(& 



5.0 CONCLUSIONS 



The September 1995 field efforts at CLIS allowed SAIC and NED to examine three 

 bottom features constructed by three different dredged material management approaches. 

 The NHAV 93 mound is an example of a highly successful CAD structure. The mound 

 was found to have maintained its lateral stability and cap integrity. The site management 

 strategy of creating a ring of mounds from smaller disposal projects to accept large 

 quantities of dredged material within the basin has proven to be an efficient method of 

 UDM lateral containment and CAD mound construction. This management strategy 

 should continue at CLIS in order to provide large cells of lateral containment and 

 maximize the available space within the 6.86 km 2 area of the disposal site. 



Overall, the NHAV 93 mound appears to be recovering from the disposal activity as 

 anticipated (Germano et al. 1994). The mound supports a stable benthic infaunal 

 population with Stage I and Stage III organisms present in the surface and subsurface 

 sediments. Three areas of concern detected during the July 1994 monitoring cruise (CTR, 

 200N, and 400S) show marked improvement with deeper RPD depths and higher OSI 

 values despite the occurrence of a hypoxic event in the central Long Island Sound region. 

 The sediments of the NHAV 93 mound are expected to support a Stage II on Stage III 

 population in the coming years barring benthic disturbance (hypoxia, trawling, etc.). 



The development of the CLIS 94 mound represents the next step in the successful 

 site management strategy. The construction of an independent capped mound to the 

 northeast of the NHAV 93 mound begins to enclose another basin at CLIS. The CLIS 94 

 mound appears to be a discrete and stable bottom feature that has completely incorporated 

 the historic CS 90-1 mound that was formed during the 1989/90 disposal season. 

 Approximately 129,900 m 3 of UDM from Norwalk Harbor, New Haven Harbor, and Long 

 Wharf Pier projects was deposited over CS 90-1. A total of 161,000 m 3 of CDM was 

 placed over the unsuitable material to isolate it from the marine environment. A CDM to 

 UDM ratio of 1.24:1.0 was found to be sufficient to cap the UDM deposit without lateral 

 containment as both disposal and capping operations were consistently controlled. 



The overall size and shape of CLIS 94, as well as the volume of new material 

 detected by bathymetry, suggests that mound development proceeded without difficulty. 

 Comparisons between the July 1994 (baseline) and September 1995 (postcap) surveys 

 performed by SAIC and the results of a precap and interim cap bathymetric surveys 

 obtained through Ocean Surveys, Inc. support that conclusion. Intensive analysis of the 

 four data sets detected significant central consolidation within the UDM layer during the 

 first phase of capping operations, supporting previous studies performed by WES in the 

 1980s. Up to 1.0 m of dredged material subsidence was detected over a 126-day period 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



