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
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