3.2.4 On-Demand Release 



In addition to the minimum flow, the IJC apportionment recommendation entitles Montana to an on- 

 demand release to be delivered during the twelve month period commencing June 1, 1991. Based 

 on the runoff volume recorded at the Poplar River at the Intemational Boundary gaging station during 

 the March 1 to May 31, 1991 period, Montana was entitled to a release of 370 dam"' from Cookson 

 Reservoir Montana requested this release to be made between May 1 and May 30, 1992. A 

 volume of 480 dam^ was delivered during this period. 



3.2.5 Water Quality 



The 1981 report by the IJC to Governments recommended: 



For the March to October period, the maximum flow-weighted concentrations should 

 not exceed 3.5 milligrams per liter (mg/L) for boron and 1 500 mg/L for total dissolved 

 solids for any three consecutive months in the East Poplar River at the International 

 Boundary. For the March to October period, the long-term average of flow-weighted 

 concentrations should be 2.5 mg/L or less for boron, and 1 000 mg/L or less for total 

 dissolved solids in the East Poplar River at the International Boundary. 



The Bilateral Monitoring Committee adopted the approach that, for the purposes of comparison with 

 the proposed IJC long-term objectives, the boron and total dissolved solids (TDS) data are best 

 graphically plotted as 5-year moving flow-weighted concentrations (FWCs) which were advanced 

 one month at a time. 



3.2.5.1 Total Dissolved Solids 



TDS data for grab samples collected by Environment Canada and the U.S. Geological Survey in 

 1992 are shown in Figure 3.3. TDS ranged from 743 mg/L (March 16) to 1 286 mg/L (May 19). The 

 short-term objective for TDS is 1 500 mg/L. A time plot of the 3-month moving FWCs for TDS is 

 presented in Figure 3.4. No exceedances of the objective have been observed during any 3-month 

 period since 1975. The 3-month FWCs remained confined within a narrow range centered around a 

 mean of approximately 1 000 mg/L during 1992. 



