18 

 3.5.2 Boron 



During 1 991 , boron concentrations in the East Poplar River at tine International Boundary 

 varied from 1.63 mg/L (Nov. 14) to 2.1 mg/L (Jun. 18 and Dec. 18) (Figure 3.7). 



Three-month boron FWCs for the period of record are shown in Figure 3.8. The short 

 term objective of 3.5 mg/L boron was not exceeded for the period 1975-1991. The 

 similarity in shape between the TDS and boron plots (Figures 3.4 and 3.8) is a strong 

 indication of the significance of discharge in FWC functions. 



The five-year boron FWCs, displayed in Figure 3.9, remained well below the long-term 

 objective of 2.5 mg/L boron. From mid-1988 to the end of 1990, there was a slight 

 increase in the five-year boron FWC. In first quarter of 1991 the five-year boron FWC 

 increased to 1 .9 mg/L. As was the case with TDS, the five-year calculations for boron 

 were significantly influenced by the relatively large discharge during 1985 and the low 

 discharges in 1986. 



The relationship between boron and conductivity at the East Poplar River sampling 

 location during the period 1975-1991 is described by the equation: 



boron = (0.00148 x specific conductance) - 0.256 

 (R'=0.70, n=422) 



As shown in Figure 3.10, boron levels undergo a statistically significant increase from 



