3.2.5.1 Total Dissolved Solids 



There is an inverse relationship between TDS and streamflow at the International Boundary 

 station. During periods of high runoff, such as spring freshet, TDS drops as the proportion of 

 streamflow derived ultimately from ground- water decreases. Conversely, during times of low 

 streamflow Gate summer, winter) the contribution of ground- water to streamflow is proportionaUy 

 greater. Because the natural 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 grab sample data collected by Environment Canada and the USGS in 1995 are shown in 

 Figure 3.3. TDS ranged from 899 mg/L on 6- July to 1 194 mg/L on 9-May. 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 3.4. No exceedences of the objective have been observed during any three 

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

 centred around a mean of approximately 984 mg/L (regression generated data) and 1 039 mg/L 

 (grab sample data). 



