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Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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3
Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation

A wide variety of metrics can be used to evaluate the effectiveness of environmental-dredging projects in reducing risks to human health and the environment. The committee reviewed a number of them and developed a framework to facilitate the evaluation of the effectiveness of environmental-dredging projects at contaminated sediment sites. The framework is based on the effectiveness criteria used by the U.S. Environmental Protection Agency (EPA) Superfund program to select remedies (40 CFR § 300.430[e][7][i]).

In conducting its evaluation, the committee defined dredging effectiveness as the achievement of cleanup goals defined for each site, which take the form of remedial-action objectives, remediation goals, and cleanup levels.¹ For CERCLA remedial actions, these goals are typically

¹

Remedial-action objectives “are intended to provide a general description of what remediation is expected to accomplish” (EPA 2005a, p. 2-15). For example, a remedial-action objective might be to reduce to acceptable levels the risks to people who ingest contaminated fish. Remediation goals are paired contaminant-specific and media-specific concentrations intended to protect human and ecologic health that incorporate site-specific information about exposure patterns and toxicity. “At most CERCLA [Comprehensive Environmental Response, Compensation, and Liability Act] sites, [remediation goals] for human health and ecologic

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Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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documented in the record of decision (ROD). However, this definition is appropriate for evaluating the effectiveness of the project in reducing risk only when cleanup goals are derived from sound, site-specific risk modeling.

An ideal evaluation of effectiveness at Superfund sites would be based on the site conceptual model, data from a baseline assessment, and a long-term monitoring program that permits sound statistical comparison of the spatial scale of contamination and the magnitude of risk before, during, and after dredging. At the outset of its work, the committee hoped to obtain that kind of information for a number of large contaminated sediment sites to inform its deliberations. However, we found that such careful and prolonged monitoring either has not been conducted, has not been completed at large-contaminated sediment sites, or simply was not available to the committee. (The committee noted that some sites where remediation had not yet occurred or been completed have electronic databases and long-term monitoring plans that would facilitate future attempts to evaluate remedy effectiveness, for example, Hudson River and New Bedford Harbor). In some cases, it is recognized that additional information, for example, raw data and consulting reports, may have been held by responsible parties, federal agencies, or their consultants. However, this information may not have been available in the public domain or to the committee, or the committee’s time and resource constraints precluded a thorough compilation, analysis, and interpretation (see further discussion in Chapter 4). In some cases a review of all site data was not necessary to determine whether cleanup goals had been met. This chapter details the committee’s process for evaluating the effectiveness of environmental dredging within the constraints imposed by the available data. The framework for this review is outlined in Box 3-1.

receptors are developed into final, chemical-specific, sediment cleanup levels by weighing a number of factors, including site-specific uncertainty factors and the criteria for remedy selection found in the NCP [National Contingency Plan]” (EPA 2005a, p. 2-16). The ROD for each site generally should include chemical-specific cleanup levels, indicating how these values are related to risk and how their attainment will be measured (EPA 2005a).

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Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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BOX 3-1

Framework for Evaluating the Effectiveness of Environmental Dredging Projects

Identify Superfund megasites and other large environmental-dredging projects.
Define criteria for selecting projects for committee evaluation from the list of environmental-dredging projects.
Select projects that represent a variety of site conditions.
Evaluate each project with respect to measures of short-term and long-term effectiveness.
Make recommendations for improved design, implementation, and monitoring of future environmental-dredging projects.

SOURCES OF INFORMATION ABOUT ENVIRONMENTAL-DREDGING PROJECTS

The statement of task (see Appendix A) indicates that the sources of information “would include megasites for which dredging has been completed; megasites for which plans have been developed, partially implemented, and operations are ongoing; and smaller sites that exhibit lessons relevant to megasites.” The committee’s evaluation focused on environmental-dredging projects at Superfund megasites, but, because remediation has not been completed at many of these sites, the committee also reviewed other environmental-dredging projects on which data relevant to the committee’s charge were available.

As described in Chapter 2, numerous environmental-dredging projects have been conducted, and many other contaminated sediment sites will require decision-making soon. At the first committee meeting, EPA outlined sites from its database of tier 1 sediment sites where dredging had been completed. From those dredging sites, EPA provided the committee with a list of sites on which there were pre-remediation and post-remediation monitoring data. To identify other dredging projects for possible evaluation, the committee reviewed information from additional government, industry, and private consulting sources that summarize remedial activities at contaminated sediment sites (see Box 3-2). Collectively, those dredging project compilations and reviews

Page 73 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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BOX 3-2

Compilations and Reviews of Sediment Remediation Projects

EPA’s Great Lakes National Program Office summarized (EPA 1998) and updated (EPA 2000) information on contaminated sediment sites in the Great Lakes Basin that had been remediated with a variety of techniques. The reports provide some details about remedies but few details on post-remedial monitoring or on whether remediation achieved expected benefits. In 1999, the Great Lakes Water Quality Board summarized 20 sediment remediation projects in the Great Lakes areas of concern (Zarull et al. 1999). The report stated that of the projects implemented so far, only two (Waukegan Harbor, IL and Black River, OH) had adequate data on long-term ecologic health. The Great Lakes binational strategy progress reports (e.g., EPA and Environment Canada 2005) provide annual updates summarizing sediment remediation activities at Great Lakes sites in the United States and Canada. The Major Contaminated Sediment Sites (MCSS) Database (GE et al. 2004) is the largest compendium of information on such sites. It contains information on 123 major projects representing 103 sites. EPA maintains, although not publicly, a database on the 60 tier 1 sediment sites where remedies include dredging or excavation of at least 10,000 cy or capping or monitored natural recovery of at least 5 acres (EPA 2005a).

Before this committee’s deliberations, several other groups reviewed data on completed projects to examine whether remediation had been successful and to draw conclusions about the likely effects of dredging at other sites in the future. The General Electric Company (GE 2000) evaluated sediment remediation case studies involving 25 sites (including sites that used removal techniques other than dredging) and attempted to determine whether data indicated the ability to reduce risks to human health and the environment. Its report concluded that the success of the projects had not been demonstrated and that technical limitations restricted the effectiveness of dredging in reducing surface sediment-contaminant concentrations. Cleland (2000) updated an earlier report prepared by Scenic Hudson (2000) and outlined experience at 15 sediment remediation sites, including many evaluated by GE (2000). Cleland presented sediment and biota concentration data and concluded that post-dredging monitoring data consistently show beneficial results, including reductions in contaminant mass and in concentrations in sediment and fish. Many of the same case studies were also reviewed by EPA (Hahnenberg 1999), and EPA presented the results of its analysis to the National Research Council’s Committee on Remediation of PCB-Contaminated Sediments (NRC 2001). EPA’s analysis indicated that dredging resulted in reduced sediment and fish-tissue concentrations. An alternative analysis was also provided to that National Research Council committee by the

Page 74 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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Fox River Group (1999, Appendix C in GE 2000), which refuted the connection between remedial actions and fish-tissue concentration declines on the basis of a paucity of data and flawed method in EPA’s linking of remediation to observed changes. During its deliberations, the previous National Research Council committee (NRC 2001) reviewed the documents produced by GE (2000), Scenic Hudson (2000), EPA (Hahnenberg 1999; Pastor 1999), and the Fox River Group (1999) to ascertain how groups reviewing the same documents could come to such disparate conclusions. It concluded: “First, in some instances, there is disagreement about the remediation goals and the measures by which achievement of the goals can be assessed. Second, in some cases, the available post-remediation monitoring data are sparse and incomplete compared with pre-remediation data and control data. Third, in some cases, it is the intention of reviewers, agencies, and industries to support their preferences, and that might lead to more conflict.”

Since the previous committee issued its report (2001), additional groups have sought to analyze the link between sediment remediation and reduced risk. Baker et al. (2001) sought to address the question “Can active remediation be implemented in such a way that it provides a net benefit to the Hudson River?” and commented on the biologic effects of sediment remediation at five sites. Thibodeaux and Duckworth (2001) evaluated measurements of environmental-dredging effectiveness in detail at three sites. Malcolm Pirnie (Malcolm Pirnie and TAMS Consultants, Inc. 2004), in an appendix to the engineering performance standards developed for the Hudson River Superfund site, briefly reviewed data on 25 remediation projects (some had not initiated remediation) and provided information on monitoring and remediation results. As part of its feasibility study for the Kalamazoo River in Michigan, BBL (2000) compiled profiles of 20 environmental-dredging projects conducted nationwide and discussed their ability to meet project-specific objectives and their overall effectiveness. Several of those profiles were presented in an earlier analysis (GE 2000). In addition, the Great Lakes Dredging Team, a partnership of federal and state agencies, provided a series of dredging project case studies (Great Lakes Dredging Team 2006). The U.S. Army Corps of Engineers Center for Contaminated Sediments also provided information on a series of environmental-dredging projects (USACE 2006).

were extremely useful in forming the short list of dredging projects on which pre-dredging and post-dredging monitoring data were likely to be suitable for evaluation.

Page 75 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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CRITERIA USED TO SELECT ENVIRONMENTAL-DREDGING PROJECTS FOR EFFECTIVENESS EVALUATION

The committee used the criteria listed in Box 3-3 to select environmental-dredging projects for evaluation. Therefore, the committee preferred projects that involved only dredging but did not limit its analysis to them. The committee did not select projects that involved dry excavation, because they are conducted under different conditions from conventional dredging. Pilot studies, although limited in scope and purpose, were also considered because they are often heavily monitored with substantial information regarding the effect of dredging under specified conditions.

The committee preferred projects with removal of at least 10,000 cy of sediment because of their similarity to megasites with respect to the spatial scale of ecologic and human health exposures. Some smaller pilot studies designed to inform decisions on larger sites were also included. This size threshold matches the threshold used by EPA to define tier 1 sediment sites (EPA 2005a).

Any evaluation of dredging effectiveness depends on sufficient high-quality pre-dredging and post-dredging monitoring data. Therefore, another criterion used by the committee to select dredging projects was whether they had pre-dredging and post-dredging monitoring data.

Environmental-dredging projects occur in a wide variety of aquatic environments, such as rivers, estuaries, bays, lakes, ponds, canals, and wetlands; and the effectiveness of dredging can be influenced by many

BOX 3-3

Criteria Used to Select Environmental-Dredging Projects for Evaluation

The remedy consists of dredging only or a combined remedy that includes dredging.
The remedy preferably includes removal of at least 10,000 yds³ of sediment.
The project has some amount of pre-dredging and post-dredging data.
The projects collectively represent a wide variety of project types (for example, environmental settings, chemicals of concern, and dredging design and implementation).

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Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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site-specific factors. Therefore, the committee endeavored to conduct a broad review of projects that represented a variety of site-specific conditions, including the type of water body, the form of chemical contamination, and the type of dredging technology.

SELECTION OF ENVIRONMENTAL-DREDGING PROJECTS

The committee chose the 26 dredging projects listed in Table 3-1 for detailed evaluation (see Figure 3-1 for the location of the projects). Selected projects involved remedies with dredging only or dredging combined with backfilling or capping. Chemicals of concern included polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides, and metals detected in sediments in a variety of aquatic environments across the United States and one in Sweden. PCBs were the primary chemicals of concern in 19 of the 26 projects. Table 3-1 contains general information on the site and the remedy; further detail on several of the sites is provided in Chapter 4 and the associated references. In addition, summaries of many of these sites and their remediation have been compiled elsewhere (e.g., GE 2004; Malcolm Pirnie, Inc. and TAMS Consultants, Inc. 2004).

The selected projects include all 12 sites (although not all the operable units at each site) on which there were pre-dredging and post-dredging data as reported by EPA at the first committee meeting (Ells 2006). The committee also chose three demonstration projects (two in the Lower Fox River, WI, and one in the Grasse River, NY) and one state-lead site (Cumberland Bay, NY) recommended for review by the Sediment Management Work Group during the committee’s second meeting (Nadeau 2006).

Scenic Hudson (Cleland 2000), an advocacy group that promotes cleanup of the Hudson River in New York, also included those demonstration projects and Cumberland Bay in its review of dredging effectiveness. In addition, Scenic Hudson identified Lake Jarnsjon in Sweden and the Black River, OH, as examples of successful dredging operations (as did Green and Savitz [unpublished] and Zarull et al. 1999), and the committee selected these two sites for evaluation. During the committee’s second meeting, remediation consultants presented results of two recently completed large-scale dredging operations: in the Lower Fox

Page 77 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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TABLE 3-1 Summary of 26 Environmental-Dredging Projects Selected for Evaluation^a

Project	Primary Chemicals of Concern	Water- Body Type	Remedy Type	Scale of Effort	Dates of Dredging	Volume of Dredged Sediment (cy)
Bayou Bonfouca, LA	PAHs	Bayou	Dredging followed by backfilling	Full-scale	1994-1995	170,000
Lavaca Bay, TX	Hg	Estuary	Dredging	Pilot	1998	80,000
Black River, OH	PAHs	River	Dredging	Full-scale	1989-1990	45,000-60,000
Outboard Marine Corp., Waukegan Harbor, IL	PCBs	Harbor	Dredging	Full-scale	1991-1992	38,000
Commencement Bay–Head of Hylebos, Tacoma, WA	PCBs, As, PAHs	Estuary	Dredging	Full-scale	2003-2006^b	419,000^c
Commencement Bay–Sitcum, Tacoma, WA	As, Cu	Estuary	Dredging	Full-scale	1993-1994	428,000^d
Duwamish Diagonal, Seattle, WA	PCBs	Tidally influenced river	Dredging followed by capping	Full-scale	2003-2004	66,000

Page 78 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

Project	Primary Chemicals of Concern	Water- Body Type	Remedy Type	Scale of Effort	Dates of Dredging	Volume of Dredged Sediment (cy)
Puget Sound Naval Shipyard, Bremerton, WA	PCBs	Estuary	Dredging	Full-scale	2000-2004	225,000^e
Harbor Island–Lockheed, Seattle, WA	PCBs, PAHs, Hg, Pb, As, Cu, Zn, tributyltin	Estuary	Dredging in open-water area, dredging and capping in nearshore area	Full-scale	2003-2004^f	70,000
Harbor Island–Todd, Seattle, WA	As, Pb, Zn, Cu, PAHs, PCBs, tributyltin, Hg	Estuary	Dredging, capping, and habitat restoration in selected areas	Full-scale	2004-2005	220,000
Cumberland Bay, NY	PCBs	Inland lake	Dredging	Full-scale	1999-2000	195,000
Dupont, Christina River, DE	Zn, Pb, Cd	River	Dredging and backfilling	Full-scale	1999	11,000
Lower Fox River (OU-1), WI	PCBs	River	Dredging	Full-scale	2004-present	Incomplete
Lower Fox River (Deposit N), WI	PCBs	River	Dredging	Pilot	1998-1999	8,200

Page 79 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

Lower Fox River (SMU 56/57), WI	PCBs	River	Dredging and backfilling	Pilot	1999-2000	82,000
Ketchikan Pulp Company, Ward Cove, AK	4-methyl phenol; ammonia	Fjord	Dredging and backfilling (thin-layer)	Full-scale	2000-2001	8,700
Newport Naval Complex–McCallister Landfill, RI	PAHs, PCBs	Bay	Dredging and backfilling	Full-scale	2001	34,000
GM Central Foundry, St. Lawrence River, NY	PCBs	River	Dredging (backfilling in one area)	Full-scale	1995	14,000
Grasse River, NY (non-time-critical removal action)	PCBs	River	Dredging	Pilot	1995	3,000
Grasse River, NY remedial options pilot study (ROPS)	PCBs	River	Dredging and backfilling	Pilot	2005	30,000
Lake Jarnsjon, Sweden	PCBs	Lake	Dredging	Full-scale	1993-1994	196,000^g

Page 80 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

Project	Primary Chemicals of Concern	Water- Body Type	Remedy Type	Scale of Effort	Dates of Dredging	Volume of Dredged Sediment (cy)
Manistique Harbor, MI	PCBs	Harbor	Dredging	Full-scale	1995-2000	190,000^h
Reynolds Metals, St. Lawrence River, NY	PCBs, PAHs, total dibenzofuran	River	Dredging (backfilling in one area)	Full-scale	2001	86,000
Marathon Battery, Hudson River, Cold Spring, NY	Cd	River	Dredging	Full-scale	1993-1995	71,000
New Bedford Harbor, MA (hot spot)	PCBs	Estuary	Dredging	Full-scale (hot spot removal)	1994-1995	14,000
United Heckathorn, Richmond, CA	DDT, dieldrin	Estuarine channel	Dredging and backfilling	Full-scale	1996-1997	110,000
^aIn the review and collection of data on dredging sites it was determined that various sources will often provide inconsistent information. For example, the committee found several different estimates for the volume of sediment removed from the Black River: 49,700 cy (Zarull et al. 1999; Cleland et al. 2000); 45,000 cy (Malcolm Pirnie and TAMS Consultants, Inc. 2004); 50,000 cy (EPA 2000); 60,000 cy (GE 2000; GE 2004; Fox R. Group 1999). ^bFrom Dalton, Olmsted & Fuglevand, Inc. 2006.

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Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

^c15,000 cy removed with upland-based equipment and 404,000 removed with marine-based equipment.

^dFrom EPA summary (EPA 2006 [Commencement Bay–Sitcum Waterway, April 26, 2006]): “Approximately 396,000 cy of sediment were dredged from Area A using hydraulic and clamshell dredges and approximately 32,300 cy were removed from Area B using a small hydraulic dredge.”

^eFrom EPA summary (EPA 2006 [Puget Sound Naval Shipyard, May 15, 2006]).

^fFrom EPA summary (EPA 2006 [Harbor Island Lockheed Shipyard Sediment Operable Unit, May 11, 2006]): “Remediation dates: These dates refer to dredging activities, not other remedial activities such as capping. November 22, 2003 to March 10, 2004 and from October 22, 2004 to November 22, 2004.”

^gBremle et al. 1998.

^hEPA 2006 (Manistique River and Harbor Site, May 10, 2006).

Sources: Data are also unpublished data from EPA, NAS Completed Dredging Summary, March 22, 2006; Malcolm Pirnie, Inc., and TAMS Consultants, Inc. 2004.

Page 82 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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FIGURE 3-1 Locations of environmental-dredging projects selected for evaluation. Several locations comprise more than one site, including Commencement Bay, Grasse River, Lower Fox River, and Harbor Island.

River Operable Unit 1 and the Grasse River Remedial Options Pilot Study (Connolly et al. 2006; Fox et al. 2006). Those two projects were selected for evaluation because extensive monitoring data on them were made available to the committee. The committee selected a pilot dredging study in Lavaca Bay, TX, and a hot spot removal in New Bedford Harbor, MA, because they were the subject of extensive monitoring efforts. The Reynolds Metals Superfund site in the St. Lawrence River was selected because it has undergone monitoring for several years after initial dredging (EPA 2005b).

Of the 26 dredging projects, five have been identified by EPA as contaminated sediment megasites, that is, sites where the dredging portion of the remedy will cost at least $50 million (see “Sediment Contamination at Superfund Sites” in Chapter 2).

Page 83 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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APPROACH TO EVALUATING DREDGING PROJECTS

The committee evaluated the effectiveness of the 26 dredging projects, where data permitted such an evaluation, by determining whether cleanup levels and remedial action objectives were achieved. The committee used lessons learned from the projects to identify means for improving future decisions about remediation at Superfund megasites. The lessons learned involved:

Factors that contributed to the success of dredging operations.
Factors that adversely affected dredging operations.
Methods for improving the monitoring of dredging effectiveness.

The committee did not attempt to substitute its own judgment about what remedial action objectives and cleanup levels should be, including the site-specific risk modeling on which they were based, but simply tried to determine whether the stated goals were achieved and why or why not. The committee chose to review sites where dredging was the only remedy (or at least the main remedy) to evaluate the effectiveness of only dredging. However, the committee acknowledges that the effects of dredging may be difficult or impossible to distinguish from other ongoing processes including additional source control and natural recovery.

The committee recognizes the importance of quantifying the net risk reduction associated with dredging, which involves consideration of possible increases in risk to the spectrum of human and environmental receptors that might be caused by dredging and the treatment, storage, transport, and disposal of dredged sediment as well as risk reduction from removal of contaminated sediments from aquatic systems. The need for considering net risk reduction and incorporating the analysis into decision-making at Superfund sites has been noted in previous National Research Council reports (NRC 2001; NRC 2005), recognized by EPA (EPA 2005a), and examined in the scientific literature (Wenning et al. 2006). However, such analysis was not possible in this case. It was difficult (in some cases impossible) to obtain requisite data on the dredging component of each project, much less some of the other measures relevant to a net risk reduction analysis (for example, number of acci-

Page 84 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

dents during transportation of dredged material) that are often not compiled. These limitations combined with time and resource constraints prevented the committee from conducting net risk reduction evaluations for each dredging project. As a result, the committee chose to focus its time and resources on the dredging component of projects rather than treatment, storage, transport, and disposal.

Methods Used to Evaluate Dredging Projects

Each project review began with the identification of the remedial action objectives and cleanup levels for the project. That was followed by review of project data to judge whether the remedial action objectives and cleanup levels had been met. Those data could include chemical concentrations in sediment, surface water, the biota, and other environmental media; indicators of exposure (such as bioaccumulation testing and human biomonitoring data); and measures of risk (such as toxicity testing). The measures have inherent natural heterogeneity and are subject to uncertainty. When, despite the variability and uncertainty, sufficient data were available to compare pre-dredging and post-dredging conditions, the committee attempted to answer the effectiveness questions listed in Box 3-4. Ideally, the evaluation should be performed in the context of a comparison of all available remedial alternatives (EPA 2005a; Bridges et al. 2006), but the committee reviewed only dredging projects in accordance with the statement of task.

Cleanup levels and remedial action objectives are not always risk-based, and some projects have no cleanup levels or other quantitative means to judge effectiveness at all. Therefore, the committee looked beyond remedial action objectives and cleanup levels to identify dredging successes and failures in reducing exposure or risk, as well as the site, the remedy, or the contaminant conditions that led to the successes and failures. In its evaluation of project data, the committee distinguished between changes in environmental-media concentration, exposure, and risk.

The committee evaluated whether baseline assessment data were available to define conditions before dredging for comparison with monitoring data collected during and after dredging. Optimally, those

Page 85 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

×

BOX 3-4

Measures of Sediment-Remedy Effectiveness in the Superfund Program

Dredging effectiveness is the achievement of cleanup goals (remedial action objectives and cleanup levels that are derived from appropriate site-specific risk modeling) in the predicted time frame with a reasonable degree of confidence that the achievement will be maintained.

Interim Measures

Short-term remedy performance. For example, have sediment cleanup levels been achieved after dredging?
Long-term remedy performance. For example, have sediment cleanup levels been maintained for at least 5 years, and thereafter as appropriate?
Short-term risk reduction. For example, have remedial action objectives been achieved? Do data demonstrate or at least suggest a reduction in fish tissue concentrations, a decrease in benthic toxicity, or an increase in species diversity or other community indexes after 5 years?

Key Measure

Long-term risk reduction. For example, have remedial action objectives been maintained for at least 5 years, and thereafter as appropriate?
Has the predicted magnitude and timing of risk reduction been achieved or are they likely to be achieved?

Source: Adapted from EPA 2005a.

assessment data would suffice to quantify exposures and risks and allow comparison with during-dredging and post-dredging monitoring data. Human and ecologic exposure and risk might increase during dredging, and these increases should also be weighed against exposure and risk reductions following dredging. Monitoring data and information collected during dredging were reviewed to identify changes in human and ecologic exposure and risk that occurred during this period. Dredging of contaminated sediment disrupts the bottom substrate, thereby destroying the existing benthic community, and can increase exposure of humans and the biota, depending on the degree of resuspension, residual generation, and release of sediment-bound, dissolved, or airborne con-

Page 86 Cite

Suggested Citation:"3 Effectiveness of Environmental Dredging in Reducing Risk: Framework for Evaluation." National Research Council. 2007. Sediment Dredging at Superfund Megasites: Assessing the Effectiveness. Washington, DC: The National Academies Press. doi: 10.17226/11968.

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tamination. The committee also reviewed monitoring data and information collected after dredging to identify changes in human and ecologic exposure and risk that resulted from dredging and to evaluate whether the changes should be expected to be maintained despite extreme weather conditions and human activities.

The committee used lessons learned from individual dredging project evaluations to inform its deliberations about how to improve future remediation decisions at Superfund megasites. Specifically, the committee sought to define site conditions and project design implementation factors that affect dredging success and to use this information in recommending improved management and monitoring to facilitate scientifically based and timely decision-making.

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BBL (Blasland, Bouck & Lee, Inc). 2000. Allied Paper, Inc./Portage Creek/Kalamazoo River Superfund Site RI/FS Feasibility Study Report—Phase I Allied Paper, Inc., Appendix D. Site Profiles of Sediment Dredging Projects. Draft for State and Federal Review. October 2000 [online]. Available: http://www.deq.state.mi.us/documents/deq-erd-kzoo-FS-apend-d.pdf [accessed Jan. 8, 2006].

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