81 



The difference in metals concentrations was partially a function of grain size. To 

 provide accurate comparisons between different sediment types, metal concentrations are 

 typically normalized to grain size (percent fines) or to one of the dominant metals in crustal 

 rocks (Al or Fe). After normalizing the metals data to the percent of fine-grained sediments 

 (the only consistent analyte available), the inner cores still had the highest average 

 concentrations of lead (Pb), mercury (Hg), Ni, and Zn (Table 3-6). 



Only Zn was measured in both the short and long cores (Table 3-5). The range of Zn 

 measurements in the long cores was narrow (70.6 to 85.5 mg/kg), except for one higher 

 measurement from the 1 to 1.6 m interval in core 4A (1 16 mg/kg). The short cores from the 

 inner zone had the highest average Zn level (131.0 mg/kg), while the long cores had the 

 lowest average Zn concentration (84.0 mg/kg). 



All the averaged metals concentrations in the short cores were higher than the reference 

 values measured at WEST REF (Table 3-5) but this was a function of grain size differences 

 (see below). Because of the difference in sampling methods of the pre-dredge samples, the 

 average of 1990 and 1994 data, representing the entire depth of the channel to be dredged, was 

 reported separately from the 1992 data (Maguire Group 1995). The 1992 data were more 

 influenced by the concentrated contaminants in the upper 3 feet (Appendix E). 



Comparing raw metals concentrations to the pre-dredge samples, the core average 

 value of the metals As, Cr, Cu, and Hg fell between the average values measured for UDM 

 and CDM in 1990 and 1994 (Table 3-5; Figure 3-23). The average Cd and Pb concentrations 

 measured in the short cores were less than all of the pre-dredge values. Overall, the raw Ni 

 and Zn values were greater than measured in the 1990 and 1994 samples collected in the 

 UDM and CDM, but still significantly less than measured in the most contaminated surface 

 sediments (Figure 3-23). 



Because there were no grain size data available for the samples collected in 1992 from 

 the project area, only the 1990 and 1994 data were normalized for comparison to the 

 normalized metals concentrations measured in the Seawolf cores (Table 3-6). Normalized to 

 the fine-grained fraction, zone-averaged Cr, Cu, Pb, and Ni were all less than or similar to the 

 average normalized value measured in the CDM of the project area. Zone-averaged Hg and 

 Zn values fell between the averaged pre-dredge UDM and CDM values. Arsenic and Cd were 

 not compared because of the values below detection. In addition, all of the zone-averaged 

 concentrations were less than that calculated for WEST REF. Plotting the average normalized 

 concentrations of all metals in the short cores (short and long cores for Zn) shows the 

 similarity of the Seawolf cores to UDM, CDM and WESTREF (Figure 3-24). 



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



