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Oil in the Sea III: Inputs, Fates, and Effects
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:
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)
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.
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