Opinion ID: 621128
Heading Depth: 4
Heading Rank: 2

Heading: Ambient Air Quality Standards

Text: In calculating stack height credit, the regulations only permit a source to use stack height that is necessary to avoid an exceedance of an ambient air quality standard. 40 C.F.R. § 51.100(kk)(1). Therefore, lower exceedance standards can be used to justify a higher stack height credit. A source seeking to justify a higher stack will seek to establish that the downwash pollution effects of the stack are excessive. In such cases, a higher stackwhich redistributes pollution over a wider areais justified in order to prevent excessive local pollution effects. Thus, it matters whether NAAQS, versus more stringent state standards, control in calculating excessive local concentrations. Montana Sulphur argues that Montana's emission rates (MAAQS) properly could be used as benchmarks for ambient air quality under § 51.100(kk)(1), because the regulation refers only to  an ambient air quality standard whereas the regulations elsewhere describe primary, secondary, and national standards. 40 C.F.R. § 51.100(kk)(1) (emphasis added); 40 C.F.R. § 51.100(c), (d), (e). The EPA, however, insists that national standards, not Montana's state-only annual SO2 standard, should apply to the determination of what is an excessive concentration of SO2 that exceeds an ambient air quality standard under these regulations. The regulation is ambiguous because it does not specifically identify which ambient air quality standard exceedances may be used to support the stack height. The preamble to the regulation, however, frequently refers to the use of NAAQS in addressing above-formula stack height and supports the EPA's interpretation that national standards should provide the benchmark. 50 Fed.Reg. at 27,898-27,899; see Las Vegas, 570 F.3d at 1117-18. Again, the EPA's interpretation of its own regulation is reasonable. Using NAAQS versus the MAAQS as the applicable benchmarks for the exceedance analysis comports with the purposes of 42 U.S.C. § 7423: using NAAQS prevents states from setting standards that might enable local industry to justify above-formula stack height credits that do not meet national standards, and better assures that the EPA will fulfill its obligations. See Sierra Club, 719 F.2d at 450 (EPA must make certain the standard it derives in fact fairly approximates the stack height level needed to protect local health and welfare; in doing so, moreover, it should err on the side of reducing stack height, in keeping with Congress's command that credit for stack heights above [formula] height be granted with `utmost caution').