26 



relatively high water content measured in 

 the Mill River sediments, increased the 

 dispersive properties of the material. In 

 addition, chemical analysis of the Mill 

 River sediments indicated high 

 concentrations for most of the heavy 

 metals tested. Cadmium (Cd), for 

 example, was measured in concentrations 

 up to 260 ppm (Table 2-1). 



Sediments to be dredged from the 

 Quinnipiac River were much more stable 

 geotechnically, lacking the fibrous wood 

 pulp component found in the Mill River 

 sediments. However, they were only 

 slightly less contaminated, with 

 concentrations of Hg, Pb, Cd, and Cu still 

 within the NERBC highly contaminated 

 category (Tables 2-2 and 2-3). Laboratory 

 bioassays and bioaccumulation studies of 

 selected contaminant levels present in the 

 dredge site material showed minimal 

 toxicity and uptake associated with 

 exposure to either Mill or Quinnipiac 

 River sediments (ERCO 1980a, b, ERCO 

 1981a, b). Despite these bioassay results, 

 the USACE determined that open-water 

 disposal would be feasible only if the 

 relatively mobile Mill River sediments 

 were capped with the more stable 

 Quinnipiac River material. Dredging and 

 disposal operations of Mill and Quinnipiac 

 River sediments are discussed in Section 

 2.4.1. 



In late spring of 1983, the Mill- 

 Quinnipiac River mound (MQR) received 

 an additional 66,800 m 3 of contaminated 

 material dredged from Black Rock Harbor 

 near Bridgeport, Connecticut (Figure 2-7). 

 This operation was conducted in 



conjunction with the Field Verification 

 Program (FVP), a multiyear joint research 

 program sponsored by the Environmental 

 Protection Agency and the USACE 

 (Peddicord 1988). Laboratory analysis of 

 sediments from Black Rock Harbor 

 indicated that the material was 

 predominantly in the NERBC highly 

 contaminated category and had high 

 concentrations of a variety of organic and 

 inorganic compounds (Table 2-1 and 2-2, 

 USACE 1982; Rogerson et al. 1985). 

 These included heavy metals, 

 polychlorinated biphenyls (PCBs), and 

 polycyclic aromatic hydrocarbons (PAHs). 

 Laboratory bioassays indicated that 

 exposure to this sediment had the potential 

 to induce unacceptable mortalities in local 

 biota (ERCO 1980c,d). 



The results of the bulk chemical 

 analyses and bioassays led to the 

 determination that open-water disposal of 

 the Black Rock sediments should be 

 followed by capping with cleaner material 

 to minimize biotic exposure and/or 

 contaminant migration. To satisfy this 

 requirement, NED proposed to cap the 

 Black Rock Harbor sediments placed at 

 MQR with silts to be dredged from New 

 Haven Harbor. Previous analyses had 

 shown the latter material to contain 

 moderate levels of the NERBC 

 contaminants (Tables 2-2 and 2-3; USACE 

 1979). 



2.4.1 MQR Disposal Operations 



Clamshell dredging of the Mill River 

 began on 31 March 1982. Material was 

 transported by hopper barge to the CLIS 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



