22_ 



5.0 CONCLUSIONS 



Dredged material deposited at the Massachusetts Bay Disposal Site since the August 

 1990 REMOTS® survey formed a distinct mound, centered slightly west of the disposal buoy 

 (Germano, Parker, and Charles 1994). Results of the 1990-1992 depth difference indicated a 

 maximum change in depth of 2 m and the formation of an elliptical mound with an average 

 diameter of 400 m. The REMOTS® survey extended the detection of dredged material to 

 400 m north and south, 600 m east, and 800 m west of the mound center. The acoustically 

 detected mound was well within the disposal site boundaries. A comparison made of the 

 depth matrices from 1988 to 1992 also showed an elliptical mound with a maximum 

 thickness of 2.25 m. Most of the dredged material deposited since 1988 had accumulated 

 within a 500 m by 500 m area, immediately west of the buoy. The successful formation of a 

 mound from disposal activities demonstrates that a distinct mound can be formed with 

 dredged material at this site providing that tight control is exercised over disposal operations. 



The fairly rapid rate of benthic recolonization at the disposal site, with the ongoing 

 disposal of Boston Blue Clay, indicated that the benthic disturbance from disposal operations 

 on the benthic fauna and infauna was minimal. The majority of disposal site stations as well 

 as all of the analyzed reference area stations showed evidence of Stage III taxa, indicative of 

 a well-colonized, healthy benthic community. At the disposal mound center, the labile 

 organic matter associated with the fresh Boston Blue Clay stimulated the colonization of 

 Stage I organisms. Only at the very center of the mound, where deposition was most recent, 

 was the successional stage indeterminate. 



With the passage of Hurricane Bob and the Halloween Storm in 1991, there was 

 concern regarding disruption to the benthic environment at MBDS as a result of the storms. 

 Although model predictions indicated that some resuspension of sediments should occur, 

 results of bathymetric/REMOTS® surveys at the disposal site and the REMOTS® surveys at 

 the reference areas showed no dramatic evidence of benthic disturbance or indications of 

 substantial resuspension of dredged material. Recolonization of the mound has occurred at 

 an acceptable rate, especially considering the ongoing disposal operations. Bathymetric 

 results showed the acoustically detected mound was well within the disposal site boundaries. 



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



