OPEN SEA
In open-water marine spills, the primary response objectives are:
- to prevent the spill from moving onto shore,
- to reduce the impact on marine life, and
- to speed the degradation of any unrecovered oil.
If weather conditions allow, booms can be used to contain or divert the spill. The spilled oil may then recovered using skimmers or simply burned off. However, if winds and/or waves are too high, booms will not be able to provide adequate containment.
Dispersants - applied to the spill via aircraft - can be effective in breaking up spills of light- or medium-density oils. Weather is a factor here too: High winds make it hard to target the spill from the air. Sorbents may be used for small-volume spills, or to "polish up" after other recovery options have been used.
Booms
These temporary floating barriers are used to contain floating spills. A boom usually includes a containment component that floats on - and extends above - the water's surface, plus an underwater "skirt" or "curtain." Booms may be deployed in various configurations, depending on current and wind conditions:
- to divert spills away from sensitive habitats and/or into collection locations
- to contain spills for on-site recovery and/or treatment; or
- to completely surround spills for in-situ burning. (Booms used in burning must be either water-cooled or made of fire-resistant material.)
Skimmers
A variety of mechanical equipment is used to physically remove floating spills from the water's surface. Many designs use a kind of conveyor belt placed at the water line to carry the spilled oil into a reservoir, where it is collected for processing and recovery. (Inevitably, a skimmer is going to collect some water mixed in with the oil.) Other skimmer technologies use suction to remove spilled material, while weir skimmers harness gravity to gather skimmed oil into underwater storage tanks. Skimmers generally are effective only in calm waters; suction skimmers are also subject to clogging by floating debris.
In-situ Burning
In some cases - usually in remote areas - it is possible to burn off spilled oil "in situ" (Latin for "in place"). Burning can eliminate large volumes quickly and effectively, but it burns off plant life and leaves a residue that can adversely affect the ecosystem. Also, because burning oil spreads rapidly in water, special fire-resistant booms must be used to contain open-water burns. On land, berms or trenches serve a similar containment function. In some cases, the contained spill area is flooded to raise the burning oil off the vegetation below.
Dispersants
Dispersants are chemical agents - similar to soaps and detergents - that help to break up an oil slick into small droplets that distribute more evenly throughout the water. While this does not remove the spilled material, it does provide a measure of protection for sensitive habitats threatened by a surface slick. Dispersants are sprayed onto spills by specially equipped ships or aircraft.
Monitor Only
Spill clean-up operations inevitably have their own environmental impacts. For example, heavy equipment can damage sensitive plants and disrupt wildlife habitats. When the potential harm caused by a spill is less than the potential harm caused by attempts to remove it, spilled petroleum products are allowed to degrade naturally. Technicians periodically monitor the breakdown of the spill to be sure there is no unforeseen threat to sensitive ecosystems and/or groundwater supplies.
Wildlife Cleanup
Oiled fish, birds and animals may absorb potentially lethal toxins through their skin. Following spills, birds, otters, seals and walruses may be collected for cleaning and treatment, then returned to the environment. This is an expensive, time-consuming undertaking and, although techniques have improved greatly in the past few years, recovery rates are often poor. Many other species cannot be rehabilitated because they are either too difficult to capture, or the stress of captivity is likely to have more negative effect than the oiling.
Sorbents
Sorbents are materials used to absorb oil, including peat moss, vermiculate and clay. Synthetic varieties - usually plastic foams or fibers - come in sheets, rolls or booms. Because oil-filled sorbents must be collected and treated, they are most often used on small spills, or as "polishers" after other recovery methods have been used.