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There is a need for research information and data on the effectiveness of
chemical dispersants to answer questions and data gaps posed by BOEMRE
regional offices, regulators and decision makers. A review of oil spill
dispersants, their efficacy and effects, recently completed by the U.S.
National Research Council (NRC 2005), recommended that research on
chemical dispersants be conducted in several different areas. In
FY-2008, the BOEMRE received a research proposal that identified a
multi-year dispersant research program to answer the questions and
address the data gaps in the efficacy of dispersants identified in the
NRC report. There were seven distinct tasks or projects proposed in this
two-year dispersant research programs. In FY-2008, the BOEMRE funded Tasks
1, 2 and 5. These three tasks were completed in TAR
project 615.
In FY-2009, the BOEMRE Oil Spill Response Research Team requested a
technical and cost proposal update of Task 4 Evaluation of Dispersant
Effectiveness in Low-Dose, Repeat Applications and Task 6 Validation of
Small-Scale Laboratory Test Dispersant Effectiveness Ranking. The
objective of this research program is to continue research and
development on the use of chemical dispersants. Two tasks will be
addressed. The period of performance would be one year.
Task 4. Evaluation of Dispersant Effectiveness in Low-Dose, Repeat
Applications
Conventional wisdom and usual practice for the application of
dispersant to large oil spills is through large, fixed-wing aircraft
spraying. However, the spray from a single pass from such spray systems
can treat a slick of only about 0.15 mm thick at the normal design
application ratio of one part dispersant to 20 parts of oil. Thick oil
patches accounting for 80 to 90 % of the total oil volume can easily be
10 to 100 times thicker than this. The application rate of dispersant
from an aircraft application hitting the thick oil could be in the range
of 1:200 to 1:2000 under such conditions. The question to be answered in
this project is: Does dispersant applied in very low doses (1:1000 to
1:200) disperse a small fraction of an otherwise dispersible oil or is
it simply ineffective until a minimum threshold concentration of
dispersant in the oil is achieved, possibly through repeated spray
passes?
The answer to this question has significant ramifications with
respect to operational decisions in dispersant application on thick oil
slicks. For example, if a test spray were completed on a thick oil slick
and no dispersion was observed the dispersant might be considered to be
in-effective, whereas multiple applications of the dispersant might be
necessary to achieve a dosage sufficient to generate dispersion. This
work will be completed at two test scales. Initial work will be
completed at a laboratory test tank scale to assess the effect of
low-dose application on a number of oils. Once trends have been
determined in the laboratory testing will be completed at Ohmsett to
verify similar behavior at full-scale.
Task 5. involves three tasks.
- Small Scale Tests
- Large Scale Ohmsett testing
- Data Analysis and Technical Report
Task 6. Validation of Small-Scale Laboratory Test Dispersant Effectiveness
Ranking
Bench scale dispersant effectiveness tests are routinely used around
the world to rank the potential effectiveness of a dispersant product on
standard oils or to study the effect of oil and dispersant type and
environmental parameters on dispersant effectiveness. In the United
States oils must achieve a measured effectiveness of 45% or greater in
the swirling flask to be placed on EPA’s NCP Product Schedule as an
approved dispersant. But, what do the effectiveness values recorded in
these laboratory tests mean with respect to likely effectiveness in the
field and do the bench scale tests fairly evaluate dispersant products?
Attempts have been made to correlate the results of bench scale tests to
one another with mixed success thus suggesting that few, if any, of the
tests are representative of real-world situations.
Very limited field data is available to allow the comparison of bench
scale test results to field success and so this has also not been
adequately done. It is proposed that the Ohmsett test facility be used
as a surrogate to the field to provide “field” effectiveness estimates
on a select number of oils for a select number of dispersants.
Bench-scale tests would be conducted using the same dispersant and oil
combinations and the results compared to establish if the bench-scale
test results can be used to provide reasonable estimates of field
performance. The EPA Baffled Flask Test (BFT) and the WSL Laboratory
test (WSL) will be the bench-scale test methods used in the study. The
BFT is being proposed as the new EPA standard and the WSL test has been
shown to be more representative of field.
Task 6 involves three tasks:
- Large Scale Ohmsett Testing
- Bench Scale DE Testing
- Data Analysis and Technical Report
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