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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations
43926 August 2, 2006. The second step in the risk assessment was to estimate the number of polar bears that could be impacted by a large spill. All modeled polar bear grid cell locations that were intersected by one or more cells of a rasterized spill path a modeled group of hundreds of oil particles forming a trajectory and pushed by winds and currents and impeded by ice were considered oiled by a spill. For purposes of the analysis, if a bear contacted oil, the contact was assumed to be lethal. This analysis involved estimating the distribution of bears that could be in the area and overlapping polar bear distributions and seasonal aggregations with oil spill trajectories.
The trajectories previously calculated for Northstar and Liberty sites were used. The trajectories for Northstar and Liberty were provided by the BOEM and were reported in Amstrup et al. 2006a.
BOEM estimated probable sizes of oil spills from a pinhole leak to a rupture in the transportation pipeline. These spill sizes ranged from a minimum of 125 to a catastrophic release event of 5,912 bbl. Researchers set the size of the modeled spill at the scenario of 5,912
bbl caused by a pinhole or small leak for 60 days under ice without detection.
The second step of the risk assessment analysis incorporated polar bear densities overlapped with the oil spill trajectories. To accomplish this, in 2004, USGS completed an analysis investigating the potential effects of hypothetical oil spills on polar bears.
Movement and distribution information were derived from radio and satellite locations of collared adult females.
Density estimates were used to determine the distribution of polar bears in the Beaufort Sea. Researchers then created a grid system centered over the Northstar production island and the Liberty site to estimate the number of bears expected to occur within each 1km2 grid cell. Each of the simulated oil spills were overlaid with the polar bear distribution grid. Finally, the likelihood of occurrence of bears oiled during the duration of the 5-year ITRs was estimated. This likelihood was calculated by multiplying the number of polar bears oiled by the spill by the percentage of time bears were at risk for each period of the year.
In summary, the maximum numbers of bears potentially oiled by a 5,912-bbl spill during the September open-water season from Northstar was 27, and the maximum from Liberty was 23, assuming a large oil spill occurred and no cleanup or mitigation measures took place. Potentially oiled polar bears ranged up to 74 bears with up to 55
bears during October in mixed-ice
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conditions for Northstar and Liberty, respectively. Median number of bears oiled by the 5,912-bbl spill from the Northstar simulation site in September and October were 3 and 11 bears, respectively. Median numbers of bears oiled from the Liberty simulation site for September and October were 1 and 3 bears, respectively. Variation occurred among oil spill scenarios, resulting from differences in oil spill trajectories among those scenarios and not the result of variation in the estimated bear densities. For example, in October, 75
percent of trajectories from the 5,912-bbl spill affected 20 or fewer polar bears from spills originating at the Northstar simulation site and 9 or fewer bears from spills originating at the Liberty simulation site.
When calculating the probability that a 5,912-bbl spill would oil five or more bears during the annual fall period, we found that oil spills and trajectories were more likely to affect fewer than five bears versus more than five bears.
Thus, for Northstar, the chance that a 5,912-bbl oil spill affected resulting in mortality 5 or more bears was 1.03.4
percent; 10 or more bears was 0.72.3
percent; and 20 or more bears was 0.2
0.8 percent. For Liberty, the probability of a spill that would affect 5 or more bears was 0.37.4 percent; 10 or more bears, 0.10.4 percent; and 20 or more bears, 0.10.2 percent.
Discussion of Prior Risk Assessment Based on the simulations, a nearshore island production site less than 5 mi from shore would potentially involve less risk of polar bears being oiled than a facility located farther offshore greater than 5 mi. For any spill event, seasonality of habitat use by bears will be an important variable in assessing risk to polar bears. During the fall season when a portion of the SBS bear stock aggregate on terrestrial sites and use barrier islands for travel corridors, spill events from nearshore industrial facilities may pose more chance of exposing bears to oil due to its persistence in the nearshore environment. Conversely, during the ice-covered and summer seasons, Industry facilities located farther offshore greater than 5 mi may increase the chance of bears being exposed to oil as bears will be associated with the ice habitat.
Conclusion of Risk Assessment To date, documented oil spill-related impacts in the marine environment to polar bears in the Beaufort Sea by the oil and gas Industry are minimal. No large spills by Industry in the marine environment have occurred in Arctic
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Alaska. Nevertheless, the possibility of oil spills from Industry activities and the subsequent impacts on polar bears that contact oil remain a major concern.
There has been much discussion about effective techniques for containing, recovering, and cleaning up oil spills in Arctic marine environments, particularly the concern that effective oil spill cleanup during poor weather and broken-ice conditions has not been proven. Given this uncertainty, limiting the likelihood of a large oil spill becomes an even more important consideration. Industry oil spill contingency plans describe methodologies put in place to prevent a spill from occurring. For example, all current offshore production facilities have spill containment systems in place at the well heads. In the event an oil discharge should occur, containment systems are designed to collect the oil before it makes contact with the environment.
With the limited background information available regarding oil spills in the Arctic environment, it is unknown what the outcome of such a spill event would be if one were to occur. For example, polar bears could encounter oil spills during the openwater and ice-covered seasons in offshore or onshore habitat. Although most polar bears in the SBS stock spend a large amount of their time offshore on the pack ice, it is likely that some bears would encounter oil from a large spill that persisted for 30 days or more.
An analysis of the potential effects of a worst case discharge WCD on polar bears in the Chukchi Sea suggested that between 5 and 40 percent of a stock of 2,000 polar bears could be exposed to oil if a WCD occurred Wilson et al. 2017. A similar analysis has not been conducted for the Beaufort Sea; however, given the extremely low probability i.e., 0.0001 that an unmitigated WCD event would occur BOEM 2015, Wilson et al. 2017, the likelihood of such effects on polar bears in the Beaufort Sea is extremely low.
Although the extent of impacts from a large oil spill would depend on the size, location, and timing of spills relative to polar bear distributions along with the effectiveness of spill response and cleanup efforts, under some scenarios, stock-level impacts could be expected. A large spill originating from a marine oil platform could have significant impacts on polar bears if an oil spill contacted an aggregation of polar bears. Likewise, a spill occurring during the broken-ice period could significantly impact the SBS polar bear stock in part because polar bears may be more active during this season.

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