149 



• Reference areas reflected conditions throughout NLDS including: seasonal responses 

 to biological and physical processes and apparent impacts of low dissolved oxygen or 

 organic enrichment. All reference areas supported stable, healthy benthic 

 communities. In 1992 reference area conditions based on the Organism-Sediment 

 Index (OSI) improved over results from 1991, improved again in 1995 and 1997 and 

 remained stable in 1998. An increased presence of Stage II and Stage III organisms at 

 NLON-REF and NE-REF has resulted in higher OSI values and increased RPD 

 depths. Conditions at WEST-REF exhibited signs of a recent benthic disturbance in 

 1992 and 1995. Low OSI values relative to NE-REF and NLON-REF, and a Stage I 

 or Stage I over Stage III population suggests the area was in recovery from a localized 

 disturbance. 



5.2 Dow/Stonington and NL-91 Mound 



• The NL-91 and D/S mound complex is located in a flat "bowl" formed by 

 surrounding disposal mounds that provides protection from storms and tidal currents. 

 This mound complex was stable throughout the survey period and supported 

 development of a healthy benthic community. 



• Sediment deposition during disposal and capping operations during the 1991-92 

 disposal season yielded a maximum mound height of 0.7 m at the D/S buoy location 

 and 0.5 m at the NDA buoy location. Disposal operations resulted in the 

 development of overlapping areas of deposition: a low mound at the NDA buoy, an 

 elongated low mound extending eastward from the D/S buoy and a layer of sand 

 mixed with shells and pebbles over a portion of both of these mounds. 



• Inconsistencies in navigation and disposal barge positioning during CDM deposition 

 caused the cap material to be placed somewhat to the east of the main disposal mound. 

 During capping operations, the coordinates for capping points were apparently 

 misinterpreted causing an offset (250 m to 400 m) to the southeast. 



• The material deposited at the CDM points was composed mainly of black silt covered 

 by a layer of biologically-reworked dredged material and fine sand. This bottom 

 feature supported a stable Stage II benthic infaunal assemblage. 



• The material deposited at the D/S buoy was composed of black silt covered with a 

 sand layer 2-7 cm thick. The sand layer was consistent with material from the Port 

 Niantic project disposed at the nearby NDA -91 buoy. This area supported a stable 

 Stage II benthic infaunal assemblage. 



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



