32 



4.1.4 Interim Cap Surveys (23-24 November 1993 and 12-13 January 1994) 



Two interim cap bathymetric surveys were conducted, one by SAIC in late 

 November (Figure 4-7) when the federal capping operations were 50% complete and 

 another by Ocean Surveys Incorporated on 12-13 January 1994 (Figure 4-8) following the 

 completion of the dredging of contaminated sediment from the private terminals. Results 

 of the depth difference comparing the 2-3 November precap survey to the 23-24 November 

 interim cap survey (Figure 4-9) showed that the volume added to the mound was 

 124,000 m 3 to the east and southeast of the buoy. Most of the capping activity following 

 the interim cap survey was concentrated in the southwestern portion of the mound where 

 the UDM originating from the private terminals was deposited. The height of the mound 

 was 2.5 m, and the diameter of the mound was approximately 550 m. The depth 

 difference comparing the November interim cap survey to the September baseline survey 

 showed the total volume of the mound to be 435,000 m 3 . 



In comparing the data from the Ocean Surveys Incorporated survey (Figure 4-8) to 

 the SAIC baseline survey (Figure 1-1) there was an average overall discrepancy of 0.92 m. 

 This difference was the result of comparing datasets corrected to dissimilar vertical datums 

 used for tidal corrections. SAIC data is referenced to observed Mean Tide Level (MTL) 

 over the survey area, while Ocean Surveys Incorporated used tidal corrections based on 

 Mean Lower Low Water (MLLW) predictions. After correcting the Ocean Surveys 

 Incorporated data to previous SAIC surveys, two depth difference plots were generated. 

 The first plot shows the thickness of material added since the baseline survey (Figure 4- 

 10). This represents a total mound volume of about 593,000 m 3 . The second depth 

 difference shows the material added between the January and precap (November 2-3) 

 surveys (Figure 4-11). The volume from this comparison, 281,000 m 3 , includes all of the 

 privately dredged contaminated sediments and some of the federal capping sediments. This 

 plot illustrates that the deposition of dredged material during this period was mostly over 

 the southeast flank of the NHAV 93 mound in accordance with the direction from NED. 



4.1.5 Postcap Survey (13-14 March 1994) 



Comparison of the postcap (Figure 4-12) and baseline (Figure 1-1) bathymetric 

 surveys shows the formation of a well-developed mound centered 125 m to the south of the 

 NHAV buoy. The water depth at the center of the mound is 17.5 m. The depth difference 

 comparison of the postcap survey versus the baseline survey (Figure 4-13) shows the 

 height of the mound to be 2.5 m and the mound diameter to be 600-800 m. The final 

 volume of the capped NHAV mound based on that comparison is approximately 

 714,000 m 3 . Differencing the postcap survey to the precap survey (Figure 4-14) shows the 

 total volume of cap material and privately dredged sediments to be approximately 



Monitoring Surveys of the New Haven Capping Project, 1993-1994 



