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3.0 RESULTS 



3.1 NL-91 and D/S Mound Complex 



3.1.1 Bathymetry 



The August 2000 bathymetric survey showed an average depth in the surveyed area 

 of 1 8.3 m, with depths ranging from 22.8 m in the deeper trough along the southern edge of 

 the area to 14.8 m along the edge of the NL-RELIC mound to the northwest (Figure 3-1). 

 The NL-91 and D/S Mound Complex, labeled "D/S" in Figure 3-1, is located in a shallow 

 seafloor depression. As a bottom feature, it is not well defined, having relatively flat 

 topography compared to the surrounding disposal mounds NL-Relic, NL-III and NL-85 

 (Figure 3-1). 



The comparison of the September 1997 and August 2000 bathymetric surveys 

 resulted in the construction of a preliminary depth difference map which showed a 

 significant number of locations scattered evenly throughout the surveyed area with apparent 

 depth differences ranging between -0.5 and +0.75 m. Most of the areas of apparent depth 

 difference were relatively small-scale and consistently aligned with more complex seafloor 

 features (i.e., areas of greater or lesser vertical relief than the surrounding seafloor). In such 

 locations, it is known that minor deviations in depth measurements can become exaggerated 

 when successive bathymetric surveys are compared. Since there was no dredged material 

 placed at these locations, the apparent depth changes were considered to be normal artifacts 

 of the depth differencing procedure. 



In the vicinity of the D/S buoy, depths were consistently shallower in the 2000 survey 

 compared to 1997 (Figure 3-2). Specifically, the area located between the former NDA-91 -2 

 and D/S buoy positions in Figure 3-2 is one where the depth differences were consistently 

 positive, ranging between 0.25 and 0.5 m. This suggests a subtle rise in the seafloor within 

 the area of the NL-91 and D/S Mound Complex, consistent with the placement of an 

 estimated barge volume of 30,000 m^ of supplemental CDM in this area between the 

 September 1997 and August 2000 bathymetric surveys. The estimated 30,000 m^ of 

 supplemental CDM emanated from several different dredging projects, and there is good 

 spatial correlation between the placement locations at the sea surface (mainly around 

 recommended Capping Points 1 and 2) and the resulting deposit detected on the seafloor 

 through bathymetric depth differencing (Figure 3-3). 



3.1 .2 REMOTS® Sediment-Profile Photography 



REMOTS® results from the NL-91 and D/S Mound Complex were used to delineate 

 the distribution of the CDM on the seafloor and to evaluate the status of the benthic 



Monitoring Cruise at the New London Disposal Site, August 2000 



