A plume study was conducted at MBDS during 1982-1983 to assess the potential 

 impact of dredged material disposal on the surrounding environment. Plume behavior was 

 examined through a combination of acoustic tracking and in situ sampling which involved 

 measurements of salinity and suspended particulate matter (SAIC 1984). Acoustic results 

 indicated a rapid, convective descent of dredged material to the bottom. Based on the 

 calibration provided by the water samples, a concentration of 750 mg-1" 1 of sediment was 

 observed in the upper layer of the plume immediately after disposal. This concentration 

 decreased rapidly to 39 mg-1" 1 within 20 minutes after disposal and to 5 mg-1" 1 

 approximately 40 minutes after disposal. The ambient concentration of suspended material 

 averaged approximately 1 mg-1" 1 (SAIC 1984). The concentration and distribution of 

 suspended material in the plume 40 minutes after disposal varied only slightly (from 5 to 

 12 mg-1" 1 ), and represented 3% of the total load of dredged material (100,000 kg). Although 

 the plume tracked in this study moved in a southeasterly direction, the dominant near-surface 

 tidal currents at MBDS are NNE-SSW with velocities of 15 to 20 cm-s" 1 (EPA 1989). These 

 currents decrease with depth to lower velocity, less periodic currents near the bottom 

 (generally < 10 cm-s 1 ; EPA 1989). 



A similar study was conducted in May 1985 at the Rockland Disposal Site (RDS) 

 located in West Penobscot Bay, Maine (SAIC 1987b). Within two hours, 90% of the 

 material was on the bottom (mostly within the disposal site), and suspended sediment 

 concentrations were similar to background levels of 3-5 mg-1" 1 . If disposal occurred on 

 maximum flood tide, it was estimated that approximately 6% of the dredged material may be 

 transported out of the disposal site while if disposal occurred evenly at all stages of the tide, 

 this estimate was reduced to 1 % . Results of current measurements at 10 m depth and 60 m 

 depth (SAIC 1984) showed that the dominant flow at RDS was to the N-NE and that the 

 maximum current velocities occurred on the flood tide (40 cm-s 1 ). The average current 

 speed at RDS was approximately 13 cm-s" 1 . Based on these measurements, once outside the 

 disposal site, the dredged material would be so widely distributed (via current transport and 

 physical mixing in the water column) as to be undetectable (SAIC 1984). 



From 13 to 17 August 1990, SAIC conducted field operations at MBDS to provide 

 information on the effects of disposal operations since the November 1988 bathymetric and 

 January 1989 REMOTS® surveys. Field operations included a precision bathymetric survey 

 and REMOTS® sediment-profile photography. The benthic community around the "MDA" 

 buoy was predicted to be similar to that observed during January 1989. In 1989, infaunal 

 successional stages at the disposal site included Stage I (small pioneering polychaetes), Stage 

 IU (larger burrowing deposit feeders), and Stage I on Stage ni communities, with 75% of the 

 stations showing evidence of Stage III taxa. Stage III taxa represent high-order successional 

 stages typically found in low disturbance habitats. The influx of Stage I species represents a 

 response to disturbance due to disposal activities. 



Monitoring Cruise at the Massachusetts Bay Disposal Site, August 1990 



