INTRODUCTION

Shoreline and nearshore areas are important public and ecological resources. However, their cleanliness and beauty, and the survival of the species that inhabit them, can be threatened by accidents that occur during oil drilling and transport activities. Although accidents during these activities are relatively rare, when they do occur oil can be spilled into the world's oceans. Despite the best efforts of response teams to contain this spilled oil, some of it may wash up onto shorelines, into marshes, or into other ecologically sensitive habitats along the water's edge. To help protect these resources from damage and to preserve them for public enjoyment and for the survival of numerous species, cleaning up shorelines following oil spills has become an important part of oil spill response.

SHORELINES: PUBLIC AND ENVIRONMENTAL RESOURCES

Nearshore and shoreline areas serve as homes to a variety of wildlife during all or part of the year. Many bird species build their nests on sand or among pebbles, while others regularly wander the shoreline searching for food. Sea mammals such as elephant seals and sea lions come ashore to breed and bear their pups. Fish such as salmon swim through nearshore zones on their upriver migrations during spawning season, and their offspring swim through these same areas on their trips to the sea in the following year.

Shorelines and nearshore areas also provide public recreation throughout the world. Many beaches are famous for their wide expanses of beautiful sand, while others are admired for their rugged rocky cliffs. Beaches provide opportunities for sports such as swimming, windsurfing and fishing. In developing strategies for cleaning up an oil spill from a shoreline, the characteristics of the

shoreline and the natural and recreational resources it provides must be considered.

FACTORS AFFECTING CLEANUP DECISIONS

Whenever possible, control and cleanup of an oil spill at sea begins immediately. If the oil spill can be controlled there is less likelihood that it will reach sensitive habitats near or on shore. If the oil does reach the shore, however, decisions about how best to remove it must be made. These decisions will be based on factors such as the

type of oil spilled

geology of the shoreline

type and sensitivity of biological communities likely to be affected

Each of these factors is described further below.

Type of oil spilled

Lighter oils tend to evaporate and degrade (break down) very quickly; therefore, they do not tend to be deposited in large quantities on beaches. Heavier oils, however, tend to form a thick oil-and-water mixture called mousse, which clings to rocks and sand. Heavier oils exposed to sunlight and wave action also tend to form dense, sticky substances known as tar balls and asphalt that are very difficult to remove from rocks and sediments. Therefore, deposits from heavy oils generally require more aggressive cleanup than those from lighter ones.

Geology of the shoreline

Shorelines can vary dramatically in their forms and compositions. Some shorelines are narrow with beaches formed from rounded or flattened cobbles and

pebbles; some are wide and covered in a layer of sand or broken shell fragments; and still others are steep cliffs with no beach at all. The composition and structure of the beach will determine the potential effects of oil on the shoreline.

Oil tends to stick to mud and to the surfaces of cobbles and pebbles. It also flows downward in the spaces between cobbles, pebbles, and sand grains, and accumulates in lower layers of beach sediments. Oil that sticks to mud particles suspended in the water column and to cobbles and pebbles on the beach is exposed to the action of sunlight and waves, which helps it to degrade and makes it less hazardous to organisms that come into contact with it. Oil that sticks to rocks and pebbles can be wiped or washed off. Oil that flows onto sandy beaches, however, can "escape" downward into sand, making it difficult to clean up and reducing its ability to degrade.

Type and sensitivity of biological communities

Biological communities differ in their sensitivity to the effects of oil spills and the physical intrusion that may be associated with various cleanup methods. Some ecosystems seem to recover quickly from spills, with little or no noticeable harm, while others experience long-term harmful effects.

Animals, such as elephant seals, that depend on the nearshore or beach environment for breeding and pupping can lose their ability to stay warm in cold water when their skin comes into contact with oil. Birds lose their ability to fly and to stay warm when their feathers are coated with oil, and fish can suffocate when their gills are covered with oil. An oil spill can disrupt a community food chain because it is toxic to some plants, which many organisms depend on for food.

CLEANUP PROCESSES AND METHODS

Both natural processes and physical methods aid in the removal of oil from shorelines. Sometimes, physical methods are used to enhance naturally-occurring processes. An example of a technology that uses both natural processes and physical methods to clean up an oil spill is bioremediation, which is described later.

Natural processes

Natural processes that result in the removal of oil from the natural environment include evaporation, oxidation, and biodegradation.

Evaporation occurs when liquid components in oil are converted to vapor and released into the atmosphere. It results in the removal of lighter-weight substances in oil. In the first 12 hours following a spill, up to 50 percent of the light-weight components may evaporate. Since the most toxic substances in oil tend to be those of lightest weight, this evaporation decreases the toxicity of a spill over time.

Oxidation occurs when oxygen reacts with the chemical compounds in oil. Oxidation causes the complex chemical compounds in oil to break down into simpler compounds that tend to be lighter in weight and more able to dissolve in water, allowing them to degrade further.

Biodegradation occurs when naturallyoccurring bacteria living in the ocean or on land consume oil, which they can use to provide energy for their various biological needs. When oil is first spilled, it may be toxic to some bacteria, which makes the initial rate of biodegradation quite slow. As the oil evaporates and the more toxic substances are removed, the population of bacteria grows and biodegradation activity accelerates.

In nature, biodegradation is a relatively slow process. It can take years for a population of microorganisms to degrade most of the oil spilled onto a shoreline. However, the rate at which biodegradation occurs can be accelerated by the addition of nutrients such as phosphorus and nitrogen that encourage growth of oil-degrading bacteria. Biodegradation rates can also be increased by adding more microorganisms to the environment, especially the species that are already used to consuming the type of oil spilled. The use of nutrients or the addition of microorganisms to encourage biodegradation is called bioremediation.

Bioremediation has been used with some success in recent oil spill events. Experiments conducted by the U.S. Environmental Protection Agency, Exxon Corporation, and the State of Alaska on cobble beaches contaminated with oil from the 1989 Exxon Valdez spill showed that the addition of nutrients more than doubled the natural rate of biodegradation, and produced no long-term injury to the shoreline or sensitive habitats.

Physical methods

Physical removal of oil from shorelines, and especially beaches, is time-consuming and requires much equipment and many personnel. Methods used to physically clean oil from shorelines include

wiping with absorbent materials

pressure washing

raking or bulldozing

Before physical cleaning methods are used, booms made of absorbent material are often set up in the water along the edge of the beach. Booms prevent oil released during beach cleanup activities from returning to the ocean, and contain the oil so that it can be skimmed from the water for proper disposal. Wiping with absorbent materials

Materials that are capable of absorbing many times their weight in oil can be used to wipe up oil from contaminated beaches.

streams. The oil is flushed from the beach into plastic-lined trenches or down to the shoreline, then collected with sorbent materials and disposed of properly.

This method has the advantage of being relatively inexpensive and simple to apply. It requires many personnel and is slow, however. Additionally, high-pressure water streams can dislodge organisms such as algae and mussels from rocks and sediments on which they live, or can force oil deeper into sediments, making cleanup more difficult.

these methods can disturb both the natural shape of the shoreline and the plant and animal species that live on and in the beach sediments. In addition, the use of bulldozers requires specially trained operators who can maneuver them without damaging the beach unnecessarily; raking and tilling are timeconsuming and require many personnel.

Response crews using high pressure hoses to wash an oil-covered beach (Source: U.S. Coast Guard)

Raking or bulldozing

When oil moves downward into the sands or between pebbles and cobbles on a shoreline, it becomes more difficult to remove. If the oil has moved downward only a short distance, tilling or raking the sand can increase evaporation of the oil by increasing its exposure to air and sunlight. If the oil has penetrated several inches into the sand, bulldozers may be brought in to remove the upper layers of sand and pebbles. This allows the oil to be exposed so it can be collected and removed from the site, washed with pressure hoses, or left to degrade naturally.

Raking and bulldozing are simple methods for helping to remove oil that might otherwise escape into sediments. However,

DISPOSAL OF OIL AND DEBRIS

Cleanup from an oil spill is not considered complete until all waste materials are disposed of properly. The cleanup of an oiled shoreline can create different types of waste materials, including liquid oil, oil mixed with sand, and tar balls. Oil can sometimes be recovered and reused, disposed of by incineration, or placed in a landfill. States and the Federal government strictly regulate the disposal of oil.

Reuse or recovery of oil requires that the oil be processed and separated from the other materials such as water that are mixed in with it. The recovered oil can then be blended with other fuels for use in power plants or boilers.

Incineration uses extremely high temperatures to convert compounds such as oil into carbon dioxide and water. When a mobile incinerator is used at a remote spill site, the need for transporting large volumes of oiled wastes to distant disposal sites is eliminated. This can be a practical and efficient method to manage large volumes of waste generated during a cleanup. Because incineration can potentially produce air pollution, it is important that it be used in strict compliance with air pollution laws.

Landfilling is another method of disposing of oiled debris. The oil is mixed with chemicals such as calcium oxide ("quicklime") that stabilizes the oil and makes it less able to leak into groundwater or soils. Mixtures of quicklime and oil must sometimes be taken to specially designed landfills for disposal.