44 



nature of this disturbance. The stressed benthic conditions observed in 1986 were attributed 

 to the widespread hypoxia prevalent at that time throughout Long Island Sound and were 

 unrelated to dredged material disposal (SAIC 1989b). 



6.3.2 NLDS: 1990 Monitoring Results 



SAIC conducted a survey of the NLDS site in July 1990. The objectives of the 

 monitoring cruise were 1) to delineate the extent and topography of dredged material 

 deposited since the August 1988 survey, 2) to determine mound stability, and 3) to assess 

 near-bottom DO concentrations relative to REMOTS® benthic analyses. 



Sampling at NLDS was concentrated in two regions of recent disposal activity. The 

 first area, designated NL-TR, was a region where contaminated sediments were covered with 

 a cap of clean material. The second disposal point, identified as NL-88, was adjacent 

 (150 m west) to the former active mound listed as NL-85 in the July-August 1988 survey 

 (SAIC 1990i). 



The bathymetric survey revealed that 46,700 m 3 of new sediment had accumulated in 

 the vicinity of the capped NL-TR mound since the July- August 1988 survey. The radius of 

 dredged sediment deposited at NL-TR was approximately 550 m by 400 m, and benthic 

 recolonization was as anticipated, indicating a healthy recovery well within expected 

 recolonization rates. However, three of the six disposal points earmarked for the 1988 

 capping operation still had not received the full cap thickness. Recommendations were that 

 future disposal operations should be directed to these three points with greater navigational 

 control. An additional 11,560 m 3 of material had accumulated in the southern portion of 

 NLDS at the two adjacent mounds (NL-85 and NL-88). The REMOTS® survey at NL-85 

 found that dredged material was distributed across the mound and that benthic recolonization 

 was as predicted (Stage II and III). 



Water column profiles of temperature, salinity, and sigma-t showed that significant 

 stratification of the water column did not exist during the period of the survey. Near-bottom 

 DO concentrations were highly uniform at all stations, both on and off the disposal site, and 

 there was no indication that dredged material disposal operations were influencing oxygen 

 concentrations adversely in the region. 



DAMOS Summary Report, 1985-1990 



