27_ 



mark the disposal point, towboats were required to navigate to the desired location via 

 LORAN-C time delay signals (TDs). Slight errors in the LORAN-C receivers used in the 

 1994 disposal operations may have resulted in the deposition of material to the northwest 

 of the F mound over the historic WLIS D mound. 



3.1 WLIS H Mound 



3.1.1 Bathymetry 



The H mound was developed during the 1995-96 disposal season by the deposition 

 of dredged material approximately 250 m northeast of the historic F mound. Composed of 

 an estimated barge voliune of 15,300 m^ of sands, silts, and clays dredged from 

 Connecticut and New York waterways in the spring of 1996, it represents the newest 

 bottom feature at WLIS. Based on the relatively small volimie of dredged material 

 disposed, a 400 m x 400 m analysis area was defmed around the WDA 95 buoy position. 



The bathymetric chart of this smaller area displays a sediment mound with a 

 minimum depth of 32.5 m over the apex of the H mound at MLLW (Figure 3-5). Depth 

 difference plots based on comparisons with 1992 data indicate the bottom feature is 

 approximately 230 m wide, and 1.5 m high at the apex (Figures 3-6 and 3-7). The apron 

 of the WLIS H mound has apparently coalesced with the northern and eastern flanks of the 

 historic F moimd. 



3.1.2 REMOTS® Sediment-Profile Photography 



REMOTS® sediment-profile photography was used to document benthic 

 recolonization as well as track the thin layers of dredged material and assess the overall 

 impact of deposition over the surface of the WLIS H mound. Complete REMOTS® results 

 for the new disposal mound are available in Appendix B. 



3.1.2.1 Sediment Grain Size and Stratigraphy 



Fresh dredged material was detected and measured at every station over the H 

 mound. Redox rebound intervals, areas showing evidence of intermittent or seasonal 

 oxidation below the currently oxidized surface layer, were noted at every station over the 

 H mound. The presence of a redox rebound interval in a new sediment deposit suggests a 

 gradual decline in pore water oxygen content, which could be attributable to a decrease in 

 regional bottom water DO concentrations. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1996 



