Study: Gulf sheens likely came from rig wreckage
By MICHAEL KUNZELMAN
NEW ORLEANS — Pockets of oil trapped in the wreckage of the sunken Deepwater Horizon are the likely source of oil sheens that have been spotted in the Gulf of Mexico near the site of the deadly 2010 explosion on the BP-leased drilling rig, a team of researchers concludes in a newly published study.
The study by researchers from the Woods Hole Oceanographic Institution and the University of California at Santa Barbara rules out BP’s sealed-off Macondo well — the site of the nation’s worst offshore oil spill — and natural oil seeps as possible sources.
The researchers said their conclusions are based on an analysis of 14 sheen samples collected from the surface of the water during two trips to the Gulf. Their study, funded in part by the National Science Foundation, was published online this week in the Environmental Science & Technology journal.
BP and federal officials already have identified the rig’s wreckage as the likely source of the persistent sheen and said there was no evidence that the plugged well was leaking. Last year, BP said it capped an abandoned piece of equipment that was believed to be the culprit.
One of the study’s lead scientists said environmental and legal concerns made it important to determine where the oil was coming from.
“First, the public needed to be certain the leak was not coming from the Macondo well, but beyond that we needed to know the source of these sheens and how much oil is supplying them so we could define the magnitude of the problem,” Woods Hole chemist Chris Reddy said in a statement.
The researchers say the samples they collected contained trace amounts of industrial chemicals that are used in drilling operations and weren’t detected in samples taken directly from the Macondo well. That meant that the samples had to come from a single source that contained both the oil and the chemicals, Dave Valentine, a professor of earth science at UC-Santa Barbara, said in a statement.
“This pointed us to the wreckage of the rig, which was known to have both, as the most likely source for the sheens,” he said.
BP said in a statement Tuesday that recent surveys have shown “minimal to no sheening” in the area where the rig exploded in April 2010, killing 11 workers.
The Coast Guard has said the sheen could not be recovered and did not pose a risk to the shoreline.