62 



Boron results moved opposite to polishing pond water levels (Figure 7.12) and by the end 



of 1990, boron had decreased dramatically to 20 mg/L. 



Discussion presented in 1990, suggested the sudden decrease in boron during 1990 

 could be explained by the pH of the lagoons. With a pH greater than 10.0, boron 

 solubility drops rapidly as shown in Figure 7.13. Information collected in 1991 still 

 supports this suggestion. In May 1 991 , the polishing pond pH was over 1 1 .8, while at the 

 same time the boron level was near a historic low of 3.61 mg/L. By mid-1991 , pH levels 

 in the lagoon had dropped and boron levels were increasing. At the end of 1991 , the pH 

 in the polishing pond had decreased to 10.1 while the boron level was 18.1 mg/L. 



One possible influence of the unusual trends seen during 1990 and 1991 , is the different 

 operating conditions seen at this time compared to other years. SaskPower has been 

 experimenting with a limestone (CaCOa) injection system called "LIFAC" to help reduce 

 sulphur dioxide emissions. Testing of the system started in the last quarter of 1990 and 

 lasted to the end of June 1991. It was during this time that a lot of the unusual results 

 were seen. The chemistry of the polishing pond was known to be changing. The scaling 

 potential of the ash water had suddenly increased and this was confirmed as the ash 

 recirculating pumps had to be cleaned of scale regularly. 



Another factor influencing lagoon water quality in 1991 was the addition in March and 

 April of approximately 224 200 m' of supply water. This had a positive influence on water 

 quality. 



