Talk:Deepwater Horizon oil spill/draft

Efforts to protect the coastline and marine environments
The fundamental strategies for addressing the spill were containment, dispersal and removal. In summer 2010, approximately 47,000 people and 7,000 vessels were involved in the project. By 3 October 2012, federal response costs amounted to $850 million, mostly reimbursed by BP. As of January 2013, 935 personnel were still involved. By that time cleanup had cost BP over $14 billion.

It was estimated with plus or minus 10% uncertainty that 4.9 Moilbbl of oil was released from the well; 4.1 Moilbbl of oil went into the Gulf. The report led by the Department of the Interior and the NOAA said that of "75% [of oil] has been cleaned up by Man or Mother Nature", however only about 25% of released oil was collected or removed while about 75% of oil remained in the environment in one form or another. In 2012, Markus Huettel, a benthic ecologist at FSU, maintained that while much of BP's oil was degraded or evaporated, at least 60% remains unaccounted for.

Containment
Containment booms stretching over 4200000 ft were deployed, either to corral the oil or as a barrier to protect a marsh, mangrove, shrimp/crab/oyster ranch or other ecologically sensitive area. Booms extend 18 - 48 in above and below the water surface and were effective only in relatively calm and slow-moving waters. Including one-time use sorbent booms, a total of 13300000 ft of booms were deployed. Booms were criticized for washing up on the shore with the oil, allowing oil to escape above or below the boom and for ineffectiveness in more than three to four foot waves.

The Louisiana barrier island plan was developed to construct barrier islands to protect the coast of Louisiana. The plan was criticised for its expense and poor results. Critics allege that the decision to pursue the project was political with little scientific input. The EPA expressed concern that the berms would threaten wildlife.

Dispersal
The spill was also notable for the volume of Corexit oil dispersant used and for application methods that were "purely experimental". Altogether, 1.84 e6USgal of dispersants were used; of this 771000 USgal were released at the wellhead. Subsea injection had never previously been tried but due to the spill's unprecedented nature BP together with USCG and EPA decided to use it. Over 400 sorties were flown to release the product. Although usage of dispersants was described as "the most effective and fast moving tool for minimizing shoreline impact", the approach continues to be investigated.

A 2011 analysis conducted by Earthjustice and Toxipedia showed that the dispersant could contain cancer-causing agents, hazardous toxins and endocrine-disrupting chemicals. Environmental scientists expressed concerns that the dispersants add to the toxicity of a spill, increasing the threat to sea turtles and bluefin tuna. The dangers are even greater when poured into the source of a spill, because they are picked up by the current and wash through the Gulf. According to BP and federal officials dispersant use stopped after the cap was in place; however, marine toxicologist Riki Ott claimed that dispersant use continued after that date.

Corexit EC9500A and Corexit EC9527A were the principal variants. The two formulations are neither the least toxic, nor the most effective, among EPA's approved dispersants but BP said it chose to use Corexit because it was available the week of the rig explosion. On 19 May, the EPA gave BP 24 hours to choose less toxic alternatives to Corexit from the National Contingency Plan Product Schedule and begin applying them within 72 hours of EPA approval or provide a detailed reasoning why no approved products met the standards. On 20 May, BP determined that none of the alternative products met all three criteria of availability, non-toxicity and effectiveness. On 24 May, EPA Administrator Lisa Jackson ordered EPA to conduct its own evaluation of alternatives and ordered BP to reduce dispersant use. BP reduced Corexit use by 25689 to 23250 USgal per day, a 9% decline. On 2 August 2010, 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 breaking it down faster. However, some independent scientists and EPA's own experts continue to voice concerns about the approach.

Underwater injection of Corexit into the leak may have created the oil plumes discovered below the surface. Because the dispersants were applied at depth, much of the oil never rose to the surface. One plume was 22 mi long, more than a mile wide and 650 ft tall. 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 water at depths of 3000 ft.

Removal
The three basic approaches for removing the oil from the water were: combustion, offshore filtration and collection for later processing. USCG said 33 e6USgal of tainted water was recovered, including 5 e6USgal of oil. BP said 826800 oilbbl had been recovered or flared. It is calculated that about 5% of leaked oil was burned at the surface and 3% was skimmed. On the most demanding day 47,849 people were assigned on the response works.

From April to mid-July 2010 411 controlled in-situ fires remediated approximately 265000 oilbbl. The fires released small amounts of toxins, including cancer-causing dioxins. According to EPA's report the released amount is not enough to pose an added cancer risk to workers and coastal residents, while a second research team concluded that there was only a small added risk.

Oil was collected from water by using skimmers. In total 2,063 various skimmers were used. For offshore, more than 60 open-water skimmers were deployed, including 12 purpose-built vehicles. EPA regulations prohibited skimmers that left more than 15 parts per million (ppm) of oil in the water. Many large-scale skimmers exceeded the limit. Due to use of Corexit the oil was too dispersed to collect, according to a spokesperson for shipowner TMT. In mid June 2010, BP ordered 32 machines that separate oil and water, with each machine capable of extracting up to 2000 oilbbl/d. After one week of testing, BP began to proceed and by 28 June, had removed 890000 oilbbl.

After the well was captured, the cleanup of shore became the main task of the response works. Two main type of affected coast were sandy beaches and marshes. On beaches the main techniques were sifting sand, removing tar balls and digging out tar mats manually or by using mechanical devices. For marshes techniques like vacuum and pumping, low-pressure flush, vegetation cutting, and bioremediation were used.

Digestion
Dispersants are said to facilitate the digestion of the oil by microbes. Mixing dispersants with 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 microbial activity might reduce subsea oxygen levels, threatening fish and other animals.

Several studies suggest that microbes successfully consumed part of the oil. By mid-September, other research claimed that microbes mainly digested natural gas rather than oil. David L. Valentine, a professor of microbial geochemistry at UC Santa Barbara, said that their oil-gobbling properties had been grossly overstated.

Some experts suggested that the bacteria may have caused health issues for Gulf residents, such as an outbreak of skin rashes. Genetically modified Alcanivorax borkumensis was added to the waters to speed digestion.