affecting the positioning accuracy of cap material deposition during 

 the capping operation. Most likely this was due to a consistent 

 Loran error, resulting in the cap layer effectively covering the 

 majority of the contaminated dredged material with the exception of 

 the northern and western borders of its distribution. 



Depth difference calculations from the pre- and 

 post-disposal bathymetric surveys of contaminated material revealed 

 the distribution of material requiring capping (Figure 4) . The 

 mapped distribution of dredged material indicated from the REMOTS® 

 survey of this area conducted in October 1988 confirmed this 

 distribution detected by bathymetric techniques, and extended it 

 roughly 50 m to the south, east and west (SAIC, 1988) . 

 Superimposing this distribution of dredged material as detected by 

 the REMOTS® survey of October 1988 over the cap distribution 

 detected in 1989 again confirmed that most of the contaminated 

 material did receive some cap material (dashed line, Figure 3) . 

 However, at disposal point "A", 70 cm of contaminated material 

 apparently received only 20 to 30 cm of cap material (Figures 3 & 

 4) . In addition, at disposal point "F" 10 to 20 cm of contaminated 

 dredged material was apparently capped by only 10 cm of clean 

 material based on the 1989 bathymetric depth difference plot (Figure 

 3). 



The depth difference plot from the pre- and post-disposal 

 bathymetric surveys of contaminated material indicated a small 

 deposit located roughly 150 m southwest of the buoy (near point "C" , 

 Figure 4) . Although this material fell outside the mapped 

 distribution of dredged material verified by the 1988 REMOTS® 

 survey, it was recommended that this deposit be capped in addition 

 to the main disposal mound because of the substantial amount of 

 material detected here in the depth difference comparison (SAIC, 

 1988) . This location should have been covered by scow loads of cap 

 material deposited at point "C" . However, the 1989-1988 depth 

 difference plot indicated little or no cap material at this 

 location. It should be noted that bathymetric surveys are limited 

 in their ability to detect thin layers of sediment typical of 

 disposal mound flank deposits. Thus, it is likely that the actual 

 borders of the cap layer extend further than indicated in the 

 bathymetric depth difference contour plot, covering locations such 

 as disposal point "C". However it is unlikely that such flank 

 layers would be thicker than the minimum change in depth detectable 

 by bathymetric techniques (10 cm) . 



It appears that additional capping material is required 

 at certain locations along the northern and western borders of the 

 disposal mound. It is recommended that additional material be 

 deposited at locations "A", "B" , "C" , and "F" in order to cover the 

 contaminated material with a sufficiently thick layer of clean 

 material (between 50 to 100 cm) . However, because of discrepancies 

 between the recommended disposal point locations and the actual 

 distribution of cap material detected, it is recommended that 



