49_ 



orientation and gridding routines between SAIC and OSI are responsible for its 

 appearance. 



Due to the effects of consolidation, tracking volumes of material throughout the 

 different phases of mound development accounted for more of the reported volumes than 

 comparisons over long expanses of time. The cumulative volume detected by the use of 

 multiple surveys is 204,362 m 3 or 70% of the total reported volume (Appendix A: Table 3- 

 2). Without the use of interim survey data, volume calculations detected 70,643 m 3 of 

 CDM, 44% of the reported cap material volume, and 169,624 m 3 or 58% of the total 

 material volume. 



These latter calculations are typically utilized as part of most disposal and/or 

 capping projects where depositional volumes are quantified using differences in depth 

 between a predisposal and a postcap survey only. Results of in-depth research studies of 

 the operations surrounding clamshell dredging and subaqueous disposal of dredged material 

 have demonstrated an apparent 41% reduction in volume between consecutive bathymetric 

 surveys (Tavolaro 1984). Differences of this magnitude are expected and are attributed to 

 barge volume over-estimation, the volume of material undetectable through acoustic 

 bathymetric data processing techniques, and dredged material consolidation over time; they 

 do not represent actual material loss. 



3.2.2 REMOTS® Sediment-Profile Photography 



REMOTS® sediment-profile photography was used to document benthic 

 recolonization, as well as map thin layers of material and assess the overall impact of 

 dredged material deposition at the CLIS 94 disposal mound. Complete REMOTS® results 

 for the disposal mound are available in Appendix B: Table 2. 



3.2.2.1 Sediment Grain Size and Stratigraphy 



Fresh dredged material was detected and measured at every station except for one 

 replicate at 200N. Replicate-averaged mean dredged material thickness ranged from 

 8.8 cm to full camera penetration (20 cm) (Appendix A: Table 3-3). Redox rebound 

 intervals, areas showing evidence of intermittent or seasonal oxidation below the oxidized 

 surface layer, were noted at stations 200 m and 300 m from the center. 



Physical REMOTS® parameters showed that the major modal grain size was 

 consistently reported as > 4 phi (silt and clay), indicating the deposition of predominandy 

 fine-grained dredged material. However, the sediments detected at Station 100E were 

 slightly coarser (4 to 3 phi) silts and fine sands. The replicate-averaged mean camera 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



