SECTION IV, DISCUSSION 



1. Dispersion and Movement of the Waste Materials 



The dispersion of waste materials, following disposal at the dumping 

 grounds, is difficult to study because of the variable and complex hydro- 

 graphic conditions prevailing in the Bight which were discussed earlier. 

 A number of hydrographic investigations of the Bight have been made. 

 Limited studies on rates and patterns of dispersion of waste materials 

 dvunped in the Bight have been conducted by Ketchum and Ford (1948) , Red- 

 field and Walford (1951), Beyer (1955), Saila (1968), Buelow (1968), and 

 more recently, by the SHL (1972) . None of these investigations has been 

 synoptic or has considered adequately the total circulation effects on 

 waste dispersion. 



Settling of waste material depends on many physical factors. Although 

 most of the waste settles to the bottom rapidly, a large percentage of the 

 finer material remains suspended in the water column. Saila (1968), in 

 his studies of dredged sediment dumping in Rhode Island Sound, found that 

 two slicks of fine waste material tend to form within an hour of dumping. 

 One slick was at the surface and another at roughly mid-depth, at the 

 density gradient of the thermocline. A thermocline, however, is not a 

 permanent feature of the waters of the Bight. During winter, the thermo- 

 cline is absent and the waters become vertically homogeneous. In winter, 

 therefore, only one slick of very fine material may be observed in the 

 surface waters. Depending on circulation and turbulence, this finer 

 waste material may stay in suspension for a long time and may be trans- 

 ported from the disposal area. 



Mixing and dispersion of the waste materials in the upper layer of the 

 ocean (0-50 feet in thickness) is affected by wind driven and tidal currents , 

 Also, fine material that has settled to the bottom may go into suspension 

 as a result of storm waves or strong bottom currents, and move laterally. 

 Knowledge of surface and bottom circulation is essential in assessing the 

 dispersion and movement of the waste materials following disposal or 

 settling. 



The SHL attempted to determine surface and circulation of waters in the 

 general areas of the dumping grounds. To accomplish this objective, SHL 

 utilized current meters and surface and seabed drifters. Unfortunately 

 only three of the four current meters that were used in this investigation 

 by the SHL gave satisfactory records, and then for only limited periods. 



The use of drifters is the most economical method of studying qualita- 

 tively net water-mass movements. It is assumed that the reaction of the 

 drifters to water movements closely approximates that of other small mov- 

 able objects at the surface and near the bottom. According to the SHL 

 report, drifter behavior provides the best estimate of the effect of water 

 movement on the transport and dispersal of waste materials. This assump- 



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