United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-067 Apr. 1984
&ER& Project Summary
Response of Crude Oil Slicks to
Dispersant Treatment at Sea
/11
A series of ocean studies was con-
ducted in 1978 and 1979 to develop quan-
titative data on the effectiveness of dis-
persants at sea and on the behavior of
dispersant-treated oil. Test spills were
made in the outer New York Bight some
80 km southeast of New York Harbor.
Ambient conditions were consistent for
both years of testing, but other factors
such as spill volume, time of dispersant
application, and dispersant dose were
varied. Oils used were Murban and La
Rosa crude.
Reasonably effective treatment was
achieved when dispersant was sprayed
30 min or less after the oil was spilled.
Little oil was found in the subsurface
water after spraying dispersant on oil
that had been on the sea surface for 2 hr.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Information about spilled oil behavior is
needed for effective responses to oil spills
at sea. If a response includes possible treat-
ment with chemical dispersants, quantitative
data are needed on the behavior of dis-
persant-treated oil to determine its chemical
and physical fate and the advisability of us-
ing dispersants. Though considerable
laboratory and field tests of dispersants were
conducted in many countries in 1977, few
quantitative data were developed on the ef-
fectiveness of dispersants at sea or on the
behavior of dispersant-treated oil. In
response to this information need, the
American Petroleum Institute (API) and the
U.S. Environmental Protection Agency
(EPA) jointly sponsored the 1978-1979 series
of ocean experiments described here.
Experimental Program
Research oil spills were made in the outer
New York Bight approximately 80 km south-
east of New York Harbor. Four spills were
made in November 1978 and four in October
1979. Some experimental factors were com-
mon to all tests. These included:
• taking background samples of ocean
water before the spill,
• recording oceanographic and meteoro-
logical data before and during each test,
• collecting large numbers of seawater
samples at various depths in the spill
area,
• repeatedly having the principal research
vessel move slowly through the oil on
sampling transects that were perpen-
dicular to each other so that a three-
dimensional view of the oil in the water
would be obtained,
• applying a commercially available disper-
sant from a helicopter to spills that were
to be dispersed, and
• guiding the helicopter and all sampling
from a spotter plane that also conducted
vertical photographic observations.
Other experimental conditions varied bet-
ween 1978 and 1979 (Table 1).
As Table 1 indicates, the 1979 tests were
intended to refine and augment the data
generated during 1978. Note that one impor-
tant difference in 1979 was the use of con-
trol spills (untreated) on the same day as
treated spills. During 1978, the approach had
been to treat all spills to maximize the infor-
mation generated on treated oil. Com-
parisons could be made with earlier
untreated spills of the same oil under similar
ambient conditions, but rigorous experi-
mental control was absent until the 1979
tests.
All test spills during 1978 and 1979 were
made in an area of the outer New York Bight
that was approved for this purpose by EPA
under Permit No. ll-MA-143-Research. Am-
bient conditions for the test were consistent
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Table 1. Principal Differences Between the 1978 and 1979 Test Series
Item
1978
1979
Reason for Difference
Volume of each spill 1.67 rrf
Biological testing Minimal
3.55 m3 Desire to minimize effect
of scale on accuracy of
simulation.
Extensive Ship mechanical failures
in 1978.
Time of dispersant
application after
oil spill
Dose (gal dispersant/
acre of slick}
Use of control spills
Within 10 min
or after 2 hr
Approxi-
mately 10
No
None or
30 min
Approxi-
mately 20
Yes
Need to assess effect
of weathering.
Desire to assure
sufficient dose.
Need for rigorous
experimental control.
for both years of testing, so weather and sea
conditions are not considered a factor in dif-
ferentiating one test from another. These
conditions were as follows:
Condition:
Description
Air temperature, °C 12-21
Water temperature, °C ... 13-16
(constant throughout sampled
depth within each test)
Wind speed, m/sec 0 - 7.5
Wave height, m 0.3-1.6
The oilds used were Murban crude (Abu
Dhabi) and La Rosa crude (Venezuela). The
primary difference between these is the
higher concentration of volatiles in Murban
crude.
Dispersant application was similar for all
treated spills. A commercially available
dispersant product (same for all tests) was
sprayed from a helicopter at an altitude of
approximately 6 m and a speed of approxi-
mately 80 km/hr. Mean droplet diameter was
approximately 1 mm.
Sampling of subsurface water was con-
ducted with a specially designed apparatus
and procedure used to avoid contamination
by surface oil. All samples were preserved
to avoid biological degradation before
analysis. Analyses were conducted by API
member laboratories using gas chromato-
graphic and infrared techniques.
Findings
The behavior of dispersed oil is generally
quite different from that of untreated oil. The
chief cause of this difference is the fact that
dispersed droplets, while still positively
buoyant, are often small enough to be kept
in suspension below the water surface by the
turbulence near the sea surface.
Figure 1 shows a typical pattern of oil-in-
water concentrations for the crossed
transects of a sampling run through dis-
persed oil. With plots such as this, volumes
of oil in the water were computed. These
computations were approximate and used
the concentration and the geometric shape
represented by each concentration iosopleth
to arrive at values for total dispersed oil
(Table 2).
Reasonably effective treatment was
achieved when dispersant was sprayed 30
min or less after the oil was spilled (Table 2).
Little oil was found in the subsurface water
after spraying dispersant on oil that had been
on the sea surface for 2 hr.
Other conclusions are briefly summarized
as follows:
• Early in the tracking of spills that were
effectively dispersed, extractable
organics in the upper meter of the water
column ranged typically from 1 to 3
mg/l.
• Little oil was found in water samples at
the 9-m depth; this result is not caused
by stratification, because the water den-
sity was found constant throughout the
sampling depth.
• Murban was more effectively dispersed
than La Rosa crudes when other factors
were held constant. Murban is lighter
and less viscous.
• One physical effect of dispersant treat-
ment was that thin films were spread
over larger areas of the sea surface than
when an equal amount of the same oil
was spilled and not treated.
• Within 3 to 5 hr of spills this size, water
samples from under the oil approach
background concentrations because of
dilution, evaporation, and perhaps other
factors.
The full report, prepared by JBF Scientific
Corporation, was submitted in fulfillment of
Grant No. R806056 with the American
Petroleum Institute under the sponsorship of
the U.S. Environmental Protection Agency.
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• Wind
421 2.94 4.13 2.22 1.45 .83 1.30
.07
.06
.06
08
.06 .05 0.6
Station 1234
Time After Spill (min) 53 60 65 69
!
700M-)
JBF2150
6 -
(Intersect)
.10 .06
.05 .05
5
72
6
75
Figure 1. Total extractable organic matter (mg/l) in water samples collected during first
sample run through treated Murban crude oil spill. Vertical exaggeration about 45 X.
Table 2. Approximate Percent of Spill Oil Accounted for in Water Samples
Crude Oil
Type
Murban
La Rosa
Untreated
<5
<1
Immediate
Dispersant
Spray
40
20
Dispersant
Spray after
30 min
70
60
Dispersant
Spray after
2hr
2
2
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This Project Summary was prepared by staff of JBF Scientific Corporation,
Wilmington, MA 01887.
Leo T. Me Carthy, Jr. is the EPA Project Officer (see below).
The complete report consists of two volumes:
"Volume I. Response of Crude Oil Slicks to Dispersant Treatment at Sea: 1978
Tests." (Order No. PB 84-164 144; Cost: $11.50, subject to change).
"Volume II. Response of Crude Oil Slicks to Dispersant Treatment at Sea: 1979
Tests." (Order No. PB 84-164 151; Cost: $10.00, subject to change).
The above reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
US GOVERNMENT PRINTING OFFICE, 1984 —759-015/7677
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
oi-
Official Business
Penalty for Private Use $300
0V0lfc2?KUTtCUUN AGENCY
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