IncidentNews Home  >>  Incident  >>  Entry

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.