The Exxon Valdez oil spill is now just past twenty years old, so today’s college students don’t remember it. Nevertheless, hopefully the event, and its ramifications, are part of their core knowledge.

Recently, it’s been shown that oil remains (how much is not really known), trapped below the sandy beach surface by capillary forces.

As reported in an abstract at the journal Nature Geoscience,

Oil spilled from the tanker Exxon Valdez in 1989 … persists in the subsurface of gravel beaches in Prince William Sound, Alaska. The contamination includes considerable amounts of chemicals that are harmful to the local fauna … . However, remediation of the beaches was stopped in 1992, because it was assumed that the disappearance rate of oil was large enough to ensure a complete removal of oil within a few years.

Here’s a government photo of some of the oil muck on a rocky beach:

Pools of Oil on Beach after Exxon Valdez Oil Spill

Pools of Oil on Beach after Exxon Valdez Oil Spill

There’s some interesting science here. First, biological remediation (or bioremediation) is a slow affair under anoxic (i.e., no dissolved oxygen) conditions. Bacteria just don’t grow (or eat) very fast without oxygen. So we ought not hold our breath if there are expectations of full clean-up under present circumstances.

Also, although oil is lighter than water, it still worked its way down beneath surface layers of sand at Prince William Sound. This is not surprising, because water at beaches gets sucked downward beneath the surface by capillary forces where waves lap the shore, pulling oil downward as well, as described in the abstract.

The extent and actual environmental effects of this trapped oil merit further consideration, to help decide if it will be worthwhile to try and stimulate biological activity there by adding nutrients (i.e. fertilizer) and perhaps getting oxygen in by mixing up the sand somehow, for example. Or see about digging it up, or leave it alone and monitor.


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