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Introduction

In the past decade the United States has spent billions of dollars trying to cleanup contaminated ground water and soils, the legacy of an era in which industry grew faster than knowledge about safe chemical disposal. Despite the large financial investment, ground water cleanup efforts are falling short of public expectations. Recent studies have revealed that, while conventional cleanup technologies have prevented the contamination problem from spreading, in most cases they are incapable of restoring the water to meet health-based standards in a reasonable time frame. Soil cleanups have been more successful in meeting regulatory standards. However, conventional soil cleanup methods may transfer contaminants to the air, posing risks that are not always acceptable to residents near the contaminated site. The limitations of conventional ground water cleanup technologies and the hazards of conventional soil cleanup methods have spurred investigations into in situ bioremediation, which uses microorganisms to destroy or immobilize contaminants in place. Bioremediation is a promising alternative to conventional cleanup technologies for both ground water and soil because it may be faster, safer, and less costly.

Conventional methods for ground water cleanup rely on pumping water to the surface and treating it there. Such pump-and-treat methods are slow; they require the withdrawal of large volumes of water to flush contaminants from aquifer solids, and they may leave



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1 Introduction In the past decade the United States has spent billions of dollars trying to cleanup contaminated ground water and soils, the legacy of an era in which industry grew faster than knowledge about safe chemical disposal. Despite the large financial investment, ground water cleanup efforts are falling short of public expectations. Recent studies have revealed that, while conventional cleanup technologies have prevented the contamination problem from spreading, in most cases they are incapable of restoring the water to meet health-based standards in a reasonable time frame. Soil cleanups have been more successful in meeting regulatory standards. However, conventional soil cleanup methods may transfer contaminants to the air, posing risks that are not always acceptable to residents near the contaminated site. The limitations of conventional ground water cleanup technologies and the hazards of conventional soil cleanup methods have spurred investigations into in situ bioremediation, which uses microorganisms to destroy or immobilize contaminants in place. Bioremediation is a promising alternative to conventional cleanup technologies for both ground water and soil because it may be faster, safer, and less costly. Conventional methods for ground water cleanup rely on pumping water to the surface and treating it there. Such pump-and-treat methods are slow; they require the withdrawal of large volumes of water to flush contaminants from aquifer solids, and they may leave

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behind reservoirs of contaminants that are lighter or denser than water and/or have low solubilities. By treating the problem close to its source, in situ, bioremediation speeds contaminant desorption and dissolution. Consequently, a cleanup that might require decades using pump-and-treat methods could possibly be completed in a few years with bioremediation. In addition, pump-and-treat methods do not destroy contaminants but simply bring them to the surface for treatment or disposal elsewhere. In situ bioremediation, on the other hand, can transform contaminants to harmless byproducts such as carbon dioxide and water. Conventional methods for soil cleanup require digging up the contaminated soil and either incinerating it or burying it at a specially designed disposal site. Soil excavation and incineration may increase the exposure to contaminants for both the workers at the site and nearby residents. Furthermore, excavation and final disposal are extremely costly. By treating the soil in place, bioremediation reduces both the exposure risk and the cleanup cost. Because bioremediation shows promise as an alternative to conventional environmental cleanup technologies, the number of vendors selling bioremediation has increased dramatically in recent years. Bioremediation is one of the fastest-growing sectors of the U.S. hazardous waste market. It is expected to become a $500 million per year industry by the year 2000. Yet despite the rapid growth in the use of this technology, bioremediation is not universally understood or trusted by those who must approve its use, and its success is a hotly debated issue. A primary reason for the lack of understanding and mistrust of bioremediation is that the technology requires knowledge not only of such fields as environmental engineering and hydrology, which are important in conventional cleanup methods, but also of the complex workings of microorganisms. The potential for large profits, when combined with the mysteriousness of applying microorganisms, makes bioremediation attractive for ''snake oil salesmen" who claim to be able to solve all types of contamination problems. Many buyers of cleanup services and regulators who approve cleanup plans lack the necessary background to evaluate whether a bioremediation project has a feasible design. Furthermore, they may be unsure how to evaluate whether an ongoing bioremediation project is progressing toward successful completion. Consequently, some regulators and clients approach bioremediation with skepticism, opting for more conventional technologies even when bioremediation is the most appropriate technology for a particular site.

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The multidisciplinary nature of bioremediation presents problems not only for clients and regulators but also for the vendors of environmental cleanup services. These vendors face a challenge in integrating the wide range of disciplines needed to carry out bioremediation in the field. Communications among engineers, microbiologists, hydrologists, and chemists are complicated by each discipline's highly specialized concepts, tools, and jargon. Even when all parties are knowledgeable and competent, evaluating the success of bioremediation (i.e., whether or not it is working) can cause confusion. Part of the confusion comes from the inherent complexity of the sites. Knowing with certainty the location and fate of all contaminants is impossible. However, evaluating the success of in situ bioremediation is further complicated by the multiple definitions of success set forth by those involved with the cleanup: Regulators want cleanup standards to be met. Clients want the cleanup to be cost-effective. Bioremediation vendors and researchers want evidence that the cleanup was caused by microbial action—that the contaminant did not, for example, simply evaporate or migrate off site. This report is designed for bioremediation clients, regulators, and vendors, who need to agree on how to define success appropriately. The report emphasizes ways to show that microorganisms aided cleanup efforts because the use of microorganisms is what distinguishes bioremediation from other technologies. Chapter 2 explains the principles of bioremediation, describing the microbiological processes that can be employed in bioremediation and providing practical guidance on what types of contaminants and site conditions are most amenable to bioremediation. Chapter 3 reviews the current state of the art in in situ bioremediation systems. These chapters provide the basis for understanding when in situ bioremediation is likely to work. Chapter 4—the most critical part of the report—presents methods and strategies for evaluating a bioremediation project in the testing or implementation phase. Finally, Chapter 5 suggests innovations that may improve the technology's capabilities in the future. This report represents the opinions of the National Research Council's Committee on In Situ Bioremediation. The National Research Council established this committee in June 1992 and assigned it the specific task of preparing guidelines for evaluating whether an in situ bioremediation project, either proposed or in the implementation stage, is likely to reach cleanup goals. The committee includes representatives of all groups with an interest in bioremediation: buyers of bioremediation services, bioremediation contractors, environmental

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regulators, and academic researchers. The committee developed the framework for this report and the guidelines it presents at a one-week workshop in October 1992. Also included in this volume are seven background papers authored by committee members to represent the range of perspectives from which bioremediation can be viewed.