Remediation efforts were stopped three years after the spill. Photo: Jim Brickett via flickr.
It's been over 20 years since the Exxon Valdez ran into a reef and spilled nearly 11 million gallons of crude oil into Prince William Sound, but according to new research published in Nature Geoscience about 20,000 gallons remain trapped in the gravel beaches of Alaska.
For those of you running for your calculators, yes it's a small fraction of one percent of the oil initially spilled, but the researchers say their findings have implications for future oil spill cleanup and that "considerable amounts of chemicals" harmful to wildlife remain:Two Layers of Gravel Keep Oil From Dispersing
What's happening is the result of the composition of the beaches affected. They have two layers of gravel: A highly permeable layer on top and a bottom layer which has very low permeability due to being compacted by tidal movement.
While the oil in the top layer was temporarily stored, it continually flowed into the bottom layer whenever the water table dropped below the place where the two layers met. Because of capillary action in the lower layer and the nearly anoxic conditions there, the oil remains trapped.
Initially oil was estimated to be dispersing at a rate of about 70% per year, but this newer research shows that rate to be just 4%. Because of that high initial estimate beach remediation was stopped in 1992.
Many of World's Beaches Have Similar Composition
As far as the implications of this for oil spill clean up, BBC News says report lead author Professor Michel Boufadel of Temple University and his team are working on ways to get oxygen into the lower layers to speed dispersal.
Prof. Boufadel says similar beach conditions could exist on tidal gravel beaches around the world and this research has "direct application for the susceptibility of beaches worldwide to long-term oil contamination and provide guidelines for remediating oil-polluted beaches."
More: Long-term persistence of oil from the Exxon Valdez spill in two-layer beaches [pay per read or subscription required]
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