are, in almost all cases, unknown at the time of a lease sale analysis. Oil 

 properties will be far better understood at the time a development ES is written. 

 Impact assessment requires knowledge of oil properties not only at the location 

 of the spill but at the time and location of contact with sensitive resources. 

 Thus, impact analysts desire quantification of oil weathering. Examination of 

 oil weathering studies reveals that time is the single most important variable. 

 Study of weathering algorithms reveals near linear dependencies on time. As a 

 first approximation then, the model retains measure of the time between spill 

 occurrence and target contact. The times for which conditional and joint 

 probabilities are accumulated (3, 10, and 30 days) were chosen for their use as 

 implicit measures of oil weathering — as well as for matters relating to contain- 

 ment and clean-up. 



Spill sizes range over seven to eight orders of magnitude. In general, 

 given such a range, the average size has little meaning. Observed OCS platform 

 spills have the least range in sizes, with pipelines second; tanker spills 

 account for the widest range in sizes. The OCS platform spills (1964 to present) 

 greater than or equal to 1,000 barrels range from 1,500 to 77,000 barrels; the 

 average is approximately 19,000 barrels. 



3. The Future 



Efforts have been underway for some time now to apply three-dimensional 

 ocean circulation models on the OCS. Results have been substantial: to our 

 understanding of coastal circulation, to our abilities to quantify stochastic 

 elements of the circulation, and to supply circulation data beneath the sea 

 surface. 



Meteorological studies have successfully established quantitative means to 

 construct at-sea time series winds from time series measured along the coast. 

 Several years of direct measurement of time series winds are being acquired 

 with anchored meteorological buoys. 



Studies of the distribution of sea ice, its properties, and oil/ice 

 interaction are yielding results applicable to oil spill risk analyses. 



ACKNOWLEDGMENTS 



I wish to acknowledge James Slack, USGS, who constructed the initial DOI 

 oil spill model; Kenneth Lanfear and the Environmental Modeling Group, USGS, 

 who so ably perform the modeling work; the several BLM field office personnel 

 who have suggested improvements to the model; and the several marine scientists 

 who have contributed data used in the model runs. 



REFERENCES 



BLM, 1981. OCS Statistical summary . U.S. Department of the Interior, Bureau of 



Land Management (4 volumes). 

 Devanney, J.W., III, and R.J. Stewart, 1976. Analysis of oil spill statistics . 



Report to Council on Environmental Quality, Washington, D.C. 



98 



