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Report
on visit to OHMSETT to observe Exxon/MMS
Cold-Water Dispersant Tests March
5-6, 2002 By
Stan Jones Public
Information Manager Prince
William Sound Regional Citizens’ Advisory Council OHMSETT
stands for Oil and Hazardous Materials Simulated Environmental Test
Tank. It is on the grounds
of Naval Weapons Station Earle, in Leonardo, New Jersey.
It is a Minerals Management Service facility operated under
contract by MAR Inc. The
test tank is a rectangular concrete basin 667 feet long, 65 feet wide,
and 11 feet deep. Water
depth is maintained at 8 feet. For
the Exxon tests, a boomed enclosure measuring 35 feet by 100 feet was
floated in the tank. The
tank is equipped with a traveling bridge that extends across the width
of the tank and is propelled along the length of the tank by steel
cables on the sides of the tank. This
bridge includes an enclosed, heated cab where the technicians work who
conduct the tests. They
record data in notebooks, take pictures, and monitor a video camera set
up to record each test from beginning to end.
The
bridge is also the platform where equipment is installed to conduct the
tests. In the case of the
Exxon tests, the main equipment installed on the bridge was as follows: ·
A sprayer on the leading edge of the bridge to lay down the crude
oils used in the tests. ·
A sprayer on the trailing edge to lay down dispersant. ·
Containers of crude oil and dispersant. ·
Two large fire-hose type nozzles used to spray water for herding
oil into the corner of the boom enclosure for recovery by dipping with a
ladle
The
tank water has a salinity of 3.5 parts per thousand, according to
OHMSETT personnel. Ordinarily
it is chlorinated to keep down algae and other organisms in the tank,
but chlorination was suspended for this test. For
these cold-water tests, the system also included a chiller to keep the
water temperature between 31-33F.
On
March 5, the morning low was 18 degrees and the salt-water tank had ice
on it at the start of the day. Temperatures
during the day were in the 20s, by my estimate, with winds from
15-30mph. On March 6,
temperatures were in the 40s and low 50s, but the wind was stronger,
probably gusting over 30mph. Each
test I saw was conducted the same way: The
bridge was positioned at the beginning of the boomed enclosure. The bridge began to move, and simultaneously oil and
dispersant began to be sprayed into the boomed enclosure.
Because the dispersant sprayer trailed the oil sprayer, oil was
sprayed with dispersant within a few seconds of hitting the water.
Randy
Belore and others involved in the tests said that typically 22-25
gallons of oil was laid down, giving a 1mm slick.
For most of the tests, approximately one-half gallon of
dispersant was laid down, giving a nominal ratio of 40:1 to 50:1.
For other tests, however, the amount of dispersant was reduced to
achieve a ratio of approximately 70:1, as one goal of the tests was to
see what was the lowest dispersant ratio that would be effective. (Note:
Above, and throughout this report, the quantities I report are
approximate and were conveyed to me orally.
I did not examine or copy data sheets, as Exxon and MMS agreed to
provide us with test results, along with the test plan and the official
videos recorded at the time of the test.) When
the bridge reached the end of the boomed enclosure, it halted and
spraying was stopped. The
wave generator was started and within a minute or two the boomed
enclosure was receiving the kind of waves described above.
Wave-making
continued for one hour, during which time the dispersant worked on the
oil and some oil usually escaped the boomed enclosure.
Then the wave generator was turned off and any oil remaining in
the enclosure was herded to a corner of the boom and ladled into a
bucket for analysis.
For
these tests, dispersant effectiveness was calculated by measuring the
oil recovered at the end and comparing it with the amount of oil laid
down by spraying. I
confirmed with Randy Belore that natural dispersion was assumed to be
zero, and that evaporation was ignored, though he said it could run 5-10
percent. (See below for
comments on these and other assumptions that appeared to compromise the
results of these tests.) Belore
said fluorimetry was not performed because the size of the tank would
have made it prohibitively difficult to get meaningful results. During
the two days I was at OHMSETT, I observed four tests.
Each will be summarized separately below, but the general
features of each were the same: Soon
after wave action began, the amount of visible oil on the surface of the
water decreased rather quickly. In
the early tests, when the water was fairly clear, it was possible to
observe a “brown cloud” (as the people at the facility called it)
spreading down into the water and expanding horizontally.
The people at the facility said this brown cloud was dispersed
oil. In
the later tests, the water in the tank was so clouded from the earlier
tests that it was not possible to observe anything but surface
phenomena, which consisted primarily of a reduction in the amount of
visible floating oil, and of oil escaping containment due to wave action
or leakage out of boom corner joints. At
the end of one hour of wave action, the remaining oil was herded to a
corner of the boom enclosure and ladled into a five-gallon plastic pail
for analysis. In all cases,
the amount of recovered oil appeared to be quite small – less than a
gallon probably, though that should be confirmed when test results are
furnished to us. Morning,
March 5:
This was a test of Corexit 9527 on fresh ANS crude.
Randy Belore estimated the oil:dispersant ratio for this test
would be 40:1 or 50:1. (The
actual ratio was computed after the test based on drawdown of oil and
dispersant from their containers and should be available in the test
results.) Afternoon,
March 5: This
was a test of Corexit 9527 on weathered ANS crude. The ratio was to be
40:1 or 50:1. Morning,
March 6: This
was a test of Corexit 9500 on fresh ANS crude, but with less dispersant
than the previous day. Belore
estimated the oil:dispersant ratio was about 70:1 for this test. Afternoon,
March 6: This
was a test of Corexit 9500 on 20 percent weathered ANS crude.
Dispersant ratio was 30:1 or 40:1. Methodological
issues: Based
on my observation of the tests, there were several issues that could
cloud the reliability of the calculated effectiveness of the
dispersants. The test
results should be examined carefully to see if any of these issues were
addressed or corrected, but, as of my visit, here they are::
4.
Because the water was not cleaned, dispersed oil was allowed to
accumulate in it. As a
result, by the second day of my visit, the water was quite cloudy and
had taken on a greenish brown color, with patchy sheen visible on the
surface. Belore said no
attempt would be made to calculate the affect of dispersed oil already
in the water on subsequent tests, but he asserted that the total volume
of dispersant used in this series of tests would not be enough to create
an appreciable concentration in a tank with a volume of more than 2
million gallons. 5.
As mentioned above, winds were quite strong on both days of the
test, but particularly on the second day, when I would estimate they
reached 35-40mph during the gusts. It
seems likely that winds this strong would increase evaporation of the
oil, as well as increasing wave action, which would increase dispersion,
whether chemical or natural. If
there were large variations in wind speed over the two weeks of testing,
that would seem to make it hard to compare results of the various tests. In
particular, it appeared the wind may have affected the third test I saw,
which involved a reduced amount of dispersant (approx. 70:1) in an
effort to ascertain the lowest effective ratio.
To reduce the amount of dispersant being applied to the oil, the
nozzles on the sprayer were adjusted to give a very fine mist.
It appeared to me the wind may have carried some dispersant
outside the boomed enclosure (which would mean the true oil:dispersant
ratio was even lower than 70:1). # # # Randy
Belore and Exxon’s Jim Clark said the purpose of these tests was to
measure the effectiveness of dispersants in cold water for comparison
with the shaking-flask cold-water tests.
(Our name wasn’t mentioned, but presumably they mean our tests
at Auke Bay.) Joe
Mullins said preliminary results of these tests would be presented at
AMOP in Calgary. Belore said detailed results of earlier Exxon tests in a
small tank would be presented. Mullins
said EPA was interested in the OHMSETT tests with an eye to calibrating
the wave energy and somehow relating it to the flask test used to
measure dispersant effectiveness. The
still photographs in this report were taken during the fourth test I
witnessed. I shot digital
video of the first three tests. That video, along with all my photographs, will be passed on
to Lisa Ka'aihue. The End
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