COASTAL WATERS
Response to spills closer to shore (in water depths less than 30 feet or so) must take into account both the potential of the spill to reach shore and its potential impact on corals, kelp and seagrass beds, and on their dependent ecosystems.
Booms may be used to divert and/or contain oil to be recovered via skimmers or, in remote areas, burned. (Booms are less effective in kelp beds, where they are likely to get tangled.) Dispersants are, generally, not a preferred option because of the potential for dispersed oil to affect shallow coastal ecosystems. They may be applied in coastal waters without significant subsurface habitats.
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:
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.
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.
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.
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.