By April 24, 2010, two days after the oil rig sank due to an explosion and fires, the oil slick was visible on surrounding surface waters. Over the following weeks and months, NASA satellite photographs—obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) mounted on the Aqua satellite and the Advanced Land Imager aboard the Earth Observing-1 (EO-1) satellite—provided evidence of an expanding surface oil slick over the northern Gulf of Mexico. Scientists using fluorometers mapped and measured clouds and plumes of subsurface oil, and later layers of subsurface oil mixed with chemical dispersants.
Although there was initial uncertainty in estimating the rate of leakage, within days of the accident it became clear that enough oil would be spilled into the Gulf of Mexico to create a significant—and perhaps unprecedented—ecological disaster.
Using remotely operated submersibles to examine the wreckage, engineers quickly discovered at least three major leaks. Oil was leaking from a ruptured drill pipe near the wellhead and from the crumpled riser pipe that had once connected the Deepwater Horizon rig to the well head.
Efforts to stop the leak were performed under difficult marine conditions. Rough seas hampered initial efforts to close the blowout preventer shut-off valves. The vertical column of pipes from the seafloor was so badly damaged that, akin to kinks in a hose, the twisted remains of the connecting pipe actually acted to slow the oil leak. Engineers had to proceed with caution because while attempting repairs, they ran the risk of opening new leaks or inadvertently increasing the rate of leaks already spewing oil into the Gulf.
BLOWOUT PREVENTER. Numerous methods to limit the impact of the Deepwater Horizon spill were attempted throughout May and early June, including using ROVs to manually close the blowout preventer (BOP), a shutoff device at the wellhead. In all, BP sent six of these ROVs to cut the flow of oil at the wellhead. These attempts ultimately failed.
RELIEF WELLS. During this time, BP also began drilling two relief wells to intercept the original well at about 12,800 feet (3,900 m) below the seafloor. These relief wells were to be used in case the other attempts failed. BP hoped that by August these relief wells would be ready to end the oil flow.
CONTAINMENT DOME. Early in May, an attempt was made to place a 98-ton steel and concrete containment dome (called a “top hat”) on top of the largest leak. The top hat, which was four feet (1.2 m) in diameter and 5 feet (1.5 m) tall, would attach to a drill pipe that would siphon the oil to a ship waiting on the ocean's surface. However, this procedure failed when the pipe became blocked with gas hydrates (crystalline solids of methane gas and water molecules). In the second week, the insertion of a Riser Insertion Tube Tool (RITT) between the platform pipe and the broken seafloor pipe was attempted. The apparatus allowed some collection of leaking oil.
TOP KILL AND JUNK SHOT. Then, on May 25, the RITT apparatus was removed so a “top kill” technique and a “junk shot” technique could be attempted to permanently close the leak. Heavy drilling fluids were pumped through two lines into the blowout preventer on the seabed. The top kill technique was designed to restrict the flow of oil so that cement could be poured in to permanently seal the leak. After temporarily stopping the flow, BP announced on May 29 that the “top kill” method had failed to permanently stop it. The junk shot technique, which consisted of shooting shredded tire bits, golf balls, knotted rope, and other selected materials into the BOP with the intention of clogging it, also failed.
LMRP CAP. Thereupon, BP began using the Lower Marine Riser Package (LMRP) Cap Containment System. A diamond saw blade began cutting the damaged riser so a custom-built cap could be placed on the newly cut pipe; however, the saw became stuck. With a substituted pair of shears, a successful cut was accomplished on June 3 and a cap attached. Recovery began the next day, with less than one-tenth of the oil captured. On June 8, according to BP, a total of about 15,000 barrels of oil had been collected that day, and about 57,500 barrels over the past four days. Ultimately, this technique also failed to contain the leaking oil.
NEW CAP ASSEMBLY. On July 10, the LMRP cap was removed so that a different cap could be installed. The new cap assembly, which was hopefully a better fit than the older one, consisted of a flange transition spool and a 3 ram stack. Five days later, BP announced that the leak had stopped when the BOP was closed shut with the new cap assembly.
STATIC KILL. With the success of the LMRP containment cap, on August 3, BP began a process called “static kill,” or hydrostatic kill. The spill prevention process involves injecting several thousand barrels of cement and mud through the containment cap and into the top of the damaged BP well. The cement plug created from the process is designed to hold back the pressure of the oil, which was estimated at about 7,000 pounds per square inch, or almost 500 times atmospheric pressure. On August 9, BP reported that the static kill procedure was holding and leaking oil was no longer present.
BOTTOM KILL. The final major step is called the “bottom kill” technique. It involved pumping cement and mud from the bottom of the well, similar to the “static kill” technique used earlier. A storm entering the Gulf Coast area delayed the bottom kill procedure for several days. However, in late August, the bottom kill was completed and the flow of oil was permanently stopped from flowing out of the damaged well.
NEW BOP. On September 4, the damaged BOP was removed from the site, and lifted to the Gulf surface, a process that lasted just over one day. A new BOP was then installed in order to prevent any new leaks from occurring.
The two relief wells were completed in September, which allowed engineers to permanently seal the well with drilling mud and cement at levels deep into the reservoir. On September 19, Incident Commander and Retired Coast Guard Admiral Thad Allen announced that the well was dead.
The oil leak was initially estimated at 1,000 barrels of oil (42,000 gallons) per day. Expert estimates of the volume of crude oil spilling into the Gulf each day quickly increased to 5,000 barrels (210,000 gallons). Many experts asserted that it was clear from pictures of the continuing underwater gusher eventually released that a significant amount of oil continued spewing into the Gulf, although BP claimed that a temporary funnel-like cap was collecting more than 15,000 (630,000 gallons) of oil per day. An array of marine and oil industry experts argued that the underwater pictures and surface observations provided clear evidence of an underreporting of the size of the spill.
Estimates of the volume of oil gushing into the Gulf increased steadily throughout the spill, ultimately reaching a total of 5 million barrels (210 million gallons) of oil. The Gulf of Mexico spill (also called the BP oil spill or Deepwater Horizon oil spill) surpassed the estimated 3.3 million barrels (approximately 140 million gallons) of oil released during the 1979 Ixtoc I spill to become the worst accidental marine oil spill in history. The Ixtoc 1 spill followed a Petroleos Mexicanos' (PEMEX) rig explosion in the Bay of Campeche (the southern Gulf of Mexico off Mexico's coast). The 2010 Gulf of Mexico spill far surpassed the 11 million gallons of oil spilled into Alaskan waters following the 1989 grounding of the tanker Exxon Valdez. Ultimately, oil washed up along more than 600 miles (966 km) of coastline.
With regards to effects on the economy and property, in April 2011, BP reported that the Gulf Coast Claims Facility, which was responsible for resolving certain economic loss and property damage claims related to the oil spill, had received 267,960 claims from people seeking compensation, whereby 107,955 had been paid, 4,343 had been denied, and the remaining 155,662 submissions were being processed. Gulffishing, sale of Gulf seafood, and tourism industries suffered devastating losses.
By June 2010, the surface slick extended over most of the northern Gulf of Mexico. While the bulk of the spill initially remained at sea, oil began washing into ecologically sensitive marshlands in Louisiana. Extending eastward into Florida waters, the surface slick spotted white-sand beaches vital to local tourist-based economies. Fishing bans extended over more than a quarter of the Gulf of Mexico, resulting in crippling economic hardship and apocalyptic predictions for the future of a Gulf seafood industry integral to the regional economy and deeply entwined with the culture of the region. In Alabama, oil flowed into inland waterways and wetland areas. Deaths of marine mammals, fish, birds, and other wildlife began to spike upwards.
In addition to the surface slick, more than 1.1 million gallons of dispersants, much of it sprayed deep underwater as oil gushed from the damaged well, reduced the surface slick at the expense of clouds and plumes of oil suspended in the water column.
The federal government formed the Deepwater Horizon Unified Command, which included BP and Transocean, along with numerous government agencies, to address the environmental problems associated with the BP Deepwater oil spill. On June 1, 2010, the organization commanded 1,400 vessels, 20,000 personnel, and seventeen staging areas. Initial mitigation and cleanup efforts include measures to both contain and directly remove surface oil. Such efforts relied on floating booms and skimmers to contain the slick until it could be pumped into container vessels. Boats and aircraft can also applied massive amounts of oil dispersants.
While still at sea, the slick killed and threatened birds, marine mammals, plankton, and species of fish that lay eggs at the surface.
CONTAINMENT BOOMS. Many miles of floating containment booms were used to restrict where oil could go, such as into mangroves, marshes, and other ecologically sensitive areas. These booms were about 1 to 4 feet (0.3 to 1.2 m) above and below the water line in order to fulfill their purpose. Over 3.7 million feet (1.13 million m) of booms were deployed.
SKIMMING AND CONTROLLED BURNS. The U.S. Coast Guard used dozens of skimmer ships (“skimmers”) to collect (“skim”) oil that was on the surface waters of the Gulf of Mexico. These skimmer vessels were used to contain this oil in preparation for controlled fires. This activity was done in an attempt to burn off the spilled oil before it reached land and devastate the environment. Over 12.1 million gallons (45.8 million l) of oily water were recovered.
DISPERSANTS. Dispersants are detergent-like chemicals that break up oil slicks. The molecular nature of the dispersants (one part of the molecular structure of dispersants has a polar affinity to water, the other end a non-polar affinity to oil) allows them to surround and coat small droplets of oil. Oil remains on the inside of the oil-dispersant glob in contact with the non-polar parts of the dispersant molecule. On the surface of the glob the polar portions of the dispersant molecules allow the glob to drop out of the spill and mix with water (a polar substance). Ultimately the oil-dispersant globs drop to the sea floor. Over thousands of years, those globules that do not wash up on beaches are consumed by microorganisms.
Chemical dispersants were used to accelerate the way that oil is naturally dispersed in water following oil spills. Such artificially made dispersants used on the Gulf oil spill were primarily Corexit EC9500A and Corexit EC9527A. Although many marine experts expressed disagreement or caution, according to their manufacturer (Nalco), “[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.”
By September 4, 2010, approximately 1.1 million gallons (4.2 million l) of chemical dispersant was applied to the wellhead. There remains much controversy with the use of such dispersants. Chemical dispersants have been used for over fifty years to treat oil spills around the world. However, the medical community has yet to decide the long-term effects of such dispersants on marine life.
Some dispersants have proven toxic to marine organisms. In addition, dispersed oil globules can also be highly toxic. By June 2010 U.S. Environmental Protection Agency (EPA) officials expressed concern about the untested toxicity of the nearly million gallons of dispersants used to reduce the surface slick. EPA officials ordered changes on the types of dispersants used and, at one point, issued a ban on the use of some types of dispersants. Experts contend that it will take years to measure the full impact of the unprecedented use of dispersants.
In addition to helping measure and remediate devastating impacts on the environment and wildlife, scientists also faced an array of continuing challenges. In addition to fighting for access to data, they had to also take into account the influence of natural factors and preexisting phenomena. For example, media reports of dolphin deaths in the northern Gulf in May 2010 were quickly attributed to the oil spill. However, there was already an observed spike in bottlenose dolphin deaths in the region prior to the oil spill, and prior to the oil spill, bottlenose dolphin deaths were already at a seven-year high. Prior to the spill, in March 2010 wildlife officials recorded more than three times the normal number of dead bottlenose dolphins. NOAA officials declared the deaths an “unusual mortality event” and ordered an investigation. Although oil residues are highly toxic to marine mammals and significant deaths and damage were observed pathologists conducting necropsies did not definitively link observed bottlenose dolphin death directly to the oil spill prior to June 2010. Scientists are also investigating alternative causes, including the influence of an abnormally cold winter, possible paralytic shellfish poisoning, or deaths caused by viruses such as the Morbillivirus.
Several official investigations were conducted, including the Deepwater Horizon Joint Investigation (by the MMS and Coast Guard) and an investigation by the National Academy of Engineering. In addition, President Barack Obama convened a bipartisan National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling to investigate the incident. In September 2011, the Joint Investigation published its final investigative report on the accident (https://homeport.uscg.mil/mycg/portal/ep/contentView.do?contentId=323899pageTypeId=13489&contentType=EDITORIAL). In that report, the spill was blamed on multiple causes and decisions involving a series of technical and human failures as well as cost-cutting measures made by BP, the Deepwater Horizon operator Transocean and the inspections and improper relationships between government regulators and oil representatives were also highlighted during ongoing investigations. In March 2011, the National Commission released its report on the disaster, stating that the oil well blowout was the product of human error, engineering mistakes, and management failures ( http://www.oilspillcommission.gov/final-report ).
A had 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 also knew that methods used to stop the leak were unlikely to succeed, but claimed otherwise.
BP initially accepted responsibility and agreed to pay all cleanup costs, but added that the accident was not entirely its fault because the rig's owner and operator was Transocean and operations potentially related to the explosion and spill were carried out by other companies. In April 2011, BP estimated that $42 billion would be required for economic claims and restoration work. As of 2012, BP, Transocean, and Halliburton were involved in lawsuits against each other concerning responsibility for the spill as well as for costs incurred in the aftermath of the disaster.
Oil spills have the potential to not only impact health of workers coming into direct contact with crude oil and dispersants, but also volunteers, residents, and visitors, who are likely to be subjected to less direct forms of exposure. Specifically, during this disaster, hundreds of workers were treated for various medical problems during the cleanup. Symptoms were present, such as vomiting, coughing, chest pain, headaches, dizziness, nausea, and respiratory stress. Experts found that these symptoms of toxic origins are common among humans exposed to oil spills. For example, workers at the Exxon Valdez spill were treated for numerous respiratory problems during the clean-up activities and subsequently showed a higher than normal rate of chronic airway disease.
On May 31, 2010, HHS, in coordination with the Louisiana Department of Health and Hospitals, set up a mobile medical unit in Venice, Louisiana, to provide triage and basic care for responders and residents concerned about health effects of the oil spill. The goal of this medical unit was to screen workers and citizens for exposure and refer those who require further care to local healthcare providers or hospitals. The HHS Secretary activated the National Disaster Medical System (NDMS), and deployed a Medical Strike Team from Arkansas to staff the first rotation of the medical unit.
HHS worked closely with the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) to monitor for and prevent illness among both those working directly to clean up the oil as well as the general population living in the Gulf Region. Because the oil spill in the Gulf region was unprecedented, the potential short- and long-term impacts of the spill on the health of workers or the region's general population was not known. HHS established a Health Surveillance Working Group, coordinated by the National Institutes of Health's National Institute of Environmental Health and Sciences (NIEHS), to coordinate the activities of various departmental agencies engaged in surveillance and monitoring related to potential health impacts in the Gulf region. HHS worked closely with State health departments in the Gulf Region, as States are responsible for population health surveillance and have systems to monitor changes in population health status seen by hospitals and other healthcare providers.
Current scientific literature was inconclusive with regard to potential health hazards resulting from the spill. Some scientists predicted little to no toxic threat to humans from exposure to oil or dispersants, while others expressed serious concern about the potential short- and long-term impacts exposure to oil and dispersants could have on the health of responders and affected persons.
Disasters, whether natural or manmade, have adverse emotional and psychological effects on people. The nature and location of the Deepwater Horizon oil spill raised specific behavioral health issues. Gulf Coast residents have survived numerous hurricanes, including the devastation of Katrina and Rita, and previous oil spills associated with hurricanes. Re-traumatization—experiencing the repetition of a traumatic event or exposure to multiple disasters—can heighten vulnerability to other traumatic events. Following the Exxon Valdez oil spill, ecological damage was compounded by economic repercussions for the fishing and oil industries. Depression and anxiety levels increased for a period before dissipating. Among fishermen whose livelihood had been impacted, an increase in depression, anxiety, stress, substance abuse, and domestic violence was seen.
Through its Substance Abuse and Mental Health Services Administration—or SAMHSA—HHS also instituted regular calls for information sharing among State Disaster Mental Health Coordinators in the affected Gulf Coast States. The States reported spreading anxieties, frustrations about the ongoing nature of the spill and its economic impact, and fears that more severe psychological and social issues will emerge. The State behavioral health agencies have also reported longer-term stressors and economic consequences of this disaster could lead to an increase in depression, substance use and abuse, family violence, high-risk behavior, suicide, and even a resurgence of trauma symptoms from previous events. The National Institute for Occupational Safety and Health (NIOSH) created a stress information pamphlet for distribution to responders that described a range of potential stress reactions and recommendations for monitoring and addressing them.
The Medical Benefits Class Action Settlement offers benefits and compensation payments to qualifying people who resided in the United States as of April 16, 2012, who were either clean-up workers or who were residents in certain defined beachfront areas and wetlands during certain time periods in 2010.
To participate in the settlement, a person must have one or more specified physical conditions, which are acute (short-term) or chronic (ongoing) medical conditions that either first appeared or got worse within specified timeframes following exposure to oil and other substances released from the well and/or the Deepwater Horizon oil rig and its appurtenances (equipment), and/or dispersants and/or decontaminants used in connection with the response activities.
In general, the specified physical conditions must fall into the following categories:
The Medical Benefits Settlement will provide for ongoing medical consultations to all medical class members who submit a qualifying claim form. The Periodic Medical Consultation Program will begin with an initial medical visit followed by an additional visit every three years during the term of the program. Medical visits will consist of a physical examination that includes a medical, occupational and environmental history, as well as vision screening. Additional specified blood, urine, cardiac and respiratory tests will be performed at the discretion of the physician. The claims administrator will assist program participants in scheduling medical visits.
In addition, the Settlement will create a Gulf Region Health Outreach Program for the benefit of Class Members and the general public. This Program will consist of integrated projects to strengthen healthcare capacity and increase health literacy in the Gulf Coast areas of Louisiana, Mississippi, Alabama, and the Florida Panhandle. An online library of health and environmental-related materials pertaining to the Deepwater Horizon Incident will also be funded for a period of twenty-one years.
If a medical class member develops a “later-manifested physical condition,” which is a disease that is first diagnosed after April 16, 2012, and is claimed to have resulted from exposure to oil or other substances released from the well and/or the Deepwater Horizon oil rig and its appurtenances equipment and/or exposure to dispersants and/or decontaminants used in the response activities; and the exposure occurred on or before April 16, 2012 (clean-up workers), or on or before September 30, 2010 (specified veachfront residents), or on or before December 31, 2010 (specified wetlands residents), the member may either claim workers' compensation benefits or file suit against BP for the condition. BP may choose mediation; if the claim is not mediated, the member can continue the suit.
Although it may take decades, the Gulf of Mexico and its ecosystem have an enormous restorative capacity. Microbial life devours an estimated 1,000 barrels of crude oil naturally seeping into Gulf waters each day and microbes flourishing in the warm Gulf waters quickly devoured significant amounts of oil. However, there are differences in scientists' estimates of how much oil was consumed. While composed primarily of hydrocarbons, crude oil contains thousands of other chemical species in trace amounts, and bacterial responses to the particular crude spill vary. Some bacteria consume selected elements of crude, leaving residues for other bacteria or for slower physical degradation. The rate at which microbes feed on oil is also related to levels of other nutrients present such as nitrogen, phosphorus, and iron.
Several species of prokaryotic microorganisms are responsible for devouring the petroleum hydrocarbons emanating from natural seafloor seeps of oil and gas found around the world. The microbe Vibrio parahaemolyticus, common in warm Gulf waters and a rare, but known source of shellfish poisoning is an avid consumer of petroleum hydrocarbons derived from oil and methane. A related species Vibrio vulnificus, sometimes found in raw oysters, is far more pathogenic (able to cause disease). The combination of warm water and abundances of hydrocarbon food fueled nearly exponential growth rates in some areas of the Northern Gulf of Mexico. Scientists remain uncertain, however, at the real extent of the enhanced growth, whether pathogenic bacteria respond differently, how long enhanced growth rates will last, and what additional threats the higher bacterial counts pose to human health.
A challenging question for marine scientists is also whether the microbial population explosion in the Gulf will create larger hypoxic regions devoid of oxygen and life. Such “dead zone” areas already existed in the Gulf prior to the spill, but experts feared that the spill will expand the number, area, and depth of such zones.
The abundance of oil may also alter the population balances between microbes and have lasting impacts on their evolutionary development. There are also unanswered questions as to how the microbes that normally feed on oil will respond to the partially emulsified oil in large undersea oil clouds and plumes. Microbiologists initially defended the use of dispersants because reducing the droplet size of the spilled oil created a larger surface area upon which microbes could feed. Some microorganisms, including Alcanivorax borkumensis naturally feed on oil by producing their own detergentlike surfactant substances to break down oil film into more digestible micro-droplets.
Adding complexity to the analysis are the natural checks on the growth of bacteria. For example, as a consequence of the higher bacterial counts, predatory bacterial viruses and protozoa not normally pathogenic to humans, but normally effective in stabilizing the populations of pathogenic bacteria such as Vibrio, also increased in numbers.
In order to prevent such disastrous oil spills in the future, the presidentially-appointed National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling made the following recommendations:
See also Environmental Protection Agency (EPA) ; Exxon Valdez ; Water pollution .
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K. Lee P. Lerner
Revised by Judith L. Sims