Oil Spills: the Fate of Spilled Oil
November 27th, 2007 by Kishore
Model depicting where the oil has and will travel (courtesy NOAA)
A few weeks ago, the Bay was inundated with 58,000 gallons of bunker oil. Most Bay Area beaches have been declared safe and that the threat is behind us….Thus far, they have recovered 20,000 gallons…so what happened to rest of that oil?
According to the EPA, oil undergoes 5 natural processes once spilled.
1. Weathering - chemical & physical actions that make the oil heavier than water so it sinks(generally from wave action)
2. Evaporation - lighter ingredients in the oil evaporate leaving behind heavier tar-like substances that can sink
3. Oxidation - when oxygen combines with the oil hydrocarbons to produce water soluble compounds. This typically happens around the edge of the oil slick
4. Biodegradation - when bacteria feed on the oil to break it down. Typically, this only happens in warmer water than the Bay.
5. Emulsification - Wave action forms emulsion of water and oil, just like mixing a salad dressing. The result can look like a tar ball.
What was spilled was #6 bunker oil, which is an extremely heavy oil. Only 5-10% was expected to evaporate over the first day. In addition, the specific gravity, the relative density compared to water, is about 0.95 to 1.05. That means a fair amount will sink to the bottom of bay.
So when only half of the oil gets recovered, we can safely assume a fair amount has sunk to the bottom of the bay, a fair amount just diffuses along the surface, and finally a fair amount is stuck to shore.
Takeaway:
Clean is a relative term. That oil will be around the bay for YEARS…..just lying below the surface.
More Info:
Cosco Busan Cleanup Site
EPA Oil Spill Education Center
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