MEMORANDUM UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711



## MAR 202015 OFFICE OF AIR QUALITY PLANNING AND STANDARDS



### SUBJECT: Updated Guidance for AreaDesignations for the 2010 Primary Sulfur DioxideNational AmbientAir Quality Standard

FROM: StephenD. Page Director

TO: Regional Air Division Directors, Regions 1

- 10

The purpose ofthis memorandum is toprovide inf ormation onthe schedule andprocess for designating
areas for the 2010 primary sulfurdioxide (S02) national ambientair quality standard (NAAQS). In addition, it identifies factors for determining the boundaries for S02areas designated nonattainment, attainment and unclassifiable. We recommendthatstates and tribes considerand address these factors when identifying boundaries for anyupdated area designationrecommendations they choose to submit forthe 2010 S02NAAQS. Please share this informationwith the state and tribal agencies in your region. As explained below, this guidance updates and replaces theprevious designation guidance for the 2010 S02NAAQS, which was issued onMarch 24,201 1. In assessing the appropriate designation for a given area, the EPA will considerthe state's previous designationrecommendations and any updated recommendations, as well as any additional relevantinformationthatwe receive.

On June 2, 2010, then-Administrator Jackson signed the revised primary S02NAAQS (75 FR35520, June 22, 2010) after review ofthe existing primary S02standardsissuedin 1971. TheEPA established the revised primary S02standard at 75 parts per billion (ppb) which is met at a monitoring site when the 3-year average ofthe 99thpercentile ofdaily maximum 1-hour concentrations does not exceed 75 ppb

.The Administrator determined that this is the level necessary to provide protection ofpublic health with an adequate margin ofsafety, especially for children, the elderly and those with asthma. These groups are particularly susceptible to the health effects associated with breathing S02

. OnAugust 5, 2013, the EPApublished a notice announcing designations of29 areas in 16 states as nonattainrnentfor the 2010 S02standard, based oncertified ambient air quality monitoring datafor the years 2009- 2011 that showed these areas were violating the standard (78 FR47 191)

.However, atthat time theEPAwas notyetpreparedto issue designations for the remaining areas. With stakeholder input, theEPA developed andproposedthe S02DataRequirements Rule (DRR) thatwould require states to gather and submitto the EPA additional information characterizing S02 airquality in areas with larger
sources ofS02emissions. (79 FR27445). TheEPA intends to usethis information to inform the designations ofthese areas. In the S02 DRR, asproposed, airagencies implementingthe 1-hour S02 standard would have the choice to use eithermonitoring ormodelingto characterize S02air quality in

Internet Address (URL) • http://www.epa

.gov Recycled/Recyclable • Printed whh V egetable 0 11 Based Inks on Recycled Paper (Minimum 25% Postconsumer)the vicinity ofpriority S02 sources, and submit the modeling and/or monitoring results to the EPA on the schedule specified in the rule. Followingthe initial August 2013 designations, three lawsuits were filed against the EPA in different U.S. District Courts, alleging that the agency had failed to perform a nondiscretionary duty under the CleanAir Act (CAA) by not designating all portions ofthe country by the June 2013 deadline. In an effort intended to resolve the litigation in one ofthose cases, plaintiffs Sierra Club and the Natural Resources Defense Council and the EPA filed with the U.S. District Court for the Northern District of California a proposed consent decree that specified a schedule for the EPA to complete the remaining S02designations for the rest ofcountry in three additional rounds. On March 2, 2015, the Court entered the consent decree andissued an enforceable order for the EPA to completethe area designations according to the consent decree schedule.

General Approach and Schedule

Pursuantto the court order, the EPA must complete the remaining designations on a schedule that contains three specific deadlines. By no later than July 2, 2016 (16 months from the court's order), the EPA must designate two groups ofareas: (I) areas that have newly monitored violations ofthe 2010 S02 standard and (2) areas that contain any stationary source that according to the EPA's Air Markets Database either emitted more than 16,000 tons ofS02 in 2012 or emitted more than 2,600 tons ofS02 and had an annual average emission rate ofat least 0.45 lbs S02/mmBtu1in 2012 and that has not been announced (as ofMarch 2, 2015) for retirement. 2 The last two deadlines for completing remaining designations are December 31, 2017, and December 31, 2020. The designations completed by these later deadlines are expected to be informed by information provided by states pursuantto the anticipated S02 DRR.3 However, even ifthe S02 DRRis notfinalized, the EPA must still complete designations pursuantto these deadlines.

In the time since states submitted their original designations recommendations in 20II, they may have obtained additional monitoring and/or modeling information that may be relevant for future designations. The CAA section 107(d) does not require states to submitupdated recommendations. However, ifstates would like to submitupdated designation recommendations for the EPA to consider inthe next rounds ofdesignations, we will consider such information.

Forthe round ofdesignations to be completed by July 2, 2016, we request that states provide updated recommendations and supporting information to the EPA by September 18, 2015, to assure that the information can be fully considered bythe EPA. Ifthe EPA intends to modify any state's designation recommendation (original orupdated), we will notify the state no later than 120 days prior to promulgatingthe final designations (e.g., no later than March 2, 2016, for designations due to be promulgated on orbefore July 2, 2016). States will then have an opportunity to comment on the EPA's intended modifications and provide additional information for the EPAto consider. While the language

1 The abbreviation "lbs/mmBtu" means pounds per one million British thermal units. 2 A stationary source with a coal-fired unit that as ofJanuary I, 20I0, had a capacity ofover 5 megawatts that otherwise meets the emissions criteria, is excluded from the July 2, 20 !6, deadline ifit had announced by March 2, 2015, that it will cease burning coal at that unit through acompany public announcement, public utilities commission filing, consent decree, public legal settlement, final state or federal permit filing or other similar means ofcommunications. 3 As a legal matter, the deadlines in the court order apply even ifthe EPA does not finalize the SO, DRR. However, the general approach described in this memorandum reflects our expectation that the EPA will in fact finalize the S02 DRR. 2in section I07 specifically addresses states, we intend to follow the same process for tribes, pursuant to section 30l(d) ofthe CAA and the Tribal Authority Rule (40 CFR Part 49). Therefore, we intend to designate tribal areas, in consultation with the tribes, on the same schedule as state designations. Ifa state ortribe does not submit an updated designation recommendation, the EPA will promulgate the designations that it deems appropriate after considering the originally submitted recommendation and any relevant additional information available to the EPA.

The states and tribes that choose to submit updated recommendations should identify areas as attainment, nonattainment orunclassifiable on the basis ofcurrently available information. The EPA intends to send "120-dayletters" to selected tribes by January 22,2016 (and not later than March 2, 2016) notifying them ofthe EPA's intended designation decisions. !fastate or tribe has additional information that it wants the EPA to consider in response to a 120-day letter, we request that such information be submittedby April 8, 2016. This will help ensure that the EPA can fully consider any such informationprior to issuing final designations. Also, although not required by statute, in order to consider public input in the designation process, we plan to provide a 30-day public commentperiod immediately following issuance ofthe EPA's 120-day letters responding to the recommendations made by states and tribes. Attachment I is the anticipated schedule for the round ofdesignations that must be completed by July 2, 2016.

We recognize that the timeline for designations by July 2, 2016, does not provide for establishment and
use ofdata from new ambient monitors. Therefore, we anticipate that in many areas the most reliable information for informing these designations will be based on source modeling. The EPA has issued guidance on the use ofsource modeling for this purpose in the S02NAAQS Designations Modeling Technical Assistance Document (Modeling TAD).4
Following this next round, the EPA is also required by the court orderto complete designations for remaining areas in up to two additional rounds. According to the court order, the EPA must sign for publication in the FederalRegister no later than December 31, 2017, designations for remaining undesignated areas in which, by January I, 2017, states have not installed and begun operating an appropriate S02 monitoring network meeting the EPA specifications referenced in the EPA's anticipated S02 DRR. We expect this round to cover mostremaining undesignated areas in the nation

- those for which states chooseto follow the modeling approach under the anticipated S02 ORRto address impacts from larger S02 sources, and those which do not contain S02 sources that would require further characterizationunder the anticipated S02 ORR. Finally, by no later than December 31, 2020, the EPA must issue designations for all remaining undesignated areas. This final round would cover areas for which states choose to follow and timely implement the monitoring approach under the anticipated S02 ORR. We will provide more information regarding the approach and schedule for the remaining rounds ofdesignations in the future.

When consideringboundaries for updated area designation recommendations, the EPA recommends that states and tribes analyze and consider the following five factors: ambient air quality data or dispersion modeling, emissions and emissions-related data, meteorology, geography/topography andjurisdictional boundaries. (See Attachment 2). In addition, the EPA has provided two TAOs to assist states and tribes with assessing modeling and monitoring datawhen determining ifan area is meeting or not meeting the

4 The Modeling TAD is available on the EPA's website at http://www.epa.gov/airqualityl.vu!furdioxide/pdf,/S02ModelingTAD.pdf 3!-hour S02 standard. These documents can be found on the EPA's website at 

### http:1 

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epa.gov/ airqual itylsulfurdioxide/implement.htmi. Identifying an Areathat is in Violation ofthe S02NAAOS

Section 107(d)(l) ofthe CAA defines an area as "nonattainment" ifit is violating the NAAQS or ifit is contributing to a violation in a nearby area. Thus, the first step in making designation decisions is to identify areas for which monitoring data or appropriate modeling information indicate a violation ofthe NAAQS.


### Monitor-based Violations. In assessing whether monitoring data indicate a violation, the EPA intends to
use the most recent three consecutive years ofquality-assured, certified ambient air quality data in the EPA Air Quality System (AQS)5using data from Federal Reference Method and Federal Equivalent Method monitors that are sited and operated in accordance with 40 CFR Parts 50 and 58. Procedures for using monitored air quality data to determine whether a violation has occurred are given in 40 CFRPart 50 Appendix T, as revised in conjunction with the 20I0 S02 NAAQS. We expect that in providing any updated recommendations to the EPA for the areas to be designated by July 2, 2016, states and tribes would review available S02 monitoring data fi·om 2012-2014. Prior to the EPA issuing letters to states and tribes concerning any intended modifications to state recommendations, certified S02 monitoring data from 2015 may become available. Ifthis is the case, the EPA intends to also consider certified 2015 S02 ambient air quality monitoring data in formulating any intended modifications to state and tribal recommendations.

Ambient air quality monitoring data affected by exceptional events may be excluded from use in identifying a violation ifthey meet the criteria for exclusion, as specified in the final rule "Treatment of Data Influenced by Exceptional Events" (72 FR 13560; March 22, 2007) codified in 40 CFR parts 50 and 51. In section VII.B ofthe S02NAAQS final rule preamble, we discussed schedules for states and tribes to flag data influenced by exceptional events and submitrelated documentation specifically for S02 dataused in the initial designations process. As previously noted, the EPA did not designate all
areas ofthe country in August 2013 and, consistent with the court order, intends to complete designations in multiple rounds beginning on or about July 2, 2016, through on or about December 31, 2020. This extended designations schedule introduces additional years ofmonitoring data in which S02 concentrations may be influenced by exceptional events. Becausethe previouslypromulgated exceptional events data flagging and documentation submittal dates associated with S02 data that could be considered in the initial area designations process have already passed, the EPA is recommending
new submittal dates in this guidance for these future data. State and tribal air agencies who wish the EPAto be able to fully consider excluding exceptional event-affected S02 data for purposes of designations are asked to flag exceptional event data and submit an initial description in the EPA's AQS, and also submit the associated exceptional event demonstrations no later than 5months prior to the date offinal designation decisions. Additionally, air agencies are asked to notify their reviewing EPA Regional Office as soon as possible about their intentto prepare and submit an exceptional event documentation.


### Model-based Violations. States and tribes may also use air quality modeling results to indicate a violation ofthe S02NAAQS. The EPA believes that dispersion modeling is an appropriate tool to

5 S02 air quality data is available from the EPA's website at www.epa.gov/ttnlairs/airsaqsl. 4indicate a violation ofthe S02NAAQS, and it has used dispersion modeling in the past for S02 designations. Thepreviously mentioned December 2013 Modeling TAD provides further recommendations ondeveloping an appropriate refined dispersion modeling analysis to support designation recommendations. Such modeling could include using the AERMOD dispersion model or other appropriate dispersion model. The Modeling TAD updates the March 24, 2011, Modeling Guidance for S02NAAQS Designations in four respects, all to ensure that a modeling approach better simulates a monitoring approach. Specifically, the ModelingTAD recommends:
• using actual emissions as an input for assessing violations to provideresults that reflect current actual air quality (i.e., modelingthat simulates a monitor);
• using 3 years ofmodelingresults to calculate a simulated design value consistent with the 3-year monitoring period required to develop a design value for comparisonto the NAAQS;
• placingreceptors only in locations where a monitor could be placed; and
• using actual stackheights rather than following the Good Engineering Practice stack height policy when using actual emissions. Identifying Attainment Areas

The EPA may designate an area as attainment ifit is clearthat it meets the S02NAAQS and does not contribute to a violation in a nearby area. An area may be demonstrated in attainment ifthe mostrecent 3 years ofambient air quality monitoring data indicate no violations and ifthe monitoring network in the
area is sufficient to be compared to the NAAQS per the S02NAAQS Designations Monitoring TAD6 An area may also be demonstrated in attainment ifappropriate modeling analysis indicates no violations ofthe 2010 S02NAAQS. (Using allowable emissions in modeling would be an appropriate approach to support an attainment determination.) In either case, it will also be necessary to show that sources in the
area are not contributing to a violation in a nearby area. In the absence ofinformation clearly demonstrating a designation of"attainment" or "nonattainment,"the EPA intends to designate the area as "unclassifiable"7 when it takes action pursuant to the court order. Determining NonattainmentArea Boundaries

Ambient S02 is apollutant that arises from direct emissions, and S02 concentrations are generally expected to be highest relatively close to the source(s) and lower at farther distances due to dispersion. Thus, S02 concentrationpatterns resemble those ofother directly emitted pollutants like lead and differ from those ofphotochemically-formed (secondary) pollutants such as ozone. Accordingly, as explained inthe 2011 guidance, we expectto continue to consider county boundaries as the analytical starting point for determining S02 nonattainment areas.

We believe it is appropriate to evaluate each potential nonattainment area on a case-by-case basis to determine an appropriate boundary that satisfies the statutory conditions. A nonattainment area should contain the area violating the NAAQS (e.g., the area around a violating monitor or encompassing

6 The Monitoring TAD is available on the EPA's website at http://www.epa.govlairqualitylsu!furdioxidelpdfilS02MonitoringTAD.pdf 7 While states have and may continue to submit designations recommendations identifying areas as "attainment," the EPA expects to continue its traditional approach, where appropriate, ofusing adesignation category of"unclassifiable/attainmentn for areas that the EPA determines meetthe NAAQS. The EPA expects to reserve the category "unclassifiable" for areas where the EPA cannot determine based on available information whether the area is meeting or not meeting the NAAQS or where the EPA cannot determine whether the area contributes to aviolation in anearby area. 5modeled violations), as well as any nearby areas (e.g., counties or portions thereof) that contain emissions sources contributing to the monitored ormodeled violations. (See CAA section 107(d)(l)(A)(i)). We recommend that states and tribes base their updated boundary recommendations on an evaluation offive factors: 1) air quality data or dispersion modeling results; 2) emissions-related data; 3) meteorology; 4) geography and topography; and 5)jurisdictional boundaries, as well as other available data. These factors are discussed in more detail in Attachment 2. Dispersion modeling, as discussed in the Modeling TAD, can be a helpful tool in this evaluation because it allows the model user to simultaneously assess multiple factors. States and tribes may identify and evaluate other relevant factors orcircumstances specific to a particular area.
While the EPA generally believes that in the absence ofother relevant information it is appropriate to
use county boundaries to define nonattainment areas, we recognize that the five-factor analysis and other information may support a nonattainment area consisting ofonly a portion ofa county. For example, a topographical feature may divide a county into two separate air basins, or contributing sources may be clustered in only a pmtion ofa county.8For detlning partial county boundaries, the EPA recommends the use ofwell-definedjurisdictional lines such as township borders or other well-established geopolitical boundaries, and immovable landmarks such as major roadways or other permanent and readily identifiable physical features. Determining Attainment Area Boundaries

An attainment ar·ea cannot contain any areathat violates the NAAQS or contributes to a violation ofthe NAAQS in a nearby area. (See CAA section 107(d)(l)(A)(i)). County boundaries may be appropriate for defining attainment areas in the absence ofany other relevant information that would help define a more specific boundary around the 

### SOz source(s) in question. To detlne more specitlc boundaries, we recommend an evaluation ofthe flve factors mentioned previously, and, in particular, the use of dispersion modeling, as discussed in the Modeling TAD, to simultaneously assess multiple factors.

While we believe this memorandum provides helpful guidance on how boundaries would be determined for S02 designations, the guidance contained herein is not binding on states, tribes the public orthe EPA. The final basis for determining areaboundaries will be addressed in the EPA's regulatory action to designate areas under the 2010 S02 NAAQS. When the EPA promulgates designations, those determinations will be final and binding on states, tribes, the public and the EPA.

Attachment 1 is a timeline ofkey dates in the round ofdesignations for the revised 2010 S02NAAQS that must be completed by July 2, 2016. Attachment 2 identifles the primary five factors that the EPA plans to consider in evaluating and making decisions on appropriate nonattainment and attainment area boundaries. The EPA recommends that states and tribes also address these factors and follow the Monitoring and Modeling TADs ifthey choose to submitupdated designation recommendations.

8 In the case ofa contributing SO, source located very near a county boundary or state border, it may be appropriate for the corresponding nonattainment area to include portions ofmultiple counties or multiple states. 6Staffmembers at the EPA's Office ofAir Quality Planning and Standards are available for assistance and consultation throughout the designations process. General questions on this guidance may be directed to Andy Chang (919) 541-2416. Modeling-related questions may be directed to James Thurman (919) 541-2703. Monitoring-related questions may be directed to Nealson Watkins (919) 541-5522.

Attachments (2)

7ATTACHMENT 1

TIMELINE FOR2010 PRIMARY S02 NAAQS DESIGNATION PROCESS- ROUND 2- AREAS ASSOCIATED WITH JULY 2, 2016, COURT-ORDERED DEADLINE' Milestone Dateh Court Order March 2, 20 15 States flag relevant exceptional event- No later than July I, 2015 influenced

# so2 monitoring data from 2012 and 20 13; provide detailed documentation to support all claims States may submitupdated recommendations No later than September 18,2015 and supporting information for area designations to the EPA States flag relevant exceptional event- No later than February 2, 2016 influenced S02 monitoring data from 2014 and 2015; provide detailed documentation to support all claims The EPA notifies states concerning any January 22, 20 16 intended modifications to their (no later than 120 days priorto final recommendations (120-day letters) designations) The EPA publishes public notice ofstate o/aFebruary 3, 2016 recommendations and the EPA's intended modifications and initiates 30-day public comment period End of30-day public commentperiod o/aMarch 4, 2016 States and tribes submit additional o/a April 8, 2016 information, ifdesired, to demonstrate why an EPA modification is inappropriate The EPA signs notice promulgatingfinal S02 No later than July 2, 2016
area designations (no later than 16 months from court order) 

### ' DesrgnatJOns f01 Round 3 must be p10mulgated by December 3!, 20 !7. Desrgnatrons f01 Round 4 must be promulgated by December 3!, 2020.
b o/a = on or about

1ATTACHMENT 2
Determining AreaDesignations and Appropriate Area Boundaries for the 2010 S02NAAQS
Designation Categories Nonattainment Attainment1 Unclassifiable An area that the EPA has An area that the EPA has An area where the EPA cannot determined violates the 2010 determined meets the 2010 SO, determine based on available 

## so, NAAQS, based on the most NAAQS and does not contribute information whether the area is recent three years ofambient air to a violation ofthe NAAQS in or is not meeting the 20 1 0 S02 quality monitoring data oran a nearby area based on either: a) NAAQS and whether the area appropriate modeling analysis, the most recent 3 years of contributes to a violation in a or thatthe EPA has determined ambient air quality monitoring nearby area. contributes to a violation in a data from a monitoring network nearby area. in area that is sufficientto be compared to the NAAQS per EPA interpretations in the Monitoring TAD, orb) an appropriate modeling analysis.

NonattainmentArea Boundaries. The EPA intends to use the county as the analytical starting pointfor assessing the appropriate geographic boundaries ofa SOz nonattainment area. The five factors listed belowcomprise a framework for area-specific analyses to supportfinal boundary determinations. The information addressing these factors could include appropriate air quality dispersion modeling as recommendedby the S02 Designations ModelingTAD2 or, where available, ambient air quality monitoring data as recommendedbythe S02 Designations MonitoringTAD.3 Formodeled violations, theportion ofthe modeling domain encompassing the modeled violations is an appropriate reference pointfor determining a nonattainment area boundary.

AttainmentArea Boundaries. Areas designated as attainment should be supported by information clearly demonstratingthat there are no violations ofthe S02 NAAQS inside the areaboundary, and that the included portions do not contain emission sources that may contribute to monitored
ormodeled violations outsidethe area boundary. County boundaries may be appropriate for defining attainment areas in the absence ofany otherrelevantinformation that would help define

1 While states have and may continue to submit designations recommendations identifying areas as "attainment,'' the EPA expects to continue its traditional approach, where appropriate, ofusing adesignation category of "unclassifiable/attainment" for areas thatthe EPA determines meet the NAAQS. The EPA expects to reserve the category "unclassifiable 11 for areas where the EPA cannot determine based on available information whether the area is meeting or not meeting the NAAQS or where the EPA cannot determine whetherthe area contributes to a violation in anearby area. 2 The Modeling TAD is available on the EPA's website at http://www.epa.govi airqua!itylsu/fiJrdioxide/pdfs/SO2Modeli ngTAD.pdf 3The Monitoring TAD is available on the EPA's website at http://www.epa.gov/airquality/sulfiirdioxide/pdfs/S02MonitoringTAD.pdf

1a more specific boundary around the S02 source(s) in question. As recommended in the Modeling TAD, appropriate modeling for establishing attainment area boundaries would include using the AERMOD dispersion model, with actual or allowable source emissions. Where appropriate modeling is conducted, the portion ofthe modeling domain demonstrated to be free ofviolations, and free ofsources that may contribute to any nearby violations is an appropriate reference point for determining the boundary ofan attainment area. Developing Supporting Information (Factor Analysis). As a framework for area-specific analyses to support final boundary determinations, the EPA intends to evaluate the five factors listed below, as well as otherrelevant available information. The purpose ofevaluating these factors is to determine the appropriate boundaries encompassing the areameeting the CAA's definitions. The guidance in the Modeling TAD discusses how modeling could be used to address several of these factors simultaneously. When considered as a whole, results may support boundaries that
are either larger or smallerthan the analytical starting point.

1. Ambient air quality data or dispersion modeling results. We intend to review S02 ambient air quality monitoring data, including the design value calculated for each monitor in the area, for the most recent 3-yearperiod. Areas where monitoring data indicate a violation ofthe !-hour, 75 ppb primary S02 standard will be designated as "nonattainment." Sourceoriented modeling may also be used to assess air quality in a particular location. The Modeling TAD provides further recommendations on using refined dispersion modeling for this type ofair quality assessment. An areamay be demonstrated to meet the S02NAAQS if appropriate modeling analysis based on either actual or allowable emissions from relevant
sources indicates no violations ofthe S02 NAAQS. As explained in the Monitoring TAD, data from a properly sited monitoring network may also be sufficientto establish that an area meets the S02NAAQS. In either case, to be designated attainment it will be necessary to show that sources in the area are not contributing to a violation in a nearby area.
2. Emissions-related data (location ofsources and potential contribution to ambient S02 concentrations). We intend to examine actual emissions ofS02 from sources located in and around the violating area. Significant emissions levels in a nearby area indicate potential for the areato contribute to observed or modeled violations ofthe NAAQS. We intend to review data from the latest National Emissions Inventory or otherrelevant sources ofthe data, such
as state inventories or inventories from other federal sources. We would also consider any additional information we receive on federally-enforceable emissions controls that are not reflected in recent inventories but which will require compliancebefore final designations are issued.

3. Meteorology (weather and transportpatterns). We intend to evaluate meteorological datato help determine howweather conditions, including wind speed and direction, affect the plume ofsources contributing to ambient S02 concentrations. This factor also can be assessed in the context ofsource-oriented dispersion modeling as recommended in the Modeling TAD.

4. Geography and topography (mountain ranges or other air basin boundaries). We intend to examine the physical features ofthe land that might affect the distribution ofS02 over an

2area. Mountains or other physical features may affect the distribution ofemissions, and may help define area boundaries.

5. Jurisdictional boundaries (e.g., counties, air districts, pre-existing nonattainment areas, reservations, metropolitan planning organizations). Fornonattainment areas, once the geographic area associated with the areaviolating the SOz NAAQS and the nearby area contributing to violations are determined, we intend to consider existingjurisdictional boundaries for the purposes ofproviding a clearly defined legal boundary for carrying out the air quality planning and enforcement functions for the area. Ifan existingjurisdictional boundary is used to help define the nonattainment area, it should encompass all ofthe area that has been identified as meeting the nonattainment definition. Where existing jurisdictional boundaries are not adequate to describe the nonattainment area, other clearly defined and permanent landmarks or physical features may be used. In certain cases geographic coordinates may be appropriate, but geopolitical boundaries are preferred. For attainment areas, these samejurisdictional considerations may play a role in determining appropriate boundaries.

The EPA plans to considerthese factors, along with any other relevant information, in determining whether to make modifications to the designation and area boundary recommendations made by states and tribes. The factors listed above, while generally comprehensive, are not intended to be exhaustive. States and tribes may submit additional information they believe is relevant for the EPA to consider. Any information provided to support a boundary recommendation for a nonattainment area should show that: I) violations are not occurring in nearby portions that are excluded from the recommended nonattainment area; and 2) the excluded portions do not contain emission sources that contribute to a monitored or modeled violation. Any information provided to support a boundary recommendation for an attainment area should showthat: I) violations are not occurring in the area; and 2) the included portions do not contain emission sources that may contribute to monitored ormodeled violations outside the area boundary. In the absence ofinformation clearly demonstrating that an area and its associated boundary are properly designated "attainment" or "nonattainment,"the EPA intends to designate the area as "unclassifiable."

3