additional year of monitoring which was to commmence when both 

 Coronach units sustained near-capacity operation. The monitoring 

 results are summarized in Table 7. 



During the last half of 1984, sulfur dioxide concentrations remained 

 less than both Montana and United States ambient air quality stan- 

 dards. The maximum 1-hour concentration of 8.5 pphm was recorded at 

 the International Boundary site during November. This concentration 

 is approximately one-sixth of the Montana standard. The highest 

 24-hour concentration of 1.2 pphm also occurred at the International 

 Boundary site, but during August. The Montana 24-hour standard is 



10 pphm. A comparison of sulfur dioxide concentrations with Class 



11 Prevention of Significant Deterioration increments demonstrates 

 that the 24-hour concentration is the averaging time which consumes 

 the most increment. The 1.2 pphm 24-hour average at the Internation- 

 al Boundary site would consume 35 percent of the available increment. 

 All of the higher sulfur dioxide concentrations noted above occurred 

 with northwest winds, indicating that the Saskatchewan Power Corpora- 

 tion generating facilities were the source. 



The Montana and United States standards for total suspended particu- 

 lates were not exceeded at any of the three monitoring sites. The 

 highest 24-hour concentration was 114 Ug/m recorded on December 20, 

 1984, at the Richardson site. The Hanrahan site recorded the highest 

 geometric and arithmetic means at 19.4 and 27.3 Mg/m-^, respectively. 

 The levels of total suspended particulates observed during 1984 

 are low and representative of rural Montana. 



In July 1984, an extended network of lead dioxide sulfation plates 

 was installed in the Poplar River area. The sulfation plate network 

 included the existing three primary monitoring sites and five addi- 



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