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Oil in the Sea III: Inputs, Fates, and Effects
TABLE E-12 Total Amount of Oil Entering the Sea from Bilge and Fuel (1989 Figures from IMO, 1990)— Worldwide
IMO 1989 (tonnes)
Year 1999 (tonnes)
Best Estimate (gallons)
Machinery Space Bilges
Fuel Oil Sludge
Oily Ballast From Fuel Tanks
sources is estimated as 272,435 tonnes (70 million gallons). The discharge of sludge accounts for about 94 percent of the total bilge oil and fuel oil input.
Fuel Oil and Bilge Oil Inputs in North American Waters
Bilge oil discharges into U.S. marine waters for vessels greater than 100 GT in size are summarized in Table E-13. Intentional discharges of cargo oil washings and sludge within U.S. and Canadian waters are believed to be small due to rigorous regulatory enforcement programs, and are assumed to be included in the spill data.
Transit miles for tankers and cargo ships operating in U.S. waters are obtained from ACOE transit data (U.S. Army Corps of Engineers Navigation Data Center, 1997b). The number and average horsepower of commercial vessels other than tankers and cargo ships is obtained from the U.S. Coast Guard Marine Safety Management System (MSMS) database. These data are used to estimate operating days in U.S. coastal waters for these other vessels. Recreational vessels and government vessels were not considered in this estimate.
The quantity of bilge oil generated is calculated assuming 0.25 gallons of bilge oil is produced per 1,000 HP per day. For MARPOL compliant vessel, it is estimated that less than 0.2 percent of bilge oil is discharged overboard. For non-compliant vessels, 100% discharge of bilge oil is assumed.
Recognizing the strong port state control measures in effect in both the U.S. and Canada, for these calculations 98% compliance with MARPOL regulations is assumed for vessels greater than 400 GT. For smaller vessels, which are not required to have oil/water separators and therefore must transfer contaminated bilge water ashore, 90% compliance is assumed. Assuming these levels of compliance, the total estimated operational discharges of bilge oil into marine U.S. waters per year is 81 tonnes (22 thousand gallons)
Table E-14 summarizes total operation discharges in North American waters. The figures for Canada and Mexico were derived by multiplying the estimated operational discharge in U.S. waters by the ratio of cargo movements in U.S. waters to the cargo movements in Canadian and Mexican waters respectively. The best estimate of total discharge in North American waters is 99 tonnes (26 thousand gallons). Approximately 38 tonnes (11 thousand gallons) are diesel oil, with the remaining 61 tonnes (16 thousand gallons) comprised primarily of heavy fuel oil and lube oil.
The tonnes of cargo moved through each region were used as a basis for distributing the total operational discharge of
TABLE E-13 Bilge Oil Discharge—U.S. Marine Waters (for vessels greater than or equal to 100 GT)