80 



bathymetric and side-scan sonar surveys, physical and chemical analyses of sediment and 

 water samples, REMOTS® sediment-profiling surveys, fisheries studies, benthic community 

 studies, and manned and unmanned submersible observations. The October 1987 and May 

 1990 surveys were conducted to determine the extent of the dredged material deposited at the 

 site and the remaining site capacity. 



Disposal of dredged material was minimal at CADS during the site designation study; 

 17,320 m 3 of dredged material was deposited from February to May 1985. Dredged material 

 disposal has increased significantly since then (Figure 6-45). Site capacity was calculated for 

 the trough within the disposal site boundaries after the October 1987 survey. Due to the 

 dispersion of barge release points (Figure 6-46) and the rough topography, the dredged 

 material did not form the distinct mounds that it would on a flat bottom. A sand layer on the 

 order of 1 m or less was found over a broad area in 1987. The bathymetric survey detected 

 the sandy dredged material layer near the buoy to be approximately 1 m thick, and the 

 REMOTS® survey located a thinner ( < 20 cm) layer up to 550 m north of the buoy (outside 

 of the disposal site boundary) (SAIC 1990k; Figure 6-47). In 1990, a detailed bathymetric 

 survey of the disposal site revealed accumulations of dredged material in the trough of the 

 disposal site and on the flanks of the ridges (Figure 6-48). 



Between 1985 and 1986, sediment chemistry and body burden studies were conducted 

 at CADS as part of the final site designation study. Sediment chemistry samples were 

 collected at the southern end of the trough where dredged material disposal had already 

 occurred and also at a reference area located in a trough to the east (Figure 6-49). In 

 addition to these two sampling areas, body burden samples were also collected from the 

 northern end of the trough (Figure 6-49). 



Sediment chemistry results indicated that levels of As, Cr, Cu, Hg, Pb, Zn, oil and 

 grease, and PCBs were low at CADS, according to NERBC sediment guidelines (Table 6-1), 

 and that concentrations of Cd and Ni were below analytical detection limits. Concentrations 

 of total organic carbon, oil and grease, and petroleum hydrocarbons (PHC) were higher at 

 CADS than at the reference area (Figure 6-50). PCBs were below detection at CADS, but 

 were measured in small quantities ( — 40 ppb) at the reference area. The lower 

 concentrations of PCBs at the disposal site relative to reference may have been due to 

 material deposited at CADS incorporating deep sediment that was deposited at the dredging 

 site before the introduction of PCBs (SAIC 1987c). The average PCB concentrations at 

 several deep-water sites in the Gulf of Maine have been reported to range from 10 to 80 ppb 

 (Larsen et al. 1985). Reported average concentrations of Pb, Zn, Cr, Cu, and Cd in 

 sediments from Penobscot Bay, Maine, are very similar to those reported at CADS (Larsen 

 et al. 1983). However, levels of petroleum hydrocarbons are considerably lower at CADS 

 than in Narragansett Bay and Long Island Sound where levels as high as 9,000 ppm have 

 been found (SAIC 1987c and references therein). 



DAM OS Summary Report, 1985-1990 



