62 



(3-4 phi), with many replicate images displaying small pebbles and recently dredged shells 

 within a sandy matrix. These sediments were found extending out to 400 m west, 500 m 

 east and south, and 200 m southwest of the NL-91 center. Isolated pockets of fine sand 

 were found 300 m north, as well as 600 m south and 600 m southeast (Figure 3-14). 

 Station 400S, lying on a relatively steep bathymetric slope, displayed evidence of a harder 

 bottom with shell, pebble, and hydrozoan growth at the sediment water interface (Figure 3- 

 15). 



Within NLDS, mean boundary roughness values ranged from 0.4 cm to 3.1 cm. 

 Two stations on the mound flanks, 100NW and 100SE, showed the highest roughness 

 values of 2.6 cm and 3. 1 cm (Table 3-1). Seventy-eight percent of the stations at the 

 disposal site were classified as having a biological boundary roughness, while 22 percent 

 had a physical boundary roughness. Ninety-four percent of the reference stations had a 

 biological boundary roughness while six percent were physical in nature. 



The mean apparent RPD depths at NLDS ranged from 0.3 cm at Stations 500SE 

 and 600ESE to 3.7 cm at Station 200NW with a majority (33%) of stations exhibiting RPD 

 depths within the 1.5 to 2.0 cm range (Figure 3-16; Table 3-1). No evidence of a redox 

 rebound layer (recent reduction in the depth of oxidized sediments) was detected in any 

 REMOTS® image collected during the 1992 survey over the NL-91 and D/S mound 

 complex. 



In general, the area surrounding the D/S mound showed strong signs of benthic 

 community recovery with a diverse population of Stages I, II, and III assemblages (Figure 

 3-17). Twenty-five of the forty-one stations sampled displayed some combination of Stage 

 I, II, or III assemblages (Table 3-1). Eight stations displayed healthy Stage I populations 

 progressing to Stage II. Stage II was denoted by the presence of distinct tubes of the 

 amphipod Ampelisca sp. at the sediment surface (Figure 3-18). Three stations (7%) 

 exhibited Stage II individuals colonizing the surface sediment while Stage III assemblages 

 were actively feeding in the layers below the sediment-water interface. Finally, six 

 stations had representatives from all three end-member assemblages present in the 

 REMOTS® photographs. 



Eight stations (20%), including the survey center, had Stage I individuals inhabiting 

 the sediments over a population of Stage III organisms (Figure 3-17). Apparently, by 

 occupying the sub-surface sediment layers, Stage III individuals (deposit feeders) were able 

 to survive a modest disposal event and migrate up through the thin layer (0.2 m to 0.3 m) 

 of newly deposited sediment. Fifteen of the remaining REMOTS® stations sampled 

 possessed an exclusive population of Stage I (27%) or Stage II (10%) individuals. 

 Exclusive Stage I populations were found at eleven stations. Stations 200 m south and 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



