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May 14, 2010 10:18 AM by Sharlee Jacobs

Where's the oil? Model suggests much may be gone..

NEW ORLEANS (AP) - For a spill now nearly half the size of Exxon
Valdez, the oil from the Deepwater Horizon disaster is pretty hard
to pin down.
Satellite images show most of an estimated 4.6 million gallons
of oil has pooled in a floating, shape-shifting blob off the
Louisiana coast. Some has reached shore as a thin sheen, and gooey
bits have washed up as far away as Alabama. But the spill is 23
days old since the Deepwater Horizon exploded April 20 and killed
11 workers, and the thickest stuff hasn't shown up on the coast.
So, where's the oil? Where's it going to end up?
Government scientists and others tracking the spill say much of
the oil is lurking just below the surface. But there seems to be no
consensus on whether it will arrive in black waves, mostly
dissipate into the massive Gulf or gradually settle to the ocean
floor, where it could seep into the ecosystem for years.
When it comes to deepwater spills, even top experts rely on some
guesswork.
One of their tools, a program the National Oceanic and
Atmospheric Administration uses to predict how oil spills on the
surface of water may behave, suggests that more than a third of the
oil may already be out of the water.
About 35 percent of a spill the size of the one in the Gulf,
consisting of the same light Louisiana crude, released in weather
conditions and water temperatures similar to those found in the
Gulf now would simply evaporate, according to data that The
Associated Press entered into the program.
The model also suggests that virtually all of the benzene - a
highly toxic flammable organic chemical compound and one of the
chief ingredients in oil - would be stripped off and quickly
vaporize.
The model was not designed for deepwater spills like the one at
the Macondo well in the Mississippi Canyon now threatening the Gulf
Coast. But experts said the analysis might give a close
approximation of what is most likely happening where the oil plume
is hitting the surface nearly 50 miles south of Louisiana.
The size and nature of the spill also has been altered by
response efforts. So far, about 436,000 gallons of chemicals have
been sprayed on the oil to break it up into smaller droplets and
about 4 million gallons of oily water have been recovered.
Of that recovered mixture, at least 10 percent is oil, BP and
NOAA said. Smaller amounts of oil also have been collected after
washing ashore, and crews have burned a negligible quantity off the
surface.
That would leave as much as 2.7 million gallons at sea as of
Friday, with about 210,000 gallons coming up from the well every
day.
The 210,000 gallons figure - specifically, about 5,000 barrels -
comes from NOAA and has frequently been cited by BP PLC and the
Coast Guard. Some scientists have said based on an analysis of BP's
video of the leak that the flow rate is much higher, while others
have concluded the video is too grainy to draw any such
conclusions.
Even with computer models and history as guides, uncertainty
reigns.
Doug Helton, the operations coordinator for NOAA's Office of
Response and Restoration, said the agency was uncertain how much
oil would sink to the bottom. For now, most of it is near the
surface.
"This oil is coming from the sea floor and coming up to the
surface in droplets and then once it comes to the surface it
re-coelesces as a slick," he said.
Ed Overton, a Louisiana State University chemist who's analyzed
the spill for NOAA, said he thinks most of the oil is within a foot
of the surface.
"Ultimately, you could have a lot of oil on the shoreline. It
won't be a black tide coming in, it will be globs coming ashore,"
he said.
"It's going to be a long, slow summer."
Wilma Subra, a chemist and MacArthur Fellow affiliated with the
Louisiana Environmental Action Network, said there was a risk that
the effort to break up the oil with dispersants would simply sweep
it to the ocean bottom and contaminate the food chain, a
possibility that has shrimpers on edge.
Merv Fingas, who has studied oil spills for 35 years and has
worked for Environment Canada, that nation's environmental agency,
predicted a bit of both: some would wash up, and some would stick
to sediment and mud and sink slowly to the bottom, much of it
likely settling near the spewing well.
"That's the fate of a lot of oil spills: sedimentation on the
bottom," Fingas said.
Overton disagreed, saying the oil from the Deepwater Horizon
spill is too light to sink all the way.
A common refrain among experts and officials is that every oil
spill is unique.
Larry McKinney, director of the Harte Research Institute for
Gulf of Mexico Studies at Texas A&M University-Corpus Christi, said
the Deepwater Horizon spill reminds him of the last catastrophic
oil flood in the Gulf.
In 1979, Mexico's Ixtoc I in the western Gulf blew out and
spewed about 420,000 gallons of oil a day for nine months. Large
quantities of oil did not reach Texas beaches.
"This was a problem we ran into with Ixtoc, we never found the
oil," McKinney said. "But I think even today if you dig down in
some sandy beaches you can find a layer of Ixtoc oil."

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