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