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3.3.2 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. The September 1997 survey 

 reoccupied the 13-station 1996 grid. The March 1998 survey sampled a 5-station grid, the 

 center, and 50-m stations for comparison. 



3.3.2.1 Sediment Grain Size and Stratigraphy 



During the September 1997 survey, we detected and measured dredged material at 

 every station over the H mound. Dredged material thickness over the H mound was 

 greater than penetration at every station except one replicate at 150W, which had a 12-cm 

 thickness over ambient material (Appendix B). With few exceptions, dredged material 

 exceeded the camera penetration depth. Redox rebound intervals, areas showing evidence 

 of intermittent or seasonal oxidation below the currently oxidized surface layer, were noted 

 at many stations over the H mound. Redox rebound is discussed further in Section 4.1.3. 

 The number of redox rebounds decreased from ten replicates in September to seven in 

 March out of a total of 15 replicates at the 5-grid stations. The depth of the redox rebound 

 also decreased 4.24 cm to 2.43 cm (or 6.36 cm to 5.21 cm, excluding stations without 

 rebounds). 



Physical REMOTS® parameters indicated the surface and near surface layers of the 

 mound were mainly composed of silt and clay with the major modal grain size consistently 

 reported at >4 phi. Mean camera penetration over the H mound showed no distinct 

 pattern, with the shallowest penetration (10.94 cm) at 50E and the deepest penetration 

 (18.14 cm) at 150W and an overall average of 15.06 cm. The range of camera penetration 

 depths were comparable to 1996 results (12.98-18.57 cm). Replicate-averaged surface 

 roughness values for the REMOTS® camera stations over the H mound ranged from 0.38 

 cm at 150N to 4.38 cm at lOOW. Again, the 1997 results were similar to those observed 

 in 1996, which ranged from 0.64 cm to 3.24 cm at lOOS. Aldiough some replicates were 

 indeterminate, surface roughness was attributed both to biogenic activity and, to a lesser 

 extent, physical effects. 



We compared the physical REMOTS® parameters of March 1998 to the September 

 survey results. The grain size was predominantly silt and clay (>4 phi). The mean 

 camera penetration depth was an average of 1.40 cm less than the September survey results 

 for the five stations. The mean boundary roughness values covering only the 5-station grid 

 were more consistent in March, ranging between 0.73 and 0.85 cm. Many of the 



Monitoring Cruise at the WLIS Disposal Site, September 1997 and March 1998 



