50 



Following UDM disposal, the mound was 2.5 m in height and 510 m in diameter 

 with a calculated volume of 312,000 m 3 based on comparisons of the baseline and precap 

 bathymetric surveys. The final CAD mound is centered approximately 125 m to the south 

 of the NHAV buoy location (Figure 4-13). The total volume of cap material accounted for 

 by bathymetry was 402,000 m 3 , the diameter of the mound expanded to 800 m, and the 

 mound height remained at 2.5 m due to significant consolidation of the underlying UDM 

 deposit. According to DAMOS barge disposal logs, the total volume of dredged material 

 was 1,159,000 m 3 ; however, the total volume accounted for by bathymetry was 

 714,000 m 3 (62% of the estimated barge volume). 



Results of previous DAMOS monitoring surveys have shown that accumulations of 

 dredged material less than 20 cm thick in the flanks of a disposal mound are typically 

 deposited in layers too thin to be detected by standard bathymetric techniques. The 38% 

 difference in final volumes between bathymetric analysis and disposal logs is accounted for 

 by consolidation of the underlying UDM deposit and the limits of the acoustic survey. 

 Due to the complex scheduling of disposal activities during this project, it is difficult to 

 determine what volumes of contaminated and cap material were present during each 

 survey. 



The depth difference comparison between the precap and the postcap surveys 

 provides the best indication of the overall distribution of cap material. This comparison 

 indicates an apparent lack of cap material in the northwestern quadrant of the final disposal 

 mound (Figure 4-14). However, disposal records indicate that 76,000 m 3 of cap material 

 was disposed in this quadrant prior to the precap survey making it undetectable in the 

 precap/postcap comparisons. In addition, subbottom profiling data and geotechnical cores 

 collected over the NHAV 93 mound in July 1994 detected 0.5 to 0.75 m of silt cap 

 material over the northwestern flank (Figures 5-2 and 5-3; Morris 1994). 



Results of the REMOTS® baseline survey showed that recolonization of the bottom 

 invertebrate community from the disturbance of historic disposal operations has proceeded 

 at a rate typical for open- water dredged material sites. Successional stages were dominated 

 by pioneering Stage I polychaetes with evidence of more mature taxa in the Stage I to 

 Stage II and Stage I on Stage III communities. Stage II taxa represent a transitional sere 

 between Stage I and III and are associated with recovery of a disturbed benthic habitat 

 (Rhoads and Germano 1986). Stage III taxa generally represent high-order successional 

 stages typically found in low disturbance regimes. Organism-Sediment Indices were 

 variable and indicative of a patchy benthic environment. 



Monitoring Surveys of the New Haven Capping Project, 1993-1994 



