93 



Samples were collected in 1987 to characterize the broad-scale concentration of 

 sediment contaminants at the site. Contaminant concentrations were very similar to those 

 measured in 1985 and 1986 (Figure 6-58). The levels of Cr, Cu, Pb, and PHCs were higher 

 in the recent dredged material than in samples from the reference areas and the sites 

 containing relic dredged material (Figure 6-58). 



Results of the 1985 - 1986 Nephtys body burden analyses indicated similar metal 

 concentrations in organisms collected in the three sampling areas. Cadmium concentrations 

 were higher in polychaetes from the reference area (Figure 6-59), and PCBs were detected in 

 organisms at the disposal site. Body burden levels in 1987 showed no major trends between 

 sampling stations (Figure 6-59). 



6.8.2 MBDS: 1990 Monitoring Results 



In August 1990, SAIC conducted routine field operations at MBDS to provide 

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

 January 1989 REMOTS® surveys. MBDS had received 260,300 m 3 of dredged sediments 

 since November 1988. Field operations included a precision bathymetric survey, REMOTS® 

 sediment-profile photography, and sediment sampling for chemical and physical analyses. 

 The surveyed areas were similar to those sampled in 1988-89. 



A comparison of the August 1990 and November 1988 precision bathymetric surveys 

 revealed that an acoustically detectable layer of dredged material, with an approximate 

 maximum thickness of 0.6 m, had been deposited at the "MDA" buoy between the time of 

 the two surveys. The objective of the REMOTS® survey was to map that portion of the 

 recently deposited dredged material not detectable with bathymetry. Information obtained 

 from the REMOTS® survey indicated the presence of "fresh" dredged material within 800 m 

 west, 500 m south, 400 m east, and 500 m north of the disposal site center. The apparently 

 fresh dredged material was indicated by chaotic sedimentary fabrics and anomalous grain size 

 distributions at the site. 



Stage IH taxa were present at 97% of the disposal site stations, compared with 75% 

 of the stations in 1989. Most of the Stage HI organisms in both surveys were associated with 

 Stage I taxa. These results confirm that the benthic community around the "MDA" buoy 

 was similar to that in 1989 and suggest a steady recovery in the benthic ecosystem. 



Future investigations should cover topics such as detailed bioaccumulation and 

 capping feasibility. Capping of contaminated sediments at MBDS appears to be a feasible 

 mitigating measure if used in conjunction with a taut-wired buoy and/or navigation systems 

 such as Global Positioning System (GPS) or microwave trisponder. Accurate navigation 

 would also permit dilution of contaminant levels through deposition of both contaminated and 

 relatively uncontaminated sediments at the same location. 



DAMOS Summary Report, 1985-1990 



