Farms or Grasslands
Spills on agricultural or grassy lands have the effect of choking off plant life. (Spilled oil prevents water absorption by the soil.) In these environments, the top response priorities are:
- To return the soil to productive use as quickly as possible, and
- To prevent oil from leaching into groundwater or running-off into waterways.
Berms and trenches can be used to contain the spill, so long as they do not lead the oil to leach into the soil. Where there is no danger to the water table, the contaminated area can be flooded to "float" the oil for recovery via vacuums and skimmers. Other possible techniques include mechanical removal of contaminated soil, in-situ burning, sorbents and bioremediation.
Berms/Trenches
Spills on land can be contained for recovery by building up berms or dikes in the path of the flow, using either soil from the area, sand bags or other construction materials. It is important to make sure the berm does not cause oil to back up and permeate the soil, where it could contaminate groundwater. If the water table is high and the oil will not permeate the soil, shallow trenches may be dug to collect oil for removal.
Manual recovery / Cleanup
Manual recovery is the most common method of shoreline cleanup, involving teams of workers using rakes, shovels and the like to pick up oil and debris. The oily materials are collected in buckets and drums for transfer to a processing station. Workers may also use suction hoses, pumps and vacuum trucks to recover spilled oil. While manual cleanup is a slow, painstaking process, it generates less waste than other techniques.
Bioremediation
Certain portions of oil are biodegradable. Proper application of certain fertilizers can speed up the biodegradation process as much as tenfold, depending on the type of oil spilled. Certain plants (and their associated microorganisms) have also shown promise in speeding the breakdown of oil. Still, even a speeded-up biodegradation process takes weeks - even years - so bioremediation is used in conjunction with other clean-up activities.
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.
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.