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
Gulf of Mexico Coast Guard Rear Adm. Sally Brice O'Hare stated that the U.S. government will be "employing booms, skimmers, chemical dispersants and controlled burns" to combat the oil spill. By May 1, 2010, the oil spill cleanup efforts were underway, but hampered by rough seas and the "tea like" consistency of the oil. Cleanup operations were resumed after conditions became favorable. On May 27, 2010, The USGS had revised the estimate of the leak from to 12,000– an increase from earlier estimates. On July 15, 2010, BP announced that the leak stopped for the first time in 88 days. In July 2015