122 



The presence of deeper RPDs at several stations in 1997 was probably due to spatial 

 variability, although also may have been a function of remnant oxidation of new, fine- 

 grained dredged material. As the dredged material (and especially the gray clay) continues 

 to be recolonized, the modal RPD should become similar to or greater than that measured at 

 the reference areas. 



In 1998, the presence of gray clay was widespread on the apex and plateau areas of 

 the mound (Figure 3-20). While most photos showed evidence that the gray clay was 

 breaking down and becoming bioturbated (Figure 4-6), some replicates on the apex (150N 

 replicates B and C) had limited colonization or development of RPDs. In 1997, a much 

 higher number of replicates appeared to be affected by fresh gray clay with restricted 

 recolonization due to the apparent low food value of ancient clays and the resistance to 

 penetration by burrowing organisms. The 1998 photographs also showed increased evidence 

 of scour lag and physical reworking of the surface sediments (Section 4.2.3). Sulfidic 

 sediments within the gray clay were also more common in 1998, as the surface sediments 

 began to reach equilibrium in the new environment (Figure 4-7). 



The combination of initial biological reworking, physical scour and development of 

 sulfidic profiles appear to be early stages in the incorporation of non-ambient ancient clays 

 into the sediment fabric of the near-surface sediments at NLDS. It is not surprising that 

 these processes have left a patchy response with areas of Stage EI succession interspersed 

 with patches of shallow RPDs. As individual clumps and blocks of clay are broken down, 

 the areas between them will collect ambient sediments and support rapid recolonization. 

 The integrated picture of benthic assemblages collected in 1997 and REMOTS® data from 



1997 and 1998 suggests that biological recolonization is progressing on the surface of the 

 Seawolf Mound, but is still moving toward equilibrium with the surrounding ambient 

 sediments. There is no biological evidence of toxic conditions in the surface sediments of 

 the Seawolf Mound as a range of sensitive Stage II and HI species are continuing to colonize. 



4.2.3 Potential Resuspension from the Seawolf Mound 



In a parallel study, oceanographic conditions at NLDS were evaluated in 1997 and 



1998 with specific reference to the Seawolf Mound (Waddell et al. 2001). The results of this 

 study were consistent with numerical modeling results for Long Island Sound (Signell et al. 

 1998) as well as the physiographic description of bottom sediments (Knebel et al. 1999). 

 Semi-diurnal (twice-daily) tidal currents dominate the physical oceanographic environment 

 at NLDS. These currents appear sufficiently strong to winnow unconsolidated fine 

 sediments, however the site is well protected from most storm-generated wave disturbances 

 (Signell et al. 1998, Waddell et al. 2001). The result is that the surface sediments at NLDS 

 (and the Seawolf Mound) should reflect the response of deposited dredged material (whether 

 it be clay, silt or sand) to twice daily tidal current stress. The prediction (and pattern of 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



