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3.1.2 REMOTS® Sediment-Profile Photography 



REMOTS® sediment profile photography was used to document benthic 

 recolonization, map thin layers of dredged material accumulation (below acoustic 

 bathymetric resolution), and assess the overall impact of dredged material deposition over 

 the surface of the Seawolf Mound. Because of the distinct nature of some of the dredged 

 material deposited during capping operations (gray clay from improvement dredging), 

 particular attention was paid to visual evidence of sediment types and physical or biological 

 disturbance. The sampling grid occupied in September 1997 was repeated in July 1998 (see 

 Figure 3-13 and Section 2 for details). The results are presented separately below. 

 Descriptive results refer to the three zones of the capped mound: a small apex; a broad, flat 

 plateau; and a sloping apron. Zones were assigned based on the location of grid samples 

 relative to the bathymetric profile (Figure 3-11). Complete REMOTS® results for the 

 Seawolf Mound for both years are presented in Appendix B. 



3.1.2.1 September 1997 Survey 



One of the primary objectives of a sediment profile survey after a capping operation 

 is to map the thin layers of dredged material that cannot be reliably detected with detailed 

 bathymetric surveys (layers less than 20-15 cm thick, see Section 2.1.3). Secondly, the 

 nature of the sediment layers near the surface and any progression towards recolonization 

 provide a baseline to compare with reference areas and subsequent surveys. 



In September 1997, dredged material was present in all profile photographs collected within 

 300 m of the center station except for 300W. It is notable that for all replicate stations with 

 dredged material, the observed thickness was greater than penetration (Table 3-1, see 

 Appendix B for replicate values). This means that the camera penetration depth did not 

 exceed the thickness of fresh dredged material, and no ambient sediments were visible 

 except where dredged material was not detected. A mix of silt-clay (>4 phi), more common 

 at the inner stations (within 150 m of center), and very fine sand (4-3 phi) characterized the 

 sediments of the surface of the Seawolf Mound (Table 3-1). Dredged material was 

 described as gray clay in many replicates. The grain size at the inner stations was finer than 

 at the reference areas, which were characterized as very fine sand (Table 3-2). One replicate 

 of Station 150S had coarser grain size (fine sand 3-2 phi). Surface sand overlying fine- 

 grained sediment (sand over mud stratigraphy) was noted for most photographs (Appendix 

 B). Many replicate photographs also showed evidence of a shell lag deposit. The dominant 

 grain size at slightly over half the stations was similar to that measured at the reference areas 

 (major mode primarily 4-3 phi, Table 3-2). About 46% of the stations consisted of silt-clay. 



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



