because we found something very, very interesting ... NOAA instead responded by trying to discredit us".

Oil on seafloor

On 10 September 2010, Samantha Joye, a professor in the Department of Marine Sciences at the University of Georgia on a research vessel in the Gulf of Mexico announced her team's findings of a substantial layer of oily sediment stretching for dozens of miles in all directions suggesting that a lot of oil did not evaporate or dissipate but may have settled to the seafloor. She describes seeing layers of oily material covering the bottom of the seafloor, in some places more than 2 inches (51 mm) thick on top of normal sediments containing dead shrimp and other organisms. She speculates that the source may be organisms that have broken down the spilled oil and excreted an oily mucus that sinks, taking with it oil droplets that stick to the mucous. "We have to [chemically] fingerprint the oil and link it to the Deepwater Horizon," she says. "But the sheer coverage here is leading us all to come to the conclusion that it has to be sedimented oil from the spill, because it's all over the place."

By January 2011, USF researchers found layers of oil near the wellhead that were “up to 5 times thicker” than recorded by the team in August 2010. USF's David Hollander remarked, “Oil’s presence on the ocean floor didn’t diminish with time; it grew” and he pointed out, “the layer is distributed very widely,” radiating far from the wellhead.

In 2013, some scientists at the Gulf of Mexico Oil Spill and Ecosystem Science Conference said that as much as one-third of the oil may have been mixed with deep ocean sediments and dragged to the bottom of the ocean floor where it remains, risking damage to ecosystems and commercial fisheries.

Independent monitoring

Wildlife and environmental groups accused BP of holding back information about the extent and impact of the growing slick, and urged the White House to order a more direct federal government role in the spill response. In prepared testimony for a congressional committee, National Wildlife Federation President Larry Schweiger said BP had failed to disclose results from its tests of chemical dispersants used on the spill, and that BP had tried to withhold video showing the true magnitude of the leak. On 19 May 2010, BP established a live feed, popularly known as spillcam, of the spill after hearings in Congress accused the company of withholding data from the ocean floor and blocking efforts by independent scientists to come up with estimates for the amount of crude flowing into the Gulf each day. On 20 May 2010, United States Secretary of the Interior Ken Salazar indicated that the U.S. government would verify how much oil had leaked into the Gulf of Mexico. United States Environmental Protection Agency (EPA) Administrator Lisa Jackson and United States Secretary of Homeland Security Janet Napolitano asked for the results of tests looking for traces of oil and dispersant chemicals in the waters of the gulf.

Journalists attempting to document the impact of the spill were repeatedly refused access to public areas, and photojournalists were prevented from flying over areas of the gulf to document the scope of the disaster. These accusations were leveled at BP, its contractors, local law enforcement, USCG, and other government officials. Scientists also complained about prevention of access to information controlled by BP and government sources. BP stated that its policy was to allow the media and other parties as much access as possible. On 30 June 2010, the USCG put new restrictions in place across the Gulf Coast that prevented vessels from coming within 20 meters (66 ft) "of booming operations, boom, or oil spill response operations". In a press briefing, USCG admiral Thad Allen said the new regulation was related to safety issues. On CNN's 360, host Anderson Cooper rejected the motivation for the restrictions outright. The Civil Air Patrol also monitored the spill on behalf of the USCG. 27 May 2010

Efforts to stem the flow of oil

Main article: Efforts to stem the Deepwater Horizon oil spill

See also: Offshore oil spill prevention and response

Short-term efforts

Oil containment dome under construction in Port Fourchon, Louisiana, at Wild Well Control on 26 April

The Q4000 and the Discoverer Enterprise during the failed top kill procedure

Concept diagram of underwater oil containment domes originally planned for the Deepwater Horizon oil spill. At this stage, there were 2 remaining oil leaks from the fallen pipeline.

The first attempts to stop the flow of oil was the use of remotely operated underwater vehicles to close the blowout preventer valves on the well head; however, all these attempts failed. The second technique, placing a 125-tonne (280,000 lb) containment dome (which had worked on leaks in shallower water) over the largest leak and piping the oil to a storage vessel on the surface, failed when gas leaking from the pipe combined with cold water formed methane hydrate crystals that blocked the opening at the top of the dome. Attempts to close the well by pumping heavy drilling fluids into the blowout preventer to restrict the flow of oil before sealing it permanently with cement ("top kill") also failed.

More successful was positioning a riser insertion tube into the wide burst pipe. There was a stopper-like washer around the tube that plugs the end of the riser and diverts the flow into the insertion tube. The collected gas was flared and oil stored on the board of drillship Discoverer Enterprise. Before the tube was removed, 924,000 US gallons (22,000 bbl) of oil were collected. By 3 June 2010, BP removed the damaged riser from the top of the blowout preventer and covered the pipe by the cap which connected it to a riser. CEO of BP Tony Hayward stated that as a result of this process the amount captured was "probably the vast majority of the oil." However, the FRTG member Ira Leifer said that more oil was escaping than before the riser was cut and the cap containment system was placed. On 16 June 2010, a second containment system connected directly to the blowout preventer became operational carrying oil and gas to service vessels where it was immolated in a clean-burning system.

On 5 July 2010, BP announced that its one-day oil recovery effort accounted for about 25,000 barrels (4,000 m³) of oil, and the flaring off of 57.1 million cubic feet (1.62×10^⁶ m³) of natural gas. The total oil collection to date for the spill was estimated at 660,000 barrels (105,000 m³). The government's estimates suggested the cap and other equipment were capturing less than half of the oil leaking from the sea floor as of late June 2010.

On 10 July 2010, the containment cap was removed to replace it with a better-fitting cap consisting of a Flange Transition Spool and a 3 Ram Stack ("Top Hat Number 10"). On 15 July BP tested the well integrity by shutting off pipes that were funneling some of the oil to ships on the surface, so the full force of the gusher from the wellhead went up into the cap. The attempt to cap the wellhead was successful and mud and cement were later pumped in through the top of the well to reduce the pressure inside it, providing a temporary stop to the flow of oil.

Considerations of using explosives

In mid-May, United States Secretary of Energy Steven Chu assembled a team of nuclear physicists, including hydrogen bomb designer Richard Garwin and Sandia National Laboratories director Tom Hunter. Oil expert Matthew Simmons maintained that a nuclear explosion would be the only way BP could permanently seal the well, and cited successful attempts by the Soviet Union using nuclear blasts to seal off runaway gas wells. A spokesperson for the US Energy Department said that "neither Energy Secretary Steven Chu nor anyone else" was ever considering a nuclear blast under the gulf. On 24 May 2010, BP ruled out conventional explosives, saying that if blasts failed to clog the well, "we would have denied ourselves all other options."

Permanent closure

Transocean's Development Driller III started drilling a first relief well on 2 May 2010. GSF Development Driller II started drilling a second relief on 16 May 2010. On 3 August 2010, first test oil and then drilling mud was pumped at a slow rate of approximately 2 barrels (320 L) per minute into the well-head. Pumping continued for eight hours, at the end of which time the well was declared to be "in a static condition." On 4 August, BP began pumping cement from the top, sealing that part of the flow channel permanently.

On 3 September 2010, the 300 ton failed blowout preventer was removed from the well and a replacement blowout preventer was installed. On 16 September, the relief well reached its destination and pumping of cement to seal the well began. On 19 September 2010, USCG's Thad Allen (ret) declared BP's well "effectively dead" and said that it posed no further threat to the Gulf.

Recurrent or continued leakage

Oil at or near the site of the spill following well closure has suggested to some that there is continued or recurrent leakage. NBC Nightly News reported the slick on March 22, 2011. In August 2011, oil and oil sheen covering several square miles of water were again reported surfacing not far from BP’s Macondo well. Scientific analysis confirmed that the oil is a chemical match for Macondo 252. The USCG said the oil was too dispersed to recover and posed no threat to the coastline.

In March 2012, "persistent oil seep" near the Macondo well was again reported. More sightings in October 2012 prompted another investigation into the source of the continued oil seepage. The USCG again found the oil was a chemical match for Macondo, and sent a Notice of Federal Interest to BP and Transocean which warned they may be held financially responsible for clean-up related to the new oil. Congressman Ed Markey called on BP to come up with a plan to "remove all remaining oil from the dome and any other wreckage". He repeated his request for the release of underwater ROV footage taken during the sheen investigation, which the USCG had promised but failed to provide.

The USCG suggested the sheen "could be residual oil associated with wreckage and/or debris left on the seabed" like the riser pipe, but said that no one yet knows its origin for sure. Marcia McNutt, director of the U.S. Geological Survey, calculated that if the riser pipe was full of oil, it could hold at most 1,000 barrels (160 m³) because it's open on both ends. She said it's unlikely to hold the amount of oil being observed.

Commenting on the ongoing leakage, oceanographer Ian MacDonald said, "it’s possible that the wreckage in 2010 somehow opened up a new fault on the seafloor". In May 2010, BP admitted they had "discovered things that were broken in the sub-surface" during the 'top kill' effort. Environmental groups share MacDonald's concern, fearing that the drilling of relief wells or the original well failure may have fractured the sea floor, allowing oil to escape.

In January 2013, the sheen grew to more than seven-miles long and one-mile wide according to aerial observations made by former NASA physicist Bonnie Schumaker, who observed "patches of rainbow and weathered mousse" in the sheen. Samples of the sheen on several occasions "have consistently found the presence of alpha olefiens, which is a chemical bond signature of a man-made chemical you would not find in pure crude form."

Efforts to protect the coastline and marine environments

United States Environmental Services workers prepare oil containment booms for deployment

A variety of techniques were used to address fundamental strategies for addressing the spilled oil, which were: to contain oil on the surface, dispersal, and removal. While most of the oil drilled off Louisiana is a lighter crude, the leaking oil was of a heavier blend which contained asphalt-like substances. According to Ed Overton, who heads a federal chemical hazard assessment team for oil spills, this type of oil emulsifies well. Once it becomes emulsified, it no longer evaporates as quickly as regular oil, does not rinse off as easily, cannot be eaten by microbes as easily, and does not burn as well. "That type of mixture essentially removes all the best oil clean-up weapons", Overton said.

On 6 May 2010, BP began documenting the daily response efforts on its web site. On 28 April, the US military joined the cleanup operation. The response increased in scale as the spill volume grew. Initially, BP employed remotely operated underwater vehicles (ROV's), 700 workers, 4 airplanes, and 32 vessels. By 29 April 69 vessels, including skimmers, tugs, barges, and recovery vessels, were in use. By 4 May, the USCG estimated that 170 vessels, and nearly 7,500 personnel were participating, with an additional 2,000 volunteers assisting.

On 31 May, BP set up a call line to take cleanup suggestions which received 92,000 responses by late June, 320 of which were categorized as promising.

Containment

An oil containment boom deployed by the U.S. Navy surrounds New Harbor Island, Louisiana.

The response included deploying many miles of containment boom, whose purpose is to either corral the oil, or to block it from a marsh, mangrove, shrimp/crab/oyster ranch or other ecologically sensitive areas. Booms extend 18–48 inches (0.46–1.2 m) above and below the water surface and are effective only in relatively calm and slow-moving waters. More than 100,000 feet (30 km) of containment booms were initially deployed to protect the coast and the Mississippi River Delta. By the next day, that nearly doubled to 180,000 feet (55 km), with an additional 300,000 feet (91 km) staged or being deployed.

Some US lawmakers and local officials claimed that the booms didn't work as intended, saying there is more shoreline to protect than lengths of boom to protect it and that inexperienced operators didn't lay the boom correctly. Billy Nungesser, president of Plaquemines Parish, Louisiana, said the boom "washes up on the shore with the oil, and then we have oil in the marsh, and we have an oily boom. So we have two problems”. According to Naomi Klein, writing for the Guardian, "the ocean's winds and currents have made a mockery of the lightweight booms BP has laid out to absorb the oil." Byron Encalade, president of the Louisiana Oysters Association, told BP that the "oil's gonna go over the booms or underneath the bottom", and according to Klein, he was right. Rick Steiner, a marine biologist who closely followed the clean-up operations, estimated that "70% or 80% of the booms are doing absolutely nothing at all". Local officials along the gulf maintained that there was a scarcity of boom, especially the heavier "ocean boom". BP, in its regional plan, says that boom is not effective in waters with waves more than three to four feet high; waves in the gulf often exceed that height.

The Louisiana barrier island plan was initialized to construct barrier islands protecting the coast of Louisiana from the spill. The plan was criticised due to expenses and ineffectiveness. It is alleged by critics that the decision to pursue the project was made on a political basis with little input from the scientific experts.

Dispersal

The spill was also notable for the volume of Corexit oil dispersant used, as well as the methods of application. This use of dispersant was questioned at the time and its effects continue to be questioned and investigated.

Choice and composition of Corexit

A C-130 Hercules sprays Corexit dispersant onto the Gulf of Mexico

Corexit EC9500A and Corexit EC9527A were the principal dispersants employed. The two formulations are neither the least toxic, nor the most effective, among the EPA's approved dispersants. Twelve other products received better toxicity and effectiveness ratings, but BP says it chose to use Corexit because it was available the week of the rig explosion. Critics contend that the major oil companies stockpile Corexit because of their close business relationship with its manufacturer Nalco.

Environmental groups attempted to obtain information regarding the composition and safety of ingredients in Corexit through the Freedom of Information Act but were denied by the EPA. After Earthjustice sued on behalf of the Gulf Restoration Network and the Florida Wildlife Federation, the EPA released a list of all 57 chemicals in the 14 dispersents on the EPA's National Contingency Plan Product Schedule. The dispersants used contain propylene glycol, 2-butoxyethanol, and dioctyl sodium sulfosuccinate.

Earthjustice and Toxipedia conducted the first analysis of the 57 chemicals found in Corexit formulas 9500 and 9527 in 2011. Results showed the dispersant could contain cancer-causing agents, hazardous toxins and endocrine-disrupting chemicals. The analysis found "5 chemicals are associated with cancer; 33 are associated with skin irritation from rashes to burns; 33 are linked to eye irritation; 11 are or are suspected of being potential respiratory toxins or irritants; 10 are suspected kidney toxins; 8 are suspected or known to be toxic to aquatic organisms; and 5 are suspected to have a moderate acute toxicity to fish”.

Method and extent of use

On 1 May 2010, two military C-130 Hercules aircraft were employed to spray oil dispersant. More than half of the 1.1 million US gallons (4,200 m³) of chemical dispersants were applied at the wellhead 5,000 feet (1,500 m) under the sea. This had never previously been tried but due to the unprecedented nature of this spill, BP along with the USCG and the EPA, decided to use "the first subsea injection of dispersant directly into oil at the source".

Dispersants are said to facilitate the digestion of the oil by microbes. Mixing the dispersants with the oil at the wellhead would keep some oil below the surface and in theory, allow microbes to digest the oil before it reached the surface. Various risks were identified and evaluated, in particular that an increase in the microbe activity might reduce the oxygen in the water. The use of dispersants at the wellhead was pursued and NOAA estimated that roughly 409,000 barrels (65,000 m³) of oil were dispersed underwater.

By 12 July 2010, BP had reported applying 1.07 million US gallons (4,100 m³) of Corexit on the surface and 721,000 US gallons (2,730 m³) underwater (subsea). By 30 July 2010, more than 1.8 million US gallons (6,800 m³) of dispersant had been used, mostly Corexit 9500.

Dispersant use was said to have stopped after the cap was in place. Marine toxicologist Riki Ott wrote an open letter to the EPA in late August with evidence that dispersant use had not stopped and that it was being administered near shore. Independent testing supported her claim. New Orleans-based attorney Stuart Smith, representing the Louisiana-based United Commercial Fisherman’s Association and the Louisiana Environmental Action Network said he “personally saw C-130s applying dispersants from [his] hotel room in the Florida Panhandle. They were spraying directly adjacent to the beach right at dusk. Fishermen I’ve talked to say they’ve been sprayed. This idea they are not using this stuff near the coast is nonsense.”

Environmental controversy over Corexit

Sign protesting use of toxic "Corexit" chemical dispersant in the BP Gulf of Mexico oil disaster, at the Bastille Day Tumble, French Quarter, New Orleans

Corexit was banned from use on oil spills in the United Kingdom a decade prior to the Deepwater Horizon explosion. According to the OSHA-required Material Safety Data Sheets (MSDSs) for both versions of Corexit used in the Gulf, "Component substances have a low potential to bioconcentrate (defined by the EPA as "accumulation of a chemical in tissues of a fish or other organism to levels greater than in the surrounding medium")....No toxicity studies have been conducted on this product".....[COREXIT 9500] is a simple blend of six well-established, safe ingredients that biodegrade, do not bioaccumulate and are commonly found in popular household products....Corexit products do not contain carcinogens or reproductive toxins. All the ingredients have been extensively studied for many years and have been determined safe and effective by the EPA".

However, 2-butoxyethanol, a component of Corexit EC9527A, was identified as a causal agent in the health problems experienced by cleanup workers after the 1989 Exxon Valdez oil spill. Warnings from the Hazardous Substance Fact Sheet for 2-Butoxyethanol include: "Cancer Hazard: 2-Butoxy Ethanol may be a carcinogen in humans since it has been shown to cause liver cancer in animals. Many scientists believe there is no safe level of exposure to a carcinogen....Reproductive Hazard: 2-Butoxy Ethanol may damage the developing fetus. There is limited evidence that 2-Butoxy Ethanol may damage the male reproductive system (including decreasing the sperm count) in animals and may affect female fertility in animals".

Environmental scientists say the dispersants, which can cause genetic mutations and cancer, add to the toxicity of a spill, and that sea turtles and bluefin tuna are exposed to an even greater risk than crude alone. According to them, the dangers are even greater for dispersants poured into the source of a spill, where they are picked up by the current and wash through the Gulf.

On 7 May 2010, Secretary Alan Levine of the Louisiana Department of Health and Hospitals, Louisiana Department of Environmental Quality Secretary Peggy Hatch, and Louisiana Department of Wildlife and Fisheries Secretary Robert Barham sent a letter to BP outlining their concerns related to potential dispersant impact on Louisiana's wildlife and fisheries, environment, aquatic life, and public health. Officials requested that BP release information on their dispersant effects. After three underwater tests the EPA approved the injection of dispersants directly at the leak site to break up the oil before it reached the surface.

In mid-May, independent scientists suggested that underwater injection of Corexit into the leak may have been responsible for the oil plumes discovered below the surface.

On 19 May, the EPA gave BP 24 hours to choose less toxic alternatives to Corexit from the list of dispersants on the National Contingency Plan Product Schedule and begin applying the new dispersant(s) within 72 hours of EPA approval or provide a detailed reasoning why the approved products did not meet the required standards.

On 20 May, US Polychemical Corporation reportedly received an order from BP for its Dispersit SPC 1000 dispersant. US Polychemical said that it could produce 20,000 US gallons (76 m³) a day in the first few days, increasing up to 60,000 US gallons (230 m³) a day thereafter. Also on 20 May, BP determined that none of the alternative products met all three criteria of availability, toxicity, and effectiveness. On 24 May, EPA Administrator Lisa Jackson ordered the EPA to conduct its own evaluation of alternatives and ordered BP to scale back dispersant use.

According to analysis of daily dispersant reports provided by the Deepwater Horizon Unified Command, before 26 May, BP used 25,689 US gallons (97.24 m³) a day of Corexit. After the EPA directive, the daily average of dispersant use dropped to 23,250 US gallons (88.0 m³) a day, a 9% decline.

The 12 July 2010 BP report listed available stocks of Corexit which decreased by over 965,000 US gallons (3,650 m³) without reported application, suggesting either stock diversion or unreported application. Under reported subsea application of 1,690,000 US gallons (6,400 m³) would account for this discrepancy. Given the suggested dispersant to oil ratio between 1:10 and 1:50, the possible use of 1.69 million US gallons (6,400 m³) in subsea application could be expected to suspend between 0.4 to 2 million barrels (64,000 to 318,000 m³) of oil below the surface of the Gulf.

On 31 July, Rep. Edward Markey, Chairman of the House Energy and Environment Subcommittee, released a letter sent to National Incident Commander Thad Allen, and documents revealing that the USCG repeatedly allowed BP to use excessive amounts of the dispersant Corexit on the surface of the ocean. Markey's letter, based on an analysis conducted by the Energy and Environment Subcommittee staff, further showed that by comparing the amounts BP reported using to Congress to the amounts contained in the company's requests for exemptions from the ban on surface dispersants it submitted to the USCG, that BP often exceeded its own requests, with little indication that it informed the USCG, or that the USCG attempted to verify whether BP was exceeding approved volumes. "Either BP was lying to Congress or to the Coast Guard about how much dispersants they were shooting onto the ocean," said Rep. Markey.

On 2 August, the EPA said dispersants did no more harm to the environment than the oil itself, and that they stopped a large amount of oil from reaching the coast by making the oil break down faster. However, independent scientists and EPA's own experts continue to voice concerns regarding the use of dispersants.

Long-term effects of Corexit

NOAA states that toxicity tests have suggested that the acute risk of dispersant-oil mixtures is no greater than that of oil alone. However, some experts believe that all the benefits and costs may not be known for decades. A study from Georgia Tech and Universidad Autonoma de Aguascalientes (UAA), Mexico reported in late 2012 that Corexit made the oil up to 52 times more toxic than oil alone. Additionally, the dispersant made oil sink faster and more deeply into the beaches, and possibly the groundwater.

University of South Florida scientists released preliminary results on the toxicity of microscopic drops of oil in the undersea plumes, finding that they may be more toxic than previously thought. The researchers say the dispersed oil appears to be negatively affecting bacteria and phytoplankton – the microscopic plants which make up the basis of the Gulf's food web. The field-based results were consistent with shore-based laboratory studies showing that phytoplankton are more sensitive to chemical dispersants than the bacteria, which are more sensitive to oil.

Because the dispersants were applied deep under the sea, much of the oil never rose to the surface – which means it went somewhere else, said Robert Diaz, a marine scientist at the College of William and Mary, "The dispersants definitely don't make oil disappear. They take it from one area in an ecosystem and put it in another," Diaz said. One plume of dispersed oil measured at 22 miles (35 km) long, more than a mile wide and 650 feet (200 m) tall. The plume showed the oil "is persisting for longer periods than we would have expected," said researchers with the Woods Hole Oceanographic Institution. "Many people speculated that subsurface oil droplets were being easily biodegraded. Well, we didn't find that. We found it was still there". In a major study on the plume, experts found the most worrisome part to be the slow pace at which the oil was breaking down in the cold, 40 °F (4 °C) water at depths of 3,000 feet (910 m) 'making it a long-lasting but unseen threat to vulnerable marine life'. Marine Sciences at the University of Georgia reported findings of a substantial layer of oily sediment stretching for dozens of miles in all directions from the capped well.

Removal

Dark clouds of smoke and fire emerge as oil burns during a controlled fire in the Gulf of Mexico, May 6, 2010.

The Taiwanese retrofitted skimmer, A Whale

The three basic approaches for removing the oil from the water were: burning the oil, filtering offshore, and collecting for later processing. On 28 April 2010, the USCG announced plans to corral and burn off up to 1,000 barrels (160 m³) of oil each day. In November 2010 the EPA reported that "situ burning" removed as much as 13 million US gallons (49 Ml) of oil from the water. There were 411 fires set between April to mid-July 2010 from which cancer-causing dioxins were released. The EPA stated that the release was minimal. A second research team concluded "there was only a small added risk of cancer to people breathing polluted air or eating tainted fish".

A Taiwanese supertanker, A Whale, was retrofitted after the Deepwater explosion for skimming large amounts of oil in the Gulf. The ship was tested in early July 2010 but failed to collect a significant amount of oil. Due to BP's use of Corexit the oil was too dispersed to collect, according to a spokesperson for shipowner TMT.

The EPA prohibited the use of skimmers that left more than 15 ppm of oil in the water. Many large-scale skimmers exceeded the limit. An urban myth developed that the U.S. government declined the offers from foreign countries because of the requirements of the Jones Act. This proved untrue and many foreign assets deployed to aid in cleanup efforts.

In mid June, BP ordered 32 machines that separate oil and water with each machine capable of extracting up to 2,000 barrels (320 m³) per day, After testing machines for one week, BP decided to use the technology and by 28 June, had removed 890,000 barrels (141,000 m³) of oily liquid. The USCG said 33,000,000 US gallons (120,000 m³) of tainted water was recovered, with 5,000,000 US gallons (19,000 m³) of that consisting of oil. BP said 826,800 barrels (131,450 m³) had been recovered or flared.

Oil budget

The table below presents the NOAA estimates based on an estimated release of 4,900,000 barrels (780,000 m³) of oil (the category "chemically dispersed" includes dispersal at the surface and at the wellhead; "naturally dispersed" was mostly at the wellhead; "residual" is the oil remaining as surface sheen, floating tarballs, and oil washed ashore or buried in sediment). However, there is plus or minus 10% uncertainty in the total volume of the spill.

Category	Estimate	Alternative 1	Alternative 2
Direct recovery from wellhead	17%	17%	17%
Burned at the surface	5%	5%	5%
Skimmed from the surface	3%	3%	3%
Chemically dispersed	8%	10%	6%
Naturally dispersed	16%	20%	12%
Evaporated or dissolved	25%	32%	18%
Residual remaining	26%	13%	39%

Two months after these numbers were released Carol Browner, director of the White House Office of Energy and Climate Change Policy, said they were "never meant to be a precise tool" and that the data "was simply not designed to explain, or capable of explaining, the fate of the oil. Oil that the budget classified as dispersed, dissolved, or evaporated is not necessarily gone".

Based on these estimates, up to 75% of the oil from BP's Gulf oil disaster still remained in the Gulf environment, according to Christopher Haney, chief scientist for Defenders of Wildlife, who called the government report's conclusions misleading. Haney reiterated "terms such as 'dispersed,' 'dissolved' and 'residual' do not mean gone. That's comparable to saying the sugar dissolved in my coffee is no longer there because I can't see it. By Director Lubchenco's own acknowledgment, the oil which is out of sight is not benign. "Whether buried under beaches or settling on the ocean floor, residues from the spill will remain toxic for decades."

Appearing before Congress, Bill Lehr, a senior scientist at NOAA's Office of Response and Restoration, defended a report written by the National Incident Command on the fate of the oil. The report relied on numbers generated by government and non-government oil spill experts, using an "Oil Budget Calculator" (OBC) developed for the spill. Based upon the OBC, Lehr said 6% was burned and 4% was skimmed but he could not be confident of numbers for the amount collected from beaches. As seen in the table above, he pointed out that much of the oil has evaporated or been dispersed or dissolved into the water column. Under questioning from congressman Ed Markey, Lehr agreed that the report said the amount of oil that went into the Gulf was 4.1 million barrels (650×10^³ m³), noting that 800,000 barrels (130,000 m³) were siphoned off directly from the well.

NOAA was criticized by some independent scientists and Congress for the report's conclusions and for failing to explain how the scientists arrived at the calculations detailed in the table above. Ian MacDonald, an ocean scientist at FSU, claimed the NIC report "was not science". He accused the White House of making "sweeping and largely unsupported" claims that 3/4 of the oil in the Gulf was gone and called the report "misleading". "The imprint will be there in the Gulf of Mexico for the rest of my life. It is not gone and it will not go away quickly", he concluded.

A formally peer-reviewed report documenting the OBC was scheduled for release in early October. Markey told Lehr the NIC report had given the public a false sense of confidence. "You shouldn't have released it until you knew it was right," he said.

By late July, two weeks after the flow of oil had stopped, oil on the surface of the Gulf had largely dissipated but concern still remained for underwater oil and ecological damage.

Markus Huettel, a benthic ecologist at FSU who has been studying the spill since 2010, maintains that while much of BP's oil was degraded or evaporated, as least 60% remains unaccounted for. Huettel cautions that only one category from NOAA's "oil budget", the 17% directly recovered from the wellhead, is actually known. "All the other categories, like oil burned, skimmed, chemically dispersed, or evaporated, are guesses that could change by a factor or two or even more in some cases". Huettel stressed that even after much research, some categories, like how much oil was dispersed at depth, will never be accurately known. "That oil is somewhere, but nobody knows where, and nobody knows how much has settled on the seafloor."

Oil eating microbes

In August, 2010, a study of bacterial activity in the Gulf led by Terry Hazen of the Lawrence Berkeley National Laboratory, found a previously unknown bacterial species and reported in the journal Science that it was able to break down the oil without depleting oxygen levels. Hazen’s interpretation had its skeptics. John Kessler, a chemical oceanographer at Texas A&M University says “what Hazen was measuring was a component of the entire hydrocarbon matrix,” which is a mix of thousands of different molecules. Although the few molecules described in the new paper in Science may well have degraded within weeks, Kessler says, “there are others that have much longer half-lives – on the order of years, sometimes even decades.” He noted that the missing oil has been found in the form of large oil plumes, one the size of Manhattan, which do not appear to be biodegrading very fast.

By mid-September, research showed these microbes mainly digested natural gas spewing from the wellhead – propane, ethane, and butane – rather than oil, according to a subsequent study. David L. Valentine, a professor of microbial geochemistry at UC Santa Barbara, said that the oil-gobbling properties of the microbes had been grossly overstated. Methane was the most abundant hydrocarbon released during the spill. It has been suggested that vigorous deepwater bacterial bloom respired nearly all the released methane within 4 months, leaving behind a residual microbial community containing methanotrophic bacteria.

Some experts suggested that the oil eating bacteria may have caused health issues for residents of the Gulf. Local physicians noted an outbreak of mysterious skin rashes which, according to marine toxicologist Riki Ott, could be the result of proliferation of the bacteria in Gulf waters. In order to eat the oil faster, oil eating bacteria like Alcanivorax borkumensis has been genetically modified. Ott claims to have spoken with numerous residents and tourists of the Gulf who have experienced symptoms like rashes and "peeling palms" after contact with the water in the Gulf.

Consequences

Ecology

Main article: Environmental impact of the Deepwater Horizon oil spill

The greatest impact was on marine species. The spill area hosted 8,332 species, including more than 1,200 fish, 200 birds, 1,400 molluscs, 1,500 crustaceans, 4 sea turtles and 29 marine mammals. In addition to the 14 species under federal protection, the spill threatened 39 more ranging from "whale sharks to seagrass". Damage to the ocean floor especially endangered the Louisiana pancake batfish whose range is entirely contained within the spill-affected area. The oil contained approximately 40% methane by weight, compared to about 5% found in typical oil deposits. Methane can potentially suffocate marine life and create "dead zones" where oxygen is depleted. During a January 2013 flyover, former NASA physicist Bonny Schumaker noted a "dearth of marine life" in a radius 30 to 50 miles (48 to 80 km) around the well. In March 2012, a definitive link was found between the death of a Gulf coral community and the spill.

The spill waters contained 40 times more Polycyclic aromatic hydrocarbons (PAH) than before the spill. PAH is often linked to oil spills and includes carcinogens and chemicals that pose various human health risks. The PAHs were most concentrated near the Louisiana Coast, but levels also jumped 2-3 fold in areas off Alabama, Mississippi and Florida. PAHs can harm marine species directly and microbes used to consume the oil would reduce marine oxygen levels. Estimates state that only 2% of the carcasses of killed mammals were recovered. In the first birthing season for dolphins after the spill, dead baby dolphins washed up along Mississippi and Alabama shorelines at about 10 times the normal number. Oil was discovered on dead dolphins along the Gulf Coast. Fifteen of the 406 dolphins that washed ashore in the first 14 months had oil on their bodies; the oil found on eight was linked to the spill. A NOAA/BP study in the summer of 2011 found that "many of the 32 dolphins studied were underweight, anemic and suffering from lung and liver disease, while nearly half had low levels of a hormone that helps the mammals deal with stress as well as regulating their metabolism and immune systems". Other conditions included drastically low weight and low blood sugar.

The oil and dispersant mixture, including PAHs, permeated the food chain through zooplankton. Signs of an oil-and-dispersant mix were found under the shells of tiny blue crab larvae. The use of dispersant made oil sink faster and more deeply into beaches, and possibly groundwater supplies. Corexit allowed the PAHs to permeate sand where, due to a lack of sunlight, degradation is slowed. Some types of spiders and other insects became far less numerous. Migratory birds carried chemicals from the spill as far as Minnesota. The vast majority of a small sample of Pelican eggs tested contained "petroleum compounds and Corexit".

Fish with oozing sores and lesions were first noted by fishermen in November 2010. Dispersant and PAHs from oil are believed to have caused "disturbing numbers" of mutated fish that scientists and commercial fishers began seeing in 2012, including 50% of shrimp found lacking eyes and eye sockets. Prior to the spill, approximately 1/10 of 1% of Gulf fish had lesions or sores. A report from the University of Florida said that many locations showed 20% of fish with lesions, while later estimates reach 50%. Fishermen say they've never seen deformities like these, as does LSU's Dr Jim Cowan, who has 20 years' experience working with Red Snapper.

After Hurricane Issac hit the Gulf in September 2012, about 565,000 pounds (256,000 kg) of oiled material traced to the spill was brought to land. Huge tar mats were uncovered during the storm, prompting beach closures. In 2013, researchers observed a phenomenon called "dirty blizzard": oil caused deep ocean sediments to clump together, falling to the ocean floor at ten times the normal rate in an "underwater rain of oily particles". The result could have long-term effects on both humans and marine life. Commercially-fished species feed on sediment creatures, meaning oil could remain in the food chain for generations. 2013 research suggested as much as one-third of the oil remains in the Gulf.

Health consequences

Main article: Health consequences of the Deepwater Horizon oil spill

By 21 June, 143 spill exposure cases had been reported to the Louisiana Department of Health and Hospitals (DHH); 108 of those cases involved workers in the clean-up efforts, while 35 were reported by gulf residents. Chemicals from the oil and dispersant are believed to be the cause of these illnesses as the addition of dispersants created an even more toxic substance (PAHs) when mixed with crude oil. Mike Robicheux, a Louisiana physician who has been treating people sick from exposure to toxic chemicals, described it as the biggest public health crisis from a chemical poisoning in the history of this country" In addition, the increased risk of mental disorders and stress-related health problems were noted shortly after the spill.

A survey of the health effects of the spill on cleanup workers reported "eye, nose and throat irritation; respiratory problems; blood in urine, vomit and rectal bleeding; seizures; nausea and violent vomiting episodes that last for hours; skin irritation, burning and lesions; short-term memory loss and confusion; liver and kidney damage; central nervous system effects and nervous system damage; hypertension; and miscarriages". Dr. James Diaz, writing for the American Journal of Disaster Medicine, said these ailments appearing in the Gulf reflected those reported after previous oil spills, like the Exxon Valdez. Diaz warned that "chronic adverse health effects, including cancers, liver and kidney disease, mental health disorders, birth defects and developmental disorders should be anticipated among sensitive populations and those most heavily exposed". Diaz also believes neurological disorders should be expected.

According to Dr. Riki Ott "people are already dying from this" According to Mississippi Riverkeeper of the Waterkeeper Alliance, blood samples from 8 people from Pensacola, Florida and Alabama, residents and cleanup workers "were analyzed for volatile solvents and all came back with ethylbenzene and m,p-Xylene in excess of 95th percentile values of 0.11 ppb for ethylbenzene and 0.34 ppb for m,p-xylene." The highest concentration value was four times the 95th percentile. The blood of all 8 individuals "had chemicals that are found in the BP crude oil".

Two years after the spill the study started by the National Institute for Occupational Safety and Health found biomarkers that are matching the oil from the spill, in the bodies of cleanup workers. Other studies have reported a variety of mental health issues, skin problems, breathing issues, coughing, and headaches. Nearly three years later, studies indicated a '"significant percentage" of Gulf residents were reporting mental health problems like anxiety, depression and PTSD.

Economy

Main article: Economic and political consequences of the Deepwater Horizon disaster

Weeks after the event, and while it was still in progress, the 2010 Deepwater Horizon oil spill was being discussed as a disaster with far reaching consequences sufficient to impact global economies, marketplaces and policies. These potentially included structural shifts to energy policy, insurance marketplaces and risk assessment, and potential liabilities of the order of tens of billions of US dollars for one or more large and well known companies - principally BP.

Offshore drilling policies

Main articles: United States offshore drilling debate and 2010 United States deepwater drilling moratorium

See also: Hornbeck Offshore Services LLC v. Salazar

On 30 April 2010 President Barack Obama ordered the federal government to hold the issuing of new offshore drilling leases and authorized investigation of 29 oil rigs in the Gulf in an effort to determine the cause of the disaster. Later a six-month offshore drilling (below 500 feet (150 m) of water) moratorium was enforced by the United States Department of the Interior. The moratorium suspended work on 33 rigs. Local officials in Louisiana expressed concern that the moratorium imposed in response to the spill would further harm the economies of coastal communities as the oil industry employs about 58,000 Louisiana residents and has created another 260,000 oil-related jobs, accounting for about 17% of all Louisiana jobs. On 22 June, a United States federal judge on the United States District Court for the Eastern District of Louisiana Martin Leach-Cross Feldman when ruling in the case Hornbeck Offshore Services LLC v. Salazar, lifted the moratorium finding it too broad, arbitrary and not adequately justified. The ban was lifted in October 2010.

On 28 April 2010, the National Energy Board of Canada, which regulates offshore drilling in the Canadian Arctic and along the British Columbia Coast, issued a letter to oil companies asking them to explain their argument against safety rules which require same-season relief wells. On 3 May California Governor Arnold Schwarzenegger withdrew his support for a proposed plan to allow expanded offshore drilling projects in California. On 8 July, Florida Governor Charlie Crist called for a special session of the state legislature to draft an amendment to the state constitution banning offshore drilling in state waters, which the legislature rejected on 20 July.

Reactions

Main article: Reactions to the Deepwater Horizon oil spill

US reactions

On 30 April President Obama dispatched the Secretaries of the Department of Interior and Homeland Security, as well as the EPA Administrator and NOAA to the Gulf Coast to assess the disaster. In his speech on 15 June Obama said: "This oil spill is the worst environmental disaster America has ever faced... Make no mistake: we will fight this spill with everything we've got for as long as it takes. We will make BP pay for the damage their company has caused. And we will do whatever's necessary to help the Gulf Coast and its people recover from this tragedy." Interior Secretary Ken Salazar has told: "Our job basically is to keep the boot on the neck of British Petroleum." Some observers suggested that the Obama administration was being unusually aggressive and often excessive in its criticism of BP, which some BP investors saw as an attempt to deflect criticism of his own handling of the crisis. Republicans such as Rand Paul accused President Obama of being anti-business and "un-American".

Public opinion polls in the U.S. were generally critical of the way the President Obama and the federal government handled the disaster and they were extremely critical of BPs response. There was a great deal of criticism of BP both in the US and worldwide for its role in the spill. Across the US, thousands of people participated in dozens of protests at BP gas stations and other locations causing sales declines at some stations of between 10% to 40%.

Industry responded by saying that disasters are infrequent and that the Deepwater Horizon is an isolated incident and refuted any claims of a loss of industry wide credibility. The American Petroleum Institute (API) stated that the offshore drilling industry is important to job creation and economic growth CEOs from the top five oil companies all agreed that industry needs to work harder at improving safety. To help prevent a recurrence of a similar disaster, API said that they are setting up their own offshore safety institute that will be separate from API's lobbying organization.

The Organization for International Investment, a Washington-based advocate for overseas investment into the United States, warned that the political rhetoric surrounding the disaster was potentially damaging the reputation of all British companies with operations in the United States and sparked a wave of U.S. protectionism that restricted British firms from winning government contracts, making political donations and lobbying.

UK reactions

In the UK, there was anger at the American press and news outlets for the misuse of the term "British Petroleum" for the company – a name which has not been used since British Petroleum merged with the American company, Amoco, in 1998 to form BP. It was said that the U.S. was 'dumping' the blame onto the British people and there were calls for British Prime Minister David Cameron to protect British interests in America. British pension fund managers (who have large holdings of BP shares and rely upon its dividends) accepted that while BP had pay compensation for the spill and the environmental damage, they argued that the cost to the company's market value from the President Obama's criticism was far outweighing the direct clean-up costs.

Initially BP downplayed the incident; its CEO Tony Hayward called the amount of oil and dispersant "relatively tiny" in comparison with the "very big ocean." Later, he drew an outpouring of criticism when he said that the spill was a disruption to Gulf Coast residents and himself adding, "You know, I'd like my life back." BP's chief operating officer Doug Suttles contradicted the underwater plume discussion noting, "It may be down to how you define what a plume is here… The oil that has been found is in very minute quantities." In June, BP launched a PR campaign and successfully bid for several search terms related to the spill on Google and other search engines so that the first sponsored search result linked directly to the company's website. On 26 July 2010, it was announced that CEO Tony Hayward was to quit and would be replaced by Bob Dudley, who is an American citizen and previously worked for Amoco.

International reactions

The U.S. State Department listed 70 assistance offers from 23 countries, all being initially declined but later 8 had been accepted. The USCG actively requested skimming boats and equipment from several countries.

Legal aspects and settlements

Investigations

Main article: Deepwater Horizon investigation

An investigation of the possible causes of the explosion was launched on 22 April 2010 by the USCG and the Minerals Management Service. On 11 May the United States administration requested the National Academy of Engineering conduct an independent technical investigation. The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling was established on 22 May to "consider the root causes of the disaster and offer options on safety and environmental precautions." The investigation by United States Attorney General Eric Holder was announced on 1 June. Also the United States House Committee on Energy and Commerce conducted a number of hearings, including hearings of Tony Hayward and heads of Anadarko and Mitsui's exploration unit.

According to the US Congressional investigation, the rig's blowout preventer, built by Cameron International Corporation, had a hydraulic leak and a failed battery, and therefore failed. The BP's internal investigation found on 20 April 2010 managers misread pressure data and gave their approval for rig workers to replace drilling fluid in the well with seawater, which was not heavy enough to prevent gas that had been leaking into the well from firing up the pipe to the rig, causing the explosion. The conclusion was that BP was partly to blame, as was Transocean, which owned the rig. On 23 March 2011, BOEMRE (former MMS) and the USCG published the forensic examination report on blowout preventer, prepared by Det Norske Veritas. The report concluded that the primary cause of failure was that the blind shear rams failed to fully close and seal due to a portion of drill pipe trapped between the shearing blocks.

The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling released a final report on 5 January 2011. The panel found that BP, Halliburton, and Transocean had attempted to work more cheaply and thus helped to trigger the explosion and ensuing leakage. The report states: "Whether purposeful or not, many of the decisions that BP, Halliburton, and Transocean made that increased the risk of the Macondo blowout clearly saved those companies significant time (and money)." BP released a statement in response to this, saying, "Even prior to the conclusion of the commission's investigation, BP instituted significant changes designed to further strengthen safety and risk management." Transocean, however, blamed BP for making the decisions before the actual explosion occurred and government officials for permitting those decisions. Halliburton stated that it was acting only upon the orders of BP when it injected the cement into the wall of the well. Halliburton also blamed the governmental officials and BP. It criticized BP for its failure to run a cement bond log test. In the report, BP was accused of nine faults. One was that it had not used a diagnostic tool to test the strength of the cement. Another was ignoring a pressure test that had failed. Still another was for not plugging the pipe with cement. The study did not, however, place the blame on any one of these events. Rather, it concluded with the following statement:

“Notwithstanding these inherent risks, the accident of April 20 was avoidable,” the panel wrote. “It resulted from clear mistakes made in the first instance by BP, Halliburton and Transocean, and by government officials who, relying too much on industry’s assertions of the safety of their operations, failed to create and apply a program of regulatory oversight that would have properly minimized the risk of deepwater drilling.”

The panel also noted that the government regulators did not have sufficient knowledge or authority to notice these cost-cutting decisions.

The US government report issued in September 2011 stated that BP is ultimately responsibility for the spill, and that Halliburton and Transocean share some of the blame. The report states that the main cause was the defective cement job, and Halliburton, BP and Transocean were, in different ways, responsible for the accident. The report states that, although the events leading to the sinking of Deepwater Horizon were set into motion by the failure to prevent a well blowout, the investigation revealed numerous systems deficiencies, and acts and omissions by Transocean and its Deepwater Horizon crew, that had an adverse impact on the ability to prevent or limit the magnitude of the disaster. The report also states that a central cause of the blowout was failure of a cement barrier allowing hydrocarbons to flow up the wellbore, through the riser and onto the rig, resulting in the blowout. The loss of life and the subsequent pollution of the Gulf of Mexico were the result of poor risk management, last‐minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response, and insufficient emergency bridge response training by companies and individuals responsible for drilling at the Macondo well and for the operation of the drilling platform.

Spill response fund

Main article: Gulf Coast Claims Facility

See also: Kenneth Feinberg

The Gulf Coast Claims Facility (GCCF) was the $20 billion fund established by BP to settle claims arising from the Deepwater Horizon casualty. The GCCF was announced on 16 June 2010, after meeting of BP executives with President Obama. The fund was established to be used for natural resource damages, state and local response costs and individual compensation but could not be used for fines or penalties. Prior to establishing the GCCF, emergency compensation was paid by BP from an initial facility.

The GCCF was administrated by attorney Kenneth Feinberg. The facility began accepting claims on 23 August 2010. On 8 March 2012, after BP and a team of plaintiffs' attorneys agreed to a class-action settlement, a court-supervised administrator Patrick Juneau took over administration. Until this more than one million claims of 220,000 individual and business claimants were processed and more than $6.2 billion was paid out from the fund. 97% of payments were made to claimants in the Gulf States. In June 2012, the settlement of claims through the GCCF was replaced by the court supervised settlement program. During this transition period additional $404 million in claims were paid.

The GCCF and its administrator Feinberg had been criticized about the amount and speed of payments as well as a lack of transparency. An independent audit of the GCCF, announced by Attorney General Eric Holder, was approved by Senate on 21 October 2011. An auditor BDO Consulting found that 7,300 claimants were wrongly denied or underpaid. As a result about $64 million of additional payments was made.

Litigation and settlements

Main article: Deepwater Horizon litigation

See also: Hornbeck Offshore Services LLC v. Salazar

By 26 May 2010, over 130 lawsuits relating to the spill had been filed against one or more of BP, Transocean, Cameron International Corporation, and Halliburton Energy Services, although it was considered likely by observers that these would be combined into one court as a multidistrict litigation. On 21 April 2011, BP issued $40bn worth of lawsuits against rig owner Transocean, cementer Halliburton and blowout preventer manufacturer Cameron. The oil firm alleged failed safety systems and irresponsible behaviour of contractors had led to the explosion, including claims that Halliburton failed to properly use modelling software to analyze safe drilling conditions. The firms deny the allegations.

On 2 March 2012, BP and plaintiffs agreed to settle their lawsuits. The deal would settle roughly 100,000 claims filled by individuals and businesses affected by the spill. On 13 August, BP asked US District Judge Carl Barbier to approve the settlement, saying its actions "did not constitute gross negligence or willful misconduct". On 13 January 2013, Judge Barbier approved a medical-benefits portion of BP's proposed $7.8 billion partial settlement. People living for at least 60 days along oil-impacted shores or involved in the clean-up who can document one or more specific health conditions caused by the oil or dispersants are eligible for benefits, as are those injured during clean-up. BP also agreed to spend $105 million over five years to set up a Gulf Coast health outreach program and pay for medical examinations. According to a group presenting the plaintiffs, the deal has no specific cap. BP says that it has $9.5 billion in assets set aside in a trust to pay the claims, and the settlement will not increase the $37.2 billion the company budgeted for spill-related expenses.

On 14 November 2012, BP and the US Department of Justice reached a settlement. BP will pay $4.5 billion in fines and other payments, the largest of its kind in US history. BP also agreed to plead guilty to 11 felony counts related to the deaths of the 11 workers. The Justice Department also filed criminal charges against one BP employee in April 2012 and against three BP employees in November 2012. Two employees have been indicted on manslaughter charges for acting negligently in their supervision of key safety tests performed on the rig prior to the explosion and failure to alert onshore engineers of problems in the drilling operation. Two employees are charged with obstruction of justice and for lying to federal investigators. Attorney General Eric Holder said that the criminal investigation is not yet over and that more company officials could be charged. In addition, the U.S. government temporary banned BP from new federal contracts over its "lack of business integrity". The plea was accepted by Judge Sarah Vance of the United States District Court for the Eastern District of Louisiana on 31 January 2013.

The settlement includes payments of nearly $2.4 billion to the National Fish and Wildlife Foundation, $350 million to the National Academy of Sciences and about $500 million to the Securities and Exchange Commission. BP still faces payouts to thousands of fishermen and businesses harmed by the spill, fines under the Natural Resources Damage Assessment and payouts to impacted states. The settlement has also not resolved what may be the largest penalty related to the spill, the fines under the Clean Water Act. The potential fine for the spill under the act is $1,100 to $4,300 a barrel spilled, meaning the fine could be as much as $21 billion.

On 3 January 2013 the US Justice Department announced "Transocean Deepwater Inc. has agreed to plead guilty to violating the Clean Water Act and to pay a total of $1.4 billion in civil and criminal fines and penalties".

See also

• Hubris – Modern use, related to BP's initial submitted exploration plan
• List of industrial disasters
• List of oil spills
• Offshore oil and gas in the US Gulf of Mexico
• Timeline of the Deepwater Horizon oil spill

External links

• Oil Spill Commission Final report to the President
• Deepwater BP Oil Spill at Whitehouse.gov
• Deepwater Horizon Incident, Gulf of Mexico from the National Oceanic and Atmospheric Administration (NOAA)
• Deepwater Horizon Joint Investigation by the U.S. Coast Guard and Mineral Management Service
• RestoreTheGulf.gov official U.S. Government Web site, taking over content and functions from Deepwater Horizon Response site
• BP Report on Accident, 8 September 2010, 14 Mb pdf download
• Bridge the Gulf Project Storytelling initiative led by Gulf Coast residents
• Smithsonian's Ocean Portal
• Science in a Time of Crisis: WHOI's response to the Deepwater Horizon Oil Spill a multimedia presentation from Woods Hole Oceanographic Institution
• Approaches for Ecosystem Services Valuation for the Gulf of Mexico After the Deepwater Horizon Oil Spill: Interim Report by the National Academy of Sciences

Lead state agency websites

• Florida Department of Environmental Protection (DEP)
• Emergency.Louisiana.gov
• Mississippi DEQ
• State of Florida Oil Spill Academic Task Force

News media

• Full coverage on C-SPAN video library
• Full coverage on Democracy Now
• Full coverage on Al Jazeera English
• Full coverage on CNN
• Full coverage on The Guardian
• Full coverage from the Los Angeles Times
• Full coverage from The Miami Herald
• Full coverage from The New York Times
• Full coverage from The Times-Picayune (New Orleans)
• Full coverage from the Press-Register (Mobile, Alabama)
• Full coverage from The Wall Street Journal
• Full coverage from GRITtv
• Full coverage from The News-Press (Ft. Myers, FL)

Interactive maps

• Mapping the Response to BP Oil Spill in the Gulf of Mexico (GeoPlatform.gov)
• Gulf Oil Spill Tracker interactive map and form for citizen reporting (SkyTruth.org)
• Map and Estimates of the Oil Spilled (The New York Times)
• Where Oil Has Made Landfall (The New York Times)

Images

• Gulf Oil Spill 2010 Projected Trajectory from Louisiana Earth
• Rig fire at Deepwater Horizon 21 April, '10 video at CNN iReport
• GOES-13 satellite images on the CIMSS Satellite Blog

Animations and graphics

• BBC News – interactive animation to the disaster and blocking efforts
• New York Times exploded view diagrams on the methods used to stop the oil spill
• Graphic: Where the oil and gas went