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Assessment and Remediation of Contaminated Sediments (ARCS) Program

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Remediation Guidance Document
Chapter 11

US Environmental Protection Agency. 1994. ARCS Remediation Guidance Document. EPA 905-B94-003. Chicago, Ill.: Great Lakes National Program Office.

Table of Contents

SUMMARY AND CONCLUSIONS

11. Summary and Conclusions

Summary

Industrial and nonpoint pollution sources have historically contributed to diminished water quality in the Great Lakes and other water bodies in the United States. Although most point sources of pollution are now regulated and controlled, nonpoint sources, including contaminated bottom sediments, have been identified as a contributing factor to continuing water quality problems.

Areas of Concern (AOCs) with impaired beneficial uses in the Great Lakes waters have been identified by the Great Lakes Water Quality Agreement between the United States and Canada. Contaminated sediments are known to adversely impact water quality, promote contamination of fish flesh, and cause contaminant uptake in other organisms, including humans. Contamination in bottom sediments has also restricted the ability to maintain navigation channels and marine structures. The remediation of contaminated sediments is being considered in many of the Remedial Action Plans being prepared for Great Lakes AOCs.

Under the auspices of the Water Quality Act of 1987, section118, paragraph (c)(3), the USEPA was directed to "carry out a 5-year study and demonstration projects relating to the control and removal of toxic pollutants in the Great Lakes, with emphasis on the removal of toxic pollutants from bottom sediments." To fulfill the requirements of the Act, the Great Lakes National Program Office initiated the Assessment and Remediation of Contaminated Sediments (ARCS) Program.

This document reflects the work effort of the ARCS Engineering/Technology Work Group. The primary purpose of this document is to provide guidance on the evaluation, selection, design, and implementation of technologies for sediment remediation. It is intended to be used in conjunction with other documents developed under the ARCS Program that address the chemistry and toxicity of contaminated sediments (the ARCS Assessment Guidance Document [USEPA 1994a]), assessment and modeling of contaminated sediment impacts (the ARCS Risk Assessment and Modeling Overview Document [USEPA 1993a]), a literature review of remediation technologies (Averett et al. 1990 and in prep.), an evaluation of methods for predicting contaminant losses during sediment remediation (Myers et al., in prep.), and others reporting on specific studies and demonstrations.

Sediment Remediation Technologies

There are a number of technologies that may be used for the remediation of contaminated sediments. Some technologies, such as dredging and confined disposal, have been widely used for the removal and disposal of contaminated sediments from navigation projects. Many of the treatment technologies have been applied to soils, sludges, or oils, but not to sediments. Other technologies that might be used in sediment remediation are routinely applied in the mining and mineral processing industry or at wastewater treatment facilities.

A remedial alternative consists of a combination of technologies used in series or in parallel to alter sediment or sediment contaminant characteristics and achieve the remediation objectives. The technologies of a remedial alternative perform specific functions. In this document, the technologies have been functionally grouped into the following components:

A sediment remedial alternative may be as simple as a single component, as with in situ capping, a nonremoval technology. An alternative may also have many components interacting and supporting one another.

A matrix of the sediment remediation components that ranks their state of development, relative potential for contaminant loss, and application costs is provided in Table 11-1. As shown, some components are made up of well-developed, proven technologies, such as removal, transport, and residue management. Other technologies are still in developmental stages or have been implemented only at the bench- or pilot-scale level. Many sediment treatment technologies, both in situ and ex situ, fall within the latter category.

Nonremoval Technologies
There are two general types of nonremoval technologies, those that isolate the sediments from the surrounding aquatic environment and in situ (or in-place) treatment. In situ capping and containment of contaminated sediments have been demonstrated at two Superfund sites in the Great Lakes--the Sheboygan and Manistique Rivers. Bottom sediments at a number of lakes and reservoirs have been treated to control the release of nutrients and limit eutrophication. In situ treatment methods for toxic contaminants have only been demonstrated on a limited scale, and the contaminant losses and operating costs are largely unknown.

Removal Technologies
There has been more full-scale experience with removal (i.e., dredging) than with any other remediation technology. For the two general types of dredges, mechanical and hydraulic, there are numerous equipment variations, including a number of dredges specifically developed to minimize the loss of contaminants, for which the removal component is relatively high. Dredging is typically one of the least costly components of a remedial alternative, and the dredging equipment can be selected to fit the requirements of other components.

Transport Technologies
Transportation modes, such as pipelines, railcars, trucks, and conveyors, are all well-developed technologies, although not all have been widely applied to sediments. For a simple remedial alternative, transportation may only involve the movement of sediments from the dredging site to the disposal site. For more complex remedial alternatives, sediments may be rehandled several times, and products (residues) of pretreatment and treatment technologies may require handling and transportation as well. The handling steps at each end of a transportation route are, in many cases, the most costly item of the transport component, as well as the source of most contaminant losses during transport. The costs and contaminant losses of the transport component are generally low in relation to other remediation components.

Pretreatment Technologies
The physical properties of sediments, in particular the amount of water and the size of sediment particles, represent one of the most challenging aspects of sediment remediation. These properties must be modified, and in some cases, used to advantage by the pretreatment technologies. Technologies commonly used in the mining and mineral processing industry can be used to prepare sediments for subsequent treatment processes and, in some cases, can separate sediments into specific fractions and thereby reduce the quantity of material requiring treatment or confined disposal. Other pretreatment technologies include passive dewatering methods used with dredged material from navigation projects and mechanical dewatering equipment more commonly used in wastewater treatment applications. The costs and contaminant losses from pretreatment technologies are moderate in relation to other remediation components, although estimates of these costs and losses from mining technologies are somewhat speculative.

Treatment Technologies
There are many technologies available for treating contaminated sediments. Treatment is generally the most costly component of a remedial alternative, and the component with the least amount of full-scale experience. Most of the treatment technologies that have been proposed for contaminated sediments were initially developed for soils, sludges, or other contaminated media. Many of the treatment technologies were developed for cleaning up chemical spills or waste oils with extremely concentrated contaminants and may be significantly less efficient with sediments having more dilute contaminant concentrations. Contaminant losses from most treatment technologies will be low in comparison to those from other remediation components, although the type and performance of controls associated with treatment technologies are quite varied.

Disposal Technologies
Technologies available for the disposal of sediments, treated sediments, and treatment residues range from unrestricted, open-water disposal to RCRA-licensed hazardous waste landfills. No single disposal method is appropriate for all materials, but confined disposal is the most commonly used technology for the disposal of contaminated sediments dredged for navigation or remediation. Remedial alternatives using almost any form of treatment will need a site for the storage and rehandling of sediments, and possibly the ultimate disposal of treatment residues. The availability and location of a suitable site for these activities is likely to be the most crucial feature in a sediment remedial alternative. Costs for disposal technologies are quite variable, although conventional confined disposal costs are moderate to low in comparison to those for treatment technologies. Methods for estimating contaminant losses from disposal technologies are well developed, although losses are variable.

Residue Management Technologies
The last component of a sediment remedial alternative discussed in this document is the management of water, solid, organic, and air residues generated by other components. The character and quantity of these residues will depend on the component technologies selected for the remedial alternative. Water is likely to be the most important residue to manage because of its volume, although treatment technologies for wastewater are well developed. Treatment and disposal technologies for residues will, in most cases, be determined by regulatory considerations. Costs for residue management technologies may be incorporated into other component costs. Contaminant loss rates are generally low in comparison to those for other remediation components.

Decision-Making Process

The process of developing a remedial alternative involves a number of activities, including:

This process is discussed in more detail in Chapter 2.

Chapters 3 through 9 of this document are dedicated to the remedial components listed above. For each component, available technology types and process options are briefly described and information needed for the formulation of remedial alternatives and selection of appropriate technologies is provided.

The first type of information needed to develop a remedial alternative is the technical features and requirements of the specific technologies. Each component of a remedial alternative must be evaluated to determine if it is compatible with the other components being considered. Some components have restrictions on site conditions or the physical properties of the materials they can accept. For example, most treatment technologies have very strict requirements for acceptable feed materials. Other remediation components (e.g., mechanical dredging) may have very few restrictions on the types of sediments that can be handled. The selection of a technology for any component cannot be made independently of those being considered for other components.

The second type of information is cost data. Cost estimates are used during all phases of project planning, design, and implementation. Available cost data provided in this document reflect January 1993 price levels. The accuracy of the available cost data depends on the level of operating experience with particular technologies. In some cases, the only available cost data are from applications of these technologies to media other than sediments (e.g., sludges, mined materials). Cost data for the most expensive technologies (e.g., treatment) are generally more speculative than for other technologies.

The third type of information is predictions of the amount of contaminant loss during implementation of the remedial alternative. Contaminant losses will occur with all components of a remedial alternative. Estimates of these losses are necessary to evaluate the environmental impacts of remedial alternatives and to compare the benefits of remediation vs. other options, including no action. These loss estimates may also be needed to evaluate the ability of a remedial alternative to maintain compliance with environmental laws and regulations. The tools for predicting contaminant losses from remediation technologies are at varying states of development, but available information suggests that losses occurring during the removal phase are greater than for other remediation components. This is primarily because losses from other components are more readily controlled.

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Conclusions

The ARCS Program conducted a series of studies, investigations, and demonstrations which examined the "state-of-the-art" for sediment remediation technologies. From the information and experience gathered during this program, the following general conclusions can be made:

Depending on one's point of view, the above conclusions may project a pessimistic outlook on the implementability of most treatment technologies to contaminated sediments. Only a limited number of contaminated sediment sites have been remediated to date, and the technologies used for the majority of these sediments were containment in place and confined disposal. Considering the entire volume of contaminated sediments and the large number of individual sites in the Great Lakes, this pattern is not likely to change on a wide scale in the near future for a number of reasons, not the least of which is the high cost associated with most treatment technologies.

The feasibility of applying treatment technologies to contaminated sediments can be greatly improved by reducing the volume of materials to be processed. For some cases, this can be accomplished by selectively treating the sediments containing the highest contaminant concentrations (i.e., "hot spots") or by using pretreatment technologies to concentrate the contaminants into a small fraction of the original sediment volume.

The technical issues discussed in this document are only a part of what is limiting the remediation of contaminated bottom sediments in the Great Lakes and other water bodies. The broader limitations are the perception, both among the general public and government managers, of sediment contamination problems and the priority these sites receive for funding.

Contaminated sediments are an unseen problem, lying beneath rivers, harbors, and lakes that rarely display the signs of their impacts in readily visualized ways. Sediment contamination is a problem with boundaries that are not easily resolved, more often a continuum than a discrete zone with clear limits. The immense volume of contaminated sediments at some sites makes remediation seem impossible, and makes the remediation of a small part of this mass seem insignificant. With these perceived limitations, the presentation of the seriousness of sediment contamination problems and the solutions to the remediation of contaminated sediments must be innovative.

In recent years, a number of initiatives have been taken by various levels of government to overcome the above limitations. One of the most innovative efforts to remediate contaminated sediments is being conducted on the Grand Calumet River in northwestern Indiana. This effort has combined a series of enforcement actions by the USEPA Region 5 and Indiana Department of Environmental Management with navigation maintenance dredging by the Corps. Additional innovative approaches include the enforcement initiative in southeastern Michigan and the cooperative approach being taken along the Fox River in Wisconsin.

The philosophy that has arisen as a common thread among these initiatives, and which may be applicable to other sites with sediment contamination, is to seek an integrated solution composed of many individual pieces. Rather than looking for one authority or responsible party to solve the problem at one time, the effort is diversified into seeking out opportunities to implement sediment remediation in a systematic, piece-by-piece fashion involving government, industry, and the public. Using such an approach, an entire waterway can be remediated.


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