- 11 - 



from a 5 year period in which 2.5 years preceded and 2.5 years fol- 

 lowed each plotted point. The FWCs in this report are calculated 

 from the five year period preceding each plotted point. For example, 

 the FWC for December 1988 refers to the FWC of the period December 

 1983 to December 1988. It should be emphasized that the calculations 

 have been based on the results of all samples collected, and not 

 restricted to samples collected during March to October. 



Total Dissolved Solids 



Grab sample TDS concentrations during 1988 ranged from 859 milligrams 

 per liter (mg/L) (September 7) to 1,169 mg/L (January 6). The 1988 

 TDS results are presented in Figure 3. 



1200 T 



1100 



1000+ 



\ 900- 



a 



800 



700- 



600 



1988 



D 1989 



Figure 3. 1988 TDS Grab Sample Data, East Poplar River at 

 International Boundary 



The proposed short-term objective for TDS is 1,500 mg/L . A time plot 

 of the three-month moving FWCs for TDS is presented in Figure 4. No 

 exceedences of the objective have been observed during any three 

 month period since 1975. The three-month FWCs moved within a narrow 

 range near 900 mg/L during 1988, reflecting lower than normal dis- 

 charges during the spring period. 



