18 



photographs taken only 12 m apart showed a thick oxidized sand layer in one and highly 

 reduced muds extending nearly to the surface in the second (Figure 3-6[A] and 3-6[B]). 

 Although the thickness of the surface sand layer varied, it was greatest at the center station 

 (7.76 cm; Figure 3-7). At most stations over the NL-TR mound, the thickness of the 

 dredged material layer exceeded prism penetration. 



In addition to the NL-TR mound, dredged material was identified in all stations of the 

 REMOTS® survey centered on the NL-85 mound (Figure 3-7). As at the NL-TR mound to 

 the north, sand-over-mud was the dominant dredged material stratigraphy. At the NL-85 

 mound, relic dredged material with presumably fresh overlying sand was present at Station 

 N100N and along the southern and western portions of the cross-grid survey (Figures 2-1, 

 3-7). At Station N300N, which is close to the 400S station of the NL-TR REMOTS® grid, 

 the poorly sorted sand overlying mud probably derived from disposal at the NL-TR mound 

 (Figure 3-8). 



The sediment grain size major mode across the active disposal region (NL-TR) 

 consisted of either fine sands (3-2 phi) or very fine sands (4-3 phi; Figure 3-9). The only 

 exception to this was Station 100SW, where medium sands (2-1 phi) were predominant. 

 Similarly, at the NL-85 mound, sediment grain size major modes were either 3-2 phi or 

 4-3 phi (Figure 3-9). The one station (N100W) which exhibited coarser grained sediment 

 (2-1 phi) was also affiliated with dredged material. All dredged material was characterized 

 by poorly sorted sands overlying mud. Patches of densely aggregated mussels (Figures 3-7 

 and 3-10) were also frequently present on the mounds, particularly in the western region of 

 NL-TR and the southern, eastern, and northern areas of NL-85. 



The reference areas were not substantially different in grain size distribution from 

 stations on the disposal mounds. At the northeast reference area (NE-REF) and the New 

 London reference area (NLON-REF), grain sizes were almost uniformly 3-2 phi, with only 

 two or three stations in either region exhibiting a major mode of 4-3 phi. Grain sizes were 

 coarser (2-1 phi) over most of the western reference area (W-REF), with the exception of the 

 northern and central stations, which were 3-2 phi. All stations at W-REF were characterized 

 by large amounts of shell fragments and low camera penetration (Figure 3-11). 



The mean boundary roughness (the difference between the maximum and minimum 

 prism penetration of the REMOTS® camera) of the NL-TR and NL-85 mounds on the 

 disposal site was 2.11 cm (s = 1.22 cm). Roughness values were highest in the central and 

 western regions of the NL-TR mound, and in the central, northern, and western areas of the 

 NL-85 mound (Figure 3-12). The mean boundary roughness of all stations on the disposal 

 site was significantly different from the mean for the pooled reference areas (p = 0.005, 

 Mann- Whitney U-test). An important contributor to the increased boundary roughness at the 

 disposal site was the presence of dense mussel aggregations at several stations in the NL-TR 



Monitoring Cruise at the New London Disposal Site, June- July 1990 



