33_ 



interface to below the imaging depth of the REMOTS® camera prism at each station 

 (dredged material thickness measurement indicated with a "greater than" sign in Table 3-3). 

 There was no dredged material observed in the images at stations 300E, 450N, and 450NE 

 located on the mound apron (Figures 3-1 1 and 3-12B). At these stations, the surface 

 sediment appeared to consist of ambient sandy mud. 



The Seawolf Mound consisted predominantly of fine-grained silt/clay sediments 

 (grain size major mode of >4 phi) having a significant fine sand component. At most of the 

 stations on the mound, the dredged material comprising the surface sediments was described 

 as a "sandy mud" or "sandy gray clay." The gray clay (Gardiners Clay) is characteristic of 

 this mound and has been observed consistently in previous surveys (SAIC 2001b). 



The boundary roughness at the Seawolf Mound ranged fi-om 0.7 to 4.0 cm, with an 

 average of 1 .5 cm, which was greater than the average value measured at the reference areas 

 (0.8 cm; Tables 3-2 and 3-3). There was no obvious spatial pattern of boundary roughness 

 values, which were attributed primarily to biological activity (tube construction). Similar to 

 the NL-91 and D/S Mound Complex, a depositional layer of organic detritus was observed 

 on the sediment surface at almost all of the stations. 



Lag deposits of shells or pebbles were noted at the sediment-water interface at several 

 stations over the Seawolf Mound (Figure 3-1 3 A and B). These lag deposits are the result of 

 minor winnowing of fine-grained sediments and serve to armor the surface of the disposal 

 mound. By blocking the winnowing effects of near bottom water currents, these armoring 

 deposits actually prevent mobilization of the underlying fine-grained material and stabilize 

 the surface of the disposal mound. 



The replicate-averaged apparent RPD depth for each station ranged fi-om 1 .76 to 

 4.35 cm (Figure 3-14; Table 3-3). The overall average for the Seawolf stations was 3 cm, 

 which was greater than the average RPD (2.66 cm) at the reference areas, suggesting healthy 

 aeration of the sediment surface on the Seawolf Mound. There was no evidence of low 

 dissolved oxygen (DO) conditions or redox rebounds observed in the Seawolf mound 

 sediment profile images. 



The successional status was advanced, with Stage II or Stage II on III communities 

 inhabiting the sediments of the Seawolf Mound (Figure 3-15). Stage III organisms were 

 present at 23 of 29 stations. Large tubes of the polychaete Chaetopterus sp. were visible in 

 several of the replicate images, providing fiirther evidence of advanced recolonization over 

 the Seawolf Mound dredged material (Figure 3-16A). Comparable with the NL-91 and D/S 

 Mound Complex, a significant proportion of the images showed dense tube mats of the 

 amphipod Ampelisca sp. Some of these tube mats appeared to be in a state of decay, but 

 active mats comprised of both adults and juveniles were widespread (Figure 3-1 6B). 



Monitoring Cruise at the New London Disposal Site, August 2000 



