22 



3.0 RESULTS 



The 2553 m x 2225 m precision bathymetric survey was conducted over the western 

 two-thirds of CLIS to monitor theregion for changes in topography and mound stability. 

 This survey yielded a bathymetric chart of a 5.68 km^ area with a minimum depth of 

 15.0 m over the CLIS 88 mound (Figure 3-1). At a contour interval of 0.25 m the mound 

 formations become more defined, depicting the remnants of eighteen discrete and/or 

 coalesced dredged material disposal mounds detected within the surveyed area (Figure 3- 

 2). 



To improve the resolution and focus on both subject disposal mounds (NHAV 93 

 and MQR), the data collected over the 2553 m x 2225 m survey area was re-gridded into 

 smaller analysis areas. Depth difference calculations for apparent accumulation and 

 consolidation of dredged material were performed within the analysis area of each mound. 



3.1 NHAV 93 Mound 



3.1.1 Bathymetry 



The NHAV 93 mound, formed with 1,159,000 m' of UDM and CDM from the 

 New Haven Harbor dredging project filled the shallow depression created by a ring of 

 disposal mounds (Figure 3-3). Comparisons to the September 1993 baseline survey display 

 a bottom feature that roughly conforms to the shape of the depression with a maximum 

 mound height of 2.5 m (compare Figures 1-2 and 3-4). The detectable footprint of the 

 mound (0.25 m) is approximately 950 m wide and overlaps seven surrounding mounds 

 (CLIS 87, CLIS 88, CLIS 89, CLIS 90, CLIS 91, SP, and Norwalk). Depth difference 

 calculations using the March 1994 postcap survey indicate small pockets of consolidation 

 (0.25 to 0.5 m) over the surface of the NHAV 93 mound (Figures 3-5 and 3-6). 



3.1.2 Subbottom 



Subbottom data were collected by the X-Star system for the entire survey area. 

 However, the analysis was concentrated on the northern half of the NHAV 93 mound. 

 Due to the deposition of CDM northwest of the NHAV 93 buoy prior to the November 

 1993 precap bathymetric survey, the results of the March 1994 postcap survey detected an 

 apparent lack of capping material over the northwest quadrant of the NHAV 93 mound 

 (Figure 3-7). A total of 76,000 m^ of capping material was deposited on the northwest 

 flank of the mound between the interim disposal and precap bathymetric surveys of 1993, 



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



