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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations possible launch points in relation to the shoreline and biological, physical, and sociocultural resource areas specific to the Beaufort Sea. The chance that a large oil spill will contact a specific ERA of concern within a given time of travel from a certain location launch area or pipeline segment is termed a conditional probability. Conditional probabilities assume that no cleanup activities take place and there are no efforts to contain the spill.
We used two BOEM launch areas LAs, LA 2 and LA 3, and one pipeline segment PL, PL 2, from Appendix A of the OSRA Figure A2; Li and Smith 2020 to represent the oil spills moving from hypothetical offshore areas. These LAs and PLs were selected because of their proximity to current and proposed offshore facilities.

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Oil-Spill-Trajectory Model Assumptions For purposes of its oil spill trajectory simulation, BOEM made the following assumptions: All spills occur instantaneously; large oil spills occur in the hypothetical origin areas or along the hypothetical PLs noted above; large spills do not weather i.e., become degraded by weather conditions for purposes of trajectory analysis;
weathering is calculated separately; the model does not simulate cleanup scenarios; the oil spill trajectories move as though no oil spill response action is taken; and large oil spills stop when they contact the mainland coastline.
Analysis of the Conditional Probability Results As noted above, the chance that a large oil spill will contact a specific ERA of concern within a given time of travel from a certain location LA or PL, assuming a large spill occurs and that no cleanup takes place, is termed a conditional probability. From the OSRA, Appendix B, we chose ERAs and land segments LSs to represent areas of concern pertinent to polar bears MMS
2008a. Those ERAs and LSs and the conditional probabilities that a large oil spill originating from the selected LAs or PLs could affect those ERAs and LSs are presented in a supplementary table titled Conditional Oil Spill Probabilities that can be found on http www.regulations.gov under Docket No. FWSR7ES20210037.
From the information in this table, we note the highest chance of contact and the range of chances of contact that could occur should a large spill occur from LAs or PLs.
Polar bears are vulnerable to a large oil spill during the open-water period when bears form aggregations onshore.
In the Beaufort Sea, these aggregations
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often form in the fall near subsistenceharvested bowhead whale carcasses.
Specific aggregation areas include Point Utqigvik, Cross Island, and Kaktovik. In recent years, more than 60 polar bears have been observed feeding on whale carcasses just outside of Kaktovik, and in the autumn of 2002, North Slope Borough and Service biologists documented more than 100 polar bears in and around Utqigvik. In order for significant impacts to polar bears to occur, 1 a large oil spill would have to occur, 2 oil would have to contact an area where polar bears aggregate, and 3
the aggregation of polar bears would have to occur at the same time as the spill. The risk of all three of these events occurring simultaneously is low.
We identified polar bear aggregations in environmental resource areas and non-grouped land segments ERA 55, 93, 95, 96, 100; LS 85, 102, 107. The OSRA estimates the chance of contacting these aggregations is 18
percent or less see Table 1, Conditional Oil Spill Probabilities, in the Supporting and Related Material in Docket No. FWSR7ES20210037.
The OSRA estimates for LA 2 and LA
3 have the highest chance of a large spill contacting ERA 96 in summer Midway, Cross, and Bartlett islands. Some polar bears will aggregate at these islands during AugustOctober 3-month period. If a large oil spill occurred and contacted those aggregation sites outside of the timeframe of use by polar bears, potential impacts to polar bears would be reduced.
Coastal areas provide important denning habitat for polar bears, such as the ANWR and nearshore barrier islands containing tundra habitat Amstrup 1993, Amstrup and Gardner 1994, Durner et al. 2006, USFWS unpubl.
data. Considering that 65 percent of confirmed terrestrial dens found in Alaska in the period 19812005 were on coastal or island bluffs Durner et al.
2006, oiling of such habitats could have negative effects on polar bears, although the specific nature and ramifications of such effects are unknown.
Assuming a large oil spill occurs, tundra relief barrier islands ERA 92, 93, and 94, LS 97 and 102 have up to an 18 percent chance of a large spill contacting them from PL 2. The OSRA
estimates suggest that there is a 12
percent chance that oil would contact the coastline of the ANWR GLS 166.
The Kaktovik area ERA 95 and 100, LS
107 has up to a one percent chance of a spill contacting the coastline. The chance of a spill contacting the coast near Utqiagvik ERA 55, LS 85 would be as high as 15 percent see Table 1, Conditional Oil Spill Probabilities, in
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the Supporting and Related Material in Docket No. FWSR7ES20210037.
All barrier islands are important resting and travel corridors for polar bears, and larger barrier islands that contain tundra relief are also important denning habitat. Tundra-bearing barrier islands within the geographic region and near oilfield development are the Jones Island group of Pingok, Bertoncini, Bodfish, Cottle, Howe, Foggy, Tigvariak, and Flaxman Islands.
In addition, Cross Island has gravel relief where polar bears have denned.
The Jones Island group is located in ERA 92 and LS 97. If a spill were to originate from an LA 2 pipeline segment during the summer months, the probability that this spill would contact these land segments could be as great as 15 percent. The probability that a spill from LA 3 would contact the Jones Island group would range from 1
percent to as high as 12 percent.
Likewise, for PL 2, the range would be from 3 percent to as high as 12 percent.
Risk Assessment From Prior ITRs In previous ITRs, we used a risk assessment method that considered oil spill probability estimates for two sites Northstar and Liberty, oil spill trajectory models, and a polar bear distribution model based on location of satellite-collared females during September and October 68 FR 66744, November 28, 2003; 71 FR 43926, August 2, 2006; 76 FR 47010, August 3, 2011; and 81 FR 52275, August 5, 2016.
To support the analysis for this action, we reviewed the previous analysis and used the data to compare the potential effects of a large oil spill in a nearshore production facility less than 5 mi, such as Liberty, and a facility located further offshore, such as Northstar. Even though the risk assessment of 2006 did not specifically model spills from the Oooguruk or Nikaitchuq sites, we believe it was reasonable to assume that the analysis for Liberty and indirectly, Northstar, adequately reflected the potential impacts likely to occur from an oil spill at either of these additional locations due to the similarity in the nearshore locations.
Methodology of Prior Risk Assessment The first step of the risk assessment analysis was to examine oil spill probabilities at offshore production sites for the summer JulyOctober and winter NovemberJune seasons based on information developed for the original Northstar and Liberty EISs. We assumed that one large spill occurred during the 5-year period covered by the regulations. A detailed description of the methodology can be found at 71 FR

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