2i 



1998 Physical Parameters 



Both physical and chemical parameters are reported in comparison to the reference 

 core (26A) collected at WEST REF. In addition, the data are compared to the 1997 data 

 presented above. Finally, the physical and chemical data are evaluated relative to samples 

 collected from the dredging area as described above (Maguire Group 1995). 



Moisture Content. The moisture content was fairly uniform throughout the core 

 samples, ranging from 38-56% (Table 3-9). The average moisture content of samples 

 collected from the upper sediment (0-50 cm; short cores) in the inner and outer zones was 

 uniformly 52%, while the middle zone was slightly lower at 48%. The average of samples 

 collected in the long cores was similar (47%), with the lowest value occurring in the deep 

 sample (1.0-2.0 m) of Core 23 A. With the exception of the middle zone, all moisture 

 content zone averages were within 2% of the 1997 averages. The middle zone was 6% less 

 than the 1997 average, due to higher percent gravel and sand values in Core 21 A. All of the 

 moisture content values from the Seawolf Mound cores were significantly higher than those 

 measured at the WEST REF reference area (28.4%) due to differences in grain size (see 

 below). 



Grain Size. Most of the samples collected from the Seawolf Mound consisted of silty 

 clay, containing less than 13% sand and gravel (Table 3-9). Notable exceptions included short 

 Core 21 A, which had a high sand component (51%) and only 44% silt/clay, and long Core 

 23 A (1.0-2.0 m), which was predominantly (57%) sand and gravel. Comparison of samples 

 collected from the top 50 cm of the short sediment cores in the three zones of the Seawolf 

 Mound indicated consistently low mean levels of gravel (1.0%, 1.7%, 0.7%, for inner, middle, 

 and outer zones, respectively). The mean percentages of sand increased with distance from 

 the mound center (3.7% to 5.5% to 7.0%), excluding core sample 21A. Core 21 A was 

 collected on the northeastern apron of the Seawolf Mound (Figure 2-6), suggesting the 

 incorporation of ambient sandy sediment in this sample. The other cores were collected well 

 within the 0.25-m bathymetric footprint on the western and southwestern sides of the mound 

 (Figure 2-6). 



The vertical stratification of the mound was assessed with respect to each zone 

 (Table 3-9). The short core samples and long core sample 23A (0.5-0.75 m) collected from 

 the inner zone had consistent grain size distributions. The sand content increased with depth 

 in the inner zone long core from 4% (0.5-0.75 m) to 11% within the 0.75-1.0 m interval. The 

 1.0-2.0 m sample had a significantly higher gravel (20%) and sand (37%) content than any 

 other sample analyzed. This sample was collected in apparent UDM, according to core 

 descriptions, because of its oily appearance. 



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



