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5.0 SUMMARY AND RECOMMENDATIONS 



5.1 Summary 



5.1.1 Sidescan 



• The southern end of the cell had low reflectance relative to the rest of cell, 

 indicating a smooth cell bottom and homogenous grain size; 



• There was an acoustic bright spot in the southeast comer indicating a 

 topographic peak lying above the shadow created by the edge of the pit; 



• The central portion of the cell showed a strong topographic signamre from 

 clamshell dredging, resulting in artificial sand waves throughout the center of 

 the cell; 



• Rough texmre of the surface of the northern end of the cell indicated sand cover, 

 but was less disturbed than central section. 



5.1.2 Bathymetry 



• Consolidation of at least 1-2 ft in some areas, especially in the southwestern 

 comer and in the center of the cell below the thickest sand layers, continued 

 between the final postcap survey conducted in late July, and the postcap 

 bathymetric survey conducted 10 weeks later in early October; 



• Total consolidation of the dredged material since the time of placement was 

 estimated to be 20-40%; 



• Evidence for material falling from the unsupported cell walls included the 

 irregular cell outline and flatter slope, as well as the anomalous topographic 

 peak in the southeast comer; 



• The dredging process, as well as propeller action along the eastem side and 

 spudding, likely weakened parts of the cell wall, enhancing the potential for 

 material slumping; 



5.1.3 Coring 



• Cores indicated that the southern end of the cell was uncapped; 



• The artificial sand waves in the central portion of the cell resulted in widely 

 varying sand thicknesses over short distances; 



• A sharp cap/dredged material boundary was present over consolidated dredged 

 material; 



• The estimated range of thickness of the sand in the capped area was estimated to 

 range from 1-7 ft; 



• Potential mixing of up to 2 ft of the cap into the dredged material in one core 

 was probably enhanced by the postcap dredging operation, but may also be a 

 result of underconsolidated dredged material prior to capping; 



MONITORING RESULTS FROM THE FIRST BHNIP CONFINED AQUATIC DISPOSAL CELL 



