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Arctic dispersant use comments sought CRRC scientists have been compiling information on what is known and what is uncertain about dispersing an Arctic offshore oil spill ALAN BAILEY Petroleum News
The Coastal Response Research Center in the University of New Hampshire is seeking comments from the public on a draft list of scientific statements about what is known and what is uncertain when it comes to using dispersants in response to an Arctic offshore oil spill. The CRRC says it has been working with the National Oceanic and Atmospheric Administration, as well as with representatives from other government agencies, academia and the private sector, to determine the current state of the science of dispersants and dispersed oil in Arctic waters. The ocean region included in the investigation includes the Bering Sea, south to the Aleutian Islands, as well as seas to the north of the Arctic Circle.
The scientists conducting the evaluation have focused on five topics: efficacy and effectiveness of dispersant use; the physical transport and chemical behavior of dispersed oil; the degradation and fate of dispersed oil; public health and food security; and eco-toxicity and sub lethal impacts.
Many factors The draft document that is out for review indicates that dispersant effectiveness in the Arctic offshore is impacted by a number of factors including the type of oil; the emulsification of the oil; the mixing energy with which the dispersant is applied; the dispersant formulation; the dose rate; and the water salinity. The complexities of the systems involved in action by dispersants lead to uncertainties that make it important to be cautious about making generalized conclusions about dispersant effectiveness in the Arctic, especially in the presence of ice, the draft document says.
However, it does appear that, although temperature impacts both the physical properties of oil and the effectiveness of oil dispersion, low to medium viscosity oils that readily disperse in warm regions remain readily dispersible in seawater at freezing temperatures, provided the temperature is high enough to allow the oil to remain fluid, the draft document says. However, the effectiveness of dispersant use on higher viscosity oils in Arctic waters is uncertain.
Mixing energy Although the mixing energy available in Arctic ice-free water is equivalent to that in warmer climates, the presence of sea ice tends to dampen the wave energy, thus slowing the oil dispersion process. However, the application of vessel propeller wash to the area being treated can boost the mixing energy level, the draft document says. There is uncertainty over both the impacts of different ice forms on dispersant effectiveness and the effectiveness of dispersants in areas of high ice concentration. And further research is needed into the interplay between the motion of small pieces of ice in wave motion, the dampening of wave energy in ice conditions and the impact of reduced oil weathering on the timeframe within which dispersant use remains effective, the draft document says.
The draft document also cautions about the drawbacks of extrapolating results obtained in laboratory tests to field conditions. In addition, much current understanding of dispersant effectiveness relates to a single dispersant product - there is potential for new dispersant formulations to improve dispersant effectiveness, the document says. It is also possible to improve dispersant effectiveness through reduced oil droplet sizes by applying dispersants subsea into a turbulent underwater oil release.
Other uncertainties There is uncertainty over the effectiveness of dispersants in seawater when the water salinity is especially high or especially low. Research is needed into the effectiveness of a range of dispersant types over a broad range of oil types and environmental conditions, and into the impact of high pressure natural gas associated with oil in a subsea oil spill. There is also a lack of general agreement on the influence of the wax, resin and asphaltene content of oil on dispersion effectiveness, the draft document says.
While there are protocols for monitoring dispersant effectiveness in ice-free surface waters, there are no equivalent protocols documented for monitoring effectiveness in ice-infested waters or under sea ice. Moreover, techniques for making quantitative assessments of dispersant effectiveness have broad ranges of uncertainty, the draft document says.
Information about the assessment can be found on the University of New Hampshire website at crrc.unh.edu/workshop/crrc/dispersant_science. CRRC is seeking comments on its findings by Feb. 22.
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