(3) If a layer of very soft mud overlies firmer substrata on the bottom, remove this 

 soft material first with a "dustpan" suction head or some other device that screens the local 

 dredging area from the surrounding water, discharging the slurry into a series of clarifying 

 ponds. After as much mud as possible has been removed in this manner, proceed with the 

 usual cutterhead operation as described earUer. 



(4) If alternate good and bad strata are encountered, control the depth of each 

 successive cut and dispose of each layer of material in a manner best suited to that material. 

 This procedure is usually too expensive for most projects, but it may be the only solution if 

 the environmental requirements are sufficiently demanding. 



(5) Dike off the area to be dredged, unwater it, and excavate with dryland equipment. 

 Allow the excavated basin to refill slowly so as not to wash the dike material into it, and 

 then remove the dike progressively with a dragline working along the crown. 



(6) Where a major concern is that basin waters clouded by dredging operations will 

 diffuse into the main water body, screen off the area where the dredge is working with a 

 vertical skirt of flexible impermeable plastic material. The skirt is suspended from a plastic 

 pipe floating on the surface, and the lower end is held on the bottom by rocks or sand bags 

 placed by divers. When dredging begins, enough water will be drawn in over the top of the 

 plastic pipe to replace the water used by the dredge. After dredging has been completed and 

 the basin waters have clarified, the screen may be removed. 



(7) Where dredge fill is to be pumped onto a beach or into the water adjacent to a 

 beach, the disposal site may be screened off (described earlier) to prevent the escape of 

 suspended fines. However, once the screen is removed, wave turbulence may again stir the 

 fine material into suspension. A better solution is first to bulldoze the beach sand into a 

 dike that is far enough offshore to contain all the dredged material between it and the 

 shoreline. A separate basin may be needed to receive and store effluent from the disposal 

 site until it has clarified sufficiently. If desired, the top of the resulting fill may be left a 

 foot or two below the adjacent ground surface and covered with beach sand or other 

 indigenous material. 



(8) If the material is dredged from a basin adjacent to the ocean or a deep sound, it 

 may be possible to obtain permission to carry the dredge slurry via floating pipeline offshore 

 to a disposal area deep enough to be undisturbed by surface waves. If the material contains a 

 high percentage of fines or colloids, however, the danger of widespread diffusion of clouded 

 waters may prevent issuance of such a permit. 



(9) A new Italian product called the Hydocy clone, when installed at the discharge 

 end of dredge pipe, is capable of separating the heavier grains from the lighter silts, clays, 

 and colloids by vortex action. Although not tested extensively in this country, it appears to 

 be capable of extracting the good material from the undesirable fraction for use in fills. If 

 not too costly to operate, this device may offer a solution to those disposal problems that 

 require selective placement of certain fractions of the dredged material. 



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