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Oil in the Sea III: Inputs, Fates, and Effects E Inputs of Petroleum Hydrocarbons into the Oceans Due to Transportation Activities Petroleum hydrocarbon inputs into the oceans from transportation activities are developed herein. Significant sources include operational discharges from ships, oil spills from tankers and non-tank vessels, operational discharges from recreational craft, and discharges from aircraft. Inputs due to atmospheric deposition of volatile organic compounds (VOC) vented from tankers are covered in Appendix H. INPUTS TO THE SEA FROM MARITIME TRANSPORTATION Operational Discharges in International Waters Oil inputs into the sea from marine sources are naturally correlated to the number and types of vessels in operation in the marine environment. The number of tankers is significant because tankers are permitted discharges related to both cargo and propulsion machinery. The number of other ships is significant because they are permitted machinery related discharges. Table E-1 shows the comparison of the world’s seagoing merchant fleet of ships not less than 100 GT for 1971, 1980, 1989, and 1999 (IMO, 1990 and Lloyd’s Register, 1999). The International Convention for Prevention of Pollution from Ships (MARPOL 73/78) regulates the design, construction, and operation of commercial vessels 100 gross tons (GT) and over worldwide with the goal of reducing or eliminating the discharge of oil and other pollutants into the sea. Many aspects of MARPOL (73/78) are of particular relevance during the calculations of estimates of input of petroleum hydrocarbon to the sea associated with marine transportation, including: All commercial vessels between 100 and 400 gross tons are required to retain all oily waste on board, unless discharged at sea through special discharge control equipment as described below. Tankers above 150 gross tons and all other commercial vessels over 400 gross tons are required to have installed oil/water separators (OWS) and oil discharge monitoring systems (ODMS), which continuously record the oil content of all overboard discharges from the bilges and, in the case of tankers, from any cargo slop tanks. For vessels above 10,000 gross tons, if oil content in the discharge stream is 15 parts per million (ppm) or greater, an alarm is supposed to sound and the discharge is terminated. No tanker is permitted to discharge cargo oil effluent, even when using an ODMS, unless the vessel is underway between ports and more than 50 nautical miles from the nearest land. Therefore, for the purposes of this report all operational discharges of cargo oil are TABLE E-1 Summary of the World’s Merchant Fleet 1971 1980 1989 1999 Number of Merchant Ships 55,014 73,832 76,100 86,817 Number of Tankers 6,292 7,112 6,383 7,270 Total Deadweight Tonnes (for Tankers) 169,354,743 339,801,719 247,556,000 298,731,000 NOTE: Non-propelled ships, ships of less than 100 gross tonnage, pleasure craft, naval auxiliaries, and ships restricted to harbor service or river/canal service are not included in the above.
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Oil in the Sea III: Inputs, Fates, and Effects presumed to occur outside the waters of the United States or any other nation. MARPOL has been adopted by nations with authority over 95 percent of the world’s merchant vessels. In the United States, MARPOL has been adopted through the Act to Prevent Pollution from Ships (33 U.S. Code 1901 et seq.) Discharges of bilge water and certain cargo tank washings from tankers are the only permitted discharges under MARPOL. Discharge of fuel oil sludge is prohibited. In order to assist vessels in complying with these prohibitions against discharge of excess quantities of oil and oil sludge into the water, waterfront facilities (where commercial vessels are received) are required to establish and maintain oil waste reception facilities. These oil waste reception facilities are suppose to have sufficient capacity to receive and process all oily wastes generated by all vessels calling at the facility. Failure to have reception facility capability is supposed to result in vessels being denied entry to the facility. For example, International Maritime Organization’s (IMO) 1998 list of waste reception facilities includes 1047 such facilities in various ports in the United States. Operational Discharges from Cargo Tanks of Oil Tankers Regulatory Background During normal operations, certain tankers may discharge into the sea an amount of oil contained in the ballast and tank washings. Under regulation 13 of MARPOL 73/78, tankers of 20,000 tonnes deadweight and above are required to have segregated ballast tanks (SBT), dedicated clean tanks (CBT), and/or crude oil washing systems (COW), depending on the vessel type, when they were built and their size. Regulation 13F adopted in 1992 restricts routing of ballast piping through cargo tanks and vice versa. These measures are designed to reduce operational and accidental pollution from tankers due to ballasting and tank washing. Generally, crude oil carriers of 20,000 deadweight and above and product tankers of 30,000 tonnes deadweight and above delivered since 1983 must have SBT. Segregated ballast tanks are ballast tanks that are completely separated from the cargo oil and fuel oil systems, and which are permanently allocated to the carriage of water ballast. SBT greatly reduces the likelihood of oily ballast discharge, as there are sufficient segregated ballast tanks for normal operation in ballast. For these vessels, ballast may be allocated to cargo tanks only when needed to insure the safety of the vessel in particularly severe weather. Unlike SBT, the piping systems for clean ballast tanks (CBT) may be common or connected with the cargo oil pump and piping systems. There are only a few CBT tankers operating today. Crude oil washing is a system of cleaning cargo tanks using the dissolving action of crude oil to reduce clingage and sludge. Crude oil washing eliminates or reduces water washing, and thereby reduces operational oil pollution. Regulation 9 of MARPOL limits the amount of oil that may be discharged into the sea to 1/15,000 of the total cargo oil volume for tankers built prior to the implementation of MARPOL73 (commonly referred to as Pre-MARPOL tankers), and 1/30,000 of the total cargo oil volume for MARPOL tankers. The requirement that the oil content of discharged effluent cannot exceed 15 ppm has the practical effect of limiting operational discharge to amounts much less than these maximum values. Table E-2 gives the number and average deadweight for tankers in year 1999, and Table E-3 presents the age profile. More than two-thirds of the current fleet has SBT or double hull (DH) arrangements. MARPOL Regulation 13G requires mandatory retirement for single hull tankers at 30 years of age. A revision to regulation 13G currently under review will phase out all Pre-MARPOL tankers by 1 January 2007, at which time all MARPOL compliant tankers will have either SBT or DH arrangements. SBT and Double Hull Crude Oil Carriers According to industry sources (INTERTANKO, unpublished), SBT and double hull crude oil carriers will water wash 3-4 cargo tanks twice a year for inspection purposes. INTERTANKO estimates an average of 6,000 m3 of wash water per tanker per year is discharged. Assuming an oil content of 15 ppm of oil, operational oil discharge is approximately 90 liters (0.08 tonnes) per year per tanker. Assuming 2/3 of the 1,782 crude oil carriers have SBT or DH arrangements, the total estimated discharge per year is as follows: SBT and DH Crude Oil Carriers: 1,782•(2/3)•0.08 = 95 tonnes For non-compliance vessels, where the ODMS is not working properly or intentionally bypassed, the estimated average discharge is 38 tonnes per year per tanker. TABLE E-2 Summary of Number and Deadweight of Tankers for Year 1999 (Lloyd’s Register, 1999) No. of Tankers Deadweight (millions of tonnes) Average Deadweight (tonnes) Crude Oil Tanker 1,782 238.5 133,838 Product Tanker 5,269 43.5 8,256 Bulk dry/Oil Tanker 219 16.7 76,256 7,270 298.7 41,087
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-3 Age Profile of Tankers as a Function of Tonnes Deadweight (World Fleet Statistics, 1999) Crude Oil Carriers Product Tankers Dry Bulk / Oil Carriers Total All Tankers 0−4 Years 22 percent 13 percent 7 percent 20 percent 5−9 Years 25 percent 11 percent 19 percent 22 percent 10−14 Years 11 percent 10 percent 21 percent 11 percent 15−19 Years 8 percent 21 percent 25 percent 11 percent 20−24 Years 28 percent 25 percent 24 percent 27 percent 25+ Years 6 percent 20 percent 14 percent 9 percent Total 100 percent 100 percent 100 percent 100 percent Pre-MARPOL Crude Oil Carriers As discussed previously, these tankers carry ballast in their cargo tanks. Based on the Lloyd’s Register (1999) statistics, the average deadweight of crude oil carriers is 133,844 tonnes. Assuming 30 percent of the deadweight is discharged as arrival ballast with an oil content of 15 ppm, the average quantity of water ballast per voyage is 40,153 tonnes and the average oil discharge is 588 liters or 0.528 tonnes. An industry survey undertaken by INTERTANKO indicates that 70 percent of all tankers carry a full load of cargo and 30 percent are partially loaded to an average of 60 percent of capacity. Consumables equaling about 5 percent of deadweight are also carried. Therefore, it is assumed that on the typical voyage a tanker carries cargo oil equal to approximately 80 percent of its deadweight. The average cargo oil moved on a crude oil carrier is 80 percent of 133,844 tonnes or about 107,075 tonnes, and the outflow factor, expressed as a fraction of the cargo oil moved, equals 0.0528 / 107,075 = 1 / 202,797. A rounded value of 1/200,000 is assumed for these calculations. This is a conservative estimate, as it assumes ballast is discharged at the maximum permissible oil content of 15 ppm, and also neglects the fact that many Pre-MARPOL tankers carry a portion of their ballast in segregated ballast tanks. As reported by Concordia Maritime AB, an operator of a large fleet of Pre-MARPOL VLCCs (Very Large Crude Carriers), the average oil discharge from their Pre-MARPOL VLCCs is 300 liters per voyage. The average cargo volume for their VLCCs is approximately 300,000 m3. Thus, the outflow factor attained by the Concordia fleet is (300/1,000) / 300,000 = 1 / 1,000,000. This is significantly better than the assumed factor of 1 / 200,000, but the performance level achieved by Concordia Maritime is believed to exceed standard practice. For a crude oil washing system to be MARPOL certified, the oil found floating on top of the departure ballast after crude oil washing cannot exceed 0.00085 times the volume of the tanks containing ballast. On this basis, the oil content in the ballast tanks for this average size tanker is 33.3 tonnes. Assuming non-compliance where the ODMS is not working properly or intentionally bypassed, the oil outflow factor becomes 33.3 / 107,075 = 1 / 3,216. A rounded value of 1/ 3,000 is assumed for these calculations. As summarized in Table E-4, the total outflow from non-SBT crude oil carriers is calculated as follows: The crude oil carriers are divided into the following size ranges: Less than 20,000 DWT 20,000 to 125,000 DWT (includes Panamax and Aframax tankers) 125,000 to 175,000 DWT (includes Suezmax tankers) Greater than 175,000 DWT (includes VLCCs and ULCCs) Within each size range, the number of crude oil carriers and the average deadweight are derived from 1999 statistics (Lloyd’s Register, 1999). The number of voyages per annum for each size is estimated from industry sources (INTERTANKO, unpublished). One-third of the crude oil carriers are assumed to regularly carry ballast in cargo oil tanks. Multiplying the number of tankers in each size range by 1/3 provides the estimated number of non-SBT tankers in 1999. Multiplying the average deadweight for each size by 80 percent provides the average quantity of cargo oil carried per voyage. The product of the number of non-SBT tankers, the quantity of cargo oil carried per voyage, and the number of voyages per annum provides the total cargo oil movement for each size range. Summing these figures gives the estimated cargo oil movements on non-SBT tankers of 1,000.8 million tonnes per year. Assuming an outflow factor of 1/200,000 as described above, the projected operational discharge in tonnes per year is as follows. Non-SBT Crude Oil Carriers: 1,000,800,000/ 200,000 = 5,004 tonnes Product Tankers For 1999, the Lloyd’s Register data show a total of 5,269 product tankers with an average deadweight of 8,256 tonnes. Their average cargo cubic is approximately 10,000 m3. Assuming the volume of the slop tanks equals 3 percent of the
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-4 Calculation of Operational Cargo Oil Discharge from pre-MARPOL (non-SBT) Crude Oil Carriers— Worldwide less than 20,000 DWT 20,000 to 125,000 DWT 125,000 to 175,000 DWT greater than 175,000 DWT all non-SBT Crude Tkrs Total No. of Crude Oil Carriers 154 923 256 449 1,782 Assumed percent non-SBT 33.3 percent 33.3 percent 33.3 percent 33.3 percent 33.3 percent No. of non-SBT Crude Oil Carriers 51 308 85 150 594 Average Deadweight (tonnes) 5,811 76,561 144,857 289,235 133,844 Cargo Oil as percent of Deadweight 80 percent 80 percent 80 percent 80 percent — Cargo Oil per Voyage (tonnes) 4,649 61,249 115,885 231,388 72,732 Voyages (per year) 40 30 15 8 23.2 Total Cargo Oil Moved (millions tonnes) 9.5 565.9 147.8 277.7 1,000.8 Discharge as percent of Cargo Oil Moved 1/200,000 1/200,000 1/200,000 1/200,000 1/200,000 Estimated Discharge (tonnes/year) 47 2,830 739 1,388 5,004 oil carrying capacity of the ship, the average slop tank capacity is 300 m3. Assuming the slop tanks when charged with water have sufficient water for tank washing without introduction of additional water into the system, and that the full contents of the slop tanks are discharged at 15 ppm oil content, the projected operational oil discharge per voyage is about 4.5 liters. This corresponds to an outflow factor less than 1/2,000,000. Applying this factor for product tankers with SBT is a conservative assumption, as tank cleaning is not required in all circumstances, and cleaning is often carried out alongside a refinery where the slops can be transported ashore. In the case of non-SBT product tankers where ballast is carried in cargo tanks, the outflow factor of 1/200,000 as applied for non-SBT crude oil carriers is appropriate. Annual discharges for non-SBT product tankers are developed similar to the crude carriers, and are summarized in Table E-5. The projected operational discharge in tonnes per year is as follows. Non-SBT Product Tankers: 382,700,000 / 200,000 = 1,914 tonnes Assuming 0.02 percent of the cargo oil remains onboard after offloading cargo, the average amount of oil remaining TABLE E-5 Calculation of Operational Cargo Oil Discharge from pre-MARPOL (non-SBT) Product Tankers—Worldwide less than 20,000 DWT 20,000 to 125,000 DWT all non-SBT Product Tkrs Total No. of Product Tankers 4,545 724 5,269 Assumed percent non-SBT 33.3 percent 33.3 percent 33.3 percent No. of non-SBT Product Tankers 1515 241 1756 Average Deadweight (tonnes) 2,894 41,911 8,255 Cargo Oil as percent of Deadweight 80 percent 80 percent — Cargo Oil per Voyage (tonnes) 2,315 33,529 5,643 Voyages (per annum) 40 30 38.6 Total Cargo Oil Moved (millions tonnes) 140.3 242.4 382.7 Discharge as percent of Cargo Oil Moved 1/200,000 1/200,000 1/200,000 Estimated Discharge (tonnes/year) 702 1,212 1,914
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Oil in the Sea III: Inputs, Fates, and Effects onboard the product tankers is 2 m3 or about 1.8 tonnes. For non-compliance where the ODMS is not working properly or intentionally bypassed, the oil outflow factor becomes 2 / 10,000 = 1 / 5,000. This 1 / 5,000 factor is applied for both SBT and non-SBT product tankers. This is a conservative estimate, as it assumes that all oil remaining onboard the non-compliant tankers is discharged at sea. The oil discharge monitoring systems (ODMS) on clean product tankers have a higher degree of reliability as compared to vessels carrying persistent oils, and the discharge due to equipment failure should be less. Summary of Operational Discharges of Cargo Oil from Tankers Table E-6 summarizes total operational discharges assuming all tankers operate in compliance with MARPOL73/ 78. The estimated discharge per year is 7,396 tonnes. In the 1990 study on inputs of petroleum into the marine environment (IMO 1990), the following estimates were made with regard to tankers complying with MARPOL maximum discharge quantities: Greater than 150,000 DWT 99 percent compliance 75,000 to 150,000 DWT 95 percent compliance 40,000 to 75,000 DWT 85 percent compliance 20,000 to 40,000 DWT 85 percent compliance Less than 20,000 DWT 80 percent compliance The rationale for this degree of non-compliance is that 1) not all tankers fly the flag of a state that is party to MARPOL 73/78, 2) not all tankers that fly the flag of a state party to MARPOL 73/78 operate in compliance with the discharge criteria; 3) there will be equipment failures onboard ships, and, 4) there are not adequate reception facilities worldwide. The higher degree of compliance allocated to the larger tankers was justified on the basis that the large majority of the larger tankers fly the flag of a state party to MARPOL 73/78, and the majority of larger tankers are on longer voyages which facilitates compliance with MARPOL 73/78. Since 1990, tanker operations have come under much closer scrutiny. Port state oversight has increased, and regulations such as the International Ship Management Code (ISM) and the Standards for Training and Certification of Watchkeepers (STCW) have encouraged more diligent operations. In view of the above, the assumed compliance rates have been increased to the following values. Greater than 125,000 DWT 99 percent compliance 20,000 to 125,000 DWT 95 percent compliance Less than 20,000 DWT 90 percent compliance Table E-7 summarizes total operational discharges assuming these levels of compliance with MARPOL73/78. The estimated discharge per year is 36,437 tonnes (10,712,461 gallons). These discharges are applicable to international waters. Discharge of oily water within 50 nautical miles from shore is prohibited. Intentional discharges within U.S. and Canadian waters are believed to be small due to rigorous enforcement programs. Bilge Oil and Fuel Oil Inputs Machinery Space Bilge Discharges from Tankers The large majority of commercial vessels above 100 GT in size are motor ships. The 1990 International Maritime Organization report estimated the average production of bilge oil at 12 gallons per day for a 20,000 HP plant. Advancements in the design and manufacture of engines and pumps, fitting of coamings around pumps and other sources of oil on new vessels, locating of the purifiers into separate spaces, and other design improvements have brought about a TABLE E-6 Calculation of Operational Cargo Oil Discharge from Tankers Assuming Full Compliance with MARPOL 73/78 Crude Oil Carriers DH or SBT Crude Oil Carriers without SBT Product Tankers DH or SBT Product Tankers without SBT No. of Tankers 1,188 594 3,513 1,756 Discharge per Tanker (tonnes per year) 0.08 — — — Oil Movements (millions of tonnes/year) — 1,000.8 765.5 382.7 Outflow Factor — 1/200,000 1/2,000,000 1/200,000 Operational Discharge (tonnes/year) 95 5,004 383 1,914 Total Discharge (tonnes/year) 7,396
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-7 Calculation of Operational Cargo Oil Discharge from Tankers Assuming Partial Non-Compliance with MARPOL 73/78—Worldwide Crude Oil Carriers DH or SBT Crude Oil Carriers without SBT Product Tankers DH or SBT Product Tankers without SBT MARPOL Compliant No. of Tankers 1,140 570 3,187 1,593 Discharge per Tanker (tonnes per year) 0.08 — — —- Oil Movements (millions tonnes/year) — 965.1 713.3 356.7 Outflow Factor — 1/200,000 1/2,000,000 1/200,000 Operational Discharge (tonnes/year) 91 4,825 357 1,783 Total discharge from compliant tkrs 7,056 Non-compliant No. of Tankers 48 24 326 163 Discharge per Tanker (tonnes per year) 38 — — —- Oil Movements (millions of tonnes/year) — 35.8 52.1 26.1 Outflow Factor — 1/3,000 1/5,000 1/5,000 Operational Discharge (tonnes/year) 1824 11,923 10,422 5,211 Total discharge from non-compliant tankers 29,381 Total Discharge (tonnes/year) 36,437 Total Discharge (gallons/year) 10,257,685 reduction in bilge oil generation for modern ships. For these calculations, a rate of 5 gallons per day for a 20,000 HP plant, or 0.25 gallons per 1,000 HP per day is assumed. An estimation of bilge oil generation for tankers is provided in Table E-8. The number of tankers is taken from the Lloyd’s Register data for 1999, and the horsepower is estimated based on the distribution of tanker sizes. Assuming 0.25 gallons of bilge oil is generated per 1,000 HP per day, and that the tankers operate 350 days per year, it is estimated that a total of 19,119 tonnes (5.3 million gallons) of bilge oil is generated per year. On crude oil tankers, oily bilge water is routinely transferred to the cargo slops system, which includes an oily water separator system where most of the oil is settled out and returned for use on the tanker. Periodically the water collected through this system must be discharged overboard through an oil discharge monitoring system set to alarm and shut down at 15 ppm. Product tankers are not able to recycle as much oil but, in any case, oil content of all overboard discharge is restricted to 15 ppm. Assuming a 15 ppm oil content for bilge discharges, it is estimated that less than 0.2 percent of bilge oil is discharged overboard. Table E-9 summarizes the expected bilge oil discharge for tankers. The rate of MARPOL compliance is assumed as described in the previous section on operation discharges, and non-compliant vessels are assumed to discharge all of their bilge oil overboard. The discharge from MARPOL compliant tankers is very small—a total of only 34 tonnes per year. Total discharge from both compliant and non-compliant tankers is estimated at 1,129 tonnes (313,621 gallons) per year. This is considered to provide a conservative estimate of legally permitted discharges. Steam tankers generate less oil to the bilges. Because steam tankers make up less than 5 percent of the world fleet, the above calculations assumed that all tankers are motorships. Machinery Space Bilge Discharges from Non-Tankers According to Lloyd’s Register data there were 79,547 non-tankers above 100 GT in size operating commercially around the world in 1999. These consisted of 38,732 commercial vessels with an average main propulsion power of about 7,500 HP, and 40,815 other vessels with an average power of about 500 HP. Bilge oil discharges for non-tankers are summarized in Table E-10. A bilge oil generation rate of 0.25 gallons/1000 HP per day was applied. Vessels between 100 GT and 400 GT, which comprise some 54 percent of the non-tanker fleet, are not required to have oily water discharge equipment installed. Although these vessels are not permitted to discharge bilge effluent, it is believed that there is a significant level of non-compliance. To account for this, 15 percent of the commercial vessels and 30 percent of the other vessels were assumed to not comply with MARPOL regulations. Total bilge oil discharge from both compliant and non-compliant vessels other than tankers is estimated at 15,607 tonnes (4.0 million gallons) per year. Fuel Oil Sludge from All Vessels Based on 1998 data collected by INTERTANKO (unpublished), the world annual use of fuel oil from marine application is estimated to be 130 million tonnes of heavy residual fuel oil and 40 million tonnes of distillate fuel. Based on
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-8 Generation of Bilge Oil for Tankers—Worldwide Crude Oil Carriers Product Tankers Dry Bulk/ Oil Carriers No. of Tankers 1,782 5,269 219 Average Size of Propulsion Machinery (HP) 21,000 3,700 15,000 Assumed Bilge Oil Generation (gal/1000 HP/day) 0.250 0.250 0.250 Average Bilge Oil Generation (gal/day/ship) 5.3 0.9 3.8 Assumed Time in Service (Days/Year) 350 350 350 Bilge Oil Generation (gallons/year) 3,274,425 1,705,839 287,438 Bilge Oil Generation (tonnes/year) 12,038 6,059 1,021 Total Tankers Bilge Oil Generation (tonnes/year) 19,119 Total Tankers Bilge Oil Generation (gallons/year) 5,267,701 databases on marine bunker supply maintained by the Energy Information Administration (EIA) and the International Energy Agency (IEA), IMO estimated consumption during 1996 as 100 million tonnes of heavy residual fuel oil and 38 million tonnes of distillate fuel (IMO 2000). An unpublished study by INTERTANKO, which assessed consumption based on the world fleet makeup in year 2000 and the estimated consumption per vessel, estimated overall consumption at 224 million tonnes. For this report, the 1998 estimate of 170 million tonnes per year of fuel oil consumption is applied when calculating sludge generation. Heavy fuel oils contain between 1 percent and 5 percent sludge or waste oil, which cannot be burned as fuel and therefore must be disposed of by other means. A value of 1.5 percent is applied for these calculations. MARPOL prohibits the discharge of any of this sludge to the sea. Diesel fuel oil does not produce any appreciable quantity of sludge and therefore is discounted from further consideration here. The total production of sludge from ships is estimated as 130 million • 0.015 = 1.95 million tonnes (499 million gallons) of sludge per year. As noted above, MARPOL requires that all sludge must either be retained on board for discharge to a reception facility ashore or for other legal treatment on board the vessel. On-board treatment includes mixing and homogenizing sludge with the fuel oil, use of on-board incinerators, and on crude oil tankers, transferring the sludge to the cargo or slop tanks. Not all vessels are equipped with incinerators or slop tanks or have the capability to otherwise treat all produced sludge on board. Waste reception facilities exist throughout the world. There are over 1,000 such facilities in the United States alone. It is widely acknowledged that such facilities are not used to the fullest extent due to a variety of reasons TABLE E-9 Bilge Oil Discharge from Tankers Greater Than 100 GT—Worldwide Crude Oil Carriers Product Tankers Dry Bulk/ Oil Carriers MARPOL Compliant No. of Tankers 1,782 5,269 219 Total Bilge Oil Generation (tonnes/year) 12,038 6,059 1,021 Percent of Tankers Assumed MARPOL Compliant 96 percent 91 percent 93 percent Discharge as a percent of Bilge Oil Generated 0.2 percent 0.2 percent 0.2 percent Bilge Oil Discharge (tonnes/year) 23.2 11.0 1.9 Total discharge from compliant tankers (tonnes/year) 36 Non-compliant Percent of Tankers Assumed Non-MARPOL Compliant 4 percent 9 percent 7 percent Discharge as a percent of Bilge Oil Generated 100 percent 100 percent 100 percent Bilge Oil Discharge (tonnes/year) 457.5 563.5 71.5 Total discharge from non-compliant tankers (tonnes/year) 1,092 Total Discharge (tonnes/year) 1,129 Total Discharge (gallons/year) 313,121
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-10 Bilge Oil Discharge from Non-Tankers Greater Than 100 GT—Worldwide Commercial Vessels Other Vessels Bilge Oil Generation No. of Ships 38,732 40,815 Average Size of Propulsion Machinery (HP) 7,500 500 Assumed Bilge Oil Generation (gal/1000 HP/day) 0.250 0.250 Average Bilge Oil Generation (gal/day/ship) 1.9 0.1 Assumed Time in Service (Days/Year) 350 100 Bilge Oil Generation (gallons/year) 25,417,875 510,188 Bilge Oil Generation (tonnes/year) 99,289 1,809 Marpol Compliant Percent of Vessels Assumed MARPOL Compliant 85 percent 70 percent Discharge as a percent of Bilge Oil Generated 0.2 percent 0.2 percent Bilge Oil Discharge (tonnes/year) 168.8 2.5 Total discharge from compliant ships (tonnes/year) 171 Non-compliant Percent of Tankers Assumed Non-MARPOL Compliant 15 percent 30 percent Discharge as a percent of Bilge Oil Generated 100 percent 100 percent Bilge Oil Discharge (tonnes/year) 14,893 543 Total discharge from non-compliant tankers (tonnes/year) 15,436 Total Discharge (tonnes/year) 15,607 Total Discharge (gallons/year) 4,009,662 including cost and timeliness. Therefore, it is generally assumed that some quantity of oily sludge is discharged to the sea in contravention of MARPOL. The previous study (IMO, 1990) estimated that quantity to be 10 percent for tankers and 25 percent for non-tankers. Recognizing improvements in vessel operations and enforcement regimes since then, for these calculations non-compliance is taken as 5 percent for tankers and 15 percent for non-tankers. As shown in Table E-11, total sludge discharge to the sea from both compliant and non-compliant vessels is estimated at 255,700 tonnes (65 million gallons) per year. Oily Ballast from Fuel Tanks Discharges of oily ballast from fuel tanks are considered to be negligible. Placing seawater in fuel tanks as ballast water introduces contaminants into those tanks, increasing engine maintenance and the risk of malfunction. Thus, the practice is avoided whenever possible. Summary of Bilge Oil and Fuel Oil Inputs Bilge oil and fuel oil inputs are summarized in Table E-12. The total amount of oil entering the sea from these TABLE E-11 Fuel Oil Sludge Discharge—Worldwide Tankers Non-Tankers No. of Ships 7,270 79,547 Average Size of Propulsion Machinery (HP) 8,281 3,908 Fuel Oil Consumption—Residual Fuel (million tonnes) 24.5 105.5 Fuel Oil Consumption—Distillate Fuel (million tonnes) 0.0 40.0 Sludge Content of Residual Fuel 1.5 percent 1.5 percent Sludge Content of Distillate Fuel 0.0 percent 0.0 percent Sludge Generation (tonnes/year) 368,004 1,581,996 Percent of Ships Assumed Non-MARPOL Compliant 5 percent 15 percent Sludge Discharge (tonnes/year) 18,400 237,299 Total Sludge Discharge (tonnes/year) 255,700 Total Sludge Discharge (gallons/year) 65,459,110
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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 64,400 16,736 4,322,783 Fuel Oil Sludge 186,800 255,700 65,459,110 Oily Ballast From Fuel Tanks 1,400 0 0 Total 252,600 272,435 69,781,893 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) Tankers Vessels > 400 GT in size Cargo Ships Other 100 GT to 400 GT Days operating in U.S. coastal waters (days/year) 67,000 209,000 110,000 235,000 Average Size of Propulsion Machinery (HP) 7,500 8,300 3,900 1,200 Assumed Bilge Oil Generation (gal/1000 HP/day) 0.250 0.250 0.250 0.250 Average Bilge Oil Generation (gal/day/ship) 1.9 2.1 1.0 0.3 Bilge Oil Generation (gallons/year) 125,625 433,675 107,250 70,500 Bilge Oil Generation (tonnes/year) 491 1,694 380 250 MARPOL COMPLIANT Total Bilge Oil Generation (tonnes/year) 491 1,694 380 250 Percent assumed MARPOL Compliant 98.0 98.0 98.0 90.0 Discharge as a Percent of Bilge Oil Generated 0.2 0.2 0.2 0.0 Bilge Oil Discharge (tonnes/year) 1.0 3.3 0.7 0.0 NON-COMPLIANT Percent of Tankers Assumed Non-MARPOL Compliant 2 2 2 10 Discharge as a Percent of Bilge Oil Generated 100 100 100 100 Bilge Oil Discharge (tonnes/year) 9.8 33.9 7.6 25.0 Total Bilge Oil Discharge (tonnes/year) 81 Total Bilge Oil Discharge (gallons/year) 21,687
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-14 Total Bilge Oil Discharge—North American Waters (for vessels greater than or equal to 100 GT) (tonnes) (gallons) United States 81 Canada 11 Mexico 7 Best estimate 99 26,465 bilge oil amongst the various zones. These results are summarized in Table E-15. Summary of Fuel Oil and Bilge Oil Inputs (for Vessels greater than or equal to 100 GT) Estimated operational discharges for both North American waters and international waters are summarized in Tables 2-2 through 2-6. Considering the high level of uncertainty in the assumptions on the extent of MARPOL compliance, the minimum estimate is taken as 50% of the best estimate, and the maximum estimate at twice the best estimate. Fuel Oil and Bilge Oil Inputs in North American Waters (for Vessels less than 100 GT) Bilge oil discharges into U.S. marine waters for vessels less than 100 GT in size are summarized in Table E-16. According to U.S. Coast Guard Marine Safety Management System (MSMS) database, in year 2000 there were 41,313 registered vessels in the U.S. under 100 GT, other than tankers, cargo ships, and recreational vessels. This average size for propulsion machinery was 350 HP. It was assumed that these vessels generated 0.09 gallons of bilge oil per day, operated 50 days per year, and that 60% of the vessels operated in marine (non inland) waters. These estimates were the best judgment of the committee, as data were not available. Based on the above, the total bilge oil generation in the vessels less than 100 GT was calculated to be 385 tonnes per year (108 thousand gallons per year). A 70% compliance level was assumed for these smaller vessels. For MARPOL compliant vessels, it is assumed that all bilge oil is retained onboard and disposed at suitable reception facilities. For non-compliant vessels, 100% discharge of bilge oil is assumed. The calculated value, also considered the best estimated, was therefore 30% of 385 tonnes per year, or 115 tonnes per year (33 thousand gallons per year). All of these discharges are assumed to be diesel oil and other light distillates. The distributions by zone are summarized in Table E-18. Due to the very high level of uncertainty in these calculations, a range from 23 tonnes per year (20% of the best estimate) to 575 tonnes per year (five times the best estimate) was selected. Worldwide estimates for vessels under 100 GT were not developed due to the lack of data. Also, estimates were not developed for Canadian and Mexican waters. Accidental Spills from Vessels in North American Waters Spill Trends in U.S. Waters Figure E-1 shows the oil spillage in U.S. waters from tank vessels during the period from 1973 to 1999. The oil spill data are from the Environmental Research Consulting Spill TABLE E-15 Operational Discharge Summary (for vessels greater than or equal to 100 GT) Best Estimate (tonnes) Minimum (tonnes) Minimum (tonnes) Best Estimate (gallons) Maximum (gallons) Maximum (gallons) North American Waters Machinery Space Bilges 99 26,465 Fuel Oil Sludge 0 0 Oily Ballast From Fuel Tanks 0 0 Total—North American Waters 99 33 300 26,000 9,000 80,000 International Waters Machinery Space Bilges 16,637 0 Fuel Oil Sludge 255,700 0 Oily Ballast From Fuel Tanks 0 0 Total—International Waters 270,000 90,000 810,000 70,000,000 23,000,000 210,000,000 Worldwide Machinery Space Bilges 16,736 4,322,783 Fuel Oil Sludge 255,700 65,459,110 Oily Ballast From Fuel Tanks 0 0 TOTAL—WORLDWIDE 270,000 90,000 810,000 70,000,000 23,000,000 210,000,000 NOTE: All totals rounded to two significant figures.
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-16 Total Bilge Oil Discharge—North American Waters (for vessels less than 100 GT) Number of Registered Vessels < 100 GT in size 41,313 Estimated percentage operating in marine waters 60 Estimated operating days per year 50 Days operating in U.S. coastal waters (days/year) 1,240,000 Days operating in U.S. coastal waters (days/year) 1,240,000 Average Size of Propulsion Machinery (HP) 350 Assumed Bilge Oil Generation (gal/1000 HP/day) 0.250 Average Bilge Oil Generation (gal/day/ship) 0.088 Bilge Oil Generation (gallons/year) 108,500 Bilge Oil Generation (tonnes/year) 385 MARPOL Compliant Total Bilge Oil Generation (tonnes/year) 385 Percent assumed MARPOL Compliant 70 Discharge as a Percent of Bilge Oil Generated 0.0 Bilge Oil Discharge (tonnes/year) 0.0 Non-compliant Percent of Tankers Assumed Non-MARPOL Compliant 30 Discharge as a Percent of Bilge Oil Generated 100 Bilge Oil Discharge (tonnes/year) 115.4 Total Bilge Oil Discharge (tonnes/year) 115 Total Bilge Oil Discharge (gallons/year) 32,885 Databases, which collate data from a number of sources, including the U.S. Coast Guard, U.S. National Response Center, the U.S. Minerals Management Service, and the Oil Spill Intelligence Report. As illustrated in Figure E-1, oil spillage dropped off significantly after 1991. This improvement followed the grounding of the Exxon Valdez in 1989, and the subsequent passage of the Oil Pollution Act of 1990 (OPA 90). Estimated Spill Rates for North American Waters In recognition of the fundamental changes to the maritime industry that took place after the Exxon Valdez accident, spill data from 1990 onward were used as the basis for estimating the amount of oil entering U.S. waters from marine vessel accidents. Because complete spill data for Canadian and Mexican waters are not available, the estimated input from these waters was based on U.S. spill data adjusted for the relative tonnage moved through Canadian and Mexican waters as compared to U.S. waters. Although effort is required to carefully evaluate data from the U.S. Coast Guard spill database to avoid double counting, the data were consistently collected during the 1990s and are considered reliable, particularly with regard to the larger spills. The database, which contains generally conservative estimates of outflow from all reported incidents, is assumed to establish the minimum estimate. Table E-17 lists the amount of petroleum hydrocarbons spilled in the sea in U.S. marine waters from 1990 through 1999. A total of 1,745 spills of 0.34 tonnes (100 gallons) or more occurred during this ten year period, discharging some 9,111 tonnes (2,520,134 gallons) into marine waters. 175 of these spills were greater than 34 tonnes (10,000 gallons) in size, and these large spills accounted for about 87% of the total spillage. Table E-18 shows the breakdown of the spillage by types of vessels and types of oil. Tankers and tank barges were responsible for 82% of the total spillage. Oil types were separated into four categories. Spillage by oil type was as follows: crude Oil (36%), heavy distillate (36%), light distillate (25%), and gasoline (3%). Estimation of Spills in Canadian and Mexican Waters Because a comprehensive spill database for Canadian and Mexican waters were not available, the spill volumes were estimated by adjusted U.S. figures by the relative movements of cargo. In 1997, approximately 715 million tonnes of crude oil and products were moved in U.S. international and coastwise trade (USACE, 1997b). In comparison, about 68 million tonnes were moved through Canadian ports (Statistics Canada, 1997), or 9.5 percent of the U.S. movements. Similarly, about 112 million tonnes of crude and products were moved through Mexican ports (BP World Statistics, 1997), or 15.7 percent of the U.S. movements. Inputs from accidental spills from tank vessels in Canada and Mexico were taken as 9.5 percent and 15.7 percent of the U.S. values respectively. Canadian and Mexican dry cargo movements are approximately one-third and one-twentieth of the U.S. international and coastwise movements respectively. However, freighters are responsible for only 18 percent of the spillage from other vessels in U.S. waters. It was assumed that spills in Canadian water from other vessels equals 15 percent of the U.S. totals, and that spills in Mexican waters from other vessels equals 6 percent of the U.S. totals. Summary of Spills in North American Waters The U.S. Coast Guard database, which contains generally conservative estimates of outflow from all reported incidents, is assumed to establish the minimum estimate. Recognizing the completeness of the data, the spill quantities were increased by just 5 percent to obtain the best estimate, and further increased by 20 percent to obtain the maximum estimate. Results are summarized in Table E-19. The recording of the location of spills was not as consistently maintained within the U.S. Coast Guard spill database. This data has been reviewed and summarized in Tables 2-2 through 2-6, in order to provide a sense of the distribution of spills within U.S. waters. Accidental Spills from Vessels in International Waters For this study, spill data from the Environmental Research Consulting database is applied. This database includes information gleaned from the International Maritime Organization, ITOPF, and other national and regional agencies. The international data excludes spills in North American waters. As shown in Table E-20, a total of 745,292 tonnes of oil spillage was recorded during the years 1990 through 1999,
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Oil in the Sea III: Inputs, Fates, and Effects FIGURE E-1 Historical trend (1973-1999) in oil spills from vessels into U.S. marine waters (data from U.S. Coast Guard and MMS databases by Environmental Research Consulting.) averaging 74,529 tonnes (22 million gallons) per year during this ten year period. Not included in these totals is the spillage associated with the Gulf War, which is estimated to be in excess of 600,000 tonnes. The international data are not consistently collected and are therefore regarded as underestimates. Smaller spills are frequently not included, and reporting is sometimes compromised for political and logistical reasons. Recognizing the TABLE E-17 Summary of Oil Input from Accidental Spills (for Vessels in U.S. Waters) Tanker Tank Barge Other Vessels Year # Spills >100 gal Amount Spilled (gallons) Amount Spilled (tonnes) # Spills >100 gal Amount Spilled (gallons) Amount Spilled (tonnes) # Spills >100 gal Amount Spilled (gallons) Amount Spilled (tonnes) 1990 24 4,605,092 16,963 58 1,389,000 5,061 193 437,584 1,589 1991 13 43,348 154 39 631,934 2,431 176 279,274 1,020 1992 22 114,431 422 41 342,823 1,319 236 319,337 1,131 1993 26 78,729 300 42 661,848 2,562 213 301,703 1,111 1994 17 62,502 237 46 900,841 3,442 186 191,300 679 1995 10 84,369 304 33 70,492 251 169 304,268 1,110 1996 11 275,223 1,032 40 1,116,606 3,983 179 226,322 819 1997 5 3,952 15 27 139,447 482 142 145,493 531 1998 9 39,330 153 27 169,490 622 162 247,736 875 1999 4 4,590 17 19 157,680 511 89 67,117 246 Totals 141 5,311,566 19,597 372 5,580,161 20,665 1745 2,520,134 9,111 Ave./yr 14 531,157 1,960 37 558,016 2,067 175 252,013 911 Total—All Vessels—U.S. Waters (average over period from 1990-1999) Number of Spills 226 spills > 100 gallons in size per year Amount of Spillage 1,341,186 gallons spilled per year (average) 4,937 tonnes spilled per year (average)
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-18 Summary of Average Total Load from Accidental Spills during Years 1990-1999, for Vessels in U.S. Waters by Type of Vessel and by Type of Oil (tonnes) Tankers Tank Barges Other Vessels Totals % of Total Crude oil 16,525 1,184 162 17,872 36% Gasoline 187 1,459 50 1,697 3% Light distillate 545 5,466 6,247 12,259 25% Heavy distillate 2,340 12,556 2,651 17,546 36% TOTALS 19,597 20,665 9,110 49,373 (Percent of total) 40 42 18 incompleteness of the data and the fact that the smaller spills, under 10,000 gallons (34 tonnes), comprised about 13 percent of the U.S. totals, the international spill quantities were increased by 25 percent to obtain the minimum estimate, by an additional 10 percent to obtain the best estimate, and further increased by 25 percent to obtain the maximum estimate. Results are summarized in Table E-21. Accidental Spills from Vessels Worldwide The North American and international spill estimates are combined to provide worldwide estimates (Tables 2-2 through 2-6). The best estimate for total spillage worldwide is 110,000 tonnes (30 million gallons) per year. The 1985 report (National Research Council, 1985) and the 1990 study (IMO, 1990) both used data from the International Tanker Owners Pollution Federation Ltd. (ITOPF) to estimate the quantity of oil entering the marine environment from tanker accidents. In the 1990 study, the spillage was averaged for the 10-year period from 1981 to 1989, establishing an annual average of 114,000 tonnes per year. In the 1990 report no adjustments were made for the deficiencies in the database, so care should taken when comparing these figures. Inputs To The Sea From The Aircraft Industry There are inputs to the sea from deliberate and continual releases of fuel from aircraft. There are two sources: deliberate discharge due to emergency conditions aboard the aircraft, and normal operation releases including the release of partially burned fuel in inefficient engines or inefficient operating modes and emptying of fuel injection bypass canisters. Modern aircraft have take-off weights exceeding their landing weights, sometimes by as much as 150 tonnes. For example, a 747 can carry as much as 220,000 L of fuel weighing about 175,000 kg or 175 tonnes. If a fully laden 747 jettisoned its fuel because it was required to return to an airport, it could dump as much as 150 tonnes of the fuel to enable it to land safely. Fuel dumping is infrequent but not rare. One airport reported on 16 fuel dumps in one year out of 7,000 flights conducted [Canadian Environmental Assess TABLE E-19 Summary of Average Annual Loads from Accidental Spills (for Vessels in North American Waters) Tank Vessels (gallons) Other Vessels (gallons) All Vessels (gallons) Tank Vessels (tonnes) Other Vessels (tonnes) All Vessels (tonnes) Spill Volume—U.S. Waters (per year) 1,089,173 252,013 1,341,186 4,026 911 4,937 Est. Spill Volume—Canada (per year) 100,000 38,000 138,000 384 137 521 Est. Spill Volume—Mexico (per year) 170,000 15,000 185,000 631 55 686 1,359,173 305,013 1,664,186 5,042 1,102 6,144 Tank Vessels Other Vessels (gallons) (tonnes) (gallons) (tonnes) North American Waters Minimum (based on 1990’s data) 1,400,000 5,000 300,000 1,100 Best Estimate (1990’s data + 5 percent) 1,400,000 5,300 300,000 1,200 Maximum (Best estimate + 20 percent) 1,700,000 6,400 400,000 1,400 NOTE: All totals rounded to two significant figures.
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Oil in the Sea III: Inputs, Fates, and Effects TABLE E-20 Summary of Oil Input from Accidental Spills for Vessels (International Waters—Spills in North American Waters Excluded) Year Tank Vessels Amount Spilled (tonnes) Other Vessels Amount Spilled (tonnes) All Vessels Amount Spilled (tonnes) 1990 39,687 4,757 44,444 1991 169,077 4,315 173,393 1992 113,171 2,454 115,624 1993 107,895 3,269 111,164 1994 96,652 6,220 102,872 1995 12,439 4,358 16,797 1996 62,507 7,358 69,864 1997 62,846 3,344 66,190 1998 20,516 3,839 24,355 1999 17,613 2,976 20,589 Totals 702,402 42,890 745,292 Ave./yr 70,240 4,289 74,529 Total—All Vessels—International Waters (average over period from 1990-1999) Amount of Spillage 21,911,596 gallons spilled per year (average) 74,529 tonnes spilled per year (average) ment Agency (CEAA), 1995]. The U.S. military reports on 938 dumps, for 7,300 tonnes per year, worldwide (Clewell, 1980). Reporting on dumping is required but is not enforced or monitored. Because of fears of dumping over residential areas, most dumping is conducted over preassigned areas of little habitation. Airports near lakes or oceans designate areas over these waters. Evaporation reduces the amount that directly deposits to between 5 and 70 percent of dump volume, depending on fuel type and weather conditions. Older engines can emit relatively large amounts of unburned fuel. In older jet and turbine engines, jet fuel is cycled through engine parts as a coolant and is then passed into the injection system. Because this flow must be maintained at certain levels, about 5 to 15 percent of fuel consumption can be emitted through the engines without fuel combustion. This loss occurs primarily during idle and take-off conditions and is least during cruise conditions. Little documentation on this has been found, and it may not contribute much oil to the sea. Some older engines also have an injection bypass tank that is emptied automatically after take-off. This is believed to be restricted to very few aircraft at this time. The preliminary estimate of oil reaching the sea is based on the probability of a dump occurring. From literature, the rate of military jettisoning varies between 0.001 and 0.002 dumps per flight (Clewell, 1980a,b; CEAA, 1995); this averages 0.0015. If civilian rates were one-third of this, then the rate for civilian aircraft would be about 0.0005, or 5 flights out of 10,000. The flights over the oceans are relatively well known (European Commission, 1996). Flights over the North Atlantic average about 700 daily, over the North Pacific about 100 (not counting those over land on polar routes), and those over the southern hemisphere, are estimated at about 200 per day. This is 1,000 flights per day, with most flights consisting of large, wide-bodied aircraft such as the 757, 767, MD-11, and similar aircraft. The dumping of fuel typically releases 50 tonnes (50,000 L), of which about 50 percent would reach the sea surface, based on experimental deposition studies (Clewell, 1980a; Cross and Picknett, 1973). This would yield 4,500 tonnes per year. The U.S. military averaged 7,262 tonnes per year in 1975 to 1978, with a steady decrease. If we place this value at 4,000 tonnes currently and presume that only one-quarter of this was over water and would hit the water, then about 1,000 tonnes per year is the U.S. military TABLE E-21 Summary of Oil Input from Accidental Spills for Vessels Worldwide Best Estimate (tonnes) Best Minimum (tonnes) Maximum (tonnes) Estimate (gallons) Minimum (gallons) Maximum (gallons) NORTH AMERICAN WATERS Tank Vessels 5,300 5,000 6,400 1,400,000 1,400,000 1,700,000 Other Vessels 1,200 1,100 1,400 300,000 300,000 400,000 Total—North American Waters 6,500 6,100 7,700 1,700,000 1,700,000 2,100,000 INTERNATIONAL WATERS Tank Vessels 96,580 87,800 120,725 28,394,621 25,813,292 35,493,276 Other Vessels 5,897 5,361 7,372 1,733,823 1,576,203 2,167,279 Total—International Waters 100,000 93,000 130,000 30,000,000 27,000,000 38,000,000 WORLDWIDE Tank Vessels 100,000 93,000 130,000 30,000,000 27,000,000 37,000,000 Other Vessels 7,100 6,500 8,800 2,000,000 1,900,000 2,600,000 Total—Worldwide 110,000 100,000 140,000 32,000,000 29,000,000 40,000,000 NOTE: All totals rounded to two significant figures.
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Oil in the Sea III: Inputs, Fates, and Effects input. If the world input from military aircraft is triple this amount, then the world input is 3,000 tonnes. The sum total of aircraft dumping input is then estimated at 7,500 tonnes. It is estimated that 1/5 of these releases would take place over North American territorial waters on the basis of air traffic loading to and from North America, compared to the rest of the world. This again is subdivided by the approximate numbers of trans-ocean flights arriving/departing from airports in the designated regions (Tables 2-2 through 2-6).
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Representative terms from entire chapter: