92 



monitor formation of the disposal mound, evaluate the ecological status of the benthic 

 environment, provide information on the physical parameters of the site, and determine the 

 extent of chemical contamination. Assessment techniques used have been extensive, 

 including precision bathymetry, side-scan sonar, REMOTS® sediment-profile photography, 

 current meter and transmissometer deployments, CTD/DO monitoring, sediment and benthic 

 sampling for physical and chemical analysis, four observational cruises utilizing manned 

 submersibles, fish collections, and the implementation of the Benthic Resources Assessment 

 Technique (BRAT). 



Approximately 597,000 m 3 of dredged sediments were disposed at MBDS from 1985 

 to 1990 (Figure 6-54). The maximum thickness of the mound in 1989 was 0.3 m with a 

 radius of 50 - 100 m as detected by bathymetry. REMOTS® results from this survey 

 extended the detected radius to 300-350 m. Results of bathymetric analyses in 1990 

 indicated development of an elliptical mound centered slightly east of the MBDS buoy with 

 gradually sloping sides and a maximum thickness of 0.6 m at the apex. The diameter of the 

 mound was estimated to be approximately 420 m. Results from REMOTS® photographs 

 showed the total area of the seafloor affected by dredged material to be 83 % greater than that 

 detected by bathymetry (Figure 6-55). MBDS is a deep-water disposal site (approximately 

 90 m), and the presence of dredged material beyond the mound may result from the 

 spreading of sediments during descent and the occasional release of dredged material up to 

 400 m from the buoy (Figure 6-56). 



REMOTS® analyses have indicated a steady recovery in the benthic ecosystem despite 

 ongoing disposal activity. Stage III organisms were dominant in the 1990 survey and 

 represent high-order successional stages typically found in low disturbance habitats. 



Sediment chemistry and body burden studies were conducted at MBDS in 1985 and 

 1986 to determine if the existing site should receive final EPA designation. Samples were 

 collected at the reference area, off-mound, and on recent dredged material (Figure 6-57). 

 The concentrations of Cd, Ni, and Hg were below or just at the analytical detection limits of 

 the methods (SAIC 19870- Results indicated that there were no significant differences 

 between stations in concentrations of As, but the concentrations of Pb, Zn, Cr, and Cu were 

 all significantly elevated at the disposal site (Figure 6-58). The sediment levels of Cr, Pb, 

 and Zn at the disposal site were moderate in terms of NERBC limits, but the levels of PCBs 

 were high (Table 6-1). Concentrations of PHCs were significantly higher in dredged 

 material than in sediments from the reference area and the off-mound station. The levels of 

 PHCs at all stations were comparable to those found in Narragansett Bay, Rhode Island 

 (SAIC 1987d). Levels of contaminants at the disposal mound were very similar for 1985 and 

 1986 with a decrease in PCBs in 1986, reflective of disposal of sediments with lower PCB 

 levels. 



DAMOS Summary Report, 1985-1990 



