- 23 - 



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 15. No ex- 

 ceedances of the objective have been observed during any three month 

 period since 1975. The three-month FWCs remained confined within a 

 narrow range centered around a mean of approximately 900 mg/L during 

 1990. 



o^ 



1600 

 1500 

 1400 

 1300 

 1200 

 1100 

 1000 

 900 



w 800 

 g 700 

 •- 600 

 500 

 400 

 300 

 200 

 100 



t — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — r 

 Short-Term Objective (1 500 mg/L) 



1 974 1 975 1 976 1 977 1 978 1 979 1 980 1 981 1 982 1 983 1 984 1 985 1 986 1 987 1 988 1 989 1 990 



Year 



Figure 15. — Three-month moving, flow-weighted TDS concentration 

 for East Poplar River at International Boundary. 



Five-year FWCs for TDS (Figure 16) remained below the long-term objective 

 of 1,000 mg/L. A 200 mg/L increase in the five-year FWCs which occured 

 in early 1988 was maintained throughout 1990. This corresponds to a 

 decline in high 1984 spring flows over that period of time. A similar 

 increase in TDS was seen during mid 1987, as a remnant of 1982 discharge. 

 Relatively low spring discharges have occurred since 1984. If this trend 

 continues, it is expected that FWCs will increase slightly or remain near 

 the present concentration level. 



