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2.1.1 1992 and 1995 Survey Activity 



During the 1992 and 1995 survey efforts, SAIC's Integrated Navigation and Data 

 Acquisition System (INDAS) was used for precision navigation and data collection 

 (Table 2-2). This system utilized a Hewlett Packard 9920 series computer to provide real- 

 time navigation, as well as collect position, depth, and time data for later analysis. INDAS 

 was interfaced with a Del Norte Model 542 Trisponder® System that provided real-time 

 positioning to an accuracy of ±3.0 m. The Del Norte Trisponder System is based on 

 multiple range (range-range) measurements from shore-based remote stations in order to 

 triangulate vessel position at a frequency of 1 Hz. SAIC established two shore stations 

 along the Connecticut coast at the known benchmarks of Millstone Nuclear Power Station 

 (41°18.312 ? N, 72°09.873' W) and New London Lighthouse (41° 18.991' N, 

 72°05.414' W) for the survey operations performed at NLDS (Figure 1-1). In order to 

 facilitate comparisons with previous data sets, all positioning information was referenced to 

 the horizontal control of North American Datum of 1927 (NAD 27). A detailed 

 description of the navigation system and its operation can be found in the DAMOS 

 navigation and bathymetry reference report (Murray and Selvitelli 1996). 



In August 1992, SAIC completed a bathy metric survey over a 1600 m x 1600 m 

 survey area centered at 41°16.235' N, 72°04.492' W. This survey required 65 lanes at 

 25 m lane spacing to cover the 2.56 km 2 area (Figure 2-1). This was an identical grid used 

 for bathy metric surveys in June- July 1990 and June 1991, permitting depth differences to 

 be calculated relative to previous surveys. In-depth analysis of the D/S mound was 

 accomplished by re-gridding the bathymetric data to a 500 m x 670 m area surrounding 

 the disposal buoy positions (Figure 2-1). 



The 1600 m x 1600 m survey area was reoccupied in August 1995 to determine the 

 changes in seafloor topography resulting from the deposition of sediments from October 

 1992 through June 1995. This survey area was later divided into smaller analysis areas 

 (NL-92 mound, NL-94 mound, USCGA mound) to yield better-defined depth difference 

 comparisons with the August 1992 survey (Figure 2-1). 



2.1.2 1997 and 1998 Survey Activity 



In 1997, a new master bathymetric survey of the disposal site utilized a different 

 positioning and survey system. Bathymetric data were collected with the use of SAIC's 

 Portable Integrated Navigation and Survey System (PINSS) during the September 1997 

 survey, as well as the effort in July 1998 (Table 2-2). This system utilizes a Toshiba® 

 3200DX series computer to provide real-time navigation, as well as collect position, depth, 

 and time data for later analysis. A Magna vox MX4200D GPS receiver was interfaced to a 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



