suspended solids will occur during the early part of the test, but reductions 

 will lessen at longer retention times (EM 1110-2-5027). 



10. The zone settling test consists of placing a slurry in a sedimenta- 

 tion column and reading and recording the fall of the liquid-solids interface 

 with time. These data are plotted as depth to interface versus time. The 

 slope of the constant velocity settling zone of the curve is the zone settling 

 velocity, which is a function of the initial test slurry concentration. A 

 series of these tests is required if the material exhibits an interface within 

 the first day. The range of initial slurry concentrations used in the series 

 should vary from a low of approximately 50 g/i to a high concentration above 

 the transition concentration, at which the slurry begins to exhibit compres- 

 sion settling (determined by the bench settling test) (EM 1110-2-5027). 



11. A compression settling test must be run to obtain data for estimat- 

 ing the volume required for initial storage of the dredged material. For 

 slurries exhibiting zone settling, the compression settling data can be 

 obtained from one of the series of zone settling tests with interface height 

 versus time recorded. The only difference is that the test is continued for a 

 period of 15 days, so that a relationship of log of concentration versus log 

 of time in the compression settling range is obtained (EM 1110-2-5027). 

 Bench test 



12. The initial solids concentration for the upper estuary composite 

 material was reduced from 418 to 111 g/JL to run a pilot test. The bench test 

 was performed in a l-£ graduated cylinder to determine if flocculent or zone 

 processes will govern initial settling. An interface was visible after only a 

 few minutes of settling, indicating that zone settling processes would govern. 



13. The bench test was not performed on the hot spot sample nor the 

 potential capping sediment since these sediments are expected to have settling 

 behavior similar to the upper estuary composite sediment. (This assumption 

 was found to be valid, as will be discussed.) 



Slurry preparation 



14. The target slurry concentration to run the settling tests was 



150 g/i. The slurry was prepared by mixing the upper estuary composite sedi- 

 ment with site water also collected from the estuary. To achieve the target 

 slurry concentration for the composite material, approximately 6 gal of sedi- 

 ment, which had a solids concentration of 418 g/i, was mixed with 11 gal of 

 site water. The slurry was pumped from a 55-gal drum with a positive 



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