In 2003, the Poplar River Bilateral Monitoring Committee decided to suspend much of the water-quality 

 sampling program until it is warranted again. The Committee has agreed to use the daily conductance 

 data collected by the specific-conductance monitor as a surrogate for the monthly water-quality 

 sampling program. Therefore, only four water-quality samples were collected for TDS and boron by the 

 uses in 2004. Hence, the 3-month FWC for TDS and boron in 2004 were calculated using the two 

 established equations (shown later in text) and the daily conductance data collected by the specific- 

 conductance monitor installed at the East Poplar River at International Boundary gauging station. 



The Bilateral Monitoring Conmiittee adopted the approach that, for the purpose of comparison with the 

 proposed IJC long-term objectives, the TDS and boron data are best plotted as a 5-year moving FWC 

 which is advanced 1 month at a time. 



Prior to 1988, long-term averages were calculated for a 5-year period in which 2.5 years preceded and 

 2.5 years followed each plotted point. Beginning in 1988, the FWC was calculated from the 5-year 

 period preceding each plotted point. For example, the FWC for December 2004 is calculated from data 

 generated over the period December 1999 to December 2004. The calculations are based on the results 

 of samples collected throughout the year, and are not restricted to only those collected during the months 

 bracketing the period of irrigation (March to October) each year. 



3.2.5.1 Total Dissolved Solids 



TDS is inversely related to streamflow at the East Poplar River at International Boundary station. During 

 periods of high runoff such as spring freshet, TDS decreases as the proportion of streamflow derived 

 from ground water decreases. Conversely, during times of low streamflow (late summer, winter) the 

 contribution of ground water to streamflow is proportionally greater. Because the ground water has a 

 higher ionic strength than the surface water entering the river, the TDS of the stream increases markedly 

 during low-flow conditions. 



TDS concentrations derived from the specific- conductance monitor readings are shown in Figure 3.4. 

 The TDS concentrations ranged from 730 mg/L on March 15 to 1,060 mg/L on May 25. The proposed 

 short-term objective for TDS is 1,500 mg/L. 



10 



