775 



approximately 1200 m to the southwest of the current disposal site boundaries 

 (Figure 3-50). 



Depth difference comparisons between the 1986 and 1997 surveys (corrected to 

 MLLW and NAD 83) show sizable accumulations of dredged material corresponding to the 

 formation of several mounds, including the Seawolf (1995) NL-TR/USCGA (1989-90), 

 and NL-88 (1988) mounds. There were no corresponding changes in depth between 1986 

 and 1997 near the "NL" buoy (Figure 3-50). As a result, this ridge represents a natural 

 geologic feature on the seafloor of eastern Long Island Sound. Survey artifacts were 

 identified in the northern area of the disposal site along the east-west slope visible in 

 Figure 3-50. The small patches of apparent accumulation in the southern portion of the 

 disposal site also may be a result of "noise" from various bottom features. 



3.4.2 NLDS Northern Region 



The Northern Region of NLDS (Figure 2-7) was surveyed in September 1997 using 

 precision bathymetry and REMOTS® photography to provide an adequate baseline for valid 

 depth difference calculations and assessment of benthic conditions in future surveys. 



3.4.2.1 Bathymetry 



Depths in the Northern Region ranged from approximately 14 m near the northern 

 end of the NL-RELIC mound to >23 m in the southwest corner (Figure 3-51). The 

 deepest area of the Northern Region was consistent with the overall topography of the 

 area. 



3.4.2.2 REMOTS® Sediment-Profile Photography 



The September 1997 REMOTS survey of the Northern Region consisted of sampling 

 at eleven stations (Figure 2-7). Historic dredged material was detected at seven of the eleven 

 stations distributed within the region. Dredged material was commonly characterized by a 

 chaotic sediment fabric, gray clay, or disturbed surficial layers, and in most cases was easily 

 distinguished from the brown, sandy ambient material. Dredged material was not detected 

 in any replicate image obtained from Stations Nl, N3, N5, and N10 (Table 3-8). However, 

 some historical material placed over 20 years ago at the NL-Relic mound, near Station N5, 

 may now appear similar to ambient material. Station N9, located at the northern edge of the 

 Seawolf Mound may have been influenced by dredged material disposed during the 1995-96 

 disposal season. 



Monitoring Cruise at the New London Disposal Site, 1992 - 7995 



