To determine cap thickness a depth difference plot was 

 prepared by subtracting the depth matrix of the October 1988 

 bathymetric survey from that of the February 1989 survey (Figure 

 3) . The cap material clearly showed a roughly circular and 

 continuous distribution varying in thickness from 10 to 80 cm. This 

 depth difference comparison resulted in a calculation of 28,270 m 



of cap material detected at the site. According to scow log records 

 an estimated 59,517 m 3 of cap mate 

 1988 and January 1989 (Table 2) . 



an estimated 59,517 m 3 of cap material was deposited between October 



4.0 DISCUSSION AND CONCLUSIONS 



The objective of the February 1989 bathymetric survey at 

 the New London Disposal Site was to assess the distribution of 

 capping material and verify coverage of the previously disposed 

 contaminated dredged material. Changes in depth from 10 to 80 cm 

 were determined by comparison of the bathymetric surveys from 1988 

 and 1989 (Figure 3) . Several isolated topographic highs were 

 identified in the distribution of cap material, indicating a notable 

 variation in cap thickness. The areas of greater thickness within 

 the cap layer probably represent disposal efforts to locate scows 

 at the six recommended disposal points within the area. 



Examination of the distribution of cap thickness in 

 relation to the six recommended disposal points revealed that cap 

 material was clearly deposited at points "D" and "E". These were 

 the locations of the two thickest parts of the cap layer, having 

 cap material accumulations of 80 cm (Figure 3) . Cap thicknesses of 

 50 to 60 cm were also established to the southwest of these two 

 disposal points. However, point "A" was intended to have received 

 the most scow loads of cap material because of the contaminated 

 dredged material thickness at this point (Table 1) . The depth 

 difference contour plot indicated only 20 cm of cap material here. 

 At disposal points "B" , "C", and "F" only 10 cm of cap material 

 appeared to have been deposited (Figure 3) . 



The erratic topography of the cap layer generally reflects 

 the spatial distribution of the recommended disposal points (Figure 

 3) . However, detected cap thicknesses surrounding these locations 

 suggests a consistent shift in cap material deposition to the 

 southeast. The largest volumes of cap material were reportedly 

 disposed of at points "A" and "B" (Table 2) . However as already 

 noted, the two thickest parts of the cap layer actually detected 

 are located at points "D" and "E". These points are offset to the 

 southeast of points "A" and "B". Similarly at point "F" little cap 

 material was indicated in the depth difference contour (Figure 3) , 

 yet a localized cap layer of 40 cm was detected just south of this 

 disposal point. Similar topographic highs in the cap material 

 distribution were indicated south of disposal points "D" and "E" 

 (Figure 3) . This suggests that some offset was consistently 



