19 



deposited at the flanks of the mounds in layers too thin to detect acoustically. Applying 

 Tavolaro's maximum 41% correction factor to the barge log estimate of 289,588 m^ resulted 

 in a corrected volume of 170,857 m\ The volume calculation from the comparison of the 

 1990 and 1992 bathymetric surveys was very close to this, 151,764 m^ or 89% of the barge 

 log volume corrected with the Tavolaro factor. 



4.2 REMOTS® Sediment-Profile Photography 



REMOTS® photographs verified the distribution of dredged material beyond the 

 boundaries of the mound determined by bathymetry, a fmding consistent with results at other 

 disposal sites (SAIC 1989, Germano, Parker, and Wiley 1994). The presence of dredged 

 material in a large number of REMOTS® stations away from the disposal buoy is primarily 

 related to vessel positioning at the time of disposal. The DAMOS capping model was used 

 to calculate the expected radius of an individual disposal event at MBDS (2,000 m^ barge 

 volume at a 90 m water depth). The model indicates material would spread 300 m from the 

 point of impact (Figure 4-5). The area oudined by a 300 m radius from known barge release 

 points (September 1990-March 1992) includes all of the disposed Boston Blue Clay and most 

 of the relic dredged material detected by REMOTS®. 



Dredged material extending to the western boundary of the disposal site was "relic" 

 dredged material, i.e., dredged material deposited prior to the Boston Blue Clay (Figure 

 3-5). In general, older dredged material has been subjected to a longer period of 

 bioturbation and smoothing of the sediment/water interface from bottom currents. 

 REMOTS® photographs showed that these older dredged sediments had a deeper redox 

 potential discontinuity (RPD) layer. The source of boundary roughness at the sediment/water 

 interface is either biological or related to current activity (sand waves, ripples, etc.) versus a 

 boundary roughness related to recent physical disturbance from dredged material disposal. 

 The successional stages in "relic" dredged material will also tend to be more advanced, 

 showing evidence of Stage III taxa, with correspondingly higher values for the Organism- 

 Sediment Index (Rhoads and Germano 1982, 1986). 



The most recently deposited or "fresh" dredged material consisted of Boston Blue 

 Clay which extended radially 300-400 m from the buoy. At the center of the disposal 

 mound, the Boston Blue Clay was devoid of any benthic infauna. However, evidence of 

 faunal reworking on fresh Boston Blue Clay was present within 100 m from the center of the 

 mound. The predicted lack of colonization immediately around the buoy was true only for 

 the center of the mound. Within 100 m of the center. Stage I or Stage III taxa were present. 

 Stage I taxa are the first fauna to recolonize a disturbed habitat and may appear within a 

 short time after the disturbance ceases. Barge logs indicate that barges were disposing of the 

 Boston Blue Clay during the time of the SAIC monitoring survey. In some REMOTS® 

 photographs, there is evidence of the initial stages of faunal reworking on very fresh Boston 

 Blue Clay. 



Monitoring Cruise at the Massachusetts Bay Disposal Site, March 31 - April 4, 1992 



