132 



UDM was classified as unsuitable based on biological testing results, but some of the 

 chemical analyses, notably those conducted in 1992, did indicate that the sediments were 

 elevated in contaminants, especially in PAHs, relative to reference data. 



Samples collected in the material from the dredging areas ranged from pure silt-clay 

 in the channel (1994 samples) to dominantly sand (>50%) in the outer channel reaches 

 (Maguire Group 1997). The sand content in the cores suggested that the upper 50 cm of the 

 Seawolf Mound was representative of CDM from the outer Thames River (sand averages 

 20% [inner, outer zones] to 31% [middle zone]). The visible presence of clay in the top 

 layers of the cores (and REMOTS® photographs) was representative of the last CDM placed 

 at the Seawolf Mound, which was predominantly material resulting from improvement 

 dredging (gray Gardiners clay). 



In addition to the core descriptions and grain size results, the overall lack of elevated 

 contaminant concentrations typical of the surface sediments of the most contaminated pier 

 areas suggested that at least the upper 50 cm of the disposal mound consisted of CDM. 

 Specifically, the PAH concentrations were low overall, with little variability in the samples 

 collected either spatially across the mound (inner, middle, and outer zones), or with depth in 

 the long cores. These results confirmed the placement of CDM across the mound, as well as 

 indicating that the thickness of CDM exceeded 50 cm in the inner, middle, and outer zones. 

 The chemistry data were evaluated in context of the different zones of the deposit in parallel to 

 the apex, plateau, and apron areas discussed above. 



Figure 4-13 depicts the core locations from 1997 and 1998 with respect to the UDM 

 deposit and final capped mound footprint. With the placement of capping material and 

 passage of time, the UDM deposit consolidated since the December 1995 precap survey. 

 Therefore, even though the figure suggests that the peaks of the capped mound and the 

 UDM deposit have a similar height, the CDM layer actually compressed the UDM (Figure 3- 

 6), which further consolidated between the 1995-96 CDM placement activity and the 1997 

 and 1998 surveys. As mentioned previously, the small area of UDM on the eastern edge of 

 the mound that did not appear to be sufficiently covered by capping material in the 

 bathymetric depth difference plots, did appear to be covered adequately by CDM in 

 REMOTS® images from Station 300E over this location. Figure 4-13 shows that the UDM 

 deposit was located primarily within the inner zone, with the apron of the deposit extending 

 into the middle zone beneath the CDM layer. 



4.2.4.1 Outer Zone 1997 



In 1997, five cores were collected in the outer zone, four short cores (2A, 2B, 3A, 

 3B), and one long core (4A). All of the short cores, collected near the boundary of the limit 

 of detectable dredged material (Figure 4-13), indicated that ambient material was collected 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



