15 



the navigational channel (Figure 2-3). 

 Material in the area ranged from fine- 

 grained silts and clays along the northern 

 reaches of the channel to sands near the 

 Harbor entrance adjoining Long Island 

 Sound. 



Bulk sediment chemical analyses and 

 elutriate tests showed the majority of New 

 Haven material to be low to moderately 

 contaminated sediments (Tables 2-2 and 2- 

 3). Based on laboratory bioassays, the 

 material was deemed suitable for use as 

 cap material. Pre-project estimates 

 indicated that the dredging required to 

 provide the desired depths in this channel 

 would entail removal of approximately 

 87,900 m 3 of sediment. This figure was 

 later revised upward to approximately 

 129,200 m 3 . 



The proposed capping project was 

 subjected to extensive public review. In 

 response to the concerns raised by the 

 SAC, NED developed a disposal plan 

 requiring the Stamford sediments to be 

 divided and placed at two distinct locations 

 within CLIS. The capped mounds were to 

 be separated along a north-south line to 

 minimize cross contamination due to 

 transport driven by the local near-bottom 

 current field. The southern deposit was to 

 be capped with fine-grained silts, and the 

 northern deposit was to be covered with 

 coarser grained silts and sands. 



The project was to be monitored 

 carefully to detail the areal extent of the 

 capped mounds and the physical integrity 

 of the cap, and to ensure a minimum cap 

 thickness of approximately 50 cm, a value 



thought to represent twice the maximum 

 thickness which might be disturbed by 

 benthic biota (Brannon et al. 1984). 

 Direct (diver), remote, and acoustic 

 observations were to be obtained along 

 defined transects in combination with 

 sediment samples for chemical and 

 biological analyses. All sampling was to 

 be conducted within an accurately 

 positioned grid with surveys continuing 

 over at least a two-year period in an effort 

 to permit initial assessment of both short- 

 and long-term effects of the disposal 

 operation (Appendix B). 



NED conducted a series of bathymetric 

 and grab sample surveys in January and 

 March 1979 to assist in siting the disposal 

 points and to establish reference points for 

 later use in the assessment of the 

 horizontal and vertical distribution of 

 deposited material (Appendix C). A CLIS 

 reference station was also sampled, a 

 location used previously by Yale 

 University investigators as a reference or 

 control for studies conducted in the CLIS 

 region. Analysis of the biological 

 characteristics of samples obtained within 

 the disposal site boundaries indicated 

 relatively low concentrations of benthic 

 organisms, making it difficult to obtain the 

 biomass required for analysis of body 

 burden concentrations of selected 

 contaminants (NUSC 1979a). 

 Consequently, body burden analyses were 

 eliminated from the initial survey results. 

 In the past three to four years, sampling 

 techniques for body burden analyses have 

 been investigated (Rhoads et al. 1994). 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



