(SAIC 1988). The bank blocks the exchange of water at depth with the Gulf and the shelf 

 beyond. Stellwagen Bank is a popular fishing and whale watching area that has been 

 designated as a national marine sanctuary. One major concern raised by regulatory agencies 

 and environmental groups is the proximity of marine mammals (specifically, humpback and 

 finback whales) on Stellwagen Bank and the potential harmful effects on their feeding 

 activities from suspended sediment transport during disposal activities at MBDS (SAIC 

 1988). 



Dredged material which settles on the bottom at MBDS can be expected to remain in 

 place for extended periods of time (EPA 1989). Physical oceanographic studies conducted 

 under the DAMOS Program as well as those by other investigators have shown that the 

 bottom current velocities at the disposal site are quite low, averaging less than 7 cm-s' 1 

 (Butman 1977, Gilbert 1975, SAIC 1987a). Occasional higher velocities, near 20 cm-s 1 in 

 a westerly direction, have been observed in near-bottom waters in response to easterly storm 

 events that occurred in fall and winter. Near-bottom currents of this magnitude were not 

 predicted to be strong enough to resuspend sediments at MBDS (EPA 1989). However, 

 surficial sediments may be resuspended by wave action on rare occasions of severe easterly 

 storm events. Waves of sufficient height and period to cause resuspension can be generated 

 by easterly storms with winds in excess of 40 mph for a period of more than 12 hours, an 

 event estimated to occur approximately once every four years (EPA 1989). Based on data 

 obtained from the National Weather Service, such a storm occurred only once during the 

 period between 1978 and 1986. Resuspension events such as these are rare and typically 

 result in resuspension of only 4% of the surface material (EPA 1989). Transport of the 

 resuspended dredged material in combination with resuspended natural sediments would be to 

 the west and southwest during these events. 



The prevailing low current velocities minimize the possibility of resuspension of 

 deposited material at this site, and the water depth tends to isolate the bottom from the 

 effects of all but the severest of storm events (SAIC 1988). The wave conditions in the 

 vicinity of MBDS normally result from both local sine wave formation and propagation of 

 long period waves generated on the adjoining continental shelf. The sheltering provided by 

 the coastline severely limits wave generation from the westerly direction; waves from the 

 westerly quadrants larger than 1.8 m occur rarely, and waves over 3.7 m are virtually 

 nonexistent (EPA 1989). 



The temperature/salinity cycle of Massachusetts Bay is characterized by seasonal 

 variability, with maximum temperatures (18° C at surface) typically occurring in a stratified 

 water column during August and September, and minimum temperatures (5° C) typically 

 occurring in an essentially isothermal water column in January and February (SAIC 1987a). 

 Salinity values range from 31 to 33 ppt (SAIC 1987a). 



Monitoring Cruise at the Massachusetts Bay Disposal Site, August 1990 



