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return encodeURIComponent('Scientists attributed the persistence of oil in Prince William Sound to its being trapped in a lower, less-permeable layer of the beach.');
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return encodeURIComponent('By HENRY FOUNTAIN');
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return encodeURIComponent('January 19, 2010');
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Twenty years after the Exxon Valdez supertanker spilled nearly 11 million gallons of crude oil into Prince William Sound in southern Alaska, everything is pristine and natural again, right?
Not exactly.
A study
in 2004 estimated that perhaps 25,000 gallons of oil remained along the
sound’s gravel beaches and was degrading very slowly. So that raised a
question for researchers: Why, despite one of the largest environmental
cleanups in history, has some oil persisted?
Michel C. Boufadel, an environmental engineer at Temple University, and a colleague, Hailong Li, have provided an answer. In a paper in Nature Geoscience, they report that the oil has become trapped in a zone of low permeability below the beach surface.
“We could only answer this question by understanding the movement of water within these beaches,” Dr. Boufadel said.
Field
measurements showed that the beaches have two layers — a top one, a few
inches to a few feet thick, that is roughly a thousand times as
permeable as the layer below. The composition of the two is not very
different, Dr. Boufadel said, but it is quite likely that compaction
due to tidal forces has made the lower one less permeable.
Dr.
Boufadel said oil floating on the water remained in the upper layer
until changes in the water table allowed it to drip slowly into the
lower layer, where it remains.
“In the lower layer there’s not enough motion and not enough oxygen for the oil to degrade,” he said.
But
the oil can be released when otters or other creatures dig into the
beaches. Even in their field studies, Dr. Boufadel said, when they
would dig into deeper sediments, “the whole place would smell of oil.”
One
possibility for cleaning up the trapped oil, Dr. Boufadel said, would
be to inject chemicals into the lower layer that would promote
biodegradation.
Thoughts In Random Patterns 