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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.