Petitioners essentially dispute IEPA's surrogate analysis, arguing that IEPA's approach only analyzed the 1-hour ozone and PM10 NAAQS and did not determine whether the Facility will cause or contribute to an exceedance of the 8-hour ozone or PM2.5 NAAQS.108 Specifically, Petitioners' argue that the 1-hour ozone NAAQS is no longer applicable and that "[t]he permit should be remanded because the Act prohibits [Prairie State] from receiving a permit until it demonstrates that it can comply with the [8-hour ozone] NAAQS." Petition at 41-42. Petitioners' argument, however, must fail.

While both the statute and the implementing regulations prohibit the issuance of a PSD permit without a demonstration that the proposed source will not cause or contribute to an exceedance of the applicable NAAQS, 42 U.S.C. § 7475(a)(3); 40 C.F.R. § 52.21(k), neither the statute nor the regulations define with precision what the applicant must do to make the required demonstration, particularly with respect to the new 8-hour ozone and PM2.5 NAAQS. Instead, the regulations provide in Appendix W to 40 C.F.R. part 51109 guidelines regarding the air quality modeling techniques that should be applied to, among other things, new source review including PSD review. 40 C.F.R. pt. 51, App. W, § 1.a.

With respect to both the 8-hour ozone and PM2.5 NAAQS for estimating the impact of individual sources, Appendix W simply states as follows:

Choice of methods used to assess the impact of an indi-
vidual source depends on the nature of the source and its
emissions. Thus, model users should consult with the Re-
gional Office to determine the most suitable approach on
a case-by-case basis (subsection 3.2.2).

40 C.F.R. pt. 51, App. W §§ 6.2.1(c), 6.2.2.1(c). Subsection 3.2.2 states further that "[d]etermination of acceptability of a model is a Regional Office responsibility." 40 C.F.R. pt. 51, App. W § 3.2.2(a). Thus, at this time, there is little by way of formal regulatory requirement governing the analysis predicting whether either the 8-hour ozone or the PM2.5 NAAQS will be exceeded, and there is much that is assigned to the permit issuer's technical judgment made in consultation with EPA's Regional Office. We generally accord broad deference to permitting authorities with respect to issues, such as this one, requiring the exercise of technical judgment and expertise. E.g., In re BP Cherry Point, 12 E.A.D. 209, 228 (EAB 2005); In re Peabody W. Coal Co., 12 E.A.D. 40, 41 (EAB 2005); In re Steel

108 Petitioners also contend at pages 89-101 of their Petition that IEPA erred in its determination that the proposed Facility will not cause or contribute to violations of the 1-hour ozone and the PM10 NAAQS. We will address these issues in the following subparts of this decision.

109 The air quality and source impacts analysis must be conducted using the methods identified

in Appendix W. 40 C.F.R. § 52.21(1).

Dynamics, Inc., 9 E.A.D. 165, 201, 214-15 (EAB 2000); In re Ash Grove Cement Co., 7 E.A.D. 387, 403 (EAB 1997) (A party wishing to obtain a grant of review of a technical issue must carry a heavy burden of convincing us that the permitting authority's technical analysis is erroneous); In re EcoEléctrica, L.P., 7 E.A.D. 56, 66 (EAB 1997) (denying review and explaining that properly framed, "the question before the [permit issuer] was not whether to 'exempt' [the applicant] from an otherwise applicable regulatory requirement to perform multi-source modeling; the question, instead, was simply how much information to demand about existing sources of air pollution as part of [the applicant's] demonstration of PSD compliance").

Here, IEPA's response to comments and other analysis in the record demonstrates that IEPA did precisely what Appendix W recommends for determining compliance with the 8-hour ozone and PM2.5 NAAQS - as explained above, IEPA followed Region 5's and EPA's guidance regarding the "most suitable approach" to be used on a case-by-case basis, which was to use the 1-hour ozone and PM 10 modeling as a surrogate. See Response to Comments at 133, 155; Memorandum from John S. Seitz, Director, U.S. EPA Office of Air Quality Planning & Standards, (Oct. 27, 1997) (Interim Implementation of New Source Review Requirements for PM2.5). Significantly, IEPA also went beyond the surrogate approach and provided additional reasons why it concluded that the Facility would not cause or contribute to a violation of either the 8-hour ozone or PM2.5 NAAQS. Response to Comments at 117, 134, 166.

In at least one other case, we declined to review an air quality and source impacts analysis that used PM10 as a surrogate for PM2.5. In re BP Cherry Point, 12 E.A.D. 209, 221-22 (EAB 2005). The Administrator has also denied review in a case where the alleged error was a failure to perform a modeling analysis for which there was no method approved by the Agency. In re Old Dominion Elec. Coop., 3 E.A.D. 779, 792 (Adm'r 1992). Determinations such as, these regarding the adequacy of the permit issuer's analysis of a particular pollutant in the absence of an applicable pollutant-specific model approved by the Agency, must necessarily be solidly grounded on the record of the case and, consequently, may not be applicable in subsequent permit proceedings if the Agency has in the intervening time developed additional methods or techniques for analyzing the particular pollutant. Here, we are convinced that the record adequately supports IEPA's decision to use modeling of 1-hour ozone and PM10 impacts as the basis for IEPA's conclusion that the proposed Facility will not cause or contribute to violations of the 8-hour ozone and PM2.5 NAAQS. Moreover, we note that Petitioners have not suggested that any other available method would more accurately predict whether the Facility will cause or contribute to a violation of the 8-hour ozone and PM2.5 NAAQS. Because IEPA's approach appears to be in full accordance with the recommendation of Appendix W and guidance from EPA and Region 5 and because Petitioners have not suggested an alternative method that would be more accurate, we must conclude that Petitioners have failed to sustain their burden of demon

strating clear error in IEPA's response to comments and analysis of this technical issue.

b. Alleged Errors in the Analysis of Compliance with the

1-hour Ozone NAAQS

Petitioners argue that IEPA committed clear error in the modeling of Prairie State's proposed Facility's compliance with the ozone NAAQS stated as a 1-hour standard. Petition at 100-01; Petitioners' Reply at 13-14. Petitioners state that IEPA's analysis used a daily average NOx emissions rate derived from the draft permit's 30-day NOx limit of 0.08 lb/MMBtu to produce the modeling input daily rate of 14.47 tons of NOx emissions. Petition at 100-01. Petitioners argue that this is clear error on the grounds that they contend Appendix W - specifically, table 9-2 set forth in Appendix W to 40 C.F.R. part 51110 - requires short-term limits to be used when modeling for short-term impacts. Id. at 101; Petitioners' Reply at 13. Petitioners thus argue that the Permit's 24-hour NOx limit of 893 lbs/hour should have been used in the modeling for compliance with the 1-hour ozone NAAQS, rather than a rate derived from the 30-day limit. Petition at 101.

Petitioners' reference to table 9-2 in Appendix W, however, is not sufficient to show that IEPA's modeling of 1-hour ozone concentrations was clearly erroneous. Although Appendix W has been promulgated as codified regulatory text, see, e.g., Requirements for Preparation, Adoption, and Submittal of Implementation Plans, 58 Fed. Reg. 38,816 (July 20, 2003),111 nevertheless, Appendix W provides permit issuers broad latitude and considerable flexibility in application of air quality modeling, id. at 38,820. Appendix W is replete with references to "recommendations," "guidelines," and reviewing authority discretion. Relevant to table 9-2 cited by Petitioners, we note that Appendix W section 9.1.2(a) merely states that "the following (b-h) [which includes table 9-2] is typical of the kind of data on source characteristics and operating conditions that may be needed." 40 C.F.R. pt. 51, App. W, § 9.1.2(a) (emphasis added). Section 9.0 provides further that "[m]ore specific data requirements and the format required for the individual models are described in detail in the users' guide for each model," and section 9.1.1(b) states that "[t]he appropriate reviewing authority [112] should be consulted

110 The Petition cites 40 C.F.R. part 52, Appendix W. However, since no such appendix exists and since 40 C.F.R. part 51, Appendix W contains a table 9-2, which summarizes data typically needed for the modeling analysis, we presume that this is the citation Petitioners intended.

111 "[T]his action amends the CFR to incorporate supplement B as codified text, as well as giving regulatory status to long-standing EPA policy regarding the use of air quality models for other regulatory programs." 58 Fed. Reg. at 38,816.

112 The "appropriate reviewing authority may be EPA's Regional Office, or delegated State and local agencies as "representatives" of the respective Regional Office. 40 C.F.R. pt. 51, App. W, § 3.0(b).

to determine appropriate source definitions and for guidance concerning the determination of emissions from and techniques for modeling the various source types." 40 C.F.R. pt. 51, App. W, §§ 9.0(a), 9.1.1(b). Here, Petitioners have not argued that the emission rate used by IEPA was contrary to the users' guide for the model IEPA used to analyze ozone concentrations. Moreover, the emissions rate IEPA used – the draft permit's proposed NOx BACT limit of 0.08 lb/MMBtu, 30-day average - is not contrary to the plain language of table 9-2, which states that the emissions limit should be the "[m]aximum allowable emission limit or federally enforceable permit limit.“ 40 C.F.R. pt. 51, App. W, tbl. 9-2. Petitioners cannot argue that the Permit's NOx BACT limit of 0.07 lb/MMBtu is not a federally enforceable limit. Thus, neither the cited table 9-2's text, nor the accompanying text of Appendix W section 9, which vest discretion in the permitting authority, provide a firm foundation for Petitioners' contention that IEPA clearly erred in the emissions rate used in the modeling for compliance with the ozone NAAQS.

We also note that Appendix W specifically states that "[s]imulation of ozone formation and transport is a highly complex and resource intensive exercise." 40 C.F.R. pt. 51, App. W, § 6.2.1(a). We generally accord broad deference to permitting authorities with respect to issues, such as this one, requiring the exercise of technical judgment and expertise. E.g., In re BP Cherry Point, 12 E.A.D. 209, 228 (EAB 2005); In re Peabody W. Coal Co., 12 E.A.D. 22, 40-41 (EAB 2005); In re Steel Dynamics, Inc., 9 E.A.D. 165, 201, 214-15 (EAB 2000); In re Ash Grove Cement Co., 7 E.A.D. 387, 403 (EAB 1997) (A party wishing to obtain a grant of review of a technical issue must carry a heavy burden of convincing us that the permitting authority's technical analysis is erroneous). Here, we conclude that Petitioners have not sustained their burden of proving, on the record of this case, that IEPA committed clear error in determining that the air quality modeling and source impacts analysis was sufficient to show that Prairie State's proposed Facility will not cause or contribute to a violation of the 1-hour ozone NAAQS. Accordingly, we deny review of this issue.

c. Alleged Violations of the NAAQS for SO2 and PM 10

Petitioners argue that air quality modeling in the present case demonstrates that Prairie State's proposed Facility will violate the SO2 and PM10 NAAQS. Petition at 89-98; Petitioners' Reply at 14-17. More specifically, Petitioners seek review of IEPA's decision to use the significant impact levels, or SILs, in a “culpability analysis" to conclude that Prairie State's proposed Facility is not predicted to violate certain NAAQS identified in the air quality and source impacts modeling. Petition at 89. Petitioners assert that IEPA's use of the SILS as a threshold for determining whether the Facility contributes to a predicted NAAQS exceedance is "clearly legally erroneous." Petition at 89. Petitioners argue that use of the SILS as a threshold for determining whether a facility will cause or contribute to a NAAQS exceedance violates Clean Air Act section 165(a)(3), which Petitioners

observe "does not use the term 'significant."" Id. at 92. For the reasons stated below, we disagree.

Prairie State's air quality and source impacts analysis, which was reviewed and approved by IEPA, followed the NSR Manual's guidance by setting forth a preliminary analysis of air quality impacts based solely on the proposed Facility's emissions. That preliminary analysis indicated that SO2 and PM at certain locations and times are likely to exceed the applicable SILS, thereby triggering a full impacts analysis for these pollutants. See Modeling Addendum No. 2113 at 1 (stating that SO2 and PM emissions resulted in predicted concentrations in excess of the SILS triggering further modeling). The full impacts analysis, which included the proposed Facility's emissions, so-called "background" emissions, and emissions from other sources, predicted violations of the 3-hour and 24-hour SO2 NAAQS at certain receptors at certain times. Id. at 7. However, as to PM, the full impacts analysis set forth in Modeling Addendum No. 2 predicted that there would not be violations of the PM10 NAAQS. Id. at 10.

At this juncture before addressing Petitioners' principal argument regarding the culpability analysis and SILS, we must address a number of background matters including factual disputes concerning the air quality and source impacts analyses. We note first that, during the public comment period and in response to comments submitted, Prairie State updated and corrected its air quality and source impact analysis and set forth the updated analysis in Modeling Addendum No. 2, which consequently is different in a number of respects from the analysis discussed in the Project Summary. See, e.g., Response to Comments at 123-24. Notably, the analysis in Modeling Addendum No. 2, unlike the earlier analysis summarized in the Project Summary, did not predict violations of the PM10 NAAQS. Modeling Addendum No. 2 at 10. Consequently, a culpability analysis of PM10 was unnecessary. Id. On the basis of this subsequent modeling, IEPA concluded that Prairie State's proposed Facility will not cause or contribute to a violation of the PM10 NAAQS (because no violations were predicted). Id. Because Petitioners have not alleged, much less shown, any error in IEPA's review of Modeling Addendum No. 2 on this point, we must reject Petitioners' contention that the relevant air quality modeling predicted violation of the PM10 NAAQS.114 Accordingly, we deny review of IEPA's conclusion that the Facility will not cause or contribute to a violation of the PM10 NAAQS.

113 The IEPA based its determination on its review of the analysis in Modeling Addendum No. 2. Response to Comments at 124 - 26.

114 Petitioners' argument appears to be based solely on the analysis Prairie State presented to IEPA in December, 2003, or earlier. See Petition at 91. To the extent that the Calculation Sheet appears to discuss the earlier air quality and source impacts analysis without an update reflecting Modeling Addendum No. 2 (see, e.g., Calculation Sheet at 17-18), it appears that the Calculation Sheet does not reflect IEPA's final analysis as set forth in the Response to Comments.