707 



Bay region. Sediments disposed at BBDS have been relatively uncontaminated sands, and 

 sands containing some silt and clay. The 1981 side-scan survey located a disposal mound 

 which was part of the historic disposal site. The present disposal site is north of this area. 

 Since 1984, the site has been used for two projects; 55,000 m 3 of dredged material was 

 disposed at the site in 1985, and 600 m 3 was disposed in 1989 (SAIC 1991b) . 



Due to the small area covered by the disposal site and the shallowness of the water, it 

 is doubtful that this site would be a suitable candidate for future capping operations. Indeed, 

 the shallowness of the water (9 m) over the present disposal area is a potential cause for 

 concern as a hazard to navigation when planning future disposal operations at this site. 



6.9.2 BBDS: 1990 Monitoring Results 



In March 1990, field operations were conducted at BBDS to provide information on 

 the effects of past disposal operations. Field operations included a precision bathymetric 

 survey, REMOTS® sediment-profile photography, and sediment sampling for benthic, 

 chemical, and physical analyses. The overall objective of the cruise was to characterize 

 existing bathymetric, sediment grain size, sediment chemistry, and benthic conditions at and 

 around the disposal site. Three reference areas were selected to provide comparisons 

 between ambient and on-site conditions and were located 3107 m northwest, 3940 m west, 

 and 2600 m southwest of the disposal site center. 



The information obtained from the bathymetric survey and REMOTS® photographs 

 permitted the detection of two disposal mounds within the surveyed area (Figure 6-62). The 

 primary mound was central to the disposal site, 1.2 m high and 60 m wide. The other, south 

 and west of the center mound, was 1.6 m high and approximately 90 m wide. 



The major modal grain size over the surveyed area ranged from medium sand 

 (2-1 phi) to silt-clay (>4 phi). All stations containing a major mode of medium (2-1 phi) 

 and fine (3-2 phi) sand fractions were rippled. The distribution of the major modal grain 

 size, as deduced from REMOTS® photographs, indicated a net bedload sediment transport of 

 fine-grained material to the southeast along an 11.6 m isobath. Currents are most likely the 

 dominant force contributing to the transport. The disposal site center consisted of rippled 

 bedforms and fine sands which limited penetration by the REMOTS® camera. 



The species composition found in this study was similar to that of benthic 

 communities in Cape Cod Bay and Boston Harbor/Massachusetts Bay. Species richness was 

 somewhat higher at the reference stations; however, both on-site and off-site stations were 

 well within the range observed in soft-bottom, shallow-water environments. Significant 

 differences existed between reference stations and on-site stations in REMOTS® parameters 

 for Redox Potential Discontinuity depth, successional stages, and Organism-Sediment Index 

 values. 



DAM OS Summary Report, 1985-1990 



