Two major storms occurred in Massachusetts Bay between 1990 and 1992. Hurricane 

 Bob passed quickly over Massachusetts Bay on August 19, 1991, and an extreme (among the 

 strongest recorded to date) Atlantic coast northeast storm occurred in October 1991. With 

 the exception of 54,792 m^ of dredged material deposited from August 1990 to mid-July 

 1991, the remaining volume (234,796 m^) of dredged sediments disposed at MBDS was 

 received after these two storms and consisted primarily of Boston Blue Clay. Hurricane Bob 

 produced an average maximum wind speed of 45 knots with peak gusts of 59 knots at the 

 Boston Buoy, 42.2° N and 70.8° W (Morris 1992). The October 1991, or Halloween 

 Storm, occurred over October 30 and 31, and has been estimated as a 100-year storm with a 

 Class 5 magnitude (Chandler 1992). An unusual feature of this northeaster was the long 

 duration of the 30-to-40-knot winds (Davis and Dolan 1992). On October 28 high waves 

 were generated, and on October 29 sustained 30-knot winds were observed. The storm 

 strengthened on October 30 as it combined with the remnants of Hurricane Grace (which had 

 begun moving north from Bermuda on October 28) creating a 10-knot increase in wind 

 speeds (Davis and Dolan 1992). The Halloween Storm lasted 114 hours and sustained 40- 

 knot winds. Wave heights in Massachusetts Bay were over 30 feet (Chandler 1992). 



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

 place for extended periods of time (EPA 1989). The prevailing low current velocities in this 

 area reduce the possibility of dredged material resuspension, and the deep water also isolates 

 the bottom from all but the strongest storm events (SAIC 1988). Physical oceanographic 

 studies conducted under the DAMOS program, as well as those by other investigators, have 

 shown that current velocities 8 m off the bottom of the site are low, averaging less than 

 7 cm- s'^ (Butman 1977, Gilbert 1975, SAIC 1987). Occasional higher velocities (near 

 20 cm- s"' in a westerly direction) have been observed at this depth in response to easterly 

 storm events that occurred in fall and winter. Prior to conditions set up by the two major 

 storms outlined above, no strong bottom currents had been observed as a result of storm 

 events, and currents of 20 cm- s"' 8 m off the bottom were not predicted to be strong enough 

 to resuspend sediments at MBDS (EPA 1989, Hubbard et al. 1988, SAIC 1988). These 

 20 cm- s"' currents 8 m off the bottom would be sufficient for transport if another 

 mechanism, such as bioturbation or wave action, were available to resuspend the sediment 

 (Hubbard et al. 1988). 



As part of the site evaluation study for MBDS, wave hindcasting procedures (CERC 

 1984) were used to predict the parameters of waves as a function of wind speed, fetch, and 

 duration (Hubbard et al. 1988). Wave generation from the westerly direction is severely 

 limited due to the sheltering provided by the Massachusetts coastline. Waves from the 

 easterly direction have essentially an unlimited fetch and with sufficient wind speed and time 

 could be expected to affect the sediment stability (Hubbard et al. 1988). Storms generating 

 easterly winds (northeast storms) approach MBDS from the west and south, and generally the 

 ocean is exposed to high wind speeds for a relatively short period of time. Model 

 predictions from the site evaluation study indicated that, for a typical northeaster to generate 



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



