From: Lydia Wegman/RTP/USEPA/US

To: nfrey@omb.eop.gov Cc: Richard Wayland/RTP/USEPA/US@EPA, James Hemby/RTP/USEPA/US@EPA,

martin.karen@epa.gov, Joseph

- J Dougherty/DC/USEPA/US@EPA Date: 06/11/2012 04:24 PM Subject: Fw: Responses to monitoring and implementation comment s
Nathan, Attached are the edits to the language we were just discussing on our call, concerning comment 26. We hope this addresses the issues raised by the commenters. Lydiac. Surrogacy Approach for the P roposed N ew S econdary PM 2.5 Visibility Index NAAQS

As summarized in section VI.F of this preamble, the EPA is proposing a distinct secondary NAAQS for PM 2.5 that will provide protection against visibility impairment, measured in terms of a visibility index using a calculated PM 2.5 light extinction indicator (see section VI.D.1 above). The PM 2.5 visibility index values are determined using a six

- step procedure involving 24

- hour speciated PM 2.5 concentration data together with climatological relative humidity factors. The EPA plans to calculate design values for the proposed new secondary
PM 2.5 visibility index NAAQS using the procedures described in section VII .A.5 above, relying
upon ambient PM 2.5 speciation measurement data available through the CSN or IMPROVE methods and spatial interpolation of historical relative humidity data. As explained above, the PSD program requires individual new or modified station ary sources to carry out an air quality analysis to demonstrate that their proposed emissions increases will not cause or contribute to a violation of any NAAQS. Such a demonstration for the proposed new secondary PM 2.5 visibility index NAAQS could require each PSD applicant to predict, via air quality modeling, the visibility impairment that will result from its proposed emissions in conjunction with an assessment of existing air quality (visibility impairment) conditions. Under 40 CFR § 51.166 (l)(1) and 40 CFR § 52.21(l)(1), all applications of air quality models for purposes of determining compliance with a NAAQS, including the proposed secondary NAAQS for PM 2.5 , must be based upon air quality models specified in Appendix W to 40 CFR § 51. Currently t here are no air quality models identified in Appendix W that are recommended for regulatory applications (Appendix W to 40 CFR § 51, Section 3.1.1(b)) for addressing the atmospheric chemistry associated with secondary formation of PM 2.5 . Thus, i f this demonstration were to be attempted using the six

- step procedure that theEPA is proposing to use for calculating PM 2.5 visibility index design values, significant technical

and regulatory issues with the modeling procedures could arise. Those technic al difficulties include the current limitations on speciated source

- specific emissions data for model input ; the lack of an EPA

- approved air quality model with the capability to address the atmospheric chemistry associated with secondary formation of PM 2.5 ; and the lack of PSD screening tools for streamlining the air quality analysis process. In addition, due to the limited monitoring network for speciated PM 2.5 , some sources may not be able to rely on existing speciated monitoring data
to adequately repres ent the background air quality and thereby satisfy preconstruction monitoring requirement s. Consequently, those prospective PSD sources could be required to collect new data in order to determine the representative background concentration s of PM 2.5 specie s (i.e., those required for calculatin g the PM 2.5 visibility i ndex values as described in section VII.A.5 above ). Recognizing these difficult technical issues, the EPA believes that there is an essential need to provide alternative approaches to enable pro spective PSD sources to demonstrate that they will not cause or contribute to a violation of the secondary PM 2.5 visibility index NAAQS , if finalized as proposed . To meet this need, the EPA believes that it is reasonable to allow the use of a surrogacy app roach , as discussed below, for at least the interim period while technical issues are being resolved, but which could potentially be continued beyond such time if shown to be appropriate. The EPA is providing notice of its intent to follow such an approach and is asking for comments on the approach as discussed in the remainder of this section. The Agency believes that following this approach will facilitate the transition to a workable PSD permitting approach under the proposed new secondary PM 2.5 visibili ty index NAAQS

. To support consideration of alternative approaches that could be used by prospective PSDsources , the EPA conducted a two

- pronged technical analysis of the relationships between the

proposed new PM 2.5 visibility index standard and the proposed primary annual and 24

- hour
PM 2.5 standards (Wayland, 2012). The first prong of the analysis addressed aspects of a PSD significant impact analysis by evaluating whether an individual source’s impact resulting in a small increase in PM 2.5 concentration would produce a comparably small increase in visibility impairment. This analysis included estimates of PM 2.5 speciation profiles based on direct PM 2.5 emission profiles for a broad range of source categories and for theoretical upper and lower bound scenarios. The analysis indicated that small increases in PM 2.5 concentrations caused by individual source s produce similarly small changes in visibility impairment for ambient conditions near the proposed standard level of either 30 dv or 28 dv . The second prong of the analysis addressed aspects of a PSD cumulative impact analysis by exploring the relationship between the 3

- year design values for the proposed primary annual and 24

- hour PM 2.5 standards and coincident desig n values for the proposed new PM 2.5 visibility index standard based on recent air quality data. This analysis showed that visibility generally decreases when daily PM 2.5 concentrations increase, and vice versa. This analysis further explored the appropriat eness of using a demonstration of attainment with the primary 24

- hour PM 2.5 standard as a surrogate for a demonstration of attainment with the proposed new secondary PM 2.5 visibility index standard. The Wayland (2012) analysis was based on 2008 to 2010 air quality data and on the proposed retention of the primary 24

- hour PM 2.5 standard with a level of 35 μg/m 3 in conjunction with a 98 th percentile form (section III.F) and the proposed new secondary PM 2.5 visibility index standard with a level of either 30 d v or 28 dv in conjunction with 24

- hour averaging time and a 90 th percentile form (see section VI.F). 1 This analysis indicated that all or nearly all areas in

1 As identified in section IX.E above, the relationships between design values characterized in the Wayland (2012) analysis and summarized here are dependent upon the specific level andattainment of the primary 24

- hour PM 2.5 standard would also likely be in attainment of the

proposed new secondary PM 2.5 visibility index standard. The EPA believe s that th is technical analys i s is robust and will have broad national application; thus, sources may choose to rely on the surrogacy demonstration even after resolution of the issues and limitations described previously, consistent with the case law on the use of surrogates. Based on this technical analysis, the EPA currently believe s that there is sufficient evidence that a demonstrat ion of compliance with the mass - based primary 24

- hour
PM 2.5 NAAQS serves as a suitable surrogate for demonstrating compliance with the proposed secondary 24

- hour PM 2.5 visibility index NAAQS under the PSD program. As such, many or all sources undergoing PS D review for PM 2.5 would be able to rely upon their analysis demonstrating compliance with the mass

- based 24

- hour primary PM 2.5 NAAQS to also show compliance with the proposed secondary PM 2.5 visibility index NAAQ S , if finalized. The described surrogate ap proach would thus serve to overcome the technical challenges discussed above and minimize otherwise burdensome and costly air quality analyses associated with individual sources being required to perform separate and distinct analyses with regard to the
pr oposed new secondary PM 2.5 visibility index standard

. The surrogate approach is not intended to replace or otherwise undermine the validity of the analytical techniques employed for air quality rel ated value assessments (AQRV’s) , including visibility, req uired under 40 CFR § 51.166 (p) and 40 CFR § 52.21 (p). The Federal Land Managers (FLM) and the Federal official with direct responsibility for management of Federal Class I parks and wilderness areas have an affirmative responsibility to protect the AQRV s of such lands, and to provide the appropriate procedures and analysis techniques for assessing AQRV’s (Appendix W to 40 CFR § 51,Sections 6.1 (b) and 6.2.3(a)). The FLM’s have developed specific modeling approaches for

AQRV assessments that are not spe cifically governed under the requirements set forth in 40 CFR § 51.166 (l)(1) and 40 CFR § 52.21(l)(1), thus the surrogate approach is not applicable to the AQRV assessments under the PSD program. The surrogate approach could be incorporated into the PSD program in any of three alternative ways. First, the decision as to whether the surrogate approach is adequate could be handled on a case

- by

- case basis in consultation with the permitting authority , similar to the existing consultation process under the EPA’s Guideline on Air Quality Models for ozone and secondary PM 2.5 impacts ( 40 CFR part 51, appendix W, section 5.2.1.c ), with no presumption regarding its adequacy. Second, the EPA could establish a rebuttable presumption that the surrogate approach is applicable for all permits through either guidance or a notice

- and

- comment rulemaking. In either the first or second alternative, there would be a possibility that reliance on a surrogate

- based demonstration could be subjected to challenge for any part icular permit analysis. Third, the EPA could establish that the surrogate approach is applicable for all permits, also through a notice

- and

- comment rulemaking. The EPA seeks comment on all of the identified issues and proposed alternative implementation me chanisms associated with the proposed surrogate approach. It is the Agency’s intention to issue either guidance or new regulatory provisions as just described for a surrogacy approach by the time any final revisions to the PM NAAQS become effective, so tha t sources seeking permits will not be unnecessarily delayed.