U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Environmental Occurrence

Multi-Component Waste

Heavy Oils

A residue from refining and cracking crude oil is blended with other, generally lighter, components to create heavy oil, also known as fuel oil No. 6 and bunker C. (CONCAWE 1998) describes the composition of residual fuels as a "complex mixture of high molecular weight compounds having a typical boiling range from 350 to 650° C. They consist of aromatic, aliphatic and naphthenic hydrocarbons, typically having carbon numbers from C20 to C50, together with asphaltenes and smaller amounts of heterocyclic compounds containing sulfur, nitrogen, and oxygen."

Bunker C is burned as fuel to power a wide range of boilers, including ships' boilers. Thus, it is no surprise that spills, which are the largest contributor of heavy oil to the environment, are most likely to occur during transportation, especially at sea.

Heavy oil can be lighter than water and hence not penetrate it. However, it also can be neutrally buoyant floating anywhere in the water column or sink into the water column (surface water or ground water) (Irwin 1998). After the Mobil spill in the Columbia River in 1984, the oil floated, sank, and eventually distributed itself throughout the water column. After a spill in San Francisco Bay in 1975, wind and tides mixed the oil with sediment, causing it to sink to the bottom only to be transported to San Pablo Bay by underwater currents (Irwin 1998). The Wabamun spill in Canada occurred when a train carrying crude oil derailed. The oil picked up sediment as it migrated overland and eventually into Wabamun Lake, a freshwater lake. There it settled to the bottom often as mats of tar (Fingas 1995).

For Further Information

Adobe PDF LogoThe Density Behaviour of Heavy Oils in Freshwater: The Example of the Lake Wabamun Spill
Fingas, M., B. Hollebone and B. Fieldhouse
Environment Canada Environmental Technology Center, Ottawa, Canada, 15 pp, 1995

This study describes the behavior of a heavy fuel released into a lake. The oil showed peculiar behavior including submergence, neutral buoyancy, resurfacing, and the formation of several types of oil aggregates, such as the usual tar balls, logs, sheets, large lumps, and sometimes an oil slick that reformed from tar balls.

Adobe PDF LogoEnvironmental Contaminants Encyclopedia
Irwin, R.J. et al.
National Park Service, Water Resources Division, Fort Collins, CO, 1998

This web page provides information on human health effects, fate and transport, production, and uses of many chemicals including fuel oils.

Adobe PDF LogoFact Sheet: No. 6 Fuel Oil (Bunker C) Spills
National Oceanic and Atmospheric Administration, 2 pp

This fact sheet briefly describes the behavior and consequences of releasing No 6 fuel oil into a water body.

Adobe PDF LogoHeavy Fuel Oils
Conservation of Clean Water and Air in Europe (CONCAWE)
CONCAWE Petroleum Products and Health Management Groups, Product Dossier No. 98/109, 1998

A 53-page document that briefly discusses the properties of heavy fuel oils and provides an extensive discussion of toxicity.



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