The one reference station on the Upper Mississippi River is located 

 377.0 miles above the confluence with the Ohio River and is designated 

 MR 377.0. The locations of the sample stations are given in Table 3.1 

 and Figures 1.1 and 1.2. In accordance with Corps of Engineers termi- 

 nology, the designation "left bank" or "right bank" assumes the observer 

 is facing downstream. 



3.2 Sampling Design 



Nineteen sampling stations were established throughout the 

 Illinois Waterway (Figures 1.1 and 1.2). Samples were collected from 15 

 stations from November 1989 to June 1990, and from all 19 stations from 

 November 1990 to June 1991 (Table 3.1). 



3.2 Sample Collection Procedures 



It is important to limit the disruption of the sediment so that 

 toxicity evaluations are conducted under conditions that closely match 

 the in situ conditions (ASTM 1991). The most appropriate sediment 

 sampling device is study specific. Sediment corers generally disrupt 

 the sediment little but collect a limited sample volume (ASTM 1991). 

 This study employed a battery of bioassays as well as the TIE proce- 

 dures, all of which used sediment porewater. The volume of porewater 

 needed for this work made the use of sediment corers impractical. We 

 used a 25.4 cm (10-inch) Ekman dredge that works well in the soft to 

 semi-soft sediments that characterize the Illinois Waterway and collects 

 a relatively large sample volume (ASTM 1991). 



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