34 



the navigational reference. CS-1 was 

 capped using only LORAN-C as an aid for 

 locating the mound. It appears that using 

 the buoy as a navigational reference 

 instead of LORAN-C during the capping 

 operation at CS-2 actually helped reduce 

 cap placement errors compared to those at 

 CS-1. 



The southwest bias of the cap at CS-1 

 may be related to navigation during the 

 disposal operation and the sources of 

 material for the capped mound. The 

 pattern of mound and cap placement at 

 CS-1 is consistent with the direction of 

 approach of the disposal barges; Black 

 Rock Harbor (mound) disposal barges 

 steamed from the northwest to the correct 

 LORAN coordinates and returned, and 

 New Haven (cap) disposal barges steamed 

 from the north to the intended disposal 

 points. LORAN-C alone does not have 

 the resolution required for precise point- 

 dumping. The bi-directional approach 

 may have caused the offset of the mound 

 and cap. 



2.5.2 Cap Site Operations: Conclusions 



The discovery that the cap at CS-1 was 

 offset from the mound is further evidence 

 that postdisposal monitoring and data 

 analysis are essential to document any 

 potential problems as a result of disposal 

 activity or changes in capped mound 

 stability in the long term. Accurate 

 navigation aided by taut-wired buoys has 

 been shown to be the most effective 

 method of both point-dumping and 

 completely covering capped mounds. 



2.6 Summary of the Early Capping 

 Experience 



The CLIS capping experience provided 

 a clear methodology to follow for the 

 formation of a completely covered mound. 

 After the first operation, Stamford-New 

 Haven, the basic disposal operation 

 guidelines were established: 



• Use a taut-wired buoy and accurate 

 navigation for both cap and mound 

 sediments. 



• Reduce the spatial distribution of 

 cohesive mound sediments by 

 point-dumping, or positioning the 

 disposal barge loads as near to the 

 buoy as possible. 



• Dispose of a portion of the cap 

 around the radius of the mound to 

 ensure complete coverage. 



• Complete a discrete disposal 

 sequence, first with a mound 

 deposition phase, followed by cap 

 placement. 



Additional guidelines were established 

 as more capping projects were completed: 



• Keep accurate records. 



• Characterize mound and cap 

 sediments prior to disposal. 



• Monitor prudently to confirm the 

 stability of the capped mounds. 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



