Contaminated Marine Sediments Assessment and Remediation (1989) / Chapter Skim
Currently Skimming:
Alternatives for Control/Treatment of Contaminated Dredged Material
Alternatives for Control/Treatment of Contaminated Dredged Material
Pages 221-238
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From page 221... ...
As the concern over dredging and disposal of contaminated sediments increases, unconfined open-water disposal of dredged material from harbors and navigation channels is being closely scrutinized by state and local governments as well as numerous federal agencies. This paper presents recent concepts and technologies for handling contaminated dredged material CONTAMINANT CONTROL DURING DREDGING OPERATIONS Dredge Selection During dredging operations all dredge plants disturb bottom sediment, creating a plume of suspended solids around the dredging 221
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From page 222... ...
Contaminated sediment may release contaminants into the water column through resuspension of the sediment solids, dispersal of interstitial water, or Resorption from the resuspended solids. Control of sediment resuspension during dredging reduces the potential for release of contaminants and/or their spread to previously uncontaminated areas.
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From page 223... ...
Special Purpose Dredges Special-purpose dredging systems have been developing during the last few years in the United States and overseas to pump dredged material slurry with a high solids content and/or to minimize the resuspension of sediment. Most of these systems are not intended for use on typical maintenance operations; however, they may provide alternative methods for unusual dredging projects, such as contaminated sediments.
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From page 224... ...
Loading and unloading operations present the greatest potential for uncontrolled release of contaminated materials. Use of clamshell and dragline attachments at the dredging site will release substantially more dredged material into the water column than vacuum/suction systems.
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From page 225... ...
CONTAMINANT CONTROL DURING UPLAND/NEARSHORE DISPOSAL OPERATIONS Six categories of contaminated media may be associated with the disposal of contaminated sediment. These include dredged material slurry, dredged material solids, site effluent, site runoff, site leachate (including flow-through dikes)
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From page 226... ...
Site characteristics that may affect the need for, or type of, treatment/control are listed in Table 1. Covers Covers are control measures designed to seal or isolate the surface of contaminated dredged material from physical, chemical, or biological processes that could release contaminants from a confined upland or nearshore disposal site.
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From page 227... ...
Table 2 lists surface-water control measures and their duration of use at disposal sites (U.S.
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From page 228... ...
EPA 1982a and 1985 for more detailed information. Leachate Collection Disposal sites for dredged material must accommodate the interstitial water associated with the sediment, dilution water that may be mixed with the sediment by the dredging operation, and precipitation or other sources of water added to the disposal area surface.
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From page 229... ...
The most appropriate solids separation method for a given site depends upon several factors, including the following: volume of contaminated solids; composition of sediment, including gradation, percent clay, and percent total solids; types of dredging or excavation equipment used, which determines the feed rate to solids separation and, in the case of slurries, the percent solids; and site location and surroundings. Types of available solids separation equipment includes settling basins, clarifiers, impoundment basins, screens, and cyclones.
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From page 230... ...
Incineration, although a demonstrated technology for organics destruction is believed to be far too costly for the treatment of contaminated dredged material. In addition, the technology has limited application for treating dredged material solids contaminated with heavy metals.
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From page 231... ...
A comparison of the relative efficiencies of the treatment levels is given in Table 3. TABLE 3 Contaminant Removal Efficiency of Water Treatment Levelsa Class of Level contaminant Percent Water concentration removal remaining I Solids 99.9+ mg/liter range Metals 80 to 99+ ppb to ppm ranged Organics 50 to 90+ ppb to ppm rangeb II Metals 99+ ppb rangeb Organics 50 to 90 ppb to ppm ranged III Metals 99+ ppb range Organics 95+ ppb range IV Nutrients 90 to 98+ mg/liter range V Metals 99+ highest quality attainable Organics 99+ highest quality attainable VI Pathogens 90 to 99+ NOTES: aAssumes influent strength defined by dredged sediment that are not classifiable as "extremely hazardous waste" under RCRA (i.e., low saturation influents)
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From page 232... ...
CONTAMINANT CONTROL/TREATMENT FOR RESTRICTED OPEN-WATER DISPOSAL Restricted open-water disposal as used here simply suggests that one or more controls beyond those normally applied in conventional projects are required to address either known risks or uncertainties associated with disposal of contaminated sediments. Most positive control measures are based on the concept of isolating the contaminants from the water column or benthic environment.
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From page 233... ...
(1985) , using the technologies discussed previously, described five conceptual designs for restricted open-water disposal sites: deep-water mound, deep-water confined, shallow-water mound, shallow-water confined, and waterway confined.
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From page 234... ...
Floating and shore-based equipment is not readily available and the cost is uncertain. SU+ARY Although the control of potential contaminant release from the dredging and disposal of contaminated sediments is a relatively new concern,
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From page 235... ...
7. With the assurance of major cost increases, selection of control/ treatment alternatives for very highly contaminated dredged material could rely on technologies developed and being implemented for control of hazardous wastes, i.e., Resource Conservation and Recovery Act (RCRA)
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From page 236... ...
The costs of both the control/treatment alternatives and testing protocols are inadequately documented and are highly variable. Additional effort must be expended to refine the costs asbociated with controlling contaminant migration from contaminated dredged material disposal sites, evaluate the potential for contaminant migration, and assess the environmental impacts associated with contaminant migration.
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From page 237... ...
1985. Handbook: Remedial Action at Waste Disposal Sites (Revised)
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From page 238... ...
1982a. Handbook for Remedial Action at Waste Disposal Sites.
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