Opinion ID: 4538714
Heading Depth: 4
Heading Rank: 2

Heading: Startup Emissions

Text: Petitioners also argue that the formaldehyde emissions solely from the Weymouth station will, in fact, exceed the applicable AAL and TEL. They argue that Algonquin's air-dispersion model, which showed that formaldehyde emissions would be no more than 70% of the AAL, underestimated the actual emission rate because it did not include emissions during intermittent startup events. The proposed SoLoNOx turbine will not run continuously. Instead, it will be shut down and restarted up to 416 times per year. Normally, the turbine will employ an oxidation catalyst to reduce formaldehyde emissions, but during the time it takes the turbine to start up, this catalyst will not be fully operational, meaning formaldehyde emissions will be higher. Algonquin estimates that startups will usually last only nine minutes, though the time may be longer if a startup fails initially. - 39 - The air permit as initially drafted by DEP staff allowed for startup times up to thirty minutes. Petitioners opposed the allowed startup period before the Presiding Officer. Their witness, John Hinckley, performed his own dispersion modeling that, unlike Algonquin's initial modeling,19 accounted for startup emissions -- one model representing thirty-minute startups, and another representing nine-minute startups. Hinckley's thirtyminute model showed that formaldehyde emissions from the Weymouth station would exceed the AAL and TEL when measured at the property line as required by DEP guidance. See 1 DEP, The Chemical Health Effects Assessment Methodology and the Method to Derive Allowable Ambient Limits 21 (1990). Hinckley's nine-minute model showed an exceedance of the AAL, but not the TEL, at the property line. In response, Algonquin's witness, Justin Fickas, put together a model representing eighteen-minute startups, which also showed an exceedance of the AAL. The Presiding Officer acknowledged that EPA's guidance does not require modeling of intermittent startups at all, but nevertheless expressed concern over the modeled exceedances. As 19 DEP policy requires an applicant to model emissions of air toxics only for sources subject to PSD, plus a few other types of facilities. See 1989 Air Toxics Update, supra, at 3. The Weymouth Station does not meet any of these criteria, but DEP exercised its discretion to request that Algonquin perform this modeling. See 310 Mass. Code Regs. § 7.02(5)(c)(6) (requiring applicants to furnish air-dispersion modeling upon request by DEP). - 40 - such, she recommended reducing the allowable startup time from thirty minutes to eighteen minutes, and the Commissioner adopted this recommendation. As to the fact that even the eighteen-minute model showed a concentration above the AAL, the Presiding Officer stated that [t]he slight exceedance shown in the revised modeling beyond the fence line . . . does not, in my opinion, justify denying the permit. Petitioners' main argument before us is straightforward: the Weymouth station will, even under the revised air permit, create an exceedance of the AAL for formaldehyde, and so the permit should have been denied, and we should vacate DEP's contrary decision as arbitrary and capricious. As its name suggests, AAL is meant to be a limit, petitioners argue, so an exceedance should not be allowed, no matter how slight. DEP counters that under the applicable policy, there was no exceedance here. EPA's guidance explains that the intermittent nature of the actual emissions associated with . . . startup/shutdown [operations] in many cases, when coupled with the probabilistic form of the standard, could result in modeled impacts being significantly higher than actual impacts would realistically be expected to be for these emission scenarios. Memorandum from Tyler Fox, Leader, Air Quality Modeling Grp., EPA, to Reg'l Air Div. Dirs., Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-Hour NO2 National Ambient - 41 - Air Quality Standard 8 (Mar. 1, 2011), https://www.epa.gov/sites/ production/files/2015-07/documents/appwno2_2.pdf. EPA thus advises against using startup modeling. See id. at 9–10; see also DEP, Modeling Guidance for Significant Stationary Sources of Air Pollution 1 (2011) (noting that DEP generally follows EPA's guidance on air modeling); cf. 40 C.F.R. § 60.8(c) (Operations during periods of startup, shutdown, and malfunction shall not constitute representative conditions for the purpose of a performance test . . . .). DEP relied on this guidance in not requiring Algonquin to account for startups in its application, and petitioners have not pointed to anything in DEP policy requiring a contrary rule. Although Algonquin provided additional (non-mandatory) modeling to explore the effects of startup events, such models have not been adopted into official department policy or regulations. Thus, DEP acted within its discretion when it relied on a model excluding startup emissions to find, without further evaluation, that there was no exceedance of AAL or TEL.