80 



The geotechnical cores are in agreement with the bathymetric and subbottom results 

 with respect to cap and dredged material thickness, as well as depth of ambient bottom. 

 Cap material can be detected in the top sections of each core. The thickness of the cap 

 varied between 40 cm in Core W to 160 cm at Core V. The depth and thickness of the 

 dredged material varied in each core, but multiple layers of black and brown sands, silts, 

 and clays were consistently part of the dredged material descriptions. Cores V and W 

 were the only samples of the NHAV 93 mound that reached ambient bottom. In both 

 cases, ambient Long Island Sound sediments, consisting of firm, olive-grey clayey silt, 

 were found at depths of 200 cm. 



Although the cap thickness over the NHAV 93 mound was found to be sufficient, 

 REMOTS® sediment-profile analysis revealed a possible problem with the quality of CDM 

 in three areas. At four months post disposal a healthy Stage I advancing to Stage II 

 community was expected to be established around the center of the NHAV 93 mound. 

 Shallow to diffusional RPD depths, slow recolonization rates, and low OSI values at 

 REMOTS® Stations 200N, CTR, and 400S indicated a possible sediment toxicity issue. 



In accordance with the DAMOS tiered monitoring protocol, these areas of concern 

 were re- visited in late September 1994 to collect sediment samples in order to perform 

 laboratory bioassay studies (Germano et al. 1994). The results of the September 1994 

 toxicity testing showed no significant difference in toxicity levels between the NHAV 93 

 capping material and sediment collected from the historic South Reference Site. The three 

 areas of concern were monitored closely for changes in benthic environment. The results 

 of the August 1995 REMOTS® survey over the NHAV 93 mound showed marked 

 improvement in benthic conditions at 16 months after CAD mound completion (Morris 

 1996). 



The results of the sediment chemistry analyses for the NHAV 93, as well as the 

 MQR mound, show that the sediments covering these mounds are equal to or below the 

 chemical concentrations of the CLIS reference areas. All PAH values are below the values 

 of the National Stams and Trends (NS&T) averages for sediments found within Long 

 Island Sound (NOAA 1991). Metals concentrations were categorized within the "low" 

 level of contamination based upon their average values and statistical variabilities when 

 compared to the guidelines set forth by the NERBC (NERBC 1980). These results indicate 

 that the capping sediments and conditions of the NHAV 93 and the MQR mounds are 

 broadly representative of the ambient seafloor conditions that are found throughout Central 

 Long Island Sound. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



