135_ 



gravel, and silty clay were recovered, indicating potential recovery of UDM. No chemical or 

 grain size samples were collected, however, in that part of the core, in accordance with the 

 sampling design (Table 2-6, but see results for 23 A below). The grain size and chemistry 

 data of the three samples collected in Core 10A were consistent with the other inner zone 

 cores, including the lowest sand percentages (5-8%), and high total fines (92-95%). 

 Because no chemistry data were available for the improvement material (gray clay), however 

 the metals concentration in the areas of higher clay may be related to the clay content. 



Trace metal and PAH concentrations of the upper 50 cm (short cores) in 1997 and 

 1998 confirmed the presence of CDM over the Seawolf Mound. The trace metal 

 concentrations stayed relatively constant from 1997 to 1998 and in most cases the 1998 

 samples were lower than values detected in the previous year, which was probably due to 

 both spatial and analytical variability. Normalized to the fine-grained fraction (silt and clay), 

 trace metal concentrations were similar or less than measured in the CDM prior to dredging 

 (Figure 3-28). The exception was the average value of Zn, because of one sample with a 

 relatively high value in one surface (0-50 cm) core (14B). This core was located in the 

 southwestern region of the mound, where ambient material was detected below the layer of 

 CDM. A similar small elevation in PAH concentrations, relative to the other short core 

 samples (see below), supports a conclusion that this sediment was not Seawolf UDM, but 

 probably reflects either an existing elevation in the ambient sediments at this location or 

 dredged material associated with other projects. In addition, the zinc value in Core 14B was 

 well below the maximum values measured at the dredging site prior to dredging. 



4.2.4.4 Core Results 1998 



Both the long and short core samples from the Seawolf Mound in 1998 contained 

 average PAH values that were less than either the UDM or the CDM PAH data collected 

 prior to dredging. For example, the average LMW PAH phenanthrene concentration 

 measured in the short cores was 25 Ug/kg, compared to 44 and 565 Ug/kg measured in the 

 UDM in 90/94 and 92, respectively. The maximum concentrations of PAHs were measured 

 in the samples from the deepest sections of long Cores 17A and 23 A and the 0.5-0.75 m 

 sample from middle Core 19A (Table 3-7). These concentrations were similar to PAHs 

 measured in CDM/UDM in 1990/94 and significantly less than that measured in 1992. 

 Some of the differences in PAH concentrations were due to the variability of organic carbon 

 (Figure 4-14). 



All of the short cores in all three zones in 1998 had TOC-normalized PAH levels that 

 were consistently less than the concentrations at the reference area (Figure 4-14; Appendix 

 D, Tables 1 and 2). PAH levels (LMW and HMW) generally increased with depth and were 

 greater than the reference area values in downcore samples from the middle and outer zones. 



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



