GuLF Study Environmental Health Sciences (NIEHS), part of the National Institutes of Health, and aims to recruit 55,000 of the 150,000 workers who volunteered or were employed to help clean up the spill. It is led by Dale Sandler, head of the NIEHS's epidemiology branch. The "Deepwater Horizon" oil spill was the world's largest accidental marine oil spill. It began on 20 April 2010 after an explosion on the "Deepwater Horizon", a drilling rig leased by BP to drill an exploratory well. Between then and 15 July, when the well was capped, over four million barrels of oil (around 170 million US
Volume and extent of the Deepwater Horizon oil spill silts and sands onshore. On 26 May 2011, the Louisiana Department of Environmental Quality extended the state of emergency related to the spill. In April 2012, oil was found dotting of Louisiana's coast. As of December 2012, of coastline remain subject to evaluation and/or cleanup operations. On 15 May 2010, researchers from the National Institute for Undersea Science and Technology, aboard the research vessel "RV Pelican", identified oil plumes in the deep waters of the Gulf of Mexico, including one as large as long, wide and thick in spots. The shallowest oil plume the group detected was at about ,