53 



5.0 CONCLUSIONS 



SAIC conducted the June 1991 monitoring cruise at the Western Long Island Sound 

 Disposal Site to delineate the area! extent of dredged material disposed during the 1990-1991 

 season and to assess the recolonization response of the benthic infauna to the newly deposited 

 material. Model predictions for the WLIS "E" mound were based on the reported volume of 

 86,462 m^ of dredged material deposited during the 1990-1991 disposal season and would 

 result in the formation of a mound up to 2.7 m in height with a radius of 200 meters. Based 

 on acoustically detected changes in depth at the buoy location, disposal operations resulted in 

 the formation of a mound with a diameter of 200 x 150 m and height of 3.0 meters. The 

 REMOTS® sediment-profile survey detected thin layers of "fresh" dredged material beyond 

 this 200 X 150 m area. The footprint of fresh material was estimated to be 400 x 175 m. . 



The stams of infaunal recolonization was predicted to be primarily Stage I at the 

 active disposal point and combinations of Stage Il/Stage III on the flanks of the moimd; 

 however. Stage III infauna rapidly recolonized much of the newly deposited dredged material 

 at the "E" mound. Stations exhibiting exclusively Stage I seres were located primarily west 

 of the active disposal point. This conspicuous clustering of Stage I stations reflects those 

 regions where the most recent dredged material disposal occurred. Several stations near the 

 WLIS "D" mound (developed during the 1989-1990 disposal season) had low reflectance, 

 high SOD sediments at depth. The presence of Stage HI organisms at these stations and at 

 stations on and near the active disposal point indicated that disturbances resulting from 

 disposal operations are primarily physical and short-term; however, imder the management 

 strategy outlined in the SAIC tiered monitoring protocol, the persistence of dark subsurface 

 sediments near the WLIS "D" mound represents the early stages of a potentially adverse 

 condition resulting from disposal operations. This potential for a detrimental environmental 

 impact warrants continued monitoring which may include REMOTS® sampling, sediment 

 chemistry analyses, and sedhnent toxicity testing. In subsequent surveys the first step will be 

 to evaluate the status of Stage HI fauna prior to determining if any additional monitoring is 

 required. 



Results of the laboratory sedunent grain size analyses were found to be consistent 

 with the visual estimate of grain size major mode determined visually from REMOTS® 

 photographs. Metal concentrations of Cd and Zn have not increased notably since the 1986 

 and 1987 surveys. 



Both REMOTS® and PAH data strongly suggest that the WLIS-REF and 2000S 

 reference areas have been affected by past disposal operations. Evidence of relic dredged 

 material at WLIS-REF and the presence of fine sand, relic RPD layers, and persistent Stage I 

 organisms at 2000S were inconsistent with their continued use as reference areas. The 

 variation in PAH concentrations within these two reference areas revealed a heterogeneity in 

 what was assumed to be areas of ambient sedunent. In addition, reference area 2000S 



Monitoring Cruise at the Western Long Island Sound Disposal Site, June 1991 



