5J_ 



correspondingly high OSI values (Table 4-1). The 1998 REMOTS® data acquired for these 

 stations showed a sharp decline in benthic habitat conditions, as OSI values of +3 were 

 calculated for both stations. This decline was primarily due to the apparent lack of Stage III 

 activity and shallow RPD depths (Figure 4-2A). The data collected over 300E and 400E 

 during the August 2000 survey showed marked improvement over the 1 998 results, with a 

 significantly deeper RPD, evidence of Stage III activity, and corresponding OSI values 

 increasing to +6 and +9, respectively (Figure 4-2B; Table 4-1). 



This cyclic deterioration and recovery within dredged sediments deemed suitable for 

 unconfined openwater disposal is not common, but has been documented at other disposal 

 sites in Long Island Sound. A similar condition exists at Station 200N on the New Haven 

 1993 (NHAV 93) mound at the Central Long Island Sound Disposal Site (CLIS; Morris 

 1998). At CLIS, this phenomenon seems to be a function of sediment oxygen demand 

 (SOD) within the organically enriched material and the timing of survey activity relative to 

 the onset of seasonal hypoxia. However, seasonal hypoxia has not been viewed as a 

 significant issue at NLDS, due to the amount of water exchange between eastern Long Island 

 Sound and open water (Block Island Sound). Although the material that comprises the 

 eastem lobe of the NL-91 and D/S Mound Complex probably contains high concentrations of 

 labile organic matter, the benthic habitat conditions detected at 300E and 400E in 1998 is 

 likely the result of a recent, localized physical disturbance (e.g., predator foraging or fishing 

 activity). Future monitoring surveys over the NL-91 and D/S Mound Complex should 

 continue to evaluate benthic conditions over the eastem lobe of this bottom feature to verify 

 continued recovery. 



Both the bathymetry and REMOTS® monitoring results from the August 2000 survey 

 indicate that the supplemental cap material placed since 1997 covers the original UDM 

 footprint. It is recommended that any future placement of supplemental cap material, designed 

 to augment the total cap thickness, be directed to the area around the former D/S buoy location. 

 In this area, a layer of supplemental cap material was detected in the August 2000 REMOTS® 

 images, but this layer was not yet thick enough to be detected acoustically (Figure 3-4). 

 Specifically, it is recommended that the two points (A and B) shown in Figure 4-3 be used for 

 future supplemental cap material placement over the NL-91 and D/S Mound Complex. 



4.2 Seawolf Mound 



In 1997, the Seawolf Mound was a recent dredged material deposit that displayed a 

 significant amount of consolidation in the one-year period following its creation. The 

 surface CDM layer was composed of dense, gray clay that was exerting pressure on a 

 relatively large deposit of silt (UDM). Apparent reductions of mound height on the order of 

 0.25 m were detected over most of the disposal mound, with as much as 1 .5 m of 

 consolidation calculated over the apex (Figure 4-4A; SAIC 2001b). In contrast, depth 

 difference comparisons 



Monitoring Cruise at the New London Disposal Site, August 2000 



