The Federal OCS includes all areas seaward of a line drawn 3 geographical 

 mi from the shoreline. Off Texas and western Florida the line is drawn 3 marine 

 leagues from the shoreline. Legislation defining the OCS is contained in the 

 Submerged Lands Act of 1953 and the Outer Continental Shelf Lands Act of 1953. 

 Seaward limits to America's OCS are either not defined or are in negotiation 

 with adjacent nations. OCS lease sales have been held within all regions of 

 the OCS except for portions of the Bering and Chukchi Seas and areas with water 

 depths greater than 2 to 3 km. 



Oil spills are a major environmental issue identified by parties associated 

 with OCS leasing (Federal and State governments, industry, conservation groups, 

 and the general public). Expressions of concern and requests for information 

 for use in analysis have led to the development of the DOI oil spill risk analysis 

 model. Model outputs address three topics: the likelihood of spill occurrence, 

 likely pathways that spills might follow, and the risks that spills will occur 

 and will contact various resources. The model treats uncertainties inherent 

 with OCS related spills as well as spills from other sources. The model serves 

 as a quantitative framework for synthesizing enormous amounts of environmental 

 information. Model outputs are intended for use by environmental analysts and 

 program decisionmakers. 



2. Scope 



Oil spill risk analysis modeling is carried out as a joint effort of BLM 

 and USGS. Because of this and the wide collection of users of the modeling 

 results, the work may be considered as a DOI project. Input data to the model 

 are provided by BLM. These data includes all environmental information as well 

 as definition of leases to be offered and transportation senerios to be used if 

 oil is found. USGS provides estimates of oil and gas resources within the lease 

 sale area and carries out all of the model computations. Reports of model output 

 are provided to BLM for use and analysis in writing environmental statements 

 and drafting DOI decision documents. Decision documents are finalized within 

 the Department. 



Input data reflect the best available information for each of the OCS lease 

 sale areas. The existing information base is supplemented through studies 

 sponsored by BLM's Offshore Environmental Studies Program. The Studies Program 

 began in the mid-seventies and continues to date. Approximately half of the 

 BLM sponsored studies have been conducted off Alaska. Data on ocean circulation, 

 local winds, and locations of various marine resources comprise the bulk of model 

 inputs . 



The spatial extent of each model accounts for spills originating from pro- 

 duction sites as well as along transportation routes. Spill trajectories are 

 analyzed for up to 30 days. For example, a recent model for the area off the 

 southeastern coast extended from Miami to Norfolk and from the shore to well 

 over the Blake Plateau. 



The oil spill risk model is predictive in that it treats future events. The 

 future, extending 2 to 3 decades, is defined by the estimated time to complete 

 production from an offshore lease. Because the model deals with uncertain 

 events and environmental circumstances, it is couched in probabilistic terms. 

 This treatment of uncertainty distinguishes the DOI model from deterministic 



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