ENVIRONMENTAL PROTECTION AGENCY

40 CFRPart 52**[EPA-RI0~OAR-2010-0669;** FRL-XXXX-XJ Approval and Promulgation ofImplementation Plans; Idaho; Interstate Transport ofPollution

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed Rule.

SUMMARY: EPAis proposing to approve a State Implementation Plan (SIP) revision submittedby the State ofIdaho for the purpose ofaddressing the "goodneighbor" provisions of the Clean Air Act (CAA) section lI0(a)(2)(D)(i) for the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS or standards) and the 1997 PM2.5 NAAQS. This SIP revision addresses the requirement that the State ofIdaho's SIP have adequate provisions to prohibit air emissions from adverselY affecting another state's air qualitythrough interstate transport. In this action, EPA is proposing to approve the Idaho Interstate Transport SIP provisions that address the requirement ofsection 11O(a)(2)(D)(i) that emissions from Idaho sources do not significantly contribute to nonattainment ofthe 1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS in any other state, interfere with maintenance ofthe 1997 8-hour ozoneNAAQS and the 1997 PM2.5 NAAQS in any other state, and interfere with measures required in the SIP ofany other

1state under part C ofsubchapter I ofthe CAAtoprevent significant deterioration ofair quality. This action is being taken under section 110 and part C ofsubchapter I ofthe Clean Air Act (the Act orCAA).

DATES: Written comments mustbereceived on or before [insert date 30 days from date of publication].

ADDRESSES: Submit your comments, identified byDocket illNo. EPA-R10-0AR-2008- 0391, byone 

### ofthe following methods:

A. www.regulations.gov. Follow the on-line instructions for submitting comments. B. E-Mail: RlO-Public_Comments@epa.gov C. Mail: Donna Deneen, U.S. Environmental Protection Agency, Region 10, 1200 Sixth Avenue, Suite 900, Mail Stop: A WT-107, Seattle,W A 98101 D. Hand Delivery: U.S. Environmental Protection Agency, Region 10, Attn: DonnaDeneen (AWT-107), 1200 SixthAvenue, Suite 900, Seattle, Washington 98101, 9th Floor. Such deliveries are only accepted during normal hours ofoperation, and special arrangements should be made for deliveries ofboxedinformation.

Instructions: Direct your comments to Docket ID No. EPA-RlO-0AR-2010-0669. EPA's policy is that all commentsreceived will be included in the public docket without change and maybe made available online at www.regulations.gov, including any personal information provided, unless the commentincludes information claimed to be Confidential Business

2Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through www.regulations.gov or email. The www.regulations.govWeb site is an "anonymous access" system, which means EPA will not know your identity orcontactinformation unless you provide it in the body ofyour comment. Ifyou send an email comment directly to EPA without going through www.regulations.gov, your email address will be automatically captured and included as part of the commentthat is placed in the public docket and made available on the Internet. Ifyou submit an electronic comment,EPArecommends that you include your name and other contact information in the body ofyou comment and with any disk or CD-ROM you submit. IfEPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consideryour comment. Electronic files should avoid the use ofspecial characters, any form ofencryption, and be free ofany defects or vimses. 

### Docket: All documents in the electronic docket are listed in the www.regulations.gov index. Although listed in the index, some information, 

### i.e., CBI or other information whose disclosure is restricted by statute, is not publicly available. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copyform. Publicly available docket materials are availableeither electronicallyin www.regulations.gov or in hard copy during normal business hours at the Office ofAir, Waste aud Toxics, U.S. Environmental Protection Agency, Region 10, 1200 Sixth Avenue, Suite 900, Seattle, Washington 9810

### 1.

FOR FURTHER INFORMATION CONTACT: Donna Deneen, (206) 553-6706 or deneen.donna@epa.gov.



### 3SUPPLEMENTARY INFORMATION: Throughout this notice, the words "we", "us", or "our" means the Environmental Protection Agency (EPA).

Table ofContents I. What Proposed Action is EPATaking? II. What is a SIP? III. What is the Background for this Proposed Action? IV. What is EPA's Evaluation ofthe State's Submission? A. EPA's Evaluation ofSignificant Contribution to Nonattainment 1. 1997 PM2.5 Nonattainment Areas and MonitoringData in States Surrounding Idaho 2. 1997 8-Hour Ozone Nonattainment Areas and Monitoring Datain States Surrounding Idaho 3. State Regulatory Provisions 4. Conclusion Regarding Significant Contribution to Nonattainment B. EPA'sEvaluation ofInterferencewith Maintenance 

### 1. Background 2. Idaho's Interference with Maintenance Demonstration 3. EPA's Supplemental Analysis 4. Conclusion Regarding Interference with Maintenance C. EPA'sEvaluation ofInterferencewith PSD Measures in Other States. V. Proposed Action VI. Statutory and Executive Order Reviews



### 4

## r. What Proposed Action is EPA Taking? EPAis proposing to approve a portion ofIdaho's Interstate Transport State Implementation Plan (SIP) revision for the 1997 8-hour ozone and 1997 PM2.5 NAAQS submittedby the Idaho Department ofQuality (IDEQ) on June 28, 2010. Specifically, we are proposing to approve the portion ofthe plan that addresses the following elements ofCAA section 110(a)(2)(D)(i): (1) significant contribution to nonattainment ofthese NAAQS in any other state, (2) interference with maintenance ofthese NAAQS by any other state, and (3) interference with any other state's required measures to prevent significant deterioration (PSD) ofits air quality with respect to these NAAQS. IDEQ addressed element (4), interference with any other state's required measures to protect visibility, byreferring to its Regional Haze SIP, which will be submitted separately. EPA will take action on the visibility element in a separate action. EPA will also take action on the portion ofIdaho's SIP that addresses the 2006 PM2 .5 NAAQS 1in a separate action. Idaho's June 28, 2010, SIP revision replaces a previously submitted section 11O(a)(2)(D)(i) SIP revision submittedby IDEQ on January 30, 2007, for the 1997 PM2.5 and PM2.5 standards. EPAproposed approval ofthat SIP revision on June 26, 2007 (72 FR 35022), but did not take final action. When Idaho submitted its June 28, 2010, SIP revision, Idaho requested that EPA replace the SIP submitted on January 30,2007, with the revised SIP submitted on June 28, 2010. In light ofIdaho's resubmittal ofits Interstate Transport SIP, EPA is withdrawing its June 26, 2007, proposal and is issuing this proposal to approve Idaho'sJune 28,2010, SIP revision in its place. Accordingly, EPA will not be responding to comments on the

I The PM2.5standard was revised in 2006. See "National AmbientAir Quality Standards for Particulate Matter," at 71 FR 61144, (October 17,2006). 

### 5June 26,2007, proposal. Any person who wishes to comment on EPA's proposed approval of Idaho's SIP revision addressing section 110(a)(2)(D)(i) for the 1997 8-hour ozone and 1997 PM2.5 standards should do so at this time.

II. What is a SIP? Section IIO(a) ofthe CAA requires each state to develop a planthat provides for the implementation, maintenance, and enforcement ofthe NAAQS. EPA establishes NAAQS under section 109 ofthe CAA. Currently, the NAAQS address six criteria pollutants: carbon monoxide, nitrogen dioxide, ozone, lead, particulate matter, and sulfur dioxide. Theplan developed by a state is referred to as the SIP. The content ofthe SIP is specified in section 110 ofthe CAA,.otherprovisions ofthe CAA, and applicable regulations. SIPs can be extensive, containing state regulations or other enforceable measures and various types ofsupporting information, such as emissions inventories, monitoring networks, and modeling demonstrations. A primarypurpose ofthe SIP is to provide the air pollution regulations, control strategies, and other means ortechniques developed by the state to ensure that the ambient air within that state meets the NAAQS. However, another important aspect ofthe SIP is to ensure that emissions from within the state do not have certain prohibited impacts upon the ambient air in other states through interstate transport ofpollutants. This SIPrequirement is specified in section 110(a)(2)(D). Pursuant to that provision, each state's SIP must contain provisions adequate to prevent emissions that significantly contribute to violations ofthe NAAQS in any other state, interfere with maintenance in any other state, interfere with any other state's required



### 6measures to prevent significant deterioration ofits air quality, and interfere with any other state's required measures to protect visibility. States are required to update orrevise SIPs under certain circumstances. One such circumstance is EPA's promulgation ofa new orrevised NAAQS. Each state must submit these revisions to EPAfor approval and incorporation into the federally-enforceable SIP.

III. 

### Whatis 

### the Background for this Proposed Action? On July 18, 1997, EPApromulgated new standards for 8-hour ozone and fine particulate matter (PM2 .5

). This action is being taken in response to the promulgation ofthe 1997 8-hour
ozone NAAQS and 1997 PM2.5 NAAQS. This action does not address the requirements ofthe 2006 PM 2.5 NAAQS or the 2008 8-hoUl' Ozone NAAQS; those standards will be addressed in a future action. Section IIO(a)(1) ofthe CAA requires states to submit SIPs to address

## ti new orrevised NAAQS within three years after promulgation ofsuch standards, or within such shorterperiod
as EPA may prescribe. Section 110(a)(2) lists the elements that such new SIPs must address, as applicable, including section 110(a)(2)(D)(i) which pertains to interstate transport ofcertain emissions. On August 15,2006,EPAissued its "Guidancefor StateImplementationPlan (SIP) Submission to Meet Current Outstanding Obligations Under Section 110(a)(2)(D)(i) for the 8- hour ozone and PM2 .5 National Ambient Air Quality Standards" (2006 Guidance) for SIP submissions that states should use to address the requirements ofsection 110(a)(2)(D)(i). EPA developed this guidance to make recommendations to states for making submissions to meet the requirements of section 11O(a)(2)(D) for the 1997 8-hour ozone standards and 1997 PM2.5 standards.



### 7On June 28, 2010, we received a SIPrevision from the State ofIdaho to address the requirements ofsection llO(a)(2)(D)(i) for the 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS. The "good neighbor" provisions in section llO(a)(2)(D)(i) require each state to submit
a SIP that prohibits emissions that adversely affect another state in the ways contemplated in the statute. Section 110(a)(2)(D)(i) identifies four distinct elements related to the evaluation of impacts ofinterstate transport ofairpollutants. In this rulemaking EPA is addressing the first three elements: (1) significant contribution to nonattainment ofthese NAAQS in any other state, (2) interference with maintenance ofthese NAAQS by any other state, and (3) interference with any other state's required measures to prevent significant deterioration (PSD) ofits air quality with respect to these NAAQS. Idaho asserts in its SIP submission that its current SIP is adequate to prevent such contribution and interference, and thus no additional controls orrevisions are needed with respect to the 1997 8-hour ozone NAAQS and 1997 PM2.5NAAQS. EPAis proposing to find that Idaho's Interstate Transport SIP provisions addressing elements (1), (2), and (3) ofsection 110(a)(2)(D)(i) are consistentwith the requirements ofthe CAA.



### IV. Whatis EPA's Evaluation oftlie State'sSubmission? A. EPA'sEvaluation ofSignificant Contribution to Nonattainment Section 11O(a)(2)(D)(i) provides thatEPAcannot approve a state's SIPfor a new or revised NAAQS unless it contains adequate measures to prohibit emissions from sources within the state from contributing significantly to nonattainment ofthe NAAQS in another state. EPA's August 2006 Guidance concerning section lI0(a)(2)(D)(i)recommended various methods by which states might evaluate whether or not their emissions significantly contribute to nonattainment ofthe 1997 8-hour ozone or the 1997 PM2.5 NAAQS in another state. Among



### 8other methods, EPA recommended consideration ofavailable EPAmodeling conducted in conjunction with the Clean Ail' Interstate Rule (CAIR),z orin the absence ofsuch EPA modeling, consideration ofotherinformation such as the amount ofemissions, the geographic location of violating areas, meteorological data, 01' various other forms ofinformation that wouldbe relevant to assessing the likelihood ofsignificant contribution to violations ofthe NAAQS in another state. The assessment ofsignificant contribution to nonattainmentis not restricted to impacts upon areas that are formally designated nonattainment. Consistent with EPA's approach in CAIR and in the Transport Rule Proposal, this impact must be evaluated with respect to monitors showing a violation ofthe NAAQS (70 FR 25172, May 12, 2005, and 63 FR 57371, October 27, 1998)? Furthermore, although relevant information other than modeling may beconsidered in assessing the likelihood ofsignificant contribution to nonattainment ofthe 8-hour ozone or PM2.5 NAAQS in another state, EPA notes that no single piece ofinformation is byitselfdispositive of the issue. Instead, the total weight ofall the evidence taken together is used to evaluate significant contributions to violations ofthe 1997 8-hour ozone 01' 1997 PMZ.5NAAQS in another state. This proposed approval addresses the significant contributionelement for the 1997 8- hour ozone and 1997 PMz.5 NAAQS in several ways. Ittakes into account Idaho's SIP submission that addressed the significant contribution element for the 1997 8-hour ozone and 1997 PM2.5 NAAQS byevaluating potential impacts from Idaho sources on 1997 8-hour ozone and 1997 PMz.5 nonattainment areas in surrounding states basedon a review ofmeteorological and other characteristics ofthose areas. The State's SIP submission also relied on provisions in

2 See "Rule to Reduce Interstate Transport afFine Particulate Matter and Ozone (Clean Air Interstate Rule); Revisions to Acid Rain Program; Revisions to the NO, SIP Call; Final Rule," at 70FR 25162 at 25263-69 (May 12, 2005). J See Section B (1) ofthis notice for more history on CAIR and the Transport Rule Proposal. EPA has taken a simi1ar approach in the recent Transport Rule Proposal discussed below. 9its air quality regulations that address Idaho's authority to address nonattainment issues. 

### In addition to the arguments presentedby Idaho to support its demonstration that its SIP satisfies the significant contribution element ofthe CAA, EPA has supplemented its analysis with monitoring data and other information related to the 1997 PM2.5 nonattainment areas identified byIdaho, and has also provided monitoring data and other information for the surrounding states generally. Our evaluationbelow regarding how Idaho's SIP satisfies the significant contribution element ofthe CAA is organized as follows. Section 1addresses the 1997 PM2 .5nonattainment
areas in surrounding states (includingPM2 .5 monitoring datafor those nonattainment areas) and PM2.5 monitoring data generallyfor surrounding states. Section 2 addresses the 1997 8-hour
ozone nonattainment areas in surrounding states (including ozone monitoring data for those nonattainment areas) and ozone monitoring data generally for surrounding states. Section 3 addresses Idaho's air quality regulations for both the 1997 8-hour ozone and 1997 PM2 .5 NAAQS which pertain to Idaho's authority to address nonattainment issues.



### 1. 1997 PM2.5 Nonattainment Areas and Monitoring Data in States SUlTounding Idaho 1997 PM2 . 5 Nonattainment Areas To address whether Idaho sources significantly contribute to nonattainment ofthe 1997 PM2.5 NAAQS in another state, Idaho reviewed meteorological and other characteristics ofany
areas designated nonattainment for the 1997 PM2 .5 NAAQS in surrounding states to determine whether transport ofemissions from Idaho significantly contribute to nonattainment in those
areas. Relying primarily on technical support documents (TSDs) prepared for EPA's 8-hour
ozone and PM2 . 5NAAQS nonattainment designations, Idaho noted that air stagnation is cited as
a major contributing factor to nonattainment in those areas and that under air stagnation

10conditions there is little to no transport ofpol)utants over long distances. Idaho also noted that
none ofthe TSDs identified Idaho sources as significant contributors to any 1997 PM2.5 nonattainment areas. As a part ofEPA's analysis ofwhether or not PM2.5 emissions from Idaho significantly contribute to nonattainmentin another state, EPA reviewed and analyzed information available for the 1997 PM2.5nonattainment areas in states surrounding Idaho. Although significant contribution mustbe measured notjust against nDnattainment areas, butalso against areas with monitors showingviolations ofthe NAAQS, nonattainment areas are aconvenient starting point for the analysis. Forthe 1997 PM2 .5NAAQS, Libby, in Lincoln County, Montana is the only designated nonattainment area in any state bordering Idaho. 4 

### In 2005, EPAdesignated this area
nonattainment for the 1997 annual PM2 .5 NAAQS. 70FR 944 (January 5,2005) and40 CFR 81.327.A number offactors provide evidence that Idaho emissions do not significantly contribute to past violations ofthe 1997 annual PM2.5 standards in Libby, Montana. First, in the process of designating Libby nonattainmentfor both the 1997 PM2.5 NAAQS and the 2006 PM2.5 NAAQS, EPA noted the predominantlylocal origins ofPM2 . 5nonattainmentinLibby.5.6 Residential wood-burning stoves during the winter-time, when frequent and persistent temperature inversions occurred, were specificallyidentified as a key source ofPM emissions. Although local sources were believed to predominatein the Libby nonattainment area, EPA specificallyconsidered in the 1997 PM2.5 designation process whetherIdaho sources

4 Libby is in anarrow valley surrounded by mountains 4,000 feet higher than the town. The Rocky Mountain Range to the west ofLibby (and east ofthe Idaho border) reaches sllmmit elevations of 12,000 feet with most summit elevations between 6000 and 7000 feet that act as abarrier to air movemenl between Idaho and Montana. 5 "Technical Support for State and Tribal Air Quality FineParticle (PM,.,) Designations," (forMontana) Chapter 6, pp. 347-352, December 2004. 6 "Technical Support for State and Tribal Air Quality FiueParticle (PM,.5) Designations," (forMontana) Chapter 4.8.1, pp. 1-15, December 2008. 

### 11contributed to PM2 .5 nonattainment in Libby. While a nonattainment designation analysis is not the same inquiry that is required under CAA section 11O(a)(2)(D), some ofthe factual findings from that effort are helpful in understanding the potential for interstate transport ofpollutants in the Libby area. Ifthere were an area in Idaho from which significant contribution would bemost likely, it would arguably be from Bonner and Boundary counties in Idaho. These counties are located in Idaho's panhandle and are the only Idaho counties located to the west ofthe Libby nonattainment area. Transport winds generally flow across Idaho from west to east, and Libby is directly east ofBonner and Boundary counties. In the process ofdesignatingLibby nonattainment for the 1997 PM2 .5 NAAQS, EPA concluded that there was insufficient data to justifyincluding those two Idaho counties (or any portion thereof) in the Libby nonattainment area? Monitoring data from 1999 through 2009 show that PM2.S design value levels for both Idaho counties have remained below 30 f.lg/m3 or 

### 85 percent ofthe 1997 PM2.5 NAAQS. This is consistent with a conclusion that local sources in Libby were a key contributor to the area's past nonattainment. Although the predominance oflocal sources does not rule out the possibility of impacts from interstate transport, this fact taken in conjunction with the mountainous topography ofthe area, supports a conclusion that Idaho emissions do not contribute significantly to the past NAAQS violations in Libby. Second, monitoring data from 1999 through 2009 from areas outside ofLibby in Montana support a determination that Idaho does not significantly contribute to nonattainmentin Libby. At all other sites in Montana, annual PM2.5 design value levels have remained below the 15**~lg/m3** nonattainment threshold. Annual PM2 .5design values for this period for most ofthese monitors remained at levels equal to, orless than, two-thirds ofthe 1997 NAAQS. Even the

7 "Technical Support for State anel Tribal Air Quality Fine Particle (PM,.5) Designations," Chapter 6, pp. 347-352, Dcceinber 2004. 

### 12three highest design values at these monitors were 20 percentbelow the level ofthe annual standard. 8 The lower PM2 .5levels elsewhere in Montana are evidence that local sources, and not interstate transport, are key contributors to past nonattainment in Libby. Monitoring data from Idaho likewise supports a finding that Idaho does not significantly contribute to nonattainment elsewhere. In Idaho, annual PM2.5 design values from 1999 through 2009 have remained below the 1997 NAAQS. The comparativelylower levels ofPM2.5 monitored throughout Idaho and elsewhere in Montana are consistent with a conclusion that local sources, and not sources in another state, are the predominant source ofPM2.slevels in Libby. The fact that monitors located in Idaho have not registered violations ofthe 1997 PM2 .5 NAAQS does notconclusively establish that emissions from Idaho could notcontribute in the aggregate to violations in Libby, butthis fact combined with the localized nature ofthe violations in Libby sppports the conclusion that sources in Idaho do not significantly contribute to PM2 .5levels in Libby. By 2007-2008, the annual PM2.5 design values for the Libby nonattainment area itselffell below the levels ofthe NAAQS. This reduction has been attributed to an effective wood stove replacement program that decreased PM2.s emissionsby approximately 

### 59 percent.9 In other words, even ifemissions from Idaho sources were reaching Libby, they would not significantly contribute to violations ofthe 1997 PM2 .5NAAQS because monitoring data demonstrate that Libbyis not violating the 1997 PM2 .5NAAQS. Finally, EPA's conclusion that emissions from Idaho do not significantlycontribute to nonattainment in Libby, Montana, is further supported by a modeling analysis for monitors in the

, In 2001,2002 and 2006, design values [or two monitors in Missoula County were 11.1, 11.4 and 11.8**~lg!m3.** Computed from AQS monitoring data. 75 FR 16028 (March 31, 2010). 9 State ofMontana,**Departm~nt** ofEnvironmental Quality, "State Implementation Plan-Libby Annual PM2.5 Control Plan," submitted to EPA April 1, 2008. 

### 13western United States.

## '0 This modeling concludes that in 2012 the average design values in Lincoln County, Montana for PM2.5will bebelow the threshold for consideration as a
nonattainment receptor. The next closest 1997 PM2.5 nonattainment area to the state ofIdaho is the San Joaquin Valley in California." This nonattainment area is over 300 miles southwest ofthe closest point
on the Idaho border and is on the other side ofthe Sierra Nevada Mountains. This 400 mile long north-south range ofmountains has peaks ofmore than 14,000 feet which act as a natural barrier to air movement between Idaho and California. In addition, San Joaquin Valley, California, is not in the predominant direction ofwinds from Idaho. Transport winds across Idaho generally flow from west to east, and not toward the southwest. Given the relatively long distance between Idaho and the San Joaquin Valley, the intervening mountainous topography, and the general west-to-east direction oftransport winds across Idaho, EPAbelieves itis reasonable to conclude that Idaho sources do not significantlycontribute to nonattainment ofthe 1997 PM2.5 NAAQS in the San Joaquin Valley.

PM2.5 Monitoring Data in Other Areas ofSurrounding States As mentioned above, EPAconsiders not only significant contribution to designated nonattainment areas, but also significant contribution to areas with monitors showing violations ofthe NAAQS. Areview ofthe most recent three years ofmonitoring data in EPA's Air Quality System (AQS) for the bordering states ofWashington, Oregon, Nevada, Utah, Wyoming and Montana shows there are no monitors violating the 1997 PM2 .5 NAAQS. Between 1999 and

10 See Section B ofthis notice for amorc complete disclIssion ofthe Transport Rule Proposal and EPA's modeling analysis ofthe western states. 11 In 2005,EPA designated this area nonattainl11en1 for violations ofthe 1997 and annual PM,., NAAQS. 70 FR 944 (January 5, 2005), and 40 CFR 8l.305 142009,justtwo monitors in any ofthese bordering states violated the 1997 PM2.5 NAAQS. Both violations were for the annual NAAQS. The first such monitor is in Libby, Montana, which has not violated the 1997 PM2.5 NAAQS since 2005. As discussed previously, EPA believes that existing information supports the conclusion that there is not significant contribution to nonattainment from Idaho sources to this area in Montana. The second is a monitor in SaltLake City, Utah, which violated the 1997 PM2 .5 NAAQS at a single monitor in 2004. Since 2004 it has not violated the NAAQS. Taking into account the total weight ofall ofthe factors discussed above, EPAconcludes that Idaho does not significantly contribute to 1997 PM2 .5 NAAQS nonattainmen't in another state.

2. 1997 Ozone NonattainmentAreas and Monitoring Data in States SurroundingIdaho 1997 8-Hour Ozone Nonattainment Areas To address whether Idaho sources significantly contribute to nonattainment ofthe 1997 8-hour ozone standard in another state, Idaho's SIP uses the same approach as itused for the 1997 PM2.5NAAQS. Relying primarily on TSDs prepared for EPA's 8-hour ozone and PM2 .5 nonattainment designations, Idaho noted that air stagnation is cited as a major contributing factor to nonattainment in those areas and that under stagnant air conditions there is little to no transport ofpollutants overlong distances. Idaho also noted that none ofthe TSDs identified Ielaho sources as significant contributors to any 1997 8-hour ozone nonattainment area. EPA also reviewed and analyzed information available for the designateel1997 8-hour
ozone nonattainment areas in states surrounding Idaho. Although significant contribution must be measured notjust against nonattainment areas, but against areas with monitors showing violations ofthe NAAQS, nonattainment areas are a convenient starting point for the analysis.

15For the 1997 8-hour ozone NAAQS, the only nonattainment area in states bordering Idaho is Clark County in southern Nevada (Las Vegas area). In 2005, EPA designated this area nonattainment for violations ofthe 1997 8-hour ozone standard. 69 FR 23858 (April 30, 2004) and 40 CFR 81.329. EPA has evaluated whether emissions from Idaho contribute significantly to the nonattainment ofthe 8-hour ozone standard in Clark County. Clark County is about 350 miles south ofthe closestpoint on the Idaho border. Distance per se is not an obstacle to long range transport ofozone and/or its precursors, as discussed in the January 30, 2004, notice proposing CAIR (69 FR4599); NOx (the primary ozone precursor that was the object ofthe CAIR transport study) maybe transported for long distances, contributing significantly to high
ozone concentrations in other states. However, with increasing distance there are greater opportunities for ozone and/or NOx dispersion and/or removal ii'om the atmosphere due to the effects ofwinds and chemical sink processes. In this context, one may conclude that the 350 mile distance between Idaho and the Clark County nonattainment area decreases, but does not exclude, the possibility ofsignificant contribution to this area's nonattainment. Another transport factor is wind direction. Clark County, Nevada is south ofIdaho and, therefore, is not in the predominant direction ofwinds from Idaho. Transport winds across Idaho generally flow from west to east, and not toward the south. Given the relatively long distance between Idaho and Clark County, Nevada and the general west-to-east direction oftransport winds across Idaho, EPA believes it is reasonable to conclude that Idaho sources do not significantly contribute to
nonattainment ofthe 1997 8-hour ozone NAAQS in Clark County, Nevada.

Ozone Monitoring Datain Other Areas ofSurrounding States

16As mentioned above, EPA considers not only significant contribution to designated nonattainment areas, but also to areas with monitor readings showing violations ofthe NAAQS, Areview ofthe most recent monitoring data from EPA's Air Quality System (AQS) for the bordering states ofWashington, Oregon, Nevada, Utah, Wyoming and Montana shows no monitors violating for the 1997 8-hour ozone NAAQS, Areview ofpast monitoring datafrom 1999 through 2008 shows that the only area in any ofthese border states that violated the 1997 8- hour ozone NAAQS was Salt Lake City, Utah, This area, however, is not currently violating and has not violated the 1997 8-hour ozone NAAQS since a violation occUlTed at a single monitorin 2007. Observed days ofhigh ozone levels in the SaltLake City metropolitan area are usually associated with a 'bowl effect' resulting from an inversion that has a stagnant air pollution mass surrounded bythe Oquirrh Mountains to the west, the Great SaltLake to the north, and the Wasatch Range on the east. 12 In light ofthese considerations, it is unlikely that Idaho makes a significant contribution ofozone and/or ozone precursors in the SaltLake City area. In addition, none ofthe ozone monitors in Idaho have themselves indicated a violation of the 1997 8-hour ozone NAAQS, and Boise, Idaho, the area ofIdaho with the highest concentrations ofozone, is almost 300miles from SaltLake City. The absence ofviolations in Idaho itselfdo not rule out the possibility oftransport, but taken in conjunction with other relevant information, this fact helps to support the conclusion that there is no such transport from Idaho to Salt Lake City. Distanceper se is also not an obstacle to long range transport ofozone and/or its precursors, as discussed above. However, with increasing distance there are greater opportunities for ozone and/orNOx dispersion and/or removal from the atmosphere due to the effects ofwinds lind chemical sink processes. In this context, the 300 mile distance between

12 Approval and Promulgation ofState Implementation Plans; State of Utah; Interstate Transport ofPollution and Other Revisions (73 FR 16543, March 28, 2008). 17Idaho and the SaltLake City area reduces but does not exclude the possibility ofsignificant contribution to this area's nonattainment. Takinginto account the total weight ofall ofthe factors discussed above, EPA concludes that Idaho does not significantly contribute to 1997 8- hour ozone NAAQS nonattainment in another state.

3. State Regulatory Provisions In addition to monitoring data providing evidence that Idaho sources do not contribute to
nonattainment in any other state, Idaho points to air qualityprovisions in its regulations that prohibit emissions that contribute significantly to nonattainment. Specifically, the Statepoints to its air quality provisions at IDAPA 58.01.01.203.02 that require that a proposed source's projected emissions will not cause or significantly contribute to a violation ofany ambient air quality standard. The state explains that this provision applies to both major and minor sources and that the owner or operator ofsuch a source must demonstrate that the source's projected emissions will not cause or significantly contribute to a violation ofany ambient air quality standard. In addition, they point outthat the demonstration is not constrained to evaluating impacts solelyin Idaho and that all estimates ofambient concentrations must be based on the requirements specified in 40 CFR 51, Appendix W, which look to the point ofmaximum concentration, not ajurisdictional boundary. The state also relies on its rules for existing sources at IDAPA 58.01.01.401.03, which provide IDEQ with the authority to require a permit (called a "TierIIpermit") ifemission rate reductions are necessary to attain any ambient air quality standard. As part ofthe Tier II permittingprocess, the facility operator (or responsible official) must demonstrate the source does not cause or significantly contribute to a violation ofany ambient air quality standards.

18The state asserts that it has used this authority in the past as part ofa suite ofcontrol measures implemented to address nonattainment and other air quality issues and this authority could be used ifthe state's emissions were significantly contributing to nonattainment in another state. For example,between 2000 and 2003 the state issued fifteen Tier IIpermits to sources in two PMIO nonattainment areas to establish federally-enforceable emission limits on PMIO emissions in order to ensure that the PMIO NAAQS would be attained and maintained. A summary ofthese 15 permits, including links to the permits on the Idaho website, is included in the docket for this rulemaking. Idaho incorporates byreference annually any updates to the NAAQS ensuring that implementation ofthe regulatoryprovisions at IDAPA 58.01.01.203.02 and IDAPA 58.01.01.40.03 are implementing the most recently revised NAAQS. In light ofthese air qualityprovisions in Idaho's regulations and evidence that Idaho has used these air quality provisions to address nonattainment and other air quality issues in the past, EPAbelieves that in this case these regulatory provisions provide additional supportfor our conclusion that emissions from Idaho sources do not significantly contribute to nonattainment in any other state and that Idaho has the ability to address nonattainment if, in the future, the state's emissions significantly contribute to nonattainment ofthe 1997 8-hour ozone and 1997 PM2.5 NAAQS in another state.

4. Conclusion Regarding Significant Contl'ibution to Nonattainment Thedata and weight ofthe evidence analysis presented above support EPA's conclusion that the Idaho Interstate Transport SIP (submitted on June 28, 2010) is adequate to ensure that emissions from Idaho do not significantly contribute to nonattainment in any other state for the

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# I I I I I

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I 

# I 

# I I I I I I1997 8-hour ozone or 1997 PM2.5 NAAQS, consistent with the requirements ofelement (1) of CAA section 110(a)(2)(D)(i)



### B. EPA's Evaluation oflnterference with Maintenance 

### 1. Background The second element ofCAA section 11O(a)(2)(D)(i) requires that a state's SIP must prohibit any source or othertype ofemissions activity 

### in the state from emitting pollutants that would "interfere with maintenance" ofthe applicable NAAQS in any other state. The CAA does not specifically mandate how interference with maintenance is to be determined. Therefore, EPA has interpreted this term in past regulatory actions, such as the 1998 NOx SIP Call, in which EPA took action to remediate emissions ofNOx that significantly contributed to nonattainment, orinterfered with maintenance of, the then applicable ozone NAAQS through interstate transport ofNOx and the resulting ozone. t3 The NOx SIP Call was the mechanism through which EPAevaluated whether or not the NOx emissions from sources in certain states had such prohibited interstate impacts, and 

### ifthey had such impacts, required the states to adopt substantive SIP revisions to eliminate the NOx emissions, whether through participation in a regional cap and trade program orbyother means. After promulgation ofthe 1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS, EPA again recognized that regional transport was a serious concern throughout the eastern United States and therefore developed the 2005 CAIRto address emissions ofS02 and NOx that exacerbate ambient ozone and PM2.5 levels in many downwind areas through interstate

13 See, 63 FR 57356 (October 27,1998). EPA's general approach to section llO(a)(2)(D) was upheld in Michigan v. EPA, 213 F.3d 663 (D.C. Cir. 2000), cert denied, 532U.S. 904 (2001). However, EPA's approach to interference with maintenance in the NOx SIP Can was not explicitly reviewed by the court. See, North Carolina v. EPA, 531 F.3d 896, 907

- 09 (D.C. Cir. 2008). 20transport. 14 Within CAIR, EPAlikewise interpreted the term "interfere with maintenance" as part ofthe evaluation ofwhether ornot theemissions ofsources in certain states had such impacts on areas that EPA determined would eitherbe in violation ofthe NAAQS, or would be injeopardyofviolating the NAAQS, in a modeled future year unless action were taken by upwind states to reduce 

### S02 and NOx emissions. Through CAIR, EPA again required states that had such interstate impacts to adopt substantive SIP revisions to eliminate the S02 and NOx emissions, whether through participation in a regional cap and trade program orbyother means. EPA's 2006 Guidance addressed CAA section 110(a)(2)(D) requirements for the 1997 8- hour ozone NAAQS and 1997 PM2.5 NAAQS. For those states subject to CAIR,EPA indicated that compliance with CAIR would meet the two requirements ofsection llO(a)(2)(D)(i)(I) for these NAAQS. For states not within the CAIR region, EPArecommended that states evaluate whether ornot emissions from their sources would "interfere with maintenance" in other states, following the conceptual approach adopted byEPA in CAIR. After recommending various types ofinformation that couldberelevant for the technical analysis to support the SIP submission, such as the amount ofemissions and meteorological conditions in the state, EPAfurther indicated that it would be appropriate for the state to assess impacts ofits emissions on other states using considerations comparable to those used byEPA "in evaluating significant contribution to nonattainment in the CAIR."IS EPA did not make specific recommendations for how states should assess "interfere with maintenance" separately, and discussed the first two elements ofsection 11O(a)(2)(D) together without explicitly differentiating between them.

" See, 70FR 25162 (May 12, 2005). 15 2006 Guidance at page 5. 21In 2008, however, the U.S. Court ofAppeals for the D.C. Circuit found that CAIR and the related CAIRfederal implementationplan were unlawful.16 Among other issues, the court held that EPAhad not correctly addressed the second element ofsection 11O(a)(2)(D)(i)(I) in CAIR. The court noted that "EPA gave no independent significance to the 'interfere with maintenance' prong ofsection 11O(a)(2)(D)(i)(I) to separately identify upwind sources interfering with downwind maintenance.,,17 EPA's approach, the courtreasoned, would leave
areas that are "barelymeeting attainment" with "norecourse" to address upwind emissions
sources. 18 The court therefore concluded that a plain language readingofthe statute requires EPA to give independent meaning to the interfere with maintenance requirement ofsection 1l0(a)(2)(D) and that the approach used byEPA in CAIR failed to do so. In addition to affecting CAIR directly, the court's decision in the North Carolinacase indirectly affects EPA's recommendations to states in the 2006 Guidance with respect to the interfere with maintenance element ofsection 11O(a)(2)(D) becausethe agency's guidance suggested that states use an approach comparable to that used by EPA in CAIR. States such as Idaho have made SIP submissions that relyupon the reconunendations in EPA's 2006 Guidance. Given the court decision on CAIR in the interim, however, EPAbelieves that it is necessary to evaluate these state submissions for section 110(a)(2)(D) in such a way as to assure that the interfere with maintenance element ofthe statute is given independent meaning and is appropriately evaluated using the types ofinformation that EPA recommended in the 2006 Guidance. To accomplish this, EPAbelieves it maybe necessary to supplement the technical analysis providedthe statein order to adequatelyevaluate the submissions with the respect to the interfere with maintenance element ofsection llO(a)(2)(D).

16 See, North Carolina v. EPA, 531 F.3d 896 (D.C. Circuit 2008). 11 Id. 531, F.3d at 909 18 Id. 22EPA has recentlyproposed a new rule to address interstate transport pursuant to section 11O(a)(2)(D), the "Federal ImplementationPlans to Reduce Interstate Transport ofFine Particulate Matter and Ozone" (Transport Rule Proposal), in orderto address thejudicial remand ofCAIR. 19 As part ofthe TransportRule Proposal, EPA specificallyreexamined the section llO(a)(2)(D) requirementthat emissions from sources in a state mustnot "interfere with maintenance" ofthe 1997 8-hourozone NAAQS and 1997 PM2.5 NAAQS inother states. In the proposal, EPAdeveloped an approach to identify areas that itpredicts to be close to the level of the 1997 8-hour ozoneNAAQS and 1997 PM2.5 NAAQS, and therefore at risk to become nonattainmentfor these NAAQS unless emissions from sources in other states areappropriately controlled. This approach starts byidentifying those specific geographic areas for which further evaluation is appropriate, and differentiates between areas where the concern is with interference with maintenance, rather than with significant contribution to nonattainment. As described in more detail below, EPA's analysis evaluates data from existing monitors
overthree overlapping three year periods (i.e., 2003-2005, 2004-2006, and 2005-2007), as well
as air quality modeling data, in order to determine which areas are predicted as likely to be violating the 1997 8-hour ozone and PM2.5 NAAQS in 2012, and which areas are predicted to potentiallyhave a difficulty with maintaining attainment as ofthat date. In essence, ifan area's projected data for 2012 indicates that it would be violating the NAAQS based on the average of these three overlappingperiods, then this monitor location is appropriate for comparison for purposes ofthe significant contribution to nonattainment element ofsection 11O(a)(2)(D). If, however, an area's projected data indicate that it wouldbe violating the NAAQS based on the highest singleperiod, but not overthe average ofthe three periods, then this monitorlocation is

19 See "Federal Implementation Plans to Reduce Interstate Transport afFine Particulate Matter and Ozone," 75 FR 45210 (August 2, 2010). 

### 23appropriate for comparisonfor purposes ofthe interfere with maintenance element ofthe 20 statute.Bythis method, EPAhas identified those areas with monitors that are appropriate "maintenance sites" ormaintenance "receptors" for evaluating whether the emissions from
sources in another state could interfere with maintenance inthat particular area. EPA then uses other analytical tools to examine the potential impacts ofemissions from upwind states on these maintenance sites in downwind states. EPAbelieves that this new approach for identifying those
areas that are predicted to have maintenance problems is appropriate to evaluate the section 110(a)(2)(D) SIP submission ofa state for the interfere with maintenance element. 2t EPA's 2006 Guidance did not provide this specific recommendation to states, but in light ofthe court's decision on CAIR, EPA will itselffollow this approach in acting upon the Idaho submission. As explained in the 2006 Guidance, EPAdoes not believe that section 110(a)(2)(D) SIP submissions from all states necessarily need to follow preciselythe same analytical approach of CAIR or the Transport Rule Proposal. In the 2006 Guidance, EPA stated that: "EPAbelieves that the contents ofthe SIP submissionrequired by section 11O(a)(2)(D) may vary, depending upon the facts and circumstances related to the specific NAAQS. In particular, the data and analytical tools available at the time the State develops and submits a SIP for a new orrevised NAAQS necessarily affects the contents ofthe required submission.,,22 EPA also indicated in

20 A memorandum in the docket for this action provides the information EPA used in order to identify monitors that arc receptors for evaluation ofinterference with maintenance for certain states in the western United States. See, Memorandum from Brian Timin ofEPA's Office ofAir Quality Planning and Standards, Air Quality Modeling Group entitled "Documentation ofFuture Year Ozone and Annual PM2.5 Design Values foJ' Westel'll States" (August 2010)(Timin Memo). 21 To begin this analysis. EPA first identifies all monitors projected to be in nonattainment 01', based on historic variabillty in air quality, projected to have maintenance problems in 2012. The "problem" is that these maintenance areas are at risk not to stay in attainmentbecause they are-so close to the level ofthe 1997 ozone and PM2. 5NAAQS thatminOl' variations in weather or emissions could result in violations ofthe NAAQS in 2012. 22 2006 Guidance at4. 24the 2006 Guidance that it did not anticipate that sources in states outside the geographic area coveredbyCAIR were significantlycontributing to nonattainment, or interfering with maintenance, in other states. 23 As noted in the Transport Rule Proposal, EPAcontinues to believe that the more widespread and serious transport problems in the eastern United States are analytically distinct.24 For the 1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS, EPA believes that nonattainment and maintenance problems in the western United States are relatively local in nature with only limited impacts from interstate transport. In the Transport Rule Proposal, EPAdid not calculate interstate ozone or PM2.5 contributions to orfrom western states. Accordingly, EPAbelieves that section 1l0(a)(2)(D) SIP submissions for states outside the geographic area ofthe Transport Rule Proposal maybeevaluated using a "weightofthe evidence" approach that takes into account available relevant information, such as that recommended byEPA in the 2006 Guidance for states outside the area affected byCAIR. Such information may include, butis not limited to, the amount.ofemissions in the state relevant to the NAAQS in question, the meteorological conditions in the area, the distance from the state to the nearest monitors in other states that are appropriate receptors, or such other information as maybe probative to consider whether sources in the state may interfere with maintenance ofthe 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS in other states. These submissions can rely
on modeling when acceptable modeling technical analyses are available, butEPA does not believe that modeling is necessarily required ifother available information is sufficient to evaluate the presence or degree ofinterstate transport in a given situation.



### 2. Idaho's Interference withMaintenance Demonstration

23 Id. at 5. 24 See, TransportRule Proposa1, 75 FR45210 (August 2, 2010) at page45227. 

### 25To show that Idaho emissions, as controlled under its SIP, do not interfere with maintenance ofthe 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS in another state, Idaho's submittal analY2:ed several types offactors to support its assertion. First, for its PM2.5 analysis, Idaho relied oninformation from the Western Regional AirPartnership (WRAP) Technical Support Systelll (TSS). The WRAPTSS is a system developed in a collaborative effort by state and tribal governments and federal agencies to provide the tools needed to comply with the federal Regional Haze Rule. Idaho used itto provide general insight on how Idaho
sources influence PM2 .5 concentrations in Class I areas in surrounding states. Forthe 8-hour
ozone NAAQS, Idaho evaluated NOx and VOC emissions data from Idaho sources. These emissions data were evaluated to understand how Idaho's emissions sources may contribute to
ozone impacts in surrounding states. The WRAPTSS results provided in Idaho's submittal to address the 1997 PM2.5 standard and Idaho's evaluation ofNOx and VOC emissions data from Idaho sources to address the 1997 8-hour ozone NAAQS are discussed later. Idaho also relied oninformation about air stagnation conditions in other states to show that Idaho sources do not interfere with maintenance ofthe 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS. Idaho argued that stagnant airconditions are associated with weak transport and were citedin technical support documents for the 8-hour ozone and PM2 .5 designations as a major contributing factor to poor air qualityin surrounding states. Idaho also identified its state air qualityregulations to demonstrate boththat Idaho can, and does, work with other states and tribes to ensure that an Idaho activity would not interfere with maintenanceby any other State with respect to the NAAQS. Idaho also relies on its permittingrules discussed earlierthat not onlyrequire for new
sources a demonstration that the proposed source's emissions will not cause or signit1cantly



### 26

## I

# II \ \ \ \ \ \
\

# I I \contribute to a violation ofany ambient air quality standard, but also specificallyrequire for existing sources an operating permit ifemission rate reductions are necessary to attain or maintain any ambient air quality standard. Italso points out that neither ofthese required demonstrations is limited to an analysis ofimpacts solely in Idaho. In light ofthese provisions and evidence that Idaho has used these air quality provisions in the past, as discussed in the section on significant contribution (section IV.A), EPAbelieves that in this case these regulatory provisions support our conclusion that Idaho does not interfere with maintenance in any other state and that Idaho has the ability to address interference with maintenance ifin the future the state's emissions interfere with maintenance ofthe 1997 8-hour ozone and 1997 PM2.5NAAQS in another state.



### 3. EPA Supplemental Analysis On July 6, 2010, the EPA proposed a rulemaldng proposal (theTransport Rule Proposal) in response to thejudicial remand ofCAIR. The Transport Rule Proposal includes a new approach to determine whether emissions from a state interfere with maintenance ofthe 1997 8- hour ozone NAAQS and the 1997 PM2.5NAAQS in other states. EPA is using a comparable approach to that ofthe Transport Rule Proposal in this action in order to evaluate whether emissions from Idaho sources interfere with maintenance ofthese NAAQS in other states. In the Transport Rule Proposal, EPA projected future concentrations ofozone and PM2.5 to identify areas that are expected to be out ofattainment with the NAAQS or to have difficulty maintaining compliance with the NAAQS in 2012. These areas are referred to as nonattainment and maintenance receptors, respectively. These nonattainment and maintenance receptors are based on projections offuture air quality at existing ozone and PM2.5 monitoring sites in those

27

# I Ilocations. EPA then used these sites as the receptors for examining the contributions of emissions from sources located in upwind states to nonattainment and maintenance problems at these monitoring locations. Monitoring data was obtained from AQS·. For the PM2 .5 NAAQS EPA evaluated concentrations ofboth the annual PM2 .5 NAAQS and the 24-hour PM2 .5 NAAQS. The 1997 annual PM2.5 NAAQS is met when the 3-year average ofthe annual mean concentrationis 15.0 micrograms per cubic meter**(~Lg/m3)** or less. The 3- year average annual mean concentration is computed at each siteby averaging the dailyFederal Reference Method (FRM) samplesbyquarter, averaging these quarterly averages to obtain an annual average, and then averaging the three annual averages to get the design value. The 2006 24-hour PM2.5 NAAQS is met when the 3-year average ofthe annual 98th percentile PM2.5 concentrations is 35**~Lg/m3** orless. The 1997 24-hour PM2.5 NAAQS is met when the 3-year average ofthe annual 98thpercentiles is 65**~Lg/m3** orless. The 3-year average mean 98th percentile concentration is computed at each site by averaging the 3 individual annual 98th percentile values at each site. The 3-year average98th percentile concentrationis referred to as the 24-hour average design value. In this action, EPA is only evaluating whether Idaho's emissions impact other states' ability to maintain the 1997 annual and 24-hourPM2.5 NAAQS and the 1997 8-hour ozone NAAQS, because those are the NAAQS at issue in this section 1l0(a)(2)(D) SIP submission. In later actions, the state and EPA will evaluate the impacts of interstate transport from emissions from Idaho sources with respect to otherNAAQS. Forthe ozone NAAQS, EPA evaluated concentrations relevant to the 1997 8-hour ozone NAAQS. The level ofthe1997 8-hour ozone NAAQS is 0.08 parts per million (ppm). The 8- hour ozone standard is met ifthe 3-year average ofthe annual 4th highest daily maximum 8-hour
ozone concentration is less than orequal to 0.08 ppm (i.e., less than 0.085 ppmbased on the

28rounding convention in 40 CFRpart 50 Appendix I). This 3-year average is referred to as the "design value." To project future ozone and annual PM2.5 design values, EPA projected future ozone values based on an average ofthree design value periods which include the years 2003-2007 (Le., design values for 2003-2005,2004-2006, and 2005-2007). The average ofthe three design values creates a "5-year weighted average" value. The 5-year weighted average values were then projected to the future years that were analyzed for theTransport Rule Proposal.25

. 26 EPA used the 5-year weighted average concentrations to project concentrations anticipated in 2012 to determine which monitoring sites are expected to be nonattainment in this future year. EPA also projected 2012 design values based on each ofthe three year periods (i.e., 2003-2005, 2004- 2006, and 2005-2007). The highest projection isreferred to as the "maximumdesign value" and gives an indication ofpotential variability in future projections due to differences in actual meteorology and emissions from what was modeled. EPAidentified those sites that are projected to be attainment based on the 5-year weighted average design value, but that have a maximum design value (based on a single three year period) that exceeds the NAAQS, as maintenance sites becauseEPA anticipates that there will be more difficulty in maintaining attainment ofthe NAAQS at these locations ifthere are adverse variations in meteorology oremissions. Theseprojected maintenance sites are the ones thatEPA has used to determine ifemissions from Idaho sources potentially interfere with maintenance ofthe 1997 8-hour ozone NAAQS and 1997 annual PM2.5 NAAQS in other states in this action.

25 See, the TransportRule Proposal at 75 FR 45210 (August 2, 20!O) 26 Additional information concerning these weighted averages is provided in the docket in the Timin Memo. 29

### ! I I I I I I I I I

I I I

I I I I I I I I I IFor the annual PM2.5 NAAQS, EPA identified from the modeling analyses conducted for the Transport Rule Proposal the following sites as maintenance receptors: a site in Cook County, Illinois in the Chicago area; a site in Harris County, Texas, in the Houston/Galveston/Brazoria
area. Fromthe modeling analysis conducted for states not included in theTransport Rule Proposal, EPA identified only sites in southern California. Based on recent monitoring data (2007-2009 design values that are under final EPA review), the highest 24-hour PM2.5 design value in the 47 states ofthe continental U.S. (notincluding California) is 50 Itg/m3, which is well below the level ofthe 1997 24-hour PM2.5 NAAQS of65 f,lg/m3.27 Therefore, outside of California, there are no areas that we would expect to have difficulty in maintaining the1997 24- hour PM2 . 5NAAQS. From the modeling analyses conducted for the Transport Rule Proposal, EPA identified a number ofmaintenance sites orreceptors for the 1997 8-hour ozone NAAQS: several sites in the Texas area and other sites in Georgia, Pennsylvania, New York and Connecticut.28 Forthe modeling analysis conducted for states not included in the Transport Rule Proposal (Le. states not included fully in the 12 kmTransport Rule Proposal modeling domain), EPAidentified several maintenance sites in southern and central Californiausing available 36 kmmodeling. 29 The 12 kmTransport Rule Proposal modeling domain extends from Texas northward to North Dakota and eastward from the Rocky Mountains to the east coast and includes 37 states and the District ofColumbia.

27 Data**UI~dergoing** review from EPA's Air Quality System which is EPA's repository ofambient air quality data, (http://www.epa.gov/ltn/airs/airsaqs/) 28 Transport Rule Proposal. 75 FR 45210, (August 2. 2010). pages 45253-45270, andTimin Memo 29 The Transport Rule Proposal identifies nonattainment and maintenance receptors in the Eastern U.S. Itdocs not include modelingresults for the West. The Timin Memo documenls further evaluation ofthe 2012 modeling to identify nonattainrnent and maintenance receptors in the West. 30Significantly, for both the 1997 PM2.5 NAAQS and the 1997 8-hour ozone NAAQS, EPA's analysis did not identify any maintenancereceptors in the states that border Idaho (Washington, Oregon, Nevada, Utah, Wyoming and Montana).

Cal Interfere with Maintenance Evaluation for the PM2.5 NAAOS For the 1997 PM2 .5 NAAQS, the closest maintenance receptor site identified bythe Transport Rule Proposal was in Cook County, Illinois. Cook County, Illinois is over 1000 miles east ofthe closestpoint on Idaho's border, and on the other side oftheRockyMountains. Given the relatively long distance and the intervening mountainous topographybetween Idaho and Cook County, EPAbelieves it is reasonable to conclude that there is a very low probability that Idaho sources interfere with maintenance in that area. Itis also reasonable to conclude that Idaho emissions would not have such impacts at other identified maintenance sites east ofCook County. In the west, the closest maintenance receptor to Idaho was in Fresno County, California. Fresno Countyis located almost 400 miles southwest ofthe closest point on tHe Idaho border and
on the other side ofthe SierraNevadaMountains, which act as a natural barrierto air movement between Idaho and California. In addition, Fresno County, located in southern California, is not in the predominant direction ofwinds from Idaho. As noted earlier, transport winds across Idaho generally flow from west to east, and not towardthe southwest. Given the relatively long distance between Idaho and southern California, the intervening mountainous topography, and the general direction ofwest-to-east transport winds across Idaho, EPA concludes that there is no reasonable basis to conclude that Idaho sources interfere with maintenance ofthe 1997 PM2.5 NAAQS in those areas. Itis likewise reasonable to conclude that Idaho emissions would not

31

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## I I 

### I I 

### I I 

### I 

### Ihave such impacts at other identified maintenance sites in California. Based onEPA modeling and all ofthese factors taken together, EPAbelieves it is reasonable to conclude that Idaho emissions under the SIP do not interfere with maintenance ofthe 1997 PMZ .5NAAQS in any other state. This conclusion is consistent with the information and analysis Idaho provided in its SIP submittal regarding interference with maintenance ofthe 1997 PMZ .5NAAQS. With respect to PMZ.5, Idaho used the WRAPTSS tools to provide general insight on how Idaho sources influence PMz.5concentrations in surrounding states and to conclude that Idaho sources did not interfere with maintenance ofthe 1997 PMZ.5NAAQS in any other state. Due to the limitations and purpose ofthe WRAPTSS, Idaho only evaluated impacts on Class I areas in surrounding states using these tools. BecauseEPA's analysis did not predict any ofthese Class I areas to have a difficulty with maintaining attainment ofthe 1997 PMZ.5 NAAQS, any impact Idaho might have on those areas would not, bydefinition, interfere with maintenance. Therefore, further evaluation ofIdaho's analysis ofPMz.5impacts on those areas is unnecessary.
(b) Interfere with Maintenance Evaluation for the 8-Hour OzoneNAAOS. Forthe 1997 8-hour ozone NAAQS, the closest maintenance receptor site to the east of Idaho was the Dallas-FtWorth area in Texas. Dallas-FtWorthis located over 1000 miles southeast ofthe closest point on Idaho's border and on the other side ofthe Rocky Mountains. Given the relatively long distance and the intervening mountainous topography between Idaho and Dallas-FtWorth, it is reasonable to conclude that Idaho sources do not interfere with maintenance in the Dallas-FtWorth area. Itis also reasonable to conclude that Idaho emissions



### 32would not have such impacts at other identified maintenance sites elsewhere further east or south ofDallas-Ft Worth. In the west, the closest maintenance receptor to Idaho was in Nevada County, California. Nevada County is almost 300 miles southwest ofthe closestpoint on Idaho's border and located
on the other side ofthe Sierra NevadaMountains, which act as a natural barrier to air movement between Idaho and California. In addition, Nevada Countyis in central California and is notin the predominant directfon oftransport winds. As noted earlier, transport winds across Idaho generally flow from west to east. Although westerly winds are not always the case, meteorological data show that transport winds in Idaho tend to be southerly or westerly during hot and stagnant weather conditions conducive to ozone formation in California. Given the relatively long distance between Idaho and central California, the intervening mountainous topography, and the general direction ofwest-to-east transport winds across Idaho, EPAbelieves it is reasonable to conclude that Idaho sources do not interfere with maintenance ofthe 1997 8- hour ozone NAAQS in Nevada County, California. Itis also reasonable to conclude that Idaho emissions would not have such impacts at other identified maintenance receptor sites elsewhere in central or southem California. Based on all ofthese factors taken together, EPAbelieves itis reasonable to conclude that Idaho emissions do not interfere with maintenance ofthe 1997 8- hour ozone NAAQS in anyother state. This conclusionis consistent with the information Idaho provided in its SIP submittal regarding interference with maintenance ofthe 1997 8-hour ozone NAAQS. Forthis element for the 8-hour ozone NAAQS, Idaho evaluated NOx and VOC emissions data to understand how Idaho's emissions sources may contribute to ozone impacts in surrounding states and to conclude that Idaho sources do not interfere with maintenance ofthe 1997 8-hour ozone NAAQS in any

33

### 1 

# I I I I
1other states. BecauseEPAmodeling did not predict any ofthe areas in states surrounding Idaho to have difficulty with maintaining attainment ofthe 8-hour ozone NAAQS, any impactIdaho might have on those areas would not, by definition, interfere with maintenance. Therefore, further evaluation ofIdaho's analysis ofozone impacts on those areas is unnecessary.



### 4. Conclnsion Regarding Interference with Maintenance The data and weight ofevidence analysis presented above support the conclusion that the Idaho Interstate Transport SIP (submitted on June28,2010) is adequate and that emissions from Idaho do not interfere with maintenance in any other state for the 1997 8-hour ozone or 1997 PM2.5 NAAQS, consistent with the requirements ofelement (2) ofCAA section 11O(a)(2)(D)(I).



### C. EPA's Evaluation ofInterference with PSD measures in otherstates 'The third element ofsection 11O(a)(2)(D)(i) requires a SIPto contain adequate provisions prohibiting emissions that interfere with any other state's required measures to prevent significant deterioration ofits air quality. EPA's2006 Guidance maderecommendations for SIP submissions to meet this requirement with respect to both the 1997 8-hour ozone NAAQS and the 1997 PM2 . 5 NAAQS. EPAbelieves that Idaho's submission is consistent with the 2006 Guidance, when considered in conjunction with PSD programrevisions that EPAproposed to approve on March 18,2010 (75 FR 13058). EPA's proposed approval ofIdaho's SIP for purposes ofmeeting the requirements of section 110(a)(2)(D)(i)(II) is contingent upon the final approval ofthePSD programrevisions in the form specified in EPA'sproposed approval, referenced above. The State's submittal indicates in Section4, "Interfere with Prevention ofSignificantDeterioration of

34Air Quality," that the State's SIP provisions include an EPA-approved PSD program. Idaho's regulations for its PSD program were last approved byEPA and made part ofthe SIP on January 16,2003 (68 FR 2217), 40CFR 52.670, effective February 18,2003. On March 18,2010, EPA proposed to approve Idaho's PSD rule revisions incorporating into the State's rules the provisions ofEPA's PSD requirements as ofJuly 1,2008, including the November 29,2005, Phase 2 rule for the 1997 8-hour ozone NAAQS (70 FR 71612), and the May 16,2008, PM2j Implementation Rule (73 FR 28321) for the 1997 PM2.5 NAAQS. We anticipate taking final action approving Idaho's PSD rule revisions before taking final action on this interstate transport proposal. Therefore, EPAproposes to approve this SIP provision as adequate for purposes of section 110(a)(2)(D)(i)(II) ifEPA has taken final action to approve the revisions to Idaho's PSD requirements that are consistent with our proposed action. EPA believes that the PSD revision for the 1997 8-hour ozone NAAQS that makes NOx
aprecursor for ozone for PSD purposes and the PSD revision for the 1997 PM2.5 NAAQS that makes S02 and NOxprecursors for PM2.5 for PSD purposes, taken together with the revised PSD SIP that EPA proposed to approve onMarch 18,2010, and the Interstate Transport SIP that EPA is proposing to approve in this action, satisfy the requirements ofthe third element ofsection 11O(a)(2)(D)(i) for the1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS. Thatis, these provisions ensurethatthere will be no interference with any other state's required PSD measures because Idaho's SIP, as proposed for approval in this action along with the March 18,2010 proposed action on the revised PSD rules, will meet current CAA requirements for PSD.

V. Proposed Action

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# IIn light ofthe data and the weight ofthe evidence analysis presented above, EPA is proposing to approve revisions to the Idaho SIP, submitted on June 28, 2010, which adequately demonstrate that for the 1997 8-hour ozone and 1997 PM2.5 NAAQS, airpollutant emissions from sources within Idaho do not (1) significantly contribute to nonattainment ofthe NAAQS in any other state, (2) interfere with maintenance ofthe NAAQS byany other state, and (3) interfere with any other state's required measures to prevent significant deterioration ofits air quality, as required by section 110(a)(2)(D)(i). As noted previously, EPA will address element (4), interference with any other state's required measures to protect visibility, in a separate action. EPA will also take action on the portion ofIdaho's SIP that addresses the 2006 PM2.5 NAAQS in a separate action.



### VI. StatutOl'Y and Executive Order Reviews Under the Clean Air Act, the Administrator is required to approve a SIP submission that complies with the provisions ofthe Act and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria ofthe Clean Air Act. Accordingly, this action merely proposes to approve state law as meeting Federalrequirements and does not impose additional requirements beyond those imposedby statelaw. For that reason, this action:
• is not a "significantregulatory action" subject to review bythe Office ofManagement and Budget underExecutive Order 12866 (58 FR 51735, October4, 1993);
• does not impose an information collection burdenunder the provisions ofthe Paperwork Reduction Act (44 U.S.c. 3501 

### etseq.);

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I

## I 1 1 1 1 1 1 1 

### 1 1 1 

## \ \ \ \ \ \ \ \ \ \ \• is certified as not having, a significant economic impact on a substantial number ofsmall entities under the Regulatory FlexibilityAct (5 U.S.c. 601 etseq.);
• does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Public Law 104-4);
• does not have Federalismimplications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• is not an economically significantregulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• is not a significantregulatory action subject to Executive Order 13211 (66 FR28355, May 22,2001);
• is not subject to requirements ofSection 12(d) ofthe National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application ofthose requirements would be inconsistent with the Clean Air Act; and
• does not provide EPA with the discretionary authority to address, as appropriate, disproportionate human health orenvironmental effects, using practicable and legally permissible methods, under Executive Order 12898 (59 FR 7629, February 16, 1994). In addition, this proposed rule does not have tribal implications as specified byExecutive Order 13175 (65 FR 67249, November 9, 2000), because the SIP is not approved to apply in Indian country located in the state, and EPA notes that itwill not impose substantial direct costs
on tribal governments orpreempt tribal law.

37List ofSubjects in 40 CFR Part 52 Environmentalprotection, 

### Air pollution control, Incorporation byreference, Intergovernmental relations, Ozone,Particulate matter, Reporting and recordkeeping requirements, Volatile organic compounds.

Dated: September 2, 2010

# ~'-'--+S{':!JJ (**l-\:('~~ ~** **~.** Dennis J. McLerran Regional Administrator Region 10

38

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