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Summary BACKGROUND Contaminated sediments in aquatic environments can pose risks to human health and other organisms. Nationwide, the full extent of the problem is poorly documented, but it is well known that many rivers, harbors, lakes, and estuaries fed by existing or former industrial, agricul- tural, or mining areas contain contaminated sediments. It is also well known that contaminants in the sediments can directly harm aquatic or- ganisms or accumulate in their tissue, which can be consumed by hu- mans. The potential adverse effects on human health and the environ- ment are compelling reasons to reduce such exposures. From a regulatory standpoint, contaminated sediments are chal- lenging to manage. The Superfund program,1 administered by the U.S. Environmental Protection Agency (EPA), is intended to protect human health and the environment from hazardous substances at contaminated sites. At most contaminated sediment Superfund sites, the remedial 1 The Superfund requirements are set forth in the Comprehensive Environ- mental Response, Compensation, and Liability Act (CERCLA) of 1980 as amended (42 USC Â§Â§ 9601-9675 ), and its implementing regulations are set forth in the National Contingency Plan (NCP) (40 CFR 300). 1
2 Sediment Dredging at Superfund Megasites process includes a site investigation, comparison of remedial alterna- tives, and selection and implementation of a remedy. The process is af- fected by numerous scientific and technical issues. Resource-intensive surveys and analyses are required to document the distribution, depth, and concentration of contaminants in sediments and contaminant con- centrations in the aquatic biota. Even if substantial resources are focused on a relatively small site, understanding the current and potential risks of contaminated sediments can be difficult and uncertain, relying heavily on surrogate measures and modeling of actual environmental effects. The process of estimating and comparing the modeled results of poten- tial remedial actions (including no action) has substantial uncertainties that depend on a host of variables, including whether environmental conditions have been adequately characterized and the accuracy of near- term and long-term predictions of post-remediation contaminant behav- ior. The uncertainties are magnified by increasing duration of a remedial action and increased extent and complexity of a contaminated site. Contaminated sediments exist in a variety of environments and can differ greatly in type and degree of contamination. Site conditions are important in determining which remediation techniques (and combina- tions thereof) are appropriate. The techniques include removing the sediments from the aquatic environment (for example, by dredging), capping or covering contaminated sediments with clean material, and relying on natural processes while monitoring the sediments to ensure that contaminant exposures are decreasing, or at least not increasing. Those approaches differ in complexity and cost; dredging is the most complex and expensive, and monitoring without active remediation is the least difficult and least expensive. Remedial approaches have trade- offs with respect to the risks that are created during implementation and that remain after remediation. Dredging may create exposures (for ex- ample, through the resuspension of buried contaminants) during im- plementation, but it has the potential to remove persistent contaminants permanently from the aquatic environment. Monitoring without removal does not itself create risks, but it leaves contaminants in the aquatic envi- ronment. Remedial operations also vary in efficacy within and among the different approaches. The variability is driven by several factors, in- cluding site conditions and implementation of the remedial approach. Decisions about whether to dredge at contaminated sediment sites have proved to be among the most controversial at Superfund mega-
Summary 3 sites.2 The scientific and technical difficulties described above are aug- mented by the challenges of implementing a program that holds respon- sible parties liable for paying for the cleanup, with parties in some cases unwilling to accept the liability. Cleanup planning must also be respon- sive to the public, which may have little tolerance for remedial actions that leave contaminants in the local environment. Those controversies often expand with the magnitude of the sites and the scope of remedial activity, as has been seen at some of the nationâs largest sediment reme- diation sites (for example, the Fox River, WI, and the Hudson River, NY). Regardless of cost or controversy, achieving the intended effect of remedial actions in terms of anticipated improvements in the environ- ment is of primary importance. That is true for regulators who require cleanup of a site, parties responsible for funding the cleanup, and com- munities and user groups, such as anglers and boaters, who are directly affected by the contamination. THE COMMITTEEâS CHARGE This study, which was conducted to evaluate the effectiveness of dredging as a remedial option at contaminated sediment sites, originated in the fiscal year 2006 appropriations bill for the Department of Interior, environment, and related agencies. The accompanying conference report (Report 109-188) states that âthe managers believe that the appropriate role for the NAS [National Academy of Sciences] is to act as an inde- pendent peer review body that will conduct an objective evaluation of some of the ongoing dredging projects underway at Superfund megasites. By undertaking such an evaluation, the Academy can serve as an objective voice on this issue.â The Committee on Sediment Dredging at Superfund Megasites was convened by the National Research Council of the National Academies. In brief, the committeeâs charge requests an evaluation of the expected effectiveness of dredging of contaminated sediments at Superfund megasites. The committee was asked to consider such aspects of dredg- ing as short-term and long-term changes in contaminant transport and ecologic effects. Overall, the committee was charged to strive to develop 2Megasites are those Superfund sites where remedial expenditures are ex- pected to exceed $50 million.
4 Sediment Dredging at Superfund Megasites recommendations that would facilitate scientifically based and timely decision-making for megasites in the future but not to recommend par- ticular remedial strategies for specific sites. The committee, chosen by the National Research Council, consists of experts in a variety of fields relevant to the statement of task. Over the course of the study, the committee held three public sessions in which it heard presentations on an array of dredging projects and received input from members of the public and other interested parties; two closed, de- liberative sessions were also held over the course of the year-long study. EVALUATION OF EXPERIENCE AT DREDGING SITES The committee examined experience at 26 dredging projects and evaluated whether, after dredging, the cleanup goals had been met. That involved evaluating whether a site achieved its quantitative cleanup lev- els (typically a specified concentration in sediment expected to be achieved in the short term, that is, immediately after remedy implemen- tation) and remedial-action objectives (often a narrative statement of what the cleanup is expected to accomplish in the long term).3 Various sites were examined, including full-scale dredging projects, pilot studies at sites, and dredging projects within a large-scale remediation effort. Conclusions The committee concluded that dredging is one of the few options available for the remediation of contaminated sediment and that it should be considered, with other options, to manage the risks that the contaminated sediments pose. However, the committee could not gener- ally establish whether dredging alone is capable of long-term risk reduc- tion. That is because monitoring at most sites does not include all the In this context, short term refers to anything caused as an immediate conse- 3 quence of the action being focused on; long-term extends beyond this time period to the time required to achieve remedy success. For dredging projects, this would include any period of natural recovery that is part of the remedy and necessary to achieve the goals of the remedy.
Summary 5 BOX S-1 Overview of Conclusions and Recommendations Sediment dredging can be effectively implemented to remove contami- nants from aquatic systems, but technical limitations often constrain its ability to achieve expected outcomes. The range of experiences and outcomes at dredging sites, coupled with shortcomings in monitoring data, the lack of sufficient time to observe long-term changes, and difficulties in separating the effects of dredging from the effects of other processes limited the committeeâs ability to establish whether dredging alone has been effective in risk reduction. However, assess- ment of data from dredging projects does indicate that dredging has encountered systematic difficulties in achieving specified cleanup levels (expected sediment- contaminant concentrations after dredging) and that monitoring to evaluate long-term success is generally lacking. The inability to meet desired cleanup lev- els is associated primarily with âresidualâ contamination that typically results from dredging operations or from leaving contaminated sediment exposed after dredging. Site assessments also indicate that contaminants can be released into the water during dredging and can have short-term adverse effects on the aquatic biota. Residual contamination and contaminant release are inevitable during dredging and should be explicitly considered in estimating risk reduc- tion. Some site conditions and dredging practices can limit the amount of resid- ual contamination remaining after dredging and can limit contaminants released into the water column. Those site conditions should be given major consideration when evaluating the potential effectiveness of dredging. Environmental monitoring is the only way to evaluate remedial success, but monitoring at most Superfund sites has been inadequate to determine whether dredging has been effective in achieving remedial objectives (that has not been the case in several highly monitored pilot studies). Basic information was not collected at some sites, and others had only recently completed dredg- ing, so long-term trends could not be assessed. EPA should ensure that adequate monitoring is conducted at all contaminated sediment megasites to evaluate re- medial effectiveness. Some current monitoring techniques have proved useful in determining short-term and long-term effects of remediation, but further devel- opment of monitoring strategies is needed. Pre-remediation monitoring is neces- sary to adequately characterize site conditions and to assemble a consistent long- term dataset that allows statistically valid comparisons with future post- remediation monitoring data. Monitoring data should also be made available to the public in an accessible electronic form so that evaluations of remedial effec- tiveness can be independently verified. (Continued on next page)
6 Sediment Dredging at Superfund Megasites BOX S-1 Continued Regarding the future practices and management of contaminated sedi- ments at megasites, the committee recommends that adaptive-management ap- proaches should be implemented in the selection and implementation of reme- dies where there is a high degree of uncertainty about the effectiveness of the remedial action. In selecting site remedies, dredging remains one of the few op- tions available for the remediation of contaminated sediment, and it should be considered along with other options, but EPA should compare the expected net risk reduction associated with each remedial alternative, taking into account the range of risks and uncertainty associated with each alternative. EPA should cen- tralize sediment-related resources, responsibility, and authority at the national level to ensure that necessary improvements are made in site tracking, in the implementation of monitoring and adaptive management, and in research to examine the relationship between the remedial actions, site conditions, and risk reduction. measures necessary to evaluate risk over time,4 dredging may have oc- curred in concert with other remedies or natural processes that affect risk, insufficient time has passed to evaluate long-term risk reduction, and a systematic compilation of site data necessary to track remedial ef- fectiveness nationally is lacking. However, the committee was able to draw several conclusions and derive recommendations on the basis of monitoring data from a range of dredging projects and by evaluating factors that affected their success. The analysis indicates that dredging can be effective for removal of mass, but that mass removal alone does not necessarily achieve risk-based goals. Monitoring data demonstrate that dredging can have short-term adverse effects, including increased contaminant concentrations in the water, increased contaminant concentrations in the tissues of caged fish adjacent to the dredging activity, and short-term increases in tissue con- taminant concentrations in other resident biota. However, monitoring for those effects was not conducted at many sites. Monitoring for risk reduction is not straightforward; there is no analytic de- 4 termination of ârisk,â and estimating risk reduction requires multiple metrics (for example, concentration, toxicity and bioavailability data) to be measured consistently through time.
Summary 7 The most frequent post-dredging measurement used to assess ef- fectiveness at the sites was contaminant concentrations in surface sedi- ment. Surface concentrations (as opposed to concentrations in deeply buried sediments) are the most relevant to risk. At some sites (for exam- ple, Bayou Bonfouca, LA; Waukegan Harbor, IL; and the Dupont New- port Site, Christina River, DE), sediments were not sampled for contami- nants immediately following dredging. The committeeâs analysis of pre- dredging and post-dredging surface sediment concentrations indicates a wide range of outcomes: some sites showed increases, some no change, and some decreases in contaminant concentrations. Residual contamina- tion after dredging can result from the incomplete removal of targeted sediments or the deposition of sediment resuspended during dredging. Residual contaminated sediments hamper the ability to achieve desired cleanup levels and are exacerbated by site conditions like obstructions in the dredging area and impenetrable or uneven formations underlying the contaminated sediments. Overall, the committee found that dredging alone achieved the desired contaminant-specific cleanup levels at only a few of the 26 dredging projects, and that capping5 after dredging was often necessary to achieve cleanup levels. The committee was able to identify factors that led to the success or failure of projects to meet desired short-term cleanup levels and, where long-term data were available, remedial-action objectives. Some sites exhibited conditions that are more conducive to dredging and less prone to releasing contaminants and less likely to result in residual contami- nated sediment after dredging. Favorable site conditions include little or no debris (for example, rocks, boulders, cables, automobiles, and I- beams), sediment characteristics that permit rapid (even visual) determi- nation of clean vs contaminated sediment, conditions that allow over- dredging into clean material beneath contaminated sediment (sites un- derlain by bedrock or hardpan are highly problematic), low-gradient bottom and side slopes, lack of piers and other structures, rapid natural attenuation processes after dredging, and absence of contaminants that distribute to the water column rapidly after sediment disturbance. 5 Capping refers broadly to the placement of a layer of uncontaminated mate- rial over material with elevated concentrations to contain contaminated sedi- ment.
8 Sediment Dredging at Superfund Megasites The design and implementation of remediation can also influence the extent of chemical release and residual contamination (as well as counteract the influence of poor site conditions). Adequate site charac- terization is needed to identify adverse conditions and potential sources of recontamination in the site or watershed. Pilot studies are particularly useful for identifying adverse site conditions and logistical problems. As discussed in the report, best-management practices during dredging can help control residuals and resuspension. Backfilling and capping can be used following dredging to manage residual contaminated sediments. Contracting mechanisms can be used to encourage a focus on specified cleanup levels and remedial-action objectives instead of on attaining mass removal targets. The combined experience indicates that dredging alone is unlikely to be effective in meeting short-term and long-term goals if a site has one or more unfavorable conditions. If conditions are unfavorable, contami- nant resuspension and release and residual contamination will tend to limit the ability to meet desired cleanup levels and will delay the achievement of remedial-action objectives unless managed with a com- bination of remedies. Recommendations â¢ Remedies should be designed to meet long-term risk-reduction goals (as opposed to metrics not strictly related to risk, such as mass- removal targets). The design should be tested by modeling and monitor- ing the achievement of long-term remedial action objectives. â¢ Environmental conditions that limit or favor the effectiveness of dredging should be given major consideration in deciding whether to dredge at a site. â¢ Resuspension, release, and residuals will occur if dredging is performed. Decision-making should include forecasts to estimate the effects of those processes, and the predictions should be explicitly con- sidered in expectations of risk reduction. To reduce adverse effects, best- management practices that limit resuspension and residual contamina- tion should be used during dredging. The ability of combination reme- dies to lessen the adverse effect of residuals should be considered.
Summary 9 â¢ Further research should be conducted to define mechanisms, rates, and effects of residuals and contaminant resuspension associated with dredging. It is known that contaminated sediment resuspension and residuals create exposures, but the relationship of the magnitude of those processes to environmental conditions, operational controls, and management practices is not well quantified. MONITORING FOR EFFECTIVENESS Conclusions Environmental monitoring is the only way to evaluate a remedyâs success in reducing risk and ensure that the objectives of remediation have been met. It is therefore an essential part of the remedy. It is impos- sible to evaluate effectiveness in the absence of sufficient baseline data and appropriate reference sites. Monitoring needs to be conducted to confirm not only that desired cleanup levels have been met, but that they result in risk reduction. In most cases reviewed by the committee, monitoring was designed or implemented inadequately to determine whether dredging was effec- tive in achieving the objectives of the remediation or long-term risk re- duction. For example, at some sites, sparse or incomplete monitoring data were collected. Pre-remediation monitoring approaches were not always consistent with those used for long-term post-remediation moni- toring. Pre-remediation trends in sediment or fish concentrations were not of sufficient duration to enable judging the effect of the remedial ac- tion. The models and forecasts used to select a remedy were not updated with post-remediation data to determine whether remediation had the expected effects (or to examine why or why not). Monitoring was of in- sufficient quality or quantity to support rigorous statistical analyses. However, some monitoring techniques have proved useful in de- termining short-term and long-term effects of remediation. Monitoring during dredging, including measurements of mass flux (contaminant transport over time) attained through upstream and downstream chemi- cal monitoring, and biologic monitoring, including caged-fish studies
10 Sediment Dredging at Superfund Megasites and passive sampling devices,6 are useful in indicating chemical releases to the water from dredging. Chemical concentrations do not always cor- respond directly with potential uptake or toxicity because contaminant bioavailability can differ among sampling locations. However, chemical analyses are among the most highly standardized and easily attainable indicators of risk and are useful in evaluating trends before and after dredging. Laboratory toxicity testing has proven valuable in long-term monitoring of risk to benthic organisms in sediment following dredging. Fish-tissue monitoring for contaminants is useful for indicating risks to the health of people and other piscivorous species, particularly if long-term monitoring trend data exist. However, linking changes in fish- tissue concentrations to remedial actions can be problematic, because fish are mobile and can be exposed to offsite conditions. For describing possible ecologic effects, benthic organisms (or organisms with home ranges limited to the site) or passive sampling devices are probably bet- ter indicators, although not necessarily sufficient indicators of exposure to higher trophic level species. Recommendations â¢ EPA should ensure that monitoring is conducted at all contami- nated sediment megasites to evaluate remedy effectiveness. Monitoring data should be made available to the public in a form that makes it pos- sible to verify evaluations of remedial efficacy independently. â¢ Monitoring plans should focus on elements required to judge remedial effectiveness and to inform management decisions about a site. Planning, evaluation, and adaptive management7 based on monitoring findings should be closely linked to the conceptual site model so that the hypotheses and assumptions that led to the selected remedy can be tested and refined. â¢ Pre-remediation baseline monitoring methods and strategies should be developed to allow statistically valid comparisons with post- Passive sampling devices accumulate chemicals of interest during an ex- 6 tended deployment period (days to weeks) in the environment to provide an integrated estimate of chemical exposure over that period. 7Adaptive management is generally used to learn from, test, assess, and mod- ify or improve remedies with the goal of meeting long-term objectives.
Summary 11 remediation monitoring datasets. The ultimate goal is to assemble a con- sistent long-term dataset that can be used in evaluations. Monitoring should be initiated during the design of the remedy to help to establish a pre-remedial time trend, integrating earlier characterization data as technically appropriate. â¢ Research in and development of rapid field monitoring tech- niques to inform dredging operations in nearly real time are needed to indicate the effects of resuspension of contaminants and their release to the water column. Biota monitoring approaches that use benthic inverte- brates (or other organisms with appropriate home ranges) as indicators of food-web transfer of contaminants should also be developed. IMPROVING FUTURE DECISION-MAKING AT SUPERFUND MEGASITES Conclusions The historical perspective and hindsight gained from the commit- teeâs retrospective analysis of sediment sites provide an opportunity to derive common lessons and to improve on the manner in which envi- ronmental dredging is planned and implemented. It is important that this type of review be on-going and be part of a shared experience among regulators, practitioners, and the public. The large spatial scale and long remedial timeframes of contaminated sediment megasites make it difficult to predict and quantify the human health and ecosystem risk- reduction benefits achieved by isolated remediations in a large-scale wa- tershed. In addition, the complexity and heterogeneity of large-scale megasites suggest that a variety and combination of remedial ap- proaches will often be appropriate. The committee concludes that three critical kinds of changes are needed to improve decision-making and the efficacy of dredging remedies at contaminated sediment megasites. First, owing to the complexity, large spatial scale, and long time frame involved, the management of contaminated megasites needs to embrace a more flexible and adaptive approach to accommodate unan- ticipated factors, new knowledge, technology changes, and results of field pilot tests. Comprehensively characterizing sediment deposits and contaminant sources on the scale of megasites presents tremendous
12 Sediment Dredging at Superfund Megasites technical challenges and uncertainties. Many large and complex con- taminated sediment sites will take years or decades to remediate and will encounter unforeseen conditions. A priori predictions of the outcome of that remediation, made on the basis of incomplete information, will also have high uncertainty. The typical Superfund approach, wherein EPA conducts a remedial investigation and a feasibility study that establishes a single path to remediation in the record of decision is not the best ap- proach to remedy selection and implementation at these sites. At the largest contaminated sediment sites, the remediation timeframes and spatial scales are in many ways unprecedented. Remedial strategies will often require unexpected adjustments, whether in response to new knowledge about site conditions or advances in technology (such as im- proved dredge or cap design or in situ treatments). Because such uncer- tainty exists, regulators and others will need to adapt continuously to evolving conditions and environmental responses that cannot be fore- seen. Thus, the process for remedy selection at large, complex sediment megasites needs to allow more adaptive site investigation, remedy selec- tion, and remedy implementation. Second, improved risk assessment that specifically considers the full range and real-world limitations of remedial alternatives is needed to allow valid comparisons of technologies and uncertainties. Each re- medial alternative offers a unique set of risk-reduction benefits, possibly with the creation of new contaminant exposure pathways and associated risks. The effects of adverse environmental conditions, such as those leading to chemical release and production of contaminated residuals, need to be accounted for in a quantitative comparison of net risk reduc- tion associated with different alternatives, and uncertainty should be quantified to the extent warranted to optimize decision-making. Some potential effects not related to chemical exposures (for example, quality of life impacts and some risks to workers or the community from imple- menting a remedy) will remain difficult to quantify and to compare. However, ignoring these risks in comparisons of remedial alternatives is not the solution and may lead to undesirable consequences. Quantitative assessment and comparison of some of these types of risks will probably never be fully achievable, but they should be identified as risks associ- ated with particular alternatives and considered at least qualitatively when remedial alternatives are being compared and the risks and bene- fits associated with various options are presented to the public.
Summary 13 Third, EPA needs to centralize and coordinate assessment and management of contaminated sediment megasites to ensure greater con- sistency in evaluations, greater technical competence, more active lead- ership at the sites, and an emphasis on what works and why. Several specific responsibilities are discussed in the corresponding recommenda- tion below. Recommendations â¢ An adaptive-management approach is essential to the selection and implementation of remedies at contaminated sediment megasites where there is a high degree of uncertainty about the effectiveness of dredging. â¢ Adaptive approaches based on the use of monitoring data from pilot studies and remedial operations should be used to learn from, test, assess, and modify or improve remedies with the goal of meeting long- term objectives. â¢ EPA should compare the estimated net risk reductions associ- ated with different remedial alternatives, taking into account the real- world limitations of each approach (such as residuals and resuspension) in selecting site remedies. â¢ EPA should centralize resources, responsibility, and authority at the national level to ensure that necessary improvements are made so that contaminated sediment megasites are remediated as effectively as possible. Responsibilities would include â Gathering data to define the scope of the contaminated sediment problem nationally and track likely future contaminated sediment megasites. Defining the scope of the contaminated sediment problem is important for two reasons: this will help place the magnitude of the problem in proper perspective by establishing how much of the problem has been addressed and how much remains, and docu- menting remaining work and associated costs should help EPA and Congress identify the most pressing program and research needs. â Reviewing site studies, remedies, and monitoring approaches at contaminated sediment megasites to assess whether best practices are being implemented, including whether regions are complying with national sedi-
14 Sediment Dredging at Superfund Megasites ment and other program guidance. Because every EPA region has on- the-ground management and remediation experience with dredging at some megasites, regular review and shared experience can inform decision-making and raise the overall level of technical expertise. The goal is to generate a greater understanding of sound remedia- tion principles and best practices and their consistent application among sites. â Ensuring that adaptive-management principles and approaches are applied at contaminated sediment megasites. As described above, a phased, adaptive approach will be required in remedy selection and implementation at large, complex megasites. EPA should ensure that monitoring data are used to support and update forecasts of the ef- fects of remedial measures and to adapt a remedy if remedial goals are not achieved in the expected time frame. â Ensuring adequate pre-remediation and post-remediation monitor- ing and evaluating sediment cleanups in nearly real time to determine whether remedies are having the intended effects. Without adequate pre- dredging and post-dredging monitoring, it is impossible to evaluate the degree to which cleanup has achieved remedial objectives. EPA should invest in better and more consistent measurement tools to monitor conditions in the field reliably and efficiently. EPA should ensure that these techniques are used before and after remediation so that the effectiveness of the projects can be assessed. To facilitate information transfer, a centralized, easily accessible, and up-to-date repository of relevant data and lessons learned regarding sediment remedies should be created. â Developing and implementing a research strategy, including new technologies, for contaminated sediment sites. EPA and its federal part- ners should develop a research and evaluation strategy to under- stand the risk reduction attained by various technologies under vari- ous site conditions and the associated uncertainty. EPAâs efforts should focus on moving forward with remedies at sites while testing and learning with each new pilot test or remedy to determine what works, what does not work, and why. Research to improve and de- velop new remediation technologies, site-characterization tech- niques, and monitoring tools is essential to advance sediment reme- diation and should be supported.
Summary 15 Many of the sites are vast and expensive, and it is worthwhile to invest time and resources now to ensure more cost-effective remedies in the future. That focus is warranted if the country is to make the best use of the billions of dollars yet to be spent on remediation.