Executive Summary

There is no simple solution to the problems created by contaminated marine sediments,1 which are widespread in U.S. coastal waters and can pose risks to human health, the environment, and the nation's economy. Marine sediments are contaminated by chemicals that tend to sorb to fine-grained particles: contaminants of concern include trace metals and hydrophobic organics, such as dioxins. polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons. Contamination is sometimes concentrated in ''hot spots" but is often diffuse, with low to moderate levels of chemicals extending no more than a meter into the seabed but covering wide areas. Approximately 14 to 28 million cubic yards of contaminated sediments must be managed annually, an estimated 5 to 10 percent of all sediments dredged in the United States.

The many challenges to be overcome in managing contaminated sediments include an inadequate understanding of the natural processes governing sediment dispersion and the bioavailability of contaminants; a complex and sometimes inconsistent legal and regulatory framework; a highly charged political atmosphere surrounding environmental issues; and high costs and technical difficulties involved in sediment characterization, removal, containment, and treatment. The need to meet these challenges is urgent. The presence of contaminated sediments poses a barrier to essential waterway maintenance and construction in many ports, which support approximately 95 percent of U.S. foreign trade. The management

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For purposes of this report, contaminated marine sediment is defined as containing chemical concentrations that pose a known or suspected threat to the environment or human health



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--> Executive Summary There is no simple solution to the problems created by contaminated marine sediments,1 which are widespread in U.S. coastal waters and can pose risks to human health, the environment, and the nation's economy. Marine sediments are contaminated by chemicals that tend to sorb to fine-grained particles: contaminants of concern include trace metals and hydrophobic organics, such as dioxins. polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons. Contamination is sometimes concentrated in ''hot spots" but is often diffuse, with low to moderate levels of chemicals extending no more than a meter into the seabed but covering wide areas. Approximately 14 to 28 million cubic yards of contaminated sediments must be managed annually, an estimated 5 to 10 percent of all sediments dredged in the United States. The many challenges to be overcome in managing contaminated sediments include an inadequate understanding of the natural processes governing sediment dispersion and the bioavailability of contaminants; a complex and sometimes inconsistent legal and regulatory framework; a highly charged political atmosphere surrounding environmental issues; and high costs and technical difficulties involved in sediment characterization, removal, containment, and treatment. The need to meet these challenges is urgent. The presence of contaminated sediments poses a barrier to essential waterway maintenance and construction in many ports, which support approximately 95 percent of U.S. foreign trade. The management 1   For purposes of this report, contaminated marine sediment is defined as containing chemical concentrations that pose a known or suspected threat to the environment or human health

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--> of these sediments is also an issue in the remediation2 of an estimated 100 marine sites targeted for cleanup under the Comprehensive Environmental Response, Cleanup, and Liability Act (CERCLA) (P.L. 96-510), commonly known as Superfund, as well as in the cleanup of many other near-shore contaminated sites. The Committee on Contaminated Marine Sediments was established by the National Research Council under the auspices of the Marine Board to assess the nation's capability for remediating contaminated marine sediments and to chart a course for the development of management strategies. In the committee's view, cost-effective management of contaminated marine sediments will require a multifaceted campaign as well as a willingness to innovate. The committee determined that a systematic, risk-based approach incorporating improvements to current practice is essential for the cost-effective management of contaminated marine sediments. The committee identified opportunities for improvement in the areas of decision making, project implementation, and interim and long-term controls and technologies, as outlined in this summary. Although the study focused on evaluating management practices and technologies, the committee also found it essential to address a number of tangentially related topics (e.g., regulations, source control, site assessment) because problems in these areas can impede application of the best management practices and technologies. As part of the three-year study, the committee compiled six case histories of recent or ongoing contaminated sediments projects, visited one of those sites, analyzed the relevant regulatory framework in depth, held separate workshops on interim controls and long-term technologies, and examined in detail how various decision-making approaches can be applied in the contaminated sediments context. The committee also examined the application of decision analysis in contaminated sediments management. IMPROVING DECISION MAKING Decision-Making Tools Contaminated sediments can best be managed if the problem is viewed as a system composed of interrelated issues and tasks. Systems engineering and analysis are widely used in other fields but have not been applied rigorously to the management of contaminated sediments. The overall goal is to manage the 2   For purposes of this report, sediment management is a broad term encompassing remediation technologies as well as nontechnical strategies Remediation refers generally to technologies and controls designed to limit or reduce sediment contamination or its effects Controls are practices, such as health advisories, that limit the exposure of contaminants to specific receptors Technologies include containment, removal, and treatment approaches. Treatment refers to advanced technologies that remove a large percentage of the contamination from sediment.

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--> system in such a way that the results are optimized In particular, a systems approach is advisable with respect to the selection and optimization of interim and long-term controls and technologies. Although unlimited time and money would make remediation of any site feasible, resource limitations demand that trade-offs be made and that solutions be optimized. A fundamental aspect of the committee's recommended approach is the delineation of the trade-offs among risks, costs, and benefits that must be made in choosing the best course of action among multiple management alternatives. A number of decision-making tools can be used in making these trade-offs. Available tools include risk analysis, cost-benefit analysis, and decision analysis. Cost-effective contaminated sediments management requires the application of risk analysis—the combination of risk assessment, risk management, and risk communication. Contaminated sediments are considered a problem only if they pose a risk that exceeds a toxicological benchmark. In its most elemental form, risk assessment is intended to determine whether the chemical concentrations likely to be encountered by organisms are higher or lower than the level identified as causing an unacceptable effect. The "acceptable risk" needs to be identified, quantified, and communicated to decision makers, and the risk needs to be managed. First, management strategies need to be identified that can reduce risk to an acceptable level. Second, remediation technologies need to be identified that can reduce the risk associated with contaminants to acceptable levels within the constraints of applicable laws and regulations. Third, promising technologies need to be evaluated within the context of the trade-offs among risks, costs, and benefits, a difficult task given the uncertainties in risk and cost estimates. The next step is risk communication, when the trade-offs are communicated to the public. At present, risk analysis is not applied comprehensively in contaminated sediments management. Risks are usually assessed only at the beginning of the decision-making process to determine the severity of the in-place contamination; the risks associated with removing and relocating the sediments or the risks remaining after the implementation of solutions are not evaluated. The expanded application of risk analysis would not only inform decision makers in specific situations but would also provide data that could be used in the selection and evaluation of sediment management techniques and remediation technologies. Cost-benefit analysis can also be useful for evaluating proposed sediment management strategies. Although risk assessments may provide information about the exposure, toxicity, and other aspects of the contamination, they may result in a less-than-optimum allocation of resources unless additional information is considered. For example, a given concentration of contaminants at a particular site might be toxic enough to induce mortality in a test species, but this information alone does not indicate the spending level that would be justified for cleanup. Cost-benefit analysis combines risk and cost information to determine the most efficient allocation of resources. The basic principle of cost-benefit analysis is

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--> that activities should be pursued as long as the overall benefit to society exceeds the social cost. The difficulty lies in the measurement of the benefits and costs, or, more to the point, the projection of what they will be, before a strategy is implemented. Cost-benefit analysis is not applied widely in contaminated sediments management. It is generally carried out only for major new navigational dredging projects, and the analyses are usually narrow in scope. Cost-benefit analysis could be used in many cases to help identify the optimum solution in which the benefits outweigh the costs (i.e., to maximize benefits for a given cost or to minimize costs for a given level of benefits). The costs and benefits involved in contaminated sediments management are difficult to calculate and cannot be measured precisely, but cost-benefit analysis may be worth the effort; comprehensive cost-benefit analysis may be warranted in very expensive or extensive projects. Informal estimates or cost-effectiveness3 analyses may suffice in smaller projects. As the demand for the remediation of contaminated sediments grows, and as costs and controversies multiply, decision makers need to be able to use information about risks, costs, and benefits that may be controversial and difficult to evaluate, compare, or reconcile. One approach that could help meet this need is decision analysis, a computational technique that makes use of both factual and subjective information in the evaluation of the relative merits of alternative courses of action. Decision analysis involves gathering certain types of information about a problem and selecting a set of alternative solutions to be evaluated The evaluation is used to determine and assess possible outcomes for each alternative. The outcomes are rated, and the results are used to develop a strategy that offers the best odds for successful risk management. Formal decision analysis is not yet widely used in the management of contaminated sediments. The committee examined this technique using a test case and determined that applications of decision analysis may be particularly timely now, because recent advances in computer hardware and software make it possible to perform such analyses in ways that are user friendly and interactive. Decision analysis could be especially valuable because it can accommodate more variables (including uncertainty) than techniques such as cost-benefit analysis that measure single outcomes. Decision analysis can also serve as a consensus-building tool by enabling stakeholders to explore various elements of the problem and, perhaps, find common ground. However, because decision analysis is technical in design and involves complex computations, it is probably worth the effort only in highly contentious situations in which stakeholders are willing to devote enough time to become confident of the usefulness of the approach. 3   Cost effectiveness is defined here as a measure of tangible benefits for money spent.

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--> Regulatory Framework Few aspects of sediment handling, treatment, or containment are unregulated at the federal, state, or local level, but the regulatory approach is inconsistent, primarily because the applicable laws were originally written to address issues other than contaminated marine sediments. As a result, the current laws and regulations affecting contaminated sediments can impede efforts to implement the best management practices and achieve efficient, risk-based, and cost-effective solutions. This is a shortcoming of the governing statutes, not a criticism of regulatory agencies charged with implementing them. The timeliness of decision making is also an issue, given that it typically takes years to implement solutions to contaminated sediments problems. In the committee's case histories, the delay between the discovery of a problem and the implementation of a solution ranged from approximately 3 to 15 years. At least six comprehensive acts of Congress, with implementation responsibilities spread over seven federal agencies, govern sediment remediation or dredging operations in settings that range from the open ocean to the freshwater reaches of estuaries and wetlands. When environmental cleanup is the driving force, the relevant federal laws include Superfund; the Resource Conservation and Recovery Act (RCRA) (P.L 94-580); and Section 115 of the Clean Water Act (CWA) (formerly the Federal Water Pollution Control Act [P.L. 80-845]) When navigational dredging is the issue, the applicable statutes are likely to be the CWA; the Rivers and Harbors Act of 1899 (P.L. 55-525); the Marine Protection, Research and Sanctuaries Act (MPRSA, commonly known as the Ocean Dumping Act) (P.L. 92-532); and the Coastal Zone Management Act (P.L. 92-583). In addition, states also exercise important authority related to water quality certification and coastal zone management. In some cases, local laws may also apply. To complicate matters further, federal, state, and local authorities often overlap. The principal federal agencies involved are the Environmental Protection Agency (EPA), which is responsible for implementing Superfund and has major site designation, regulation development, and veto responsibilities under the CWA and MPRSA; the National Oceanic and Atmospheric Administration, which assesses the potential threat of Superfund sites to coastal marine resources and exercises significant responsibilities for research, under the MPRSA, and review and comment, under CWA and MPRSA; and the U.S Army Corps of Engineers (USACE), which assists in the design and implementation of remedial actions, under Superfund, and has responsibilities for dredged material, under the CWA, MPRSA, and Rivers and Harbors Act. The federal navigational dredging program is the joint responsibility of the EPA and USACE; the EPA regulates disposal, whereas USACE handles the dredging. The committee identified several areas of the current regulatory framework in which changes might be beneficial. For example, the CWA, the MPRSA, and

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--> Superfund use different approaches for evaluating remedial alternatives, but none fully considers either the risks posed by contaminated marine sediments or the costs and benefits of various solutions. The MPRSA requires biological testing of dredged material to determine its inherent toxicity but does not fully consider site-specific factors that may influence the exposure of organisms in the receiving environment, meaning that, at best, risk is considered only indirectly and the actual impact is approximated. Although the CWA procedures, which consider chemical and physical as well as biological characteristics in assessing whether the discharge of dredged material will cause unacceptable adverse impacts, are not risk-based, at least they do not specify rigid pass-fail criteria. They are geared to identification of the least environmentally damaging, implementable alternative. The Superfund remedial action program addresses risks and costs to some degree—an exposure assessment (but not a full risk analysis) is required to assess in-place risks; remedial alternatives are identified based on their capability of reducing exposure risks to an acceptable level; and the final selection involves choosing the most cost-effective solution. However, there are no risk-based cleanup standards for underwater sediments. Insufficient attention to risks, costs, and benefits impedes efforts to reach technically sound decisions and manage sediments cost-effectively. Similar inattention to risk is evident in the permitting processes for sediment disposal. It is currently necessary to secure different types of permits for the placement of sediments in navigation channels or ocean waters as part of the construction of land or containment facilities (under the Rivers and Harbors Act), the dumping of sediments in the ocean (under the MPRSA), the discharge of sediments in inland waters or wetlands (CWA), and the containment of contaminated sediments on land (RCRA). In addition, different regulations come into play depending on whether sediments are removed during navigational dredging (CWA or MPRSA) or are excavated for environmental remediation (Superfund). The committee can see little technical justification for the differential regulation of contaminated sediments, given that neither the location of the aquatic disposal site (freshwater versus saltwater) nor the reason for dredging (navigational dredging versus environmental remediation) necessarily affects the risk posed by the contamination. The regulatory regime does not adequately address risk; instead it focuses rigidly on the nature of the activities to be carried out. This problem has been eased in some instances by the interpretation of regulations based on the intent of the underlying statute(s). Systematic, integrated decision making can also be undermined by dredging regulations governing cost allocation and cost-benefit analysis. The federal government pays for most new-work dredging and all maintenance dredging but not for sediment disposal, except in open water. The local sponsors of federal navigation projects bear the burden of identifying, constructing, operating, and maintaining dredged material disposal sites, under the "project cooperation agreement"

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--> of the Water Resources Development Act (WRDA) of 1986 (P.L. 99-662). Because project sponsors must pay for disposal on land, whereas open-water disposal is paid for by the federal government as a component of dredging costs, the WRDA provision creates a strong preference for open-water disposal. Furthermore, a local sponsor bearing the full burden of disposal costs has little incentive to seek out opportunities for the beneficial uses of dredged material (discussed in the next section). The cost of making use of dredge material adds to the project cost and may benefit only third parties. This inconsistent approach to cost sharing can lead to the economically irrational allocation of scarce societal resources. Additional inconsistencies are introduced in the area of cost-benefit analysis. As noted earlier, costs and benefits must be weighed for new dredging projects but not for the maintenance dredging of existing channels or for the disposal of dredged material. IMPROVING PROJECT IMPLEMENTATION Stakeholder Interests Contaminated sediments are not managed in a political or social vacuum. Most contaminated sediments sites are located in highly populated areas near the Great Lakes or the oceans. The nature of these sites virtually ensures that complicated ecological situations and difficult technical problems will have to be accommodated along with complex political circumstances involving multiple resource users and interest groups. Stakeholders include port managers and transportation officials who have strong economic reasons for dredging; federal, state, and local regulators responsible for protecting natural resources and enforcing regulations; and environmental groups, local residents, fishermen, and other marine resource users who are concerned about public health and natural resources. The successful management of contaminated sediments must respond to all dimensions of the problem: ecological, technical, social, and political. The committee determined that remediation and disposal projects need strong proponents and that the identification and timely implementation of effective solutions depend heavily on how project proponents interact with stakeholders, who often have different perspectives on the problem and proposed solutions. Because any participant in the decision-making process can block or delay remedial action, project proponents need to identify all stakeholders and build a consensus among them. The development of a consensus can be fostered by the use of various tools, including mediation, negotiated rule making, collaborative problem solving, and effective communication of risks. Stakeholder acceptance of contaminated sediments management projects can be fostered by the reuse of dredged material. Dredged material has been used for many purposes, including the creation of thousands of islands for seabird nesting,

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--> landfills for urban development, and wetlands, as well as for beach nourishment and shoreline stabilization. The policy focus and most of the experience to date have concerned the use of clean materials, but some contaminated sediments can also be used safely for certain beneficial purposes. Reuse can provide alternatives to increasingly scarce disposal sites while also making management plans more attractive, or at least palatable, to stakeholders. Some contaminated sediment sites have been successfully transformed into wetlands, and productive USACE research is under way on the safe use of contaminated sediments for "manufacturing" topsoil and landfill covers. However, funding for this type of research is limited, and technical guidelines have yet to be developed. Other barriers include the USACE policy of selecting lowest-cost disposal options with little regard to the possibilities of beneficial use and the uncertainties about whether the incremental costs of beneficial use should be borne by the project proponent or the beneficiary. Source Control Because accumulations of sediments interfere with deep-draft navigation, ports have no alternative but to dredge periodically in order to remain economically viable. If the sediments to be dredged are contaminated, then ports become responsible for both sediment disposal and any necessary remediation, even though they have no control over the source of the contamination. Upstream generators of contaminants often cannot be identified or held accountable, leaving ports to manage a problem that is not of their making. This responsibility could be shared by states (when states do not already operate or oversee port agencies). which benefit economically from dredging and already engage in watershed management. Under the CWA (Section 303), the EPA and the states set total maximum daily loads for waterway segments and develop load allocations for pollution sources in an effort to control water pollution. This approach could be readily expanded to address sources of sediment contamination. In addition, government regulators and ports could use all available legal and enforcement tools for ensuring that polluters bear a fair share of cleanup costs. Site Characterization Accurate site characterization is essential to the cost-effective management of contaminated sediments. Site assessments need to be sufficiently comprehensive and accurate to ensure that the contamination is well defined both chemically and geographically. Inaccuracies and incompleteness can leave areas of unidentified contamination that pose continuing unmanaged risks. Another compelling argument for accurate site assessment is the need to control remediation costs; precise site definition is necessary to facilitate removal of only those sediments

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--> that are contaminated, thus controlling the volume of material that requires expensive remediation. But the high cost of commonly used site characterization technologies (i.e., physical profiling and chemical testing) has limited the precise definition of either horizontal or vertical contaminant distributions, which may have led to the removal and "remediation" of large quantities of uncontaminated sediments at unnecessarily high costs. Thus, the development and wide use of new or improved site characterization technologies that are less expensive than current methods would enhance the cost-effective management of contaminated sediment sites One technology that may prove useful in the future is acoustic profiling, 4 which helps define the thickness and distribution of disparate sediment types. Because contaminants tend to be associated with fine-grained material, acoustic profiling may provide for cost-effective remote surveying of contaminated sediments, thereby increasing the precision and accuracy of site assessment. Additional research and development is needed, however. Sediment characterization may also be enhanced through the adaptation of chemical sensors now used in the assessment of soil and groundwater sites. INTERIM AND LONG-TERM CONTROLS AND TECHNOLOGIES The following is a brief assessment of the controls and technologies that are applicable to contaminated sediments. The section concludes with a comparative analysis reflecting the committee's overall judgments of the feasibility, effectiveness, practicality, and cost of each control and technology. Interim Controls Interim controls may prove helpful when sediment contamination poses an imminent hazard. Identification of an imminent hazard is usually a matter of judgment, but in general an imminent hazard exists when contamination levels exceed by a significant amount the sum of a defined threshold level plus the associated uncertainty. Administrative interim controls (e.g., signs, health advisories) have been used a number of times. Only two applications of structural interim approaches (e.g., thin caps) were identified by the committee, but additional structural approaches, such as the use of confined disposal facilities (CDFs) for temporary storage, appear promising. Few data are available concerning the effectiveness of interim controls because to date they have not been used often or evaluated in detail. 4   Acoustic profiling involves high-resolution mapping of the acoustic reflectivity of sediments.

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--> Long-Term Controls and Technologies Technologies for remediating contaminated sediments are at various stages of development. Sediment-handling technologies are the most advanced, although benefits can be realized from improvements in the precision of dredging (and, concurrently, site characterization). The state of practice for in situ controls ranges from immature (e.g., bioremediation) to evolving (e.g., capping). Ex situ containment is commonplace. A number of existing ex situ treatment technologies can probably be applied successfully to treating contaminated sediments, but full-scale demonstrations are needed to determine their effectiveness. But these technologies are expensive, and it is not clear whether unit costs would drop significantly in full-scale implementation. The cost of cleanup depends on the number of steps involved-the more handling required, the higher the cost-and the type of approach used. The costs of removing and transporting contaminated sediments (generally less than $15 to $20/yd3) tend to be higher than costs of conventional navigational dredging (seldom more than $5/yd3) but much lower than the costs of treatment (usually more than $100/yd3). Volume reduction (i.e., removing only sediments that require treatment and entraining as little water as possible) will mean greater cost savings than increased production rates; improved site characterization coupled with precision dredging techniques hold particular promise for reducing volume. Treatment costs may also be reduced through pretreatment. In situ management offers the potential advantage of avoiding the costs and potential material losses associated with the excavation and relocation of sediments. Among the inherent disadvantages of in situ management is that they are seldom feasible in navigation channels that are subject to routine maintenance dredging. In addition, monitoring needs to be an integral part of any in situ approach to ensure effectiveness over the long term. Natural recovery is a viable alternative under some circumstances and offers the advantages of low cost and, in certain situations, the lowest risk of human and ecosystem exposure to sediment contamination. Natural recovery is most likely to be effective where surficial concentrations of contaminants are low, where surface contamination is covered over rapidly by cleaner sediments, or where natural processes destroy or modify the contaminants, so that contaminant releases to the environment decrease over time. A disadvantage of natural recovery is that the sediment bed is subject to resuspension by storms or anthropogenic processes. For natural recovery to be pursued with confidence, the physical, chemical, and hydrological processes at a site need to be understood adequately; however, no capability currently exists for completely quantifying chemical movements. Extensive site-specific studies may be required. In situ capping promotes chemical isolation and may protect the underlying contaminated sediments from resuspension until naturally occurring biological degradation of contaminants has occurred. The original bed must be able to

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--> support the cap, suitable capping materials must be available to create the cap, and suitable hydraulic conditions (including water depth) must exist to permit placement of the cap and to avoid compromising the integrity of the cap. Changes in the local substrate, the benthic community structure, or the bathymetry at a depositional site may subject the cap to erosion. Improved long-term monitoring methods are needed. A regulatory barrier to the use of capping is the language of Superfund legislation (Section 121[b]), which gives preference to ''permanent" controls. Capping is not considered by regulators to be a permanent control, but available evidence suggests that properly managed caps can be effective. Neither in situ immobilization nor chemical treatment of contaminated sediments has been demonstrated successfully in the marine environment, although both concepts are attractive because they do not require sediment removal. Their application would be complicated by the need to isolate sediments from the water column during treatment, by inaccuracies in reagent placement, and by the need for long-term follow-up monitoring. Other constituents (e.g., natural organic matter, oil and grease, metal sulfide precipitates) could interfere with chemical oxidation. Immobilization techniques may not be applicable to fine-grained sediments with a high water content. Biodegradation has been observed in soils, in groundwater, and along shorelines contaminated by a variety of organic compounds (e.g., petroleum products, PCBs, polyaromatic hydrocarbons, pesticides). However, the use of biodegradation in subaqueous and especially marine environments presents unresolved microbial, geochemical, and hydrological issues and has yet to be demonstrated When sediments must be moved for ex situ remediation or confinement, efficient hydraulic and mechanical methods are available for removal and transportation. Most dredging technologies can be used successfully to remove contaminated sediments; however, they have been designed for large-volume navigational dredging rather than for the precise removal of hot spots. Promising technologies offering precision control include electronically positioned dredge heads and bottom-crawling hydraulic dredges. The latter may also have the capability to dredge in depths beyond the standard maximum operating capacity. The cost effectiveness of dredging innovations can best be judged by side-by-side comparisons to technologies in current use. Containment technologies, particularly CDFs, have been used successfully in numerous projects. A CDF can be effective for long-term containment if it is well designed to contain sediment particles and contaminants and if a suitable site can be found. A CDF can also be a valuable treatment or interim storage facility, allowing the separation of sediments for varying levels of treatment and, in some cases, beneficial reuse. Costs are reasonable; in some parts of the country it may be cheaper to reuse CDFs than to build new ones. Disadvantages of this technology include the imperfect methods for controlling contaminant release pathways. There is also a need for improved long-term monitoring methods.

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--> Contained aquatic disposal (CAD) is applicable particularly to contaminated sites in shallow waters where in situ capping is not possible and to the disposal and containment of slightly contaminated material from navigation dredging. Although the methodology has been developed, CAD has not been widely used. Among the advantages of CAD are that it can be performed with conventional dredging equipment and that the chemical environment surrounding the cap remains unchanged. Disadvantages include the possible loss of contaminated sediments during placement operations. Improved tools are needed for the design of sediment caps and armor layers and for the evaluation of their long-term stability and effectiveness. Scores of ex situ treatment technologies have been bench tested and pilot tested, and some warrant larger-scale testing in marine systems, depending on their applicability to particular problems. Chemical separation, thermal desorption, and immobilization technologies have been used successfully but are expensive, complicated, and only effective for treating certain types of sediments. Similarly, because of extraordinarily high unit costs, thermal and chemical destruction techniques do not appear to be near-term, cost-effective approaches for the remediation of large volumes of contaminated dredged sediment. Ex situ bioremediation, which is not as far along in development as are other ex situ treatment approaches, presents so many technical problems that its application to contaminated sediments would be expensive. If these technical problems can be resolved, however, ex situ bioremediation has the potential, over the long term, for the cost-effective remediation of large volumes of sediments. Ex situ bioremediation is much more promising than in situ bioremediation because conditions can be controlled more effectively in a contained facility. The approach has been demonstrated on a pilot scale with some success, but complex questions remain concerning how to engineer the system. Comparative Analysis of Controls and Technologies Table S-1 summarizes the committee's overall assessment of the feasibility, effectiveness, practicality, and costs of controls and technologies. For each control and technology, the four characteristics were rated separately on a scale of 0 to 4, with 4 representing the best available (not necessarily the best theoretically possible) features. The effectiveness rating is an estimate of contaminant reduction or isolation and removal efficiency; scores represent a range of less than 90 percent to nearly 100 percent. The feasibility rating represents the extent of technology development, with 0 for a concept that has not been verified experimentally and 4 for a technology that has been commercialized. The practicality ranking reflects public acceptance; 0 means no tolerance for an activity and 4 represents widespread acceptance. The cost ranking is inversely related to the cost of using the control or

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--> TABLE S-1 Comparative Analysis of Technology Categories Approach Feasibility Effective Practicality Cost INTERIM CONTROL Administrative 0 4 2 4 Technological 1 3 1 3 LONG-TERM CONTROL In Situ Natural recovery 0 4 1 4 Capping 2 3 3 3 Treatment 1 1 2 2 Sediment Removal and Transport 2 4 3 2 Ex Situ Treatment Physical 1 4 4 1 Chemical 1 2 4 1 Thermal 4 4 3 0 Biological 0 1 4 1 Ex Situ Containment 2 4 2 2 SCORING 0 < 90% Concept Not acceptable, very uncertain $1,000/yd3 1 90% Bench   $100/yd3 2 99% Pilot   $10/yd3 3 999% Field   $1/yd3 4 99 99% Commercial Acceptable, certain < $1/yd3 technology (not including expenses associated with monitoring, environmental resource damage, or the loss of use of public facilities). The overall pattern of the ratings underscores the need for trade-offs in the selection of technologies. No single approach emerges with the highest scores across the board, and each control or technology has at least one low or moderate ranking. In general, interim controls and in situ approaches are feasible and low in cost but less effective than the most practical ex situ approaches, which tend to be high in cost and complexity. Decisions about which approach is the most appropriate must be made on a project-by-project basis.

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