13 



In accordance with the bathymetric surveys performed by Gahagan and Bryant 

 Associates, a 1000 x 1000 m bathymetric survey grid, centered on the reported position of 

 the US Navy disposal buoy (41° 16.506' N, 72° 04.797' W), was established over the 

 northwest quadrant of NLDS (Figure 2-1). A total of 41 lanes, oriented north-south with a 

 25 m lane spacing, were occupied during the September 1997 and July 1998 field operations 

 to confirm disposal mound stability and quantify mound consolidation. 



2.1.2 Bathymetric Data Collection 



During the 1997 and 1998 bathymetric surveys, an ODOM DF3200 Echotrac® 

 Survey Fathometer equipped with a narrow beam, 208 kHz transducer was used to measure 

 individual depths to a vertical resolution of 3.0 cm (0.1 ft; Murray and Selvitelli 1996). The 

 fathometer was interfaced directly with the navigation system. Depth soundings were 

 collected along each of the 41 survey lanes established over the Seawolf project area. The 

 depth soundings collected by the Odom fathometer were adjusted for transducer depth and 

 transmitted to PINSS at a frequency of 10 Hz. The soundings were averaged by PINSS, 

 merged with positional and time information, and recorded at a frequency of 1 Hz. Survey 

 vessel speed and course were tightly controlled (2 to 3 meters per second) to ensure adequate 

 numbers of depth values collected along the survey lane. 



A Seabird Instruments, Inc. SEACAT SBE 19-01 Conductivity, Temperature, and 

 Depth (CTD) probe was used to obtain sound velocity measurements at the start, midpoint, 

 and end of each survey day. The data collected by the CTD probe were bin-averaged to 

 1 meter depth intervals to account for any pycnoclines, rapid changes in density that create 

 distinct layers within the water column. Sound velocity correction factors were then 

 calculated using the bin-averaged values. 



2.1.3 Bathymetric Data Processing 



During data analysis, the raw bathymetric data from PINSS were corrected for 

 changes in tidal height and sound velocity. Tidal height corrections were based on the 

 observed National Oceanic and Atmospheric Administration (NOAA) data for the New 

 London, Connecticut tidal station. Six-minute observed tidal data obtained via NOAA's 

 Ocean and Lake Levels Division's National Water Level Observation Network were utilized 

 for the surveys performed over NLDS. 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



