2.0 METHODS 



2.1 Bathymetry and Navigation 



The precision navigation required for all field operations was provided by the SAIC 

 Integrated Navigation and Data Acquisition System (INDAS). This system uses a Hewlett- 

 Packard 9920 series computer to collect position, depth, and time data for real-time 

 navigation and for subsequent data analysis. Positions were determined to an accuracy of 

 ±3 meters from ranges provided by a Del Norte Trisponder® System. For the present 

 survey, shore stations were established in Connecticut at known benchmarks at Millstone 

 Point and the New London Lighthouse (SAIC 1985). A detailed description of the 

 navigation system and its operation can be found in DAMOS Contribution No. 60 (SAIC 

 1989). Quality assurance and quality control procedures utilized throughout this survey are 

 explained in the QA/QC plan for the DAMOS Program (SAIC 1990b). 



Depths were determined to a resolution of 3.0 cm (0.1 feet) using an Odom DF3200 

 Echotrac® Survey Recorder with a narrow-beam 208 kHz transducer. The speed of sound 

 used in depth calculations was determined from water temperature and salinity data measured 

 by an Applied Microsystems CTD probe (see Section 2.3 below). During analysis, raw 

 bathymetric data were corrected for speed of sound in seawater and standardized to Mean 

 Low Water by compensating for transducer depth and changes in tidal height during the 

 survey. However, the acoustic records could reliably detect changes in depth on the order of 

 only 20 cm or more due to the accumulation of errors introduced by the positioning system, 

 tidal corrections, the calibration of the fathometer (speed of sound through the water 

 column), the slope of the bottom, and the vertical motion of the vessel. A detailed 

 discussion of the bathymetric analysis technique was given in DAMOS Contribution No. 60 

 (SAIC 1989). 



The bathymetric survey conducted at the New London Disposal Site on 28 June, 

 6 July, and 9 July 1990 encompassed a 1600 x 1600 m grid with 25 m lane spacing, 

 centered at coordinates 41°16.235' N and 72°04.492' W (Figure 1-2). This was the same 

 grid used for the bathymetric survey in July- August 1988, permitting depth differences to be 

 calculated relative to the 1988 survey. The coordinates of the disposal buoy during the 

 present survey were 41° 16.450' N and 72° 04. 260' W, placing it approximately 100 m 

 northeast of its location during the February 1989 capping survey (Figure 1-2). Depth 

 difference calculations at the NL-TR mound were done by extracting the appropriate data 

 from the present master survey and comparing the results to the February 1989 survey at the 

 Thames Shipyard and Repair Company disposal mound (SAIC 1990a). 



Monitoring Cruise at the New London Disposal Site, June-July 1990 



