22 May 1985 - Plume Study 



The second plume study began at 0645 as one scow of 

 1900 cu yds (1450 m-^) completed disposal operations approximately 

 150 meters south of the disposal buoy (Fig. 3-4) . With low tide 

 occurring at 0623 EST, flood tide was just beginning to develop. 

 Again, the heavy concentrations of suspended material, averaging 

 greater than 1000 mg/1 (Fig. 3-5) , occurred directly beneath the 

 disposal location throughout the water column. Within forty 

 minutes of disposal, concentrations averaging greater than 25 

 mg/1 (Fig, 3-5) occurred below 30 m to the bottom and extended 

 approximately 3 50 meters to the north. One hundred minutes after 

 disposal, concentrations averaging only 12 mg/1 (Fig. 3-5) 

 occurred at depths below 50 m and extended less than 500 meters 

 north-northeast of the disposal point, still within the disposal 

 site. 



24 May 1985 - Plume Study 



The third plume study began at 1025 EST as two scows 

 (tandem load) containing a total of 3640 cu yds (2780 m^ ) 

 completed disposal operations within 50m SE of the disposal buoy 

 (Fig. 3-6) . With low tide occurring at 0744 EST and high tide at 

 1355 EST, the flood tide was fully in progress, producing maximun 

 tidal current velocities to the N-NE . Heavy concentrations 

 averaging about 1400 mg/1 of suspended material (Fig. 3-7) were 

 detected directly beneath the disposal location throughout the 

 water column. Within one hour of disposal, concentrations of 

 suspended material of 110 mg/1 (Fig. 3-7) occurred from 20 m to 

 the bottom and were centered at a point approximately 7 00 meters 

 north of the disposal location. After more than two hours, low 

 concentrations of suspended material, averaging about 13 mg/1 

 (Fig. 3-7), occurred below 50 m and were measured within a 400 m 

 radius around a point 1700 meters N-NE of the disposal location, 

 or as much as 1000 meters beyond the northern boundary of the 

 disposal site. Background levels of 3-5 mg/1 were measured at 

 the disposal buoy just before this survey was conducted and just 

 outside of the disposal site when no disposal operations were 

 being conducted. 



3.4 Discussion 



Of the three plume studies conducted at the Rockland 

 disposal area during the period 21 to 24 May 1985, the first two, 

 although occurring on the flood tide, did not detect any elevated 

 concentrations of suspended material above background levels (3-5 

 mg/1) outside of the designated disposal area. The survey 

 conducted on 24 May 1985 resulted in measurable concentrations 

 (averaging 13 mg/1) of suspended material as far north as 1000 

 meters beyond the disposal site boundary. 



10 



