An oilspill risk analysis for the Norton Sound, Alaska (proposed sale 57), outer continental shelf lease area

Abstract

An oil spill risk analysis was conducted to determine the relative environmental hazards of developing oil in different regions of the Norton Sound, Alaska, (Proposed Sale 57) Outer Continental Shelf (OCS) lease area. The probability of spill occurrences, likely movement of oil slicks, and locations of resources vulnerable to spilled oil were analyzed. The times between spill occurrence and contact with various resources were also estimated. The combined results yielded estimates of the overall risks associated with development of the proposed lease area. Assuming that oil exists in the lease area (a 14-percent chance) and depending upon the routes chosen to transport oil from OCS platforms to the shore, the leasing of the tracts proposed for OCS Sale 57 will result in an expected 2.8 oil spills (of 1,000 barrels or larger). The estimated probability that land will be contacted by one or more oil spills (of 1,000 barrels or larger) that have been at sea less than 30 days is 0.51 to 0.53, depending on the proposed transportation method chosen. Summary of the Proposed Action and the Major Alternatives The proposed action is to lease 429 tracts on the Outer Continental Shelf off the Norton Sound coast. The study area for this analysis includes all of these tracts and extends from latitude 62 degrees N to 56 degrees 5 minutes N, and from longitude 159 degrees 24 minutes W to 169 degrees 7 minutes W. The study area and the proposed tracts are shown on a Mercator projection in figure 1. The subdivisions of the proposed tracts are shown in figure 2. The launch points, which represent platform locations, pipeline routes, and tanker routes, are shown in figure 3. Two oil transportation scenarios were analyzed for the proposed action and each of three tract deletion alternatives. In the first scenario (referred to as "onshore"), all the oil from the lease area would be piped to a terminal onshore (P8) near Nome, Alaska. From there, the oil would be transported south by tankers out of the study area. In the second scenario, (referred to as "offshore") all the oil would be piped to an offshore terminal (Pll) near the center of the lease area. From there the oil would be tankered south out of the study area. The three tract deletion Average shorefast ice zone 5 (winter) Average shorefast ice zone 6 (winter) Mid-boundary area 1 (summer) Mid-boundary area 2 (summer) Mid-boundary area 3 (summer) Mid-boundary area 4 (summer) Mid-boundary area 5 (summer) Mid-boundary area 1 (winter) Mid-boundary area 2 (winter) Mid-boundary area 3 (winter) Mid-boundary area 4 (winter) Mid-boundary area 5 (winter)

An oilspill risk analysis for the St. George Basin, Alaska, (proposed sale 70) outer continental shelf lease area

“…In addition to oil from the proposed lease tracts, the tankering of oil produced in Norton Sound leases (OCS Lease Sale 57) through the St. George Basin study area was also considered in a cumulative analysis of oil spill risks. The estimated conditional mean value of oil produced in Norton Sound and tankered through the St. George basin study area is 480 million barrels (Samuels and Lanfear, 1980). We cannot overemphasize that these estimates are based on the assumption that oil is present; if it is not present (a 72-percent probability), then, obviously, no oil spill risks exist.…”