Calculations for the Inland Rivers of the United States and Canada

The following methodology was used to estimate the loading of oil and grease to the sea from inland river basins in the United States and Canada:

  1. The location of the mouth of each river was determined on a map. These locations were then expanded into regions of interest (generally defined by the latitude and longitude of the lowest U.S. Geological Survey (USGS) gauging station and a radius around that point; see Table I-1) for which water quality data were requested from STORET. Searches were made for all surface water quality data collected within these regions.

    Data for the following parameter codes were then requested from STORET if they were included in the data summaries for the regions:

    • Parameter code 00550: oil-grse tot-sxlt (mg L−1)

    • Parameter code 00552: oil-grse tot-hexn (mg L−1)

    • Parameter code 00556: oil-grse freon-gr (mg L−1)

    • Parameter code 00560: oil-grse freon-ir (mg L−1)

    • Parameter code 03582: oil and grease tot wtr (mg L−1)

    • Parameter code 45501: hydrocarbon ir (mg L−1)

  1. Averages of all reported values in STORET for the parameter codes listed were compiled for each river (Table I-2) with the following assumptions (rivers not shown in Table I-2 did not have any usable oil and grease data):

    • Only ‘ambient’ readings in freshwater rivers were included; this means that values reported for industrial or municipal effluents, nonambient conditions, sediment, and/or ocean/estuary locations were not included in the average.

    • Some values were reported to be ‘off-scale low,’ which meant that the actual value was not known, but was known to be less than the value shown. To calculate our averages, we set these values to one-half their reported value.

    • For those rivers with data in the 1990s, average concentrations for that period were calculated.

  1. An average annual load in tonne yr−1 was calculated for those rivers with reported oil and grease data by using the following formula:

TABLE I-1 Regions Searched for Oil and Grease and Hydrocarbon Data from STORET

River

Latitude

Longitude

Radius (mi)

Alabama-Tombigbee

32º00′00″, 30º00′00″

−87º15′00″, −88º15′00″

See notea

Altamaha

32º31′30″

−81º15′45″

50

Apalachicola

See note b

 

 

Brazos

29º34′56″

−95º45′27″

50

Colorado (TX)

28º58′26″

−96º00′44″

30

Columbia

46º10′55″

−123º10′50″

50

Copper (AK)

61º00′00″

−144º45′00″

50

Delaware

39º30′03″

−75º34′07″

30

Hudson

41º43′18″

−73º56′28″

40

James

37º24′00″

−77º18′00″

50

Mississippi

29º16′26″

−89º21′00″

50

Neuse

35º06′33″

−77º01′59″

50

Potomac

38º55′46″

−77º07′02″

75

Rio Grande

25º52′35″

−97º27′15″

30

Roanoke

35º54′54″

−76º43′22″

70

Sabine

30º18′13″

−93º44′37″

50

Sacramento

37º30′00″, 38º30′00″

−121º00′00″, −123º00′00″

See notea

St. Lawrence

45º00′22″

−74º47′43″

50

Santee

33º14′00″

−79º30′00″

40

San Joaquin

37º30′00″, 38º30′00″

−121º00′00″, −123º00′00″

See notea

Saskatchewan

See noteb

 

 

Savannah

32º31′30″

−81º15′45″

50

Susitna

61º35′00″

−150º22′00″

40

Susquehanna

39º42′00″

−76º15′00″

50

Trinity

29º50′10″

−94º44′57″

30

Yukon

62º45′00″

−164º30′00″

30

NOTES: aRectangular polygons formed by the latitudinal and longitudinal coordinates shown were requested for these rivers; bNo data were requested for the Appalachicola and Saskatchewan Rivers.



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