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Shoreline Clean-Up and Response
When oil reaches the shoreline, considerable effort may be required to clean the affected areas. It is therefore essential that comprehensive and well-rehearsed arrangements for shoreline clean-up are included in contingency plans. The techniques available for shoreline clean-up are relatively straightforward and do not normally require specialised equipment. However, inappropriate techniques and poor organisation can aggravate the impacts caused by the oil itself.
The selection of the most appropriate clean-up techniques requires a rapid evaluation of the degree and type of contamination, together with the length, nature and accessibility of the affected coastline. Where possible, it is important to start removing oil from contaminated shorelines as quickly as practicably possible. As time passes and the oil weathers, it will stick more firmly to rocks and sea walls, and may become mixed or buried in sediments.
Shoreline clean-up operations are often considered in three stages; Stage 1 - bulk oil is removed from the shore to prevent remobilisation; Stage 2 - removal of stranded oil and oiled shoreline material which is often the most protracted part of shoreline clean-up, and; Stage 3 - final clean-up of light contamination and removal of stains, if required. Depending upon the nature of the contamination, progression through each of these stages may not be required. Consideration will also need to be given to the environmental sensitivity of the shoreline so as to ensure the planned level of cleaning will not cause more harm than leaving the oil in place.
Experience from many incidents has shown that the most costly and time-consuming component of the overall oil spill response is the treatment or disposal of collected waste. As a result, the chosen clean-up strategy should aim to minimise the waste generated.
For many shoreline types and response scenarios, the removal of all traces of oil will be extremely difficult or inadvisable due to environmental or health and safety concerns. As a consequence, it is important that the criteria for deciding when a particular work site is sufficiently clean to allow work to terminate. The criteria for termination of the clean-up are usually discussed jointly and agreed following joint inspections by representatives of the various organisations involved in the response.
There are a wide range of clean-up techniques available for affected shorelines but many of these may be more appropriate to just one stage of the response or one shoreline type.
During Stage 1 clean-up, the use of vacuum trucks, pumps and skimmers may be useful on pooled liquid bulk oil. For very viscous or emulsified bulk oil or oiled-soaked soft sediment, mechanical collection using a variety of non-specialised civil engineering or agricultural machinery could be used to collected and remove stranded oil and contaminated material. In many parts of the world, the use of manpower to collect oil and contaminated shoreline material is an important strategy and can be particularly useful on sensitive shores and areas inaccessible to vehicles.
Stage 2 clean-up might involve flushing, a technique that uses high volumes of low-pressure water to wash stranded or buried oil from shorelines. Similar in principle to flushing is surf washing, whereby the natural cleaning action of the shoreline waves are used to release the oil from within the shore sediment.
During the latter stages of a shoreline clean-up, other techniques may be deployed to complete the work. High pressure washing using either hot or cold water can be used on most hard surfaces, particularly on man-made structures within commercial and similar areas where natural cleaning is likely to be insufficient or too slow. Machinery can be employed to attain the required level of cleaning; pebbles and cobbles can be washed successfully in the revolving drums of concrete mixers or purpose built facilities and ploughs towed behind tractors and sand sieving/beach cleaning machines can both be used to clean high amenity use beaches to a high standard.
In situations where restricted access to rocky or cobble shorelines prevents the use of pressure washing or other equipment, wiping by hand may be the only option for the active removal of oil.
In certain circumstances, the use of bioremediation products can be considered. Bioremediation is the term used to describe the range of processes, and related products, which can be used to accelerate the natural degradation of oil into simple compounds. Natural biodegradation can be sometimes usefully accelerated in areas where nutrients or microbes may be limited such as the clean-up of old industrial areas. Use of this process on the open shoreline is rarely advocated.
In time, most shorelines will clean naturally as the oil weathers and degrades. On high-energy shorelines, natural cleaning can be very effective, and the majority of oil is likely to be removed within a seasonal cycle. However, along sheltered shorelines, particularly with fine sediment, eg saltmarshes, or in cold climates, natural degradation can proceed very slowly and oil may persist for many years.
Shoreline type plays an important role in determining the most suitable clean-up techniques that might be most suitable for removing the oil. In considering the clean-up of a specific shoreline type, three factors are important to consider; the level of amenity use, the environmental sensitivity and the exposure of the shoreline to natural cleaning action.
Ports, harbours, sea defences and similar man-made structures are usually in areas of high amenity use, are constructed from concrete or similar materials and have low environmental sensitivity. Clean-up techniques for this type of shoreline might utilise high pressure washing or flushing with the priority being a high level of oil removal. Natural hard surfaces, such as bedrock or boulders, can be cleaned using similar methods to man-made structures. However, the natural shore often has greater environmental sensitivity and exposure to wave action. Consequently, clean-up activities must take care to minimise impact on fauna and flora and the termination of active cleaning should consider the natural cleaning potential.
Cobble, pebble and shingle shores are one of the most difficult to clean satisfactorily as the oil can penetrate into the spaces between the stones and deep into the beach. Often the poor load-bearing structure of these shores means that mechanical collection is problematic. As a result, flushing and surf washing techniques, together with mechanical washing are typically the most useful clean-up techniques.
Sand beaches are often regarded as having high amenity value and a priority is given to cleaning them. Oil penetration into many beaches is limited and this makes them one of the easiest shorelines to clean. However, oil can become buried due to tidal or wave action. Mechanically-assisted manual clean-up, flushing and surf washing can all be useful on this shoreline type. Ploughing and sand sieving can produce a high level of cleaning where the beach has important amenity value. Care should be taken with all techniques to avoid removing clean sand from the beach which may cause erosion problems.
Muddy shores are amongst the hardest to clean as they are sensitive to physical damage by clean-up operations and often have high environmental sensitivity. In temperate climates, the marsh vegetation typical of these shores often survives a single oil smothering. In the tropics, the impact of oil on the mangrove vegetation is less predictable and dependent on species. Wherever possible, it is preferable to allow oil that arrives on this type of shoreline to whether naturally. Where the removal of oil is essential, flushing and manual cleaning are most likely the best options.
Management and Organisation
The efficient management of resources engaged in shoreline clean-up is vital to the success of the operation. In deciding which clean-up techniques are to be used, the management team have to consider the interests of all concerned with the various local uses of the marine environment eg recreation, tourism, fisheries, industry and marine conservation. Proper organisation of the workforce and activities on the shoreline is also crucial so that the clean-up is undertaken in the most safe and effective way possible and that unnecessary impacts on the environment are avoided.
The successful management and organisation of a shoreline clean-up can be greatly assisted by a well-designed contingency plan that incorporates a high degree of local knowledge and has been prepared by those agencies, organisations and stakeholders that might be involved in a shoreline response.
Bioremediation is the term used to describe a range of processes which aim to accelerate natural biodegradation. This approach is not suitable for use on bulk oil, but has been promoted as an aid to the breakdown of final traces after clean-up by other methods.
To work effectively, microbes require sufficient levels of carbon, nitrogen and phosphorus. When a spill occurs a huge amount of carbon from the oil becomes available leaving a shortfall in the corresponding nitrogen and phosphorous levels. Biostimulation is the application of fertilisers to adjust the balance in the C:N:P ratio and enhance the degradation rate by the indigenous microbial community. Biostimulation has not yet been demonstrated to be beneficial for large scale restoration projects.
Bioaugmentation or seeding is the addition of microbes specially selected to degrade oil. Oil degrading microbes are distributed widely throughout the world's coastal areas and are more abundant in chronically polluted waters. In these areas the addition of microbes will probably not be necessary. Even in regions where the oil-degrading community is likely to be less abundant it is unlikely that bioaugmentation will significantly enhance biodegradation. Research and trials during oil spills have shown that the addition of cultured, specialist bacteria is ineffective because they are rapidly out-competed by naturally occurring oil degrading bacteria which are adapted to local conditions.
Limitations of Bioremediation
Although bioremediation may be a useful tool, it is certainly not a 'miracle cure'. Frequently, the concentration of oil residue remaining after significant biodegradation has taken place, i.e. the 'end-point', will be the same whether nutrients or microbes are added or not. Although this 'end-point' may be reached quicker, the time scale for bioremediation is still of the order of months.
Bioremediation should not be used on oil on the sea surface since any materials added are likely to be rapidly diluted and lost from the slick. Natural biodegradation can be most usefully accelerated when bioremediation is used on land ('landfarming'). Here the physical, chemical and biological factors that affect bioremediation can be controlled to provide optimum conditions for biodegradation. Use of this process on the shoreline is more controversial as the same level of control is impossible to obtain in the marine environment. The evidence has not conclusively shown that bioremediation works for oiled shorelines.
The oxygen required for biodegradation to occur is only available at the oil-water interface and not within the oil itself. As a result, where this process is used the amount of oil degraded will be greater if the oil is dispersed in water or distributed thinly over and through sediments. Bioremediation is therefore not suitable for removing large amounts of oil and should only be considered where the concentration of oil is low as a final polishing technique. The more complex components of the oil may remain partially or totally undegraded.
Biostimulation or bioaugmentation in sensitive environments, such as salt marshes and mud flats, may cause unacceptable physical and biological damage. Excessive biostimulation may alter the nature of these areas irreparably by altering the natural balance of species and encouraging the growth of alien plant species. Bioremediation products should be applied with care and the methods used must be specifically tailored to the environment and pollutant at each contaminated site.