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DEVELOPMENTS IN EQUIPMENT DESIGNED FOR HANDLING CONTAMINATED SEDIMENTS John B. Herbich Texas A&M University ABSTRACT Conventional dredging equipment typically handles large volumes of material in maintaining or deepening navigational channels. Such equipment may be operated in a modified pro- cedure to handle relatively small volumes of contaminated material. However, in some cases, it may be more appropri- ate to use special purpose dredges (either specially devel- oped, or adapted), which are more suitable for handling con- taminated sediments. Several special purpose dredges are described and their capabilities discussed. INTRODUCTION The selection of proper dredging equipment for any project is impor- tant to achieve an efficient operation (Andrassy and Herbich, 1988~. In the case of contaminated sediments, it is even more important since any additional contamination generated during dredging must be avoided. Selection depends on a number of factors: 1. characteristics of sediments, 2. quantity of sediments to be removed, 3. degree of contamination, 4. toxicity of contaminants, 5. location, 6. environmental conditions etc.), 7. distance to the disposal site, 8. type of disposal, and 9. availability of particular equipment location, environmental conditions at the site (waves, currents, tides, There are several types of dredges for conventional operations designed principally for moving large volumes of material efficiently. Conventional equipment operated in a modified procedure can be effec- tive, as reported by Hayes et al. (1988~; however, in some cases it may be more appropriate to use special purpose dredges (either developed or adapted) suitable for handling contaminated sediments. 239

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category: 3. 240 There are several dredges that may be placed in a special purpose 1. mechanical--enclosed clamshell; 2. mechanical-hydraulic--Mud Cat, remotely controlled Mud Cat, and Clean-up system; hydraulic--Refresher, waterless, matchbox, and wide sweeper, cutterless dredge; and 4. pneumatic--Pneuma and Dozer. MECHANICAL DREDGES Enclosed Clamshell The Japanese have developed a watertight clamshell for use with grab bucket dredges. An evaluation of the watertight bucket was made by the U.S. Army Engineer Waterways Experiment Station in 1982 (Figure 11. Experiments conducted at the Jacksonville District indicated that the watertight bucket significantly reduced water column turbidity and did not reduce production. Figure 2 shows the benefit of using an enclosed bucket. Operation of the dredge can be modified slightly to reduce sediment resuspension by slowing the raising and lowering of the bucket through the water column. It must be noted that this operation modification reduces the production rate of the dredge, and generally high unit costs are associ- ated with this type of mechanical dredging. 1 Comer ~ Cover ~ .She1 1 FIGURE 1 Open and closed positions of the watertight clamshell bucket. SOURCE: Hayes et al., 1984.

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24i 300 - Cat 200 o Oh By AL 1 00 Oh O \ 0 200 Open Clamshell ___ Enclosed Clamshell \ - _~ I cram I ~ = I 400 600 800 DISTANCE FROM DREDGE, FT FIGURE 2 Resuspended sediment levels from open and enclosed clamshell dredge operations in the St. John's River. SOURCE: Hayes, 1986. MECHANICAL HYDRAULIC DREDGES Mud Cat The Mud Cat has a horizontal Butterhead equipped with knives and spiral augers that cut the material and move it laterally toward the center of the augers where it is picked up by the suction (Figure 3~. The dredge can remove sediments in a 2.6-m width and in water depths up to 4.9 m. The dredge operates on anchor cables, and the manufacturer claims that it leaves the bottom of the dredged area flat and free of windrows characteristic of typical cutterhead and hopper dredge operations. l '_' I',~n ~ '_ al _ - - FIGURE 3 the Mud Cat--notice that the cover is lifted to show two augers .

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242 By covering the cutter-auger combination with a retractable mud shield the amount of turbidity generated by Mud Cat's operation can be minimized. Remotely Controlled Mud Cat A remotely controlled unit has been developed in which the control cab is located on land and is remotely connected to the Mud Cat by an umbilical cord. This allows dredging of hazardous or toxic materials. The remote control provides the shore-based dredge master with a vari- able traversing winch control, a variable auger control, a variable dredge pump speed control, and a manually controlled emergency shut down . The usual instrumentation is also displayed in the control cab and visual alarms are provided. Clean-up System To reduce or minimize resuspension of the sediment, Toa Harbor Works, Japan has developed a unique Clean-up system for dredging highly contaminated sediment (Herbich and Brahme, 1988; Sato, 19849. The Clean-up head consists of a shielded auger that collects sediment as the dredge swings back and forth and guides it toward the suction of a submerged centrifugal pump (Figure 4~. To minimize sediment resuspen- sion, the auger is shielded and a moveable wing covers the sediment as it is being collected by the auger. Sonar devices indicate the topo- graphy of the bottom. An underwater television camera also indicates the amount of material being resuspended during a particular opera- tion. Figure 5 shows details of a shielded auger (Sato, 1984~. Fairly large volumes (2.2 million ~ up to 1981) have been excavated by Clean-up dredges in soft muds and sand containing various contaminants such as mercury, cadmium, PCBs, oily and organic substances. Table 1 summarizes the specifications of Clean-up dredges. Pro plump ~ ~ Crow Of SWIM ,':1` , CC~HLaL - CD 1 - WINC: Ji - HER ~ ~ ~ ~ BOr~ SEDI~t~ ~////~//////////~/~//D/~///~//~ FIGURE 4 The Clean-up system. SOURCE: Sato, 1984.

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243 FIGURE 5 Clean-up shielded auger head. SOURCE: Sato, 1984. ~l~ Performance of various Clean-up dredges between 1973 and 1981 is summarized in Appendix A. HYDRAULIC SUCTION DREDGES Refresher The Refresher dredge was developed purposely for removal of contami- nated materials by a Penta-Ocean Construction Company, Ltd. (Shinsha, 1988~. The dredge material is confined by a specially designed flex- ible enclosure that completely covers the cutter, preventing escape of sediments to the outside of the immediate dredging area (Figure 6~. The working open section is always on the swing side of the cutter- head. A gas removal system is also installed and can be activated as needed to prevent gas moving up the section pipe. The flexible enclo- sure of the Butterhead is automatically adjusted to bottom contours. -~,~ SIDEVIEW OF LADDER FIGURE 6 Refresher dredge. SOURCE: After Shinsha, 1988. FRONT VIEW

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244 General Specif ications The Refresher dredge is equipped with the main pump and an addi- tional pump on the ladder to provide a high level of production. Auto- matic valves in the suction pipe prevent sediment-water mixture from flowing back in case of power failure (Figure 7~. Refresher No. 3 and Mini-Refresher Tokyo Maru specifications are given in Table 2. Pump specifications for both the ladder pump and the main pump are given in Table 3. Waterless Dredge Waterless Dredging Company developed a dredging system in which the cutter and centrifugal pump are enclosed within a half-cylindrical shroud. By forcing the Butterhead into the material, the cutting blades remove the sediment near the front of the cutterhead with little entrainment of water. According to the manufacturer, this waterless system is capable of pumping slurry with a solids content of 30 to 50 percent by weight with little generation of turbidity. The dredge pipeline sizes range from 15 to 30 cm. The waterless dredge development is relatively new and and experience with it is quite limited. PIPELINE ANT l-BACK F LOW ~ OUTLET VALVE / , ~ r 7? / DIRECTIONAL \ /_ ~ =\ \ ON eBoAARDG'NEG ~ ~` _ \ ON BOARD \ \ NON-POLLUTING SYSTEM MONITORING SOUND MONITOR FOR DREDGING THICKNESS `~ 11 I MONITOR MUD PUMP \ \ I RECORDER DIRECTIONAL ~ \ \ VALVE WINCH I IVI~^L \ TV E ~4 LADDER PUMP \ '< SUCTION PIPE / \ MUD-MEASURING FIGURE 7 Description of a Refresher dredge. SOURCE: Shinsha, 1988. DIRECTIONA DE VALVE ~ \ \ / ANTI-BACKFLOW INTAKE VALVE TV CAMERA HYDRAULIC CYLINDER MOVABL ~ COVER ~~\ - HEAD ~ ~ CTOR . . . . . . . . .

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246 TABLE 2 General Specifications for the Refresher Dredge. GENERAL SPECIFICATIONS MINI REFRESHER REFRESHER NO. 3 TOKYO MARU . SHIP DIMENSIONS ( LxBxD) DISPLACED TONNAGE DISPLACED DEPTH DISCHARGE DISTANCE 1 OR EDG I NG CAPAC ITY _ MAXIMUM OR EDG ING DEPTH . 45.60x13.50x3.30 m 1,200 t 2.20 m BARG E ~3.000m LOADING 150 ~ 400m3/h . 20 m SOURCE: After Shinsha, 1988. TOKYO MARU 17.00x6.40x1.35 m 80 t 0.80 m ARGE ~ 500 m LOAD I NG 50 ~120m3/h 7.5 m _ Matchbox Dredge TABLE 3 Pump Specifications for Refresher No. 3 and Mini- Refresher Tokyo Maru Dredges. . CL G m Z 0 . _ . MODEL _ RATED HORSEPOWER PUMPING CAPAC ITY PUMPING HEIGHT MODEL RATED HORSEPOWE R PUMPING CAPAC ITY PUMPING HEIGHT PUMP SPECIFICATIONS REFRESHER NO. 3 CENTRIFUGAL TYPE 150PS _ . 800 ~ 2,000 m3/h . . 10 ~ 20m . CENTR I FUGAL TYPE I. 1,800PS it, 800 ~ 2,000 math l 20 ~50 SOURCE: After Shinsha, 1988. A special suction head was developed by a dredging contractor in the Netherlands to replace the traditional Butterhead (d 'Angremond et al., 1984~. The main design points are as follows (Figure 8~: MINI REFRESHER TnKyo MARU . _ _ 1 CENTRIFUGAL TYPE _ 100PS 250 ~ 600 m3/h 11 - 1 5 m CENTRIFUGAL TYPE 1 50PS 250 ~ 600 m3/h 10~ 35m 1. A large plate covers the top of the dredge head to avoid inflow of water and escape of gas bubbles. 2. Adjustable angle between the drag head and the ladder to create an optimum position of the drag head independent of the dredging depth. 3. There are openings on both sides of the drag head to improve dredging efficiency. During swinging action the leeward side is closed to prevent water inflow. 4. Dimensions of the head must be carefully designed for the average flow rate and swing rate (Figure 9~. A diffuser may be installed at the submerged end of the discharge pipe to reduce the dispersion of fine sediment in the water column (d'Angre- mond et al., 1984; Neal et al., 1978~. By its gradually widening cross section, the flow could decelerate to an acceptable velocity to reduce turbulence. Outflow velocities are designed to be between 0.2 to 0.3 m/see (Figure 10~; however, it is unlikely that contaminated material would be discharged in open water. A possible application may be to employ such a diffuser in a containment area. A degassing system is also installed to prevent or reduce the amount of gas moving up the suction pipe.

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247 / an- ~.- . ;,_ At, - _- ~ ~ ;. i' I 61 " ~ 'I 8 1 laid ~ LULL O~ DutL-h d~s.~-1 OWL; su"-tic`~ 8~ p To acme sedun~~nts-~it8'~ a snu~n of rcsuspens~r~. Suitable For unnail v~"s~u;:S o'- ;lea'~u,? jobs lo fu``d). klun~ts Faust ~ ~. ~~ ;.~`s~s~n~,re~t~ ~t,8 ,~ free 8l'`;~8,,~r ~8;t.`t . ~LL-L-bJ ~~ Dorm b4WEb D`lt.1l built.~..t Al ELF all; t;`,- ;~`,lt-~.~i aquatic d`~pc`:;al(;appin`~) 1~ this luff ot dis~>~al the -"b..~c,~.1 . ffusu all1 s a ~l~.t placc,~l~rit of poll~lt~ ;.1~i~~s Tail ~ In pit Diffuser is theft Used to plum- ~ `.~.' 1~;' ~ cap of ~lca' nix ~ Trill to ~sscr`tiall`~ scat us taut polt``ta`~ts . o - - L4, Ail FIGURE 8 Dutch Matchbox dredge. SOURCE: After IJ. S . Army Engineer District, Chicago . i' FIGURE 9 Schematic of Matchbox suction head. SOURCE: After d'Angremond et al ., 1984 . {_,~

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248 r l 1 Io Ant 1~:''r '-, he :2~ 22QO . .1 FIGURE 10 Schematic of diffuser (all dimensions are in millimeters). SOURCE: d'Angremond et al., 1984. TABLE 4 Plume Area for 10-mg/liter Contour for the Cutterhead, Clamshell, and Matchbox Dredges. Depth percent Cutterhead Clamshell Matchbox acres acres acres 50 80 95 SOURCE: Hayes et al., 1988. 0 1.7 0 0 1.8 0 0 --- 0.4 1.2 3.5 2.95 A direct comparison between a Matchbox suction head and a conven- tional butterhead was made by the Waterways Experiment Station in Calumet Harbor (Hayes et al., 1988~. The Matchbox was specifically designed to be fitted on the ladder of the U.S. Army Corps of Engi- neers' dredge Dubuque . The Calumet Harbor demonstration indicated that the clamshell dredge generated the largest suspended sediment plume affecting the entire water column. The butterhead slightly outperformed the Matchbox dredge as shown in Table 4. Wide Sweeper Cutterless Dredge Wide Sweeper No. 6 hydraulic suction dredge does not have a cutter and is principally employed for removal of contaminated materials without resuspending the sediment particles (Shinsha, 1988~. The main

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249 features of Wide Sweeper are that 1. bottom sediments can be removed essentially without resuspen- sion of particles, 2. acoustic sensors determine the characteristics of sediment to be dredged, 3. the suction head can follow seabed configuration to some ex- tent, or can be kept in a horizontal position, 4. turbidity generated is monitored by a television camera, and 5 the dredge is equipped with a ladder pump and a main pump. General specifications are shown in Table 5. Figure 11 shows the general arrangement of the suction head. TABLE 5 General Specifications of Wide Sweeper No. 6 Name of Hull Ship Type Dimensions Main Pump Ladder Pump Including "Wide Diesel Length: 58.2m 3,200 PS, 950 PS, Single- Sludge Sweeper Electric Breadth: 14m Single-stage, stage. Single- observation No. 6" Depth: 3.7m Single-suction. Suction. system Draft: 2.3m Centrifuge type Centrifuge type Operation SOURCE: Shinsha, 1988. control system T 0~ I'm ~~F .: ~ ~ _ C' Direction of swing FIGURE 11 General arrangement of the suction head on dredge Wide Sweeper No. 6. SOURCE: Shinsha, 1988.

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251 is applied during the cylinder- filling stage when the hydrostatic pres - sure is not sufficient to rapidly fill the cylinders. The pump is usually mounted at the end of a ladder and equipped with special suc- tion heads and cutter units depending on the type of material being dredged. The conditions around the dredging system, such as thickness, bottom elevation after dredging, and amount of resuspension, are moni- tored by high-frequency acoustic sensors and an underwater television camera. A large Dozer pump has a dredging capacity ranging from 300 to 500 m /fur. During one dredging operation, suspended solids levels within 3 m of the dredging head were all within background concentra- tions of less than 6 mg/liter. Figure 13 is a sketch of the oozer dredge; Figure 14 describes the ooze dredging system DREX, consisting of a suction mouth and a device that permits a back and forth movement of the suction mouth. This modified system is said to increase solids concentration up to 60 percent. , I hi FIGURE 13 Outline of oozer dredge ~ dimens ions 4 ooze collecting tan are In m~lllmeters). SOURCE: Herbich and Brahme, ' clear 1988 . FIGURE 14 Sketch of oozer dredging system. SOURCE: Herbich and Brahme, 1988. s'~ctlon couth 2 pump 3 "gnctic [low-meter 5 drt~ring DC motor 6 test soil 8 carriage 9 rail \\\ \\ ~ adds t~rdrsut is aoto' tr'~-' 1' ~ move ~ u

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252 The main features of the oozer dredge are as follows: 1. The dredge can effectively remove contaminated sediments from a maximum depth of 18 m. . Since the swing speed can be adjusted from 0 to 20 m/min, the dredge can be effective in removing suspended sediments. . Five acoustic sediment sensors can measure the bearing pressure of sediment to be removed and the thickness of various sediment layers. 4. Underwater television cameras monitor the presence of turbidity near the suction intake. Toxic gases released during dredging pass through gas scrubbers to remove toxic content before gases are released to the atmosphere. 6. A screen is located at the suction mouth to prevent large ob- jects from entering. Double-suction valves and electrically controlled check valves provide secondary protection. 7. Dozer dredges can, under ideal conditions, pump sediments at in situ density. 8. Different cutters and suction heads are available for dredging sediments ranging from clay to sand. 5. Specifications for oozer dredge Taian Mare are given in Table 6 and her performance between 1974 and 1980 is listed in Table 7. RESUSPENSION LEVELS OF SEDIMENT FOR SPECIAL PURPOSE DREDGES The special purpose dredges that appear to have the most potential in limiting resuspension are shown in Table 8. SUGARY Conventional dredging equipment may be operated in a modified procedure to handle contaminated material. A decision about whether to use modified equipment should be made on economic grounds. Several special purpose dredges were developed, principally overseas, and have been successfully employed in removal of contaminated sediments. Capabilities of mechanical, mechanical-hydraulic, and hydraulic suction dredges are summarized in Tables 9, 10, and 11. Capabilities of pneumatic dredges are shown in Table 12. ACKNOWLEDGMENTS This symposium paper was reviewed by Mr. Charles C. Calhoun, Jr., Assistant Chief, Coastal Engineering Research Center (CERC), U.S. Army Engineer Waterways Experiment Station, and by Dr. Cliff L. Truitt, CERC. Their comments were appreciated.

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253 TABLE 6 Specifications of Dozer Dredge Taian Maru Hull: Engine: Winch Overall length Breadth ...... Depth . Draft ... Dredging depth ...~- m 12 m 3 m 2.2 m 17 m 1 Type: Cylindrical twin-barrel, negative pressure suction and positive pressure discharge. Dredging capacities (Pressure intensity: 7kg/cm2) Discharge Pumping Density distance production (%) (m) . (m /h) 60 100 580 350 60 500 500 300 60 1,000 420 250 Discharge pipe: 450 A Air compressors ......... Dredging production (m /h) 3 Type: Screw rotary system 2 Capacity: 34.2 m /min x 7 kg/cm x 1,770 r.p.m. Driving generator: 190 KW x AC 440 V x 60 Hz x 4P Vacuum pump a~ em 1 Type: Roots system 3 Capacity: -400 mmHg x 44.8 m /min Driving generator: 110 KW x AC 440 V x 60 Hz x 6P Main generator Type: Horizontal drip -proof rest self - excite Capacity: 450 KVA x 3 0 x 60 Hz x 445 V x 8P Continuous output: 5 30 ps x 900 r . p . m . Ladder winch: 12T x 24 m/min x 75 KW x 6P 1 Swing winch: 15T x 0-12 m/min x 70 KW 1 Spud winch: 12T x 17 m/min x 50 KW x 6P 1

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254 TABLE 7 Performance of Dozer Dredge Taian Maru Undisturbed Volume of Construction Soil Moisture Deleterious Dredging Place Period Condition Content (X) Material Soil (m ) Treatment Iyo-Mishima April-May Sandy silt 144 Pulpwood 30,000 Direct discharge Ehime Pref. 1974 length 356 m Natural sedimentation No treatment of return flow water ~ -Do- July 1974 -Do- 400 - 800 -Do- 27,000 Direct discharge length 356 m 1000 m Natural sedimentation No treatment of return flow water Chiba Port January- June Silt 300 - 400 Be, Pb 40,800 Transport with barge Chiba Pref. 1975 Secondary pumping ! with centrifugal pump Natural s:.dimont~1~.i On Takasa8 Port Hyogo Pref. August - December 1975 Sandy silt 150 - 200 PCB 224,816 Direct discharge length 300-1,20G m Solidity Removal of deleterious material Direct discharge length 460 m Natural sedimentation Removal of deleterious _ material Direct discharge length 300-800 m Natural sedimentation Removal of deleterious mater) at Sakaide Port July- Silt 90 - 100 He Kagawa Prep. September 1975 14,000 Iwakunt Port Yamaguchi Pref. January- February 1976 Sandy silt 100 - 200 Pulpwood 31,Q00 Tokuyama Port July- Yamaguchi December Pref. 1976 Sandy silt SO ~ 300 Be 128, 16Q Transport with barge Natural sedimentation Removal of deleterious material Transport with barge Natural sedimentation Removal of.deleterious material Discharge with booster pump Natural sedimentation Removal of deleterious __ material -Do- Dec~mbor 1976- Sandy silt March 1877 SO - 300 B., C6814 82,000 Yokkaichi Port Mie Pref. April 1977- Sandy silt February 1978 280 -500 He 655,000 Mizush~ma July- Silt 40 - 100 C6H14 92,800 Transport with barge Port September Natural sedimentation Okayama Pref. 1978 Removal of deleterious material Osaka Bay March 1980 Silt 150 - 250 Organics 6,000 Pilot Corks HYORO Pref. - --- -- Yokkichi Port June 1980 Silt lS0 -Do- 44.000 Excavation of ses bed

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255 TABLE 8 Resuspended Sediments by Special Purpose Dredges Dredge Reported suspended sediment concentrationsa Pneuma pump 48 mg/liter, 3 ft above bottom 4 mg/liter, 23 ft above bottom (16 ft in front of pump) Clean-up system 1.1 to 7.0 mg/liter above suction 1.7 to 3.5 mg/liter at surface Dozer pump Background level (6 mg/liter), 10 ft from head Refresher system 4 to 23 mg/liter, 10 ft from head NOTES: aSuspended solids concentrations were adjusted for background concentrations. SOURCE: Herbich and Brahme, 1988. TABLE 9 Summary Table of Mechanical Dredges Depth Resuspens ion Type Production limitation of sediment Comments Open clam- shell bucket Low Watertight Low clamshell bucket 30-40 ft High 30-40 ft Low Experiments conducted in the St. John' s Rearer

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256 TABLE 10 Summary Table of Mechanical-Hydraulic Dredges Depth Resuspension Type Production limitation of sediment Comments Mud Cat Moderate 15 ft Low to Extensively moderate used Remotely Low 15 ft Low to New develop- controlled moderate ment Mud Cat Clean-up Moderate 70 ft Low to Extensively system moderate used in Japan TABLE 11 Summary Table of Hydraulic Suction Dredges Depth Resuspension Type Production limitation of sediment Comments Refresher Moderate 60-115 ft Low Extensively to high used in Japan Waterless Moderate Low Limited experience Moderate 85 ft Low Experiments to high conducted at Calumet Harbor Wide Moderate 100 ft Low Used in Japan Sweeper TABLE 12 Summary Table of Pneumatic Pumps (Dredges) Depth Resuspension Type Production limitation of sediment Comments Pneumatic Low to +100 ft Low moderate Evaluated by COE Waterways Experi ment Station Dozer Moderate 59 ft Low Used extensively to high in Japan

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257 REFERENCES Andrassy, C., and J. B. Herbich. 1988. Generation of suspended sediment at the Butterhead. The Dock and Harbour Authority 68~797~:207-216. d'Angremond, K., A. J. de Jong, C. P. de Waard. 1984. Dredging of pol- luted sediment in the first petroleum harbor, Rotterdam. Proc. 3rd U.S.-the Netherlands meeting on Dredging and Related Technology. Fort Belvoir, Va.: U.S. Army Engineer Water Resources Support Center. Hayes, D. F., G. L. Raymond, and T. N. McLelland. 1984. Sediment resus- pension from dredging activities. Dredging '84. Clearwater, Fla.: American Society of Civil Engineers. Hayes, D. F. 1986. Guide to selecting a dredge for minimizing resuspen- sion of sediment. Environmental Effects of Dredging, Technical Notes, EEDP-09-1. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. Hayes, D. F., T. N. McLelland, and C. L. Truitt. 1988. Demonstration of innovative and conventional dredging equipment at Calumet Har- bor, Illinois. MP EL-88-1. U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. Herbich, J. B. 1975. Coastal and Deep Ocean Dredging. Houston, Tex.: Gulf Publishing Company. Herbich, J. B. and S. B. Brahme. 1988. A Literature Review and Techni- cal Evaluation of Sediment Resuspension During Dredging. TR-88 (in press). Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station. McLellan, T. N., R. N. Davis, and D. F. Hayes. 1988. Field studies of sediment resuspension characteristics of selected dredges. TR HL-88-(in press). Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station. Neal, R. W., G. Henry, and S. H. Greene. 1978. Evaluation of the Sub- merged Discharge of Dredged Material Slurry During Pipeline Dredge Operations. TR D-78-44. Vicksburg, Miss.: U.S. Army Engineer Water- ways Experiment Station. Richardson, T. W., J. E. Hite, R. A. Shafer, and J. D. Ethridge. 1982. Pumping Performance and Turbidity Generation of Model 600/100 Pneuma Pump. TR HL-82-8. Vicksburg, Miss.: U.S. Army Engineer Water- ways Experiment Station. Sato, E. 1984. Bottom sediment dredge CLEAN UP. Principles and results, management of bottom sediments containing toxic substances. Proc. 8th U.S./Japan Experts Meeting, T. R. Patin, ed. Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station. Pp. 403-418. Shinsha, H. 1988. Personal Communication. Refresher Dredge, Technical and Research Institute, Penta-Ocean Construction Company, Ltd., Japan. Yamaguchi, A. 1988. Personal Communication. Kumamoto Prefectural Govern- ment, Kwmamoto City, Japan.

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