Frank Galgano, chair of the geography and environment department at Villanova University near Philadelphia, says oil embedded in the ocean floor is much more stationary because of the sheer depth and the frigid temperatures, but coastal oil "is just not going to sit there."
The hydraulics particular to each coastal system can potentially shift the oil to deeper layers in the sediment. "That's the most insidious part of that oil that's trapped. Eventually, over many years, it'll seep lower and lower into the system," he says.
One way being developed to quickly degrade trapped oil is biomediation, in which oxygen is injected into the sand through trenches or spraying. Michel Boufadel, chair of the department of civil and environmental engineering at Temple University in Philadelphia, is working with NOAA to implement the technique.
He says past cleanup efforts "looked at the beach like a box" and ignored the fact that it is a continually moving organism that needs to be treated according to its particular characteristics.
So far, NOAA's directives for Gulf Coast beach cleanup include cosmetically washing surface contamination, collecting tar balls, and removing the top layers of certain areas where oil is concentrated.
John Tarpley, chief scientific support coordinator for NOAA, says the agency's goal is to clean beaches so they have "1 percent of oil or less." Highly trafficked public beaches are a priority, he adds. However, environmentalists warn that the departure of cleanup crews will not mean the beaches have a clean bill of health.
"They will never clean it all up,'' says Doug Inkley, a senior scientist for the National Wildlife Federation. "It is impossible to remove all the oil from the environment. That cannot be done."