US releases first subsea BP spill report

Research vessel Brooks McCall sampling stations, 8-25 May, 2010. (Image: NOAA) Research vessel Brooks McCall sampling stations, 8-25 May, 2010. (Image: NOAA)
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The first analysis about subsea monitoring in the Deepwater Horizon vacinity has been released.

The report contains analysis of samples taken by the R/V Brooks McCall, a research vessel conducting water sampling from half a mile to nine miles of the wellhead. Its data has been used on an ongoing basis to help guide the US government’s decisions about the continued use of subsea dispersant.

The report comes from the Joint Analysis Group (JAG), which was established to facilitate cooperation and coordination among the best scientific minds across the government and provide a coordinated analysis of information related to subsea monitoring in the Gulf of Mexico.

This comprehensive analysis helps define the characteristics of the water and presence of oil below the surface in the area close to the well-head from 8-25 May.

The JAG report, which can be found on the NOAA website, contains data analysis of dissolved oxygen levels and presence of total petroleum hydrocarbons from water samples and oil droplet size – tests that EPA, the US Coast Guard, and NOAA use to determine whether dispersant is likely being effective and whether it is having significant negative impact on aquatic life.

The report concludes that decreased oil droplet size in deep waters is consistent with chemically-dispersed oil. It also shows that dissolved oxygen levels remained above immediate levels of concern, although there is a need to monitor dissolved oxygen levels over time. 

The report also confirms the existence of a previously discovered cloud of diffuse oil at depths of 3,300 to 4,600 feet near the wellhead.  

Preliminary findings indicate that total petroleum hydrocarbon (TPH) concentrations at these depths are in concentrations of about 1-2 parts per million (ppm).  Between that depth and the surface mix layer, which is defined as 450 feet below the surface, concentrations fell to levels that were not readily discernable from background levels. 

The tests detection limit is about 0.8 ppm. Analysis also shows that this cloud is most concentrated near the source of the leak and decreases with distance from the wellhead. Beyond six miles from the wellhead, concentrations of this cloud drop to levels that are not detectable.

Dispersant has been used as part of the overall strategy to prevent more oil from impacting the Gulf Coast’s fragile wetlands, marshes and beaches by breaking up the oil and speeding its natural degradation offshore. 

EPA has required BP to undertake rigorous monitoring of dispersant use to ensure it continues to be effective and does not negatively impact the environment. EPA posts data from these and other monitoring missions daily online. This data will continue to inform the federal government's actions.

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