122 



3.5 NL-92 Disposal Mound 



The NL-92 mound is a small dredged material disposal mound formed by the 

 disposal of approximately 18,000 m 3 of dredged material at the NDA 92-2 buoy. This 

 small deposit was detected in the August 1995 bathymetric survey (Figure 3-35). A 

 0.56 km 2 area surrounding the NDA 92-2 buoy position was selected as the area of detailed 

 analysis. The NL-92 mound was found to be 140 m wide, with a maximum height of 0.6 

 m (Figure 3-54). A REMOTS® sediment-profile photography survey was not conducted 

 over the NL-92 mound, because this location was planned to be used for dredged material 

 disposal relatively soon after the bathymetric survey. 



3.6 NLDS Reference Areas 



Three reference areas for NLDS (NLON REF, NE REF and WEST REF) were 

 surveyed with the REMOTS® sediment-profile camera in August 1992, August 1995, 

 September 1997 and July 1998. These reference areas provide a basis for comparison with 

 the images collected over the NLDS project mounds and aid in determining the health of 

 the benthic community within the disposal site. The condition at NLON REF, NE REF, 

 and WEST REF is presumed to reflect seasonal and annual variations in environmental 

 conditions. Three replicate photographs were collected at each reference area station and 

 subjected to the identical series of measurements and criteria used to characterize benthic 

 habitat within the disposal site. A complete set of REMOTS® image analysis results for 

 each reference area and each survey are presented in Appendix B. 



3.6.1 August 1992 Survey 



A 13-station cross-shaped grid was established over each of the three NLDS 

 reference areas in August 1992 (Figure 2-8). The results obtained from the reference areas 

 were used in comparison to the data collected over the NL-91 and D/S mound complex. 



Dredged material was not apparent at any of the reference stations. Sediment 

 layering (sand-over-mud stratigraphy) was noted in multiple replicate photographs at NE 

 REF and NLON REF. The surfaces at these stations were characterized by shell fragments 

 and fine sands overlying silt and clay, with the formation of some bedforms (ripples). 



The stations over NE REF and NLON REF displayed very similar sediment grain 

 size distributions, relative to the disposal site, with a major mode of 3 to 4 phi (very fine 

 sand; Table 3-9). The WEST REF was also characterized as predominantly sand, but 

 sediment grain size major modes varied between 2 to 3 phi (medium to fine sand), 



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



