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material (Figure 3-10) whereas surrounding the new mounds, the surface sediments were 

 reworked older dredged material (lighter in color). 



The surface of these deposits converged over time with the development of a 

 reworked shelly sand surface seasonally occupied with amphipod tubes. The lateral edges 

 of the original deposit were clear in 1992, but became less clear as subsequent deposition 

 and reworking caused the surface sediments to converge in appearance. This similarity in 

 appearance indicates a continual effect of biological and physical reworking as amphipods 

 trap mud and tidal currents transport fine sand and shell fragments. In 1997 the pattern of 

 distribution was quite uniform with fine to very fine sand over the entire survey area 

 including the NL-91 and D/S mound complex, and similar to the reference areas. 



After deposition of new material in 1997-1998, a fresh layer was found over the 

 center of the Dow/Stonington UDM (Figure 3-29). The 1997-1998 disposal logs indicated 

 that 6,850 m 3 of sediments were placed over the northern area of the D/S mound as 

 supplemental cap (Figure 3-30). This material was seen as distinctive layers of fresh 

 dredged material in stations over the older D/S Mound sediments and to the north (Figure 

 3-33). In some stations to the east, the new material was not sufficiently distinct to 

 measure thickness but was darker and showed fewer signs of biological reworking. 



One location beyond the southern margin of the NL-91 and D/S mound complex 

 (1992 Station 400 S) had a distinctive layer of pebbles, shells and sand on the surface 

 (Figure 3-15). This station is located on the top of a slope at the very edge of older 

 dredged material accumulation. It is likely to represent a lag deposit formed from older 

 dredged material. It also provides a useful reference mark because this coarse material 

 was detected in each subsequent survey (400S 1992 became Stations 200S in 1995, 1997, 

 1998; Figures 3-21,3-26,3-31). The consistency of results from this station located just 

 beyond the margin of the disposal mound complex over a period of six years combined 

 with no net topographic change is clear evidence of the physical stability (armoring) of this 

 area. 



The NL-91 and D/S mound complex is located in a depression surrounded by 

 disposal mounds which provide protection from tidal currents and waves. This mound 

 complex has remained physically stable from 1992 through 1998. During this time the 

 mound and surrounding areas have supported a stable, healthy benthic community. Any 

 significant physical erosion (more than about a centimeter) or impact from biologically 

 unsuitable sediments would have been evident in the REMOTS® sediment profile 

 photographs collected during this period. 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



