16 

 Five-year FWCs for TDS (Figure 3.5) remained below tine long-term objective of 1000 

 mg/L A 200 mg/L increase in the five-year FWCs which occurred in early 1988 was 

 increased further in 1991 to approximately 950 mg/L. This corresponds to a decline in 

 high spring flows over that period of time. A similar increase in TDS was seen during 

 mid-1987, as a remnant of the 1982 discharge. Relatively low spring discharges have 

 occurred since 1 984. If this trend continues, it is expected that FWCs will soon approach 

 the 1 000 mg/L objective. 



Using the Seasonal Kendall Tau test for trend assessment, TDS showed a statistically 

 significant increase from 1981 to 1991 (90% confidence level). The Seasonal Kendall 

 Sen Slope estimates the approximate TDS increase to be 2.63 mg/L/year (Figure 3.6). 

 This positive trend could be explained by the drought conditions that occurred over the 

 later half of the data record. The TDS increase comes from salt buildup in the reservoir 

 as a result of water being used for cooling. High evaporation of this water (as a result 

 of drought conditions) causes salts to remain within the reservoir. In addition, low flow 

 conditions (when flows are derived largely from groundwater sources) likely increase TDS 

 concentrations and yields a positive TDS trend in the data. 



The relationship between TDS and conductivity generated from data collected from 1 975 

 to 1991 is as follows: 



TDS = (0.640 X specific conductance) + 12.149 

 (R2=0.87, n=422) 



