Approval and Promulgation of Implementation Plans; Idaho; Interstate Transport of Pollution, 55494-55503 [2010-22773]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 75, Number 176 (Monday, September 13, 2010)]
[Proposed Rules]
[Pages 55494-55503]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-22773]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R10-OAR-2010-0669; FRL-9200-5]


Approval and Promulgation of Implementation Plans; Idaho; 
Interstate Transport of Pollution

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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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 
110(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 110(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 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 or CAA).

DATES: Written comments must be received on or before October 13, 2010.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R10-
OAR-2008-0391, by one of the following methods:
    A. https://www.regulations.gov. Follow the online instructions for 
submitting comments.
    B. E-Mail: R10-Public_Comments@epa.gov.
    C. Mail: Donna Deneen, U.S. Environmental Protection Agency, Region 
10, 1200 Sixth Avenue, Suite 900, Mail Stop: AWT-107, Seattle, WA 
98101.
    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-R10-OAR-
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 
https://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be 
Confidential Business 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 https://www.regulations.gov or email. The https://www.regulations.gov Web 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 https://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 viruses.
    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 
https://www.regulations.gov or in hard copy during normal business hours 
at the Office of Air, Waste and Toxics, U.S. Environmental Protection 
Agency, Region 10, 1200 Sixth Avenue, Suite 900, Seattle, Washington 
98101.

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

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 of Interference 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 of Interference With PSD Measures in Other 
States
V. Proposed Action
VI. Statutory and Executive Order Reviews

I. 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

[[Page 55495]]

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 of Idaho's SIP that addresses the 2006 PM2.5 
NAAQS \1\ in a separate action.
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    \1\ The PM2.5 standard was revised in 2006. See 
``National Ambient Air Quality Standards for Particulate Matter,'' 
at 71 FR 61144, (October 17, 2006).
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    Idaho's June 28, 2010, SIP revision replaces a previously submitted 
section 110(a)(2)(D)(i) SIP revision submitted by IDEQ on January 30, 
2007, for the 1997 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 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 110(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 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 PM2.5 NAAQS or the 2008 8-hour 
ozone NAAQS; those standards will be addressed in a future action.
    Section 110(a)(1) of the CAA requires states to submit SIPs to 
address a 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 110(a)(2)(D) for the 1997 8-hour 
ozone standards and 1997 PM2.5 standards.
    On June 28, 2010, we received a SIP revision from the State of 
Idaho to address the requirements of section 110(a)(2)(D)(i) for the 
1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS. The ``good 
neighbor'' provisions in section 110(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 PM2.5 NAAQS. 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 the State's submission?

A. EPA's Evaluation of Significant Contribution to Nonattainment

    Section 110(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 110(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 other 
methods, EPA recommended consideration of available EPA modeling 
conducted in conjunction with the Clean Air Interstate Rule (CAIR),\2\ 
or in the

[[Page 55496]]

absence of such EPA modeling, consideration of other information such 
as the amount of emissions, the geographic location of violating areas, 
meteorological data, or 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 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 of the NAAQS 
(70 FR 25172, May 12, 2005, and 63 FR 57371, October 27, 1998).\3\ 
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 or 1997 PM2.5 NAAQS in 
another state.
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    \2\ See ``Rule to Reduce Interstate Transport of Fine 
Particulate Matter and Ozone (Clean Air Interstate Rule); Revisions 
to Acid Rain Program; Revisions to the NOX SIP Call; 
Final Rule,'' at 70 FR 25162 at 25263-69 (May 12, 2005).
    \3\ See Section B(1) of this notice for more history on CAIR and 
the Transport Rule Proposal. EPA has taken a similar approach in the 
recent Transport Rule Proposal discussed below.
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    This proposed approval addresses the significant contribution 
element for the 1997 8-hour ozone and 1997 PM2.5 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 PM2.5 
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 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 nonattainment areas in 
surrounding states (including PM2.5 monitoring data for 
those nonattainment areas) and PM2.5 monitoring data 
generally for 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 Surrounding 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 nonattainment 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 conditions 
there is little to no transport of pollutants over long distances. 
Idaho also noted that none of the 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 nonattainment areas in states surrounding Idaho. 
Although significant contribution must be measured not just against 
nonattainment 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 
nonattainment for the 1997 annual PM2.5 NAAQS. 70 FR 944 
(January 5, 2005) and 40 CFR 81.327.
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    \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 summit elevations of 
12,000 feet with most summit elevations between 6000 and 7000 feet 
that act as a barrier to air movement between Idaho and Montana.
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    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.
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    \5\ ``Technical Support for State and Tribal Air Quality Fine 
Particle (PM2.5) Designations,'' (for Montana) Chapter 6, 
pp. 347-352, December 2004.
    \6\ ``Technical Support for State and Tribal Air Quality Fine 
Particle (PM2.5) Designations,'' (for Montana) Chapter 
4.8.1, pp. 1-15, December 2008.
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    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 contributed 
to PM2.5 nonattainment in Libby. While a nonattainment 
designation analysis is not the same inquiry that is required under CAA 
section 110(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.\7\ 
Monitoring data from 1999 through 2009 show that PM2.5 
design value levels for both Idaho counties have remained below 30 
[mu]g/m\3\ or 85 percent of the 1997 PM2.5 NAAQS. This is 
consistent with a conclusion that local sources in Libby were a key

[[Page 55497]]

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.
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    \7\ ``Technical Support for State and Tribal Air Quality Fine 
Particle (PM2.5) Designations,'' Chapter 6, pp. 347-352, 
December 2004.
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    Second, monitoring data from 1999 through 2009 from areas outside 
of Libby in Montana support a determination that Idaho does not 
significantly contribute to nonattainment in Libby. At all other sites 
in Montana, annual PM2.5 design value levels have remained 
below the 15 [mu]g/m\3\ 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 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 
nonattainment in Libby.
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    \8\ In 2001, 2002 and 2006, design values for two monitors in 
Missoula County were 11.1, 11.4 and 11.8 [mu]g/m\3\. Computed from 
AQS monitoring data. 75 FR 16028 (March 31, 2010).
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    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 PM2.5 levels 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 supports the conclusion 
that sources in Idaho do not significantly contribute to 
PM2.5 levels 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 
PM2.5 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.
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    \9\ State of Montana, Department of Environmental Quality, 
``State Implementation Plan-Libby Annual PM2.5 Control 
Plan,'' submitted to EPA April 1, 2008.
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    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 western United 
States.\10\ 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 nonattainment receptor.
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    \10\ See Section B of this notice for a more complete discussion 
of the Transport Rule Proposal and EPA's modeling analysis of the 
western states.
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    The next closest 1997 PM2.5 nonattainment area to the 
state of Idaho is the San Joaquin Valley in California.\11\ 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.
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    \11\ In 2005, EPA designated this area nonattainment for 
violations of the 1997 and annual PM2.5 NAAQS. 70 FR 944 
(January 5, 2005), and 40 CFR 81.305.
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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 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 
nonattainment in another state.
2. 1997 Ozone Nonattainment Areas and Monitoring Data in States 
Surrounding Idaho
1997 8-Hour Ozone Nonattainment 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 Idaho sources as 
significant contributors to any 1997 8-hour ozone nonattainment area.
    EPA also reviewed and analyzed information available for the 
designated 1997 8-hour ozone nonattainment areas in states surrounding 
Idaho. Although significant contribution must be measured not just 
against nonattainment areas, but against areas with monitors showing 
violations of the NAAQS, nonattainment areas are a convenient starting 
point for the analysis. 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

[[Page 55498]]

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 from 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 nonattainment of the 1997 8-hour ozone NAAQS in Clark 
County, Nevada.
Ozone Monitoring Data in Other Areas of Surrounding States
    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 
occurred 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.
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    \12\ Approval and Promulgation of State Implementation Plans; 
State of Utah; Interstate Transport of Pollution and Other Revisions 
(73 FR 16543, March 28, 2008).
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    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 and chemical sink processes. In this context, the 300 
mile distance between 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 nonattainment 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. 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 PM10 nonattainment 
areas to establish federally-enforceable emission limits on 
PM10 emissions in order to ensure that the PM10 
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 Contribution 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 nonattainment in any other 
state for the

[[Page 55499]]

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 of Interference With Maintenance

1. Background
    The second element of CAA section 110(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.\13\ 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.
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    \13\ See, 63 FR 57356 (October 27, 1998). EPA's general approach 
to section 110(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 
Call was not explicitly reviewed by the court. See, North Carolina 
v. EPA, 531 F.3d 896, 907-09 (D.C. Cir. 2008).
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    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 SO2 and 
NOX that exacerbate ambient ozone and PM2.5 
levels in many downwind areas through interstate 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 SO2 and NOX emissions. Through 
CAIR, EPA again required states that had such interstate impacts to 
adopt substantive SIP revisions to eliminate the SO2 and NOX 
emissions, whether through participation in a regional cap and trade 
program or by other means.
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    \14\ See, 70 FR 25162 (May 12, 2005).
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    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 110(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 nonattainment in the 
CAIR.''\15\ EPA did not make specific recommendations for how states 
should assess ``interfere with maintenance'' separately, and discussed 
the first two elements of section 110(a)(2)(D) together without 
explicitly differentiating between them.
---------------------------------------------------------------------------

    \15\ 2006 Guidance at page 5.
---------------------------------------------------------------------------

    In 2008, however, the U.S. Court of Appeals for the DC 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 110(a)(2)(D)(i)(I) in 
CAIR. The court noted that ``EPA gave no independent significance to 
the `interfere with maintenance' prong of section 110(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 110(a)(2)(D) and that the approach used by EPA in CAIR failed 
to do so.
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    \16\ See, North Carolina v. EPA, 531 F.3d 896 (D.C. Circuit 
2008).
    \17\ Id. 531, F.3d at 909.
    \18\ Id.
---------------------------------------------------------------------------

    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 110(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 
recommendations 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 110(a)(2)(D).
    EPA has recently proposed a new rule to address interstate 
transport pursuant to section 110(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 110(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.
---------------------------------------------------------------------------

    \19\ See ``Federal Implementation Plans to Reduce Interstate 
Transport of Fine Particulate Matter and Ozone,'' 75 FR 45210 
(August 2, 2010).
---------------------------------------------------------------------------

    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

[[Page 55500]]

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 of the significant contribution to 
nonattainment element of section 110(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 appropriate for comparison for 
purposes of the interfere with maintenance element of the statute.\20\
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    \20\ A memorandum in the docket for this action provides the 
information EPA used in order to identify monitors that are 
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 for Western States'' (August 
2010) (Timin Memo).
---------------------------------------------------------------------------

    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.\21\ 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.
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    \21\ To begin this analysis, EPA first identifies all monitors 
projected to be in nonattainment or, based on historic variability 
in air quality, projected to have maintenance problems in 2012. The 
``problem'' is that these maintenance areas are at risk not to stay 
in attainment because they are so close to the level of the 1997 
ozone and PM2.5 NAAQS that minor variations in weather or 
emissions could result in violations of the NAAQS in 2012.
---------------------------------------------------------------------------

    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 
110(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 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.
---------------------------------------------------------------------------

    \22\ 2006 Guidance at 4.
    \23\ Id. at 5.
    \24\ See, Transport Rule Proposal, 75 FR 45210 (August 2, 2010) 
at page 45227.
---------------------------------------------------------------------------

    Accordingly, EPA believes that section 110(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
    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 analyzed 
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 System (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 significantly 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

[[Page 55501]]

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 rulemaking 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 
nonattainment and maintenance receptors are based on projections of 
future air quality at existing ozone and PM2.5 monitoring 
sites in those 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 ([mu]g/m\3\) 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 [mu]g/m\3\ or 
less. The 1997 24-hour PM2.5 NAAQS is met when the 3-year 
average of the annual 98th percentiles is 65 [mu]g/m\3\ 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 110(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 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 (i.e., 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.
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    \25\ See, the Transport Rule Proposal at 75 FR 45210 (August 2, 
2010).
    \26\ Additional information concerning these weighted averages 
is provided in the docket in the Timin Memo.
---------------------------------------------------------------------------

    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.
    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 included 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 [mu]g/m\3\, which is 
well below the level of the 1997 24-hour PM2.5 NAAQS of 65 
[mu]g/m\3\.\27\ Therefore, outside of California, there are no areas 
that we would expect to have difficulty in maintaining the 1997 24-hour 
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \27\ Data undergoing review from EPA's Air Quality System which 
is EPA's repository of ambient air quality data. (https://www.epa.gov/ttn/airs/airsaqs/).
---------------------------------------------------------------------------

    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 (i.e. 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 km 
modeling.\29\ The 12 km Transport Rule Proposal modeling domain extends 
from Texas northward to North Dakota and eastward from the Rocky 
Mountains to

[[Page 55502]]

the east coast and includes 37 states and the District of Columbia.
---------------------------------------------------------------------------

    \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 does not include 
modeling results for the West. The Timin Memo documents further 
evaluation of the 2012 modeling to identify nonattainment and 
maintenance receptors in the West.
---------------------------------------------------------------------------

    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).
(a) Interfere With Maintenance Evaluation for the PM2.5 
NAAQS
    For the 1997 PM2.5 NAAQS, the closest maintenance 
receptor site identified by the Transport Rule Proposal was in Cook 
County, Illi