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 Dispersant Decision Overview

Federal regulations establish a process for making decisions to use dispersants in response to any oil spill. The process requires input, review and approval by many stakeholders, including the responsible parties, the United States Environmental Protection Agency (EPA), the United States Coast Guard, Natural Resource Trustees, Regional Response Teams (RRT) and Area Committees for the affected areas. 

The process begins when EPA prepares and maintains a schedule of dispersants that are approved for use on oil discharges, as required by the National Contingency Plan (NCP), 40 CFR §300.900 and §300.905. Corexit is one of the 18 dispersants on the NCP product schedule. It has been used to effectively treat other oil spills, and there are many published studies regarding its potential effects on marine life. 

Use of dispersants requires additional approval from the Coast Guard's Federal On-Scene Coordinator (FOSC). When there is a spill, the FOSC determines whether and how to use dispersants in response to the conditions that exist at the time. In deciding whether to use dispersants to respond to the oil leaking from the Mississippi Canyon 252 well, the FOSC consulted with EPA and other members of the RRT, and then issued directives that govern the use of dispersants in response to the leaking well. These limit how much dispersant is used, where it can be applied, and the circumstances in which it is applied. 

When the incident occurred, Corexit was the only dispersant on the NCP product schedule that was available immediately in the quantities needed to respond to the spill. Availability is essential because dispersants are most effective on fresh oil, and become less effective when oil is allowed to weather in the ocean environment. 

The primary tools in oil spill response are containment and recovery of the oil, using mechanical methods such as containment booms and skimmers. The effectiveness of these tools depends on size and location of the release, as well as the weather. Mechanical methods work well in calm seas with few waves and in good weather, when the oil can be contained near the source in sufficient quantities to easily skim. In rough weather with high waves and other challenging conditions, mechanical methods may not be as effective. Dispersants complement skimming efforts and can be effective in conditions such as these where skimming is more difficult. 

Dispersants increase the rate at which oil mixes in the water column naturally as a result of waves, wind and other environmental conditions. They reduce the amount of oil floating on the water surface, which reduces the potential for surface slicks to reach shoreline habitats, and reduces the potential for contact with birds, marine mammals, and other species that exist on the water surface and shoreline. Dispersants are used when there are high waves and other conditions or circumstances that require response measures in addition to booms and skimmers. 

Shortly after the MC 252 well began leaking oil into the Gulf, the FOSC approved the use of the Corexit brand of dispersant on surface sheens, and the trial use of dispersants underwater, where oil was leaking out of the MC 252 well. The use of dispersants underwater, at the oil source, had the additional benefit of reducing the levels of volatile organic chemicals to which persons working on the water surface might be exposed. This improved air quality in the area immediately above the leaking well, where people were working to contain the oil, cap the well, and perform other types of emergency response. 

After several weeks of dispersant use, EPA asked BP to evaluate other dispersants on the NCP product schedule, to determine whether more effective and lower toxicity dispersants might be available. BP provided its preliminary findings to EPA on May 20. Since that time, both BP and EPA have studied the combined effectiveness and relative toxicity of alternative dispersants in more depth. 

Related links

Directives on EPA website


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