Controversial federal estimates of how much oil remained in Gulf in July were mostly accurate, study says
By Mark Schleifstein, The Times-Picayune
Tuesday, November 23, 2010, 11:58 AM A peer-reviewed report on the controversial federal estimates of how much oil from the Deepwater Horizon oil spill disaster remained in the Gulf of Mexico in mid-July found that the estimates were largely accurate, National Oceanic and Atmospheric Administration Administrator Jane Lubchenco said Tuesday. Lubchenco and other Obama administration officials released a pie chart on Aug. 4 that concluded that 26 percent of the 4.9 million barrels of oil released from the Macondo well remained as “residual,” on or just below the surface as light sheen and weathered tarballs, washed ashore or buried in sand and sediments. The original report relied on the results of the government’s “oil budget calculator” that was created as a tracking system for the gushing oil, and was being used to direct response and clean-up operations, including the use of offshore in-situ burns of surface oil and of dispersants. The new report does not address how much oil remains in the Gulf today or the ultimate impact of the oil release, Lubchenco said. That information is awaiting the compilation of results of more than 125 sampling expeditions using 25 deepwater vessels, which have produced 30,000 water and sediment samples from areas along the coast from the Texas-Louisiana border to the Florida Keys and 300 miles out to sea, she said. … The biggest change in the new report is in the estimate of the amount of oil that was turned into tiny droplets by chemical dispersants. The original report said 16 percent of the oil had been naturally dispersed, while 8 percent was chemically dispersed. Tuesday’s report found that 16 percent of the oil was chemically dispersed and only 13 percent was naturally dispersed. The additional oil moved into the chemically-dispersed category included 2 percent that was originally thought to have evaporated or dissolved, reducing that category to 23 percent, and 3 percent from the “residual” category. Remaining the same were estimates of the amount of oil that was directly recovered, 17 percent; burned, 5 percent, and skimmed, 3 percent. Lubchenco said information from sampling taken during research cruises helped the authors of the new report in changing the estimates. The new report, authored by scientists with the U.S. Geological Survey, National Institute of Standards and Technology and NOAA, reduced to 23 percent the amount of residual oil. But Lubchenco said both the earlier estimate and the new estimate were within the range of error calculated in the new report. …
