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3.0 RESULTS 



3.1 D/S and NL-91 Disposal Mounds 



3.1.1 Bathymetry 



The August 1992 precision bathymetric survey showed a minimum depth of 13.0 m 

 over the NL-Relic mound to the north and a maximum depth of 23.5 m along the southern 

 edge of the survey area (Figure 3-1). At a contour interval of 0.25 m, the seven inactive 

 disposal mounds located within the New London Disposal Site (NL-RELIC, NL-I, NL-II, 

 NL-III, NL-85, NL-88, and NL-TR) were clearly defined. 



The August 1992 bathymetric survey was performed following the placement of 

 capping dredged material (CDM) associated with the Dow/Stonington project. A 

 comparison of this survey with the baseline survey of June 1991 (conducted prior to any 

 placement of either UDM or CDM) resulted in detection of an irregularly shaped mound 

 approximately 500 m in diameter (Figure 3-2). The depth difference plot revealed a 

 mound complex with four distinct peaks. Two of the larger peaks, with heights of 0.7 m 

 and 0.5 m, corresponded to the placement of the D/S and NDA buoys (NDA-91-1 and 

 NDA-91-2) . The NL-91 and D/S mound complex is composed of 8,800 m 3 of material 

 deposited at the NDA buoy from 26 September 1991 to 22 January 1992. The other two 

 peaks, approximately 250 m east-northeast of the D/S buoy, had mound heights of 0.5 m 

 and 0.4 m. These mounds were developed over the southwestern flank of the historic NL- 

 III mound, and spread into the slightly deeper areas between the NL-III and NL-85 

 mounds. They were connected to the western lobe of the NL-91 and D/S mound complex 

 by a narrow ridge of dredged material. 



In December 1991, a bathymetric survey was performed for the Dow Chemical 

 Company by Ocean Surveys Incorporated, Old Saybrook, CT. This "precap" survey, 

 conducted following the placement of UDM but before the placement of CDM, covered a 

 940 m x 840 m area centered on the D/S buoy (Figure 3-3). By incorporating this precap 

 survey into the existing SAIC data set, a mound development time-series was produced. 

 This time-series data set provided a perspective on the placement of material and resulting 

 changes in bathymetry. 



The Ocean Surveys Incorporated bathymetry data were re-gridded to a 500 m x 

 670 m area along with SAIC's June 1991 and August 1992 bathymetric surveys to focus 

 the depth difference analysis. Close examination of the June 1991 bathymetry showed a 

 relatively flat area with no major topographic features capable of influencing the 

 distribution or spread of material within the immediate vicinity of the disposal points 



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



