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Report - Technical

DATE  4 October, 1984  To  Capt. Timothy McKinna   MSO, Port Arthur   Capt. Kyle Shaw
MSO, Galveston  From  Lt. Todd Baxter   NOAA SSC  Subject Questions on dispersant use
during the ALVENUS spill incident. Several NOAA Spill Reports have been generated which
deal with the subject of dispersant usage, or were used in the decision not to attempt
dispersion of the ALVENUS oil at the spill site. Since both the ALVENUS incident and the
general subject of dispersant usage are scheduled topics for the upcoming RRT meeting, I
have attempted to briefly review the major considerations which led to the decision not to
apply disparsant to the ALVENUS oil. Environmental considerations-  The resources at risk
and dispersant use scenarios were available quite early in the spill (References 3,7 and
27). In addition, resource agencies were informally polled during an RRT conference call
on 31 August 1984. The overall reaction of the RRT representatives was mixed, but no
single agency actively opposed the test application of a dispersant to the spill. The
pivitol point in the discussion was if an available dispersant would be effective on the
Merey-Pilon oil. Physical Considerations-  To be effective any dispersant chemical must be
able to penetrate an oil slick to reach the oil-water interface. This penetrating ability
is influenced by the chemical composition of the dispersant, the wind and wave energy
present, and the consistency of the oil to be dispersed.  At the ALVENUS two types of oil
were involved in the spill, Merey and Pilon. The Merey oil is slightly lighter than the
Pilon. When mixed together by the spill the two oils were indistinguishable, and exhibited
the highly viscous characteristics of the Pilon stock. This high viscosity (later found to
be 52,000 cs, Reference A) was one of the major factors which indicated that dispersants
would not have a signifigant effect on the oil.   The sea state during the period of the
spill when dispersant application was desirable was too calm to assist in breaking the
surface trension of the slick. In fact, the slick was so coalescent that the rotor wash
from a helicopter hovering close over the slick could not break through the slick to
expose the water below. As a result a well defined, and heavy slick 300 feet wide and 70
miles long formed from the spilled oil.  Oil spill responce agencies in the United States
have had very limited first hand experience in the actual use of spilled oil dispersants.
The reasons for this lack of experience are numerous, with political and administrative
obstacles being the most obvious. This lack of field experience on our part makes us rely
quite heavily on the opinions and experiences of foreign response personnel who have had
the opertunity to obtain experience through actual use. In this case the representatives
from ITOPF, such as Captain Mike Garnett, were available to provide an experienced opinion
on the question of dispersant usage. The opinion of Captain Garnett was that the available
dispersant, Corexit 9527, was not capable of penetrating the slick, and would have had
little effect on the oil as a result. His opinion carried considerable weight in the final
decision not to apply dispersants. Cost-Benifit Considerations-  Dispersant use was very
actively considered during the first days of the spill when trajectory forcasts indicated
that oil could reach the sensitive Calcasieu Pass area. As the trajectory forcasts
developed and showed the oil tending to the south and seaward, the consideration of
dispersant use had become a moot point due to the size and condition of the oil slick. The
ideal time to apply a dispersant, assuming it would be effective had passed for all
practical purposes.  If the dispersant was applied and had been only partially effective,
a large quantity of oil would still have reached Galveston Island. Dispersion might reduce
the quantity, but not the geographic distribution of oil landings. Based on simple cost
considerations, it would have been a great saving to the ALVENUS to use dispersants,
assuming they would be effective. But, if only half of the oil was removed by dispersion,
the other half would still have impacted Galveston Island. An unsuccessful attempt at oil
dispersion would have diverted funds away from the beach cleanup efforts yet to come.
Conclusion-  With no clear cut potential for environmental damage (once the oil was moving
away from the Calcasieu), and the low probablity of dispersant success, the decision not
to use dispersants was sound. The funds that would have been used on the dispersant
application were better spent on cleaning of beaches that would have been polluted even if
the dispersant had been partially successful.   References- NOAA Spill Reports for Spill
4, MV ALVENUS:  1 July 30 Trajectory 2 July 31 Trajectory and Dispersant notes. 3
Resources at Risk, by RPI. 4 Revised July 31 trajectory, by MASS. 5 Revised August 1
Trajectory, by MASS. 7 Living Marine Resources at Risk, by RPI. 27  RPI Dispersant Use
Scenario, by PRI.  Other Reports:  A Summary of Chemical Analysis and Physical
Properties...ALVENUS Oil Spill. Dan McNabb, Chemist , Science Applications Inc., September
4, 1984.  B CONOCO Information Sheets,"Crude Properties of Merey, Pilon". Obtained from
Mr. Jim Leeman, Conoco Oil Co., Houston, Texas.