43 



4.0 DISCUSSION 



The original hypothesis of this study was that the slow recolonization rates 

 documented by REMOTS® photographs, and the bioassay results, were due to a surface layer 

 remnant of the 3,000 m 3 of Black Rock material which was disposed of last in the MQR 

 depositional sequence. The coring data were used to construct a stratigraphic sequence to 

 test this hypothesis by identifying New Haven, Black Rock, Mill River, and Quinnipiac River 

 materials. These stratigraphic units were identified by (1) estimating the thickness of each 

 material disposed; (2) comparing the core sample metals data with historical metals data 

 collected from each source area; and (3) evaluating the organic contaminant data on the basis 

 of more recent sediments also collected from capped mounds at CLIS. 



Core descriptions indicated that the top 1-1.5 meters of each core recovered relatively 

 homogenous material. In order to identify whether a thickness of over 1 meter of a similar 

 material was realistic, the thicknesses of each dredged material unit were estimated using the 

 DAMOS Capping Model. Results of the model also were compared with bathymetric depth- 

 difference volume maps between successive depositional intervals. These volume estimates 

 were used as a first-order prediction of thicknesses of individual units recovered in the cores 

 (Section 4.1). 



Historical metals data from the source areas (Mill and Quinnipiac Rivers, Black Rock 

 and New Haven Harbors), and from the MQR mound itself, were compared with the MQR 

 core data in order to identify the origin of individual samples in the MQR cores (Section 

 4.2). If successful, these comparisons would allow a stratigraphic correlation of the cores, 

 and potentially allow identification of the source of the surficial sediments causing the 

 retrograde benthic faunal conditions at MQR. 



Finally, chemistry results indicated that several samples, specifically MQR-3F, and 

 MQR-5E, contained distinctively elevated levels of organic contaminants. The suite of 

 organic contaminant data from the MQR cores was compared with recent coring results from 

 other CLIS capped mounds to further elucidate the source areas for each MQR sample 

 (Section 4.3). These data were also analyzed in light of the current knowledge of 

 bioaccumulation potential and resulting negative effects. 



4.1 Volume Estimates of MQR Source Materials 



The DAMOS Capping Model, a computer program developed for NED that predicts 

 the thicknesses of disposed dredged material, was used to estimate the volumes of each of the 

 different source materials at MQR. These estimates do not consider postdepositional settling 

 of the mound sediments. The model allows for a dual-phase depositional scenario; since 

 MQR was actually completed in at least 4 phases, several runs were completed. Thicknesses 

 were estimated over a predicted 150 m radius of operations, unless otherwise stated. The 



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



