9.? 



The middle zone short Cores 18A and 20A had similar grain size percentages as 

 middle zone long Core 19 A, which had remarkably consistent distributions of gravel, sand, 

 and fine sediments with depth. All of these samples were dominated by the fine-grained 

 fraction (>90%). Both the short and long outer zone cores also contained mostly silt and clay 

 (Table 3-9). 



The cores collected from the Seawolf Mound overall consisted of a much higher fine- 

 grained fraction compared to the reference core (26A). The exception was the grain size 

 distribution of 21 A (5%: 51%: 44% for gravel, sand, silt/clay, respectively), which resembled 

 the reference WEST REF sample (3%: 65%: 32%). Again, these data suggested this core 

 consisted primarily of ambient material, consistent with the bathymetric footprint (Figure 2-6). 



Comparing the 1998 core results with those from the previous year indicated a slight 

 increase in the percentage of fine-grained sediments (87.2%) on the Seawolf Mound than 

 observed in 1997 (81.4%). This is a relatively modest change given the high inherent 

 variability of dredged material. Finally, both of the long cores collected from approximately 

 the same location of the inner zone in 1997 (Core 10A) and in 1998 (23 A), indicated patches 

 of black, oily sediment with sand and gravel in deeper intervals. Below 2.4 m, Core 10A was 

 described as an oily gravel, which was the only visual indication of UDM apparent in the 1997 

 coring survey. Core 23 A (Appendix D) showed a black, gravelly sand region from 1 . 1 to 1 .9 

 m. The oily gravel was not sampled for chemical parameters in 1997, but was sampled in 

 1998 (see below). 



TOC. Concentrations of total organic carbon (TOC) measured in the core samples 

 showed a bimodal distribution, with one group of values ranging from 1.8 to 2.4%, and a 

 second group ranging from 5.1 to 6.7%. Overall, TOC ranged from 1.8 to 6.7%, with an 

 average of 2.9% (Table 3-9). The higher TOC values were all in cores from the inner zone, 

 resulting in the highest mean TOC value of the surface samples (0-50 cm) in the inner zone 

 (4.27%) relative to the middle and outer zones (2.17 and 1.97%, respectively). The Seawolf 

 Mound mean TOC value was higher than that measured at WEST REF, (1.6%). The overall 

 mean for the 1998 mound data (2.9%) was greater than the 1997 mean TOC (2.13%). No 

 TOC data were reported for the pre-dredge samples (Maguire Group 1996). 



1998 Geochemistry 



Metals. Trace metals (As, Cd, Cr, Cu, Pb, Hg, Ni and Zn) were analyzed from the top 

 0-0.5 m of the short cores (Table 3-10). Mercury (Hg) was detected in only two of ten 

 samples at levels barely above the detection limit, with the remaining samples below the 

 detection limit of 0. 10 mg/kg. Uniformity of concentrations was apparent in all cores for As 

 (4.1-9.4 mg/kg), Cd (0.12-0.25 mg/kg), and Cr (23-51 mg/kg), with standard deviations of 



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



