76 



3.1.2.3 September 1997 Survey 



In September 1997, a second follow-up REMOTS® sediment profile photography 

 survey was conducted to document the continued benthic recovery over the NL-91 and D/S 

 mound complex. Station locations were based on the same modified 13-station grid 

 occupied in August 1995 (Figure 2-4B). 



Recent and/or historic dredged material was both detected and greater than the 

 penetration of the camera prism in all replicates, with averaged thickness ranging from 6.8 

 to 18.2 cm (overall average of 14.2 cm). The replicate-averaged mean camera penetration 

 over the mound was somewhat deeper than the previous survey. As a result, the images 

 displayed more layering of material relative to the 1995 survey, with fine sand over 

 reworked dredged material, over fine organic silt at several stations (Figure 3-25 A). 



As in previous years, fine to very fine sand characterized the sediment over the NL- 

 91 and D/S mound complex (Table 3-3). The major modal grain size was 4 to 3 phi (very 

 fine sand) in most photographs, with a mix of silt-clay in nine of the 42 images. Station 

 200W displayed medium-grained sand (2 phi), along with shell fragments and remnants of 

 decaying amphipod tube mats (Figure 3-25B). Surface sand overlying fine-grained 

 sediment (sand-over-mud stratigraphy) was noted at every station over the disposal mound. 

 Granule and pebble sized grains were noted at the sediment-water interface in multiple 

 replicates collected at Stations 100S and 200S (Figure 3-26A & B). 



The replicate-averaged boundary roughness values ranged from 0.6 to 2.2 cm 

 (Table 3-3). In contrast to samples collected in 1995, boundary roughness was primarily 

 attributed to physical forces, although some surface disturbances were indeterminant or 

 caused by biogenic activity. Evidence of physical disturbance of the surface included 

 abundant disturbed amphipod tube mats, surface scour, and shell lag deposits. Individual 

 replicates at Stations 200N (a) and 300N (b and c) showed evidence of winnowing of fines 

 at the sediment surface. 



The replicate-averaged apparent RPD ranged from 1.0 to 6.7 cm (4.47 average; 

 Figure 3-27). Stations 200E, 400E, and 300N had a visible redox rebound layer ranging 

 from 5 cm to 10 cm below the sediment-water interface, indicating a recent reduction in the 

 RPD depth. 



The successional status was advanced, showing healthy Stage II or Stage II on III 

 communities inhabiting the sediments of the NL-91 and D/S mound complex (Figure 3-28). 

 Some of the photographs were identified as Stage I to II due to the presence of disturbed and 



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



