ENVIRONMENTAL PROTECTION AGENCY 

40 CFR Part 52 

[EPA-RI0~OAR-2010-0669; FRL-XXXX-XJ 

Approval and Promulgation of Implementation Plans; 

Idaho; Interstate Transport of Pollution 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Proposed Rule. 

SUMMARY: EPA is proposing to approve a State Implementation Plan (SIP) revision 

submitted by the State of Idaho for the purpose of addressing the "good neighbor" 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 of Idaho's SIP have adequate provisions to prohibit air 

emissions from adverselY affecting another state's air quality through interstate transport. In this 

action, EPA is proposing to approve the Idaho Interstate Transport SIP provisions that address 

the requirement of section 11O(a)(2)(D)(i) that emissions from Idaho sources do not significantly 

contribute to nonattainment of the 1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS in 

any other state, interfere with maintenance of the 1997 8-hour ozone NAAQS and the 1997 

PM2.5 NAAQS in any other state, and interfere with measures required in the SIP of any other 

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state under part C of subchapter I of the CAA to prevent significant deterioration of air quality. 

This action is being taken under section 110 and part C of subchapter I of the Clean Air Act (the 

Act orCAA). 

DATES: Written comments must be received on or before [insert date 30 days from date of 

publication]. 

ADDRESSES: Submit your comments, identified by Docket ill No. EPA-R10-0AR-2008-

0391, by one of the 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 9810 1 

D. Hand Delivery: U.S. Environmental Protection Agency, Region 10, Attn: Donna Deneen 

(AWT-107), 1200 Sixth Avenue, Suite 900, Seattle, Washington 98101, 9th Floor. Such 

deliveries are only accepted during normal hours of operation, and special arrangements 

should be made for deliveries of boxed information. 

Instructions: Direct your comments to Docket ID No. EPA-RlO-0AR-2010-0669. EPA's 

policy is that all comments received will be included in the public docket without change and 

may be made available online at www.regulations.gov, including any personal information 

provided, unless the comment includes information claimed to be Confidential Business 

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Information (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 or contact information unless you provide it in the body of your 

comment. If you 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 comment that is placed in the public docket and made available on the Internet. If you 

submit an electronic comment, EPA recommends that you include your name and other contact 

information in the body of you comment and with any disk or CD-ROM you submit. If EPA 

cannot read your comment due to technical difficulties and cannot contact you for clarification, 

EPA may not be able to consider your comment. Electronic files should avoid the use of special 

characters, any form of encryption, and be free of any 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 copy form. 

Publicly available docket materials are available either electronically in www.regulations.gov or 

in hard copy during normal business hours at the Office of Air, 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. 

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SUPPLEMENTARY INFORMATION: Throughout this notice, the words "we", "us", or 

"our" means the Environmental Protection Agency (EPA). 

Table of Contents 

I. What Proposed Action is EPA Taking? 

II. What is a SIP? 

III. What is the Background for this Proposed Action? 

IV. What is EPA's Evaluation of the State's Submission? 

A. EPA's Evaluation of Significant Contribution to Nonattainment 

1. 1997 PM2.5 Nonattainment Areas and Monitoring Data in States Surrounding Idaho 

2. 1997 8-Hour Ozone Nonattainment Areas and Monitoring Data in States Surrounding 

Idaho 

3. State Regulatory Provisions 

4. Conclusion Regarding Significant Contribution to Nonattainment 

B. EPA's Evaluation ofInterference with Maintenance 

1. Background 

2. Idaho's Interference with Maintenance Demonstration 

3. EPA's Supplemental Analysis 

4. Conclusion Regarding Interference with Maintenance 

C. EPA's Evaluation ofInterference with PSD Measures in Other States. 

V. Proposed Action 

VI. Statutory and Executive Order Reviews 

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r. What Proposed Action is EPA Taking? 

EPA is proposing to approve a portion of Idaho's Interstate Transport State 

Implementation Plan (SIP) revision for the 1997 8-hour ozone and 1997 PM2.5 NAAQS 

submitted by the Idaho Department of Quality (IDEQ) on June 28, 2010. Specifically, we are 

proposing to approve the portion of the plan that addresses the following elements of CAA 

section 110(a)(2)(D)(i): (1) significant contribution to nonattainment of these NAAQS in any 

other state, (2) interference with maintenance of these NAAQS by any other state, and (3) 

interference with any other state's required measures to prevent significant deterioration (PSD) 

of its air quality with respect to these NAAQS. IDEQ addressed element (4), interference with 

any other state's required measures to protect visibility, by referring 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 1 in a separate action. 

Idaho's June 28, 2010, SIP revision replaces a previously submitted section 

11O(a)(2)(D)(i) SIP revision submitted by IDEQ on January 30, 2007, for the 1997 PM2.5 and 

PM2.5 standards. EPA proposed approval of that 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 of Idaho's resubmittal of its Interstate Transport SIP, EPA 

is withdrawing its June 26, 2007, proposal and is issuing this proposal to approve Idaho's June 

28,2010, SIP revision in its place. Accordingly, EPA will not be responding to comments on the 

I The PM2.

5 standard was revised in 2006. See "National Ambient Air Quality Standards for Particulate Matter," at 

71 FR 61144, (October 17,2006). 

5 

June 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) of the CAA requires each state to develop a plan that provides for the 

implementation, maintenance, and enforcement of the NAAQS. EPA establishes NAAQS under 

section 109 of the CAA. Currently, the NAAQS address six criteria pollutants: carbon 

monoxide, nitrogen dioxide, ozone, lead, particulate matter, and sulfur dioxide. 

The plan developed by a state is referred to as the SIP. The content of the SIP is 

specified in section 110 of the CAA,. other provisions of the CAA, and applicable regulations. 

SIPs can be extensive, containing state regulations or other enforceable measures and various 

types of supporting information, such as emissions inventories, monitoring networks, and 

modeling demonstrations. 

A primary purpose of the SIP is to provide the air pollution regulations, control strategies, 

and other means or techniques developed by the state to ensure that the ambient air within that 

state meets the NAAQS. However, another important aspect of the 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 of pollutants. This SIP requirement 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 of the NAAQS in any 

other state, interfere with maintenance in any other state, interfere with any other state's required 

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measures to prevent significant deterioration of its air quality, and interfere with any other state's 

required measures to protect visibility. 

States are required to update or revise SIPs under certain circumstances. One such 

circumstance is EPA's promulgation of a new or revised NAAQS. Each state must submit these 

revisions to EPA for approval and incorporation into the federally-enforceable SIP. 

III. What is the Background for this Proposed Action? 

On July 18, 1997, EPA promulgated new standards for 8-hour ozone and fine particulate 

matter (PM2.5). This action is being taken in response to the promulgation of the 1997 8-hour 

ozone NAAQS and 1997 PM2.5 NAAQS. This action does not address the requirements of the 

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) of the CAA requires states to submit SIPs to address ti new or revised 

NAAQS within three years after promulgation of such standards, or within such shorter period 

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 of certain 

emissions. On August 15,2006, EPA issued its "Guidance for State Implementation Plan (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 of section 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. 

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On June 28, 2010, we received a SIP revision from the State of Idaho to address the 

requirements of section 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 of interstate transport of air pollutants. In this rulemaking EPA is addressing the first 

three elements: (1) significant contribution to nonattainment of these NAAQS in any other state, 

(2) interference with maintenance of these NAAQS by any other state, and (3) interference with 

any other state's required measures to prevent significant deterioration (PSD) of its 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 or revisions are 

needed with respect to the 1997 8-hour ozone NAAQS and 1997 PM2.5NAAQS. EPA is 

proposing to find that Idaho's Interstate Transport SIP provisions addressing elements (1), (2), 

and (3) of section 110(a)(2)(D)(i) are consistent with the requirements of the CAA. 

IV. What is EPA's Evaluation of tlie State's Submission? 

A. EPA's Evaluation of Significant Contribution to Nonattainment 

Section 11O(a)(2)(D)(i) provides that EPA cannot approve a state's SIP for a new or 

revised NAAQS unless it contains adequate measures to prohibit emissions from sources within 

the state from contributing significantly to nonattainment of the 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 of the 1997 8-hour ozone or the 1997 PM2.

5 NAAQS in another state. Among 

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other methods, EPA recommended consideration of available EPA modeling conducted in 

conjunction with the Clean Ail' Interstate Rule (CAIR),z or in the absence of such EPA modeling, 

consideration of other information such as the amount of emissions, the geographic location of 

violating areas, meteorological data, 01' various other forms of information that would be relevant 

to assessing the likelihood of significant contribution to violations of the NAAQS in another 

state. The assessment of significant contribution to nonattainment is not restricted to impacts 

upon areas that are formally designated non attainment. 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 of the NAAQS (70 FR 25172, May 12, 2005, and 63 FR 57371, October 27, 

1998)? Furthermore, although relevant information other than modeling may be considered in 

assessing the likelihood of significant contribution to nonattainment of the 8-hour ozone or PM2.5 

NAAQS in another state, EPA notes that no single piece of information is by itself dispositive of 

the issue. Instead, the total weight of all the evidence taken together is used to evaluate 

significant contributions to violations of the 1997 8-hour ozone 01' 1997 PMZ.

5 NAAQS in 

another state. 

This proposed approval addresses the significant contribution element for the 1997 8-

hour ozone and 1997 PMz.5 NAAQS in several ways. It takes into account Idaho's SIP 

submission that addressed the significant contribution element for the 1997 8-hour ozone and 

1997 PM2.

5 NAAQS by evaluating potential impacts from Idaho sources on 1997 8-hour ozone 

and 1997 PMz.5 nonattainment areas in surrounding states based on a review of meteorological 

and other characteristics of those 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 70 FR 25162 at 25263-69 (May 

12, 2005). 

J See Section B (1) of this 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. 

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its air quality regulations that address Idaho's authority to address nonattainment issues. In 

addition to the arguments presented by Idaho to support its demonstration that its SIP satisfies 

the significant contribution element of the CAA, EPA has supplemented its analysis with 

monitoring data and other information related to the 1997 PM2.5 nonattainment areas identified 

by Idaho, and has also provided monitoring data and other information for the surrounding states 

generally. Our evaluation below regarding how Idaho's SIP satisfies the significant contribution 

element of the CAA is organized as follows. Section 1 addresses the 1997 PM2.5 non attainment 

areas in surrounding states (including PM2.5 monitoring data for those non attainment areas) and 

PM2.5 monitoring data generally for surrounding states. Section 2 addresses the 1997 8-hour 

ozone non attainment 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 of the 1997 

PM2.5 NAAQS in another state, Idaho reviewed meteorological and other characteristics of any 

areas designated nonattainment for the 1997 PM2.5 NAAQS in surrounding states to determine 

whether transport of emissions from Idaho significantly contribute to non attainment in those 

areas. Relying primarily on technical support documents (TSDs) prepared for EPA's 8-hour 

ozone and PM2.

5 NAAQS nonattainment designations, Idaho noted that air stagnation is cited as 

a major contributing factor to nonattainment in those areas and that under air stagnation 

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conditions there is little to no transport of pol)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 of EPA's analysis of whether or not PM2.5 emissions from Idaho significantly 

contribute to nonattainment in another state, EPA reviewed and analyzed information available 

for the 1997 PM2.

5 non attainment areas in states surrounding Idaho. Although significant 

contribution must be measured not just against nDnattainment areas, but also against areas with 

monitors showing violations of the NAAQS, nonattainment areas are a convenient starting point 

for the analysis. For the 1997 PM2.5 NAAQS, Libby, in Lincoln County, Montana is the only 

designated nonattainment area in any state bordering Idaho.4 In 2005, EPA designated this area 

non attainment for the 1997 annual PM2.5 NAAQS. 70 FR 944 (January 5,2005) and 40 CFR 

81.327. 

A number of factors provide evidence that Idaho emissions do not significantly contribute 

to past violations of the 1997 annual PM2.5 standards in Libby, Montana. First, in the process of 

designating Libby nonattainment for both the 1997 PM2.5 NAAQS and the 2006 PM2.5 NAAQS, 

EPA noted the predominantly local origins of PM2.

5 nonattainment in Libby.5.6 Residential 

wood-burning stoves during the winter-time, when frequent and persistent temperature 

inversions occurred, were specifically identified as a key source of PM emissions. 

Although local sources were believed to predominate in the Libby nonattainment area, 

EPA specifically considered in the 1997 PM2.5 designation process whether Idaho sources 

4 Libby is in a narrow valley surrounded by mountains 4,000 feet higher than the town. The Rocky Mountain Range 

to the west of Libby (and east of the Idaho border) reaches sllmmit elevations of 12,000 feet with most summit 

elevations between 6000 and 7000 feet that act as a barrier to air movemenl between Idaho and Montana. 

5 "Technical Support for State and Tribal Air Quality Fine Particle (PM,.,) Designations," (for Montana) Chapter 6, 

pp. 347-352, December 2004. 

6 "Technical Support for State and Tribal Air Quality Fiue Particle (PM,.5) Designations," (for Montana) Chapter 

4.8.1, pp. 1-15, December 2008. 

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contributed to PM2.5 nonattainment in Libby. While a non attainment designation analysis is not 

the same inquiry that is required under CAA section 11O(a)(2)(D), some of the factual findings 

from that effort are helpful in understanding the potential for interstate transport of pollutants in 

the Libby area. If there were an area in Idaho from which significant contribution would be most 

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 of the Libby 

nonattainment area. Transport winds generally flow across Idaho from west to east, and Libby is 

directly east of Bonner and Boundary counties. In the process of designating Libby 

nonattainment for the 1997 PM2.5 NAAQS, EPA concluded that there was insufficient data to 

justify including 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 of the 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 of local sources does not rule out the possibility of 

impacts from interstate transport, this fact taken in conjunction with the mountainous topography 

of the 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 of Libby in 

Montana support a determination that Idaho does not significantly contribute to non attainment in 

Libby. At all other sites in Montana, annual PM2.5 design value levels have remained below the 

15 ~lg/m3 nonattainment threshold. Annual PM2.5 design values for this period for most of these 

monitors remained at levels equal to, or less than, two-thirds of the 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. 

12 

three highest design values at these monitors were 20 percent below the level of the annual 

standard. 8 The lower PM2.5 levels elsewhere in Montana are evidence that local sources, and not 

interstate transport, are key contributors to past non attainment 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 comparatively lower levels of PM2.5 

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 of PM2.slevels in 

Libby. The fact that monitors located in Idaho have not registered violations of the 1997 PM2.5 

NAAQS does not conclusively establish that emissions from Idaho could not contribute in the 

aggregate to violations in Libby, but this fact combined with the localized nature of the 

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 itself fell below the levels of the NAAQS. This reduction has been attributed 

to an effective wood stove replacement program that decreased PM2.s emissions by 

approximately 59 percent.9 In other words, even if emissions from Idaho sources were reaching 

Libby, they would not significantly contribute to violations of the 1997 PM2.5 NAAQS because 

monitoring data demonstrate that Libby is not violating the 1997 PM2.5 NAAQS. 

Finally, EPA's conclusion that emissions from Idaho do not significantly contribute 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 of Montana, Departm~nt of Environmental Quality, "State Implementation Plan-Libby Annual PM2.5 Control 

Plan," submitted to EPA April 1, 2008. 

13 

western United States. '0 This modeling concludes that in 2012 the average design values in 

Lincoln County, Montana for PM2.

5 will be below the threshold for consideration as a 

non attainment receptor. 

The next closest 1997 PM2.5 nonattainment area to the state of Idaho is the San Joaquin 

Valley in California." This nonattainment area is over 300 miles southwest of the closest point 

on the Idaho border and is on the other side of the Sierra Nevada Mountains. This 400 mile long 

north-south range of mountains has peaks of more 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 of winds 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 of transport winds across Idaho, EPA believes it is reasonable to conclude 

that Idaho sources do not significantly contribute to nonattainment of the 1997 PM2.5 NAAQS in 

the San Joaquin Valley. 

PM2.5 Monitoring Data in Other Areas of Surrounding States 

As mentioned above, EPA considers not only significant contribution to designated 

nonattainment areas, but also significant contribution to areas with monitors showing violations 

of the NAAQS. A review of the most recent three years of monitoring data in EPA's Air Quality 

System (AQS) for the bordering states of Washington, Oregon, Nevada, Utah, Wyoming and 

Montana shows there are no monitors violating the 1997 PM2.5 NAAQS. Between 1999 and 

10 See Section B of this notice for a morc complete disclIssion of the Transport Rule Proposal and EPA's modeling 

analysis of the western states. 

11 In 2005, EPA designated this area nonattainl11en1 for violations of the 1997 and annual PM,., NAAQS. 70 FR 944 

(January 5, 2005), and 40 CFR 8l.305 

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2009, just two monitors in any of these 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 Salt Lake 

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 of all of the factors discussed 

above, EPA concludes that Idaho does not significantly contribute to 1997 PM2.5 NAAQS 

nonattainmen't in another state. 

2. 1997 Ozone Nonattainment Areas and Monitoring Data in States Surrounding Idaho 

1997 8-Hour Ozone N onattainment Areas 

To address whether Idaho sources significantly contribute to nonattainment of the 1997 

8-hour ozone standard in another state, Idaho's SIP uses the same approach as it used for the 

1997 PM2.

5 NAAQS. 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 of pollutants over long distances. Idaho also noted that none of the 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 non attainment areas in states surrounding Idaho. Although significant contribution must 

be measured not just against non attainment areas, but against areas with monitors showing 

violations of the NAAQS, non attainment areas are a convenient starting point for the analysis. 

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For 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 of the 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 of the 8-hour ozone standard in Clark County. Clark County is about 350 

miles south of the closest point on the Idaho border. Distance per se is not an obstacle to long 

range transport of ozone and/or its precursors, as discussed in the January 30, 2004, notice 

proposing CAIR (69 FR 4599); NOx (the primary ozone precursor that was the object of the 

CAIR transport study) may be 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 of winds 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 of significant contribution to this area's nonattainment. Another transport 

factor is wind direction. Clark County, Nevada is south of Idaho and, therefore, is not in the 

predominant direction of winds 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 of transport winds across Idaho, 

EPA believes it is reasonable to conclude that Idaho sources do not significantly contribute to 

non attainment of the 1997 8-hour ozone NAAQS in Clark County, Nevada. 

Ozone Monitoring Data in Other Areas of Surrounding States 

16 

As mentioned above, EPA considers not only significant contribution to designated 

nonattainment areas, but also to areas with monitor readings showing violations of the NAAQS, 

A review of the most recent monitoring data from EPA's Air Quality System (AQS) for the 

bordering states of Washington, Oregon, Nevada, Utah, Wyoming and Montana shows no 

monitors violating for the 1997 8-hour ozone NAAQS, A review of past monitoring data from 

1999 through 2008 shows that the only area in any of these 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 monitor in 

2007. Observed days of high ozone levels in the Salt Lake City metropolitan area are usually 

associated with a 'bowl effect' resulting from an inversion that has a stagnant air pollution mass 

surrounded by the Oquirrh Mountains to the west, the Great Salt Lake to the north, and the 

Wasatch Range on the east. 12 In light of these considerations, it is unlikely that Idaho makes a 

significant contribution of ozone and/or ozone precursors in the Salt Lake City area. 

In addition, none of the ozone monitors in Idaho have themselves indicated a violation of 

the 1997 8-hour ozone NAAQS, and Boise, Idaho, the area of Idaho with the highest 

concentrations of ozone, is almost 300 miles from Salt Lake City. The absence of violations in 

Idaho itself do not rule out the possibility of transport, 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. Distance per se is also not an obstacle to long range transport of ozone 

and/or its precursors, as discussed above. However, with increasing distance there are greater 

opportunities for ozone and/or NOx dispersion and/or removal from the atmosphere due to the 

effects of winds lind chemical sink processes. In this context, the 300 mile distance between 

12 Approval and Promulgation of State Implementation Plans; State of Utah; Interstate Transport of Pollution and 

Other Revisions (73 FR 16543, March 28, 2008). 

17 

Idaho and the Salt Lake City area reduces but does not exclude the possibility of significant 

contribution to this area's nonattainment. Taking into account the total weight of all of the 

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 

non attainment in any other state, Idaho points to air quality provisions in its regulations that 

prohibit emissions that contribute significantly to nonattainment. Specifically, the State points 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 of any ambient air 

quality standard. The state explains that this provision applies to both major and minor sources 

and that the owner or operator of such a source must demonstrate that the source's projected 

emissions will not cause or significantly contribute to a violation of any ambient air quality 

standard. In addition, they point out that the demonstration is not constrained to evaluating 

impacts solely in Idaho and that all estimates of ambient concentrations must be based on the 

requirements specified in 40 CFR 51, Appendix W, which look to the point of maximum 

concentration, not a jurisdictional 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 "Tier II permit") if emission rate 

reductions are necessary to attain any ambient air quality standard. As part of the Tier II 

permitting process, the facility operator (or responsible official) must demonstrate the source 

does not cause or significantly contribute to a violation of any ambient air quality standards. 

18 

The state asserts that it has used this authority in the past as part of a suite of control measures 

implemented to address nonattainment and other air quality issues and this authority could be 

used if the state's emissions were significantly contributing to nonattainment in another state. 

For example, between 2000 and 2003 the state issued fifteen Tier II permits 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 of these 

15 permits, including links to the permits on the Idaho website, is included in the docket for this 

rulemaking. 

Idaho incorporates by reference annually any updates to the NAAQS ensuring that 

implementation of the regulatory provisions at IDAPA 58.01.01.203.02 and IDAPA 

58.01.01.40.03 are implementing the most recently revised NAAQS. 

In light of these air quality provisions 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, 

EPA believes that in this case these regulatory provisions provide additional support for 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 of the 1997 8-hour ozone and 1997 PM2.5 

NAAQS in another state. 

4. Conclusion Regarding Significant Contl'ibution to Nonattainment 

The data and weight of the 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 non attainment in any other state for the 

19 

1997 8-hour ozone or 1997 PM2.5 NAAQS, consistent with the requirements of element (1) of 

CAA section 110(a)(2)(D)(i) 

B. EPA's Evaluation oflnterference with Maintenance 

1. Background 

The second element of CAA section 11O(a)(2)(D)(i) requires that a state's SIP must 

prohibit any source or other type of emissions activity in the state from emitting pollutants that 

would "interfere with maintenance" of the 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 of NOx that significantly contributed to 

nonattainment, or interfered with maintenance of, the then applicable ozone NAAQS through 

interstate transport of NOx and the resulting ozone. t3 The NOx SIP Call was the mechanism 

through which EPA evaluated whether or not the NOx emissions from sources in certain states 

had such prohibited interstate impacts, and if they 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 or by other means. 

After promulgation of the 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 CAIR to address emissions of S02 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, 532 U.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). 

20 

transport. 14 Within CAIR, EPA likewise interpreted the term "interfere with maintenance" as 

part of the evaluation of whether or not the emissions of sources in certain states had such 

impacts on areas that EPA determined would either be in violation of the NAAQS, or would be 

in jeopardy of violating 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 or by other 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 of section llO(a)(2)(D)(i)(I) for 

these NAAQS. For states not within the CAIR region, EPA recommended that states evaluate 

whether or not emissions from their sources would "interfere with maintenance" in other states, 

following the conceptual approach adopted by EPA in CAIR. After recommending various types 

of information that could be relevant for the technical analysis to support the SIP submission, 

such as the amount of emissions and meteorological conditions in the state, EPA further 

indicated that it would be appropriate for the state to assess impacts of its emissions on other 

states using considerations comparable to those used by EPA "in evaluating significant 

contribution to non attainment 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 of section 11O(a)(2)(D) together without explicitly differentiating between them. 

" See, 70 FR 25162 (May 12, 2005). 

15 2006 Guidance at page 5. 

21 

In 2008, however, the U.S. Court of Appeals for the D.C. Circuit found that CAIR and 

the related CAIR federal implementation plan were unlawful. 16 Among other issues, the court 

held that EPA had not correctly addressed the second element of section 11O(a)(2)(D)(i)(I) in 

CAIR. The court noted that "EPA gave no independent significance to the 'interfere with 

maintenance' prong of section 11O(a)(2)(D)(i)(I) to separately identify upwind sources 

interfering with downwind maintenance.,,17 EPA's approach, the court reasoned, would leave 

areas that are "barely meeting attainment" with "no recourse" to address upwind emissions 

sources. 18 The court therefore concluded that a plain language reading of the statute requires 

EPA to give independent meaning to the interfere with maintenance requirement of section 

1l0(a)(2)(D) and that the approach used by EPA in CAIR failed to do so. 

In addition to affecting CAIR directly, the court's decision in the North Carolina case 

indirectly affects EPA's recommendations to states in the 2006 Guidance with respect to the 

interfere with maintenance element of section 11O(a)(2)(D) because the 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 rely upon the reconunendations in EPA's 2006 Guidance. 

Given the court decision on CAIR in the interim, however, EPA believes 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 of the statute is given independent meaning and is 

appropriately evaluated using the types of information that EPA recommended in the 2006 

Guidance. To accomplish this, EPA believes it may be necessary to supplement the technical 

analysis provided the state in order to adequately evaluate the submissions with the respect to the 

interfere with maintenance element of section 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. 

22 

EPA has recently proposed a new rule to address interstate transport pursuant to section 

11O(a)(2)(D), the "Federal Implementation Plans to Reduce Interstate Transport of Fine 

Particulate Matter and Ozone" (Transport Rule Proposal), in order to address the judicial remand 

of CAIR. 19 As part of the Transport Rule Proposal, EPA specifically reexamined the section 

llO(a)(2)(D) requirement that emissions from sources in a state must not "interfere with 

maintenance" of the 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS in other states. In the 

proposal, EPA developed an approach to identify areas that it predicts to be close to the level of 

the 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS, and therefore at risk to become 

nonattainment for these NAAQS unless emissions from sources in other states are appropriately 

controlled. This approach starts by identifying 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 

over three 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 

potentially have a difficulty with maintaining attainment as of that date. In essence, if an area's 

projected data for 2012 indicates that it would be violating the NAAQS based on the average of 

these three overlapping periods, then this monitor location is appropriate for comparison for 

purposes ofthe significant contribution to nonattainment element of section 11O(a)(2)(D). If, 

however, an area's projected data indicate that it would be violating the NAAQS based on the 

highest single period, but not over the average of the three periods, then this monitor location is 

19 See "Federal Implementation Plans to Reduce Interstate Transport afFine Particulate Matter and Ozone," 75 FR 

45210 (August 2, 2010). 

23 

appropriate for comparison for purposes of the interfere with maintenance element of the 

20 statute. 

By this method, EPA has identified those areas with monitors that are appropriate 

"maintenance sites" or maintenance "receptors" for evaluating whether the emissions from 

sources in another state could interfere with maintenance in that particular area. EPA then uses 

other analytical tools to examine the potential impacts of emissions from upwind states on these 

maintenance sites in downwind states. EPA believes 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 of a state for the interfere with maintenance element. 2t EPA's 

2006 Guidance did not provide this specific recommendation to states, but in light of the court's 

decision on CAIR, EPA will itself follow this approach in acting upon the Idaho submission. 

As explained in the 2006 Guidance, EPA does not believe that section 110(a)(2)(D) SIP 

submissions from all states necessarily need to follow precisely the same analytical approach of 

CAIR or the Transport Rule Proposal. In the 2006 Guidance, EPA stated that: "EPA believes 

that the contents of the SIP submission required 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 or revised 

NAAQS necessarily affects the contents of the 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 of interference with maintenance for certain states in the western United States. 

See, Memorandum from Brian Timin of EPA's Office of Air Quality Planning and Standards, Air Quality 

Modeling Group entitled "Documentation of Future 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 attai nment because they are -so close to the level of the 1997 ozone 

and PM2.

5 NAAQS that minOl' variations in weather or emissions could result in violations of the NAAQS in 

2012. 

22 2006 Guidance at 4. 

24 

the 2006 Guidance that it did not anticipate that sources in states outside the geographic area 

covered by CAIR were significantly contributing to nonattainment, or interfering with 

maintenance, in other states. 23 As noted in the Transport Rule Proposal, EPA continues 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, EPA did not calculate interstate ozone or PM2.5 contributions to or from western states. 

Accordingly, EPA believes that section 1l0(a)(2)(D) SIP submissions for states outside 

the geographic area of the Transport Rule Proposal may be evaluated using a "weight of the 

evidence" approach that takes into account available relevant information, such as that 

recommended by EPA in the 2006 Guidance for states outside the area affected by CAIR. Such 

information may include, but is not limited to, the amount. of emissions 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 

may be probative to consider whether sources in the state may interfere with maintenance of the 

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, but EPA does not 

believe that modeling is necessarily required if other available information is sufficient to 

evaluate the presence or degree of interstate transport in a given situation. 

2. Idaho's Interference with Maintenance Demonstration 

23 Id. at 5. 

24 See, Transport Rule Proposa1, 75 FR 45210 (August 2, 2010) at page 45227. 

25 

To show that Idaho emissions, as controlled under its SIP, do not interfere with 

maintenance of the 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS in another state, 

Idaho's submittal analY2:ed several types of factors to support its assertion. First, for its PM2.5 

analysis, Idaho relied on information from the Western Regional Air Partnership (WRAP) 

Technical Support Systelll (TSS). The WRAP TSS 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 it to provide general insight on how Idaho 

sources influence PM2.5 concentrations in Class I areas in surrounding states. For the 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 WRAP TSS results provided in Idaho's submittal to 

address the 1997 PM2.5 standard and Idaho's evaluation of NOx and VOC emissions data from 

Idaho sources to address the 1997 8-hour ozone NAAQS are discussed later. 

Idaho also relied on information about air stagnation conditions in other states to show 

that Idaho sources do not interfere with maintenance of the 1997 8-hour ozone NAAQS and 

1997 PM2.5 NAAQS. Idaho argued that stagnant air conditions are associated with weak 

transport and were cited in technical support documents for the 8-hour ozone and PM2.5 

designations as a major contributing factor to poor air quality in surrounding states. Idaho also 

identified its state air quality regulations to demonstrate both that Idaho can, and does, work with 

other states and tribes to ensure that an Idaho activity would not interfere with maintenance by 

any other State with respect to the NAAQS. 

Idaho also relies on its permitting rules discussed earlier that not only require for new 

sources a demonstration that the proposed source's emissions will not cause or signit1cantly 

26 

contribute to a violation of any ambient air quality standard, but also specifically require for 

existing sources an operating permit if emission rate reductions are necessary to attain or 

maintain any ambient air quality standard. It also points out that neither of these required 

demonstrations is limited to an analysis of impacts solely in Idaho. In light of these 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), EPA believes 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 if in the future the 

state's emissions interfere with maintenance of the 1997 8-hour ozone and 1997 PM2.5 NAAQS 

in another state. 

3. EPA Supplemental Analysis 

On July 6, 2010, the EPA proposed a rulemaldng proposal (the Transport Rule Proposal) 

in response to the judicial remand of CAIR. The Transport Rule Proposal includes a new 

approach to determine whether emissions from a state interfere with maintenance of the 1997 8-

hour ozone NAAQS and the 1997 PM2.5 NAAQS in other states. EPA is using a comparable 

approach to that of the Transport Rule Proposal in this action in order to evaluate whether 

emissions from Idaho sources interfere with maintenance of these NAAQS in other states. 

In the Transport Rule Proposal, EPA projected future concentrations of ozone and PM2.5 

to identify areas that are expected to be out of attainment 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 non attainment and maintenance receptors are 

based on projections of future air quality at existing ozone and PM2.

5 monitoring sites in those 

27 

locations. 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 of both 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 

of the annual mean concentration is 15.0 micrograms per cubic meter (~Lg/m3) or less. The 3-

year average annual mean concentration is computed at each site by averaging the daily Federal 

Reference Method (FRM) samples by quarter, 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 of the annual 98th percentile PM2.5 

concentrations is 35 ~Lg/m3 or less. The 1997 24-hour PM2.5 NAAQS is met when the 3-year 

average of the annual 98th percentiles is 65 ~Lg/m3 or less. 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 average 98th percentile concentration is 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-hour PM2.

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 other NAAQS. 

For the ozone NAAQS, EPA evaluated concentrations relevant to the 1997 8-hour ozone 

NAAQS. The level of the 1997 8-hour ozone NAAQS is 0.08 parts per million (ppm). The 8-

hour ozone standard is met if the 3-year average of the annual 4th highest daily maximum 8-hour 

ozone concentration is less than or equal to 0.08 ppm (i.e., less than 0.085 ppm based on the 

28 

rounding convention in 40 CFR part 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 of three design value periods which include the years 2003-2007 

(Le., design values for 2003-2005,2004-2006, and 2005-2007). The average of the 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 the Transport 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 of the three year periods (i.e., 2003-2005, 2004-

2006, and 2005-2007). The highest projection is referred to as the "maximum design value" and 

gives an indication of potential variability in future projections due to differences in actual 

meteorology and emissions from what was modeled. 

EPA identified 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 because EPA anticipates that there 

will be more difficulty in maintaining attainment of the NAAQS at these locations if there are 

adverse variations in meteorology or emissions. These projected maintenance sites are the ones 

that EPA has used to determine if emissions from Idaho sources potentially interfere with 

maintenance of the 1997 8-hour ozone NAAQS and 1997 annual PM2.5 NAAQS in other states 

in this action. 

25 See, the Transport Rule 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 

For 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. From the modeling analysis conducted for states not incl uded in the Transport 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 of the continental U.S. (not including California) is 50 Itg/m3, which is well 

below the level of the 1997 24-hour PM2.5 NAAQS of 65 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.

5 NAAQS. 

From the modeling analyses conducted for the Transport Rule Proposal, EPA identified a 

number of maintenance sites or receptors for the 1997 8-hour ozone NAAQS: several sites in the 

Texas area and other sites in Georgia, Pennsylvania, New York and Connecticut. 28 For the 

modeling analysis conducted for states not included in the Transport Rule Proposal (Le. states 

not included fully in the 12 km Transport Rule Proposal modeling domain), EPA identified 

several maintenance sites in southern and central California using available 36 kmmodeling. 29 

The 12 km Transport 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 of Columbia. 

27 Data UI~dergoing review from EPA's Air Quality System which is EPA's repository of ambient air quality data, 

(http://www.epa.gov/ltn/airs/airsaqs/) 

28 Transport Rule Proposal. 75 FR 45210, (August 2. 2010). pages 45253-45270, and Timin Memo 

29 The Transport Rule Proposal identifies nonattainment and maintenance receptors in the Eastern U.S. It docs not 

include modeling results for the West. The Timin Memo documenls further evaluation of the 2012 modeling to 

identify nonattainrnent and maintenance receptors in the West. 

30 

Significantly, for both the 1997 PM2.5 NAAQS and the 1997 8-hour ozone NAAQS, 

EPA's analysis did not identify any maintenance receptors 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 by the 

Transport Rule Proposal was in Cook County, Illinois. Cook County, Illinois is over 1000 miles 

east of the closest point on Idaho's border, and on the other side of the Rocky Mountains. Given 

the relatively long distance and the intervening mountainous topography between Idaho and 

Cook County, EPA believes it is reasonable to conclude that there is a very low probability that 

Idaho sources interfere with maintenance in that area. It is also reasonable to conclude that 

Idaho emissions would not have such impacts at other identified maintenance sites east of Cook 

County. 

In the west, the closest maintenance receptor to Idaho was in Fresno County, California. 

Fresno County is located almost 400 miles southwest of the closest point on tHe Idaho border and 

on the other side of the Sierra Nevada Mountains, which act as a natural barrier to air movement 

between Idaho and California. In addition, Fresno County, located in southern California, is not 

in the predominant direction of winds from Idaho. As noted earlier, transport winds across Idaho 

generally flow from west to east, and not toward the southwest. Given the relatively long 

distance between Idaho and southern California, the intervening mountainous topography, and 

the general direction of west-to-east transport winds across Idaho, EPA concludes that there is no 

reasonable basis to conclude that Idaho sources interfere with maintenance of the 1997 PM2.5 

NAAQS in those areas. It is likewise reasonable to conclude that Idaho emissions would not 

31 

have such impacts at other identified maintenance sites in California. Based on EPA modeling 

and all of these factors taken together, EPA believes it is reasonable to conclude that Idaho 

emissions under the SIP do not interfere with maintenance of the 1997 PMZ.5 NAAQS in any 

other state. 

This conclusion is consistent with the information and analysis Idaho provided in its SIP 

submittal regarding interference with maintenance of the 1997 PMZ.5 NAAQS. With respect to 

PMZ.5, Idaho used the WRAP TSS tools to provide general insight on how Idaho sources 

influence PMz.5 concentrations in surrounding states and to conclude that Idaho sources did not 

interfere with maintenance of the 1997 PMZ.5NAAQS in any other state. Due to the limitations 

and purpose of the WRAP TSS, Idaho only evaluated impacts on Class I areas in surrounding 

states using these tools. Because EPA's analysis did not predict any of these Class I areas to 

have a difficulty with maintaining attainment of the 1997 PMZ.5 NAAQS, any impact Idaho 

might have on those areas would not, by definition, interfere with maintenance. Therefore, 

further evaluation of Idaho's analysis of PMz.5 impacts on those areas is unnecessary. 

(b) Interfere with Maintenance Evaluation for the 8-Hour Ozone NAAOS. 

For the 1997 8-hour ozone NAAQS, the closest maintenance receptor site to the east of 

Idaho was the Dallas-Ft Worth area in Texas. Dallas-Ft Worth is located over 1000 miles 

southeast of the closest point on Idaho's border and on the other side of the Rocky Mountains. 

Given the relatively long distance and the intervening mountainous topography between Idaho 

and Dallas-Ft Worth, it is reasonable to conclude that Idaho sources do not interfere with 

maintenance in the Dallas-Ft Worth area. It is also reasonable to conclude that Idaho emissions 

32 

would not have such impacts at other identified maintenance sites elsewhere further east or south 

of Dallas-Ft Worth. 

In the west, the closest maintenance receptor to Idaho was in Nevada County, California. 

Nevada County is almost 300 miles southwest of the closest point on Idaho's border and located 

on the other side of the Sierra Nevada Mountains, which act as a natural barrier to air movement 

between Idaho and California. In addition, Nevada County is in central California and is not in 

the predominant directfon of transport 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 of west-to-east transport winds across Idaho, EPA believes 

it is reasonable to conclude that Idaho sources do not interfere with maintenance of the 1997 8-

hour ozone NAAQS in Nevada County, California. It is 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 of these factors taken together, EPA believes it is 

reasonable to conclude that Idaho emissions do not interfere with maintenance of the 1997 8-

hour ozone NAAQS in any other state. 

This conclusion is consistent with the information Idaho provided in its SIP submittal 

regarding interference with maintenance of the 1997 8-hour ozone NAAQS. For this 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 of the 1997 8-hour ozone NAAQS in any 

33 

other states. Because EPA modeling did not predict any of the areas in states surrounding Idaho 

to have difficulty with maintaining attainment of the 8-hour ozone NAAQS, any impact Idaho 

might have on those areas would not, by definition, interfere with maintenance. Therefore, 

further evaluation of Idaho's analysis of ozone impacts on those areas is unnecessary. 

4. Conclnsion Regarding Interference with Maintenance 

The data and weight of evidence analysis presented above support the conclusion that the 

Idaho Interstate Transport SIP (submitted on June 28,2010) 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 of element (2) of CAA section 11O(a)(2)(D)(I). 

C. EPA's Evaluation of Interference with PSD measures in other states 

'The third element of section 11O(a)(2)(D)(i) requires a SIP to contain adequate provisions 

prohibiting emissions that interfere with any other state's required measures to prevent 

significant deterioration of its air quality. EPA's 2006 Guidance made recommendations for SIP 

submissions to meet this requirement with respect to both the 1997 8-hour ozone NAAQS and 

the 1997 PM2.5 NAAQS. 

EPA believes that Idaho's submission is consistent with the 2006 Guidance, when 

considered in conjunction with PSD program revisions that EPA proposed to approve on March 

18,2010 (75 FR 13058). EPA's proposed approval ofIdaho's SIP for purposes of meeting the 

requirements of section 110(a)(2)(D)(i)(II) is contingent upon the final approval of the PSD 

program revisions in the form specified in EPA's proposed approval, referenced above. The 

State's submittal indicates in Section 4, "Interfere with Prevention of Significant Deterioration of 

34 

Air Quality," that the State's SIP provisions include an EPA-approved PSD program. Idaho's 

regulations for its PSD program were last approved by EPA and made part of the SIP on January 

16,2003 (68 FR 2217), 40 CFR 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 of EPA's PSD requirements as of July 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, EPA proposes to approve this SIP provision as adequate for purposes of 

section 110(a)(2)(D)(i)(II) if EPA 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 

a precursor for ozone for PSD purposes and the PSD revision for the 1997 PM2.

5 NAAQS that 

makes S02 and NOx precursors for PM2.5 for PSD purposes, taken together with the revised PSD 

SIP that EPA proposed to approve on March 18,2010, and the Interstate Transport SIP that EPA 

is proposing to approve in this action, satisfy the requirements of the third element of section 

11O(a)(2)(D)(i) for the1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS. That is, these 

provisions ensure that there 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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In light of the data and the weight of the 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, air pollutant emissions 

from sources within Idaho do not (1) significantly contribute to nonattainment of the NAAQS in 

any other state, (2) interfere with maintenance of the NAAQS by any other state, and (3) 

interfere with any other state's required measures to prevent significant deterioration of its 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 of Idaho'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 of the 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 of the Clean Air Act. Accordingly, this action merely 

proposes to approve state law as meeting Federal requirements and does not impose additional 

requirements beyond those imposed by state law. For that reason, this action: 

• is not a "significant regulatory action" subject to review by the Office of Management 

and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993); 

• does not impose an information collection burden under the provisions of the Paperwork 

Reduction Act (44 U.S.c. 3501 et seq.); 

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• is certified as not having, a significant economic impact on a substantial number of small 

entities under the Regulatory Flexibility Act (5 U.S.c. 601 et seq.); 

• 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 Federalism implications as specified in Executive Order 13132 (64 FR 

43255, August 10, 1999); 

• is not an economically significant regulatory action based on health or safety risks 

subject to Executive Order 13045 (62 FR 19885, April 23, 1997); 

• is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, 

May 22,2001); 

• is not subject to requirements of Section 12(d) of the National Technology Transfer and 

Advancement Act of 1995 (15 U.S.C. 272 note) because application of those 

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 or environmental 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 by Executive 

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 it will not impose substantial direct costs 

on tribal governments or preempt tribal law. 

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List of Subjects in 40 CFR Part 52 

Environmental protection, Air pollution control, Incorporation by reference, 

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 

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