TABLE I-17 Comparison of STORET Oil and Grease Data Used in this Study with 1990s USGS Oil and Grease Data for Louisiana

Description

Delaware River

Mississippi River

USGS Data

All Data

Statistics

Number of observations

99

46

704

849

Minimum concentration (mg L−1)

1.0

0.5

0.5

0.5

Maximum concentration (mg L−1)

122.7

6

81

122.7

Average concentration (mg L−1)

5.80

0.84

1.27

1.77

Standard deviation (mg L−1)

13.21

0.94

4.65

6.35

Percent exceedence

Mississippi 1990s average = 0.84 mg L−1

100 percent

24.6 percent

21.1 percent

30.4 percent

Delaware 1990s average = 5.80 mg L−1

21.2 percent

2.3 percent

2.6 percent

4.7 percent

automobile exhaust based), and (2) fuel oil was completely consumed (i.e., there was no oily waste discharged by users of fuel oil), then the land-based sources would be derived only from the use of middle distillate fractions that end up on the land surface or in municipal and industrial discharges. Expressing the best estimate of the land-based oil that was returned to the sea as a fraction of the total middle distillate consumption gives a ratio of 3.4/320, or 1.1 percent, which is still a very small percentage.

Table I-18 shows comparisons of the computed land-based loads presented in the current study for North America and other locations with the BP Amoco (2000) data. Note the ratio of land-based sources was very consistent for all countries shown.

The best estimate of petroleum hydrocarbon loading from land-based sources was about 8 times smaller than the best estimate from the National Research Council (1985), and was much smaller than other previous world estimates (Table I-19). Although estimates presented here were considerably different than the studies in Table I-19, the calculations used in this analysis were based on more measured data than in these previous studies, including the National Research Council (1985). The approach used in the current study was also consistent with methods for estimating pollutant loads from urban runoff. The upper range of the current estimates agreed fairly well with previous studies, but the 1990s STORET data suggest that the best estimate may be much lower than previous studies indicated.

Literature-reported data and data provided by Baker (2001) on the Susquehanna River confirmed that the Michel (2001) data were within a reasonable range for river total PAH concentrations (Table I-20). In addition, estimation of river PAH concentrations were made using average annual flows calculated from available flow data (Table I-3) with PAH loadings calculated for corresponding rivers in this study (Table I-13). The average of these calculated concentrations ranged from 242 to 2,900 ng L−1, with a best average concentration of 800 ng L−1 (Table I-21). While this concentration was greater than ambient river concentrations reported by other studies, it represents a conservative estimate of PAH concentrations in river water using the best available data. Furthermore, the calculated concentrations of PAH in the Mississippi River corresponded nicely with the range of total PAH measured by Michel (2001).

TABLE I-18 Comparison of Oil Consumption with Estimated Oil and Grease Loading from Land-based Sources to the Sea

Location

1999 Oil Consumptiona (million tonne yr−1)

Oil and Grease Loading to the Sea from Land-based Sourcesb (million tonne yr−1)

Ratio of Oil and Grease Loading to the Sea to Oil Consumption (percent)

North America

1047.1

3.4

0.3

South and Central America

218.8

0.7

0.3

Europe

755.2

3.1

0.4

Africa

115.5

0.2

0.2

NOTES: aSource: BP Amoco (2000); bCalculated in this study.



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