78 



Grain Size. The balance between the gravel/sand (coarse fraction) and silt/clay (fine 

 fraction) content of the Seawolf Mound core samples was quite consistent among all of the 

 samples from all of the cores. The fine fraction ranged from 63 to 95%, with an average of 

 81% and a narrow standard deviation of 9.5% (Table 3-4). Comparing the average silt/clay 

 concentration of samples collected in the upper 50 cm of the three zones around the Seawolf 

 Mound, the inner and outer zones were most similar (80%) with the lowest occurrence (69%) 

 in the middle zone. On average, the long cores had the highest fine fraction (88.6%). It 

 appears that sediments sampled in the middle zone were enriched in sand compared to the 

 other zones and that the long cores had consistently high silt and clay content throughout their 

 lengths (Table 3-4). 



The grain size of the Seawolf Mound cores was clearly different from the WEST REF 

 core which was dominated by sand (72%). The average silt and clay fraction of the core 

 samples (81%) was markedly higher than the average of both the pre-dredge UDM (43%) and 

 CDM (47%) samples collected in 1990 (Maguire Group). The reported fine-grained fraction 

 (silt and clay) measured in 1994, however, was 100%. 



TOC. Concentrations of total organic carbon (TOC) measured in all of the cores 

 ranged from 1.1 to 2.9%, with an average of 2.1% (Table 3-4). The majority of values were 

 greater than 1.8%, except for one short core sample from the outer zone (2A). The averaged 

 TOC values from the surface samples (0-50 cm) in each zone were higher in the inner zone 

 (2.23%) and lower in the middle and outer zones (2.1%). The sediment collected below the 

 upper 50 cm in the long cores had the highest average TOC concentration (2.26%). 

 Consistent with the grain size data, the measured TOC values in the core samples from the 

 Seawolf Mound were all higher than the value of 0.5% measured at WEST REF. No TOC 

 data were reported for the pre-dredge samples. 



1997 Geochemistry 



Metals. Arsenic and cadmium were not detected in any sample, at detection limits 

 ranging from 14-15 ppm (As) and approximately 0.6 ppm (Cd; Table 3-5). Of the other 

 measured metals, the average concentrations were consistently highest in the short cores of the 

 inner zone for all metals, and lowest in the outer zone for copper (Cu), nickel (Ni), and zinc 

 (Zn). Zone-averaged Cu values ranged from 24.4 mg/kg (outer zone) to 28. 1 mg/kg (middle 

 zone) to 34.6 mg/kg (inner zone), although there was much intra-zone variability (Table 3-5). 

 Similarly, zone-averaged Ni ranged from 20.7 mg/kg (outer zone) to 21.5 mg/kg (middle 

 zone) to 25.4 mg/kg (inner zone), and Zn ranged from 82.7 mg/kg (outer zone) to 103.6 

 mg/kg (middle zone) to 131.0 mg/kg (inner zone). 



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



