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Report - Technical

(NOTE- THIS IS A LATE ENTRY TO THE SPILL SYSTEM. IT WAS COMPILED BY RPI  ON JULY
30, 1984 AS A COMPANION PIECE TO SPILL REPORT NO. 6, AND WAS  DISTRIBUTED IN THE
USER FILES AS 'GULFSPILL'. ENTERED BY TODD 10-4-84)  .  Dispersant use scenario
 .  The use of dispersants on a spill of this size and type would have  several
immediate effects.  The use of dispersants could result in  the diminution of
impacts to intertidal habitats such as sand  beaches and exposed coastal
marshes, but may result in some  limited (but difficult to predict) impacts to
subtidal habitats  and organisms such as seagrass beds, marine fin- and 
shell-fisheries. At this time jacks and mackeral are reported to  be spawning in
the area. The impacts to these subtidal resources  will be reduced with
increasing depth. Dilution into the ocean is  the primary goal of dispersant
application, so if dispersants are  applied it should be done as far from shore
as possible, in water  depths of 10 fathoms  or more.  Also, timing of
dispersant  application is critical because dispersants is more effective on 
oil that is fresh. The location of the tanker appears to be within  the 10
fathom line, but it is fairly close.  .  The shoreline in this area appears to
be dominated by sand  beaches, which are not highly sensitive to oil.  Any
exposed  marshlands will be very sensitive, as will any sheltered estuarine 
areas.  .  Application of dispersants to a slick located several miles  offshore
would cause the introduction of oil into the upper water  column to a depth of
less than approximately 10 meters.  Exposure  of shrimp and fish in this area
might result in some toxic  effects, but this would probably be relatively short
lived.  Concentrations of oil that would cause toxicity to shrimp range  from
0.5 to 20 parts per thousand depending on the oil type, with  the upper range
probably being more likely for Venezuelen crude  oil.  The use of dispersants
would probably cause local oil  concentrations of at least this range, but
should rapidly decline  with distance from the application site.  .  Shrimping
occurs in the offshore areas up to 40 fathoms, but is  closed in all the Texas
coast bays, as is Calcasieu Pass.  The  primary species caught are white and
brown shrimp, and harvesting  occurs day and night.  Harvesting of shrimp occurs
from the  shoreline (2-3 fathoms) out to approximately +30 miles (40 fathom 
line).  The time of peak shrimp larval abundance is from August to  October.  In
addition to shrimp, there are larval forms of many  different species present in
the area.  These organisms are very  sensitive to oil.  .  Menhaden fishing is
the primary finfish catch in this area, and  this time of year is the peak
fishing season. This species forms  large schools that congregate near the
surface of the water.  .  Water movement in this area is controlled primarily by
wind driven  currents.  The longshore current will vary with location along the
 coastline due to the presence of coastal eddies. Average surface  current
velocities in this area range from 0.7 to 1.0 knots.  Farther offshore the Loop
Current dominates with easterly water  flow.  The present wind direction is
towards the west, at a speed  of 10-15 knots.  The general direction of flow
will be in that  direction for now.  This condition is unusual for this time of
 year and may change.  The application of dispersants will cause  the oil to
flow with the upper water column and should become  entrained in the eddies
mentioned above.  This would result in a  general offshore movement of oil,
rather than eventual landfall if  no dispersants were used.  For more
information call Gene Nakamara  (904) 234-6541.  .  .  No Dispersant Scenario 
If the decision is made to not use dispersants on this spill, the  resources at
risk will consist mainly of the exposed marshlands  and resident bird
communities.  Large volumes of oil floating on  the water surface can result in
severe impacts to coastal wetlands  and birds.  The Louisiana coastline has
large areas of wetlands  which are very sensitive to oil.  The Texas coastline
is dominated  by barrier islands backed by large estuarine areas.  The outer 
beaches are not highly sensitive but oil entering the passes  between island
could impact nesting birds, shellfish beds, and  marshlands.  Protection
strategies would be similar to those use  during Ixtoc 1 and focus on preventing
oil from entering the  passes. See our response of 30 July for more info since
that was  written with the intention of not using dispersants.