35
Dominion‟s analysis, Mingo and Mammoth Cave. At Mammoth Cave and Isle Royale, the “Proposed Alternative” scenario provides fewer days exceeding 0.5 deciviews, compared to the “Presumptive BART” scenario. In contrast, the “Presumptive BART” scenario provides fewer days exceeding 0.5 deciviews than does the “Proposed Alternative” scenario at Mingo and Hercules Glade. At all other Class I areas, there is no difference in the number of days exceeding the threshold between the two scenarios. The Illinois EPA concludes that the modeling results demonstrate that Dominion‟s proposed alternative control plan will provide equivalent visibility improvements as will controls that meet the presumptive BART emission limits.
Table 4.10 Comparison of Visibility Impacts from Dominion Kincaid Emissions Control Scenarios – Number of Days with Impacts Greater Than 0.5 Deciviews Class I Area Presumptive BART Proposed Alternative 1 year 3 years 1 year 3 years
Mammoth Cave
5
9
4
7
Mingo
1
3
2
5
Seney
2
3
2
3
Isle Royale
2
3
1
2
Hercules Glade
1
1
1
2
Boundary Waters
1
1
1
1
Great Gulf
1
1
1
1
Tables 4.11 and 4.12 compare the emission reductions expected from Dominion Kincaid‟s alternate control plan and the emission reductions that would occur from compliance with the presumptive BART emission limits for NOx and SO2, respectively. As shown in the tables, expected NOx emission reductions from Dominion Kincaid‟s alternate control plan exceed the reductions that would occur from implementation of BART by about 1,000 TPY. Meeting the presumptive BART SO2 emission limits at Kincaid would achieve about 1,000 TPY greater SO2 emission reductions relative to the alternate control plan. Since air quality modeling has
