Subsea Dispersant Application records collected during the Deepwater Horizon (DWH) accident near the Mississippi Canyon block 252 wellhead from April 30 to July 22, 2010

The use of dispersants began shortly after the Deepwater Horizon (DWH) accident occurred in April of 2010, and ended shortly after the Mississippi Canyon lease block 252 (MC-252) well was capped in July 2010. The U.S. Coast Guard Federal On-Scene Coordinator (FOSC) and U.S. Environmental Protection Agency (EPA) authorized their use to disperse oil that could not be removed by other methods, with the goal of reducing the amount of oil in areas where persons were working onsite to cap and contain the well, and reducing the amount of oil that reached nearshore and shoreline habitats. Dispersants were applied underwater at the source of the leaking well, located nearly 50 miles offshore. EPA, BP, and others collected samples of water and air around the areas where dispersants were used, and along the Gulf shoreline, to determine whether any person or marine life was exposed to potentially significant levels of the dispersants or dispersed oil. This report contains information about subsurface dispersant use, and provides additional context for the posted dataset. During the Response to the DWH accident, dispersant was applied by subsurface injection into the oil plume emanating from the MC-252 well at different injection points that changed over time. Subsurface dispersant injection was one of the operational response strategies to reduce the amount of oil in the area where people were working to cap and contain the well, and to reduce the overall impact of released oil to the environment. Corexit EC9500A dispersant was injected at a known pumping rate and volume from the Subsea 7 vessel Skandi Neptune into the oil plume. Feasibility studies to evaluate the effectiveness and potential effects of subsea dispersant use were conducted between April 30 and May 15, 2010. Subsea injection continued on days and at times when it was approved for use, until the well was capped on July 15, 2010. A final subsurface release of dispersant occurred on July 22, 2010 when the discharge line was disengaged. The focus of this data posting is subsurface dispersant application records. These data have been compiled in a database that includes reporting period, average dispensing rate (gal/min), daily dispersant dispense volume, and cumulative total dispense. A map was produced to show the location of the subsurface dispersant injection. The parameters provided in this data posting for the subsurface dispersant application include: • Reporting period • Average subsurface dispersant dispensing rate during reporting period • Volume of subsurface dispersant dispensed during reporting period • Cumulative volume of subsurface dispersant dispensed.