Newsgroups: sci.chem
Date: Tue, 17 Nov 1992 12:46:47 -0500 
From: Lawrence Curcio <lc2b+@andrew.cmu.edu>
Subject: Re: Oil Spills

I studied the Exxon spill at length shortly after it happened. I'm
talking from the top of my head now, years later. Perhaps the best
source on this is a report issued to the President by the (then)
Secretary of Transportation.

Anyway, the effects of oil spills will depend on many factors including:

1) The composition of the spilled mixture;

2) The environmental sensitivity of the area;

3) The cleanup equipment available at the scene;

4) The early cleanup efforts;

5) The weather;

6) The volume of the spill.

All these factors worked against the Exxon disaster. 

In the Exxon spill, the spilled mixture was heavy crude. The lighter
components of this evaporated or emulsified fairly quickly, leaving a
largely non-volatile residue consisting mostly of asphalt froth. The
Valdez effectively PAVED Prince William Sound. The mixture, especially
in the bitterly cold temperatures, was not easliy picked up by skimmers
nor by absorbants. It was not easily emulsified either. (Attempts to use
surfactants were marred by weather and human error as well.) Skimming
devices spent several times as many hours in maintenance as they spent
in the water because of weather and composition.

There is never enough cleenup equipment in any area to remediate a big
spill. Such equipment is expensive and rarely used. Oil companies call
contractors, who use their equipment nation-wide. These contractors are
mostly the oil companies themselves (who else would have the equipment),
but, again, the hardware is not all concentrated locally. It takes days
for the equipment to arrive. Thus, early containment is extremely
important. Unfortunately, Alieska's barge with the bulk of the
containment equipment was in dry dock for repairs at the time. By the
time enough boom became available, the priority had shifted from
containment to exclusion: protecting estuaries from contamination. The
Valdez had containment boom aboard, but did not deploy it effectively.

The sheer volume of the spill was another factor. It was the third
largest spill in history, and the largest by far to hit the US
coastline. Problem is that the distribution of oil spill volume is
extremely skewed, with much area under the long tail. It is, in fact,
approximately lognormal in the higher volumes. (One can actually propose
a reasonable argument that the distribution of liquids in all containers
is approximately lognormal.) It is hard to get enough data from such
distributions to tell you how much equipment you will actually need in
the long run. About one third the total volume of oil is spilled in only
about 2% of spills! The fact is, big spills are so rare that oil
companies kid themselves into believing that less equipment is needed
than actually is. People were simply overwhelmed in this case.

The area had been virtually untouched, and was particularly sensitive.

Oil certainly does persist in the local environment for long periods of
time after a spill. Material sinks to the bottom as tar balls, and can
be found in the water decades later when turbulence causes the bottom to
be stirred. The stuff undoubtedly has an impact on the benthic ecology.
Note that the very existence of crude oil is testimony to its ability to
persist in the environment. 

It should be noted that, with better weather, lighter oil, and less
sensitive ecology, cleanup is often more (though not perfectly)
successful, as the million-gallon Gulf of Mexico spill (two years later)
demonstrated. Also, the persistence of some petroleum components is no
more remarkable than the ability of other components to apparently
disappear. The jury is still out on the long term effects of oil
traportation worldwide.
Newsgroups: sci.chem