Gulf oil spill: After it hit beaches, where did it go?, Christian Science Monitor, September 15, 2010:
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. ...
The risks of having oil hidden so deep below the surface are numerous... Drinking water is degraded; the food chain is affected because organisms like mussels and crustaceans are threatened...
Oil that makes its home below sand is also vulnerable to seasonal storms, which means it is potentially mobile and can represent “a new release of oil into the environment” when it returns to the freshwater table, Kinner says.
Frank Galgano, chair of the geography and environment department at Villanova University near Philadelphia, says ... “That’s the most insidious part of that [coastal] oil that’s trapped. Eventually, over many years, it’ll seep lower and lower into the system,” he says.
Read the report here.