Fate and Effect Studies
of
Shell Oil Spill - December 1970
Executive Summary
RESOURCES TECHNOLOGY CORPORATION • 1275 Space Park Dr., Suite 111. Houston. Texas 77058 • A/C 713—488-0817
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EXECUTIVE SUMMARY
A Synopsis of Fate and Effect Studies
Of the Shell Oil Spill Platform B,
Block 26, South Timbalier Bay
January 1972
Prepared By:
RESOURCES TECHNOLOGY CORPORATION
1275 Space Park Drive, Suite 111
Houston, Texas 77058
(Contract 68-01-0051)
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Executive Suninary
Introduction
This study was accomplished for the Environmental Protection
Agency by RESOURCES TECHNOLOGY CORPORATION under Basic Ordering Agree-
ment NO. 68-01-0051. Its purpose was to assess the fate and effects of
the crude oil spill which resulted from a blowout on Shell Oil Company,
Platform “B” in Block 26 approximately 7 miles offshore of South Timbalier
Bay on December 1, 1970. Eleven of the twenty-two producing wells were
Involved in the incident.
obtained from three field
incident. Their purpose
material, the fate of
biota of the area. They
• Oceanographic and Remote-Sensory Survey by Texas
Instruments, January 1971.
• The joint physical, chemical, and biological sampling
surveys conducted by an EPA team in Caminada Bay—
Barataria Bay and by a Resources Technology Corporation
team on three transects across Shell Platform “B” In
the Gulf of Mexico June of 1971.
Laboratory analyses were conducted by RESOURCES TECHNOLOGY COR-
samples collected in the vicinity of Platform “B” as well as
inshore bay samples.
In addition to the three cited studies, an extensive background
data base was developed by RESOURCES TECHNOLOGY CORPORATION from litera-
ture dating back to 1904 on the physical, biological and zoogeographical
characteristics of the Northern Gulf of Mexico with particular emphasis
on the South Timbalier Bay Area. Although attempts were made, very lit-
tle background chemical data was found in the literature for use In the
study.
This report is based on information
surveys directed by the EPA as a result of this
was to determine the areal extent of the spilled
the spill, and the effect of the material on the
were:
• The Caminada Bay—Barataria Bay physical,
and biological sampling conducted by EPA
December, 1970.
chemical,
personnel,
PORATION on
many of the
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2.0 Geologic, Climatic and Oceanographic Setting of
the Area in the Vicinity of South Timbalier Bay
2.1 Geology--Geomorphology
The area studied lies in the coastal region between Vermililon
Bay on the west and the southeastern margin of the Mississippi flelta. The
area is characterized by extensive marshland and vast areas of estuarine
and marine waters. The coastline contains numerous bay systems, communi-
cating with the Gulf through natural and artificial passes and with fresh-
water distributaries of the P tchafalaya River. The lower tchafalaya
Basin exhibits an intricate system of lakes and channels. The Mississippi
River, being leveed almost to its mouth, permits little drainage to the
east below Baton Rouge to the Atchafalaya Basin.
The inland coastal plain of the study area slopes southward
at about five feet per mile into the tidal marshes just inland from the
secondary bay, lake and channel areas bordering the very irregular Gulf
shoreline. The coastal plain then increases in slope at the shoreline
to about 10 feet per mile except in the immediate vicinity of the Mis-
sissippi Delta.
The Louisiana Gulf Coast may be classified as ‘emergent” or
depositioflal in nature, formed by deltaic processes as the Mississippi
River and its distributaries sought outlets to the Gulf of Mexico. Since
1900 the Atchafalaya River has been the main distributary to the Missis- .
sippi. The deltaic deposits consist primarily of sand and silt, with
deposits of clay. Underlying the silt and sand are the extensive sand
and gravel deposits which resulted from deposition in the final cycle of
the most recent glaciation.
2.2 Climate
The study area lies within the temperate humid zone with a
mean average precipitation of from 35 to 54 inches per year and temper-
ature ranges from mean lows in January of 190 to 44°F to mean highs In
July of 85° to 91°F.
The tropical and equatorial tidal actions are damped within
the Gulf of Mexico ranging from 2 to 3.5 feet. Tidal currents, however,
in narrow inlets do appreciably affect the migration of organisms through
the passes.
In addition to tidal action the study area is affected by se-
vere storm surges from hurricane waves. Hurricane wave heights of 55 feet
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have been recorded at deep water (100 fathom) stations. Wave heights
are decreased as they travel toward shore by shoaling, refraction and
friction, but cause a “piling up” of water and severe tides in excess
of 15 feet along the coast.
2.3 Hydrology
The Mississippi water shed covers 1,243,600 square miles and
has a maximum discharge rate of 1,360,000 cfs and a minimum of 49,200 cfs.
Rainfall in the vicinity of Barataria Bay ranged from a monthly average
of 3.5 to 7.0 inches with a monthly mean of 5.18 inches. Since these data
cover a time span of nearly 30 years they serve well as baseline values
for the study area.
Modifications of the lower Mississippi for flood control pur-
poses have greatly altered the various bay ecosystems within the area.
Blockage of the lower Mississippi distributaries have resulted in high-
er salinities in the bays due to diminished fresh water sources and en-
croachment of salt water from the Gulf of Mexico. These man-made changes
have caused a new deposition—erosion equilibrium to be established.
Characterization of inshore currents of the study area was
hampered by a scarcity of available information. Recent current studies,
however, reveal that near shore surface currents are primarily wind-driven.
The current and remote sensing survey conducted just following
the December spills showed a high correlation of oil slick movement, as
monitored with ultraviolet photography and thermal infrared imagery, to
nearsurface current data. Current monitoring during this study by Texas
Instruments suggested that the current regime in the area near Platform
“B” is relatively uniform.
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3.0 BIological and Zoogeographical Description of
the South Timbalier Bay Area
Investigations of the indigenous fauna of the northern Gulf
of Mexico have been completed. Specific catch records and data have been
compiled from the literature and a biological and zoogeographic description
of the study area has been made. This investigation was quite complex due
to the vigorously dynamic oceanographic and climatic conditions of the stu-
dy area.
The study area lying between Vermillion Bay on the west and
the western margin of the Mississippi Delta ranges from subtropical in the
sumer to temperate in the winter. Because of such a variation, the fau—
nal assemblages are subjected to severe ecological stresses and populations
are maintained largely through recruitment. Endemic forms constitute less
than 10% of the native population while the distribution of these popula-
tions is dependent on the prevailing currents within the Gulf and subject
to primary current inflow through the Yucatan Passage.
During fall and spring periods, larvae production is at its
peak and large Influxes of animals occur. Animals entering during the
spring find environmental conditions similar to their normal habitat and
thrive. Those entering during the fall, and who survive the winter ex-
tremes, establish themselves by spawning under more favorable spring con-
ditions. The currents, upon which the recruitment depends, may flow east-
ward west of the Mississippi Delta without a reversal pattern during the
year resulting in a strong correlation of the faunal populations between
the northwestern and northcentral areas of the coast.
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4.0 Bases for Analysis of Data and Techniques Employed
Hydrocarbons are quite universally distributed in nature.
Certain hydrocarbon compounds are stable to the extent that they can be
used to determine feeding habits and ranges of some fishes and maninals.
Accordingly, distinguishing between natural hydrocarbons and those re-
sulting from introduction of oil requires careful analysis of character-
istic differences in molecular size and type distribution. With this
knowledge the study effort pursued the following basic methodology:
1. Compare, as a function of time, the results of
the incident-related studies to determine the
effects on the ecosystems in the vicinity of the
Shell spill.
2. Compare the laboratory results of the time re-
lated comparison to data compiled as background
information characterizing the study area under
“normal” conditions.
3. Determine the fate of the crude oil spilled.
4. Determine the effect of the spilled material on
the environment.
Differences in sampling and laboratory analysis precluded an
extensive comparison of data acquired during post—spill surveys. There-
fore, the data from the three surveys performed as a direct result of the
Shell incident were analyzed and compared to “normalized” background data.
Sediment and water chemical analyses were made of inshore and
offshore samples. Total organic carbon contents were determined using a
Beckman TOC analyzer; hydrocarbon content of water extractable and carbon
tetrachloride extractable fractions were determined by Infrared Spectro-
photometric techniques; using a gas chromatograph a fingerprint of sample
crude from Shell Oil Co. Platform “A” was made; and tissue samples from
selected animal and sediment samples were analyzed. Plankton, Van Veen
grab, Phleger core and Otter trawl samples, as well as samples collected
by divers, were analyzed. Histological examinations were made of trawl
specimens. Physical measurement of salinity, temperature, conductivity,
current velocity and wind directions were collected during the three sur-
veys and such data were used in analyses performed.
Several oil sheens were observed in the near vicinity of Plat-
form “B”, within the ring of relief wells, during the sampling mission in
June 1971. A major sheen was observed during this mission 4 to 6 miles
north and northwest of Platform “B.” Very little sedimental water-disper-
sable hydrocarbons were found imediately north of Platform “B” but were
found to gradually increase from 2 to 4 miles north of the platform on
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the north transect, the highest concentration being 5 to 6 mIles north.
A complete absence of these hydrocarbons was noted 7 miles north of the
platform. Carbontetrachioride extractable hydrocarbons were in high
concentration at the platform, measuring 4.5 ppt, but decreased to near
75 ppm at 4 miles north of the rig. However, gradual increases to ap-
proximately 175 ppm were found to 7 miles north of the platform.
Very high concentrations of CCL4 extractable hydrocarbons
were found in near proximity to the platform but decreased on all 3
transects to about 300 ppm at one mile and 50 to 100 ppm 4 miles from
the platform. In the south transect at 2 and 3 miles from the platform,
in 90 feet of water, significant concentration of CCL4 extractables were
present.
Bottom water samples analyzed showed 1.3 ppm total hydrocarbon
within the area of the surface sheen but decreased to near zero at a dis-
tance of 3 miles south and 7 miles north of the sheen. Hydrocarbon con-
centrations of 3.8 ppm were found both in near bottom and near surface
samples taken four miles from the platform on the south transect but de-
creased to 1.3 ppm at a distance of 5 miles in the same transect.
Biological samples taken by divers near the platform and bot-
tom trawl and grab samples taken at all stations one mile from the plat-
form revealed low faunal counts imediately around the platform. Counts
along the three transects showed a general numerical increase at the 2
mile stations. The south transect revealed its highest faunal count at
the 2 mile mark and counts along the north transect reached a maximum at
the 4 mile mark. Beyond the 4 mile mark on the north transect there was
a marked decrease. Populations along the northwest transect were inter-
mediate in numbers and altered in population diversity.
Megafaunal counts taken from grab samples on all transects
diminished as they approached the platform. This revealed an inverse
relationship between megafaunal counts/square meter and the concentration
(ppm) of CCL4 extractable hydrocarbons.
Catch data from trawl samples revealed an inverse relation-
ship In distribution and density patterns for the scavenger starfish,
Luidia ciathrata, and its normal food supply, ophiuroid echinoderms, and
gastropod molluscs. Distributional patterns of the starfish, Luidja, were
fairly similar to the northwest and south, showing only one high numerical
density peak at the 2 mile station on each transect. The north transect,
on the other hand, shows two distinct numerical peaks, one at 2 miles and
the other at 4 miles with a void of Luidia at the 2 mile station. Con-
centrations of the Luidia are very close to “normal” along the south tran-
sect and much higher than expected along the northwest transect. When
comparing starfish concentrations along each transect with recorded salin-
Ities, (using a salinity of 20-23% as minimal for survival) it was found
that the salinities were compatible to support the Luidia In all locations.
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On the north transect ophiuroid and gastropod populations
show a numerical increase away from the platform. However, at the 2
mile station the life zone is almost devoid of any species with a com-
plete absence of Luidia, ophiuroids and gastropods. Normal benthic
inhabitants such as polychaete annelids and the pelecypod molluscs are
also greatly reduced.
Adult and larval stomatopods are almost uniformly absent
from the north transect. Along the northwest transect, however, nu-
merical abundance of stomatopods is quite noticeable. All stomatopods
taken within 4 miles of the platform were larval. No indigenous adults
In the sediments could be found within 4 miles of the platform which Is
in contrast to the large numbers of adults found in the sediments far-
ther out along this northwest transect.
Pelecypod molluscs were nominally present along the south
transect. The predominant pelecypod near the rig was Corbula awiftiana.
Farther out along the south transect, however, Corbula populations were
gradually replaced - first, by Nucula and then by Teilina. This repre-
sents a fairly normal succession from clay to sandy bottoms.
Along the northwest transect, the pelecypod populations were
uniformly low, but a trend of increased numbers of Tellina was detected
as the transect neared shore. Along the north transect, there was es-S
sentially no pelecypod population near Platform “B’, but the numbers tend-
ed to increase at greater distances from the platform. At miles 3, 4, and
5, the predominant pelecypods were Tellina, with the population peak at
mile 4. Beyond the 5 mile station, the Tellina populations were replaced
by Naa8ariua and Mulinia. Both of these latter species are euryhaline
organisms with a habitat preference for sandy-mud bottoms and are char-
acteristic of inshore and bay entrance biotopes.
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5.0 Conclusions
Carbontetrachioride extractable and some water dispersable
hydrocarbons, probably aroniatics, were transported through the water
column and deposited in sediments to observed depths of 90 feet. The
water dispersable compounds appeared to redisperse into the overlying
waters imediately after deposition.
Analysis of sedimental and water samples under an observed
oil sheen verified that water dispersable fractions of crude oil were
deposited In underlying sediments. This free movement of aromatic com-
pounds of the crude oil are potentially damaging to the ecosystem. The
aromatics are, In general, more toxic than aliphatic hydrocarbons and
the fact that they are also more soluble in salt water increases their
biological accessability in the marine environment. The benthic popu-
lations may be damaged by these transient materials which, because of
their redispersibility and subsequent dilution in the water column, may
be undetectable a short time later. Pelagic organisms may also be dam-
aged by these aromatic fractions prior to their disposition and upon
redispersing, at which time these toxic fractions again may be poten-
tially damaging even though diluted.
To detect the presence of the crude oil in the biota of the
area a “fingerprint” of the Shell crude oil from Platform “A” was made
using gas chromatography. The analysis showed a predominance of carbon
compounds with carbon numbers between 15 and 31 with a concentration of
crude fractions of carbon numbers less than 24. “Uncontaminated” mega—
fauna reveal a preference for aliphatic hydrocarbon compounds from 22
through 30 carbons. Organisms of different types tend to reflect this
same preference. Suspected megafauna were examined and revealed the
presence of even-numbered hydrocarbon chains of 16, 18, 20, and 22 car-
bons. The presence of odd-numbered chains was noticeably low in these
organisms. (Insufficient data Is available at this time to explain the
absence of these odd numbered chains). The fact that the uncontaminated
organisms that were examined revealed the lack of hydrocarbon compounds
with carbon numbers below 22 is a baseline used for determining the pre-
sence of crude oil contamination in organisms examined in the study.
Samples of fish from Caminada and Timbalier Bays revealed
the presence of even-numbered chain hydrocarbons below 24 which indi-
cates contamination by crude oil.
Findings in the vicinity of the oil sheen on the northwest
transect showing the presence of hydrocarbon in the water column and in
the sediments directly underlying the sheen formed the basis for further
investigation. Supportable evidence exists that various petroleum frac-
tions are toxic to pelagic marine species. This study has shown that such
hydrocarbon fractions were transported from the water surface to the sedi-
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ments and back again. Because of these factors, fish could be expect-
ed to show very recent signs of gill damage within the vicinity of the
sheen. Histological examinations were performed on both benthic and
nectonic fish samples taken on the three transects and at transect sta-
tions nearest the platform. Fish from Aransas Bay were used as control
specimens for this investigation.
Specimen fish taken from the south transect did not exhibit
abnormal loss of gill tissue. Abnormalities were found, however, in all
fish from the north and northwest transects. Two bottom swimming fish
taken 3 miles north of the platform In the wake of the observed sheen,
fish taken 4 miles northwest of the platform and those specimens examin-
ed from transect stations near the platform exhibited damaged gill tis-
sue. The evidence of the presence of hydrocarbon in the water column and
in the sediments, and the damaged gill tissues of bottom dwelling and
pelagic organisms strongly infer environmental stress due to the presence
of crude oil. It is of interest to note also that the area immediately
around the platform was almost devoid of fish and those areas along the
transects which theoretically showed environmental stress exhibited very
low fish populations.
Stomatopod populations are valuable ‘Indicators of differen-
tial environmental stress since the adults are burrowing benthic organ-
isms and the larvae are planktonic. In the north transect, both the
stomatopod adult and larval forms were conspicuously low in numbers which
correlates well with the high hydrocarbon concentration found along that
transect. Only larval forms were found, however, within 4 miles of the
platform with no evidence of indigenous adults or settling of larvae.
Two conclusions can be drawn from this evidence. First, the
absence of adult stomatopods and settling of larvae indicate a continuing
environmental stress in the sediment; while, secondly, the large numbers
of planktonic stomatopod larvae indicate that recovery in the area may
be in process.
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