Contaminated Sediments in Ports and Waterways Cleanup Strategies and Technologies (1997) / Chapter Skim
Currently Skimming:
5 Interim and Long-Term Technologies and Controls
5 Interim and Long-Term Technologies and Controls
Pages 80-153
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From page 80... ...
needs for both interim controls, which can be used to reduce high-risk levels quickly, and engineered technologies for longer term, more complete remediation. Costs, which often dictate the selection of technologies, are examined as well.
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The 1987 Amendments to the CWA authorized the EPA, in conjunction with other federal agencies, to conduct a five-year study of treatment processes for toxic pollutants in Great Lakes sediments. The resulting assessment and remediation of contaminated sediments (ARCS)
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The first section examines interim controls, including administrative and technology-based measures, which may be used to reduce imminent hazards. The second major section deals with in situ management, including natural recovery processes that reduce contaminant bioavailability through either destruction or isolation; in-place contaminant isolation by capping; and active treatment through thermal, chemical, or biological processes.
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INTERIM AND LONG-TERM TECHNOLOGIES AND CONTROLS FIGURE 5-1 Process of defining a remediation system. Note: See Box 5-2 for details.
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The use of remediation technologies and controls in the management of contaminated marine sediments is still emerging. For the most part, the field has been dominated by tools developed for navigation dredging, and few full-scale treatment systems have been implemented.
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INTERIM AND LONG-TERM TECHNOLOGIES AND CONTROLS 85 FIGURE 5-2 Remediation technologies subsystem structure.
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. INTERIM CONTROLS A previous report by the NRC (1989)
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Interim controls include a broad spectrum of administrative and technology-based approaches based principally on isolation or avoidance techniques. Controls considered by the committee range from issuing public warnings or health advisories to constructing barriers blocking access to contaminated areas by humans or other biota.
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From page 88... ...
For example, a temporary sand cap might render dredging impractical, but extensive or armored capping is appropriate as a permanent solution and is not considered to be an interim control. Administrative Interim Controls Restrictions on catching or marketing high-risk fish and shellfish species can reduce the risks to human health in areas where unconfined contaminated sediments must remain in place for long periods of time (i.e., where natural restoration is planned or the selection and implementation of a remediation strategy drags on for years)
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From page 89... ...
The researchers concluded that the broad-scale rejection of the health advisories was due to a combination of factors: the way the media were used, the nature and delivery of the health advisory, and personal predispositions that tended to reduce the credibility or usefulness of the communication. Technology-Based Interim Controls The committee could identify only two instances in which a technologybased interim control was implemented to control the dispersion of contaminated sediments.
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From page 90... ...
. Management guidelines are available for the reuse of dredged material disposal areas (Montgomery et al., 1978)
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Natural Recovery Natural recovery involves leaving the contaminated sediments in place and allowing the ongoing aquatic processes to contain, destroy, or otherwise reduce the bioavailability of the contaminants. Although no action is required to initiate or continue the process, natural recovery is considered the result of a deliberate, thoughtful decision.
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From page 92... ...
It is seldom known, for example, the percentages of in-bed contaminants that undergo intrinsic degradation, are buried deep within the bed, are released to the water column by passive processes, such as diffusion or active biological processes, are extracted by organisms migrating and feeding, or are moved by erosion and resuspension. The monitoring strategy at a site undergoing natural recovery must test the claim that the numerous relevant processes are indeed operating to isolate or eliminate the offending chemicals.
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chemical release environmental risk to await processes that govern principles to describe the considered at Port of rates are low; (c) interim natural capping than to chemical containment and/or process of natural recovery; Tacoma site.
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. Capping can be considered where discharges of contaminants have been halted substantially but natural recovery is too slow to solve the problem.
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Among the major benefits of in situ capping are that it eliminates the need to move the contaminated sediments and that it promotes the in situ isolation of the contaminants by significantly retarding their release to the benthic community. For example, an estimated 99 percent reduction in release rates of Aroclor-1254 and Aroclor-1242 (PCBs)
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natural recovery sediments; (b) effective in benthic community; demonstrations to support pleted (more than 20 is too slow; (c)
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Nevertheless, attention must be given to several in situ treatments, including immobilization, chemical treatment, and biological treatment. Immobilization and Chemical Treatment The goal of in situ immobilization is to isolate sediment contaminants from the benthic and aquatic ecosystem.
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xxx CONTAMINATED SEDIMENTS IN PORTS AND WATERWAYS
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However, because marine sediments of even moderate organic content are likely to be rich in sulfides, which naturally limit the mobility of metals, the addition of sulfides is not likely to be an appropriate treatment. The in situ immobilization of sediments is likely to be based on the concepts of solidification and stabilization and to involve the addition of Portland cement, fly ash, or other binding agents to keep contaminated sediments in place and to reduce contaminant mobility.
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. However, neither has been applied to the treatment of in situ contaminated marine sediments (see Table 5-4)
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analysis of cost effectiveness; (g) exploration of combining in situ bioremediation with capping.
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In situ bioremediation technologies are used in land-based soils to degrade many, but not all, contaminants. With respect to marine sediments, however, bioremediation technologies are experimental.
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In sum, the in situ bioremediation of PCB-contaminated sediment has only recently been recognized as a potential alternative. Although the technology looks promising, given the current level of application and the regulatory focus on total PCBs, it is unclear whether in situ bioremediation can achieve the cleanup levels required at a reasonable cost.
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From page 104... ...
SEDIMENT REMOVAL AND TRANSPORT TECHNOLOGIES In some cases, contaminated sediments must be moved for ex situ remediation or confinement. Efficient hydraulic and mechanical methods -- dredges, pipelines, and barges -- for removing and transporting sediments are available but may have to be modified to mitigate additional risks to the ecosystem and to facilitate remediation.
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From page 105... ...
In a systems approach, the cost of the treatment or placement method is a consideration in deciding how precise site assessment and dredging need to be. Adjustments in the dredging process to minimize the capture of water and uncontaminated sediments can reduce the costs of treatment and placement and hence reduce overall project costs.
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From page 106... ...
For example, a state-of-the-art backhoe dredge was designed specifically to remove creosote-contaminated sediments at the Bayou Bonfouca Superfund site in Louisiana. Significant elements of this dredging system include an array of position sensors installed on the backhoe arm and excavator; a computer-based monitoring system that enabled the operator to monitor turret rotation, arm angle, and bucket angle and depth relative to the vessel, and a topographic map of the bottom; and a slurry processing unit that greatly reduced the water content of the dredged material (Taylor, 1995)
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From page 107... ...
It is important to realize, however, that precision sediment removal must be appropriate for the degree of site definition; conversely, the characterization of the site must match the precision of the available dredging equipment. Time and money are often wasted in the precise mapping of layers of contaminated sediment to the centimeter when the dredging equipment removes layers tens of centimeters thick.
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From page 108... ...
There are also concerns that the propulsion tracks could cause mixing of spilled contaminated sediments with clean sediments (van der Veen, 1995) , but this problem can be overcome by adjusting the cutter width to greater than the track width.
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Environmental Risks The disturbances created by removing and transporting contaminated sediments may increase the risk of contaminant release to the environment. This section summarizes the results of recent research into the extent of these releases and discusses ongoing technology developments in this area.
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developed mathematical models for predicting rates of sediment resuspension for conventional bucket and cutter-head dredges for a limited range of conditions at a few sites. Designing models is difficult because the vast number of operational choices for each dredging operation and the disparity in conditions among field studies mean that very sparse data are available for evaluating a large array of possible combinations.
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No unusual problems were associated with the dredging of highly contaminated sediments from the New Bedford Harbor Superfund site.
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Sediments with the potential to release free sulfides during transport and handling may be a nuisance if not a contamination concern. On-Site Controls Regardless of the control measures, some contaminated sediments will escape from the dredging operation.
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From page 113... ...
At a Superfund site in Cedarburg, Wisconsin, the flow in Cedar Creek was diverted into pipelines, and a 1,000-ft segment of the riverbed was drained so that 25,000 yd3 of PCB-contaminated sediments could be excavated with conventional earth-moving equipment (J. Miller, USACE, personal communication to Marine Board staff, June 7, 1996)
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The cable arm was modified recently with a vertical side plate to prevent the lateral flow of contaminated material from the bucket during the environmental dredging of contaminated sediments. The cable arm has been used for a number of projects in the United States and Canada.
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. At the Manistique Harbor Superfund site, diver-assisted dredging is being used to remove approximately 1,900 yd3 of PCB-contaminated sediments.
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To be economical, dredging operations are done at a high rate and nearly continuously. The slurry is usually produced at a flow rate and with a water content that are not suitable for immediate input into a treatment process.
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The second driving factor for using interim storage is the frequent need that different treatment processes be carried out sequentially. (Additional information on treatment technologies applicable to contaminated sediments can be found elsewhere [Averett et al., 1990; EPA, 1993a, 1994b; Tetra Tech and Averett, 1994]
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. Five general ex situ treatment processes are described below: pretreatment and solids-water separation; physical separation; chemical separation, thermal desorption, and immobilization; thermal and chemical destruction; and biological treatment.
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treatment; (b) soil washing can be used to recover CDF space for later reuse.
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Sometimes schemes are combined. An example of multistage physical separation is the process used at the largest particle separation system for dredged material in the world at the Port of Hamburg in Germany, where all dredged sediments from the highly contaminated Elbe River are pretreated.
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From page 121... ...
Chemical Separation, Thermal Desorption, and Immobilization The contaminants accumulating in bottom sediments preferentially associate with fine particles rather than dissolving in the water. Chemical separation and thermal desorption processes attempt to mobilize these contaminants into a fluid or gas phase where the contaminants can be concentrated, isolated, or destroyed.
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From page 123... ...
. At the Waukegan Harbor Superfund site, thermal desorption was used to reduce PCB concentrations in excess of 500 ppm to less than 2 ppm in the residual sediments at a cost of approximately $250/yd3, plus fixed costs of $150/yd3 (see Appendix C)
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Problems that must be addressed prior to the large-scale application to dredged material include mixing of reagents, solids separation, reagent recovery and disposal, solids disposal, and treatment of the
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From page 127... ...
Costs for all ex situ biological treatments are likely to be higher than costs for in situ alternatives because the sediments and other materials must be handled and greater energy is required for mixing. Ex situ treatment is also complicated by a number of other issues: large volumes of sediment must usually be treated; the sediments usually contain mixtures of organic and inorganic pollutants; the contaminant concentration is often relatively low; and aged polyaromatic hydrocarbons and PCBs are often less bioavailable than more recently sorbed compounds.
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From page 129... ...
Indeed, ex situ bioremediation has many potential applications for the cleanup of contaminated environments and the treatment of hazardous wastes. It is generally recognized, however, that long-term programs and unusual efforts would be required to resolve the relevant R&D issues before treatment would be cost effective for contaminated sediments.
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From page 130... ...
. The two objectives in the design and operation of CDFs that are used for contaminated sediments are to provide adequate storage capacity to meet dredging requirements and to maximize efficiency in controlling contaminant releases.
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INTERIM AND LONG-TERM TECHNOLOGIES AND CONTROLS FIGURE 5-3 Conceptual illustration of containment, disposal, and natural recovery technologies. Dumping contaminated sediments in waters anywhere but in the open ocean is not permitted under the Marine Protection, Research and Sanctuaries Act.
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Effects on surface water quality, groundwater quality, air quality, plants, and animals depend on the characteristics of the dredged material, the management and operation of the site during and after filling, and the proximity of the CDF to potential receptors of the contaminants. If evaluations of contaminant pathways indicate that impacts will be unacceptable, special or additional management and contaminant control measures can be considered, including modification to the dredging operation or site; treatment of effluent, runoff, or leachate; treatment of dredged material solids; and site controls, such as surface covers or liners (USACE and EPA, 1992)
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compatible detoxify contaminants unless as covers and liners, needed contaminated sediments; conditions. with a variety of dredging combined with treatment; for low-cost contaminant (b)
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The CAD approach is particularly useful for disposing of contaminated dredged material. It is also applicable to contaminated sites in waters that are too shallow to permit in situ capping.
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consequences of mixing; (f) potential loss of contaminants to the water column may require controls during placement.
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From page 136... ...
In addition to their utility in civil engineering projects and in the dewatering of dredged sediments, geotextile containers could provide a unique system for demonstrating emerging ex situ bioremediation technologies for certain contaminants. As disposal sites become increasingly difficult to find, the treatment of contaminated sediments in constructed cells, CDFs, or geotextile containers could be ways of reusing scarce sites.
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And because of the expense of the long-distance ocean transport of contaminated sediment, the costeffectiveness of this idea needs to be closely examined. Landfill Disposal Contaminated dredged material sometimes is placed in licensed solid-waste landfills.
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requires handling transporting dredged contaminated sediments. most cost effective for small and transport to the landfill; sediments.
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, would not only provide physical evidence of performance but could also be designed to evaluate risk reduction. To be most useful, monitoring should be done with an eye toward improving the future application of interim controls.
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Given the chemical complexity of the waste mixtures, it is likely that a sequence of treatment processes will be required. It is important to emphasize that the absence of detailed, reliable cost data for many remediation technologies does not pose a major barrier to project planning because the unique conditions (geographical and otherwise)
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Specifically: • Few data are available on the use or effectiveness of interim control tech nologies, and some promising approaches, such as using CDFs for the temporary storage and treatment of contaminated sediments, have yet to be developed fully. • The use of in situ technologies is limited by a lack of understanding of the fundamental processes of the transport, degradation, and biological accu mulation of contaminants under both natural and engineered conditions, coupled with the difficulty of implementation and process control in ex tremely variable and complex natural environments.
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From page 142... ...
program, in which manufacturers pay for the demonstration of new technologies for the cleanup of toxic and hazardous waste sites. Following the SITE program model, a mechanism could be established for making unbiased technical evaluations of innovative sediment-handling and remediation technologies based on real-time, realistic project conditions.
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From page 143... ...
TABLE 5-14 Qualitative Comparison of the State of the Art in Remediation Technologiesa State-of-design Number of Scale of Cost (per Feature technology Guidance Times Used Application cubic yard) Limitationsb Natural recovery Nonexistent 2 Full scale Low Source control Sedimentation Storms In-place containment Developing rapidly < 10 Full scale < $20 Limited technical guidance Legal/regulation uncertainty In-place treatment Nonexistent ≈2 Pilot scale Unknown Technical problems Few proponents Need to treat entire volume Excavation and containment Substantial and well developed Several hundred Full scale $20 to $100 Site availability Public assistance INTERIM AND LONG-TERM TECHNOLOGIES AND CONTROLS Excavation and treatment Limited and extrapolated < 10 Full scale $50 to $1,000 High cost from soil Inefficient for low concentration Residue toxic Need for treatment train aEstimates for North America.
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Higher scores represent, in ascending order, a pilot-scale demonstration using contaminated sediments in a volume on the order of a few cubic yards, a field-scale demonstration using tens of cubic yards, and finally, a commercial operation. The practicality ranking reflects public acceptance; a score of 0 means the public would not tolerate such an activity, and a score of 4 means a technology would be viewed favorably.
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Technology-based interim controls have the potential to effectively limit contaminant releases to the ecosystem, although there has been little experience with this approach. The practicality score is low because of concerns that the contamination will not be remediated completely.
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From page 146... ...
commercial experience base for this technology with navigation dredging and the placement of dredged material. Sediments can be recovered and isolated with contaminant losses of approximately 2 to 5 percent.
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Ex situ approaches require sediment removal and transport, which receive high scores, combined with treatment and containment approaches, which receive good scores for feasibility and practicality but low scores for effectiveness and cost. Thus, the decision maker is left in the uncomfortable position of trading off low-cost, less-effective, less-practical, yet feasible interim controls and in situ approaches, as compared with the most practical ex situ approaches, which can be effective but tend to be expensive and complex.
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From page 148... ...
1993. Environment Canada demonstrations: remediation technologies for the removal of contaminated sediments in the Great Lakes.
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1994. Dredged Material-Filled Geotextile Containers, En vironmental Effects of Dredging.
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1995. Presentation at the Workshop on Interim Controls held July 31, 1995.
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1989. Theoretical Models for Evaluation of Volatile Emissions to Air During Dredged Material Disposal with Application to New Bedford Harbor, Massachusetts.
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From page 152... ...
1987b. Engineering Considerations for Capping Subaqueous Dredged Material Depos its -- Design Concepts and Placement Techniques.
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Background material provided for the Committee on Contaminated Marine Sediments. Workshop on Handling and Treatment Technologies and Associated Costs held April 21–22, 1994, in Chicago, Illinois.
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