Opinion ID: 4020089
Heading Depth: 4
Heading Rank: 1

Heading: The “Upper Prediction Limit”

Text: Several factors complicate the process of setting MACT floors. The first is the CAA itself, which mandates that all MACT floors (1) must be achievable, see 42 U.S.C. 7 The four major boiler subcategories for which the EPA established work-practice standards include “[n]ew and existing units that have a designed heat input capacity of less than 10 MMBtu/hr, and new and existing units in the Gas 1 (natural gas/refinery gas) subcategory and in the metal process furnaces subcategory.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613. 15 § 7412(d)(2); (2) must ensure continuous regulation of the covered sources, see id. § 7602(k); and (3) must be no less stringent than the emissions levels being achieved by the bestcontrolled sources, see id. § 7412(d)(3). The second is that no source emits any HAP at a constant level; rather, HAP emissions fluctuate over time and for many reasons, including, e.g., “operation of control technologies, variation in combustion materials and combustion conditions, variation in operation of the unit itself, and variation associated with the emission measurement techniques.” Memorandum from Stephen D. Page, EPA Director of Air Quality Planning and Standards, EPA’s Response to Remand of the Record for Commercial and Industrial Solid Waste Incineration Units (Page Mem.) (July 14, 2014), at 3 (No. 11-1125 J.A. 1316). Finally, most sources do not measure their HAP emissions at all times and under all conditions.8 Id. at 6. Instead, data are usually gathered when a source conducts a “three-run stack test.” Id. This test provides three “snapshots” of a source’s emissions in a limited set of conditions and, accordingly, it fails to demonstrate accurately a source’s emissions during all times and under all conditions. Id. To compensate for the lack of adequate emissions data, the EPA uses a statistical tool known as the “upper prediction limit” (UPL) to account for the expected variability in emissions levels. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,630. The UPL, in turn, allows the Agency to set a MACT floor that is continuously achievable. Id. We discuss the UPL mechanics at greater length below, see infra § IV.C, but, in short, the EPA: (1) ranks all sources in a given 8 As discussed below, however, the EPA does allow sources to demonstrate MACT compliance by use of “continuous monitors.” See infra § IV.I. 16 category based on their three-run stack-test data; (2) determines the HAP emissions level of the “best controlled similar source” to establish standards for new sources, 42 U.S.C. § 7412(d)(3), and determines the average HAP emissions levels of the best performing 12 per cent of sources to establish standards for existing sources, id. § 7412(d)(3)(A); and then (3) applies the UPL methodology to provide the cushion necessary to account for the expected peaks and valleys in HAP emissions not reflected in the threerun stack-test “snapshots.” See Page Mem. 4, 6.