«This page left intentionally blank. United States Environmental Protection Agency EPA-540-R-05-012 Office of Solid Waste and Emergency Response OSWER ...»
Most treatment technologies require that the sediment be relatively homogeneous and that physical characteristics be within a relatively narrow range. Pretreatment technologies may be used to modify the physical characteristics of the sediment to meet these requirements. Additionally, some pretreatment technologies may divide sediment into separate fractions, such as organic matter, sand, silt, and clay. Often the sand fractions contain lower contaminant levels and may be suitable for unrestricted disposal and/or beneficial use if it meets applicable standards and regulations. Selection factors, costs,
pilot-scale demonstrations, and applicability of specific pretreatment technologies are discussed in detail in EPA’s Assessment and Remediation of Contaminated Sediments (ARCS) Program Remediation Guidance Document (U.S. EPA 1994d).
6.7.2 Treatment Depending on the contaminants, their concentrations, and the composition of the sediment treatment of the sediment to reduce the toxicity, mobility, or volume of the contaminants before disposal may be warranted. Available disposal options and capacities may also affect the decision to treat some sediment. In general, treatment processes have the ability to reduce sediment contaminant concentrations, mobility, and/or sediment toxicity by contaminant destruction or by detoxification, by extraction of contaminants from sediment, by reduction of sediment volume, or by sediment solidification/stabilization.
Treatment technologies for sediment are generally classified as biological, chemical, extraction or washing, immobilization (solidification/stabilization), and thermal (destruction or desorption). In some cases, particle size separation is also considered a treatment technology. The following treatment technologies are among those which might be evaluated.
Generally, bioremediation is the process in which microbiological processes are used to degrade or transform contaminants to less toxic or nontoxic forms. In recent years, it has been demonstrated as a technology for destroying some organic compounds in sediment. The project manager should refer to EPA (1994d), Myers and Bowman (1999), and Myers and Williford (2000) for a summarization of bioremediation technologies and their application under site-specific conditions.
Generally, chemical treatment refers to processes in which chemical reagents are added to the dredged or excavated material for the purpose of contaminant destruction. Contaminants may be destroyed completely, or may be altered to a less toxic form. Averett and colleagues (1990) reviewed several general categories of chemical treatment. Of the categories reviewed, treatments including chelation, dechlorination, and oxidation (of organic compounds) were considered most promising.
Generally, the primary application of extraction processes is to remove organic and, in some cases, metal contaminants from the sediment particles. “Sediment washing” is another term used to describe extraction processes, primarily when water may be a component of the solvent. In the extraction process, dredged or excavated material is slurried with a chemical solvent and cycled through a separator unit. The separator divides the slurry into the three following fractions: 1) particulate solids; 2) water;
and 3) concentrated organic contaminants. The concentrated organics are removed from the separator for post-process treatment. Extraction or washing may also generate large volumes of contaminated wastewater that generally must be treated prior to discharge.
6-30 Chapter 6: Dredging and Excavation Immobilization or Solidification/Stabilization Generally, immobilization, commonly referred to as solidification/stabilization, alters the physical and/or chemical characteristics of the sediment through the addition of binders, including cements and pozzolans (U.S. EPA 1994d). Immobilization technologies primarily work by changing the properties of the sediment so contaminants are less prone to leaching. Alteration of the physical character of the sediment to form a solid material, such as a cement matrix, reduces the accessibility of the contaminants to water and entraps the contaminated solids in a stable matrix (Myers and Zappi 1989). Another form of immobilization, chemical stabilization, minimizes the solubility of metals primarily through the control of pH and alkalinity. Chemical stabilization of organic compounds may also be possible (Barth et al. 2001, Wiles and Barth 1992, Myers and Zappi 1989, Zimmerman et al. 2004).
Generally, thermal technologies include incineration, pyrolysis, thermal desorption, sintering, and other processes that require heating the sediment to hundreds or thousands of degrees above ambient temperatures. Thermal destruction processes, such as incineration, are generally effective for destroying organic contaminants but are also expensive and have significant energy costs. Generally, thermal treatment does not destroy toxic metals.
Particle Size Separation
Generally, particle size separation involves separation of the fine material from the coarse material by physical screening. A site demonstration of the Bergman USA process resulted in the successful separation of less than 45 micron fines from washed coarse material and a humic fraction (U.S.
EPA 1994f). As previously noted, particle size separation may serve as a pretreatment step prior to implementation of a treatment alternative. Many treatment processes require particle sizes of one centimeter or less for optimal operation.
Effluent Treatment/Residue Handling
Generally, treatment of process effluents means treatment of liquid, gas, or solid residues and is a major consideration during selection, design, and implementation of dredging or excavation. As shown in Highlight 6-1, dredging or excavation may require management of several types of residual wastes from the pretreatment and operational treatment processes that include liquid and/or air/gas effluents from dewatering or other pretreatment/treatment processes, residual solids, and runoff/discharges from active CDFs. Generally, these wastes can be handled through the use of conventional technologies for water, air, and solids treatment and disposal. However, the technical, cost, and regulatory requirements can be important considerations during the evaluation of dredging or excavation as a cleanup method.
Pilot and full-scale treatment processes have been conducted at a number of sites, although there is limited experience at Superfund sites. Where treatment has been used at Superfund sites, the most common treatment method is immobilization by solidification or stabilization. Additional information concerning treatment technologies for contaminated sediment may be found in U.S. EPA Office of Water’s Selecting Remediation Technologies for Contaminated Sediment (U.S. EPA 1993d). Specific applications, limitations, specifications, and efficiencies of many sediment treatment processes are discussed in the ARCS program’s Remediation Guidance Document (U.S. EPA 1994d). The NY/NJ
Harbor Project is an example of a large-scale demonstration of several dredged decontamination technologies (Highlight 6-9).
Highlight 6-9: NY/NJ Harbor - An Example of Treatment Technologies and Beneficial Use The goal of the NY/NJ Harbor Sediment Decontamination Project is to assemble a complete decontamination system for cost effective transformation of dredged material (mostly from navigational dredging projects) into an environmentally safe material that can be used in the manufacturing of a variety of beneficial use products.
The following four treatment technologies are being used at the NY/NJ site: 1) sediment washing; 2) thermal treatment; 3) solidification; and 4) vitrification. Each technology has a sponsor from the private sector that will provide the capital needed for facility construction and operation.
Sediment washing (extraction) uses high-pressure water jets and proprietary chemical additives to extract both organic and inorganic contaminants from the sediment. The resulting materials can be used to produce manufactured soil for commercial, and in some cases, residential landscaping applications. Advantages to this treatment include modest capital costs and high throughput. The patented washing system has been demonstrated capable of decontaminating sediments containing high quantities of silt and clay.
A thermal treatment being used is a thermo-chemical manufacturing process that, at high temperatures, will destroy organic contaminants. The process will melt a mixture of sediment and modifiers, and the resulting product is a manufactured grade cement comparable to Portland Cement. This is a very effective treatment, but expensive.
A third process is a “treatment train” that includes dewatering, pelletizing, and transport to an existing light-weight aggregate facility. Pelletizing is a type of solidification treatment. After the sediment is dewatered, it is mixed with shale fines and extruded into pellets. The pellets are fed into a rotary kiln, and the organic matter explodes. The resulting material can be used as a structural component in concrete, insulation (pipeline) and for other geotechnical uses.
Finally, the process includes a high temperature vitrification, which uses an electrical current to heat (melt) and vitrify the soil in place. This process can destroy organic contaminants and incorporate metals into a glassy matrix that can be used to produce an architectural tile.
Source: Stern et al. 2000, Mulligan et al. 2001, Stern 2001, NRC 1997 Potential sediment treatment technologies will evolve as new technologies are developed and other technologies are improved. EPA has recognized the need for an up-to-date list of treatment
alternatives and has developed the following databases:
• EPA Remediation and Characterization Innovative Technologies (EPA REACH IT):
Provides information on more than 750 service providers that offer almost 1,300 remediation technologies and more than 150 characterization technologies (includes a variety of media, not just sediment).
More information is available at http://www.epareachit.org/index3.html; and • EPA National Risk Management Research Laboratory (NRMRL) Treatability Database:
Provides results of published treatability studies that have passed the EPA quality assurance reviews, it is not specific to sediment, and is available on CD from the EPA’s ORD National Risk Management Research Laboratory in Cincinnati, Ohio. Detailed contact information is available at http://www.epa.gov/ORD/NRMRL/treat.htm.
6-32 Chapter 6: Dredging and Excavation 6.7.3 Beneficial Use Although not normally considered a treatment option, beneficial use may be an appropriate management option for treated or untreated sediment resulting from environmental dredging projects.
Significant cost savings may be realized if physical and chemical properties of the sediment allow for beneficial use, especially where disposal options are costly. For example, at Rouge River/Newburgh Lake, Michigan, a Great Lakes Area of Concern, significant cost savings were realized by using lightly contaminated dredged sediment as daily cover at a local sanitary landfill, where it did not pose risk within the landfill boundary. The Bark Camp Mine Reclamation Project in Pennsylvania provides another reuse example. Information is available through the Pennsylvania Department of Environmental Protection Web site at http://www.dep.state.pa.us/dep/DEPUTATE/MINRES/BAMR/bark_camp/ barkhomepage.htm. However, beneficial use of dredged or excavated sediment has been only implemented infrequently for remedial projects, mainly due to lack of cost-effective uses in most instances. Where beneficial use is considered, the contaminant levels and environmental exposure, including considerations of future land use, should be assessed.
Options for beneficial use may include the following:
A series of technical notes on beneficial uses of contaminated material has been developed by the USACE (Lee 2000), and the USACE maintains a Web site of beneficial use case studies currently available at http://el.erdc.usace.army.mil/dots/budm/budm.html. Use of contaminated materials from CDFs (to include treated material) is a major thrust of the USACE Dredging Operations and Environmental Research (DOER) program (http://el.erdc.usace.army.mil/dots/doer). In addition, Barth and associates evaluated beneficial reuse using an effectiveness protocol (Barth et al. 2001).
In some cases, a CDF (see description in Section 6.8.2) can be integrated with site reuse plans to both reduce environmental risk and simultaneously foster redevelopment in urban areas and brownfields sites. For example, at the Sitcum Waterway cleanup project in Tacoma, Washington, contaminated sediment was placed in a near shore fill in the Milwaukee Waterway, which was then developed into a container terminal. Also, there may be innovative and environmentally protective ways to reuse dredged contaminated sediments in habitat restoration projects (e.g., placement of lightly contaminated material over highly contaminated materials to build up elevations necessary for eventual creation of clean emergent marshlands).
6.8 SEDIMENT DISPOSAL For purposes of this guidance the term “disposal” refers to the placement of dredged or excavated material and process wastes into a temporary or permanent structure, site, or facility. The goal of disposal is generally to manage sediment and/or residual wastes to prevent contaminants associated with them from impacting human health and the environment. Disposal is typically a major cost and logistical component of any dredging or excavation alternative. The identification of disposal locations can often be the most controversial component of planning and implementing a dredging remedy and, therefore, should be considered very early in the feasibility study.
Historically, contaminated sediment from Superfund sites has been typically managed in upland sanitary landfills, or hazardous or chemical waste landfills, and less frequently, in CDFs. Contaminated sediment has also been managed by the USACE in contained aquatic disposals (CADs). Also, the material may have a beneficial use in an environment other than the aquatic ecosystem from which it was removed (e.g., foundation material beneath a newly constructed brownfields site), especially if the sediment has undergone treatment. As noted below, all disposal options have the potential to create some risk. These risks may result from routine practices (i.e., worker exposure and physical risks and volatilization), while other risks may result from unintended events, such as transportation accidents and contaminant losses at the disposal site. All potential risks should be considered when comparing alternatives. The ARCS program’s Remediation Guidance Document (U.S. EPA 1994d) provides a discussion of the available disposal technologies for sediment, including an in-depth discussion of costs, design considerations, and selection factors associated with each technology. Averett and colleagues (1990), EPA (1991b), and Palermo and Averett (2000) provide additional discussion of disposal options and considerations.
6.8.1 Sanitary/Hazardous Waste Landfills