Definitions

The definitions in title 40 Code of Federal Regulations part 51, section 301, as they exist on July 1, 2019, are incorporated by reference into this chapter. For purposes of this chapter only: 1. "Boiler operating day" means any twenty-four-hour period between midnight and the following midnight during which any fuel is combusted at any time at the steam generating unit. 2. "Contributes to visibility impairment" means a change in visibility impairment in a class I federal area of five-tenths deciviews or more (twenty-four-hour average) above the average natural visibility baseline. A source exceeds the threshold when the ninety-eighth percentile (eighth highest value) of the modeling results based on any one year of the three years of meteorological data modeled exceeds five-tenths deciviews.