Gulf Oil Spill: After It Hit Beaches, Where Did It Go?

Sept. 18, 2010— -- On a morning stroll down the serene beaches of Grand Isle State Park, a visitor can watch as waves quietly lap the shore, birds sail overhead, a porpoise pokes above the water.

Yet it takes only minutes of digging into the sand to reveal a menace that experts say permanently threatens this picturesque landscape: pools of crude oil lurking less than a foot below the surface.

The April 20 explosion of an oil rig in the Gulf of Mexico released an estimated 205 million gallons of oil into these waters. It remains unclear how much oil was actually recovered, how much remains, and -- most important for the fragile coastal ecosystems -- where it ended up.

A report published in August by the National Oceanic and Atmospheric Administration (NOAA) concluded that 74 percent of the oil has been recovered, evaporated, or naturally dispersed, leaving a residual 26 percent "on or just below the surface" of water or in sand.

But many scientists question the validity of that report, saying that, due to the unprecedented scope of the spill and the record volume of dispersants used to mitigate its impact, it is too soon to make any determination about where or when the oil landed.

Recently, NOAA itself has indicated that the report is a work in progress.

Ron Kendall, director of The Institute of Environmental and Human Health at Texas Tech University in Lubbock and a member of the assessment team for the Exxon Valdez spill in 1989, says it will take "extensive environmental sampling" over a period of years to determine how much oil is embedded into coastal habitats, and where.

Oil that remains trapped under a marsh or buried beneath a beach is particularly threatening because the lack of oxygen will prevent bacteria from breaking down the oil, meaning "it will be there for all time," says Nancy Kinner, codirector of The Coastal Response Research Center at the University of New Hampshire in Durham.

Twenty-one years after the Valdez spill, oil remains submerged in the beaches of Prince William Sound in Alaska.