30 



larger area of dredged material detected by 

 the REMOTS® survey could be due to the 

 release of dredged material at a distance 

 from the disposal point or to the spread of 

 dredged material in deeper water depths. 

 The cohesive nature of the dredged material 

 found away from the disposal location and 

 the reported location of barge release points 

 indicate that the large area of dredged 

 material may be due to releasing material 

 away from the buoy. A plot of the barge 

 release locations, which were LORAN-C 

 positions reported in the barge logs rather 

 than actual positions printed out on the tug, 

 showed dredged material released at a 

 distance from the disposal point up to 400 

 m from the buoy (Figure 3-5). 



The acoustic detection of dredged 

 material at MBDS, which delineated a 

 smaller area of dredged material than 

 detected by REMOTS®, was apparent for 

 the first time after a taut-wired buoy and 

 LORAN-C navigation were used to mark 

 the disposal point in 1987. Consecutive 

 bathymetric surveys revealed a distinct 

 dredged material mound that increased in 

 height as the amount of dredged material 

 increased. For both the Port Gardner and 

 Elliott Bay disposal operations, navigation 

 equipment on the tugs guaranteed that all 

 release points were within the 183 m radius 

 target zone. The footprint of the 762,000 

 m 3 of material released at Port Gardner 

 extended northwest and southwest of that 

 predicted by the model (Figure 3-9). 

 Because dredged material placement was 

 tightly controlled, the deposition of 

 material away from the target zone would 

 have been due to the transport of material 

 after it was released by the barge. The 

 release of a smaller amount of dredged 



material within an identical target area at 

 the Elliott Bay disposal site produced a 

 dredged material deposit over a smaller 

 area (1347 m by 915 m). These examples 

 illustrate the importance of placement 

 control during the disposal operation and of 

 an understanding, prior to modeling the 

 predicted mound configuration, of any 

 conditions unique to the disposal area. 



Early capping operations in Long Island 

 Sound demonstrated that operational 

 control over the placement of the 

 contaminated dredged material and the cap 

 material is the prime determinant in the 

 success of the capping operation. A lack of 

 operational control in the placement of cap 

 material at CS-1 resulted in cap coverage 

 that was less than 50 cm on portions of the 

 mound. Similar lack of emphasis on 

 placement of dredged material at MBDS in 

 1982/1983 resulted in unfocused disposal of 

 dredged material and the lack of any 

 mound formation. As demonstrated by all 

 successful capping operations conducted so 

 far, tight operational control during 

 disposal is of primary importance in the 

 success of capping regardless of the water 

 depth. This holds true for all sites above 

 the depth of neutral buoyancy 

 (approximately 350 m). No information is 

 available on mound formation from 

 dredged material disposed in waters of 

 greater depths. 



When there has been tight operational 

 control during the disposal operation, a 

 distinct dredged material mound can be 

 detected by bathymetry and REMOTS® 

 sediment-profile photography. The 

 bathymetric survey delineates the height of 

 the mound and the optimum location for 



Deep Water Capping 



