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be another factor causing large discrepancies between barge estimates and detected 

 volumes. By restricting the window of analysis to the area immediately around the CLIS 

 94 mound and performing various depth and volume differencing routines, physical 

 changes in the dredged material deposit and in the volume of material were detected. 



A large central pocket of dredged material consolidation within the CLIS 94 mound 

 was detected during the interim cap survey of the bottom feature. This pocket of 

 consolidation is believed to be the chief cause of the mass balance shortfall. Although the 

 use of multiple surveys improved the tracking of large volumes of material disposed, rapid 

 consolidation due to compression and de-watering complicate precise volume comparisons. 



Studies conducted at CLIS by the US Army Corps of Engineers, Waterways 

 Experiment Station (WES), have documented significant amounts of dredged material 

 consolidation over short periods of time (0.5 m in 30 days; Poindexter-Rollings 1990). 

 The observed behavior of the CLIS 94 mound supports those findings with up to 1 .0 m of 

 consolidation over a 126-day period of time without evidence of UDM surface movement 

 or collapse of the mound. If the CLIS 94 mound continues as predicted, the mound should 

 subside an additional 0.5 m to 0.75 m over the next year and then show gradual reduction 

 due to compression of the basement material over the next 5 to 10 years. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



