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Data Set #068

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About the Data

About petroleum spills in Washington State:

    In 1997, the Washington State Department of Ecology published an historical analysis of oil spills, that assembled the available information on spill type, size and method of occurrence. The Department of Ecology paper summarized oil spills going back to the 1960's, however it was not until the early 1990's that systematic reporting of all spills, regardless of size, took place. Before 1990, only larger spills were systematically reported, which makes a statistical analysis of the older data very problematic.

    The data include both marine and land-based spills (underground leaking storage tanks are excluded), and include a wide variety of petroleum byproducts such as crude oil, fuel oil, lubricating oils, diesel fuel, jet fuel and gasoline (but no vegetable or animal oils). While all of these petroleum products are serious contaminants, the heavier hydrocarbons (crude oil and fuel oil) are much less volatile and much more persistent, even in high energy coastal environments such as Prince William Sound, Alaska. Heavy hydrocarbons that settle into beach deposits can be excavated by storms, re-contaminating the nearshore environment for decades following the spill.

    Because the Washington State petroleum spills in the data set range from 30 gallons to 600,000 gallons, over 4 orders of magnitude, the logarithm of the spill size is calculated, binned and plotted against its frequency. As expected, small spills are the most abundant, whereas large spills are rather infrequent. Many phenomena such as landslides, earthquakes, volcanic eruptions, nuclear accidents, auto wrecks, and wildfires show a similar distribution of sizes; many small events, some medium sized events, and few large events. Size versus frequency for these phenomena often exhibit a power law relationship. If petroleum spills in Washington State follow this same relationship, then the Department of Ecology's compilation under-represents the smallest spills, which should be 2-3 times more frequent. This under-representation is consistent with the historical lack of comprehensive reporting.

    Since the period of record is known (5 years, from 1991-1996), the recurrence interval for a spill of a given size can be calculated. Extrapolation to larger sizes using the power law can yield recurrence intervals for these rare events. On New Year's day in 1972, the General M. C. Meigs, a US Navy supply vessel, spilled 2.3 million gallons of heavy fuel oil into the Straights of Juan de Fuca between Washington State and Canada. What is the recurrence interval for an event of this size?

Source: Oil Spills in Washington State: An Historical Analysis; Washington State Department of Ecology Report 97-252.

     
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Selected petroleum spills in Washington State, 1991-1996
Washington State Department of Ecology Report 97-252
spills in gallons of product

year

spill size

bin size (log)

frequency

1991

600,000

1-2

38

1991

3,025

2-3

37

1991

210,000

3-4

17

1991

210

4-5

4

1991

100,000

5-6

4

1991

3,528

sum

100

1992

2,100

   

1992

850

   

1992

100

   

1992

70

   

1992

370

   

1992

30

   

1992

20,000

   

1992

500

   

1993

800

   

1993

495

   

1993

5,400

   

1993

900

   

1993

6,260

   

1993

60

   

1993

35

   

1993

3,000

   

1993

100

   

1993

2,995

   

1993

50

   

1993

80

   

1993

360

   

1993

30

   

1993

3,295

   

1993

50

   

1993

264,000

   

1993

25

   

1993

560

   

1993

308

   

1994

40

   

1994

2,771

   

1994

300

   

1994

40

   

1994

30

   

1994

483

   

1994

5,500

   

1994

85

   

1994

200

   

1994

50

   

1994

1,000

   

1994

700

   

1994

325

   

1994

200

   

1994

100

   

1994

25

   

1994

500

   

1994

3,700

   

1994

100

   

1994

80

   

1994

50

   

1994

26,900

   

1995

300

   

1995

200

   

1995

2,520

   

1995

50

   

1995

30

   

1995

1,000

   

1995

400

   

1995

37

   

1995

250

   

1995

50

   

1995

200

   

1995

100

   

1995

55

   

1995

100

   

1995

30

   

1995

25

   

1995

100

   

1995

50

   

1995

30

   

1995

40

   

1995

50

   

1995

75

   

1995

50

   

1995

50

   

1995

85

   

1995

120

   

1996

30

   

1996

241

   

1996

25

   

1996

200

   

1996

378

   

1996

50

   

1996

308

   

1996

1,561

   

1996

450

   

1996

37

   

1996

65,000

   

1996

700

   

1996

35

   

1996

4,000

   

1996

100

   

1996

70

   

1996

1,500

   

1996

49,000

   
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