For any given particle size distribution, the 

 concentration of total suspended matter will be proportional to 

 the measured rms voltage output of the receiver, when corrected 

 for depth. 



3 . 3 Results 



The plume studies were conducted at disposal events 

 when the towed scow was unloaded by opening the bottom doors. As 

 soon as disposal was complete and the scow was underway, the 

 research vessel, with navigational control and the Acoustic 

 Remote Sensing System aboard, began executing patterns of 

 parallel tracks to determine the boundaries of the plume. After 

 the motion of the plume was determined, the ship's track was 

 modified to continually encompass the boundaries. Figure 3-1 

 presents an actual ship's track followed during the first two 

 hours of the plume study on 24 May 1985. 



During each study, water samples were collected with 

 Niskin water samplers as the acoustic sensing transducer passed 

 through the plume. Sampling depths were determined from the 

 acoustic results of a pass through the area immediately prior to 

 sampling. The samples were analyzed for total suspended sediment 

 (mg/1) and used to calibrate the output voltages from the 

 acoustic record. 



21 May 198 5 - Plume Study 



The plume study began at 0920 EST as the scow began the 

 disposal operation. One scow of 1575 cu yds (1205 m-^) was dumped 

 approximately 2 00 m east of the disposal buoy. The study was 

 continued until 1051 EST. Low tide occurred at 0547 EST and high 

 tide at 1157 EST. Flood tide was in progress during the survey, 

 providing a N-NE flov/. Figure 3-2 presents the results of the 

 plume survey. 



The area of heavy concentrations (averaging about 1000 

 mg/1, Fig. 3-3) occurred below a depth of 50m and did not extend 

 far beyond the area directly beneath the disposal location. 

 Within 15 minutes of the completion of the disposal operation, 

 concentrations averaging approximately 40 mg/l (Fig. 3-3) 

 occurred from a depth of 2 m to the bottom and extended 

 approximately 3 00 m from the initial location in the N-NE 

 quadrant. Within forty minutes of disposal, suspended sediment 

 concentrations were averaging less than 10 mg/1 (Fig. 3-3) at 

 depths below 35 m and extended less than 500 m from the disposal 

 point, still within the boundaries of the designated disposal 

 site. Further surveying detected no significant levels of 

 suspended sediment above background concentrations of 3-5 mg/1. 



