A Risk-Management Strategy for PCB-Contaminated Sediments (2001) / Chapter Skim
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Assessing Management Options
Assessing Management Options
Pages 189-241
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From page 189... ...
at the least cost and with the most benefit to the environment and the community. The identification and selection of a risk-management strategy and its component management options should be based on a range of considerations, including effectiveness, permanence, implementability, risks associated with implementation, costs, and state and community acceptance.
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From page 190... ...
The primary purpose _ ~11 _ 1 , . .~ - .~ Assessing Options · Identifying Options · Analyzing Options for —Benefits Effectiveness Costs Feasibility Adverse Consequences or this chapter Is to outline the process of identifying and evaluating contaminated-sediment management options and identify the characteristics of specific technologies that influence their selection at a particular site.
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From page 191... ...
The application of ex situ treatment or disposal of sediments, for example, typically introduces a complete train of technologies, including removal by dredging, temporary storage or pretreatment to reduce water content or volume, final dredged material treatment or disposal, and management of any residually contaminated materi'Treatment Technologies for Site Cleanup: Annual Status Report, 9th Ed.
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From page 192... ...
Generally, large contaminated-sediment sites also require the application of different options at different portions ofthe site, each containing multiple technologies. The identification of sediment management options must recognize the entire train of technologies that constitute each option so that a fair evaluation and comparison of these options can be accomplished.
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From page 193... ...
The evaluation of sediment management options must take into account the entire train of technologies that constitute an option and the costs and potential risks throughout the life cycle of the options. Evaluation, screening, and ultimately, selection of an option depends on recognition of the full environmental, human, social, and economic costs of implementing that option.
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From page 194... ...
The primary goal of contaminated-sediment management is the protection of resources at risk, such as human or ecological health, commercial or recreational fishing stocks, or a particular endangered species. Ultimately, it would be preferable to choose management options that best protect affected resources or lead to their recovery.
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From page 195... ...
Component Technologies of Sediment Management Options A wide variety of management options exist for addressing contaminatedsediment problems. Socioeconomic options might provide offsets that improve human or ecological health or quality of life.
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From page 196... ...
The application of ex situ treatment or disposal typically introduces a complete train of component technologies, including removal by dredging, temporary storage or pretreatment to reduce water content or volume, final dredged material treatment or disposal, and management of any residually contaminated materials, including air and water waste streams. All of these options pose varying degrees of effectiveness for any particular PCB-contaminated site.
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From page 197... ...
There are several general categories of institutional controls: government controls; informational devices; proprietary controls; and enforcement tools with institutional control components. Institutional controls involving PCBcontaminated sediments often take the form of government controls, such as fishing bans or fishing catch-and-release requirements, or informational devices, such as fishing advisories.
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From page 198... ...
. Institutional controls involving PCB-contaminated sediments may also take the form of legal restrictions on the use of aquatic or adjacent upland property (proprietary controls)
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From page 199... ...
. In summary, institutional controls "may be advisable when sediment contamination poses an imminent danger and immediate risk reduction is required" (NRC 19971.
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From page 200... ...
If a significant external source is not identified or is allowed to persist, then efforts to reduce risk through other management options might not be successful. Controlling on-going sources is consistent with the EPA contaminated sediment management strategy (EPA
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From page 201... ...
Tn such a situation, continuous monitoring and periodic remediation ofthe contaminated sediments mightbe alternative management options. Tn any event, no "walk-away" solution is possible without adequate source control.
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From page 202... ...
It is clear, however, that this source was and continues to be sufficiently significant that it must be included in the assessment and evaluation of the potential effectiveness of management options for the river. The continuing source might have gone largely unnoticed without the gate failure, but seepage from the bedrock could have posed a long-term source that would have at least slowed any natural attenuation of the system and could have substantially reduced the effectiveness of any management option undertaken prior to its identification.
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From page 203... ...
The question then is not whether natural attenuation should be considered a part of a risk management strategy, but how much should it be relied upon for reduction of risk to humans and the environment, and how can this risk reduction be measured? (See Chapter 4 for a discussion of community concerns regarding natural attenuation.)
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From page 204... ...
A similar decrease in PCB discharges from the upstream reaches of the Tower Fox River in Wisconsin is discussed in Box 7-3. Natural Attenuation by Biodegradation Of the natural-attenuation processes, biodegradation is generally considered the most desirable because it can result in elimination of risk.
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From page 205... ...
If natural attenuation is included as part of the management strategy, continued long-term monitoring should provide the time-series data needed to validate and calibrate the model and improve its predictions. During the early l990s, the Wisconsin Department of Natural Resources sponsored the development of such a model for the upstream reaches of the lower Fox River (WDNR 1995~.
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From page 206... ...
The particular processes involved in change in PCB mass must be clearly understood by site risk assessors to draw valid conclusions about risk reduction. Natural Attenuation by Sedimentation One of the most important natural-attenuation processes affecting risk reduction of PCB-contaminated sediments is sedimentation itself.
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From page 207... ...
Whether natural-attenuation processes can be viewed as natural recovery depends on whether risk-management goals are met and maintained over the long term. That is, natural recovery depends on the ability of attenuation processes to maintain risk reduction to humans and ecological health over an extended time and not necessarily on the reduction of concentration levels in the contaminated sediments.
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From page 208... ...
In summary, it is clear that some natural-attenuation processes, notably burial in a stable system, can reduce risk, and others, such as bed erosion, dilution, dispersion, and volatilization, may simply transport the risk elsewhere. Because different natural-attenuation processes have such different impacts on risk management, it is not sufficient to quantify natural attenuation without adequate characterization of the particular processes involved at a given site.
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From page 209... ...
Similarly, in situ containment by capping with clean sediments has been proposed as a sediment management option. The extremely slow transport processes of diffusion or advection in the region below the biologically active zone provide effective containment of sorbing contaminants, such as PCBs (e.g., Palermo et al.
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From page 210... ...
Due to the potential for contaminant losses during removal and subsequent placement, capping dredged material is generally only considered for the management of marginally contaminated sediments in regions where navigation needs necessitate sediment removal. Capping contaminated sediment is usually implemented by either Thin-layer capping, also referred to as enhanced natural attenuation.
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From page 211... ...
Thick-layer capping is the conventional approach to containment of contaminated sediments. Cap thicknesses are normally 20 cm to as much as ~ m.
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From page 212... ...
Guidance exists for the design, placement and monitoring of a cap as a sediment management option (Palermo et al.
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From page 213... ...
Isolation of the contaminated sediments by capping with clean sediments from the Puyallup River. · Habitat restoration and enhancement of near-shore and intertidal areas.
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From page 214... ...
Solutions to this problem include hydraulic control of groundwater (e.g., a slurry wall or trench system to divert water around the contaminated sediments) or control of the permeability of the capping layer to minimize
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From page 215... ...
Sediment management options that include beneficial outcomes exhibit many advantages and are often more acceptable to the community than those that are viewed strictly as remediation efforts. Capping with clean sediments, with proper design and implementation, is a widely used and highly effective means of ensuring isolation of contaminated sediments in areas for which the resulting reduction in water depth is acceptable or desired.
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From page 216... ...
This discussion of removal options will consider the applicable component technologies separately: · Sediment removal via mechanical or hydraulic dredging. · Dredged material pretreatment technologies, including dewatering and particle-size separation.
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From page 218... ...
that are predominantly mechanical in action but also withdraw water to control migration of a resuspension plume. The selection of a particular dredging technology, or the risks associated with dredging relative to other management options, is dependent upon site-specific factors, and no general guidance can be provided.
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From page 219... ...
. ram size Sediment cohesion Organic matter content Sediment density Volatiles concentration Type of dredge Dredge production rate Condition of equipment Equipment reliability Operating precision of equipment Sediment loss during operations Training and skill of operators Water depth Morphology of shoreline Flows and suspended solids Waves, tides, and currents Hydraulic effects of dredging operations Temperature Salinity Density Source: St.
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From page 220... ...
220 A Risk-Management Strategy for PCB-Contaminated Sediments
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From page 221... ...
Containment of sediments resuspended by dredging operations was originally attempted with silt curtains, but high flows in the river forced the placement of sheet piling to separate the dredging area from the river flow. The contaminated sediments were underlain with dense glacial till, which made it impossible to use overdredging to increase sediment removal efficiency.
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From page 222... ...
Because at least short-term exposure and risk is related to surficial sediment concentrations within the biologically active zone, mass removal itself might not achieve risk-management goals. Although the contaminated-sediment management strategy (EPA ~ 998)
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From page 223... ...
At high suspended-sediment concentrations within the silt curtain, the dissolved PCB concentrations would approach those found in the pore water of the sediment. The effectiveness of a silt curtain and other means of controlling contaminant releases during dredging and shore operations are illustrated in Box 7-7, which describes a hot-spot dredging operation in the Grasse River, New York.
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From page 224... ...
Less than 0.0045 kg of PCBs were returned to the Grasse River following treatment by the activated carbon treatment system. However, significant savings in water treatment costs would have been obtained if untreated water were returned to the area within the silt curtains.
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From page 225... ...
This approach has important advantages with respect to control of resuspension and minimization of residual contamination. Through this approach, the degree of control afforded land excavation can be applied to contaminated sediments.
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From page 226... ...
Multiple dre(lging passes may be required to achieve desired sediment and contaminant recoveries even under ideal conditions. Pretreatment Technologies Dredged material removed from a contaminated-sediment site normally requires pretreatment prior to ultimate treatment or disposal.
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From page 227... ...
Even when pumping hydraulically dredged material as a slurry through a pipeline, wide variations in production rate result because of sediment heterogeneity and the presence of debris. Subsequent treatment or disposal steps often cannot maintain effectiveness if the feed rate is widely variable, and so a temporary storage system is normally required to serve as a basin for watering and volume equalization.
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From page 228... ...
In a confined disposal facility, the ultimate disposal is typically at the same facility in which primary dewatering has taken place. In an upland landfill, the partially dewatered dredged material may be further dewaterea, for example, via filtering, and then transported for ultimate disposal.
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From page 229... ...
Nonthermal destruction technologies, such as biodegradation, are generally not suitable for PCBs because of slow or limited biological-degradation rates, as discussed previously in the section on natural attenuation. Soil-washing technologies serve to reduce contaminant levels by partial removal of fine-graineU particles and organic material that contain the majority of the contaminants.
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From page 230... ...
Saginaw River: Washing of Saginaw River, Michigan, sediments using a system designed by Bergman USA was demonstrated by the EPA Assessment and Remediation of Contaminated Sediments (ARCS) and Superfund Innovative Technology Evaluation (SITE)
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From page 231... ...
Both processes illustrate a key feature of extractive technologies: the products and residuals require further treatment or disposal. Stabilization technologies involve introduction of adclitives to the dredged material to prevent mobility of contaminants, providing a more secure material for disposal, or a reusable product, such as flowable or solid fill for construction.
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From page 232... ...
Waukegon, Illinois: High-temperature (up to 1207 OF) thermal desorption was used for the full-scale remediation of the Outboard Marine Corporation site in Waukegan, Illinois, during 1992 (EPA 1995~.
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From page 233... ...
are achieved in the plasma torch, causing vaporization and degradation of organic materials in the dredged material. The final product is of high quality and essentially contaminant free.
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From page 234... ...
The contaminant Tosses, treatment and disposal of the residuals, and the risks involved need to be considered when identifying, evaluating, and selecting sediment management options. Inadequate consideration of such problems can give rise to inaccurate and misleading comparisons between removal and nonremoval sediment management options.
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From page 235... ...
Seven broad rules govern the analysis of management options: T All sites require a conceptual model of the system, and the interaction of the management options with the sediments and contaminants IS reqUlreC ..
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From page 236... ...
5. Natural attenuation is a component of all contaminated-sediment management options.
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From page 237... ...
A third particular area of uncertainty is the assessment of the financial costs of a management alternative. Part of this uncertainty is due to the inability to adequately describe site conditions that influence the effectiveness and cost of management options.
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From page 238... ...
1998. EPA's Contaminated Sediment Management Strategy.
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From page 239... ...
1978. Development and Application of Design and Operation Procedures for Coagulation of Dredged Material Slurry and Containment Area Effluent.
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From page 240... ...
1988. Long-Term Sand Cap Stability: New York Dredged Material Disposal Site.
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From page 241... ...
1995. Modeling air emissions from contaminated sediment dredged materials.
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