66 



5.0 CONCLUSIONS 



Since 1992, the WLIS seafloor has seen hght to moderate disposal activity, 

 receiving a total estimated barge volume of 148,000 m^ of sediment dredged from the ports 

 and harbors of coastal Connecticut and New York. In accordance with the successful 

 management strategy demonstrated at CLIS, the recent disposal activity at WLIS has been 

 tightly controlled to construct rings of disposal mounds in order to form an artificial 

 contaiimient cell (Morris et al. 1996). The implementation and long-term use of this 

 management strategy will facilitate the deposition of large volumes of dredged material, 

 minimizing its lateral spread on the seafloor, and maximizing the available space within the 

 5.29 km^ area of the disposal site. The July 1996 field efforts allowed SAIC and NAE to 

 document the development of three individual disposal mounds as well as examine the 

 stams of the artificial containment cell and observe changes in the benthic environment 

 resulting from the deposition of new material. 



The controlled disposal of this material was successful in forming two new sediment 

 mounds, WLIS G and H, as well as further developing the preexisting WLIS F mound. 

 Depth difference comparisons between with the 1996, 1992, and 1990 bathy metric surveys 

 display the three disposal mounds as discrete bottom feamres connected by a ridge of 

 material 0.25 m thick, formed by overlapping mound aprons. As of July 1996, the first 

 artificial containment cell on the WLIS seafloor nears completion as the historic WLIS D 

 and E moimds, in conjunction with the F, G, and H mounds, begin to form an artificial 

 containment ridge. Supplemental containment facilities could also be formed by employing 

 the properties of the namrally occurring ridges and basins within the boundaries of WLIS. 



As the most recent bottom feamre on the WLIS seafloor, the H mound displayed 

 evidence of moderate to deep RPD depths over most of the mound surface, as well as 

 strong benthic recolonization. Stage I individuals were discovered in every replicate 

 photograph, and Stage III activity was dociunented at six of the thirteen stations occupied. 

 With the exception of Station H50W, OSI values ranging from 4.0 to 8.0, suggesting 

 benthic recovery over this disposal mound, should continue as expected. Disposal 

 operations over WLIS H were completed on 29 May 1996 (Julian Day 149). According to 

 the 1996 CTDEP data set, benthic recovery over the surface of this sediment deposit 

 progressed for approximately six weeks before declining bottom water DO concentrations 

 would have caused elevations in environmental stress levels. Given the history of the 

 WLIS A and D mounds and the severity of recurring seasonal hypoxia in the region, 

 continued monitoring of this new sediment deposit on an annual or every other year basis 

 is recommended to ensure long-term benthic recovery. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1996 



