PART II: EXPERIMENTAL PROCEDURES 

 Settling Tests 



Background 



7. The settling tests followed procedures found in Palermo, Montgomery, 

 and Poindexter (1978) and Engineer Manual (EM) 1110-2-5027 (USACE 1987). The 

 tests involve mixing sediment and site water to simulate a dredged material 

 slurry, placing the material in a settling column, and observing each of sev- 

 eral types of settling behavior. The general procedure is described below. 



8. A bench test conducted in a 1-X, graduated cylinder is the method 

 used to determine if a flocculent or a zone process will describe the initial 

 settling. The bench test should be run at a slurry concentration of approxi- 

 mately 150 g/l. If an interface forms within the first few hours of the test, 

 the slurry mass is exhibiting zone settling, and the fall of the interface 

 versus time should be recorded. The break in the curve will define the con- 

 centration at which compression settling begins. If no break in the curve is 

 evident, the material has begun settling in the compression zone, and the 

 bench test should be repeated at a lower slurry concentration. If no inter- 

 face is observed in the bench test within the first few hours, the slurry mass 

 is exhibiting flocculent settling. In this case, the bench test should be 

 continued until an interface is observed between the turbid water above and 

 the more concentrated settled solids below. The concentration of the settled 

 solids (computed assuming zero concentration of solids above) is an indication 

 of the concentration at which the material exhibits compression settling 



(EM 1110-2-5027). 



9. The flocculent settling test consists of measuring the concentration 

 of suspended solids at various depths and time intervals in a settling column. 

 If an interface forms near the top of the settling column during the first day 

 of the test, sedimentation of the material below the interface is described by 

 zone settling, confirming the bench test. In that case, the flocculent test 

 procedure should be continued only for that portion of the column above the 

 interface. If an interface has not formed on the first day, flocculent set- 

 tling is occurring in the entire slurry mass. One allows the slurry to set- 

 tle, withdraws samples from each sampling port at regular time intervals, and 

 determines the suspended solids concentrations. Substantial reductions of 



