Public Review Draft 9/22/2011

EPA 453/R-XX-XXX Month 2011



# Guidance for 1-Hour SO 2 

# NAAQS SIP SubmissionsPublic Review Draft 9/22/2011

i EPA 453/R-XX-XXX Month 2011



# Guidance for 1-Hour SO 2 

# NAAQS SIP Submissions

Office of Air Quality Pl anning and Standards U.S. Environmental Protection Agency Research Triangle Park, North CarolinaPublic Review Draft 9/22/2011

ii TABLE OF CONTENTS Preface................................................................. Page iii I. Purpose.................................................................................... Page 1 II. Background ......................................................................... Page 1 A. Roles of EPA and state governments B. How this guidance applies to tribes III. Schedule for implementation of the 1-hour SO 2 NAAQS........ Page 6 IV. Section 110(a)(1) and (2) NAAQ S maintenance/infrastructure elements................................................................. Page 8 A. Section 110(a)(1)-(2) SIP submission B. Section 110(a)(1) SIPs C. Redesignation to attainment for areas designated as unclassifiable V. SO 2 nonattainment area planning elements ....................... Page 27 A. SO 2 SIP planning B. New source review C. Conformity VI. Transition from the existing SO 2 NAAQS to a revised SO 2 NAAQS........................................................................... Page 31 VII. Redesignation to attainment for areas designated as nonattainment............................................................. Page 33 A. Attainment of the NAAQS B. Consequences of a nonattainment area failing to attain by the statutory attainment date Appendix A Modeling Guidance for Nonattainment Areas and Section 110(a)(1) Plans.............................................................................. Page A-1 Appendix B Guidance on Section 110(a)(2) Infrastructure SIP Elements ....... Page B-1 Appendix C Guidance on Non-modeling Technical Demonstration of Attainment.................................................................... Page C-1Public Review Draft 9/22/2011

iii Preface In the final primary National Ambient Air Quality Standard for Sulfur Dioxide (SO 2 NAAQS) rulemaking, published at 75 FR 35520 (J une 22, 2010), EPA provided initial guidance in the preamble concerning the Clean Air Act (CAA) provisions that states and emissions

sources would need to address wh en implementing the new 1-hour SO 2 NAAQS. We stated that we intended to develop and seek public comm ent on additional guidance on modeling and the development of state implementation plans (SIPs) to be submitted under sections 110 and 191 of the CAA. To this end, EPA is issuing the draf t guidance contained in this document so that states and other interested parties may comment on our preliminary recommendations for how to meet the section 110(a)(1) requirement that all areas submit a SIP no later than June 3, 2013, and the section 191 requirement that all areas that are designated as nonattainment under the 1-hour

SO 2 NAAQS submit a SIP providing for attainment of that standard. This draft guidance is not final agency action, and imposes no binding or enforceable requireme nts. We intend to re-issue this guidance, revised as appropriate, after re ceiving and considering the public comments that we receive on this pr eliminary draft. In addition to this guidance document, EP A is also planning a rulemaking to address

some of the 1-hour SO 2 NAAQS implementation program elements. These elements include: (1) establishing that complia nce with the 1-hour SO 2 NAAQS is appropriately based on the results of both air quality modeling and monitoring; (2) establishing the modeling requirements necessary to determine compliance with the 1-hour SO 2 NAAQS; (3) establishing the minimum scope of analysis required to demonstrate attainment and maintenance of the 1-hour SO 2 NAAQS to comply with the SIP requirements in CAA section 110(a)(1 ); (4) establishing a reasonable time period for sources to comply with any new emissions limita tions states need toPublic Review Draft 9/22/2011

iv establish in the 110(a)(1) SIPs to demonstrat e attainment and maintenance of the 1-hour SO 2 NAAQS; (5) to set an attainment date for areas designated as unclassifiabl e; and (6) establishing the criteria for redesignating areas from “unclassif iable” to “attainment.” These elements are also addressed in this guidance document. EPA will consider any comments that we receive on these elements in this draft guidance as we develop the proposed rulemaking. EPA will re-issue the guidance as expeditiously as practicably foll owing the public comment period so that states can use the guidance to begin developing their pl ans as soon as possible. EPA will also propose a rulemaking that would codify the hybrid mode ling and monitoring implementation approach in order to ensure compliance with the 1-hour SO 2 NAAQS in a timely manner. EPA developed the proposed hybrid modeli ng and monitoring approach to show compliance with the 1-hour SO 2 NAAQS due to the unique challenges presented by this pollutant. EPA does not believe that this implemen tation approach is necessarily transferable to other NAAQS pollutants. For NAAQS pollutants other than SO 2 , air quality monitoring is more appropriate for determining whether all ar eas are attaining the NAAQS, and there is comparatively less dependence upon conducting re fined air quality modeling. EPA recommends

that states coordinate with their respective EPA Regional Offi ces during the SIP development process, as early and often as possible, in order to ensure that critical issues related to the implementation of this approach are resolved as expeditiously as practicable in order for the SIP to be submitted and approved in a timely manner.Public Review Draft 9/22/2011

1 I. Purpose This guidance document discusses the CAA stat utory requirements that states need to address when implementing the new 1-hour SO 2 NAAQS based on the structure outlined in the CAA and existing rules. It supplements existing guidan ce documents and regulations, and contains additional guidance on attainment m odeling (Appendix A), and developing SIPs under sections 110(a)(1)-(2) and 191-192 of the CAA. 1 In this document, we also describe in more detail how and when we expect states to dem onstrate attainment, implementation, maintenance,

and enforcement of the new 1-hour SO 2 NAAQS.

II. Background On June 2, 2010, the Administrator signed a notice establishing a new 1-hour primary

SO 2 NAAQS of 75 parts per billion ( ppb), which is attained when the 3 year average of the 99 th percentile of 1-hour daily maximum c oncentrations does not exceed 75 ppb. 2 EPA revised the primary SO 2 NAAQS to provide the requisite protecti on of public health with an adequate margin of safety, as required by CAA section 109(b). We explained in the preamble to the final NAAQ S rule that we anticipate that most areas will initially be designated under CAA section 107( d) as “unclassifiable” for the revised primary

SO 2 NAAQS, meaning that they would not initia lly be subject to the nonattainment area SIP requirements of CAA sections 191-192. This is b ecause we do not expect most states to have either monitoring data or appropriate modeling in formation sufficient to determine whether those areas are meeting or not meeting the 1-hour SO 2 NAAQS for initial designations

recommendations due to EPA in June 2011. Howe ver, we anticipate that unclassifiable areas

1 See also SO 2 Guideline Document, Office of Air Quality Planni ng and Standards, Research Triangle Park, NC 27711, EPA-452/R-94-008, February 1994. 2 EPA publicly disseminated the signed notice on June 3, 2010. The new 1-hour SO 2 NAAQS became effective on August 23, 2010.Public Review Draft 9/22/2011

2 will contain sources of SO 2 emissions that could potentially ca use or contribute to a violation of the primary SO 2 NAAQS. In such cases, EPA believe s that a post-designation implementation approach that relies on robust state implement ation plans submitted in accordance with CAA sections 110(a)(1) 3 and (2) 4 is appropriate and necessary to ensure public health protection under the 1-hour NAAQS. These SIPs have sometimes b een referred to respectively as “maintenance” and “infrastructure” SIPs. To be approve d, EPA believes such plans should provide for

attainment and maintenance of the new 1-hour SO 2 NAAQS as expeditiously as practicable. In the final NAAQS preamble we explained that we be lieve it is reasonable to expect any necessary emissions controls and limits to be in place and e ffective no later than five years after initial area designations (or by approximately August 2017), whic h is consistent with the timeframe that would otherwise apply to any area designated as nonattainment in 2012. For the primary 1-hour SO 2 NAAQS, we anticipate that initial designations will be promulgated by June 2012, two years following promulgation of the NAAQS. In guidance

issued on the 1-hour SO 2 NAAQS designations process we indi cated that an area that has monitoring data or refined modeling results showing a violation of the NAAQS would be designated as “nonattainment”; an area that has an appropriate demonstration showing no violations would be designated as “attainment”; and all other areas with sources that have the potential to cause or contribute to a violation of the NAAQS, which may include areas with SO 2 monitors showing no violations but without refined modeling that shows no violations, would be designated as “unclassifiable.” Areas with no SO 2 monitors would be designated as

“unclassifiable” as we ll, absent any other appropriate data to support a designation of “attainment” or “nonattainment.” We anticipate that most areas of the coun try will be designated

3 CAA section 110(a)(1) directs states to submit, no later than three years following promulgation or revision of a primary NAAQS, SIPs that provides for “implementation, maintenance, and enforcement of” the NAAQS. 4 CAA section 110(a)(2) lists the programma tic elements that each SIP must contain.Public Review Draft 9/22/2011

3 as “unclassifiable” due to a lack of both m onitoring and refined modeling information, in advance of states conducting further refi ned modeling at the time of designation. 5 Subpart 5, of Part D, of Title I of th e CAA (sections 191 and 192) describes the requirements that apply to area s designated nonattainment. A s ubstantial set of longstanding guidance has been issued and continues to re flect EPA recommendations for interpreting these requirements, most notably in the General Preamble published in the Federal Register on April 16, 1992 (see, e.g., 57 FR 13498, at 13545). The guida nce below addresses additional statutory state planning and control requirements th at apply regardless of designation, such as

infrastructure SIP elements. A. Roles of EPA and state governments The CAA assigns important roles to EPA a nd state governments to achieve the NAAQS. States have the primary responsibility for de veloping and implementing SIPs that contain measures necessary to achieve the air quality standards in each area once EPA has established the NAAQS. EPA provides technica l tools, assistance, and guid ance to states and tribes, including information on the potential control measures that may help areas attain the standards. Under section 110 of the CAA, and related provisi ons, states are directed to submit, for EPA approval, SIPs that provide for the attainment, implementation, maintenan ce, and enforcement of such standards through control progr ams directed at sources of SO 2 emissions. (CAA sections 110(a), and 191-192). If a state does not adopt and implement approved SIPs by the time periods provided in the CAA, EPA has the responsibility to adopt a federa l implementation plan (FIP) to ensure that areas attain the NAAQS in an expeditious manner.

5 See guidance memorandum on designations entitled “Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standard, March 24, 2011.”Public Review Draft 9/22/2011

4 States, in conjunction with EPA, also administer the prevention of significant deterioration (PSD) program for SO 2 . (CAA sections 160-169). The primary feature of this program is a requirement that certain stationary sources of air pollutant s obtain a permit (“PSD permit”) before commencing construction. (CAA s ection 165(a)(1)). To obtain such a permit, one of the things that a permit applicant must s how is that the proposed source will not cause or

contribute to a violation of any NAAQS. (CAA section 165(a)(3); 40 CFR 52.21(k); 40 CFR 51.166(k)). Most states implement the PSD pe rmitting program under state regulations approved by EPA as part of a SIP. Federal rules supplement state emissions cont rol measures and provide for nationwide or regional reductions in emissions of SO 2 and other air pollutants. U nder Title II of the CAA there

are rules that limit the sulfur content of the fuel used by automobiles, trucks, buses, motorcycles, non-road engines and equipment, marine ve ssels and locomotives. Emissions of SO 2 are also limited by new source performance standards (NSPS) for stationary sources under sections 111 and 129 of the CAA; and the national emission standards for hazardous air pollutants (NESHAP) for stationary sources under sec tion 112 of the CAA (such reducti ons resulting due to control of hazardous air pollutants (HAP) such as hydrogen chlo ride (HCl) under those rules). Title IV of the CAA, sections 402-416, specifically provides for major reductions in SO 2 emissions from fossil-fuel fired power plants. EPA has also promulgated the Cross St ate Air Pollution Rule (CSAPR) to define additional SO 2 emission reductions needed in the eastern United States by 2012 and 2014 to eliminate significant contribu tion of upwind states to downwind states’ nonattainment, or inability to maintain, the PM 2.5 NAAQS pursuant to CAA section 110(a)(2)(D). 6 States may rely on these federal measures in their SO 2 SIPs.

6 The final Cross State Air Pollution Rule (CSAPR) was sign ed by the EPA Administrator on July 6, 2011, and was published at 76 FR 48208, August 8, 2011Public Review Draft 9/22/2011

5 B. How this guidance applies to tribes CAA section 301(d) authorizes EPA to treat e ligible Indian tribes in the same manner as states under the CAA and requires EPA to promulga te regulations specifying the provisions of the statute for which such treatment is appropr iate. EPA has promulgated these regulations – known as the Tribal Authority Rule or TAR – at 40 CFR Part 49. (63 FR 7254, February 12, 1998). The TAR establishes the process for Indian tribes to seek treatment -as-a-state eligibility

and sets forth the CAA functions for which such treatment will be available. Under the TAR, eligible tribes may seek approval for all CAA a nd regulatory purposes other than a small number

of functions enumerated at section 49.4. Im plementation plans under section 110 are included within the scope of CAA functions for which eligible tribes may obtain approval. Section 110(o) also specifically describes tribal roles in submittin g implementation plans. Eligible Indian tribes may thus submit tribal implementation plans (TIPs) covering their reserv ations and other areas under their jurisdiction. The CAA and the TAR do not, however, direct tr ibes to apply for treatment as a state or implement any CAA program. In promulgating the TAR, EPA explicitly determined that it was not appropriate to treat tribes similarly to st ates for purposes of, among other things, specific plan submittal and implementation deadlines for NAAQS-related requirements. (40 CFR § 49.4(a)). In addition, where trib es do seek approval of C AA programs, including section 110 implementation plans, the TAR provides flexibility and allows them to submit partial program elements, so long as such elements are reasonably severable – i.e. , “not integrally related to program elements that are not included in the pl an submittal, and are consistent with applicable statutory and regulatory requi rements.” (40 CFR § 49.7).Public Review Draft 9/22/2011

6 To date, very few tribes ha ve sought treatment as a state for purposes of section 110 implementation plans. In the event that a tribe is unable to develop a plan that addresses the implementation of the 1-hour SO 2 NAAQS, the Administrator, pur suant to the discretionary authority explicitly granted to the Administra tor under sections 301(a) and 301(d)(4) of the CAA, has the authority to promulgate a FIP to pr otect air quality. Consiste nt with the provisions of sections 304(a) and 301(d)(4 ), if a tribe does not submit a TIP meeting the completeness criteria of 40 CFR part 51, appendix V, or does not receive EPA approval of a submitted TIP, EPA has authority to develop a FIP to protect air quality in the affected area. (40 CFR 49.11(a)). In addition, upon request from a tribe that has un dertaken the responsibility for developing a TIP to address the requirements to implement the 1-hour SO 2 NAAQS, EPA will provide assistance as necessary to complete the development of the plan. III. Schedule for Implementation of the 1-hour SO 2 NAAQS The timeline below shows the expected steps from promulgation of the new NAAQS through attainment, assuming timely action at each step and assuming that initial area designations are effec tive in August 2012:Public Review Draft 9/22/2011

7 Date Action

June 2010 EPA issues 1-hour SO 2 NAAQS. This action starts the 2-year clock for CAA section 107 initial area designati ons and the 3-year clock for CAA section 110(a)(1)-(2) SIP submissions. August 2010 Effective date of 1-hour SO 2 NAAQS. Under the PSD program, EPA and states that issue PSD permits under delegated federal authority begin requiring a demonstration in the permitting record that the proposed source will not cause or contribute to a viol ation of the 1-hour SO 2 NAAQS. States that issue PSD pe rmits under a SIP-approved state program should also require such a demonstration for permits issued on or after August 23, 2010 to ensure that sources commencing construction in such states have permits that conform to the requirements of CAA section 165(a)(3). June 2011 States submit initial area designa tions recommendations, based on available monitoring data and any refined modeling they choose to perform for designations purposes. June 2012 EPA issues final initial area desi gnations. Monitored or modeled violations would result in a designa tion of “nonattainment.” Areas would be designated “attainment” if they submit appropriate modeling data (where needed) showing evidence of no violations and if all available monitoring data indicate attainment for the affected area. Generally, all other cases would be initially designated “unclassifiable.” June 2013 All states submit CAA section 110(a)(1 )-(2) SIPs. SIPs address PSD and infrastructure requirements, and provide for implementation and maintenance of the 1-hr NAAQS in all areas throughout the state, particularly in areas initially desi gnated unclassifiable and attainment. SIPs for unclassifiable areas woul d rely on refined modeling and any monitoring that demonstrates attain ment and maintenance of the new SO 2 NAAQS as expeditiously as practi cable, which EPA anticipates should be no later than the attainment dead line for areas initially designated nonattainment. SIPs should contain a ny additional federally enforceable control measures necessary to ensure maintenance of the NAAQS. Attainment demonstration SIPs for nonattainment areas have a separate deadline. February 2014 Assuming designations are effective in August 2012, states submit SIPs for nonattainment areas consistent with CAA section 191-192 that demonstrate attainment as expeditiously as practicable and no later than 5 years from the effective date of designations (August 2017). June-December 2014 EPA approves or disapproves timely submitted (by June 2013) and complete CAA section 110(a)(1)-(2) SIPs. EPA’s action would be based on adequacy of the states’ modeli ng demonstrations (and any obtained monitoring) showing attainment as expeditiously as practicable and continued maintenance of the NAAQS. Demonstrations can take into account SO 2 reductions from national and re gional standards that require compliance by the attainment date. EPA would also have discretion to re-Public Review Draft 9/22/2011

8 Date Action designate attainment and unclassifiabl e areas if SIPs are inadequate, as well as propose FIPs. February-August 2015 EPA approves or disapproves timely submitted (by February 2014) and complete CAA section 191-192 attain ment SIPs for areas initially designated nonattainment, with simila r remedies as discussed above if SIPs are deficient. June 2016 CAA section 110(c) deadline by which EPA must issue a final FIP for any area whose section 110(a)(1) SI P is disapproved in June 2014. February 2017 CAA section 110(c) deadline by which EPA must issue a FIP for a nonattainment area whose section 192 SIP is disapproved in February 2015. August 2017 If designations are effective in August 2012, CAA section 192 would require nonattainment areas to attain the 1-hour SO 2 NAAQS as expeditiously as practicable, but no later than August 2017. Depending on installation dates and impact of other regulations on SO 2 , as discussed below, many areas will likely at tain earlier than August 2017. EPA expects unclassifiable areas to attain on a similar schedule as nonattainment areas.

IV. Section 110(a)(1) and (2) NAAQS main tenance/infrastruc ture elements CAA section 110(a)(1) specifies th at states are to develop plans to implement, maintain,

and enforce the new SO 2 NAAQS. For areas designated nonatta inment, states will follow the more common and familiar attainment planning a nd emissions control requirements of CAA part D, section 172 and 191-192. For all other areas, st ates are expected to follow the more general requirements of CAA section 110(a). In the context of the 1-hour SO 2 NAAQS, EPA believes this means states are expected to develop and su bmit SIPs showing that all areas of the state will

attain and maintain the 1-hour SO 2 NAAQS. This should be accomplished by evaluating whether significant sources of SO 2 emissions, either individually or in combination with other nearby sources, cause or contribute to violations of the 1-hour SO 2 NAAQS. Where sources of

SO 2 are determined to cause or contribute to NAAQS violations, states s hould include in thePublic Review Draft 9/22/2011

9 110(a)(1) SIPs sufficient permanent and enforcea ble control measures to ensure the NAAQS is

attained and maintained as e xpeditiously as practicable.

For the short-term 1-hour SO 2 standard, EPA believes it is mo re accurate and efficient to use modeling to assess medium to larger source s and to rely on monitori ng for groups of smaller sources and sources that may not be as conducive to modeling. We expect that states would focus performance of attainment demonstrati on modeling on areas with larger sources (e.g., those sources emitting over 100 tons per year (tpy) of SO 2 ), and any other sources that we anticipate to cause or contribu te to a violation to determine compliance with the new SO 2 NAAQS 7

. Almost all SO 2 in the United States is emitted by stationary sources. EPA has promulgated requirements for low sulfur motor fu els that have substant ially reduced on-road

vehicle contributions to ambient SO 2 concentrations, such that on-road contributions may generally be addressed merely as part of th e unmodeled background concentrations included in modeling analyses. Further restrictions will reduce other mobile source emissions (such as from ships and locomotives) in the next few years. Thus, only in exceptional cases would modeling of mobile source emissions be necessary. A. Section 110(a)(1)-(2) SIP submission The CAA establishes a 3-year deadline afte r revision of a NAAQS for states to submit SIPs under sections 110(a)(1) and (2) to EPA. Additionally, nonattainment area SIPs are due

within 18 months from the effective date of th e designation, under secti on 191 of the CAA. EPA anticipates that designations should be issued by June 2012 and take effect by August 2012.

7 In cases where large sources of SO 2 emissions are located on the borders of other states, EPA suggests that these states coordinate with each other during the development of the SIP submittals for the affected areas.Public Review Draft 9/22/2011

10 Therefore, the nonattainment area SIP submission deadline is anticipated to be by no later than February 2014. Section 192 requires nonattainment areas to achieve the 1-hour SO 2 NAAQS as expeditiously as practicable, but no later than 5 years after designation, which EPA expects to be by no later than August 2017. Section 110(a)(1), unlike section 192, does not specify a deadline by which states are required to show when th ey have met the requirements to implement, maintain, and enforce a NAAQS. However, EP A believes it is generally reasonable for

attainment to be achievable in unclassifiable area s within the same five year timeframe as is mandated for nonattainment areas. In many cases , federally promulgated regulations, including the CSAPR for the eastern United States, and nationally applicable regulations mandating

maximum achievable control tec hnology (MACT), may result in at tainment sooner than the five year timeframe. These regulations are expe cted to reduce emissions from certain source categories emitting large amounts of SO 2, such as Electric Genera ting Units (EGUs), industrial boilers, and solid waste incinerators.

In order to demonstrate attainment and maintena nce, SIPs for unclassifiable areas, just as for nonattainment areas, should include enforc eable emissions limitations, timetables for compliance, appropriate testing/reporting to assu re compliance, and incl ude air quality modeling

for SO 2 sources showing that the SIP- adopted emissions limits are cons istent with attainment of the 1-hour NAAQS. EPA believes it is reasonabl e to expect states to demonstrate, at a minimum, that major SO 2 sources ( ≥ 100 tpy) are not causing or cont ributing to violations of the

1-hour SO 2 NAAQS. Several recently promulgated and forthcom ing national and regional rules will likely result in significant reductions in SO 2 emissions over the next several years. A limitedPublic Review Draft 9/22/2011

11 qualitative assessment based on the results of pre liminary modeling of sample facilities indicates

that effective SO 2 source control, such as the installation of SO 2 scrubbers, should generally

suffice for areas to meet the 1-hour SO 2 NAAQS (see Brode 2010b). Exceptions could include unique sources with specific characteristics that contribute to higher ambi ent impacts (short stack heights, complex terrain, etc.). These national and regional rules are anticipated to lead to SO 2 reductions that will help achie ve compliance with the new SO 2 NAAQS prior to August 2017. If, upon EPA review of SIP submittals that rely upon those reductions or other local control measures, it appears that states will nevertheless fail to attain or maintain the NAAQS, the CAA provides authorities for EPA to address these situations, incl uding, as appropriate, disapproving SIP submittals, re-designating areas to nonattainmen t, issuing SIP calls, and promulgating FIPs.EPA will make decisions concerning what actions should be taken on SIP submittals on a caseby-case basis. EPA will also continue to work wi th states during the SIP development process in

order to address SIP deficiencies and to ensure that SIPs are approve d in a timely manner. EPA expects that most areas of the country wi ll be designated as unclassifiable for the 1-

hour SO 2 NAAQS

, due to a lack of both monitoring and refined modeling data concerning the attainment status of areas, in advance of states conducting further refined modeling at the time of designations. Areas that have both monitoring data and appropriate modeling results showing no violations would be designated as “attainment.” For areas desi gnated as attainment, we expect that section 110(a)(1) SIPs only n eed to ensure any applicable SO 2 emissions limits are permanent and enforceable, and address the “inf rastructure” requirements set forth in section 110(a)(2). In such areas EPA expects that the PSD program required by section 110(a)(2)(C) will regulate future growth and should provide for continued maintenance of the standard.Public Review Draft 9/22/2011

12 B. Section 110(a)(1) SIPs Section 110(a)(1) of the CAA directs each st ate, after reasonable notice and opportunity for public comment, to adopt and submit to EPA, within 3 years after promulgation, a SIP which provides for the implementation, maintenance, an d enforcement of any new or revised NAAQS throughout the state. These plans shoul d ensure timely attainment of the SO 2 NAAQS on a schedule that is as expeditious as would be required if an area had been designated nonattainment (i.e., no later than five years). The section 110(a)(1) SIP should also contain the following elements: (1) an attainment emissions i nventory; (2) a control strategy, as appropriate; (3) a maintenance demonstration using an EP A-approved air quality dispersion model, as appropriate; (4) a contingency plan ; and (5) a plan for verification of continued attainment of the

standard. These elements are discussed in detail below. 1. Attainment emissions inventory The state should develop an accurate attainme nt inventory to identify the level of

emissions in the area sufficient to attain the 1-hour SO 2 NAAQS. This inventory should be consistent with EPA’s most recent guidance on emissions inventories cu rrently available, and should include the emissions for the time peri od associated with the modeling and monitoring data showing attainment. Majo r source size thresholds for SO 2 are currently listed as 100 tpy. However, in cases where sources, individually or collectively, that are below this level may potentially cause or contribute to a violation of the standard, these sources should also be included in the emissions inventory for the affected area. Future SO 2 emissions projections in the attainment emissions inventory can account for modeled controlled maximum allowable emissions levels associated with a sources’ comp liance with enforceable national, regional, or local rules that will occur by the SO 2 NAAQS compliance date.Public Review Draft 9/22/2011

13 2. Maintenance demonstration In general, EPA does not believe that air quality monitoring alone is sufficient to

demonstrate attainment and maintenance with the 1-hour SO 2 NAAQS. EPA does not generally expect that monitoring data alone will fully ch aracterize short-term ambient concentrations around major stationary sources of SO 2, and as a result may not capture the maximum SO 2 impacts. For SO 2, the state could generally demonstrat e attainment and maintenance of the NAAQS by using refined dispersi on modeling (see Appendix W to 40 CFR Part 51) to show that

the current or future mix of sources and enforcea ble emission rates in an identified area will not

lead to a violation of the 1-hour SO 2 NAAQS. In counties that do not have larg e sources, or any sources, of SO 2 , refined modeling specific to those counties may not be needed to show that the county or portions of the county are in attainment of the NAAQS. Appendix C contains guidance for states on making a nonmodeling technical attainment demonstra tion for areas meeting these criteria. a. Refined dispersion modeling With representative and appropriate mete orological and other input data, refined dispersion models are able to characteri ze air quality impacts from the modeled SO 2 sources across the domain of interest on an hourly basis with a high degree of spatial resolution, overcoming the limitations of an approach ba sed solely on monitoring. By simulating plume dispersion on an hourly basis acro ss a grid of receptor locations, dispersion models are able to estimate the detailed spatial gradients of ambient concentrations resulting from SO 2 emission sources across a full range of meteorological and source operating conditions. To capture such results on a monitor would normally require a prohibitively expensive air quality monitoring network. Further, as we have observed in prior acti ons (see., e.g., 43 FR 45993, 45997, 46000-Public Review Draft 9/22/2011

14 03 (October 5, 1978)), monitoring data would not be adequate to demonstrate attainment if sources are using stacks with he ights that are greater than good engineering practice (GEP), or other prohibited dispersion techni ques, since in those cases mon itoring would implicitly reflect credit for such practices in c ontravention of section 123 of th e CAA and our regulations at 40

CFR sections 51.100 and 51.118. Refined dispersion modeling for the sec tion 110(a)(1) SIP should follow EPA’s Guideline on Air Quality Models , Appendix W to 40 CFR Part 51, which provides recommendations on modeling techniques and guid ance for estimating pollutant concentrations

in order to assess control strate gies and determine emission limits. These recommendations were originally published in April 1978 and were incorporated by refere nce in the PSD regulations at

40 CFR sections 51.166 and 52.21 in June 1978 (43 FR 26382-26388). The purpose of Appendix W is to promote consistency in the use of modeling within the air quality management process. Appendix W is periodically revised to ensure that new model developments or expanded regulatory requirements are incorporat ed. The most recent revision to Appendix W was published on November 9, 2005 (70 FR 68218), wherein EPA adopted the American Meteorological Society (AMS) and Environmenta l Protection Agency (EPA) Regulatory Model ( AERMOD) as the preferred dispersion model for a wide range of regulatory applications in all types of terrain. To support the promulgati on of AERMOD as the preferred model, EPA evaluated the performance of the model across a total of 17 field study data bases (Perry, et al., 2005; EPA, 2003), including severa l field studies based on mode l-to-monitor comparisons of

SO 2 concentrations from operating power plants. AERMOD is a steady-state plume dispersion model that employs hourly sequentia l preprocessed meteorological da ta to simulate transport and dispersion from multiple point, ar ea, or volume sources for aver aging times from one hour toPublic Review Draft 9/22/2011

15 multiple years, based on an advanced characte rization of the atmospheric boundary layer. AERMOD also accounts for building wake e ffects (i.e., downwash) on plume dispersion. Appendix A contains modeling guidance supplem ental to that provided in the preamble to the final rulemaking promulgating the 1-hour SO 2 NAAQS. It clarifies our recommendations on how to conduct refined dispersion modeling under Appendix W to support the implementation of the new 1-hour SO 2 NAAQS. Although AERMOD is identified as the preferred model under Appendix W for a wide range of applications and would be appropriate for most modeling applicatio ns to support the 1-hour SO 2 NAAQS, Appendix W allows flexibility to consider the use of alternative models on a case-by-case basis when an adequate

demonstration can be made that the alternat ive model performs better than, or is more appropriate than, the preferred m odel for a particular application.

b. Source emissions threshold levels for the maintenance demonstrations In most cases, we expect that the cl earest way to determine whether an SO 2 source has the potential to emit (PTE) at levels that could cause or contribute to a violation of the 1-hour

SO 2 NAAQS would be to conduct refined air qua lity dispersion modeling for the source in question in combination with any nearby sour ces. Based on data in EPA's 2008 National Emissions Inventory (NEI), there are over 33,000 SO 2 point sources in the United States. It is unlikely that every one of these sources has the po tential to emit at levels that would violate or

contribute to violati ons of the 1-hour SO 2 NAAQS. Several factors other than a source’s emissions help determine its impact on ground level SO 2 concentrations. These factors include the influence of stack parameters (stack height, stack exit temper ature, stack exit velocity, stack diameter), complex terrain (i.e., where receptor el evation is above the source elevation), building downwash, proximity of stacks to ambient air, as well as the urban or rura l classification of thePublic Review Draft 9/22/2011

16 area around the source. The discussion that follo ws suggests some ways in which states and sources might consider managing the overall burden of assessing whether SO 2 source emissions will adversely impact public health. EPA recognizes the resource burden potentially involved in conducti ng refined air quality modeling for every source of SO 2 emissions. As one example, states might focus their limited modeling resources on the largest sources of SO 2 , such as those sources that are emitting at least 100 tpy, in recognition that these sources emit nearly all the emissions of SO 2 (just over 99% of

all SO 2 emissions in 2005 from point sources in the country). States might also focus on those sources located in areas where there is the highe st potential for citizen exposure to elevated

ambient SO 2 levels. Therefore, EPA is seeking co mments and recommendations on reasonable approaches to determining which sources should be modeled. EPA examined the 2005 NEI for purposes of judging how much of the inventory would be categorized as higher versus lo wer priority in such an appro ach. This inventory is based on actual emissions, which may not accurately reflec t the distribution of sources on an allowable emissions basis, but EPA used this inventory because a comparable data base of allowable

emissions is not available. The 2005 NEI identif ies over 33,000 sources in the United States that

emit SO 2 . Of these sources, about 1928 sources are estimated to have actual emissions above 100 tpy. Furthermore, as noted above, the la rger sources emit a preponderance of the SO 2 emissions. Accordingly, we expect these sources also represent a substantial share of the areas with potential to violate the SO 2 NAAQS. Thus, EPA believes that focusing limited resources on sources with emissions in excess of 100 tpy can address the areas of greatest concern with only a fraction of the workload that would be needed to address all sources that emit SO 2 .Public Review Draft 9/22/2011

17 Given the influence of stack parameters and ot her factors on the concen trations that result from a given quantity of emissions, EPA recognizes that an approach that only considers sources emitting more than a specified emissions threshold may in some cases overlook sources that have lower emissions but nevertheless have the potenti al to cause or contribute substantially to violations of the standard. EPA also recogni zes that EPA and the states have substantial experience with modeling SO 2 concentrations, and so EPA a nd the states have substantial experience in judging the kinds of circumstances that might be expected to have relatively high

SO 2 concentrations. This suggests the possibili ty of hybrid approaches in which the state addresses all sources emitting more than a given th reshold, and in addition addresses sources that by reasonable judgment might be expect ed to contribute to ambient SO 2 concentrations above the NAAQS. An example of this approach woul d be for a state to model all sources with emissions of at least 100 tpy as well as all smalle r sources that are judged to be in circumstances that might create high ambient SO 2 concentrations, such as low stack heights, building downwash, complex terrain, or clustering of multiple sources. States may wish to also place priority on conducting additional analyses in ar eas where significant population exposure to

elevated ambient SO 2 may be occurring. An approvable CAA section 110(a)(1) SIP woul d need to appropriately and accurately assess the degree that sources thr oughout the state cause or contri bute to violations of the SO 2 NAAQS, but it might not be necessary for states to address all sources of SO 2 in an area in order

to demonstrate attainment and maintenance of the NAAQS. However, any source that is modeled at less than its PTE for purposes of de monstrating attainment of the standard should receive a SIP enforceable emission or operating pe rmit limit that is consistent with the modeled levels. These decisions, of course, should be made by the state on a case-by-case basis dependingPublic Review Draft 9/22/2011

18 on the attainment needs of the a ffected area(s). We are seeki ng input on approaches such as those discussed above for states to identify appr opriate threshold levels, as well as any other emissions-related parameters, or guiding principles , that may help states and EPA better focus on

the sources of SO 2 most likely to cause or contribute to a violation of the new 1-hour SO 2 NAAQS and impact the most populated areas. For example, we welcome any supportable information on the configurations and operating characteris tics for typical SO 2 sources that might be most likely to cause a violation (e.g., uncont rolled coal-fired power plants greater than 250MW with stack height less than 50 feet). Conversely, we woul d also appreciate supportable information on the configurations and operating characteristics for SO 2 sources that are not likely

to cause a violation. 3. Control strategy The SIP should reasonably attribute the expect ed improvement in the air quality for the

affected area to SO 2 emission reductions resulting from controls that are permanent and

enforceable. 8 If no emissions reductions are needed to ensure attainment and maintenance of the

1-hour SO 2 NAAQS, the SIP should indicate the mechanisms that the state will use to ensure the

area remains in attainment. Attainment result ing from temporary reductions in emission rates (i.e., reduced production or shutdown due to temporary adverse economic conditions) or unusually favorable meteorological conditions would not qualify as an air quality improvement due to permanent and enforceable emissions reductions. In making the showing that the improvement in air quality (or already accepta ble air quality) is due to permanent and

8 This is consistent with EPA’s exis ting policy on redesignations as stated in a memorandum titled “Section 107 designations policy Summary.” (April 21, 1983). This memo randum indicates that in order for an area to be redesignated to attainment, the state should show that “actua l enforceable emission reductions are responsible for the recent air quality improvement.” We expect to apply the principles of this guidance to the section 110(a)(1) SIP submittals.Public Review Draft 9/22/2011

19 enforceable measures, the state should estimate the percent emission reductions achieved from national, regional, and local control measures. The EPA expects that in orde r to meet the implementation, maintenance and enforcement plan goals of section 110(a)(1) for the 1-hour SO 2 NAAQS, states should consider all control measures that are reasonable to implement in lig ht of the attainment and maintenance needs for the affected area(s). Where additional controls ar e necessary to attain it would be appropriate for

the level of controls in these areas to be similar to that required in areas that are designated as nonattainment, to provide fo r the attainment and maintenance of the 1-hour SO 2 NAAQS as expeditiously as practicable. EPA expects that expeditious attainment in these areas will in many cases occur when national and regional control measures are implemented, and will be within 5 years of the effective date of designation of an area. This approach would allow states

to take into consideration emission reductions that we expect to be achieved from the implementation of future controls from nationa l and regional control measures well before 2017, as well as any needed local control measures. It would also help to reduce the risk of such areas failing to meet the NAAQS as expeditiously as n onattainment areas are e xpected to meet the

standard

.

a. National measures under development th at are expected to help reduce SO 2 emissions Several recent and upcoming EPA regulations have the potential to significantly reduce

SO 2 emissions in the United States. The first of these regulations is the CSAPR which contains federally-imposed restrictions on SO 2 and NOx emissions from el ectricity generation units (EGUs) in 28 states in the eastern Un ited States (76 FR 48208, August 8, 2011). This rule does not specify plant-specific emissi on limits. Instead, this rule es tablishes caps on total emissions

from the set of affected facili ties in each state, and provide s for issuance of a number ofPublic Review Draft 9/22/2011

20 emissions allowances in each state corresponding to the applicable caps. It allows trading of allowances, so that each source may have more or less emissions so long as the source emits no

more than the number of allowances it holds e ither through issuance or through purchase. Thus, the rule does not require that a specific degree of emissions control will be achieved at any particular facility. Nevertheless, the emission caps are such that the rule w ill result in substantial

additional control of SO 2 and NOx emissions. This control is mandated by 2012 and 2014 (representing start dates for two stages of caps under CSAPR) , which is well within expected

attainment timeframes for the 1-hour SO 2 NAAQS. EPA expects th ese controls generally to suffice for achieving attainment. Therefore, for su ch facilities, negotiati on and establishment of suitable emission limits will be far simpler than would be the case if the state and the company had to negotiate whether control equipment was n ecessary. Furthermore, the state has the option to negotiate with its sources to pursue a distribution of controls under CSAPR that optimizes the

achievement of attainment of the SO 2 standard. For example, the state has the option under

CSAPR to revise the allocation of allowances to mirror the distribution of emissions that best serves the purpose of attaining the SO 2 standard 9

. A second regulation that EPA is preparing would mandate maximum achievable control technology (MACT) at EGUs and is known as the Mercury and Air Toxics Standards (MATS). This regulation will be designed to address haza rdous air pollutants (HAP) pursuant to section

112 of the CAA. HAPs listed under section 112 (b) that are emitted by EGUs include mercury, hydrochloric acid (HCl), hydrogen fluoride (HF), dioxin, and various metals. SO 2 is a criteria

9 In general, cap and trade programs require emission reductions from among a set of sources but do not require controls at particular sources. SO 2 concentrations are generally sensitive to emissions from individual nearby plants and less sensitive to region-wide restrictions common to trad ing programs. Therefore, to demonstrate attainment, it may be necessary to establish plant-specific SO 2 limits irrespective of any emission reductions that the facility may be implementing to address trading program requirements. For such demonstrations the allowable emissions should reflect the specific limits given in an enforceable document (e.g. a rule or permit).Public Review Draft 9/22/2011

21 pollutant and is not a HAP listed under CAA secti on 112(b). Nevertheless, for facilities that comply with this regulation by installing exhaus t gas scrubbing equipmen t in order to control HCl and acid gas emissions, EPA expects such a dd-on controls to also reduce emissions of SO 2 substantially. EPA proposed this rule on May 3, 2011 (76 FR 24976). EPA is on a court ordered time line to finalize this rule by November 2011. EPA anticipates th at the implementation of this rule will be completed no later than February of 2015. A third regulation, published on March 21, 2011 (76 FR 15608), is known as the

Industrial Boilers MACT. This ru le establishes limits for merc ury, dioxin, HCl, and assorted

metals for industrial boilers. This rule does not establish limits on emissions of the non-HAP

SO 2 , but EPA expects this rule to result in wi despread installation of exhaust gas scrubbing equipment that would reduce SO 2 emissions substantially. EPA has published a notice deferring compliance dates under this rule, and the rule is undergoing further review by EPA, but the following discussion of the possible impact of the Industrial Boilers MACT reflects impacts that could result from the rule as published on March 21, 2011.

b. SO 2 limits for sources using control measures to meet the Cross-state Air Pollution Rule and MACT rules

EPA envisions that control measures that so urces use to comply with requirements of

these federal rules will facilitate atta inment and maintenance of the 1-hour SO 2 NAAQS, but states would need to ensure that the covered sources have, as appropriate, federally-enforceable

1-hour SO 2 emissions limits. As noted above, the CS APR may result in many sources installing add-on controls or using other control measures , but the specific prospective impact of these rules at specific locations is uncertain. For SO 2 controls to be creditable for SO 2 NAAQS planning purposes, they need to apply to the source as enforceable 1-hour SO 2 emission limits on the specific source. The cont rols and associated 1-hour SO 2 emissions limits would need toPublic Review Draft 9/22/2011

22 become permanent and enforceable under the SIP, ev en if they might not be required to be so

under the CSAPR. Unlike the CSAPR, the MACT rules would im pose specific requireme nts, including HAP emissions limitations, for facilities in the s ubject source categories. While MACT standards generally do not specify the type of control measure or technology a source must use to meet an emission standard, they are based upon the HAP emissions performance that is achieved by an average of the best performing sources in the su bject source category. E ach facility that is subject to these rules would be subject to HAP emission limits that in many cases may necessitate installation of control equipment or th e use of other control m easures to substantially

reduce SO 2 emissions. However, as promulgated, the Industrial Boilers MACT does not set specific limits on emissions of SO 2 . Therefore, to rely upon SO 2 reductions resulting from this

rule to assure attainment and maintenance of the 1-hour SO 2 NAAQS, states would need to also

establish 1-hour SO 2 emission limits to assure that any c ontrol measures used to comply with MACT requirements are designed and/or operate d to provide the necessary control of SO 2 emissions as well. If the MATS Rule is promulga ted similarly, i.e., it sets emission limits for HAPs but does not set specific 1-hour SO 2 emission limits, then states would need to set 1-hour

SO 2 emission limits for these facilities as well, to the extent such limits are needed to assure

attainment and maintenance of the 1-hour SO 2 NAAQS.

c. What SO 2 control levels does EPA expect sources will achieve under the CSAPR and the MACT rules? Source-specific factors can si gnificantly influence the SO 2 emissions of facilities subject to the CSAPR and pertinent MACT rules. When a facility opts to comply with the CSAPR by installing SO 2 control equipment, the company ma y choose among various levels of SO 2 control efficiency, taking into account the number of SO 2 allowances it holds or plans to hold. Flue gasPublic Review Draft 9/22/2011

23 desulfurization systems that have been installed under other emissions trading programs, such as the Acid Rain Program and the Clean Air Inte rstate Rule (CAIR), have commonly achieved between 90 and 98 percent control efficiency. Si milarly, controls for HAPs may achieve varying degrees of efficiency. For example, facilities that install flue gas scrubb ing equipment to comply with HCl emission limits in a MACT regulation may have varying fuel chlorine content, leading to varying degrees of control n eeded to meet HCl limits, and may use varying degrees of reagent

for SO 2 removal. Controlled SO 2 emissions are also a function of the fuel sulfur content and various other factors. Dry sorbent inj ection is another control option, achieving SO 2 control efficiencies from 30 to 60 percen t or higher. However, the ac tual post-control emission level that can be achieved at a particul ar facility is a function of severa l site-specific factors. The SIP

to address the 1-hour SO 2 emission limits for specific faciliti es would need to reflect sourcespecific factors influencing control efficiency as well as the attainment and maintenance needs of

the area. 4. Contingency Plan Establishing contingency measures for the 1-hour SO 2 NAAQS may involve different

considerations than for some ot her criteria pollutants. The anal ytical tools for quantifying the relationship between SO 2 reductions and resultin g air quality improvements produce relatively certain results compared to the tools for other pollutants. Also, controls for SO 2 are generally well understood and are far less prone to complian ce rate and control efficiency uncertainty relative to control plans for regional pollutants li ke ozone and fine partic ulate matter, since the latter typically invol ve many control assumptions for many small sources. Since SO 2 control measures are based on what is directly a nd quantifiably necessary to attain the SO 2 NAAQS, we expect that it would be unlikel y for an area to implement the n ecessary and appropriate emissionPublic Review Draft 9/22/2011

24 controls yet fail to atta in and maintain the NAAQS. Thus if a state provides a modeling analysis showing that compliance with specific SO 2 emission limits provides for attainment, if the pertinent source(s) continues to meet the limits, and there are no significant future changes to the area’s inventory of allowable emissions or b ackground concentrations, th ere would generally be no cause for implementing contingency measur es. Therefore, EPA believes it would be appropriate, specifically for SO 2 programs, for states to adopt for contingency measure purposes a comprehensive program to identify sour ces of violations related to the SO 2 NAAQS and to undertake an aggressive follow-up for complia nce and enforcement, including expedited procedures for establishing enforceable consent agreements with affected sources pending the adoption of any needed revised SIP for the area in question. This approach to contingency measures for the SO 2 NAAQS would not, however, preclude a state from requiring additional cont ingency measures that are enforceable and appropriate for a particular so urce or source category. As stat ed previously, a contingency

measure for an SO 2 SIP might be a consent agreement requiring a source to reduce emissions further in the event that certain contingency pr ovisions are triggered. Alternatively, the source might adopt a contingency measure such as switchi ng to low sulfur coal or reducing load until more permanent measures can be put into place to address emissions interfering with maintenance of the NAAQS. In either case, th e contingency measures identified in the SIP should be implemented as expeditiously as pr acticable following the determination that the affected area is failing to atta in or maintain the standard.

5. Verification of continued attainment States should provide an indication of how they will track the progress of the section 110(a)(1) plan. In most cases, tracking complia nce with applicable emission limits, along withPublic Review Draft 9/22/2011

25 tracking whether background concen trations are changing, should su ffice for verifying continued attainment. We expect that a need for more thorough tracking of emissions and air quality would arise mainly in areas with multiple area source s, areas with sources for which emissions are difficult to track, and areas where the success of the attainment plan may be particularly

uncertain. C. Redesignation to attainment for areas designated as unclassifiable The CAA does not clearly specify the condi tions for redesignating an area from

“unclassifiable” to “attainment .” CAA section 107(d)(3)(E) only addresses conditions for redesignating areas from “nonattainment” to “atta inment.” Nonetheless, EPA believes that for

the 1-hour SO 2 NAAQS the criteria closely derived from section 107(d)(3)(E) would be appropriate. Accordingly, for an area initially de signated as “unclassifiabl e” to be redesignated as attainment, EPA expects to apply the following criteria to meet the principles of CAA section 107(d)(3): (1) EPA has determined that the area is attaining the NAAQS; (2) the area has a fully approved section 110(a)(1) SIP; (3 ) EPA has determined that the at tainment-level air quality in

the affected area is attributable to any necessary permanent and enforceable emissions measures; (4) the area has met all of th e requirements of section 110 of the CAA; and (5) the state has verified implementation of the approved 110( a)(1) SIP control measures. The following subsections provide additional de tails on the anticipated criteria for redesignation to attainment.

a. Attainment of the NAAQS EPA would consider redesignating areas from unclassifiable to attainment if all relevant

information indicates that the area is attaining the 1-hour SO 2 NAAQS. There are two components involved in making this demonstration th at should be consider ed interdependently. The first component is monitoring data, in situations where there is one or more SO 2 air qualityPublic Review Draft 9/22/2011

26 monitors located within the affected area. Moni toring data indicate attainment of the NAAQS if the 3-year average of the annual 99 th percentile of 1-hour daily maximum concentrations does not exceed 75 ppb. The second component is mode ling data. Since modeling is generally an essential means of addressing whether existing em issions limits suffice to provide for attainment at all ambient locations around sources, states may in most cases address this component by attesting that the relevant sources of SO 2 in the area are in compliance with limits that have been shown by suitable modeling to provide for attain ment. The justification for redesignation from

unclassifiable to attainment w ould need to include modeling information except where modeling is shown to be inappropriate (if, for example, sources are poorly characterized) or unnecessary (if an unclassifiable area is found to have only de minimis emissions). In most cases, EPA expects the modeling submitted as a part of the attainment demonstration for the plan would suffice to address this requirement.

b. Approved 110(a)(1) SIP meeting the require ments of section 110(k) of the CAA The 110(a)(1) SIP for the area should be fully approved under section 110(k) of the CAA and satisfy all of the requirements that apply to the affected area. An area could not be redesignated to attainment if a required element of the plan is the subject of a disapproval action, a finding of failure to submit or to implement the SIP, a partial approval, a conditional approval, or a limited approval.

c. Attainment-level air quality for the aff ected area must be attributable to permanent and enforceable measures The state should be able to reasonably demonstrate that attainment-level air quality is attributable to SIP-enforced emissions limits, wher e necessary. In making this showing, the state should provide reliable estimates of the percent reduction in SO 2 emissions from national, regional, and local measures that have been implemented in the affected area.Public Review Draft 9/22/2011

27 d. The area meets all of the require ments of section 110 of the CAA For the purposes of redesignation, a state shoul d meet all of the requirements of section 110 of the CAA prior to the submittal of the rede signation request. This would include meeting all of the requirements under sec tion 110(a)(2) addressing the genera l infrastructure requirements necessary to provide for the implementation of the 1-hour SO 2 NAAQS.

e. Verification of attainment The state would need to verify implementati on of all control measures identified in the approved 110(a)(1) SIP, that all affected sources are in compliance with the control measures, and that any emissions reductions projected in the approved plan for the affected area have been

realized.

V. SO 2 nonattainment area planning elements

A. SO 2 SIP planning Any state containing an area desi gnated as nonattainment for the SO 2 NAAQS is directed by the CAA to develop and submit to EPA a SIP m eeting the requirements of subpart 5, of part D, of Title I of the CAA, providing for attainment by the applicable statutory attainment date. CAA sections 191(a) and 192(a). As indicated in section 191(a), all components of the SO 2 part D SIP are to be submitted within 18 months of the effective date of an area’s designation as

nonattainment.

Section 172 of the CAA addre sses the general requirement s for areas designated as nonattainment. Section 172(c) directs states w ith nonattainment areas to submit a SIP that contains an attainment demonstration showing th at the affected area will attain the standard by the applicable statutory attainme nt date. To be approved, the SIP would need to show that the area will attain the standard as expeditiously as practicable, and “provide for the implementationPublic Review Draft 9/22/2011

28 of all reasonably available control measures [R ACM] as expeditiously as practicable (including such reductions in emissions from existing sour ces in the area as may be obtained through the adoption, at a minimum, of reasonably availabl e control technology [RACT]).” (CAA section 172(c)(1)). SIPs submitted under part D of the CAA also need to provide for reasonable further progress (RFP). (CAA section 172(c )(2)). Given the fact that SO 2 concentrations are often dominated by emissions from a limited number of sources, and emissions controls often yield swift and dramatic air quality improvement, EPA expects to continue its historic policy of treating as RFP for SO 2 “adherence to an ambitious compliance schedule.” (74 FR 13547, in the General Preamble published on April 16, 1992). As a general matter, nonattainment area SI Ps would need to include contingency measures that would be implemented in the event th at an area fails to meet RFP or fails to attain the standards by its attainment date. (CAA s ection 172(c)(9)). These contingency measures should be fully adopted rules or control measures that take effect wit hout further action by the

state or the Administrator. Ho wever, given the relative cert ainty of attainment of the SO 2 NAAQS when sources are complying with emissi on limits found to provide for attainment, EPA expects to continue to a ddress the requirement for SO 2 contingency measures as meaning “that the state agency [or other applicable authority] has a comprehensive program to identify sources

of violations of the SO 2 NAAQS and to undertake an aggres sive follow-up for compliance and enforcement, including expedited procedures fo r establishing enforceable consent agreements pending the adoption of revised SI Ps.” (57 FR 13547, April 16, 1992).

Emission inventories are also critical for the e fforts of state, local, and federal agencies to attain and maintain the NAAQS. Section 191(a) in conjunction w ith section 172(c) directs areasPublic Review Draft 9/22/2011

29 designated as nonattainment for SO 2 to submit an emission inventory to EPA no later than 18 months after designation as nonatt ainment. Sections 191(a) and 172(c) also direct states to submit such periodic emission inventories for SO 2 nonattainment areas as EPA may determine necessary to assure compliance w ith part D, of title I of the CAA. Where so determined, EPA may direct that the periodic i nventory include emissions of SO 2 for point, nonpoint, mobile, and

area sources. B. New source review Part D of title I of the CAA prescribes th e procedures and conditions under which a new major stationary source or major modification ma y obtain permits to construct or modify in an area designated nonattainment for any criteria pollutant. States that already have a nonattainment area new source review (NA NSR) permitting program for SO 2 nonattainment areas may be able to use the existing program to authorize the construction and modification of major stationary sources of SO 2 . Because there are very few existing SO 2 nonattainment areas, many states may not have NA NSR rules that apply to SO 2 . Such rules would need to be developed specifically for any nonattainment for the new 1-hour SO 2 NAAQS. The NA NSR permitting requirements in section 172(c)(5) and 173 of the CAA are among “the requirements of this part” to be submitted to EPA as part of a revised SIP for a nonattainment area within 18 months of the effective date of a designation or redesignation to nonattainment. Until such time that EPA approves a state’s revised SI P containing a NA NSR program for SO 2 , on and after the effective date of a nonattainment designation for the new 1-hour SO 2 NAAQS, states may rely on the nonattainment area permitting requirement s under 40 CFR part 51 appendix S to govern review and approval of permits fo r major stationary sources of SO 2 .Public Review Draft 9/22/2011

30 In general, the NA NSR program is to ensure that the construction and modification of major stationary sources of SO 2 will not interfere with RFP toward the attainment of the new

1-hour SO 2 NAAQS. More specifically, the statutor y NA NSR requirements include but are not

limited to:

 The installation of Lowest Achievable Em issions Rate (LAER) control technology;

 The acquisition of emissions reductions to offset new emissions of nonattainment pollutant(s);

 Certification that all major sources owned a nd operated in the state by the same owner are in compliance with all applicab le requirements under the CAA;

 A demonstration via an alternat ives and siting analysis that the benefits of a proposed source significantly outweigh the environmental and social cost s imposed as a result of its location, construction, or modification; and

 An opportunity for public comment on the proposed permit. The NA NSR requirements apply on a pollutant -specific basis with respect to each nonattainment pollutant emitted by a source in amount s greater than the app licable major source threshold for the pollutant. (40 CFR 51.165(a)(1 )(iv)). In areas th at are designated as

nonattainment for the 1-hour SO 2 NAAQS, the major source threshold is 100 tpy of SO 2 . Similarly, NA NSR requirements apply to major m odifications of such a source that result in a significant net emissions increase of the nonatt ainment pollutant. EPA’s NA NSR requirements at 40 CFR 51.165(a) currently define as “significant” a net emissi ons increase of at least 40 tpy

SO 2 (the significant emissions rate or SER for SO 2 ).Public Review Draft 9/22/2011

31 C. Conformity Section 176(c) of the CAA requires that all federal actions conform to an applicable implementation plan developed pursuant to secti on 110 and part D of the CAA. The EPA rules at 40 CFR part 93 developed under the authority of section 176(c) prescribe the criteria and procedures for demonstrating and assuring conformity of federal actions to a SIP. Each federal agency must determine that any actions covered by the general conformity rule conform to the applicable SIP before the action is taken. The criteria and pro cedures for conformity apply only

in nonattainment areas and those nonattainment areas redesignated to attainment since 1990 (“maintenance areas”) with respect to the criteria pollutants under the CAA 10 . The general conformity rules apply one year following the e ffective date of designations for any new or revised NAAQS. The general conformity determ ination examines the impacts of direct and

indirect emissions related to federal actions. The general conformity rule provides several options to satisfy air quality criteria, such as m odeling or offsets, and requires the federal action to also meet any applicable SIP requirements a nd emissions milestones. The general conformity rule also requires that notices of draft and fi nal general conformity determinations be provided directly to air quality regulatory agencies and to the public by publicati on in a local newspaper. Transportation conformity is required under CAA section 176(c) to ensure that federally supported highway and transit projec t activities are consistent with (“conform to”) the purpose of the SIP. Transportation conformity applies to areas that are designated nonattainment, and those areas redesignated to attainment after 1990 (“ma intenance areas” with plans developed under CAA section 175A) for transportation-related criter ia pollutants. Due to the relatively small amounts of sulfur in gasoline and on-road diesel fuel, transportati on conformity does not apply to

the SO 2 NAAQS. (40 CFR 93.102(b)(1)).

10 Criteria pollutants are those pollutants for which EPA ha s established a NAAQS under section 109 of the CAA.Public Review Draft 9/22/2011

32 VI. Transition from the existing SO 2 NAAQS to a revised SO 2 NAAQS In implementing the new 1-hour SO 2 NAAQS, states will need to insure that the health protection provided under the prior SO 2 NAAQS continues to be achieved as well as maintained.

This means that states should continue im plementing attainment and maintenance SIPs associated with the prior 24-hour and annual primary SO 2 NAAQS until such time as they are subsumed by any new EPA-approved SIPs refl ecting planning and control requirements associated with the new NAAQS. CAA section 110(l) provides that EPA may not approve a SIP revisi on if it interferes with any applicable requirement concerning at tainment and RFP, or any other applicable requirement under the CAA. In addition, section 193 of the CAA prohibits the modification of a control, or a control re quirement, in effect or required to be adopted as of November 15, 1990 (i.e., prior to the promulgati on of the Clean Air Act Amendments of 1990), unless such a modification would ensure equivalent or greater emissions reductions.

In the final SO 2 NAAQS, EPA provided that the pr ior 24-hour and annual primary SO 2 NAAQS will remain in effect for one year follo wing the effective date of the initial area designations under section 107(d)(1) for the new SO 2 NAAQS before being revoked in most attainment areas. (40 CFR 50.4(e)). Any ex isting SIP provisions under CAA sections 110, 191

and 192 associated with the annual and 24-hour SO 2 NAAQS would need to remain in effect,

even after the 24-hour and annual primary SO 2 NAAQS are no longer in effect, including all currently implemented planning and emissions c ontrol obligations. This includes both those in the state’s SIP and those that have been promulgated by EPA in FIPs. This will ensure that both the new nonattainment NSR requirements and the ge neral conformity requirements for a revised standard are in place so that there will be no gap in the public health protections provided byPublic Review Draft 9/22/2011

33 these two programs. It will also ensure that all nonattainment areas under the annual and/or 24- hour NAAQS and all areas for which SIP calls have been issued will continue to be protected by currently required control measures. EPA also provided that the annual and 24- hour NAAQS remain in place for any current nonattainment area, or any area for which a state ha s not fulfilled the requirements of a SIP call, until the affected area submits, and EPA approves, a SIP with an attainment, implementation, maintenance and enforcement SIP which fully addresses the attainment and maintenance requirements of the new SO 2 NAAQS. (40 CFR 50.4(e)). The re gulatory text provides that such a SIP must be submitted and approved pursuant to CAA section 191. This means that the SIP would need to meet part D nonattainme nt planning requirements under the new SO 2 NAAQS, as

described above 11

. It is important to understand that for PSD purposes, even after the time that the annual

and 24-hour SO 2 NAAQS are no longer in e ffect, the annual and 24-hour SO 2 increments contained in the CAA and PSD regulations will rema in in effect. Thus, th e owner or operator of a new or modified source will still be require d to demonstrate compliance with the annual and

24-hour SO 2 increments, even when the corresponding SO 2 NAAQS no longer apply. The

annual and 24-hour increments are established in section 163 of the CAA. Thus, they remain applicable even after EPA has revoked the SO 2 NAAQS for the annual and 24-hour averaging

times. EPA does not believe that it can eliminate the annual and 24-hour SO 2 increments without appropriate legislativ e changes to the statutory SO 2 increments. For example, in 1990,

11 The areas that are currently designate d as nonattainment for the pre-existing SO 2 primary NAAQ S are Hayden, AZ; Armstrong, PA; Laurel, MT; Piti, GU; and Tanguisson , GU. The areas that are designated nonattainment for both the primary and the secondary standards are East Helena, MT, Salt Lake Co, MT, Toole Co, UT, and Warren Co, NJ. ( See http://www.epa.gov/oar/oaqps/greenbk/lnc.html ). The Billings/Laurel, MT area is the only area currently subject to a SIP call.Public Review Draft 9/22/2011

34 Congress amended the CAA to make clear that EPA could substitute PM 10 increments for the statutory PM increments that we re based on the TSP indicator.

VII. Redesignation to attainment for areas designated as nonattainment The latest date by which an area designated as nonattainment is required to attain the SO 2 NAAQS is determined from the effective date of the nonattainment designation for the affected area. As stated previously, assumi ng that designations for the 1-hour SO 2 NAAQS are effective in August 2012, states would submit SIPs for n onattainment areas by no later than February 2014. For areas designated nonattainment for the revised SO 2 NAAQS, approvable SIPs would need to provide for attainment of the NAAQS as expeditiously as practicable, but no later than 5 years from the effective date of the nonattainment designation for the area, or in this case by no later than August 2017. (CAA section 192(a)). The EPA expects to determine, under CAA section 179(c), whether an area has dem onstrated attainment of the new SO 2 NAAQS by evaluating air quality monitoring and modeling data consistent with 40 CFR part 50, Appendix T and 40 CFR part 51, Appendix W. A. Attainment of the NAAQS There are five basic conditions provided unde r section 107(d)(3)(E) of the CAA that a

nonattainment area would need to meet in or der for EPA to redesignate it as attainment:

 EPA determines that the area has met the SO 2 NAAQS;

 EPA has fully approved the SIP for the area;

 EPA determines the improvement in air quality in the affected area is due to permanent and enforceable reductions in emissions;

 EPA has fully approved a maintenance plan m eeting the requirements of section 175A of the CAA for the area; andPublic Review Draft 9/22/2011

35  the state containing the area has met all ap plicable requirement s under section 110 and part D of the CAA.

These conditions are discussed in more detail in the 1994 SO 2 Guideline Document. ( See http://www.epa.gov/ttn/oarpg/t1pgm.html ). B. Consequences of a nonattainment area failing to attain by the statutory attainment date Any SO 2 nonattainment area that fails to attain by its statutory attainment date would become subject to the requirements of sections 1 79(c) and (d) of the CAA. EPA is required to make a finding of attainment or failure to atta in no later than 6 months after the specified attainment date and publish a notice in the Federal Register . If EPA finds the area has failed to attain, the state would then need to submit an im plementation plan revision no later than one year following publication of the Federal Register notice making the determ ination of the area’s

failure to attain. This submission would need to de monstrate that the standard will be attained as expeditiously as practicable, but no later than 5 years from the da te of EPA’s publication of the

notice that the area failed to at tain. In addition, section 179(d)(2 ) provides that the SIP revision is to include any specific additional measures as may be reasonably prescribed by EPA, including “all measures that can be feasibly implemented in th e area in light of technological achievability, costs, and any nonair quality and other air quality-related h ealth and environmental impacts.”Public Review Draft 9/22/2011

A-1 Appendix A Modeling Guidance for Nonattainment Areas and Section 110(a)(1) plans 1. Purpose On June 2, 2010, Administrator Jackson signed a final rulemaking notice that revised the primary SO 2 NAAQS (75 FR 35520, published on June 22, 2010) after review of the existing two primary SO 2 standards, promulgated on April 30, 1971 (36 FR 8187). 12 EPA established the revised primary SO 2 standard at 75 parts per billion (ppb ) which is attained when the 3-year average of the 99 th percentile of 1-hour daily maximum concentrations does not exceed 75 ppb. In the final rule preamble, EPA outlined a possibl e analytic approach to determining compliance with the new NAAQS that would include th e use of both modeling and monitoring. EPA explained that this analytic approach to determining complia nce with the new 1-hour NAAQS could be the technically appropriate and accurate means of assessing peak 1-hour SO 2 concentrations, and would be consistent with historic (past and more recent) implementation practice of using models to determine compliance with the SO 2 NAAQS. This guidance explains the expected applica tion of dispersion mode ls to support the SIP process regarding:

1. The use of modeling in the developm ent of CAA Section 191-192 SIPs for nonattainment areas, and 2. The use of modeling in the developmen t of Section 110(a)(1) and (2) SIPs (commonly referred to as “mainten ance” and “infrastructure” SIPs). While this guidance explains the expected general application of dispersion models, there will be applications of di spersion models unique to specifi c areas, (i.e., there may be areas of the country where it is necessary to model uni que specific sources or types of sources). In such cases, there should be consultation with the state or appropriate reviewing authority with the appropriate Regional Office modeling contact to discuss how best to model a particular source. 2. Guidance on Air Quality Models This guidance is based on a nd is consistent with EPA’s Guideline on Air Quality Models , also published as Appendix W of 40 CFR Part 51. Appendix W is the primary source of information on the regulatory application of ai r quality models for State Implementation Plan (SIP) revisions for existing sources and for New Source Review (NSR) and Prevention of Significant Deterioration (PSD) pr ograms. Air quality modeling in this SIP process would need to employ air quality dispersion models 13 that properly address the source-oriented nature of SO 2 and, thus, should rely upon the principl es and techniques in Appendix W.

12 EPA publicly disseminated a copy of the signed notice on June 3, 2010, and therefore treats June 3, 2010, as the date of the rule’s promulgation, for purposes of the deadlines in CAA section 107(d) and 110(a)(1). 13 Dispersion modeling uses mathematical formulations to characterize the atmospheric processes that disperse a pollutant emitted by a source. Based on emissions and meteorological inputs, a dispersion model can be used to predict concentrations at selected downwind receptor locations.Public Review Draft 9/22/2011

A-2 Appendix W was originally published in Apri l 1978 and was incorporated by reference in the regulations for the Prevention of Significant De terioration of Air Qua lity, Title 40, Code of Federal Regulations (CFR) sections 51.166 and 52.21 in June 1978 [43 FR 26382-26388]. The purpose of Appendix W guidelines is to promote c onsistency in the use of modeling within the air quality management process. These guideline s are periodically revise d to ensure that new model developments or expanded regulat ory requirements are incorporated. Clarifications and interpretations of modeli ng procedures become official EPA guidance through several courses of action: 1) the procedures are published as regulations or guidelines; 2) the procedures are formally transmitted as gui dance to Regional Offi ce managers; 3) the procedures are formally transmitted as guidance to Regional Modeling Contacts as a result of a Regional consensus on technical issues; or 4) th e procedures are a result of decisions by the EPA’s Model Clearinghouse that effectively establish national precedent. Formally located in the Air Quality Modeling Group (AQMG) of EPA’s Office of Air Quality Planning and Standards (OAQPS), the Model Cl earinghouse is the single EPA fo cal point for the review of criteria pollutant modeling techniques for speci fic regulatory applica tions. Model Clearinghouse and related Clarification memora nda involving decisions with re spect to interpretation of modeling guidance are available at the Support Center for Regulatory Atmospheric Modeling (SCRAM) website. 14 Recently issued EPA guidance of relevance fo r consideration in modeling for attainment and maintenance demonstrations includes:

 “Applicability of Appendix W M odeling Guidance for the 1-hour SO 2 NAAQS” August 23, 2010—confirming that Appendix W gui dance is applicable for NSR/PSD permit modeling for the new SO 2 NAAQS (U.S EPA, 2010a).

 “Additional Clarification Regarding Applicat ion of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard” March 1, 2011– provides additional guidance regarding NO 2 permit modeling and also relevant to SO 2 (U. S. EPA, 2011a).

 “Area designations for the 2010 Revised Prim ary Sulfur Dioxide National Ambient Air Quality Standards” March 24, 2011 – provides guidance for designating areas for the purpose of implementing the 2010 revised primary SO 2 NAAQS, including modeling guidance (Attachment 3) (U. S. EPA, 2011b). The guidance listed above, in addition to other relevant s upport documents can be found on the SCRAM website at http://www.epa.gov/ttn/scram/so2_modeling_guidance.htm . This website will be made publicly available at the time of release of this SO 2 implementation guidance document. The following sections will refer to the re levant sections of Appendix W and other existing guidance with summaries as necessary. Please refer to those original guidance

14 The Support Center for Regulatory Atmospheri c Modeling (SCRAM) website is available at: http://www.epa.gov/ttn/scram/

.Public Review Draft 9/22/2011

A-3 documents for full discussion and consult with the appropriate EPA Regional Modeling Contact if questions arise about interpretatio n on modeling techniqu es and procedures 15

. 3. Model selection Preferred air quality models for use in regul atory applications are addressed in Appendix A of EPA's Guideline on Air Quality Models . If a model is to be used for a particular application, the user should follow the guidance on the preferred model for that application. These models may be used without an area specifi c formal demonstration of applicability as long as they are used as indicated in each model summary of Appendix A. Further recommendations for the application of these models to specific source problems are found in subsequent sections of Appendix W. In 2005, EPA promul gated the American Meteorological Society/Environmental Protection Agency Re gulatory Model (AERMOD) as the Agency’s preferred near-field dispersion m odeling for a wide range of regulat ory applications in all types of terrain based on extensive develo pmental and performance evaluation. For SIP development under the 1-hour SO 2 primary NAAQS, AERMOD should be used unless use of an alternative model can be ju stified (Section 3.2, Appe ndix W), such as the Buoyant Line and Point Source Dispersion Model (BLP). As outlined in the August 23, 2010 clarification memo “Applicab ility of Appendix W Modeling Guidance for the 1-hour SO 2 National Ambient Air Quality Standard”, AERMOD is the preferred model for single source modeling to address the 1-hour SO 2 NAAQS as part of the NSR/PSD permit programs (U.S. EPA, 2010a). AERMOD is appropriate fo r the SIP development process because SO 2 concentrations result from dir ect emissions from combustion sour ces so that concentrations are highest relatively close to sour ces and are much lower at greate r distances due to dispersion. Given the source-oriented nature of this polluta nt (see, e.g., 75 FR at 35570), dispersion models are the most appropriate air quality modeling tools to predict the near -field concentrations of this pollutant. The AERMOD modeling system includes se veral components. The regulatory components are:

 AERMOD: the dispersion model (U .S. EPA, 2004a; U.S. EPA, 2011c)

 AERMAP: the terrain processor for AERM OD (U.S. EPA, 2004b, U.S. EPA, 2011d)

 AERMET: the meteorological data processo r for AERMOD (U.S. EPA, 2004c; U.S. EPA, 2011e)

 BPIPPRIME: the building input processor (U.S. EPA, 2004d) and non-regulatory components are:

 AERSURFACE: the surface char acteristics processor for AERMET (U.S. EPA, 2008)

 AERSCREEN: a recently released screeni ng version of AERMOD (U.S. EPA, 2011f)

15 List of Regional Modeling Contacts by EPA Regional Office is available from SCRAM website at: http://www.epa.gov/ttn/scram/guidance_cont_regions.htmPublic Review Draft 9/22/2011

A-4 Before running AERMOD, the user should become familiar with the user’s guides associated with the modeling components listed above and the AERMOD Implementation Guide (AIG) (U.S. EPA, 2009). The AIG lists several reco mmendations for applications of AERMOD which would be applicable for SIP modeling. 4. Modeling Framework Figure 1 presents a flow chart of the SI P modeling framework from identifying sources and emissions inputs to design value calculations. The genera l steps include the following:

1. Gather statewide information about SO 2 sources including source emissions and locations, as well as other pe rtinent source characteristics (e.g., building information for modeling building downwash). While maximum allowable emissions would be used in the refined SIP modeling demonstrat ion, initial information gathering could be focused on actual emissions for larger so urces of 100 tpy or more as an initial screening of sources to possibl y include in refined modeling 16 ; 2. Map selected sources to identify any possi ble geographic clusters of sources within the state. It may also be useful to map monitor locations to identify source clusters around monitors, especially monitored areas that are expected to be designated nonattainment. The mapping of the sources a nd monitors will aid in identification of the appropriate modeling domain for each geographic area to be addressed in the SIP demonstration. The sources to be explicitly modeled within each area should include the larger sources and others that potentially contribute to violations for the state to have the greatest flexibility in determining controls across sources, as necessary, to attain the NAAQS; 3. Beginning with the maximum allowable emissi ons or federally enforceable emission limits, apply control strategies that may be employed from nationally enforceable rules 17 ; 4. Input the initially controlled emissions along with receptors, meteorology, and background concentrations into the disper sion model and calculate design values based on cumulative concentrations (a ll modeled sources and background); 5. If there are no predicted exceedances of the NAAQS from the initial dispersion modeling results, the area ha s demonstrated attainment; 6. If there are predicted exceedances of the NAAQS, additional control strategies would need to be implemented on sources and a ssessed, which may n ecessitate re-running the dispersion model; 7. If additional controls result in no predicted violations of the NAAQS, the area has demonstrated attainment. 8. If there are still predicted violations of the NAAQS, continue to assess additional controls until no predic ted violations occur.

16 Please note that sources may have actua l emissions much lower than their allo wable limits, so it may be prudent to gather information about sources that are lower than 100 tpy of actual emissions.

17 See Section B.3 of the SO 2 SIP guidance document for more information about national rules.Public Review Draft 9/22/2011

A-5 Figure 1. Flowchart of SO 2 Modeling Framework for SIP Demonstration.

The following sections provide details of the SO 2 modeling framework and each element in the modeling analysis for the SIP developm ent effort. Section 5 describes the modeling domain and receptor grid. Section 6 describes th e input emissions and controls, while Section 7 describes meteorological inputs. Section 8 describes the inclus ion of background, and Section 9 describes the calculations of the design values. 5. Modeling domain Selection of the modeling domain is important in terms of how many sources to explicitly model and what kind of receptor network to creat e. Two questions may arise in model domain selection:

1. Where to center the modeling domain?, and 2. How large should the modeling domain be? (i.e., in terms of the number of sources to model and size of the receptor network in order to account for th e areas of impact).Public Review Draft 9/22/2011

A-6 If the nonattainment or unclassifiable area boundaries were determined using the five designations factors or refined dispersion m odeling outlined in the March 24, 2011 designations guidance memo (U.S. EPA, 2011b), the modeling domain should encompass the nonattainment or unclassifiable area and be cente red on the center of the designated area. The designated area should already include the sources thought to cause or contribute to a NAAQS exceedance, if a nonattainment area, or include sources, if any, that are thought to influence an unclassifiable area and be eligible for consideration in application of controls. However, if the nonattainment or unclassifi able area is the presumptive county boundary and no efforts were made in the designations pr ocess to alter the desi gnations area size or boundaries, states will need to consider the two questions above and consider the emission source selection process discusse d in Section 5.1 below. If th e modeling is being performed around a violating monitor, the domain should be centered on the violat ing monitor. If the modeling is being done for an area without a vi olating monitor, the domain should be centered on the dominant source or cluster of sources in an area, that is, th e source or sources expected to contribute the most to SO 2 air quality levels. In both cases , the domain should then extend to include nearby sources that are t hought to cause or contribute to a potential NAAQS violation or unclassifiable area, as explained further below in Section 5.1.

As stated in Section 4 and s hown in Figure 1, the first step of the SIP modeling exercise is to determine the sources to include in the m odeling. The determination of sources to include in modeling is a multi-step process. If modeling is being performed for a violating monitor, the first basic step would be to consider those sources within th e nonattainment area defined in designations or those thought to cau se or contribute to violations within 50 km of the monitor, the nominal distance within in which EPA consider s most steady state Gaussian plume models to be applicable. States will need to consider sources throughout th eir state and determine the areas to focus on that appropri ately account to these SO 2 sources 5.1. Determining sources to model As stated above, the determination of sources to explicitly model for each area is a multistep process:

1. As discussed in Section 4 and Figure 1, the fi rst step in the implementation modeling is to gather statewide information about SO 2 sources and map them along with any nonattainment monitors to identify cluste rs of sources and, thereby, the geographic area(s) of concern. If monito rs are mapped with the sources, clusters of sources can be identified around those monitored areas. It is reasonable to initially focus on the most significant sources of SO 2 emissions, e.g., sources emitting more than 100 tons (maximum allowable) 18 per year. Please note, however, that smaller sources can also cause or contribute to a NAAQS violation (75 FR 35552), es pecially sources with short stacks and/or located in complex terrain (i .e., where receptor elevation is above stack height), or sources with high maximum hourly emissions rates. As a first-tier screen it may be reasonable to use actual emissions in th e screening process. If actual emissions

18 See Section 6.1 for details regarding the use of maximum allowable vs. actual emissions.Public Review Draft 9/22/2011

A-7 are used, it may be necessary to map s ources with actual emissions less than 100 tons/year, bearing in mind that actual emissions may be much less than maximum allowable or federally enforceable permit lim it emissions, which will be the emissions inputs for the implementation modeling. States should use best professional judgment in determining an emissions threshold for ma pping, or consult the appropriate Regional Office modeling contact. 2. Once the geographic areas of concern has b een identified, the spat ial distribution of sources within either the nona ttainment area or 50 km of the violating monitor or dominant source should be spatially analyzed to determine what source(s) will need to be explicitly modeled. Again, it is reasonabl e to initially focus on the most significant sources of SO 2 emissions, e.g., sources emitting greater than 100 tons (maximum allowable) per year. While the analysis be gins with a nonattainme nt area or initially assumes an area within 50 km of a violati ng monitor or dominant source, it may not be necessary to explicitly model all sources with in these initial areas of consideration based on steps 3 and 4 below. 3. Sources should be examined and every effort made to determine if any sources can be accounted for without explicitly modeling them, i.e., use of monitored background concentrations (if available). Accounti ng for such sources through the use of a background monitor will depend upon whether that monitor reflects impacts from those sources. 4. Sources found not to be represented by mon itored background may also be examined through the use of screening models to see if they should or should not be included in the refined modeling. We recommend th e use of EPA’s new screening model AERSCREEN (U.S. EPA, 2011f, U. S. EP A, 2011g) and following recommendations based on pre-existing screening guidance (U.S. EPA, 1992). For small isolated sources, screening may be useful on a source by source basis. However, for a cluster of small sources, their cumulative impact should also be assessed. Individual sources may not be significant by themselves, but in clusters together they may potentially cause or contribute to a NAAQS violation. Alt hough AERSCREEN does not output a design value concentration based on the 99 th percentile form of the 1-hour SO 2 standard, it does output the overall maximum 1-hour concentrati on which could be used as a conservative estimate for comparison with the NAAQS and EPA’s suggested interim significant impact level (SIL) for the 1-hour SO 2 NAAQS of 3 ppb 19 . If the maximum 1-hour concentration output from AERSCREEN violat es the NAAQS, it does not mean that the source is in nonattainment, but that the source should be evaluated using refined dispersion modeling (See Step 3 below for more details).

Figures 2 and 3 provide a hypothetical exam ple of the screening process by mapping sources to identify possible nonattai nment or unclassifiable areas a nd those sources to explicitly model. Figure 2 shows a partial map of a state wi th sources of 10 tons/year or greater of actual emissions indicated by circles of varying size based on emissions intensity. Also shown in

19 The 3 ppb interim SIL for new 1-hour SO 2 NAAQS was suggested by EPA for st ates to consider using for the PSD program in the August 23, 2010 memorandum “Guidance Concerning the Implementation of the 1-hour SO 2 NAAQS for the Prevention of Significant Deterioration Program”Public Review Draft 9/22/2011

A-8 Figure 2, are violating SO 2 monitors as represented by stars. Based on this figure, an example application of the four step process is described below. Step 1 : In Figure 2, clusters of sources, especia lly around monitors can be seen. Any violating monitor is a nonattainment area with a geographi c area defined in the designations process that constitutes the potential modeling domain. For example, for monitor 1, the modeling domain should encompass the 100+ ton pe r year sources within the desi gnated nonattainment area. The modeling domain for monitor 2 could be the cluste r of 100+ ton emitters in its vicinity, and the same for monitor 3. The cluster of sources nor theast of monitor 3 could be combined into a separate area centered on the large 10,000+ ton em itter. To the southeast of monitor 3, the large 10,000+ ton source may be the center of a potential modeling domain that includes the monitor. Alternatively, the modeling domain could be centere d at monitor 3 and include all large sources in its vicinity. These are just illustrative examples only and the states may have their own criteria for initially creati ng modeling domains.

Figure 2. Example of screening process: Mapp ing of spatial distribution of sources to determine geographic areas of focus for SIP implementation.Public Review Draft 9/22/2011

A-9 Step 2 : Figure 3 shows source emissions rangin g from less than 100 to over 10,000 tons per year within the potential area to be modeled centered around a vi olating monitor (or dominant source(s). There are three 10,000+ ton emitters near the center and two 100 to 1,000 ton emitters west-southwest of the domain center. At this poin t, it could be initially assumed that all facilities greater than 100 tpy should be included in re fined modeling before co mpleting steps 3 and 4 below.

Figure 3. Illustrative example of possible mo deling domain centered on violating monitor (star) with emissions (circles) within 50 km (large circle) and 10 km (inner circle). Note: Other monitors are shown by plus sign and asterisks, while shaded contours represent terrain. Step 3 : Determine whether any source or source s can be accounted for by a representative background monitor. In Figure 3, there are two other monitors in the area, one north and one south-west of the domain center. The south-we stern monitor may be representative of the two sources in that part of the domain so that th ese sources would not be explicitly modeled and instead accounted for through inclusion of ambient data from this monitor. Background concentrations should be calculated following th e guidance in Section 7 of this document. Step 4 : Screening modeling may be used to determine additional sources or combinations of sources to be excluded from refined modeling, es pecially smaller sources whose impacts may bePublic Review Draft 9/22/2011

A-10 largely dependent on their stack parameters (heigh t, exit velocity, etc.). AERSCREEN could be used to exclude such sources through scr eening modeling. AERSCRE EN does not output an SO 2 design value but does output the overall maximum 1-hour con centration for an individual stack. If a facility contains more than one emission point or stack, each stack should be processed in AERSCREEN and the maximum 1-hour concentrations can be added together to represent impacts from the w hole facility after running AERS CREEN. While AERSCREEN can be used with the surface characteristics of the source being screened, given the documented sensitivity of AERMOD to surface characteristics (Brode et al., 2008), it ma y be useful to also model the source in AERSCREEN using the surf ace characteristics of the meteorological site being used in the refined modeling, to ensure that the source is below de minimis impact levels with either set of surface ch aracteristics. When analyzi ng AERSCREEN output, the following general criteria could be followed:

1. If the facility’s maximum 1-hour con centration exceeds 75 ppb, then the source should be included in refine d dispersion modeling. 2. If the facility’s maximum 1-hour con centration is below 75 ppb but above the suggested interim 1-hour signi ficant impact level of 3 ppb or the state’s 1-hour SIL, it should be included in th e refined modeling. 3. If the facility’s maximum 1-hour concentra tion is below the sugge sted interim 1-hour significant impact level or th e state’s 1-hour SIL, that source may not have to be included in refined modeling. However, th e facility should not be excluded on the sole basis of being below the SIL wit hout first looking at surrounding sources and their maximum 1-hour concentrations. Th e case may arise when there are several small sources that singularly are below the SIL but their cumulative impact may lead to concentrations that contribute to violations of the NAAQS. In summary, for the example in Figure 3, the smaller sources of emi ssions to the north of the domain center may be excluded from refined modeling if screening in dicates they are not likely to cause or contribute to potential NAAQS violations. Other larger sources to the west southwest of the monitor may be represente d by background monitors. The largest emitters within 10 km of the violated monitor would be included in refined modeli ng as they are likely contributing to potentia l NAAQS violations. This is just one example of how to dete rmine the modeling domain and sources to explicitly model. In some cas es, an analysis out to 50 km ma y not be needed. Please consult with the appropriate EPA Regional Office modele r if there is uncertainty in deciding which sources to explicitly model, which sources to represent based on background monitoring, and/or which to exclude from refined m odeling based on screening modeling. 5.2. Receptor grid The model receptor grid is unique to the par ticular situation and depends on the size of the modeling domain, the number of modeled sources , and complexity of th e terrain. Receptors should be placed in areas that are considered am bient air (i.e., where the public generally has access) and placed out to a distance such that area s of violation can be detected from the model output to help determine the size of nonattainment areas. Receptor placement should be ofPublic Review Draft 9/22/2011

A-11 sufficient density to provide resolution needed to detect significant gradients in the concentrations with receptors placed closer together near the source to detect local gradients and placed farther apart away from the source. In addition, the user should place receptors at key locations such as around facility fence lines (which define the ambient air boundary for a particular source) or monitor lo cations (for comparison to mon itored concentrations for model evaluation purposes). The receptor network shou ld cover the modeling domain. States may already have existing receptor placement strate gies in place for regulatory dispersion modeling under NSR/PSD permit programs. If this strategy is considered adequate for the implementation modeling, states should continue with their respective receptor placement strategies. If modeling indicates elevated levels of SO 2 (near the standard) near the edge of the receptor grid, consideration should be given to expanding the grid or conducting an additional modeling run centered on the area of concern. As noted above, terrain comp lexity should also be considered when setting up the re ceptor grid. If complex terrain is included in the model calculations, AERMOD requires that receptor elevations be included in the model inputs. In those cases, the AERMAP terrain processor (U.S. EPA, 2004b; U. S EPA, 2011d) should be used to generate the receptor elevations and hill heig hts. The latest version of AERMAP (version 09040 or later) can process either Digitized Elev ation Model (DEM) or National Elevation Data (NED) data files. The AIG recommends the use of NED data since it is more up to date than DEM data, which is no longer upda ted (Section 4.3 of the AIG). 6. Source inputs This section provides guidance on source characterization to develop appropriate inputs for dispersion modeling with the AERMOD modeli ng system. Section 6.1 provides guidance on use of allowable vs. actual emission levels, Sec tion 6.2 discusses control strategies for emissions, Section 6.3 covers guidance on Good Engineerin g Practice (GEP) stack heights, Section 6.4 discusses dispersion techniques, Section 6.5 provides details on s ource configuration and source types, Section 6.6 provides details on urban/rural dete rmination of the sources, and Section 6.7 provides general guidance on source grouping, wh ich may be important for design value calculations.

6.1. Allowable vs. Actual emissions Consistent with past SO 2 modeling guidance (Section 4.5.2 of U.S. EPA (1994)) and regulatory modeling for other programs (Appendix W, Section 8.1), dispersion modeling for the purposes of SIP development should be based on the use of maximum allowable emissions or federally enforceable permit limits. Also consis tent with past and cu rrent guidance, in the absence of allowable emissions or federall y enforceable permit limits, potential to emit emissions (i.e., design capacity) should be used. Because of the short-term nature of the new SO 2 NAAQS, the maximum short term or hourly em ission rate should be input into AERMOD for each modeled hour. As stated in th e August 23, 2010 memo (U. S. EPA, 2010a),

“Since short-term SO 2 standards ( ≤ 24 hours) have been in existence for decades, existing SO 2 emission inventories used to support m odeling for compliance with the 3-hour and 24-hour SO 2 standards should serve as a useful st arting point, and may be adequate inPublic Review Draft 9/22/2011

A-12 many cases for use in assessing co mpliance with the new 1-hour SO 2 standard since issues identified in Table 8-2 of Appendix W related to short-term vs. long-term emission estimates may have already been addressed.” 20 The necessary emissions information for attainment demonstration modeling should be available from existing SO 2 inventories used for permitting or SIP demonstrations. If short-term emissions are not readily available, they ma y be calculated using the methodology shown in Table 8-1 of Appendix W. For the short term NAAQS standards this is a product of the maximum allowable emission limit or federally enforceable emission limit, the operating level and operating factor. Th e operating level is defined in Sect ion 8.1 of Appendix W as the actual or design capacity (whichever is greater) or federally enforcea ble permit condition. Appendix W also recommends modeling at 50% and 75% of capaci ty to determine the load that may cause the highest concentration because ch anges in stack parameters in loads less than 100% of capacity may cause higher ground level concen trations. The operating factor is assumed to be continuous operation 21 . For an example, calculation of s hort term emissions, see the June 28, 2010 memorandum “Applicability of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard” (U. S. EPA, 2010b). Although the example is for NO 2 , the calculation methodology would be the same for SO 2 . Regarding the use of allowable emissions and the modeling of intermittent emissions sources from such sources as emergency ge nerators and startup/shutdown emissions, the inclusion of such emissions fo r the purpose of modeling for SO 2 attainment demonstrations should follow the recommendations in the Ma rch 1, 2011 memo “Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard” (U. S. EPA, 2011a) . As stated in this memo, EPA believes the most appropriate data to use for comp liance demonstrations for the 1-hour NO 2 NAAQS are those based on emissions scenarios that are c ontinuous enough or freque nt enough to contribute significantly to the annual dist ribution of maximum daily 1-hour concentrations. Although the referenced guidance in this memo is for NO 2 permit modeling, the common 1 hour averaging time and form of both the NO 2 and SO 2 standards makes this mode ling guidance applicable to the 1-hour SO 2 NAAQS and, thus, applicable to SO 2 modeling in support of attainment and maintenance demonstrations. For more details, refer to the NO 2 memo. If any questions arise regarding preparation of emissions inputs fo r dispersions modeling including intermittent emissions from sources, then users should c onsult the appropriate EPA Regional Modeling Contact.

6.2. Controls

Once sources have been identified within th e nonattainment or uncla ssifiable area that may cause or contribute to NAAQS violations, the process of iden tifying and modeling the effect of control strategies begins. In some cases, co ntrol of one source may allow an area to be in

20 The August 23, 2010 memo refers to modeling for PSD and Table 8-2 refers to PSD applications. 21 As stated in Table 8-1 of Appendix W, “If an operation does not occur for all hours of the time period of consideration (e.g. 3 or 24 hours) and the source oper ation is constrained by a fe derally enforceable permit condition, an appropriate adjustment to the modeled emission rate may be made. (e.g., if operation is only 8 a.m. to 4 p.m. each day, only these hours w ill be modeled with emissions from the source. Modeled emissions should not be averaged across non-operating time periods.”Public Review Draft 9/22/2011

A-13 attainment, while in other cases, controls could be implemented on several sources to share the control responsibility to demonstrate the area to be in attainment. As stated in Section B.1 of the SIP guidance document, states should develop an accurate attainment inventory to identify the level of emissions in the area su fficient to attain the 1-hour SO 2 NAAQS and be consistent with EPA’s most recent guidance on emissions inventor ies. These emissions are maximum allowable emissions levels that reflect enforceable national, regional, or local rule s that will be in place within the timeframe for demonstrating attain ment of the standard. When modeling with emissions from the emissions inventory, the inpu t emissions should be re flective of implemented control strategies that will allow the area to be in attainment of the NAAQS. The controlled emissions should be tested using Table 8-1 of A ppendix W. See Section B.3 of the SIP guidance document for more information about control strategies. As stated in Section 4 and shown in Figure 1, the initial modeling for the SIP can include the national rules that will be in place by the attain ment date. Therefore, if these initial controls allow for the area to be in attainment by the at tainment date, additional controls may not be necessary. However, if additi onal controls are necessary to achieve attainment, identifying additional sources to control may be necessary (see Figure 1). Often these sources can be determined by analyzing spatial relationships between the sources and receptors whose concentrations exceed the NAAQS. When identifying sources to control, control of a particular source that leaves other sources unchanged will obviously change hourly cumu lative concentrations. This in turn, may change the daily maximum 1-hour concentration for a given receptor and day, and subsequently may alter the annual distribution of daily maximu m 1-hour concentrations and the magnitude of the 4 th highest concentration from the annual distri bution. This would change the cumulative design value which may still be above the NAAQS but now driven by a different source that earlier may not have been identifi ed as a source to control. An alysis of sources to control may need to be extended to percentiles below the 99 th percentile of the annua l distribution of daily maximum 1-hour concentrations. While the cu mulative (all sources) de sign value is based on the multiyear average 99 th percentile (i.e. 4 th highest) of the annual distribution of the daily maximum 1-hour concentrations, lowe r percentiles, such as 98th (8 th highest) , 97th (11 th highest), etc. can exceed the NAAQS level. A modeling anal ysis should include multiyear averages of the daily maximum 1-hour concentrations beginning with the 4 th highest and proceeding downward to 5 th , 6 th , 7 th , etc. highest until the cumu lative impact at all recep tors is below the NAAQS. Since the form of the standard is based on the maximum 1-hour concentration for each day, the analysis should be limited to the daily maxi mum 1-hour concentrations, not for example, 2 nd or 3 rd highest of the 1-hour concentrat ions for a day. Also, the rank, 4 th , 5 th , etc. highest, should be consistent across all averaged years, i.e. the Nt h highest from the distri bution of daily maximum 1-hour concentrations should be chosen for each year, not 4 th highest for one year, and 5 th highest for another year. AERMOD (version 11059 or la ter) has an output opt ion, MAXDCONT, to aid in this type of analysis and is discussed in more detail in Section 8.2. Such an analysis will lead to a more comprehensive identification of sources to possibly control to reach attainment of the NAAQS.Public Review Draft 9/22/2011

A-14 6.3. Good Engineering Practice (GEP) stack height Consistent with previous SO 2 modeling guidance (U.S. EPA, 1994) and Section 6.2.2 of Appendix W, for stacks with heights that are w ithin the limits of Good Engineering Practice (GEP), actual heights should be used in m odeling. Under EPA’s regulations at 40 CFR 51.100, GEP height, H g , is determined to be the greater of:

 65 m, measured from the ground-level el evation at the base of the stack;

 For stacks in existence on January 12, 1979, and for which the owner or operator had obtained all applicable permits or approva ls required under 40 CFR Parts 51 and 52 H g =2.5H provided the owner or operator produces evidence that this equation was actually relied on in designing the stack or establishing an emission limitation to ensure protection against downwash; For all other stacks,

H g =H + 1.5L, where H is the height of the nearby structure( s) measured from the ground-level elevation at the base of the stack and L is the lesser dimension of height or projected width of nearby structure(s), or

 the height demonstrated by a fluid mode l or a field study approved by EPA or the State/local agency which ensures that th e emissions from a stack do not result in excessive concentrations of any air polluta nt as a result of atmospheric downwash, wakes, eddy effects created by the source it self, nearby structures or nearby terrain features. For more details about GEP, see the Guideline for Determination of G ood Engineering Practice Stack Height Technical Suppor t Document (U.S. EPA, 1985). If stack heights exceed GEP, then GEP heights should be used with the individual stack’s other parameters (temperature, diameter, exit velo city). For stacks modeled with actual heights below GEP, building downwash should be considered as this can impact c oncentrations near the source (Section 6.2.2b, Appendix W). If build ing downwash is being considered, the BPIPPRIME program (U.S. EPA, 2004d) should be used to input building parameters for AERMOD. More information about build ings and stacks is in Section 6.5. 6.4. Dispersion techniques As stated in past SO 2 modeling guidance (U .S. EPA, 1994), the CAA and EPA regulations generally prohibit stationary sources from taking credit for dispersion techniques in determiningPublic Review Draft 9/22/2011

A-15 allowable emission limitations. As stated in Section 5.3 of the 1994 SO 2 modeling guidance prohibited dispersion techniques are:

 Using that portion of a stack in excess of good engineering pr actice stack height

 Varying the pollutant emission rate accord ing to atmospheric c onditions or ambient concentrations of that pollutant (referred to as intermittent or supplemental control systems – ICS or SCS) or,

 Increasing final exhaust gas plume rise by ma nipulating source process parameters, exhaust gas parameters, stack parameters or combini ng exhaust gases from several existing stacks into one stack, or other selective handling of exhaust gas streams so as to increase the exhaust gas plume rise. Exceptions to the prohibitions are:

 Merging of gas streams in original design and construction, or as part of a change that includes installation of contro ls and a net reduction in allo wable emissions affected by the change

 Utilizing techniques which increase final, exhaust gas plume rise, provided facility-wide allowable emissions of SO 2 are less than 5,000 tons per years

 Smoke management techniques involved in agricultural or silvicultural programs

 Episodic restrictions on residentia l wood burning and open burning and,

 Reheating after a pollution control system

6.5. Source configurations and source types

An accurate characterization of the modeled f acilities is critical for refined dispersion modeling, including accurate stack parameters and physical plan t layout. Accurate stack parameters should be determined for the emi ssions being modeled. Since modeling would be done with maximum allowable or potential emissions levels at each stack, the stack’s parameters such as exit temperature, diameter, and exit ve locity should reflect those emissions levels. Accurate locations (i.e. latitude and longit ude or Universal Transverse Mercator (UTM) coordinates and datum) 22 of the modeled emission sources are also important, as this can affect the impact of an emission source on receptors, de termination of stack base elevation, and relative location to any nearby building structures. Not only are accurate stack locations needed, but accurate information for any nearby buildings is important. This information would include location and orientation relativ e to stacks and building size pa rameters (height, and corner coordinates of tiers) as these parameters ar e input into BPIPPRIME to calculate building parameters for AERMOD. If stack locations and or building information are not accurate, downwash will not be accurately accounted for in AERMOD. Emission source type characterization within th e modeling environment is also important. As stated in the AERMOD User’s Guide (U .S. EPA, 2004a; U.S. EPA, 2011c), emissions

22 Latitudes and longitudes to four deci mal places position a stack within 30 feet of its actual location and five decimal places place a stack within three feet of its act ual location. Users should use the greatest precision available.Public Review Draft 9/22/2011

A-16 sources can be characterized as several different source types: POINT sources, capped stacks (POINTCAP), horizontal stacks (POINTHO R), VOLUME sources, OPENPIT sources, rectangular AREA sources, circ ular area sources (AREACIRC), and irregularly shaped area sources (AREAPOLY). Note that POINTCAP a nd POINTHOR are not pa rt of the regulatory default option in AERMOD because the user must invoke the BETA option in the model options keyword MODELOPT while not in cluding the “DFAULT” modeling option for these options to work properly. While most sources can be char acterized as POINT sources, some sources, such as fugitive releases or nonpoint sources (emission s from ports/ships, airports, or smaller point sources with no accurate locations) may be be st characterized as VOLUME or AREA type sources. Sources such as fl ares can be modeled in AERMOD using the parameter input methodology described in Section 2.1.2 of the AE RSCREEN User’s Guide (U. S. EPA, 2011f). If questions arise about proper source characte rization or typing, users should consult the appropriate EPA Regional Modeling Contact.

6.6. Urban/rural determination For any dispersion modeling exercise, the urba n or rural determination of a source is important in determining the boundary layer charact eristics that affect th e model’s prediction of downwind concentrations. Figure 4 gives exampl e maximum 1-hour concentration profiles for a 10 meter stack (Figure 3a) and a 100 m stack (F igure 3b) based on urban vs. rural designation. The urban population used for the examples is 100,000. In Figure 4a, the urban concentration is much higher than the rural concentration for dist ances less than 750 m from the stack but then drops below the rural concentration beyond 750 m. For the taller stack in Figure 4b, the urban concentration is much higher than the rural concentration even as distances increase from the source. These profiles show that the urban or rural designation of a source can be quite important. In addition, for SO 2 modeling, the urban/rural determination is important because AERMOD invokes a 4-hour half life 23 for urban SO 2 sources. This would only be done for urban sources when the POLLUTID ke yword in AERMOD is set to “SO 2 ” and the MODELOPT keyword includes the DFAULT option. Rural sour ces within the same AERMOD run would not be affected. If the DFAULT option is not in cluded with the MODELO PT keyword, the 4-hour half life would not be used and the user would specify the 4-hour half life using the HALFLIFE or DCAYCOEFF keywords in order to account fo r the chemical transformation. See Section 3.2.6 of the AERMOD User’s Guid e (U.S. EPA, 2004a) for more details about these keywords. If the user invokes the HALFLI FE or DCAYCOEEF option, then any rural sources included in the modeling would need to be run in separate AE RMOD runs so that they are not subject to the 4-hour half life. Note that if the DFAULT option is used, the rural sources would not need to be in a separate run from the urban sources. Determ ining whether a source is urban or rural can be done using the methodology outlined in Secti on 7.2.3 of Appendix W and recommendations outlined in Sections 5.1 through 5.3 in the AIG (U.S. EPA, 2009). In summary, there are two methods of urban/rural clas sification described in Section 7.2.3 of Appendix W.

The first method of urban determination is a land use method (Appendix W, Section 7.2.3c). In the land use method, the user analyzes th e land use within a 3 km radius of the source

23 Over a 4-hour period, SO 2 concentrations decrease by half from the initial value.Public Review Draft 9/22/2011

A-17 using the meteorological land use scheme desc ribed by Auer (1978). Using this methodology, a source is considered urban if the land use t ypes, I1 (heavy industrial), I2 (light-moderate industrial), C1 (commercial), R2 (common residential), and R3 (com pact residential) are 50% or more of the area within the 3 km radius circle . Otherwise, the source is considered a rural source. The second method uses population de nsity and is describe d in Section 7.2.3d of Appendix W. As with the land use method, a circle of 3 km radius is used. If the population density within the circle is greater than 750 people/km 2 , then the source is considered urban. Otherwise, the source is modeled as a rural source. Of the tw o methods, the land use method is considered more definitive (Section 7.2.3e, Appendix W).

Caution should be exercised with either classi fication method. As stated in Section 5.1 of the AIG (U.S. EPA, 2009), when using the land use method, a source may be in an urban area but located close enough to a body of water or ot her non-urban land use category to result in an erroneous rural classification for the source. The AIG in Section 5.1 cautions users against using the land use scheme on a source by source basis, but advises considering the potential for urban heat island influences across the full modeli ng domain. When using the population density method, Section 7.2.3e of Appendix W states, “Popul ation density should be used with caution and should not be applied to highly industrialize d areas where the population density may be low and thus a rural classification woul d be indicated, but the area is sufficiently built-up so that the urban land use criteria would be satisfied...” With either method, Section 7.2.3(f) of Appendix W recommends modeling all sources within an ur ban complex as urban, even if some sources within the complex would be c onsidered rural using either the land use or population density method.Public Review Draft 9/22/2011

A-18 Figure 4. Urban (red) and rural (blue) conc entration profiles fo r (a) 10 m buoyant stack release, and (b) 100 m buoyant stack release.Public Review Draft 9/22/2011

A-19 Another consideration that may need attention by the user and is discussed in Section 5.1 of the AIG relates to tall stacks lo cated within or adjacent to small to moderate size urban areas. In such cases, the stack height or effective plume height for very buoyant sources may extend above the urban boundary layer height. The a pplication of the urban option in AERMOD for these types of sources may artificially limit the plume height. The use of the urban option may not be appropriate for these sour ces, since the actual plume is likely to be transported over the urban boundary layer. Section 5.1 of the AIG gives details on determining if a tall stack should be modeled as urban or rural, based on compar ing the stack or effective plume height to the urban boundary layer height. The 100 m stack illustrated in Figur e 3b, may be such an example as the urban boundary layer height for this stack would be 189 m (based on a population of 100,000) and equation 104 of the AERMOD formula tion document (Cimorelli, et al., 2004). This equation is:

4 1        



o iuo iuc P P z z where z iuo is a reference height of 400 m corresponding to a reference population P o of 2,000,000 people. Given that the stack is a buoyant releas e, the plume may extend above the urban boundary layer and may be best char acterized as a rural source, ev en if it were near an urban complex. Exclusion of these elevated sources from application of the urban option would need to be justified on a case-by-case ba sis in consultation with the a ppropriate reviewing authority. AERMOD requires the input of urban populat ion when utilizing the urban option. Population can be entered to one or two significant digits (i .e., an urban population of 1,674,365 can be entered as 1,700,000). Users can enter mu ltiple urban areas and populations using the URBANOPT keyword in the runstream file (U.S . EPA, 2004a; U.S. EPA, 2011c). If multiple urban areas are entered, AERMOD requires that each urban source be associated with a particular urban area or AERMOD model calculations will abor t. Urban populations can be determined by using a method described in Section 5.2 of the AIG (U.S. EPA, 2009). 6.7. Source groups In AERMOD, individual emission sources’ conc entration results can be combined into groups using the SRCGROUP keyword (Sectio n 3.3.11 of the AERMOD User’s Guide (U.S, EPA, 2004a). The user can automatically calculat e a total concentration (from all sources) using the SRCGROUP ALL keyword. For the purposes of attainment demonstra tions and design value calculations, source group ALL should be used, esp ecially if all sources in the modeling domain are modeled in one AERMOD run. Design values should be calculated from the total concentrations (all sources and background). For the purposes of SIP modeling, individual source contributions outputs to the total concentration may be necessary to determine the effectiveness of control strategies. To avoid any confusi on, source groups that are used to calculate the design value concen trations or determine source contributions to design values should be mutually exclusive (i.e. an emission sour ce should not be in two source groups). This would be especially important if the design value concentrati ons are calculated outside of AERMOD by adding the individual groups togeth er to calculate a tota l concentration (SeePublic Review Draft 9/22/2011

A-20 Section 8.1 of this document for examples). If individual source groups th at are used in design value concentrations are not mutually ex clusive, there would be double counting of concentrations when calculating design values either in AERMOD or outside of AERMOD. 7. Meteorological data Section 7 gives guidance on the selection of meteorological data for input into AERMOD. Much of the guidance from Secti on 8.3 of Appendix W is applicable to SIP modeling and is summarized here. In Secti on 7.2.1, the use of a new tool, AERMINUTE (U.S. EPA, 2011h), is introduced. AERMINUTE is an AERMET pre-processor that calculates hourly averaged winds from ASOS (Automated Surface Observing System) 1-minute winds. 7.1. Surface characteristics and representativeness The selection of meteorologica l data that are input into a dispersion model should be considered carefully. The selection of data should be based on spatial and climatological (temporal) representativeness (Appendix W, Section 8.3). The representativeness of the data is based on: 1) the proximity of the meteorologica l monitoring site to the area under consideration, 2) the complexity of terrain, 3) the exposure of the meteorological site, and 4) the period of time during which data are collected. Sources of me teorological data are: National Weather Service (NWS) stations, site-specific or onsite data, a nd other sources such as universities, Federal Aviation Administration (FAA), military stations , and others. Appendix W addresses spatial representativeness issues in Sections 8.3.a and 8.3.c. Spatial representativeness of the meteorologi cal data can be adversely affected by large distances between the source and receptors of interest and the complex topographic characteristics of the area (Appendix W, Secti on 8.3.a and 8.3.c). If the modeling domain is large enough such that conditions vary drastically across the do main then the selection of a single station to represent the domain should be car efully considered. Also, care should be taken when selecting a station if the area has comp lex terrain. While a source and meteorological station may be in close proximity, there may be complex terrain between them such that conditions at the meteorological station may not be representative of the source. An example would be a source located on the windward side of a mountain chain with a meteorological station a few kilometers away on the leeward side of the mountain. Sp atial representativeness for off-site data should also be assessed by co mparing the surface characteristics (albedo, Bowen ratio, and surface roughness) of the meteorological monitoring site and the analysis area. When processing meteorological data in AERMET (U.S . EPA, 2004c; U.S. EPA, 2011e), the surface characteristics of the meteorological site shou ld be used [Section 8.3.c of Appendix Wand the AERSURFACE User’s Guide (U.S. EPA 2008)]. Spatial representativeness should also be addressed for each meteorological variable separa tely. For example, temperature data from a meteorological station several kilometers from th e analysis area may be considered adequately representative, while it may be necessary to co llect wind data near the plume height (Section 8.3.c of Appendix W).

Surface characteristics can be cal culated in several ways. Fo r details see Section 3.1.2 of the AIG (U.S. EPA, 2009). EPA has developed a tool, AERSURFACE (U.S. EPA, 2008) to aidPublic Review Draft 9/22/2011

A-21 in the determination of surface characteristics. The current ve rsion of AERSURFACE uses 1992 National Land Cover Data. Note that the use of AERSURFACE is not a regulatory requirement but the methodology outlined in Section 3.1.2 of the AIG should be followed unless an alternative method can be justified. 7.2. Meteorological inputs Appendix W states in Secti on 8.3.1.1 that the user should acquire enough meteorological data to ensure that worst-case conditions are ad equately represented in the model results. Appendix W states that 5 years of NWS meteorological data or at least one year of site-specific data should be used(Section 8.3.1.2, Appendix W) and should be adequately representative of the study area. If one or more years (including partial years) of site-s pecific data are available, those data are preferred. While the form of the SO 2 NAAQS contemplates obt aining three years of monitoring data, this does not pr eempt the use of 5 years of NWS data or at least one year of site-specific data in the modeling. The 5-year average based on the us e of NWS data, or an average across one or more years of available site specific data, serves as an unbiased estimate of the 3-year average for purposes of modeling de monstrations of compliance with the NAAQ (See the August 23, 2010 Clarification Memorandum on “Applicability of Appendix W Modeling Guidance for the 1-hour SO 2 National Ambient Air Quality Sta ndard” (U. S. EPA, 2010a). See the memorandum for more details on the use of 5 y ears of NWS data or at least one year of sitespecific data and applicability to the NAAQS.

7.2.1. NWS data

NWS data are available from the National Climatic Data Center (NCDC) in many formats, with the most common one in recent years being the Integrated Surface Hourly data (ISH). Most available formats can be processed by AERMET. As stated in Section 7.1, when using data from an NWS station alone or in conj unction with site-specifi c data, the data should be spatially and temporally representative of conditions at the modeled sources. A recently discovered issue with ASOS is that 5-second wind data that are used to calculate the 2-minute average wi nds are truncated rather than rounded to whole knots. For example, a wind of 2.9 knots is reported as 2 knots, not 3 knots. To account for this truncation of NWS winds (either standard obser vation or AERMINUTE output), an adjustment of 1⁄2 knot or 0.26 m/s is added to the winds in stage 3 AERM ET processing. For more details refer to the AERMET User’s Guide Addendum (U.S. EPA, 2 011e) and/or the appropriate EPA Regional Modeling Contact.

7.2.1.1. AERMINUTE In AERMOD, concentrations are not calcu lated for variable wind (i.e., missing wind direction) and calm conditions, resu lting in zero concentrations for those hours. Since the SO 2 NAAQS is a one hour standard, these light wind conditions may be the controlling meteorological circumstances in some cases becau se of the limited dilution that occurs under low wind speeds which can lead to higher concentrat ions. The exclusion of a greater number of instances of near-calm conditions from the mode led concentration distribution may thereforePublic Review Draft 9/22/2011

A-22 lead to underestimation of daily maximum 1-hour concentrations for calculation of the design value.

To address the issues of calm and variable winds associated w ith the use of NWS meteorological data, EPA has developed a preprocessor to AERMET, called AERMINUTE (U.S. EPA, 2011h) that can read 2-minute ASOS winds and calculate an hourly average. Beginning with year 2000 data, NCDC has made the 1-minute wind data, reported every minute from the ASOS network freely available. The AERMINUTE program reads these 2-minute winds and calculates an hourly average wind. In AERMET, these hourly averaged winds replace the standard observation time winds read from the ar chive of meteorological da ta. This results in a lower number of calms and missing winds and an increase in the number of hours used in averaging concentrations. For more details re garding the use of NWS data in regulatory applications see Section 8.3.2 of Appendix W and for more information about the processing of NWS data in AERMET and AERMINUTE, see the AERMET (U.S. EPA, 2004c; U. S. EPA, 2011e) and AERMINUTE User’s gu ides (U.S. EPA, 2011h). Since the release of AERMINUTE in 2011, some permitting agencies have expressed concern that the inclusion of AERMINUTE output in AERMOD will lead to an increase in the conservatism of AERMOD output. This perceived incr ease in conservatism is due to an increase in hours with lower wind speeds input into AE RMOD. The purpose of AERMINUTE is not to lead more conservative concentration estimat es, but to increase the data quality and representativeness of the meteorological inputs into AE RMOD. Concentrations are not calculated for hours with reported calm winds or variable winds. These calm or variable winds are due to the METAR reporting code used to re port ASOS observations. In the METAR coding used to report surface observ ations beginning July 1996, a calm wi nd is defined as a wind speed less than 3 knots and is assi gned a value of 0 knots. The M ETAR code also introduced the variable wind observation that may include wind speeds up to 6 knots, but the wind direction is reported as missing, if the wind direction varies more than 60 degrees during the 2-minute averaging period for the observation. These are often hours of interest because these are light wind conditions and important for an hourly SO 2 standard. With the use of AERMINUTE, hourly averages can be calculated for those hours with reported calm or missing winds, because the 2-minute average winds in the one-minute data files have not been subjected to the METAR coding. In effect, AERMINUTE is obtaining da ta that was unavailable because of METAR coding, making the meteorological data more representative of the area. 7.2.2. Site-specific data The use of site-specific meteorological da ta is the best way to achieve spatial representativeness. AERMET can process a variet y of formats and variables for site-specific data. The use of site-specific data for regulatory applications is discussed in detail in Section 8.3.3 of Appendix W. Due to the range of data that can be collected onsite and the range of formats of data input to AERMET, the user should consult Appendix W, the AERMET User’s Guide (U.S. EPA, 2004c; U. S. EPA, 2011e), and Meteorological Monitoring Guidance for Regulatory Modeling Applications (U.S. EPA, 2000). Also, when processing site-specific data for an urban application, Section 3.3 of the AERMOD Implementation Guide offers recommendations for data processing. In summ ary, the guide recommends that site-specificPublic Review Draft 9/22/2011

A-23 turbulence measurements should not be used wh en applying AERMOD’s urban option, in order to avoid double counting the effects of enhan ced turbulence due to the urban heat island. 7.2.3. Areas without representative meteorological data

In areas with SO 2 sources where the state has determin ed that there is no representative meteorological data, it may be difficult to pe rform accurate refined dispersion modeling for the implementation modeling. In nonattainment or unclassifiable areas composed of isolated sources, it may be possible to use AERSCREEN (U .S. EPA, 2011g) to conservatively determine the attainment status of an area. As noted in Section 5.1, AERSCREEN does not output a design value metric to compare to the SO 2 NAAQS but does output the ma ximum 1-hour concentration which can be used as a conservative estim ate to compare to the NAAQS. Any use of AERSCREEN or screening meteorology in the abse nce of hourly representative meteorological data should be considered carefully and in consultation with the a ppropriate Regional Office modeling contact. Currently, the screening mete orology created by the MAKEMET processor for use with AERSCREEN cannot be used to calculate an SO 2 design value. If scre ening meteorology is used in AERMOD, the SO2 design value cannot be ca lculated. AERMOD will abort processing if screening meteorology is used and an SO 2 design value is requested in the input file. 7.2.4. Upper air data AERMET requires full upper air soundings to calculate the convective mixing height. For AERMOD applications in the U.S., the early morning sounding, usually the 1200 UTC (Universal Time Coordinate) sounding, is typica lly used for this purpose. Upper air soundings can be obtained from the Radiosonde Data of North America CD for the period 1946-1997. Upper air soundings for 1994 through the present ar e also available for free download from the Radiosonde Database Access webs ite. Users should choose all levels or mandatory and significant pressure levels 24 when selecting upper air data. Selecting mandatory levels only would not be adequate for input into AERMET as the use of just mandatory levels would not provide an adequate char acterization of the potenti al temperature profile. 8. Background concentrations The inclusion of ambient background concen trations is important in determining cumulative impacts. The modeled contribution to the cumulative analysis should follow the form of the standard and be calculated as described in Section 2.6.1.2 of the August 23, 2010 clarification memo on “Applicability of Appe ndix W Modeling Guidance for the 1-hour SO 2 National Ambient Air Quality Standard” (U. S. EP A, 2010a) This memo suggested a “first tier” approach to including a uniform monitored b ackground contribution based on adding the overall highest hourly background SO 2 concentration from a represen tative monitor to the modeled design value. We recognize that this approach could be overly conservative in many cases and

24 By international convention, mandatory levels are in millibars: 1,000, 850, 700, 500, 400, 300, 200, 150, 100, 50, 30, 20, 10,7 5, 3, 2, and 1. Significant levels may vary depending on the meteorological conditions at the upper-air stationPublic Review Draft 9/22/2011

A-24 may also be prone to reflecting source-orien ted impacts, increasing the potential for doublecounting of modeled and monitore d contributions. As discusse d in EPA’s March 1, 2011 memo “Additional Clarification Regarding Applicati on of Appendix W Modeling Guidance for the 1- hour NO 2 Ambient Air Quality Standard” (U. S. EPA, 2011a), and the March 24, 2011 SO 2 designations guidance memo (U.S. EPA, 2011b) we recommend a less conservative “first tier” approach for a uniform monitored background concentration based on the monitored design values for the latest 3-year period, regardless of the years of meteorological data used in the modeling. Adjustments to this approach may be considered in consultation with the appropriate EPA Regional Modeling Contact with adequate justification and documentation of how the background concentration was calculated. Section 8.2.2 of Appendix W gives guidance on background concentrations for isolated single sources and is also applicable for multi-source areas. One option is, as described in Section 8.2.2.b: “Use air quality data in the vicinity of the source to determine the background concentration for the averaging times of concern. Determine the mean background concentration at each monitor by excluding concen trations when the source in question is impacting the monitor... For shorter time periods, the meteorological conditions accompanying concentrations of concern should be identified. Concentrations for meteorological conditions of concern, at monitors, not impacted by the source in question, should be averaged for separate averaging time to determine the average background value. Monitoring sites inside a 90° degree sector downwind of the source may be used to determine the area of impact.” When no monitors are located in the vicinity of the sources being modeled a “regional site” (i.e., one that is located away from the area of interest but is impacted by similar natural and distant man-made sources) may be used to de termine background (Section 8.2.2.c, Appendix W). In multi-source areas, background includes two co mponents, nearby sources and other sources (Section 8.2.3 of Appendix W). Nearby sources ar e those sources that are expected to cause a significant concentration gradient in the vicinity of the source or sources under consideration, and should be explicitly modeled. Identifica tion of nearby sources calls for professional judgment and consultation with the appropriate EPA Regional Modeling Contact. For other sources, such as natural sources, minor source s and distant major sources, the methodology of Section 8.2.2 should be used. EPA’s March 24, 2011 memo for SO 2 designations guidance (U.S. EPA, 2011b) describes an appropriate met hodology of calculating temporally varying background monitored concentrations by hour of day and season (exclu ding periods when the source in question is expected to impact the monitored co ncentration). The methodology for SO 2 is to use the 99 th percentile concentration for each hour of the day by season and average across three years, excluding periods when the dominant source(s) are influencing the monitore d concentration (i.e., 99 th percentile, or 4 th highest, concentrations for hour 1 for January or winter, 99 th percentile concentrations for hour 2 for January or wint er, etc.). Recent updates included in AERMOD allow for the inclusion of temporally varying background concentrations in the design valuePublic Review Draft 9/22/2011

A-25 calculation in combination with modeling resu lts. See the AERMOD User’s Guide Addendum for more details (U. S. EPA, 2011c). As an illustrative example Figure 5 shows the 1-hour SO 2 NAAQS level, the design value (the 3-year average of the 99 th percentile of the annual dist ribution of daily maximum 1- hour concentrations), and 3- year averages of the 99 th percentile concentr ations by season and hour of day. To calculate the 99 th percentile concentration for a season and hour of day combination (no consideration for day of week ), the second highest concentration for that combination should be selected. Also shown are 3-year averages of the 99 th percentile concentration by hour of day (acr oss all seasons), and the averag e concentration by hour of day across the three years 25 . In this example, the winter bac kground concentrations show a distinct diurnal variability, with less for each of the other seasons.

Figure 5. SO 2 monitored concentrations for various averaging times.

In summary background concentr ations can be included as:

 Highest monitored hourly SO 2 background concentration

 “First tier” approach based on monitored de sign values added to modeled design values;

or

25 Modelers should use the 1 st -highest value for more detailed pairings, such as month by hour-of-day or season by hour-of-day and day-of-week (consider day of week in calculating values).Public Review Draft 9/22/2011

A-26  Temporally varying based on the 99 th percentile monitored con centrations by hour of day and season added to modeled design values. 9. Determining design value metrics Refined dispersion modeling for SIPs will provide predictions of SO 2 design values at each receptor that includes contributions from all modeled sources and background. Based on the form of the 1-hour SO 2 NAAQS, the design value should be calculated as the average of the 99 th percentile of the annual distribution of daily maximum 1-hour concentrations averaged across the modeled years. 9.1. Design value calculation methodology Whether design values are calculated with in AERMOD or outside of AERMOD, to calculate a design value to compar e against the standard, the followi ng steps should be followed:

1. At each receptor, for each hour of the mode led period, calculate a total concentration across all sources includ ing background concentrations if ap plicable. This can be done in AERMOD using SRCGROUP ALL or by adding individual source groups outside of AERMOD, using hourly POSTFILEs. If the user is totaling the concen trations outside of AERMOD, the source groups need to be mutua lly exclusive, i.e. no one source should be in multiple source groups. 2. From the total concentrations calculated in step 1, obtain the 1-hour maximum concentration at each receptor for each modeled day. 3. From the output of step 2, for each year modeled, calculate the 99 th percentile (4 th highest) daily maximum 1-hour c oncentration at each receptor. If modeling 5 years of meteorological data, this results in five 99 th percentile concentrati ons at each receptor. 4. Average the 99 th percentile (or 4 th highest) concentrations across the modeled years to obtain a design value at each receptor. 5. Modeled source contributions to a NAAQS violation can be determined by analyzing the hourly concentrations from the individual source groups corresponding to the same hour as the 4 th daily maximum 1-hour concentration from each year. See 75 FR at 35540. For example, a receptor has a 5-year average design value of 200.8 mg/m 3 (or approximately 77 ppb) and AERMOD was modeled for the period January 1, 2005 through December 31, 2009 for four source groups. From the AE RMOD output, the user can determine the date of the 4 th highest daily maximum 1-hour concentrations that are used to calculate the 5-year average design value. Table 1 shows the 4 th highest daily maximum 1-hour concentrations for each year and associated dates that are used in the design value calculation.Public Review Draft 9/22/2011

A-27 Table 1. 4th highest daily maximum 1-hour concentrations (μg/m 3 ) for 2005-2009. Date (YYMMDDHH) Concentration

05080101 200.1 06073105 201.5 07080403 207.1 08072705 197.1 09080104 198.1 5-YEAR AVG. 200.8 If output by source group is available, the user can extract each source group’s concentration at each of the hours listed in Table 1. Table 2 shows example source contributions for each hour shown in Table 1 and indicates that Source 1 is the main contributor to the design value for all hours. Table 2. Source contributions to 4th highest daily maximum 1-hour concentrations (μg/m 3 ) and 5-year average design values. Date (YYMMDDHH) TOTAL SOURCE 1 SOURCE 2 SOURCE 3 SOURCE 4

05080101 200.1 155.1 25.1 1.5 18.4 06073105 201.5 157.4 26.2 0.5 17.4 07080403 207.1 161.5 20.5 2.1 23.0 08072705 197.1 159.2 23.1 1.7 13.1 09080104 198.1 155.3 22.6 2.0 18.2 5-YEAR AVG. 200.8 157.7 23.5 1.6 18.0 When calculating design values and there ar e exceedances of the NAAQS, one may need to consider other pe rcentiles below the 99 th percentile as well. Exam ining percentiles below the 99 th percentile would be useful in the context of determining sources that may be significant contributors to a NAAQS violation, i.e. a source’s contribution ma y be above the SIL. There may be cases in which a source is not a significant contributor to the design value as defined in the NAAQS, but may be a significant contributor at a lower percentile that is still above the NAAQS level. Sources that fit this categor y should not be immedi ately discounted when determining sources to control for attaining th e NAAQS. To calculate design values based on other percentiles, one can just step down through the 5 th , 6 th , 7 th , etc. highest of the annual distributions of daily maximum 1- hour concentrations in steps 3 th rough 5 in the five steps listed above until no concentrations ex ceed the NAAQS level. The indi vidual sources’ contributions can then be determined to be significant or not. 9.2. Running AERMOD and implications for design value calculations Recent enhancements to AERMOD include optio ns to aid in the calculation of design values for comparison with the SO 2 NAAQS. These enhancements include:Public Review Draft 9/22/2011

A-28  The output of daily maximum 1-hour concentrati ons by receptor for each day in the modeled period for a specified source group. This is the MAXDAILY output option in AERMOD.

 The output, for each rank specified on the RECTABLE output keyword, of daily maximum 1-hour concentrations by receptor for each year for a specified source group. This is the MXDYBYYR output option.

 The MAXDCONT option, which shows the cont ribution of each source group to the high ranked values for a specified ta rget source group, paired in time and space. The user can specify a range of ranks to analyze, or specify an upper bound rank, i.e. 4 th highest, and a lower threshold value, such as the NAAQS for the target source group. The model will process each rank within the range specified, but will stop after the first rank (in descending order of concentration) that is below the th reshold, specified by the user. A warning message will be generated if the threshold is not reache d within the range of ranks analyzed (based on the range of ranks specified on the RECTABLE keyword). This option may be needed to aid in determining which sources should be considered for controls. For more details about the enhancements s ee the AERMOD User’s guide Addendum (U. S. EPA, 2011c). Ideally, all explicitly modeled sources, receptors, and background should be modeled in one AERMOD run for all modeled years. In this case, the use of the one of the above output options can be used in AERMOD to calculate design values for comparison to the NAAQS and determine the area’s attainment status and/or inform attain ment/nonattainment boundaries. The use of these options in AERMOD allows AERMOD to internally calculate concentration metrics that can be used to calculate design values and th erefore lessen the need for large output files, i.e. hourly POSTFILES. However, there may be situations where a single AERMOD run with all explicitly modeled sources is not possible. These situati ons often arise due to runtime or storage space considerations during the AE RMOD modeling. Sometimes se parate AERMOD runs are done for each facility or group of facilities, or by year, or the receptor network is divided into separate sub-networks. In some types of th ese situations, the MAXDAILY, MXDYBYYR, or MAXDCONT output option may not be an option for design value calculati ons, especially if all sources are not included in a single run. If the user wishes to utilize one of the three output options, then care should be taken in developing the model inputs to ensure accurate design value calculations.

Situations that would eff ectively preclude the use of the MAXDAILY, MXDYBYYR, and MAXDCONT option to calculate meaningful AERMOD design value ca lculations include the following examples:

 Separate AERMOD runs for each source or groups of sources.

o SIP modeling includes 10 facilities for five years of NWS data and each facility is modeled for five years in a separate AERMOD run, resulting in 10 separate AERMOD runs.Public Review Draft 9/22/2011

A-29  Separate AERMOD runs for each source and each modeled year.

o 10 facilities are modeled for 5 years of NWS data. Each facility is modeled separately for each year, resulting in fifty individual AERMOD runs. In the two situations listed above, the MAXDAILY, MXDYB YYR, or, MAXDCONT option would not be useful as the different AE RMOD runs do not include a total concentration with contributions from all faci lities. In these situations th e use of hourly POSTFILES, which can be quite large, and external post-processing would be needed to calculate design values. Situations in which the MAXDAILY, MX DYBYYR, or, MAXDCONT options may be used but may necessitate some external post-pr ocessing afterwards to calculate a design value include:

 The receptor network is divided into sections and an AERMOD run, with all sources and years, is made for each sub-network.

o A receptor network of 20,000 receptors is divided into four 5,000 receptor subnetworks. Ten facilities are modeled with five years of NWS data in one AERMOD run for each receptor network, resulting in four AERMOD runs. After the AERMOD runs are complete , the MAXDAILY, MXDYBYYR, or, MAXDCONT results for each network can be re-combined into the larger network.

 All sources and receptors are modele d in an AERMOD run for each year.

 Ten facilities are modeled with five years of NWS data. All facilities are modeled with all receptors for each year individually, re sulting in five AERM OD runs. MAXDAILY, MXDYBYYR, or, MAXDCONT output can be us ed and post-processed to generate the necessary design value concentrations. The r eceptor network is divided and each year is modeled separately for each s ub-network with all sources. Ten facilities are modeled with five y ears of NWS data for 20,000 receptors. Thereceptor network is divided into four 5,000 receptor networks. For each subnetwork, all ten facilities are modeled for each year separately, resulting in twenty AERMOD runs. MAXDAILY, MXDYBYYR , or, MAXDCONT output can be used and post-processed to generate the necessary design value concentrations.

10. Documentation It is expected that the state would submit a modeling and analys is protocol that details the methodology and model inputs before commence ment of the modeling exercise. This information should support the states’ implem entation plans and provide a basis for EPA’s review and evaluation. The protocol should include the following:

 Characterization of the nonattain ment problem or characteriza tion of the modeled area in absence of a violating monitor,Public Review Draft 9/22/2011

A-30  An emissions analysis around the violating m onitor or area under c onsideration for the attainment and maintenance demonstration in absence of a violating monitor, and

 Methodology for preparing air quality and meteorology inputs including choice of meteorological data and repr esentativeness of the data. Additionally, post-modeling documentation should include:

 Summary and analysis of modeling results, and

 Provision of modeling data inputs and outputs in electronic form. A meeting with the appropriate EPA Regiona l Modeling Contact and other technical and planning staff to discuss the modeling and analys is protocol is recommended before submitting the protocol and beginning any refined modeling. For example modeling protocols, please see the SCRAM website on SO2 Implementation at: http://www.epa.gov/ttn/scram/so2_modeling_guidance.htm

. 11. Summary In summary, we emphasize the following key points of this modeling guidance:

 AERMOD is EPA’s preferred n ear-field dispersion model fo r regulatory applications and is applicable for SO 2 SIPs modeling consistent with EPA’s Guideline on Air Quality Models , also published as Appendix W of 40 CFR Part 51.

 Sources should be modeled with maximum a llowable 1-hour or short-term emission rates in the SIP modeling based on continu ous operations at the source.

 It is reasonable to initiall y focus on larger emitters, i.e. –100 or more tons per year but smaller sources, especially those with short stacks and/or located in complex terrain can possibly cause or contribute to NAAQS violations.

 Modeling should be done with fi ve years of representative NWS meteorological data or at least one year of si te specific meteorology.

 Background concentrations can be included as:

o “First tier” approach based on monitore d design values added to modeled design values; or

o Temporally varying based on the 99 th percentile monitored concentrations by hour of day and season added to modeled design values.

 States should submit a modeling and analysis protocol that details the methodology and model inputs before commencement of the mo deling exercise. This information should support the states’ recommended SIPs, and provide a basis for EPA’s ev aluation of them.

 At any time during the SIP process when th ere are questions regarding modeling or interpretation of this guida nce, the appropriate EPA Regi onal Modeling Contact should be consulted.Public Review Draft 9/22/2011

A-31 12. References Auer, Jr., A.H., 1978: Correlation of Land Use and Cover with Meteorological Anomalies. Journal of Applied Meteorology, 17(5), 636-643. Brode, R., K. Wesson, J. Thurman, and C. Tillerson, 2008: AERMOD Sensitivity to the Choice of Surface Characteristics, Paper 811, Air And Waste Management Association Annual Conference. Cimorelli, A. J., S. G. Perry, A. Venkatram, J. C. Weil, R. J. Paine, R. B. Wilson, R. F. Lee, W. D. Peters, R. W. Brode, and J. O. Pa umier, 2004. AERMOD: Description of Model Formulation, EPA-454/R-03-004. U.S. Enviro nmental Protection Agency, Research Triangle Park, NC. http://www.epa.gov/ttn /scram/7thconf/aerm od/aermod_mfd.pdfU.S. EPA, 1985: Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack He ight Regulations), Revised. EPA-450/4- 80-023R. U.S. Environmental Protection Ag ency, Research Triangle Park, NC 27711. http://www.epa.gov/ttn/scram/guidance/guide/gep.pdf U.S. EPA, 1992: Screening Procedures for Es timating the Air Quality Impact of Stationary Sources. EPA-454/R-92-019. U.S. Environmenta l Protection Agency, Research Triangle Park, NC 27711. http://www.epa.gov /ttn/scram/guidance/guide/scrng.wpd U.S. EPA, 1994: SO 2 Guideline Document. EPA-452/R-95-008. U.S. Environmental Protection Agency, Research Triangle Park, NC 27711. U.S. EPA, 2000: Meteorological Monitoring Gu idance for Regulatory Modeling Applications. EPA-454/R-99-005. U.S. Environmental Protecti on Agency, Research Triangle Park, NC 27711. http://www.epa.gov/ttn/scram /guidance/met/mmgrma.pdf U.S. EPA, 2004a: User's Guide for the AM S/EPA Regulatory Model – AERMOD. EPA-454/B03-001. U.S. Environmental Protection Ag ency, Research Triangle Park, NC 27711. http://www.epa.gov/ttn/scram/models/aermod/aermod_userguide.zip U.S. EPA, 2004b: User's Guide for the AE RMOD Terrain Preprocessor(AERMAP). EPA454/B-03-003. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/models /aermod/aermap/aermap_userguide.zip U.S. EPA, 2004c: User’s Guide for the AE RMOD Meteorological Preprocessor (AERMET). EPA-454/B-03-002. U.S. Environmental Prot ection Agency, Research Triangle Park, NC 27711. http://www.epa.gov/ttn/scram/7t hconf/aermod/aermet_userguide.zip U.S. EPA, 2004d: User's Guide to the Build ing Profile Input Progr am. EPA-454/R-93-038. U.S. Environmental Protection Agency, Res earch Triangle Park, North Carolina 27711. U.S. EPA, 2005. Guideline on Air Quality Models . 40 CFR Part 51 Appendix W. http://www.epa.gov/ttn/scram/guidance/guide/appw_05.pdf U.S. EPA, 2008: AERSURFACE User’s Gu ide. EPA-454/B-08-001. U.S. Environmental Protection Agency, Research Tr iangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/7thc onf/aermod/aersurface_userguide.pdf U.S. EPA, 2009: AERMOD Implementation Guid e. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/7thcon f/aermod/aermod_implmtn_guide_19March 2009.pdf U.S. EPA, 2010a: Applicability of A ppendix W Modeling Guidance for the 1-hour SO 2 National Ambient Air Quality Standard. Tyler Fox Memorandum dated August 23, 2010,Public Review Draft 9/22/2011

A-32 Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/Clarif icationMemo_AppendixW_Hourly-SO2- NAAQS_FINAL_08-23-2010.pdf U.S. EPA, 2010b: Applicability of A ppendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard. Tyler Fox Memorandum dated June 28, 2010, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/Clarif icationMemo_AppendixW_Hourly-NO2- NAAQS_FINAL_06-28-2010.pdf U.S. EPA, 2011a: Additional Clarification Re garding the Application of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard. Tyler Fox Memorandum dated March 1, 2011, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/Additional_ Clarifications_AppendixW_Hourly-NO2- NAAQS_FINAL_03-01-2011.pdf U.S. EPA, 2011b: Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards. Stephen D. Page Memorandum dated March 24, 2011, Research Triangle Park, North Carolina 27711. http://www.epa.gov/air/sulfurdioxide /pdfs/20110411so2designationsguidance.pdf U.S. EPA, 2011c: Addendum – User’s Guide for the AMS/EPA Regulatory Model – AERMOD. EPA-454/B-03-001, Research Triang le Park, North Carolina 27711. http://www.epa.gov/ttn/scram/models/aermod/aermod_userguide.zip U.S. EPA, 2011d: Addendum - User's Guid e for the AERMOD Terrain Preprocessor (AERMAP). EPA-454/B-03-003. U.S. Environm ental Protection Agency, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/models/a ermod/aermap/aermap_userguide.zip U.S. EPA, 2011e: Addendum - User’s Guide for the AERMOD Meteorological Preprocessor (AERMET). EPA-454/B-03-002. U.S. Enviro nmental Protection Agency, Research Triangle Park, NC 27711. http://www.epa.gov/ttn/scram/7thc onf/aermod/aermet_userguide.zip U.S EPA, 2011f: AERSCREEN User’s Guid e. EPA-454-/B-11-001. U.S. Environmental Protection Agency, Research Tr iangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/mode ls/screen/aerscreen_userguide.pdf U.S. EPA, 2011g: AERSCREEN Released as the EPA Recommended Scre ening Model. Tyler Fox Memorandum dated April 11, 2011, Resear ch Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/20110411_AERSCREEN_Release_Memo.pdf U.S EPA, 2011h: AERMINUTE User’s Guide. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. http://www.epa.gov/ttn/scram/7t hconf/aermod/aerminute_v11059.zipPublic Review Draft 9/22/2011

B-1 Appendix B Guidance on Section 110(a)(2) Infrastructure SIP Requirements The Clean Air Act (CAA) directs states to address basic SIP requirements to assure attainment and maintenance of th e standards. States are to su bmit these SIPs, pursuant to CAA sections 110(a)(1) and 110( a)(2), within 3 years after promul gation of a new or revised primary standard. Many of the section 110(a)(2) SIP elements relate to the general information and authorities that constitute the "infrastructure" of a state's air quality management program, and these have been in place since the initial SIPs we re submitted in response to the 1970 CAA. It is the responsibility of eac h state to review its ai r quality management program's infrastructure SIP provisions in light of each new or revised NAAQS. States should review and revise , as appropriate, their existing SO 2 SIPs to ensure that they are adequate to address the 2010 1-hour SO 2 NAAQS. States should, in consultation with EPA Regional Offices, follow applicable EPA re gulations governing SIP submittals in 40 CFR Part 51. See, e.g. , Subpart H ("Prevention of Air Pollu tion Emergency Episodes"), Subpart I ("Review of New Sources and M odifications"), Subpart J (Ambient Air Quality Surveillance), Subpart K (Source Surveillance), Subpart L (Leg al Authority), Subpart M ("Intergovernmental Consultation"), Subpart O (Misce llaneous Plan Content Requiremen ts), Subpart P ("Protection of Visibility"), and S ubpart Q ("Reports"). For many infrastructure SIP elements, a SIP submittal should refer to and include citations to relevant st ate regulations. See, e.g. , our guidance below regarding elements (F), (H), (J), and (M). For EPA's genera l criteria for SIP submittals, refer to 40 CFR Part 51, Appendix V, "Criteria for Determining the Completeness of Pl an Submissions." For example, in accordance with Appendix V, paragraph 2.1(d), a SIP s ubmittal would include a copy of the actual regulation that the state is submitting for approval and incorporation by reference into its SIP, if a copy of that regulation has not already been provided by the state. Pursuant to section 110(a), states must provide reasonable notice and opportunity for public hearing for all infrastructure SIP submittals. Pursuant to EPA's regulations at 40 CFR Part 51, a SIP submittal is to incl ude a certification by th e state that the pub lic hearing was held in accordance with EPA's procedural requirement s for public hearings. See paragraph 2.1(g) of Appendix V to Part 51 and 40 CFR 51.102.Public Review Draft 9/22/2011

B-2 If a state believes that its existing (already approved) infrastr ucture SIP is adequate with respect to one or more section 110(a)(2) infras tructure elements (or sub-elements), then the state's SIP submission may be a cer tification that the existing SIP contains provisions that fully address those section 110( a)(2) infrastructure elements (or s ub-elements) as applicable for the 2010 1-hour SO 2 NAAQS. 26 Such certification ( e.g. , in the form of a letter to EPA from the Governor or her/his designee) should cite the applicable provisions in the existing SIP and provide a specific description of how complian ce with each element is achieved. EPA's policy position is that a state's certification made in connection with the 2010 1-hour SO 2 NAAQS should be included in a SIP submittal only afte r the state has provide d public notice and opportunity for public hear ing on its certification. Section 110(a)(2) of the CAA di rects all states to develop and maintain an air quality management infrastructure that includes enfor ceable emission limitations , an ambient monitoring program, an enforcement program, air quality mo deling capabilities, a nd adequate personnel, resources, and legal authority. Section 110(a)(2)(D) also directs SIPs to pr ohibit emissions, from within the state, that contribute significantly to nonattainment in any other state or that interfere with maintenance in any other state, or that in terfere with programs under part C of the CAA to prevent significant deterioration of air quality or to protect vi sibility in any other state. Two elements identified in section 110(a)(2) include requi rements that are not governed by the 3-year submission deadline of section 110(a)(1 ). The requirements pertain to part D, of title I of the CAA, which addre sses plan requirements for nonatta inment areas. Therefore, the following section 110(a)(2) elements are cons idered by EPA to be outside the scope of infrastructure SIP actions: (1) section 110(a)(2)(C) to the extent it refers to permit programs (known as "nonattainment new source re view") required under part D; and (2) section 110(a)(2)(I) in its entirety. EPA does not expect infrastructure SIP submittals to include regulations or emission lim its developed specifically for atta ining the relevant standard. Those submittals are due at the time the nonatt ainment area planning requirements are due (18 months following designation).

26 This certification does not serve as a demonstration for purposes of CAA section 110(l) that the state has in fact attained and maintained the 1-hour SO 2 NAAQS. That demonstration, which is part of a required attainment plan for unclassifiable areas, is specific to the 2010 1-hour SO 2 NAAQS and is addressed elsewhere in our implementation guidance.Public Review Draft 9/22/2011

B-3 Except as described above, subs ections (A) through (M) of se ction 110(a)(2) set forth the infrastructure elements that a SIP should address in order to be approved by EPA. The elements are presented below in context of the 2010 1-hour SO 2 NAAQS.

Section 110(a)(2)(A): Emission lim its and other control measures “Each such plan shall [. . .] includ e enforceable emission limitations and other control measures, means, or tec hniques (including economic incentives such as fees, marketable permits, and aucti ons of emissions rights), as well as schedules and timetables for compliance, as may be necessary or appropriate to meet the applicable requirem ents of this chapter.” EPA would not expect infrastructure SIP submissions to identify nonattainment emissions controls. Emissions limitations and ot her control measures to attain the 2010 NAAQS in areas designated nonattainment for the 2010 1-hour SO 2 NAAQS are on a different schedule from the section 110(a) infrastructure elemen ts and will be reviewed and acted upon through a separate process. However, the infrastructure SIP submission should include a list or table referencing all SO 2 emission reduction measures adopted and relied on by the state to meet other CAA requirements. Such SO 2 emission reduction measures ma y be a required part of a "maintenance track" attainment plan for the SIP submittal due in June 2013. The measures identified by the state should show, through disp ersion modeling, that aff ected areas would be projected to be in compliance with the NAAQS as expeditiously as practicable, which we would expect to be no later than the ye ar 2017. The attainment plan elements are specific to the 2010 1- hour SO 2 NAAQS and are addressed elsewhere in our implementation guidance. There are two issues that generally fall under this part icular element of section 110(a)(2)(A) for which we are not prepared to issu e guidance at this time. They are: (1) how states would need to address previously appr oved emissions limitations that may treat startup, shutdown and malfunction (SSM) events incons istently with our longstanding guidance on excess emissions; and (2) how states would n eed to address previously approved variance provisions and “director’s discre tion” provisions that do not comport with EPA policy. We are currently discussing options for resolving these is sues, taking into consid eration several actionsPublic Review Draft 9/22/2011

B-4 on state provisions relating to SSM and director's discretion in which EPA is currently engaged 27 ( e.g., infrastructure SIPs for Utah and North Dakota). Also, EPA has proposed to enter a settlement agreement that would obligate EP A to respond by August 31, 2012, to a petition for rulemaking filed by the Sierra Club that concerns SSM provisions in 39 states' SIPs . (See notice published in the Federal Register on September 1, 2011, at 76 FR 54465.) Under terms of this "Ozone Settlement Agreement," by August 31, 2012 EPA would either grant or deny the SSM petition with respect to states' i ndividual provisions and further would take final action (such as an SSM SIP Call) with respect to those provisions on which we grant the petition. Nevertheless, in the meantime EPA wishes to provide infrastructure SIP guidance to the extent possible. Therefore, as general guida nce, EPA can advise that states not make infrastructure SIP submissions that rely on previously approved but potentially flawed provisions. Further, we wish to make clear that for infrastructure SIP submissions such as for the 2008 Pb NAAQS, any "new" ( i.e., not already SIP-approved) pr ovisions should be consistent with EPA's longstanding policies on SSM and director's discretion, which are briefly summarized as follows. 28 See page 25652 at http://69.175.53.6/register/2011/may/05/2011- 10995.pdf

. Because excess emissions might aggravate air quality so as to prevent attainment and maintenance of the NAAQS and compliance with other CAA requirements, EPA would view all periods of excess emissions as violations of th e applicable emission limitation. Therefore, new provisions as part of an approvable SIP subm ittal could not exempt from enforcement excess emissions that may occur at a facility during a period of startup or s hutdown. Further, new provisions as part of an approvable SIP s ubmittal could not automatically exempt from enforcement excess emissions claimed to result from an equipment malfunction. In addition, new provisions as part of an approvable SIP su bmittal could not allow a state air director the discretion to determine whether an instance of excess emissions is a violation of an emission limitation, because such a determination could ba r EPA and citizens from enforcing applicable requirements.

27 See e.g., infrastructure SIPs for Utah and North Dakota. EPA has also proposed to enter a settlement agreement that would obligate EPA to respond by August 31, 2012, to a petition for rulemaking filed by the Sierra Club that concerns SSM provisions in 39 states' SIPs . (See notice published in the Federal Register on September 1, 2011, at 76 FR 54465.) 28 For further description of EPA's policy on SSM and director's discretion, see, e.g. , a memorandum dated September 20, 1999, entitled, "State Implementation Plans: Policy Regarding Excess Emissions During Malfunctions, Startup, and Shutdown," from Steven A. Herman, Assistant Administrator for Enforcement and Compliance Assurance, and Robert Perciasepe, Assistant Administrator for Air and Radiation.Public Review Draft 9/22/2011

B-5 Section 110(a)(2)(B): Ambient air quality monitoring/data system “Each such plan shall [. . .] prov ide for establishment and operation of appropriate devices, methods, systems, and procedures necessary to (i) monitor, compile, and analyze data on ambient ai r quality, and (ii) upon request, make such data available to the Administrator.” To meet section 110(a)(2)(B) requirements for this NAAQS, the state should provide in the SIP for a monitoring system to:

 Monitor air quality for SO 2 at appropriate locations th roughout the state using EPA approved Federal Reference Method or equiva lent monitors. States would need to install new SO 2 monitors in accordance with recent revisions to the SO 2 monitoring network requirements.

 Submit data to EPA’s Air Quality System (AQS) in a timely manner, in accordance with EPA's air quality data reporting regulations. See 40 CFR 51.320, "Annual air quality data report."

 Submit approvable annual monitoring plans to EPA that describe how the state has complied with monitoring requirements and explain any proposed changes to the network.

 Provide the EPA Regional Office prior notification of any planned changes to monitoring sites or to the network plan.

Section 110(a)(2)(C): Programs for enforcement, PSD, and NSR “Each such plan shall [. . .] incl ude a program to provide for the enforcement of the measures described in subparagraph (A), and regulation of the modification and construction of any stationary source within the areas covered by the plan as necessary to assure that national ambient air q uality standards are achieved, including a permit program as required in parts C and D of this subchapter.” The Prevention of Significant Deterior ation (PSD) and nonattainment New Source Review (NNSR) programs contained in parts C and D of title I of the CAA, and collectively referred to as the major New Source Review (N SR) program, govern preconstruction review andPublic Review Draft 9/22/2011

B-6 permitting of any new or modified major stationa ry sources of air pollutants regulated under the CAA as well as any precursors to the formation of that pollutant when identified for regulation by the Administrator. 29 The EPA rules addressing these programs can be found generally at 40 CFR 51.166 and 52.21 (for PSD), and 51.165, 52.24, and Part 51, Appendix S (for NNSR). To meet section 110(a)(2)(C) requirements for this NAAQS, the SIP submittal should:

 Reference relevant state and federal regulations that provide for enforcement of SO 2 emission limits and control measures.

 Identify the various state regulations th at govern permitting of new and modified stationary sources (minor and major) of SO 2 in the state.

 Revise its PSD program regulations to a ddress any applicable EPA amendments to SO 2 PSD rules within 3 years from the date of such amendments. For areas subject to a stat e’s SIP-approved PSD program, the state should demonstrate that it is authorized to implement its existing PS D permit program to ensure that the construction and modification of major stationa ry sources does not cause or c ontribute to a violation of the new 1-hour primary SO 2 NAAQS. The state's PSD program s hould ensure that new or modified sources will apply the Best Availa ble Control Technology to reduce SO 2 emissions in accordance with CAA sections 165(a)(3) and (4). The state's PSD program should apply to sources that emit greenhouse gases (GHG) in accordance with EPA's Tailoring Rule. 30 Among other things, the state's PSD program must either: (i) limit PSD applicab ility to GHG-emitting sources by adopting the applicability thresholds included in the Tailoring Rule; or (i i) adopt lower GHG thresholds and show that the state has adequate personnel a nd funding to administer and implement those lower thresholds. Otherwise, the state is directed to remove from EPA’s consideration for approval that portion of the SIP (or SIP submission) for which EPA resci nded our previous approval of the PSD program (in a rulemaking referred to as the "GHG PSD SIP Narrowing Rule"). 31 To request such removal, a state may choose to follow the example of the letter request submitted by South

29 The terms “major” and “minor” categorize a stationary source, for NSR applicability purposes, in terms of an annual emissions rate (tons per year, tpy) for a pollutant. Generally, a minor source is any source that is not “major.” “Major” is defined in the applicable NSR regulations—PSD or nonattainment NSR.

30 Prevention of Significant Deterioration and Title V Greenhouse Gas Tailoring Rule; Final Rule. 75 FR 31514 (June 3, 2010). 31 Limitation of Approval of Prevention of Significant Deterioration Provisions Concerning Greenhouse GasEmitting Sources in State Implem entation Plans; Final Rule, 75 FR 82536 (December 30, 2010).Public Review Draft 9/22/2011

B-7 Carolina. 32 If a state lacks a SIP-approved PSD program , it is subject to a federal implementation plan (FIP), and major stationary sources within its jurisdiction are subject to the federal PSD requirements in 40 CFR 52.21. Some states are subject to a FIP for PSD permitting of all regulated NSR pollutants, and fewer states are su bject to a FIP for PSD permitting that is limited to GHG. Note that a state subject to a FI P for PSD permitting, whether applicable to all regulated NSR pollutants or limited to GHG, remains obligated to adopt and submit a PSD program for EPA approval that applies to all re gulated NSR pollutants, including GHG. Until a state provides such a program, its SIP woul d not be approvable with respect to section 110(a)(2)(C). 33 EPA has historically and recently interpretated that the status of an infrastructure SIP's approval with respect to the state's PSD program would not adversely affect a state's request for redesignation of an ar ea from nonattainment to attainment. In the past, EPA has approved area redesignations without having approv ed infrastructure SIPs, on the basis that infrastructure SIPs do not involve nonattainment requirements, and w ith the expectation that infrastructure SIP requirements regarding PSD will be addressed for those areas once redesignation has become effective. Minor NSR programs are subject to the stat utory requirements in section 110(a)(2)(C) of the CAA, which requires “...regulation of the m odification and constructi on of any stationary source ...as necessary to assure that the [NA AQS] are achieved.” These programs are to be established in each state within 3 years of the promulgation of a new or revised NAAQS. EPA has not proposed to amend the PSD regul ations with regard to the new 1-hour SO 2 NAAQS. As an interim measure, we have issued SO 2 modeling guidance to supplement the guidance contained in EPA’s Guideline on Air Quality Models (40 CFR Part 51, Appendix S), which will assist states and prospective sources in carrying out the analyses necessary to satisfy

32 South Carolina's letter request can be found at http://www.regulations.gov , at EPA-R04-OAR-2010-0721-0006. 33 For sources subject to a FIP for PSD permitting, either the EPA Regional Office or the state acting as EPA's delegate is the permitting authority. EPA recognizes that many states have been implementing a PSD FIP program for some time. When a state is alr eady subject to a FIP for PSD permitting (whether or not the state has been delegated authority to implement the PSD FIP), and EPA di sapproves this element of the state's infrastructure SIP submittal, we expect the permitting authority would simp ly continue implementation of the PSD FIP, and EPA would have no additional FIP obligations. In addition, the state would not be subject to any potential mandatory sanctions in connection with such disapproval, as such sa nctions do not apply to infrastructure SIP deficiencies.Public Review Draft 9/22/2011

B-8 the PSD requirements for SO 2 . 34 That supplemental guidance recommended use of an interim significant impact level (SIL) of 3 ppb for modeling the 1-hour SO 2 impacts of proposed new major stationary sources and major modifications. States may wish to consider use of this recommended interim SIL to help determine the scope of the modeling analysis needed with regard to the 1-hour SO 2 NAAQS. States may also wish to use this recommended interim SIL to determine whether the proposed source’s emissions, in conjunction with other emissions in the area, would cause or contribute to a violation of the 1-hour SO 2 NAAQS.

Section 110(a)(2)(D)(i): Interstate transport provisions “Each such plan shall [. . . ] contain adequate provisions: (i) prohibiting, consistent with the pr ovisions of this subchapter, any source or other type of emissions activity within the state from emitting any air pollutant in amounts which will— (I) contribute significantly to nonatta inment in, or interfere with maintenance by, any other state with resp ect to any such national primary or secondary ambient air quality standard, or (II) interfere with measures required to be included in the applicable implementation plan for any other state unde r part C of this subchapter to prevent significant deterioration of air quality or to pr otect visibility.” Section 110(a)(2)(D)(i) provide s for SIPs to include provisi ons prohibiting any source or other type of emissions activity in one state fr om contributing significantly to nonattainment, or interfering with maintenance, of the NAAQS in another state. (The preceding sub-elements, from subsection (2)(D)(i)(I), respectively refer to what may be called prongs 1 and 2.) Further, this section directs SIPs to in clude provisions prohibiting any s ource or other type of emissions activity in one state from interfering with measures required to prevent significant deterioration of air quality, or from interfering with measures required to protect visibility ( i.e. , measures to

34 See EPA memorandum titled “Guidance Concerning the Implementation of the 1-hour SO 2 NAAQS for the Prevention of Significant Deterioration Program,” dated August 23, 2010. In this guidance, EPA recommends an interim screening tool to help determine when a source’s proposed emissions increase would be considered to have a significant hourly ambient impact as part of the required source imp act analysis for the new 1-hour SO 2 NAAQS.Public Review Draft 9/22/2011

B-9 address regional haze) in any state. (The prec eding sub-elements, from subsection (2)(D)(i)(II), respectively refer to what ma y be called prongs 3 and 4.) To address prongs 1 and 2 of section 110(a)(2 )(D), the state’s submission should include an assessment whether or not emissions from SO 2 sources located close to state borders ( e.g. , within the 50-km modeling domain us ed to assess source-specific SO 2 impacts 35 ) have associated interstate transport impacts and if so, address th e impacts. The assessment might include, but is not limited to, information concerning emissions in the state, meteorolog ical conditions in the state and the potentially impacted states, monitored ambient concentrations in the state and the potentially impacted states, the distance to the ne arest area that is no t attaining the NAAQS in another state, and air quality modeling. For areas designated as unclassifiable, this assessment could also be informed by the analysis conducted to satisfy 110(a)(1) maintenance SIP requirements. EPA has proposed several rules that will or may reduce emissions of SO 2 , such as the CSAPR, the Industrial Boilers MACT, and the MATS. The emissions re ductions achieved under these rules should resu lt in reduced impacts from transported SO 2 emissions and states should consider these measures, among others measur es, in fulfilling the se ction 110(a)(2)(D)(i)(I) requirements. Under section 110(a)(2 )(D)(i)(II), the PSD sub-elemen t (prong 3) may be met by the state’s confirmation in a SIP submission that ne w major sources and major modifications in the state are subject to PSD and (if the state contains a nonattainment area for the relevant pollutant) NNSR programs that implement the 2010 1-hour SO 2 NAAQS. 36 As described more fully under element (C) of this infrastructure SIP guidance, if a state lacks a SIP-approved PSD program, it is subject to a FIP, and major stationary sources within its jurisdiction are subject to the federal PSD requirements in 40 CF R 52.21. States relying on a FIP (whether applicable to all regulated NSR pollutants or lim ited to GHG) to satisfy the PSD subelement of section 110(a)(2)(D)(i )(II) have programs that are technically deficient and not approvable. Although these programs are defici ent and these states have not "submitted" anything to EPA, EPA would not be required to take further ac tion with respect to this sub-

35 See Section 5 Modeling domain in Appendix A, “Modeling Guidance for Nonattainment Areas and Section 110(a)(1) Plans.” 36 Memorandum issued by William T. Harnett, Direct or, OAQPS/AQPD, “Guidance on SIP Elements Required Under Sections 110(a)(1) and (2) for the 2006 24-Hour Fine Particle (PM 2.5 ) National Ambient Air Quality Standards (NAAQS),” dated September 25, 2009.Public Review Draft 9/22/2011

B-10 element because the federal ru les represent a FIP that fully addresses PSD. In addition, mandatory sanctions would not apply because the deficiencies are neither with regard to a required submittal under part D nor in response to a SIP call under section 110(k)(5). As described in this infrastructure SIP guidance for element (C), such states remain obligated to adopt and submit a PSD program for EPA approval th at applies to all regulated NSR pollutants. Until a state provides such a program, its SIP wo uld not be approvable with respect to prong 3, the PSD sub-element of s ection 110(a)(2)(D)(i)(II). The sub-element providing for protec tion of visibility (prong 4) under section 110(a)(2)(D)(i)(II) may be met by the stat e’s confirmation that an approved regional haze SIP (or FIP) is in place. The development of th e regional haze SIPs occurred in a collaborative environment among the states. Through this pr ocess, the states coordinated on emissions controls to protect visibility on an interstate ba sis. The regional haze rule also specifically requires that a state participating in a regional planning process include "a ll measures needed to achieve its apportionment of emission reduction ob ligations agreed upon through that process." 37 We anticipate that an approved regional haze SIP (or FIP) addressing this requirement will ensure that emissions from sources within the st ate are not interfering with measures to protect visibility in other states.

Section 110(a)(2)(D)(ii): Interstate and international transport provisions “Each such plan shall [. . .] contain adequate provisions insuring compliance with the applicab le requirements of sections 126 and 115 (relating to interstate and internatio nal pollution abatement).” Section 126(a) of the CAA directs each SIP to include provisions requiring a new or modified source to notify neighborin g states of potential impacts fr om the source. States with SIP-approved PSD programs should have a regulato ry provision in place, consistent with 40 CFR 51.166(q)(2)(iv), that requires such notification of other stat e and local agencies. States relying on federal program requirements of 40 CFR 52.21(q), which provide for notification of affected state and local air agencies, to satisfy this element have programs that are technically deficient and not approvable. Although these programs are defici ent and these states have not

37 40 CFR 51.308(d)(3)(ii).Public Review Draft 9/22/2011

B-11 "submitted" anything to EPA, EPA would not be required to take further action with respect to this element because the federal rules represent a FIP that fully addresses the notification issue. In addition, mandatory sanctions would not appl y because the deficiencies are neither with regard to a required submittal under part D nor in response to a SIP call under section 110(k)(5). As described in this infrastructure SIP guidance fo r element (C), such states remain obligated to adopt and submit a PSD program for EPA approval th at applies to all regulated NSR pollutants, including GHG. Until a state provides such a pr ogram, its SIP would not be approvable with respect to section 110(a)(2)(D)(ii). Sections 126(b) and 126(c) of the CAA affect a state only if the Administrator has been petitioned to make a finding of vi olation that is related to ei ther interstate transport or international transport of emissions from sources in the state. Thus, unless a state has been the subject of such a petition, the state has no con tinuing obligations under sections 126(b) or 126(c). Section 115 of the CAA authori zes the Administrator to requir e a state to revise its SIP under certain conditions to alle viate international transport. Because there are no pending actions pursuant to section 115 of the CAA, at this time EPA has no reason to approve or disapprove any existing state rules with regard to sect ion 115 provisions.

Section 110(a)(2)(E): Adequate p ersonnel, funding, and authority “Each such plan shall [. . .] provide: (i) necessary assurances that the state (or, except where the Administrator deems inappropriate, the general purpose local government or governments, or a regional agency designated by the state or general purpose local governments for such purpose) will have adequate personne l, funding, and authority under state (and, as appropriate, local) law to carry out such implementation plan (and is not prohibited by any provision of Federal or state law from carrying out such implementation plan or portion thereof), (ii) requirements that the state comp ly with the requirements respecting state boards under section 128, andPublic Review Draft 9/22/2011

B-12 (iii) necessary assurances that, where the state has relied on a local or regional government, agency, or instrume ntality for the implementation of any plan provision, the state has responsibili ty for ensuring adequate implementation of such plan provision.”

The SIP should assure that the state has ade quate authority under it s rules and regulations to carry out the state's SIP obligat ions with respect to the 2010 SO 2 NAAQS and to revise the SIP as necessary. See EPA's regulations at 40 CFR Part 51, subpart L (“Legal Authority”) and subpart O (“Miscellaneous Plan Cont ent Requirements”). For example:

 In accordance with EPA's regulations at subpa rt L, the SIP should show that the state has the legal authority to carry out the pl an; the provisions of the state's laws or regulations that provide that authority are to be specifically identified in the SIP, and copies of the laws or regulations should be included in the SIP submittal. See 40 CFR sections 51.230 through 51.231.

 A state may assign responsibility for ca rrying out a portion of a SIP to a state government agency other than the state air pollution control agency, if the SIP demonstrates that such other agency has th e necessary legal authority. Similarly, the state may authorize a local agency to carry out a SIP or portion of a SIP within the local agency's jurisdiction, if the SIP dem onstrates that the local agency has the necessary legal authority; however, the authorizing state is not relieved of responsibility for ca rrying out the SIP. See 40 CFR 51.232, "Assignment of legal authority to local agencies." In accordance with EPA's regulations at s ubpart O, the SIP submittal should include copies of rules and regulati ons that show that the st ate has adopted the emission limitations and other measures necessary fo r attainment and maintenance of the 2010 SO 2 NAAQS. See 40 CFR 51.281, "Copies of rules and regulations." Further, the SIP should assu re that the state has adequa te funding and personnel to implement the SO 2 NAAQS. See EPA's regulations at 40 CFR Part 51, subpart M ("Intergovernmental Consu ltation") and subpart O ("Mi scellaneous Plan Content Requirements"). For example:Public Review Draft 9/22/2011

B-13  In accordance with EPA's regulations at subpart M, the SIP should identify the organizations that will participate in developing, implementing, and enforcing the SIP. The SIP should identify the responsibil ities of such organizations and include related agreements among the organizat ions. See 40 CFR 51.240, "General plan requirements."

 In accordance with EPA's regulations at subpa rt O, the SIP should describe resources for carrying out the SIP. Resources to be de scribed include: (1) those available to the state (and local agencies, where appropriate) as of the date of SIP submittal; (2) those considered necessary during the 5 years fo llowing SIP submittal; and (3) projections regarding acquisition of the described resources. See 40 CFR 51.280, "Resources."

Section 110(a)(2)(F): Stationary source monitoring and reporting “Each such plan shall [. . .] requi re, as may be prescribed by the Administrator:

(i) the installation, maintenance, and replacement of equipment, and the implementation of other necessary steps, by owners or operators of stationary sources to monitor emissions from such sources, (ii) periodic reports on the nat ure and amounts of emissions and emissions-related data from such sources, and (iii) correlation of such reports by the state agency with any emission limitations or standards established pursuant to this chapter, which reports shall be available at reasonable times for public inspection.” The SIP should provide cita tions to the state's regulat ions for source monitoring, recordkeeping, and reporting re quirements applicable to SO 2 . In accordance with EPA regulations at 40 CFR Part 51, subpart K ("Source Surveillance"), the SIP should provide for monitori ng the status of sources' compliance with the SO 2 NAAQS. For example, the SIP should incl ude provisions for owners or operators of stationary sources to maintain r ecords of emissions and other information as may be necessary to enable the state to determine whether the source s are in compliance, and the SIP should furtherPublic Review Draft 9/22/2011

B-14 include provisions for the sources to periodically report that in formation to the state. See 40 CFR 51.211, "Emission reports and recordkeeping." The SIP should include provisions for stationary sources subject to the SO 2 NAAQS to install, calibrate, maintain, a nd operate equipment for continuously monitoring and recording emissions, and the SIP should further include pr ovisions for the sources to maintain the monitoring data and periodica lly submit it to the state. See 40 CFR 51.214, "Continuous emission monitoring." In accordance with EPA regulations at 40 CFR Part 51, subpart A ("Air Emissions Reporting Requirements") and subpart Q ("Reports "), the responsible state agency should analyze the SO 2 emissions data and correlate such data with applicable emission limitations or standards. The SIP should provide for periodic reporting of emissi ons inventory data by the state to the Administrator (through the ap propriate Regional Office). See e.g. , 40 CFR 51.321. All reports should be made available to the public.

Section 110(a)(2)(G): Emergency episodes “Each such plan shall provide for author ity comparable to that in section 303 of this title and adequate contingen cy plans to implement such authority.” Section 303 of the CAA provide s authority to the EPA Admi nistrator to restrain any source from causing or contributi ng to emissions which present an “imminent and substantial endangerment to public health or welfare, or the environment.” Each state should have an approved SO 2 emergency episode plan in place. The pl an should be updated as appropriate for purposes of implementing the 2010 SO 2 NAAQS. As part of the infrastructure SIP submittal, the plan should be consistent with emergenc y episode requirements in 40 CFR 51.150 through 51.153. Appendix L to 40 CFR Part 51 includes ex ample regulations for Prevention of Air Pollution Emergency Episodes and can be used fo r an example. The emergency episode plan should include provisions to trigger successive acti ons to prevent air quality concentrations from reaching the “significant harm level” (SHL), which represents an imminent and substantial endangerment to public health. Unless EPA in the future proposes and promul gates regulations to revise the emergency episode requirements related to section 110(a)(2 )(G), EPA recommends that states follow the guidance as stated in 40 CFR 51.150.Public Review Draft 9/22/2011

B-15 To address the section 110(a)(2)(G) element, states with air quality control regions identified as either Priority I, Priority IA, or Priority II unde r the “Prevention of Air Pollution Emergency Episode” rules at 40 CFR 51.150 should develop emergency episode contingency plans.

 A Priority I Region means any area with ambient concentration greater than 100 μg/m 3 (0.04 ppm) annual arithmetic mean; 455 μg/m 3 (0.17 ppm) 24-hour maximum.

 A Priority IA Region means any area that is classified as Priority I primarily because of emissions from a single point source.

 A Priority II Region means any area that is not classified as a Priority I Region and has ambient concentrations between 60-100 μg/m 3 (0.02-0.04 ppm) annual arithmetic mean; 260-445 μg/m 3 (0.10-0.17 ppm) 24-hour maximum; any concentration above 1,300 μg/m 3 (0.50 ppm) 3-hour average.

 Areas that do not meet the above criteria are classified as Pr iority III and are not required to submit contingency plans under the regulations. Significant harm level for SO 2 : In accordance with 40 CFR 51.151, each plan for a Priority I region should include a contingency plan that provides for taking action necessary to prevent ambient pollutant concentrations at any location in the region fr om reaching the SHL for SO 2 of 2.620 μg/m 3 (1.0 ppm) 24-hour average. Exemption of Contingency Plans for areas designated as “attainment” and “unclassifiable” : Per 40 CFR 51.152(d)(1), areas designa ted as attainment or unclassifiable under section 107 of the CAA may, at the Admini strator’s discretion, be exempted from the requirements of 40 CFR 51.152 as the regulation relates to the requirement to develop contingency plans required under Prio rity I, IA, and II Regions. Appendix L to 40 CFR Part 51 provides example regulations that states can use to inform decisions concerning air pollution emergency episodes. The exam ple regulations provided in Appendix L reflect generally rec ognized ways of preventing air pollution from reaching levels that would cause imminent and substantial endanger ment to the health of persons located within affected areas. Subpart H of 40 CFR Part 51 directs stat es to have emergency episode plans that contain alert levels, but it does not require adoption of the regula tions as stated in Appendix L.Public Review Draft 9/22/2011

B-16 Section 110(a)(2)(H): Future SIP revisions “Each such plan shall [. . .] prov ide for revision of such plan— (i) from time to time as may be necessa ry to take account of revisions of such national primary or secondary ambient air quality standard or the availability of improved or more expeditious methods of attaining such standard, and (ii) except as provided in paragraph (3)(C), whenever the Administrator finds on the basis of inform ation available to the Admi nistrator that the plan is substantially inadequate to attain the na tional ambient air quality standard which it implements or to otherwise comply with any additional requirements established under this chapter (CAA).” The SIP should provide citations to the state regulatory provi sions requiring the state to (1) revise its CAA section 110 plan from time to time as may be necessary to take into account revisions of such primary or secondary NAAQS or the availability of improved or more expeditious methods of attaining such standards; and (2) revise its CAA section 110 plan in the event the Administrator finds the plan to be s ubstantially inadequate to attain the NAAQS. See 40 CFR 51.104, “Revisions.” Section 110(a)(2)(I): Nonattainment area plan or plan revision under Part D “Each such plan shall [. . .] in the case of a plan or plan revision for an area designated as a nonattainment ar ea, meet the applicable requirements of part D of this subchapter (rela ting to nonattainment areas).” As noted in the introductory text of this a ppendix, EPA does not expect infrastructure SIP submissions to address subsecti on 110(a)(2)(I). Nonattainment area plans required under part D are required on a different schedu le from the section 110 infrastructure elements and will be reviewed and acted upon th rough a separate process.Public Review Draft 9/22/2011

B-17 Section 110(a)(2)(J): Consultation with governme nt officials, public notification, PSD and visibility protection “Each such plan shall [. . .] me et the applicable requirements of section 121 of this title (rel ating to consultation), secti on 127 of this title (relating to public notification), and part C of this subchapter (relating to prevention of significant deteriorati on of air quality and visi bility protection).”

The SIP should reference the state rules th at provide a process of consultation with general purpose local governments, designated organizations of elected officials of local governments, and any federal land manager having authority over federal la nd to which the plan applies, consistent with the requirements of CAA section 121. The SIP should provide citations to regulations requiring the state to regularly notify the public of: instances or areas in which any prim ary NAAQS was exceeded; the associated health hazards; and ways in which the public can particip ate in regulatory and other efforts to improve air quality. See 40 CFR 51.285, “Public notification.” Pursuant to the CAA, a SIP should allow a state to implement any new PSD requirements that are triggered upon the effective date of a ny new NAAQS. However, sources in a state may be subject to the federal PSD requirements pursuant to 40 CFR 52.21, if a state does not have a SIP-approved PSD program. As described in this infrastructure SIP guidance for element (C), such states remain obligated to adopt and s ubmit a PSD program for EPA approval that applies to all regulated NSR pollutants, including GHG. Until a state provides such a program, its SIP would not be approvable with re spect to secti on 110(a)(2)(J). With regard to the requirement of the plan to meet the applicable requirements for visibility protection, EPA would notexpect to treat this provisi on as applicable for purposes of the infrastructure SIP approval process. EPA r ecognizes that states are subject to visibility protection and regional haze prog ram requirements under part C of the Act (which includes sections 169A and 169B). However, in the ev ent of the establishment of a new primary NAAQS, the visibility protection and regional haze program requirements under part C do not change. Thus, EPA has concluded that there are no new applicable visibility protection obligations under section 110(a)(2 )(J) as a result of the 2010 SO 2 NAAQS.Public Review Draft 9/22/2011

B-18 Section 110(a)(2)(K): Air quality modeling/data “Each such plan shall [. . .] provide for— (i) the performance of such air quality modeling as the Administrator may prescribe for the purpose of predicting the effect on ambient air quality of any emissions of any air pollutant for whic h the Administrator has established a national ambient air quality standard, and (ii) the submission, upon request, of da ta related to such air quality modeling to the Administrator.”

The SIP should demonstrate that the state ha s the authority and tec hnical capability to conduct air quality modeling in order to assess th e effect on ambient air quality of relevant pollutant emissions; and that the state can provide relevant data as part of the permitting and NAAQS implementation processes. The SIP shoul d also provide that, upon request, the state will submit current and future data relating to su ch air quality modeling to the Administrator. EPA anticipates that the predomin ant type of air quality modeling to be conducted with respect to implementing the SO 2 NAAQS will be source-oriented dispersion modeling with models such as AERMOD.

Section 110(a)(2)(L): Permitting fees “Each such plan shall require the owner or operator of each major stationary source to pay to the permitting authority, as a condition of any permit required under this chapter, a fee sufficient to cover— (i) the reasonable costs of review ing and acting upon any application for such a permit, and (ii) if the owner or operator receiv es a permit for such source, the reasonable costs of implemen ting and enforcing the term s and conditions of any such permit (not including any court cost s or other costs associated with any enforcement action), until such fee requirement is superseded with respect to suchPublic Review Draft 9/22/2011

B-19 sources by the Administrator’s appro val of a fee program under subchapter (title) V of this chapter.” The SIP should provide citations to the regul ations providing for collection of permitting fees under the state’s EPA-approved title V permit program. See 40 CFR 70.9 (“Fee determination and certification” ); 40 CFR Part 70, Appendix A (“ Approval Status of State and Local Operating Permits Programs”).

Section 110(a)(2)(M): Consultation/participation by affected local entities “Each such plan shall [. . .] prov ide for consultation and participation by local political subdivisions affected by the plan.” To satisfy this element (M), and in accord ance with EPA's regulations at 40 CFR Part 51, subpart M ("Intergovernmental Cons ultation"), the SIP should identi fy the organizations that will participate in developing, implementing, and enforc ing the SIP. Further, the SIP should identify the responsibilities of such organizations and include related agreements among the organizations. See 40 CFR 51.240, "G eneral plan requirements." The SIP should identify policies or procedur es requiring consultati on and participation by local political subdivisions affected by the SIP. For example, the SIP should provide a citation to the state regulations that provide notice and oppo rtunity for public hear ing in accordance with EPA regulations at 40 CFR Part 51, subpart F ("Pr ocedural Requirements"). Prior to submitting a SIP revision or a compliance schedule, the CAA and EPA regulations dire ct states to provide notice, provide the opportunity to submit written comments, and allow the public the opportunity to request a public hearing. See 40 CFR 51.102, "Public hearings."Public Review Draft 9/22/2011

C-1 Appendix C Guidance on Non-modeling Technica l Demonstration of Attainment A state may have counties that do not ha ve large sources, or any sources, of SO 2 . For these counties, refined modeling may not be needed to show that al l or portions are in attainment of the SO 2 NAAQS. This section offers guidan ce for conducting a non -modeling technical demonstration in cases where there are: (a) existing modeling results of nearby SO 2 sources, or (b) no existing modeling results or plans to model nearby (i.e. within 50 km) SO 2 sources. At any time during the SIP process when there are questions regarding non-modeling technical demonstrations or interpretation of this gui dance, the appropriate EPA Regional Modeling Contact should be consulted. The firs t step in both cases is to map the SO 2 sources surrounding the county, extending out to 50 km be yond the county boundaries, if necessary. A. Approach with existi ng modeling of nearby sources If there are dispersion model results of those SO 2 sources within the buffer around the county boundary from other modeling efforts (i .e., modeling of nonattain ment areas or large sources), those results may be used to determine the spatial extent of the impact of a particular source or sources. If a nearby s ource, or sources, has modeled SO 2 NAAQS violations, singularly or in a cumulative sense, the following questions s hould be considered:

1. How far do those violations occur from the sources? 2. How far are these sources from the county in question?

If violations occur at a distance that does not impact the county in que stion or parts of the county not already part of an existing nonattainment area, then it may be a reasonable conclusion that the sources will not cause or contribute to a viol ation in the portion of the county in question and that the unaffected portions of the county could be considered in attainment with the 1-hour SO 2 standard. B. Approach with no m odeling of nearby sources In the absence of any prior modeling efforts, analysts may need to rely on their best professional judgment and consider the following questions for each SO 2 source within the 50 km county buffer:

1. How far is the source from the county in question? 2. What is the maximum allowable emission rate of the source? More emissions mean higher concentrations. 3. If the source has stacks, what are the stack pa rameters (height, temperature, exit velocity, and diameter)? A short stack may have lo cal impacts but may not have impacts that extend that far, while a tall stack will have impacts farther away. If there are any available modeled results for similar stacks, what are their impacts and can they inform any nonattainment problem associated with the source in question?Public Review Draft 9/22/2011

C-2 4. If the source has fugitive emissions, how far can the impacts from those sources potentially extend? 5. Would downwash play a role in the dispersion of SO 2 from the source such that it impacts the county in question? 6. What are the terrain features around the s ource and county in question? Terrain can affect the travel of a plume from a source. 7. What is the meteorology around the source? Meteorology, together with terrain can influence the impact of a source in a particul ar location. A wind rose may be useful for this question to see if the wind blows fr om any of the sources toward the county. Based on the answers to the questions above, an alysts should then ask “Can this source potentially cause or contribute to a violation of the 1-hour SO 2 NAAQS in this county?” If the answer to that question is “no,” for all of the sources thought to influence a county’s attainment status, then it may be a reasonable conclusion th at the county in questio n is in attainment. However, if there is a question th at a source could cause or contribute to a vi olation of the 1-hour SO2 NAAQS in the county, then it may be necessa ry to perform refined dispersion modeling of the sources thought to influence the county. C. Example of non-modeling approach Figure C.1 shows an example of the met hodologies outlined above for Collingsworth County, TX. This example is fo r illustrative purposes only. In Figure C. 1, the total 2005 NEI SO 2 point source emissions in tons per year ar e shown for each surrounding county. While the displayed emissions are from the NEI, the exer cise should be carried out using the maximum allowable or potential to emit emissions. Also shown in Figure C.1 is a 50 km buffer around Collingsworth County. The colore d dots represent individual SO 2 facilities with colors denoting 2005 NEI annual SO 2 emissions (tons). In Figure C.1, it can be seen that there are a few 100+ ton emitters near the 50 km buffer of Collingsworth County (i.e., only in Gray a nd Beckham Counties). Other than those two counties, all of the other c ounties within the 50 km buffer of Collingsworth County contain sources that are below 100 tons. If modeling was done for the 100+ ton sources in Gray and Beckham Counties, the existing mo deling could show if there are any predicted violations that extend into Collingsworth County (See Section A). If the results indicate such potential violations in Collingsworth County, then porti ons of Collingsworth County may already be designated as nonattainment as part of the overall ar ea. The attainment stat us of the remainder of Collingsworth County could be analyzed using th e methodology described in Section B. If existing modeling does not show modeled violati ons in Collingsworth County, the attainment status for the entire county could be determ ined using methodology described in Section B. Also shown in Figure C.1 are two wind ro ses showing 2006-2010 data for the National Weather Service ASOS stations in the area (i.e., Borger, TX in the northwest and Clinton, OK in the east). These wind roses could be used in the analyses of th e other counties around Collingsworth County. Given that most of the surrounding counties contain emissions sources of less than one ton, they should not present a non attainment problem for Collingsworth County. Also, given that the 30 ton emitter in Greer County, OK is outside the 50 km buffer ofPublic Review Draft 9/22/2011

C-3 Collingsworth County, it may not present a nona ttainment problem in Collingsworth County given the distance from the county and prevailing wind patterns. If ther e is any question about the potential impact of a source to a low em itting county’s nonattainment status the seven questions in Section B sh ould be considered. A similar approach could be applied in the other low emitting counties (e.g., Wheeler, Donley, Hall, etc).

Figure C.1. Illustrative example of non-modeli ng technical analysis for Collingsworth County, TX.