46_ 



buoy locations (Figure 3-2). Placement of the supplemental CDM from several different 

 dredging projects was concentrated around these former buoy locations, which correlates 

 well with the depth difference results (Figure 3-3). Overall, the August 2000 bathymetric 

 survey results serve to verify the prediction that the placement activities since September 

 1997 would result in an accumulation of supplemental CDM on the seafloor having a 

 thickness on the order of 0.5 m. 



A second, related objective of the August 2000 monitoring survey over the NL-91 and 

 D/S Mound Complex was to map the spatial distribution of the supplemental CDM on the 

 seafloor. Aside from the CDM detected through depth difference comparisons, the August 

 2000 REMOTS® photographs identified layers of recently placed (1997-2000) capping 

 material over the majority of the mound complex. Specifically, recently placed CDM was 

 noted at 9 of the 13 REMOTS® stations over the NL-91 and D/S Mound Complex, 

 coinciding very well with the accumulations of CDM detected by bathymetry (Figure 3-4). 

 The combined bathymetry and REMOTS® results indicate that the supplemental cap material 

 completely covers the original deposit of UDM that was placed during the 1991-1992 

 disposal season (Figure 3-4). 



A change in surface sediment composition was the primary indicator of recent CDM 

 deposition, as marked by the presence of sandy mud (predominant grain size major mode of 

 >4 phi) comprising the surface sediment during the August 2000 survey where fine sand 

 (4 to 3 phi) existed previously (Table 4-1). The layers of new CDM often exceeded the 

 penetration depth of the REMOTS® camera prism, yet were below the threshold of detection 

 for the bathymetric depth difference comparisons. Therefore, while the sediment profile 

 photography results generally coincide with the bathymetric depth difference results, the 

 contour line in Figure 3-4 indicates a wider CDM distribution due to the ability of the 

 sediment profile camera to reveal relatively thin layers which were not detected acoustically. 



Over the past few years. Station lOON has been subjected to multiple cap placement 

 events. As a result, the images collected at this station are ideal for fracking the composition 

 of each new layer of CDM placed over the historic mound complex (Figure 4-1). Figure 4- 

 1 A depicts the siu-face of NL-91 and D/S in September 1997 before cap augmentation 

 operations began. A layer of fine sand over silt and clay deposited during the 1991-92 

 disposal season is visible in this image. Figure 4- IB is a photograph collected in July 1998 

 after the deposition of over 6,500 m' of Shennecossett Yacht Club material near Capping 

 Points 1 and 2 during the 1997-98 disposal season (Figure 3-3). A surface layer composed of 

 medium sand to pebble-sized grains over brown, fine sand indicates the presence of 

 supplemental cap material. The final image (Figure 4-lC), obtained during the August 2000 

 survey, shows another change in surface sediment composition over Station lOON. A third 

 layer of CDM having a thickness of 9 cm and consisting primarily of silt was detected after 



Monitoring Cruise at the New London Disposal Site, August 2000 



