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ALTERNATIVES FOR CONTROL/TREATMENT OF CONTAMINATED DREDGED MATERIAL M. John Cullinane, Jr., Daniel E. Averett, Richard A. Shafer Clifford L. Truitt, and Mark R. Bradbury U.S. Army Engineer Waterways Experiment Station and James W. Male, University of Massachusetts ABSTRACT As concern over dredging and disposal of contaminated sediments increases, unconfined open-water disposal of dredged material from harbors and navigation channels is closely scrutinized by state and local governments and numer- ous federal agencies. Although control of potential contami- nant release from dredging and disposal of contaminated sedi- ments is a relatively new concern, practical methods are available for handling such materials in an environmentally sound manner. Alternative technologies for dredging, trans- port, and disposal of contaminated dredged material are reviewed in this paper. Cont~mi~nant control/treatment during three basic operations are discussed: dredging, material transport, and disposal operations. BACKGROUND Because many contaminants become attached to sediment particles, concentrations in sediment are generally much greater than in water. 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
222 operation. Limitations may be placed on levels of suspended solids even during normal dredging operations (Lunz et al., 1984~. Contami- nated 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 resus- pension during dredging reduces the potential for release of contami- nants and/or their spread to previously uncontaminated areas. Selection of dredging equipment and method in general depends on the following factors: physical characteristics of material to be dredged, quantities of material, depth, distance to disposal area, phys- ical environment of and between the dredging and disposal areas, con- tamination level of sediment, mobility of contaminants, method of dis- posal, production required, and type of dredges available. Dredging of contaminated sediments requires the additional consideration of con- taminant loss during the extraction process and meeting of applicable criteria pertaining to removal efficiencies and/or environmental protection. Different dredging methods appear more appropriate for certain con- taminant classes. For volatile contaminants, mechanical dredges are likely to produce less loss than hydraulic dredges. Soluble contamin- ants can be removed more efficiently by a hydraulic dredge, but are difficult to control at.the disposal site and treatment of the effluent water may be required. Equipment and Operational Controls Hopper Dredge Operation The rate of solids loss in the overflow (which may determine if overflow is acceptable) will vary with amount of water in the hopper, hopper capacity and drainage characteristics, material characteristics (settleability), pumping rate, and elapsed time of overflow. Reduction of sediment resuspension can be accomplished by reducing the flow rate of the slurry being pumped into the hopper during the latter phases of the hopper-filling operation, reducing the solids concentration in the plume by reducing the sediment concentration in the overflow. By using this technique, the solids content of the overflow can be reduced by as much as 50 percent while the loading efficiency of the dredge is simul- taneously increased. In extreme cases, pumping past overflow may be prohibited. Another approach is a submerged discharge system for hop- per dredge overflow, called an antiturbidity overflow system (ATOS) (Ofuji and Naoshi, 1976~. Cutterhead and Suction Dredge Operation Concentrations of suspended sediments from a cutterhead dredging operation range from 200 to 300 mg/liter near the butterhead to a few mg/liter at 1,000-2,000 ft from the dredge. Resuspension of sediment during butterhead excavation is dependent on the operating techniques
223 used. The sediment resuspended by a Butterhead dredge depends on thick- ness of cut, rate of swing, and cutter rotation rate (Barnard, 1978~. Proper balance of these operational parameters can decrease sediment resuspension while having little or no effect on production (Hayes et al., 1984~. Modifications to Butterhead and suction dredges have improved their production capabilities and reduced dredged sediment resuspension. Greater production rates are achieved by pumping a higher solids concentration, reducing the quantity of return water that may be contaminated and require treatment. Recent modifications in- clude matchbox heads, walking spuds, ladder pumps, flow and density instrumentation, underwater video and sensor equipment, shape of the Butterhead, and rake angle. Dust Pan Dredges Dust pan dredges are not well suited for dredging contaminated materials. However, when used in this application, the angle of the water jets on the head and the water pressure from these jets should be adjusted to achieve the minimum amount of sediment resuspension. Special Purpose Dredges Special-purpose dredging systems have been developing during the last few years in the United States and overseas to pump dredged mate- rial slurry with a high solids content and/or to minimize the resuspen- sion 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. Clamshell Bucket Dredge Operations Resuspension of sediments during clamshell dredging operations can be reduced by implementing operational controls and/or altering the bucket design. Operational controls can be applied to hoist speed, placement of the dredged material in the hopper barge, loading the hopper past overflow and dragging the bucket along the bottom. Equip- ment design includes the fit of the bucket and the use of enclosed clamshell buckets. Watertight buckets have been developed in which the top is enclosed so that the dredged material is contained within the bucket (Barnard, 1978 ~ . Comparisons between standard open clamshell bucket and a watertight clamshell bucket indicates that watertight buckets generate 30 to 70 percent less resuspension in the water column than the open buckets. The enclosed bucket did, however, produce increased resuspension near the bottom, due to a shock wave that precedes the watertight bucket.
224 Additional Control Techniques Several additional techniques and/or considerations have been sug- gested to assist in controlling resuspension and contaminant release during dredging. Typical control techniques that are commonly eval- uated include silt curtains; barriers, such as dikes, weirs, and sheet pile enclosures; and operational controls, such as dredging only during a specific time in the tidal cycle. Success with these has been varied and their application is very site specific. CONTAMINANT CONTROL DURING TRANSPORT Primary transportation methods used to move dredged material in- clude pipelines, barges, scows, trucks, and rail. The primary emphasis during this phase of the overall dredging process is toward spill/leak prevention. Accidental release of contaminated materials into a pre- viously uncontaminated environment has extremely costly consequences in monetary and public relations aspects. Thus, each step in the trans- port system must be carefully evaluated. Controls for Pipeline Transport Pipelines are commonly used to transport bulk materials over rela- tively short distances. During the design stage, planners should care- fully consider pipeline routes, climatic conditions expected, corrosion resistance of the material, redundancy of safety devices (i.e., addi- tional shutoff valves, loop/by-passes, pressure relief valves), cou- pling methods and systems to detect leaks. Souder et al. (1978) out- lines specific pump and pipeline design procedures. Controls for Scow/Barge Transport Barge/scow transport of dredged material has historically been one of the most used methods to move large quantities over long distance. Controls to prevent spread of contaminated materials when utilizing barge transport are primarily concerned with loading/unloading proce- dures, fugitive emissions, route and navigation hazards, and decontam- ination of equipment. 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 sys- tems. However, when planning for pumping dredged material into barges, planners should consider how the material will be transferred from the dredge onto a barge. Overflow during such operations can cause a sig- nificant return of contaminants to the water column. Flexible connec- tions from dredge to barge will reduce the possibility of pipe damage due to wave action. If the dredged material is tremied into the barge,
225 then movement of the boom between barges or dredge and barges must be carefully controlled to prevent material from falling directly into the waterway. Controls for Truck/Rail Transport Trucks are used for dredged material when the distance from the dredging site is beyond the range normally used for overland pipelines and less than the distance for rail car transport (> 50 to 100 ml). Controls associated with transporting dredged material by truck/rail parallel those for barge/scow transport. Primary concerns include weight restrictions, routing, and loss in transport, loading, and unloading operations. Loading and unloading operations present the greatest potential risk of contaminating nearby clean areas. Controls suggested for consideration are drainage of water from loading and unloading area into central sump for periodic removal, daily removal of spilled material, specially designed loading ramps to collect spilled material, use of watertight clamshells for transferring materials from barges into truck. Decontamination of truck/rail under carriages may be necessary to control contaminated materials from falling onto public roadways when leaving loading/unloading areas. CONTAMINANT CONTROL DURING UPLAND/NEARSHORE DISPOSAL OPERATIONS Six categories of contaminated media may be associated with the dis- posal of contaminated sediment. These include dredged material slurry, dredged material solids, site effluent, site runoff, site leachate (in- cluding flow-through dikes), and residual solids. Upland disposal of contaminated dredged material must be planned to contain the dredged material within the site and restrict contaminant mobility out of the site in order to control or minimize potential envi- ronmental impacts. Francingues et al. (1985) identified and described five possible mechanisms for transport of contaminants from upland dis- posal sites: 1. release of contaminants in the effluent during dredging operations, 2. surface runoff of contaminants in either dissolved or suspended particulate form following disposal, 3. leaching into ground water and surface waters, 4. plant uptake directly from sediments, followed by indirect animal uptake from feeding on vegetation, and 5. animal uptake directly from the sediments.
226 TABLE 1 Site Characteristics Affecting the Need for Control/Treatment Technologies Site area Site configuration Dredging method Climate (precipitation, temperature, wind, evaporation) Soil texture and permeability Soil moisture Topography Drainage Vegetation Site Selection Depth to aquicludes Direction and rate of groundwater flow Existing land use Depth of groundwater Ecological areas Drinking water wells Receiving streams (lakes, rivers, etc.) Level of existing contamination Nearest receptors Site Control Strategies Site location is an important, if not the most important, consid- eration in minimizing the cost of required restrictions. Selection of a technically sound site can reduce or eliminate the need for applying contaminant control/treatment technologies. 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. Surface covers can be as simple as a 1- to 3-ft thick layer of clean dredged material or as complex as a multi- layer cap that includes impermeable membranes, filters, gas channels, biobarriers, and top soil. Functions of a cover could include one or more of the following: prevent or minimize surface water infiltration, promote aesthetics, reduce water erosion and dissolution of contaminants in surface water runoff, reduce wind erosion and fugitive dust emissions, contain and control gases and odors, provide a surface for vegetation and/or site reclamation, and prevent direct bioturbation (human and animal) Since these functions address all of the migration pathways (i.e.,
227 TABLE 2 Normal Duration of Surface Water Diversion and Collection Measures Technology Duration of normal use Dikes and berms Temporary Channels (earthen and CMP) Temporary Waterways Permanent Terraces and benches Temporary and Permanent Chutes Permanent Downpipes Temporary Seepage ditches and basins Temporary Sedimentation basins Temporary Levees Temporary Floodwalls Permanent SOURCE: U.S. Environmental Protection Agency (by. EPA, 1985~. surface water, groundwater, air, and direct contact), some type of surface cover will likely be a component of any upland or nearshore disposal system. Surface-Water Controls The overall objective of surface water controls is to minimize the volume of water that becomes contaminated via contact with the contami- nated sediment. Surface-water controls accomplish this objective by pre- venting surface water runon from areas adjacent to the disposal site, by draining the disposal site efficiently to reduce infiltration and leachate generation, and by preventing erosion and sediment loss from the cover of the site. Surface-water controls also aid in collecting and transferring water that may be contaminated to treatment or dis- posal systems. Surface-water control methods are well established and are familiar to the engineering and construction industry. Lee et al. (1985a) provides a detailed discussion of management practices of U.S. Army Corps of Engineers (COE) construction sites. Table 2 lists surface-water control measures and their duration of use at disposal sites (U.S. EPA, 1985~. Groundwater Controls Liners Lining a site is a technique designed to contain leachate within the site and minimize groundwater contamination. A variety of liner
228 materials are available for use in confined disposal operations. Soil liners are suitable for use as the only liner in most dredged material upland and nearshore sites. However, in certain upland applications, a combination of synthetic membrane and soil liner may be required to achieve maximum containment of contaminants. To ensure continued effec- tiveness of the liners whether soil or flexible membrane, they must be compatible with the dredged material and leachate they are to contain and be properly installed (Phillips et al., 1985~. Groundwater Recovery Groundwater recovery technologies are usually considered as reme- dial actions where sites containing hazardous materials have released contaminants to the groundwater. Control of groundwater contamination involves one of four options: 1. containment of a plume; 2. removal of a plume after measures have been taken to halt the source of contamination; 3. diversion of groundwater to prevent clean groundwater from flowing through a source of contamination or to prevent con- taminated groundwater from contacting a drinking water supply; or 4. prevention of leachate formation by lowering the water table beneath a source of contamination. Ideally, adequate site investigation and installation of appropriate controls at a newly selected disposal site will prevent groundwater contamination and hence the need for groundwater controls. The reader is referred to other documents such as U.S. EPA 1982a and 1985 for more detailed information. Leachate Collection Disposal sites for dredged material must accommodate the inter- stitial 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. A leachate collection system is usually a network of perforated pipes placed under and around the perimeter of the site. The pipes drain to a sump or series of sumps from which the leachate may be withdrawn either by grav- ity, if topography allows, or by pumping. Spacing and sizing of the pipes depends on the allowable leachate head in the site and the rate at which water must be removed. Detail design of a collection system for leachate control is described in U.S. EPA, 1985.
229 Dewatering Two mechanisms exist for dewatering and densifying fine-grained dredged material using pervious underdrainage layers: gravity under- drainage or vacuum-assisted underdrainage. The gravity underdrainage technique consists of providing free drainage at the base of the dredged material. Downward flow of water from the dredged material into the underdrainage layer takes place by gravity. Vacuum-assisted underdrainage is similar to gravity underdrainage, but a partial vacuum is maintained in the underdrainage layer by vacuum pumping. Site Security Any time contaminated sediment is being dredged, transported, or disposed, site security for the protection of safety and health of the public and of workers must be addressed. In addition to the time when the site is being filled, site security must be considered for the time after disposal is completed. The extent of security measures will de- pend on the nature and concentration of contaminants, the migration pathways affected by the contaminants, the risk to humans and wildlife, and future use of the site. For unusual conditions, where justified by the risk presented by the nature and location of the site, a site- specific safety plan may be developed in accordance with guidance pre- sented in EM 1110-1-505 (U.S. Army COE, 1986~. Treatment of Dredged Material Slurries Solids Separation and Classification Processes The objective of separating solids from slurries is to attain two distinct waste streams: a substantially liquid waste stream that can be subsequently treated for removal of dissolved and fine suspended contaminants, and a concentrated slurry of solids and minimal liquid that can be dewatered and treated. The most appropriate solids separa- tion 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.
230 Solidification/Stabilization Solidification and stabilization are terms which are used to des- cribe treatment that accomplishes one or more of the following objec- tives (U.S. EPA, 1982b): improves waste handling or other physical characteristics of the waste, decreases the surface area across which transfer or loss of contained pollutants can occur, limits the solubili- ty or toxicity of hazardous waste constituents. Methods involving combinations of solidification and stabilization techniques are often used (U.S. EPA, 1982b; Cullinane and Jones, 1985~. Thermal Destruction Processes Thermal destruction is a treatment method that uses high tempera- ture oxidation under controlled conditions to degrade a substance into products that generally include gases, vapors, and ash. The most common incineration technologies applicable to the treatment of dredged material slurries include rotary kiln, fluidized bed, and multiple hearth. Because of the cost of incineration and the extremely low fuel value of most dredged material slurries, it is doubtful that thermal destruction technologies would ever be an economically viable option for treating dredged material slurries. However, projects involving small volumes of highly contaminated material may be candidates for application of thermal destruction technologies. Treatment of Dredged Material Solids Dredged material solids are those solid materials remaining after initial or final dewatering of the dredged material slurry. Treatment of the dredged material solids can be accomplished before or after placement in a disposal area. Conceptually, dredged material solids can be treated with 8 variety of technologies. Among these are inciner- ation, solidification/stabilization, extraction, immobilization, degra- dation, attenuation, and reduction of volatilization. Incineration, although a demonstrated technology for organics destruction is believed to be far too costly for the treatment of contaminated dredged mate- rial. In addition, the technology has limited application for treating dredged material solids contaminated with heavy metals. Solidifica- tion/stabilization technologies have been demonstrated at the field scale for hazardous wastes and at the laboratory scale for dredged mate- rial. However, this technology has not been proven for the containment of organics or in the marine environment. The remaining technologies are in various stages of development for application to hazardous waste sites and, although they may have some potential for application to dredged material solids, are many years away from being demonstrated technologies.
231 Treatment of Site Waters A variety of physical, chemical, and biological processes have been developed for municipal and industrial water and waste treatment requirements. Many of these processes have potential in treating site waters generated by the disposal of contaminated dredged material at confined nearshore and upland disposal sites. However, few processes have actually been required or applied to dredged material disposal. Among the processes widely applied in confined disposal operations are plain sedimentation for solids and sediment-bound contaminant removal, and chemical clarification and filtration for enhanced removal of par- ticulate (suspended solids) and sorbed metals and organics. Use of activated carbon for removal of soluble organics has received some limited application to dredged material. Other processes not previous- ly applied to dredged material include organics oxidation, dissolved solids removal methods (e.g., distillation), and volatiles stripping. 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). bConcentrations based on capability of best-available treatment technology.
232 Reuse of Contaminated Dredged Material Reuse has been proposed as a potential alternative for long-term man- agement of contaminated dredged material. Reuse of contaminated dredged material serves at least two beneficial functions: continued use of con- fined sites located close to dredging areas and creation of a potential construction material resource. The concept of a reuse alternative may also incorporate beneficial uses of materials such as sand and gravel reclaimed by classification/separation processes. The development and evaluation of reuse alternatives is extremely site specific and will de- pend on several factors: physical and chemical characteristics of the mate- rial to be dredged, availability of temporary storage and/or treatment sites, and identification of long-term disposal sites or suitable bene- ficial uses. 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. Recently, concepts based on either the separation of contaminants from the dredged material slurry or chemically stabilizing the contaminants in the dredged material have also been pro- posed. Site Characteristics as a Control Technology A level of increased control or restriction can be achieved during dis- posal simply by taking advantage of the best features of the site, by con- sidering natural mixing processes, and by using conventional techniques and equipment to their best potential. At least six considerations can be identified that are important in evaluating the engineering acceptability of a proposed open-water disposal site: currents (velocity and structure), average water depths, salinity/temperature stratifications, bathyme try (bottom contours), dispersion and mixing, and navigation and positioning (location/distance, surface sea state, etc.~. Engineered Control Technologies Submerged Discharge The use of a submerged discharge or closed conduit of some type to place dredged material is a second level of restriction or control avail- able. In general, a conduit is used primarily to ensure more accurate placement of the material and to reduce the exit velocity during formation of the surge phase. A conduit extending from the surface to the bottom
233 will isolate the material from the water column during descent, reduce entrainment, and negate the effects of currents or stratifications. Sub- merged diffusers have been successfully field tested in the Netherlands at Rotterdam Harbor and as part of an equipment demonstration project at Calu- met Harbor, Illinois (Hayes et al., 1984~. The diffuser minimizes upper water column impacts, and especially improves placement accuracy, and con- trols sediment spreading, reducing benthic impacts. Some hopper dredges have pump-out capability by which material from the hoppers can be discharged like a conventional hydraulic pipeline dredge. In addition, some have further modifications that allow pumps to be reversed so that material can be pumped down through the dredge's ex- tended dragarms. Because of the expansion at the draghead, the result is similar to use of a diffuser section. Lateral Confinement at the Site An increased degree of positive control over the movement of the mate- rial placed at a site can be achieved by using lateral barriers to confine the disposed material. Such confinement can be accomplished by using depressions or contour irregularities existing at a site, by excavating such depressions, or by construction of subaqueous dikes. Lateral con- finement addresses the short-term benthic impact by ensuring accurate initial placement and attenuation of the spreading dredged material. It also addresses long-term benthic and water column impacts by providing an inherent degree of isolation from the aquatic environment, reducing the effects of convective currents, and increasing the ease and effectiveness of capping when used. Capping Capping is simply the addition of a layer of some type of material over the mass of dredged sediment at the disposal site to effect isolation from the environment. The long-term impacts associated-with soluble diffu- sion, convective transport, and bioturbation are reduced when a capping control measure is used. Physical stability of the disposal mass over time is also increased by capping, although short-term instability may be a concern if capping material is applied too rapidly over weak underlying dredged material. Phillips et al. (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. The general features of these concepts are shown in Figure 1. Dredged Material Treatment and Open-Water Disposal Restricted open-water disposal is necessitated by the presence of contaminants associated with the sediment. On a mass basis, these
DEPTH OF STORM WAVE INFLUENCE SOLUBLE CONVECTION DIFFUSION ~~ 'if, c UR ~ EN AS ~ RATION 3 FOOT CAP OF CLEAN SEDIMENTS SOLUBLE =: BOTTOM DIFFUSION CONVECTION DEEP WATER MOUND _ _ UPLAND WATER HIGH TIDE SURFACE LOW TIDE r T TORSO FEET BIOTURBATION ~ \ ~ ~ \ DEPTH OF I +6 FEET CAP ~ / \ STORM WAVE / DIKE \ INFLUENCE \ CONTAMINATED SEDIMENTS / 2(b) SHALLOW WATER CONF INED ~ \ · _ f =\ _ _ EXISTING BOTTOM UPLAND PR ECIPITATION VOLATILIZATION , I ~ ~ CAP (3~ FEET) o | \ GROUND F TRATI N SOLUBLE WATER ~ TIN IL O I i\ CONVECTION =1~ UNSATURATED~CONTA~INATED ¢1 ~ ~ PU - PING SATURATED SEDI ENTS SOLUBLE 3~ ~ 1 DlfFUS10 h ~ | , ~ SEEPAGE W O Aft- Z BOTTOIlII LEACHATE SEEPAGE NEAR SHORE DISPOSAL WATER SURFACE BOO FEET SOLUBLE DIFFUSION, ~ CONVECTION etOTURBATION EXISTING ~; ;3 FT. CAP OF CLEAN SEDIMENTS it a\ CONTAMINATED \ SEDIIVIENTS <a j S~OLUBLE ~D. WE NATURAL OR DIFFUSION. EXCAVATED CONVECTION DEPRESSION DEEP WATER CONFINED FIGURE 1 General concepts for restricted open-water disposal. DEPTH OF STORY WAVE INFLUENCE contaminants are a very small fraction of the total amount of dredged mate- rial. Recently, concepts based on the treatment of the dredged material followed by either unrestricted open-water disposal or open-water disposal with less stringent restrictions than would be applied to the untreated dredged material have been proposed. These concepts generally fall into three categories: separation of the contaminants from the dredged mate- rial, immobilization of the contaminants in the dredged material, or con- taminant destruction. Although treatment of the contaminated dredged material followed by unrestricted open-water disposal is an attractive concept, there have been no field-scale demonstrations. 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 dredg- ing and disposal of contaminated sediments is a relatively new concern,
235 practical methods are available for handling such materials in an environ- mentally sound manner. The current state of the art for handling contami- nated dredged materials is summarized below. 1. The short and long-term release of contaminants via various migra- tion pathways from dredged material disposal sites cannot be ignored. Several techniques for predicting releases through speci- fic pathways have been developed; however, the development of addi- tional techniques and more information is needed to assess environ- mental effects and the need for implementing control/ treatment design features. 2. Control/treatment technologies are available and have been proposed for use at dredged material disposal sites. Beyond removal of sus- pended sediment from disposal area overflow, few technologies have been demonstrated for control/treatment of contaminated dredged material. 3. Design procedures for site water treatment technologies at upland and nearshore disposal sites are available and proven. Nearshore sites that involve saline waters present unusual, but not insur- mountable, design problems. 4. A variety of site-control measures such as lining and capping have been developed for control of hazardous waste materials. Such control measures are not easily adaptable to conditions at a con- fined disposal site for dredged material. Placement of liners, particularly at nearshore sites, has not been sufficiently demon- strated. Dewatering of confined contaminated dredged material will require special equipment, treatment of site water, and a manage- ment plan for controlling contaminant release. 5. Procedures for designing restricted open-water disposal sites are not well developed. In particular, designs for submerged diffusers and downpipes for deep open-water sites have not been thoroughly developed and their implementation has not been documented. To date, the feasibility of implementing lateral confinement and cap- ping in deep water has not been demonstrated. Projects are pre- sently under design that will be used to demonstrate these technol- ogies. 6. The selection of an appropriate control/treatment alternative depends on both site (dredging and disposal) and sediment charac- teristics. Because of site specificity and lack of experience in applying the available control/treatment alternatives to dredged material, no single alternative will emerge as the best alterna- tive. 7. With the assurance of major cost increases, selection of control/ treatment alternatives for very highly contaminated dredged mater- ial could rely on technologies developed and being implemented for control of hazardous wastes, i.e., Resource Conservation and Recov- ery Act (RCRA) and Comprehensive Environmental Response, Compensa- tion, and Liability Act (CERCLA) programs. A variety of proven and demonstrated technologies for disposal of low-level contaminated dredged material is also readily available. 8. A recurring limitation is the evaluation of alternative technical
236 feasibility, environmental effectiveness, costs interactions. Tech- nical feasibility can only be addressed through the continued devel- opment and demonstration of new control/treatment technologies. The evaluation of environmental effectiveness will require analysis of the results obtained applying the proposed control/treatment technologies combined with the continued development of criteria against which the effectiveness of a control/treatment alternative can be evaluated. Procedures must be developed that enable planner or engineers to perform site-specific contaminant migration analy- sis. The costs of both the control/treatment alternatives and testing protocols are inadequately documented and are highly vari- able. Additional effort must be expended to refine the costs asbo- ciated with controlling contaminant migration from contaminated dredged material disposal sites, evaluate the potential for contami- nant migration, and assess the environmental impacts associated with contaminant migration. ACKNOWLEDGMENTS Funding for preparation of this paper was provided under the Dredging Operations Technical Support Program of the U.S. Army Corps of Engineers. Information and data presented in this paper were developed as part of the Puget Sound Dredged Disposal Analysis (PSDDA) segment of the Puget Sound Estuary Program sponsored by the U.S. Environmental Protection Agency, the Washington State Department of Ecology, and the Washington Department of Natural Resources. The lead agency for PSDDA was assigned to the U.S. Army Engineer District, Seattle. Permission to publish this information was granted by the Chief of Engineers. REFERENCES Barnard, W. D. 1978. Prediction and Control of Dredge Material Dispers ion Around Dredging and Open-Water Pipeline Disposal Operation. Technical Report DS-78-13. Vicksburg, Miss.: U.S. Army Engineer Waterways Experi- ment Station. Cullinane, M. J. and L. U. Jones. 1985. Technical Handbook for Stabiliza- tion/Solidification of Hazardous Waste. Cincinnati, Oh.: EPA Hazardous Waste Engineering Research Laboratory. Cullinane, M. J., D. E. Averett, R. A. Shafer, J. W. Male, C. L. Truitt, and M. R. Bradbury. 1986. Guidelines for selecting control and treat- ment options for contaminated dredged materials requiring restric- tions. Prepared for U.S. Army Engineer District, Seattle. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. Francingues, N. R., Jr., M. R. Palermo, C. R. Lee, and R. K. Peddicord. 1985. Management strategy for disposal of dredged material: Contami- nant testing and controls. Miscellaneous Paper D-85-1. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. Hayes, D. F., G. L. Raymond, and T. N. McLel~an. 1984. Sediment resuspen- sion from dredging activities. In Dredging and Dredged Material
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