M 



Models were constructed using SAIC's HDAS program. The models generated by 

 HDAS contained a distance-weighted average depth value within each cell (25 m x 

 12.5 m). Models were then contoured to produce isopach maps of sediment layer 

 thicknesses. The thickness of the dredged material layers determined from the subbottom 

 profile data within the project area was compared to measurements obtained from both the 

 March 1994 postcap and July 1994 large bathymetric surveys. 



2.4 Surface Sediment Characterization 



SAIC's Sediment Acoustic Characterization System (SACS) was utilized to 

 remotely characterize the surface sediments at CLIS. This system uses acoustic bottom 

 reflection data collected concurrently with bathymetric survey data to continuously map the 

 surface sediments of a survey area. SACS is a dual-beam acoustic system that gathers 

 bottom reverberation and interprets the acoustic returns as surface sediment type. The 

 high-frequency (208 kHz) transducer of the ODOM DF3200 Echotrac® Survey Fathometer 

 is used to obtain precise surface reflection data. A low-frequency (24 kHz) transducer is 

 used to collect subbottom reflection data. The wavelength of the low-frequency transducer 

 results in a subbottom depth resolution of approximately 6 cm. The bottom surface area 

 sonified by the 23 ° beam of the 24 kHz transducer, using an average water depth of 20 m 

 at CLIS, was calculated to be a circle approximately 8 m in diameter. 



2.5 REMOTS® Sediment-Profile Photography 



REMOTS® photography was used to detect the distribution of dredged material 

 layers, map benthic disturbance gradients, and monitor the benthic infaunal recolonization 

 and/or successional status of the NHAV 93 and MQR mounds in relation to the CLIS 

 reference areas. Cross-sectional photographs of the top 20 cm of sediment were taken for 

 analysis and intercomparison with the adjacent CLIS reference areas. Three replicate 

 photographs were taken at each of the NHAV 93, MQR, 2500W, 4500E, and CLIS-REF 

 stations. A detailed description of the REMOTS® sediment-profile camera and its 

 operation can be found in DAMOS Contribution No. 48 (SAIC 1985). 



The REMOTS® surveys centered on the NHAV 93 (41°09.122' N, 72°53.453' W) 

 and MQR (41°08.637' N, 72°53.859' W) disposal mounds were conducted in 13-station 

 cross grids with station spacing at 200 m and 50 m, respectively (Appendix A, Table 2; 

 Figure 2-5). The reference areas 2500W (41°09.254' N, 72°55.569' W) and 4500E 

 (41 °09.254' N, 72 50.565' W) were sampled at four randomly selected stations. CLIS- 

 REF (41°08.085' N, 72°50.109' W) was sampled at five randomly selected stations 



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



