portrayal of the sale area environment as it would be without the proposed sale. 

 Third, the cumulative circumstances, a portrayal of the sale area environment 

 as it would be if the lease sale were held and all other activities continued. 

 Sources of accidental spills considered in the model framework for the cumulative 

 circumstance include: production and transportation of petroleum hydrocarbons 

 into and within the area. 



For each of these portrayals the analysts must consider the proposal in its 

 entirety as well as various alternative sale configurations. Oil volumes, used 

 as exposure variables in the oil spill risk model, are also used in sale specific 

 economic analyses thereby affording a common basis for cost/benefit analysis. 



Analytical attempts have been made to maximize oil production while minimizing 

 oil spill risk (Smith et al. 1979). Although this can be readily accomplished, 

 numerical solution would presumably require assignment of weights to the targets. 

 Without weights the targets would be treated with equivalence, which implies 

 that spill contacts yield equivalent consequences. Weights can be assigned in 

 terms of acceptable numbers of contacts. It seems reasonable to assume that 

 decisionmakers make such judgments during their personal deliberations. 



At the final stages of a proposed OCS sale process, the model results are 

 incorporated into decision documents. Decision documents are used by agencies 

 within DOI to make recommendations, concerning the proposed sale and its 

 alternatives, to the Secretary. 



2. Complications 



The oil volumes used in the model analysis are mean estimates of economically 

 recoverable amounts. In analyzing sale alternatives (tract deletions for 

 example), one often encounters circumstances where volume dependencies (for 

 economic and geologic reasons) exist. The analysis thus goes well beyond simply 

 deleting an element from the volume vector. 



Quite often we observe that oil spills from transportation routes present 

 greater threat to resources than spills from production sites. This is expected 

 based upon proximity. The DOI is committed to write an ES in frontier areas 

 which addresses the development stage of the offshore leasing process. (Frontier 

 areas are those in which there has been no previous production; the development 

 stage follows leasing but precedes actual production.) A development ES will 

 be greatly enhanced by the capabilities of the oil spill risk model to evaluate 

 alternative transportation routes. 



Model outputs consist of thousands of numbers. The majority of the proba- 

 bilities is negligible; nevertheless, analysis of the remaining values is a 

 difficult and complex task. Not all of the values can be analyzed. All of 

 the probabilities are presented in the ES, however, to enable readers to apply 

 their own judgments and analyses. 



The model deals with contacts; impacts are quite another matter. Impacts 

 from oil spills are very much dependent upon how and where a spill occurs 

 (underwater blowout versus blowout into the atmosphere; pipeline failure at sea 

 versus tanker spill near shore, etc.). Impacts are also very much dependent 

 upon the physical-chemical properties of the spilled oil. These properties 



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