Alaska Dept. of Environmental Conservation v. EPA, 540 U.S. 461, 17 (2004)

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Cite as: 540 U. S. 461 (2004)

Opinion of the Court

fered by Cominco. To achieve nitrogen oxide emission reductions commensurate with SCR's 90% impact, Cominco proposed fitting the new generator MG-17 and the six existing generators with Low NOx. Ibid.8 Cominco asserted that it could lower net emissions by 396 tons per year if it fitted all seven generators with Low NOx rather than fitting two (MG-5 and MG-17) with SCR and choosing one of them as the standby unit. Id., at 87. Cominco's proposal hinged on the "assumption . . . that under typical operating conditions one or more engines will not be running due to maintenance of standby-generation capacity." Ibid. If all seven generators ran continuously, however, Cominco's alternative would increase emissions by 79 tons per year. Ibid. Accepting Cominco's submission, ADEC stated that Cominco's Low NOx solution "achieve[d] a similar maximum NOx reduction as the most stringent controls; [could] potentially result in a greater NOx reduction; and is logistically and economically less onerous to Cominco." Id., at 87-88.

On the final day of the public comment period, June 2, 1999, the United States Department of the Interior, National Parks Service (NPS), submitted comments to ADEC. App. to Pet. for Cert. 33a; App. 97, 108. NPS objected to the projected offset of new emissions from MG-5 and MG-17 against emissions from other existing generators that were not subject to BACT. Letter from John Notar, NPS Air Resources Division, to Jim Baumgartner, ADEC (June 2, 1999). Such an offset, NPS commented, "is neither allowed by BACT, nor achieves the degree of reduction that would result if all the generators that are subject to BACT were equipped with SCR." Id., at 3. NPS further observed that the proposed production-increase project would remove operating restrictions that the 1994 PSD permit had placed on four of the existing generators—MG-1, MG-3, MG-4,

8 Two generators already were fitted with a technology called Fuel Injection Timing Retard that results in a 20% to 30% reduction in nitrogen oxide emissions. App. 75-76, 86.


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