Spill Remediation

Introduction

Remediation is the removal of a toxic compound from water or soil, or the containment of a spill so that the area that is contaminated does not increase. Spill remediation refers to the response to an environmental spill that occurs in freshwater and marine water, and on land.

The responses to a spill are varied and depend on a number of factors including the type of spill, and whether people or wildlife are immediately threatened by the spill. A spill may be handled at the site, or the contaminated soil and sand can be trucked to another site to be treated.

Spill remediation can be a task that involves various experts including those familiar with the geology of the area, water flow patterns (hydrology), behavior of chemically diverse compounds, and people who can generate computer models of the spill site.

In developing countries in North America and western Europe, the extent and nature of spills are now well-known. As well, legislation has been passed and penalties imposed to lessen the risk of accidental spills and to make the deliberate dumping of toxic material less likely. But, the situation in developing countries is far different. Dumping can be widespread and deliberate, and can go undetected for decades.

Historical Background and Scientific Foundations

Spill remediation depends on the nature of the spill. For example, when the spill involves a liquid on soil or a beach, the clean up will be both at the surface and underground. This is because the liquid can percolate down into the ground in between the spaces in between the soil and sand particles. As the liquid moves downward, the pollutant will bind to the particles. This binding can be very strong, particularly if the pollutant tends not to mix with water. A spill that occurs on more impermeable terrain, such as rock or concrete, needs to be treated quickly to prevent the spill from spreading out over the surface to adjacent land or watercourses.

Spills involving compounds that tend not to mix with water can be very difficult to contain if the response is delayed. This is because the compound will spread out on the surface of the water. As the spill continues, the surface layer will become thinner and larger in diameter, rather than remaining the same diameter and increasing in thickness. This is why oil spills in freshwater and marine water can quickly grow to cover hundreds of square miles/kilometers in area. Clean up of a spill of such a large area presents difficult challenges.

Oil spills that coat the rocks, soil, and sand beaches of coastal shorelines can be treated in several ways. Hot water sprayed onto the shore can help dislodge pollutants. However, as was found in the analysis of the outcome of the clean up of the Exxon Valdez spill off Alaska in 1989, the use of high pressure, steaming water can destroy microbial life in the area being treated. Most bacteria cannot tolerate the boiling water temperature that is used in spill clean up. Although there are a few bacteria that are able to tolerate such temperatures, such as bacteria found naturally in hot springs, these extremely hardy bacteria typically do not degrade the pollutants, whereas the bacteria that are naturally present in the area of a spill may have developed the ability to use the pollutants as nutrients. The loss of the natural microbial population can reduce the efficiency of a spill remediation, since bacteria that are in the soil or sand may be able to use some of the pollutants as sources of food and degrade them. The compounds that are left over following this degradation may not be as toxic, if at all.

Another strategy for remediating a spill, especially if it involves hydrocarbons or other compounds that cling tenaciously to rocks, soil, and sand, is to spray on a solution that contains chemicals that contain dispersants that

WORDS TO KNOW

BIOREMEDIATION: The use of living organisms to help repair damage such as that caused by oil spills.

EXXON VALDEZ: A tanker that spilled almost 11 million gallons of oil in Prince William Sound, Alaska, beginning on March 24, 1989.

GROUNDWATER: Fresh water that is present in an underground location.

SUPERFUND: Legislation that authorizes funds to clean up abandoned, contaminated sites.

gather around the oil and form oil-containing droplets. The dispersant compounds are described as being amphipathic; they have a region of their structure that tends to associate with water (the hydrophilic region) and a different region that tends not to associate with water (the hydrophobic region). When added to water, the hydrophobic portion will want to escape water. The way that this can be achieved is by the formation of a sphere composed of the dispersant compounds, in which the hydrophobic regions are on the inside and the hydrophilic regions are on the outside. Since hydrocarbons also tend to be hydrophobic, they will associate with the hydrophobic regions of the dispersant, and so will tend to gather on the inside of the spheres as they form. In this way the pollutant can be trapped inside the spheres, which aids in the dispersion of the spill from rocks, soil, and sand. The dispersed oil is then collected by vacuuming or, if it has re-entered the water, by gathering it in an ever-decreasing space using a floating barrier known as a boom, or by the addition of sponge-like material that can soak up the liquid. Spills that occur on the surface of the ground or on an artificial surface like concrete can be treated by adding an absorbent, powdery material. The soaked material needs to be collected afterward and properly disposed of, such as by incineration or storage in leak-proof bags and burial in a landfill.

Spill remediation can be less exotic. For example, when a heavy oil spill has washed up on a beach, much of the spill may be removed manually by shoveling or using a grader. This option is not appropriate in gravely areas, however. The choice of strategy depends on the nature of the spill, the urgency of the clean up (for example, a spill that threatens coastal regions may be more urgent than an inland spill), and whether or not a spill is in an urban or a rural area.

The reliance on bacteria to degrade spills has grown since the time of the Exxon Valdez disaster. At the time of this oil spill, this strategy, which is known as bioremediation, was known but had not been widely used, out of concern for the possible adverse consequences of the rapid growth of the bacteria. Their sudden and explosive increase in numbers could upset the balance of the particular ecosystem. Those advocating the approach argued that since the ecosystem had already been drastically affected by the spill, this concern was not as great as the need to deal with the spill itself.

In the Exxon Valdez response, a spray that contained nutrients was applied to the area of the spill. The intent was to stimulate the growth of the bacteria that were already resident in the soil and sandy beaches, with the hope that their growth would aid in the degradation of the pollutants. Although not completely successful, the strategy worked well enough to earn approval as a spill remediation technique from the U.S. Environmental Protection Agency (EPA).

Another example of bioremediation is the use of bacteria to clean up a site contaminated with polychlorinated biphenyls (PCBs). Over 1.5 million pounds of PCBs were made and used in the United States before being banned in 1977, due to concerns about their adverse health effects and their persistence in the environment. Even given this environmental longevity, bacteria have been successfully used to degrade PCBs.

Bioremediation can also be done by tailoring organisms to be capable of degrading target pollutant compounds. This approach usually involves genetic engineering—an alteration of the genetic material so that either a gene coding for the production of the pollutant degrading protein is introduced into the bacteria, or that a gene already present is made able to function more efficiently.

The genetic engineered approach to bioremediation is still controversial. Critics argue that the release of bacteria that are not naturally present in the particular environment really could disrupt the ecosystem. There is merit in this argument, and so genetically engineered bioremediation is typically done when the polluted material has been collected and moved to a controlled site, where escape of the engineered bacteria does not occur.

Spills that occur in soil can be treated at the site of the spill. Typically, a well is drilled down into the main site of the spill. If bioremediation is being done, a nutrient solution can be pumped into the ground. Often this can be as simple as water, since the water can contain traces of nutrients that are sufficient to stimulate the growth of bacteria dwelling underground. Another well drilled nearby is used to pump up the underground fluid allowing time for degradation to occur. The cycle of nutrient addition and fluid removal can be repeated over and over. The fluid that is recovered after each cycle can be tested for the presence and concentration of the pollutant. Hopefully, with time the level of the contaminant drops. Remediation is complete when the level of the recovered pollutant is at a safe level, according to regulations in place that govern the clean up.

The same strategy can be used for contaminated soil that has been collected and taken to another site. The soil is deposited in an enclosed area. Alternately, the contaminated soil can be spread out over a wide area of leak-proof plastic. This can be advantageous since it increases the amount of contaminated soil that is exposed, which can make it easier to treat.

Spill remediation regulations also govern how the clean up is done. For example, if a spill site is near a watercourse such as a stream or river, the shoreline must be protected so that any accidental release of recovered contaminant does not drain into the surface water. This can be done by the installation of a barrier of synthetic material such as plastic or straw. The site must be monitored during the spill remediation to ensure that the barrier is intact, and the material must be removed and properly disposed of once the job is completed.

Spill remediation also involves caring for the wildlife that has been affected. Marine birds and mammals can be especially affected, since a pollutant such as oil can destroy the insulation ability of fur and the water repellent properties of feathers. Clean up of pollutant-soiled birds and animals has to be done creature by creature, and typically involves trying to wash off as much of the pollutant as possible. Even so, ingestion of the chemical as the bird or animal tries to groom itself can be fatal.

Impacts and Issues

Spill remediation is occurring constantly in developed countries. For example, the EPA estimates that there are nearly 14,000 oil spills each year. Many of these are handled by federal, state, and even local personnel trained in the specialized clean up that is required. However, some spills are so toxic that even clean up is too dangerous. In such cases, the spill site is isolated from development and any use, and the site is abandoned. An example is the Chernobyl nuclear plant accident that occurred in Russia in 1986. The reactor was entombed rather than an attempt made to clean up the toxic levels of radioactivity.

Spills involving oil are an inevitable consequence of the global use of oil and the need to transport the oil long distances from the site of recovery to the refinery. According to the U.S. National Oceanic and Atmospheric Administration (NOAA), the United States uses about 700 million gallons of oil every day. Globally, the daily figure is almost 3 billion gallons.

In the United States, responsibility for a spill clean up varies depending on the location of the spill. Typically, either the U.S. Coast Guard or the EPA takes charge. NOAA can also be called in to assist.

In most countries, the extent and consequences of spills became better known in the 1960s. In the United States, incidents such as New York’s Love Canal contamination in the 1970s increased public awareness of chemical spills, after the passage of the National Environmental Policy Act in 1969. The legislation requires stringent analysis of federal projects, in part to reduce the likelihood of a spill. Other legislation directly pertained to spill remediation. The best example in the United States is the Comprehensive Emergency Response Compensation and Liability Act that was passed in 1980. This legislation specifies who has legal responsibility for spill remediation, including the federal government when clean up of an abandoned site was necessary. The federal government’s role is through a program popularly known as Superfund. As of 2008, 1,305 Superfund sites have been scheduled for remediation, and over 14 million Americans live within one mile of a Superfund site, according to the National Institute for Environmental Health Sciences.

The actual number of soil-contaminated sites in the United States is much higher, with estimates ranging up to 200,000. In developing and underdeveloped countries the situation is much worse, since legislation governing pollution and clean up is not as extensive. Chemicals that persist in the environment that have been banned in the United States can in some cases still be used in other areas of the world. One example is the pesticide DDT; although its use in the control of malaria has been sanctioned in Africa by the World Health Organization, concerns over its use remain.

The natural impacts of a spill can be disastrous. Images of oil-soaked birds and other wildlife struggling to survive are real and all too frequent. For example, an oil spill that occurred off the coast of Spain in late 2002, when an estimated 64,000 tonnes of oil leaked from the tanker Prestige, killed thousands of sea birds and fouled hundreds of miles of coastline.

Clean up of an oil spill can be difficult, time consuming, and expensive. As an example, the 1989 spill from the Exxon Valdez released enough oil to fill almost 125 Olympic-sized swimming pools (still, this amount represents only about 2% of the oil used by the United States each day in 2008). It was the location of the spill in an area of Alaska that was rich in fish and wildlife that generated the most concern. The slick, which fouled over 1,000 mi (1,600 km) of Alaskan coastline, took four summers to clean up. The clean up involved 10,000 workers and 1,000 boats. Exxon’s bill for the clean up, compensation to local fishermen and other business owners whose jobs were affected by the spill, penalties, and other expenses reached $3.5 billion.

Still, all this time and effort does not necessarily restore an area to its pre-spill state. As of 2008, the region affected by the Exxon Valdez spill has not fully recovered from the spill in terms of fish stocks and the health of the coastline. In February 2008, the U.S. Supreme Court considered a civil action filed on behalf of those affected by the 1989 spill, who consider Exxon’s compensation of about $15,000 per person too little, arguing that the lasting damage has jeopardized their jobs. An additional $75,000 per person has been sought in the civil suit. A decision has yet to be announced.