Sediments to be dredged from the Quinnipiac River were geotechnically more stable, 

 lacking the fibrous wood pulp component found in the Mill River sediments. However, they 

 were only slightly less contaminated, with concentrations of mercury (Hg), lead (Pb), 

 cadmium (Cd), and copper (Cu) still within the highly contaminated category of the New 

 England River Basins Contaminated Sediment Classification (NERBC 1980; Table 1-2; 

 Oceanic Society 1982). Laboratory bioassays and bioaccumulation studies of selected 

 contaminants present in the dredging site materials showed minimal toxicity and uptake 

 associated with exposure to either Mill or Quinnipiac River sediments (ERCO 1980a,b, 

 ERCO 1981a,b). The Corps determined that open water disposal would be feasible only if 

 the relatively mobile Mill River sediments were capped with the more stable Quinnipiac 

 River materials. 



Clamshell dredging of the Mill River began on 31 March 1982. Materials were 

 transported by hopper barge to the MQR buoy. Water depths in this area ranged from 

 20 to 21 m. Barge logs indicated that approximately 42,000 m 3 of high water-content Mill 

 River sediments were placed prior to the initiation of Quinnipiac River dredging. This latter 

 operation, beginning in early May 1982 and completed prior to the first of June, resulted in 

 the placement of approximately 133,200 m 3 of silts as a cap layer over the Mill River 

 sediments. Dredged material volume estimates obtained by comparing bathy metric profiles 

 before and after disposal of each unit disagreed substantially with the barge log values. 

 Volume calculations based on depth differences were approximately 70,000 m 3 of sediment 

 dredged from the Mill River and 190,000 m 3 from the Quinnipiac River (Morton et al. 

 1984a). The volume calculation data based on depth differences showed in-place volumes to 

 be significantly larger than those detailed on the NED log. This in part may be a result of 

 the unique textural quality of the disposed materials. 



In late spring of 1983, the MQR mound received additional contaminated materials 

 dredged from Black Rock Harbor near Bridgeport, Connecticut (Figure 1-3). Laboratory 

 analyses of sediments from Black Rock Harbor indicated that the materials were 

 predominantly classified as highly contaminated (NERBC 1980) with a variety of organic and 

 inorganic compounds (Table 1-1; USACE 1982; Rogerson et al. 1985). Laboratory 

 bioassays indicated that exposure to these materials 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 

 materials to minimize biotic exposure and/or contaminant migration. To satisfy this 

 requirement, NED proposed to cap the Black Rock Harbor sediments placed at the MQR 

 mound with silts to be dredged from New Haven Harbor (Figure 1-4). Previous analyses 

 had found these latter materials as containing generally moderate levels of the NERBC 

 contaminants (Table 1-1; USACE 1978). 



Sediment Core Chemistry Data Summary from the MQR Mound, August and December 1991 



