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Independent Observer (ENSR 1997b). The recommendations were designed around the 

 primary concerns raised by the dataset, including lack of spatial coverage of sand, variable 

 thicknesses of sand, and potential mixing between sand and dredged material. The 

 recommendations are intended as practicable methods of improving the CAD capping 

 process for Phase 2 of the BHNIP and other projects. 



• Operational Control During Capping 



The primary source of both uneven spatial coverage and variable cap thicknesses 

 was the method of sand placement in the first CAD cell. For Phase 2, operations will be 

 designed to improve placement of the material, as well as increase the ability to diffuse the 

 sand while capping. In addition, physical dismrbance of the sand cap after placement will 

 be minimized. 



• Increase Bearing Capacity of Dredged Material Prior to Capping 



Increasing the consolidation time for the fme-grained maintenance sediments will 

 increase the bearing capacity of the material, increasing the likelihood for a sharp 

 cap/dredged material boundary. The Phase 1 monitoring studies provided no clear 

 guidance for the time required for sufficient consolidation, as there was no hard evidence 

 that the consolidation time for Phase 1 (9 days) was insufficient. The time allowed for 

 consolidation partially will be governed by the potential risk of resuspension of this 

 material. Future geotechnical studies will be conducted to address this issue for further 

 projects. 



The most cost-effective method to increase bearing capacity is to allow more time 

 for self- weight consolidation to take place. The subbottom data provided an estimate of 

 the maximum time necessary for the dredged material to be able to support an overlying 

 load, because of the apparent ability of the uncapped dredged material to support the mass 

 of material at the southeast comer of the cell. The topographic peak appeared sometime 

 between the last postcap survey in July and the October survey, providing a maximum 

 waiting period of 10 weeks. The actual waiting period may be shorter (perhaps much 

 shorter depending on when the block fell or could have been supported), and will also 

 depend on the geotechnical character of the actual dredged material as it is placed. This 

 waiting period will be established through careful monitoring of the first few cells. 



Another method to increase the bearing capacity of the dredged material is to reduce 

 the water content of the material prior to disposal in the cell. Dewatering, however, is 

 expensive and time-consuming. Use of the environmental clamshell bucket increased the 

 water content of the material, ultimately decreasing the strength of the placed dredged 

 material. The final potential method for increasing the bearing strength of the material 

 prior to placement is to phase the capping process. By adding additional material to the 



MONITORING RESULTS FROM THE FIRST BHNIP CONFINED AQUATIC DISPOSAL CELL 



