52 



February 1996 and September 1997 surveys serves to confirm that up to 1.5 meters of 

 presumed additional consolidation had occurred, primarily in the central, thicker portions of 

 the mound (Figure 3-9). 



A small area of apparent accumulation is visible in Figure 3-9, in the northwestern 

 area over the naturally occurring slope. It is likely that this apparent change does not 

 represent actual net accumulation of material but rather some settling and redistribution of 

 cap material along the apron of the deposit (this result is discussed further in Section 4.2.1). 

 In the southwestern region of the mound, some apparent accumulation is located in the area 

 where additional CDM was placed after the postcap survey. CDM from the Mystic River 

 (4,900 m 3 ) was placed near the NDA 95 buoy from February 1 to March 1 1 1996, and 

 3,400 m 3 material was placed near the NDA 96 buoy during the 1996-97 disposal season. 

 The isolated areas of apparent accumulation in the eastern area of the survey are probably 

 survey artifacts (small errors from sequential surveys, most noticeable over slopes, see 

 Section 2.1.3). The elongated area of apparent consolidation west of NDA 96 is an artifact 

 from the steep slope in this area (see Figure 3-8). 



The July 1998 bathymetric survey over the Seawolf Mound showed depths ranging 

 from 13.4 m over the apex of the NL-RELIC Mound to 23.0 m in the southwestern corner of 

 the 1000 x 1000 m area (Figure 3-10). Water depths over the Seawolf Mound varied from 

 16 to 23 m and the mound area appeared as a flat region with a small oval apex, 50 m x 

 100 m. Depth difference calculations between the July 1998 survey and the October 1995 

 baseline survey (pre-Seawolf Project) showed a mound with peak heights of 3 to 4 m above 

 the pre-existing seafloor, with an approximate diameter of 600 m (Figure 3-11). The overall 

 configuration of the Seawolf Mound in 1998 was very similar to that measured in 1997 

 (Figure 3-8). 



The apparent stability of the Mound was further shown by the minimal amount of 

 consolidation calculated for the period between the September 1997 and July 1998 surveys 

 (Figure 3-12). The decrease in the rate of consolidation two years after placement of the cap 

 followed the typical pattern for dredged material mounds, with most of the consolidation 

 occurring within the first year (Poindexter-Rollings 1990). 



On the northeast side of the NDA 97 buoy location, a small isolated area of apparent 

 accumulation appeared (Figure 3-12). The disposal logs indicated, however, that no 

 sediment was directed to the NDA 97 buoy, but instead to the NL-91 and D/S Mound 

 Complex (500 m east at the southeast corner of this survey, Figure 1-2). This area of 

 apparent accumulation is located on the same steep slope that produced a survey artifact of 

 consolidation in 1997 (see above). Survey artifacts account for the other isolated apparent 

 increases and decreases of material throughout the survey area (see Section 2.1.3). 



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



