[Federal Register Volume 76, Number 75 (Tuesday, April 19, 2011)]
[Proposed Rules]
[Pages 21835-21847]
[FR Doc No: 2011-9451]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2007-1037; FRL-9297-4]

Approval and Promulgation of State Implementation Plans; State of
Colorado; Interstate Transport of Pollution Revisions for the 1997
PM2.5 and 8-Hour Ozone NAAQS: ``Significant Contribution,''
``Interference with Maintenance,'' and ``Interference with Prevention
of Significant Deterioration'' Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to approve portions of a State Implementation
Plan (SIP) revision submitted by the State of Colorado for the purpose
of addressing the ``good neighbor'' provisions of Clean Air Act
(``Act'' or ``CAA'') section 110(a)(2)(D)(i) for the 1997 8-hour ozone
National Ambient Air Quality Standards (``NAAQS'' or ``standards'') and
the 1997 fine particulate matter (``PM2.5'') NAAQS. This SIP
revision addresses the requirement that the State of Colorado's SIP
(``Interstate Transport 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
Colorado Interstate Transport SIP provisions that address the
requirement of section 110(a)(2)(D)(i) that emissions from Colorado
sources do not significantly contribute to nonattainment of the 1997
PM2.5 NAAQS in any other state, interfere with maintenance
of the 1997 PM2.5 NAAQS by any other state, or interfere
with any other state's required measures to prevent significant
deterioration of air quality for the 1997 PM2.5 and 8-hour
ozone NAAQS. This action is being taken under section 110 of the CAA.

DATES: Comments must be received on or before May 19, 2011.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2007-1037, by one of the following methods:
     http://www.regulations.gov. Follow the on-line
instructions for submitting comments.
     E-mail<EMAIL_ADDRESS>     Fax:<PHONE_NUMBER> (please alert the individual listed in
the FOR FURTHER INFORMATION CONTACT if you are faxing comments).
     Mail: Deborah Lebow Aal, Acting Director, Air Program,
Environmental

Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop Street,
Denver, Colorado 80202-1129.
     Hand Delivery: Deborah Lebow Aal, Acting Director, Air
Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-
AR, 1595 Wynkoop, Denver, Colorado 80202-1129. Such deliveries are only
accepted Monday through Friday, 8 a.m. to 4:30 p.m., excluding Federal
holidays. Special arrangements should be made for deliveries of boxed
information.
    Instructions: Direct your comments to Docket ID No. EPA-R08-OAR-
2007-1037. EPA's policy is that all comments received will be included
in the public docket without change and may be made available online at
http://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 http://www.regulations.gov or e-mail. The http://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 e-mail comment directly to EPA, without
going through http://www.regulations.gov, your e-mail 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 your 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. For additional instructions on submitting
comments, go to Section I. General Information of the SUPPLEMENTARY
INFORMATION section of this document.
    Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly-available docket materials are available either electronically
in http://www.regulations.gov or in hard copy at the Air Program,
Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595
Wynkoop, Denver, Colorado 80202-1129. EPA requests that if at all
possible, you contact the individual listed in the FOR FURTHER
INFORMATION CONTACT section to view the hard copy of the docket. You
may view the hard copy of the docket Monday through Friday, 8 a.m. to 4
p.m., excluding Federal holidays.

FOR FURTHER INFORMATION CONTACT: Adam Clark, Air Program, U.S.
Environmental Protection Agency, Region 8, Mailcode 8P-AR, 1595
Wynkoop, Denver, Colorado 80202-1129,<PHONE_NUMBER>,
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Definitions

    For the purpose of this document, we are giving meaning to certain
words or initials as follows:
    (i) The words or initials Act or CAA mean or refer to the Clean Air
Act, unless the context indicates otherwise.
    (ii) The words EPA, we, us or our mean or refer to the United
States Environmental Protection Agency.
    (iii) The initials SIP mean or refer to State Implementation Plan.
    (iv) The words Colorado and State mean the State of Colorado.

Table of Contents

I. General Information
    What should I consider as I prepare my comments for EPA?
II. What proposed action is EPA taking?
III. What is the background for this proposed action?
IV. What is the state process to submit these materials to EPA?
V. EPA's Review and Technical Information
    A. Background on Section 110(a)(2)(D)(i)(I)
    B. EPA's Evaluation of Colorado's Significant Contribution to
Nonattainment
    C. EPA's Evaluation of Colorado's Interference With Maintenance
    D. EPA's Evaluation of Colorado's Prevention of Significant
Deterioration (PSD)
VI. Summary of Proposed Action
VII. Statutory and Executive Order Review

I. General Information

What should I consider as I prepare my comments for EPA?

    1. Submitting CBI. Do not submit CBI to EPA through http://www.regulations.gov or e-mail. Clearly mark the part or all of the
information that you claim to be CBI. For CBI information in a disk or
CD-ROM that you mail to EPA, mark the outside of the disk or CD-ROM as
CBI and then identify electronically within the disk or CD-ROM the
specific information that is claimed as CBI. In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket.
Information so marked will not be disclosed except in accordance with
procedures set forth in 40 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments,
remember to:
    a. Identify the rulemaking by docket number and other identifying
information (subject heading, Federal Register date and page number).
    b. Follow directions--The agency may ask you to respond to specific
questions or organize comments by referencing a Code of Federal
Regulations (CFR) part or section number.
    c. Explain why you agree or disagree; suggest alternatives and
substitute language for your requested changes.
    d. Describe any assumptions and provide any technical information
and/or data that you used.
    e. If you estimate potential costs or burdens, explain how you
arrived at your estimate in sufficient detail to allow for it to be
reproduced.
    f. Provide specific examples to illustrate your concerns, and
suggest alternatives.
    g. Explain your views as clearly as possible, avoiding the use of
profanity or personal threats.
    h. Make sure to submit your comments by the comment period deadline
identified.

II. What proposed action is EPA taking?

    EPA is proposing to approve a portion of Colorado's Interstate
Transport SIP revision for the 1997 8-hour ozone and 1997
PM2.5 NAAQS. This revision was submitted by the State on
March 31, 2010.\1\ Specifically, we are proposing to approve the
portion of the plan that addresses the following requirements of CAA
section 110(a)(2)(D)(i) which prohibit air pollutant emissions within
the State that: (1) Significantly contribute to nonattainment of the
1997 PM2.5 NAAQS in any other state; (2) interfere with
maintenance of the 1997 PM2.5 NAAQS by any other state; and
(3) interfere with any other state's required measures to prevent
significant deterioration of its air quality with

respect to the 1997 PM2.5 and 8-hour ozone NAAQS.
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    \1\ The March 31, 2010 submission superseded earlier SIP
submissions with respect to the section 110(a)(2)(D)(i) requirements
that are the subject of this proposed action.
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III. What is the background for this proposed action?

    On July 18, 1997, EPA promulgated new NAAQS for ozone and for
PM2.5. This action is being taken in response to the
promulgation of both the 1997 ozone and PM2.5 NAAQS. Section
110(a)(1) of the CAA requires states to submit SIPs to address a new or
revised NAAQS within 3 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) Submissions 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'').\2\ The 2006 Guidance recommends ways
states may, in their submissions, meet the requirements of section
110(a)(2)(D)(i) for the 1997 8-hour ozone and PM2.5
standards.
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    \2\ Memorandum from William T. Harnett entitled, ``Guidance for
State Implementation Plan (SIP) Submissions 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''
(Aug. 15, 2006).
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    As identified in the 2006 Guidance, 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 requirements related to the impacts of interstate
transport. The SIP must prevent sources in the state from emitting
pollutants in amounts which will: (1) Contribute significantly to
nonattainment of the NAAQS in any other state; (2) interfere with
maintenance of the NAAQS by any other state; (3) interfere with
required measures to prevent significant deterioration of air quality
in any other state; or (4) interfere with efforts to protect visibility
in any other state. In this rulemaking EPA is addressing the first
three requirements of section 110(a)(2)(D)(i).
    On June 11, 2008, the State of Colorado submitted to EPA an
Interstate Transport SIP addressing all four requirements of CAA
section 110(a)(2)(D)(i) for the 1997 8-hour ozone and PM2.5
NAAQS. In response to EPA's concerns regarding the June 11, 2008
submission, the State later submitted two superseding interstate
transport SIP revisions: (a) A June 18, 2009 submission addressing
requirements (1) and (2) of section 110(a)(2)(D)(i) for the 1997 8-hour
ozone NAAQS; and (b) a March 31, 2010 submission addressing
requirements (3) and (4) for the 1997 8-hour ozone NAAQS and
requirements (1) through (4) for the 1997 PM2.5 NAAQS. EPA
has previously approved the ``significant contribution to
nonattainment'' and the ``interfere with maintenance'' requirements for
the State of Colorado for the 1997 8-hour ozone NAAQS in final rule
actions published June 3 and November 22, 2010 (75 FR 31306; 75 FR
71029). EPA proposed approval of the ``interfere with visibility''
requirement for the 1997 8-hour ozone and PM2.5 NAAQS on
February 14, 2011 (76 FR 8326). In this rulemaking EPA is evaluating
only the portions of Colorado's March 31, 2010 submission that address
requirements (1), (2), and (3) for the 1997 PM2.5 NAAQS, and
requirement (3) for the 1997 8-hour ozone NAAQS. In its submission, the
State indicated that its current SIP already contains provisions
adequate to prevent such contribution and interference. EPA is
proposing to find that, as stated by Colorado in the March 31, 2010
submission, the Colorado Interstate Transport SIP has adequate
provisions addressing requirements (1), (2), and (3) of section
110(a)(2)(D)(i) for the 1997 PM2.5 NAAQS and requirement (3)
for the 1997 8-hour ozone NAAQS.

IV. What is the state process to submit these materials to EPA?

    Section 110(k) of the CAA addresses EPA's rulemaking action on SIP
submissions by states. The CAA requires states to observe certain
procedural requirements in developing SIP revisions for submission to
EPA. Sections 110(a)(1) and (2) of the CAA require that each SIP
revision be adopted after reasonable notice and public hearing. This
must occur prior to the revision being submitted by a state to EPA.
    The Colorado Air Quality Control Commission (AQCC) held a public
hearing in December 2009 for the Interstate Transport SIP revision:
``State of Colorado Implementation Plan To Meet the Requirements of the
Clean Air Act Section 110(a)(2)(D)(i)(I) and (II)--Regarding Interstate
Transport for the 1997 8-Hour Ozone and PM2.5 NAAQS.'' The
AQCC adopted this revision on January 13, 2010, and the State submitted
it to EPA on March 31, 2010. As discussed above, the March 31, 2010
submission addresses the elements of 110(a)(2)(D)(i) that are the
subject of this proposed action.
    EPA has reviewed the March 31, 2010, submission from the State of
Colorado and has determined that the State met the requirements for
reasonable notice and public hearing under section 110(a)(1) and (2) of
the CAA.

V. EPA's Review and Technical Information

    EPA is evaluating the State's submission in light of the statutory
requirements of section 110(a)(2)(D)(i). In particular, section
110(a)(2)(D)(i)(I) requires that a SIP contain provisions adequate to
prevent emissions from sources in that state from contributing
significantly to nonattainment of the relevant NAAQS, or interfering
with maintenance of the relevant NAAQS, in any other state. Section
110(a)(2)(D)(i)(II) contains a similar requirement that a SIP contain
provisions adequate to prevent emissions from sources in the state from
interfering with measures required to prevent significant deterioration
of air quality in any other state.
    To assist states with SIP submissions for the 1997 8-hour ozone
NAAQS and the 1997 PM2.5 NAAQS, EPA issued the 2006 Guidance
to make recommendations with respect to all four requirements of
section 110(a)(2)(D)(i). More recently, EPA has proposed a rule
(``Transport Rule Proposal'') addressing the ``significant contribution
to nonattainment'' and ``interfere with maintenance'' requirements of
110(a)(2)(D)(i) for many states located in the eastern United
States.\3\ Although Colorado is not among the states that EPA is
considering for inclusion within the geographic region that may be
covered by the final rule that will be based upon the Transport Rule
Proposal, EPA is using a comparable approach to evaluate the emissions
from sources in Colorado, as well as considering certain data developed
to support the Transport Rule Proposal as discussed in more detail
below, as part of evaluating the issue of interstate transport from
Colorado for the first two requirements. For the third requirement, EPA
is evaluating the SIP submission from the state in light of the
recommendations contained in the Agency's prior 2006 guidance document
and in light of other subsequent actions as discussed below.
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    \3\ ``Federal Implementation Plans To Reduce Interstate
Transport of Fine Particulate Matter and Ozone,'' 75 FR 45210 (Aug.
2, 2010).

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A. Background on Section 110(a)(2)(D)(i)(I)

    The first two elements of section 110(a)(2)(D)(i) require states to
have SIPs with adequate provisions to prevent any source or other type
of emissions activity within the state from emitting air pollutants in
amounts that will ``contribute significantly'' to nonattainment in
other states or will ``interfere with maintenance'' of the NAAQS by any
other state. The terms ``contribute significantly'' and ``interfere
with maintenance'' are not defined in the statute. Therefore, EPA has
interpreted these terms in past regulatory actions addressing
interstate transport, such as the 1998 NOX SIP Call, in
which EPA took action to eliminate 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.\4\ 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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    \4\ See, 63 FR 57356 (Oct. 27, 1998). EPA's general approach to
section 110(a)(2)(D) was upheld in Michigan v. EPA, 213 F.3d 663 (DC
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 (DC Cir. 2008).
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    After promulgation of the 1997 8-hour ozone and PM2.5
NAAQS, EPA again recognized that regional transport was a serious
concern throughout the eastern U.S. and therefore developed the 2005
Clean Air Interstate Rule (CAIR) to address emissions of SO2
and NOX that exacerbate ambient ozone and PM2.5
levels in many downwind areas through interstate transport.\5\ Within
CAIR, EPA likewise interpreted the terms ``contribute significantly''
and ``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 actions 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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    \5\ See, 70 FR 25162 (May 12, 2005).
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    EPA's 2006 Guidance addressed section 110(a)(2)(D)(i) requirements
for the 1997 8-hour ozone and 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 ``contribute
significantly'' or ``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.'' \6\ 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.
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    \6\ 2006 Guidance at 5.
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    In 2008, however, the U.S. Court of Appeals for the D.C. Circuit
found that CAIR and the related CAIR federal implementation plans were
unlawful.\7\ 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.'' \8\ EPA's approach, the court reasoned, would leave
areas that are ``barely meeting attainment'' with ``no recourse'' to
address upwind emissions sources.\9\ 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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    \7\ See, North Carolina v. EPA, 531 F.3d 896 (DC Cir. 2008).
    \8\ Id. at 909.
    \9\ Id.
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    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)(i)(I) because the agency's guidance
suggested that states use an approach comparable to that used by EPA in
CAIR. States such as Colorado developed and adopted their Interstate
Transport SIPs not long after the Court's July 2008 decision, but well
before EPA, in the Transport Rule Proposal (see below), was able to
propose a new approach for the interference with maintenance element.
Without recommendations from EPA, Colorado's SIP may not have
sufficiently differentiated between the significant contribution to
nonattainment and interference with maintenance elements of the
statute, and relied in a general way on the difference between
monitored concentrations and the 1997 PM2.5 NAAQS to
evaluate the impacts of State emissions on maintenance of the NAAQS in
other states. It is necessary to evaluate these state submissions for
section 110(a)(2)(D)(i)(I) 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, it is
necessary to use an updated approach to this issue and to supplement
the technical analysis provided by the State in order to evaluate the
submissions with respect to both the significant contribution and the
interfere with maintenance elements of section 110(a)(2)(D)(i)(I).
    EPA has recently proposed a new rule, the ``Federal Implementation
Plans to Reduce Interstate Transport of Fine Particulate Matter and
Ozone'' (``Transport Rule Proposal''), in order to address interstate
transport under section 110(a)(2)(D)(i)(I) and the judicial remand of
CAIR.\10\ As part of the Transport Rule Proposal, EPA specifically
reexamined the section 110(a)(2)(D)(i)(I) 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 by 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 in the future, and therefore at
risk to become or continue to be 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 differentiating between areas where the concern is with
interference with maintenance with those where the concern is with
significant contribution to nonattainment.
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    \10\ 75 FR 45210 (Aug. 2, 2010).
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    As described in more detail below, EPA's Transport Rule 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
to be violating the 1997 8-hour ozone and PM2.5 NAAQS in
2012, and which areas are predicted potentially to have 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)(i). If, however, an area's projected data indicate that it
would be violating the NAAQS based on the highest single three year
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.
    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/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 1997 24-hour
PM2.5 NAAQS is met when the 3-year average of the annual
98th percentiles is 65 [mu]g/m3 or less.\11\ 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.
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    \11\ The 2006 24-hour PM2.5 NAAQS, which is not the
subject of this action, is met when the 3-year average of the annual
98th percentile PM2.5 concentrations is 35 [mu]g/
m3 or less.
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    To project future annual PM2.5 design values, EPA relied
on monitoring data from the AQS combined with photochemical air quality
modeling results. The Transport Rule Proposal generates the projected
future PM2.5 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.\12\ 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 base design value year periods (i.e.,
2003-2005, 2004-2006, and 2005-2007). The highest future 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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    \12\ Transport Rule Proposal, 75 FR at 45246-51. Additional
information concerning these weighted averages is provided in the
Western States Design Values Memo.
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    EPA then used these weighted averages and maximum design values to
identify nonattainment and maintenance receptors. For the 1997 annual
PM2.5 NAAQS, EPA defined nonattainment receptors as those
sites with an annual PM2.5 5-year weighted average
concentration (average design value) above 15.05 [mu]g/m3 in
2012. EPA then defined as maintenance receptors 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 projected
single three year period) above 15.05 [mu]g/m3 in 2012.
These maintenance sites are attaining the NAAQS based on the projected
average design values, but 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.
    By this method, EPA has identified those areas--the nonattainment
receptors--that are appropriate for evaluating whether emissions from
sources in another state could significantly contribute to
nonattainment. Likewise, EPA has identified those areas--the
maintenance receptors--that are appropriate for evaluating whether the
emissions from sources in another state could interfere with
maintenance. EPA then uses a ``weight-of-evidence'' analysis, separate
from that used in the Transport Rule Proposal, to examine the potential
impacts of emissions from upwind states on these nonattainment and
maintenance receptors in downwind states. This proposed approach for
identifying those areas that are predicted to have nonattainment or
maintenance problems is appropriate to evaluate the section
110(a)(2)(D)(i) SIP submission of a state for the significant
contribution and interfere with maintenance elements. 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 Colorado submission.
    As explained in the 2006 Guidance, section 110(a)(2)(D)(i) SIP
submissions from all states do not necessarily need to follow precisely
the same analytical approach as CAIR. In the 2006 Guidance, EPA stated
that: ``EPA believes that the contents of the SIP submission required
by section 110(a)(2)(D)(i) 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.'' \13\ 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.\14\ As
noted in the Transport Rule Proposal, the more widespread and serious
transport problems in the eastern United States are analytically
distinct. For the 1997 8-hour ozone NAAQS and the 1997 PM2.5
NAAQS, nonattainment and maintenance problems in the western United
States are relatively local in nature with only limited impacts from
interstate transport.\15\ In the Transport Rule Proposal, EPA did not
calculate interstate ozone or PM2.5 contributions to or from
western states, including Colorado.
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    \13\ 2006 Guidance at 3.
    \14\ Id. at 5.
    \15\ Transport Rule Proposal, 75 FR at 45227.
---------------------------------------------------------------------------

    Accordingly, section 110(a)(2)(D)(i) SIP submissions for states not
evaluated in the Transport Rule Proposal may be evaluated using a
weight-of-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 significantly contribute to
nonattainment or interfere with maintenance of the 1997
PM2.5 NAAQS in other states. These submissions can rely on
modeling when acceptable modeling technical analyses are available, but
modeling is not necessarily required if other available information is
sufficient to evaluate the presence or degree of interstate transport
in a given situation.

B. EPA's Evaluation of Colorado's Significant Contribution to
Nonattainment

    To meet the requirements of section 110(a)(2)(D)(i), the State of
Colorado on March 31, 2010 made a submission to EPA addressing all four
110(a)(2)(D)(i) requirements for the 1997 PM2.5 NAAQS, and
requirements (3) and (4) for the 1997 8-hour ozone NAAQS. The State
used many of the methods recommended in the 2006 Guidance. This
included consideration of information such as the geographic location
of violating areas and meteorological data. The State's submission also
considered AQS monitoring data from Colorado and surrounding states.
The State's submission concluded that its own analysis ``supports the
assertion that Colorado does not contribute significantly to
nonattainment in, or interfere with maintenance by, any other state
with respect to the 1997 PM2.5 NAAQS.'' \16\ In its
submission, the State of Colorado further indicated that its current
SIP is adequate to prevent such contribution and interference, and
therefore no additional reductions would be necessary to prevent such
contribution or interference.
---------------------------------------------------------------------------

    \16\ See ``State of Colorado Implementation Plan to Meet the
Requirements of the Clean Air Act Section 110(a)(2)(d)(i)(I) and
(II)--Regarding Interstate Transport for the 1997 8-Hour Ozone and
PM2.5 NAAQS'' at 46, available in the docket for this
action.
---------------------------------------------------------------------------

    Colorado submitted its Interstate Transport SIP before the
Transport Rule Proposal was completed and available. Therefore, the
State could not have anticipated which nonattainment receptors EPA
would consider most appropriate for the analysis of the impact of
transport from Colorado's sources on PM2.5 levels in other
states. In this proposal, EPA therefore conducts additional analysis,
using a weight-of-evidence approach separate from that used in the
Transport Rule Proposal, to determine if emissions from Colorado
sources significantly contribute to nonattainment of the 1997
PM2.5 NAAQS in any other state. This analysis considers: (a)
Portions of EPA modeling and analysis conducted for the 2005 CAIR and
the 2010 Transport Rule Proposal;\17\ (b) projections of western
nonattainment and maintenance receptors based on Transport Rule
modeling; \18\ and (c) geographical, topographical and meteorological
factors relevant to the potential for pollution transport. None of
these factors is by itself determinative of whether emissions from
Colorado significantly contribute to nonattainment of the 1997
PM2.5 NAAQS in any other state. However, when considered
together through the weight-of-evidence approach, the factors provide
the basis for a reliable qualitative assessment of significant
contribution.
---------------------------------------------------------------------------

    \17\ Specifically, from CAIR, EPA considers only CAIR Proposal
PM2.5 zero-out modeling analysis. From the Transport Rule
Proposal, EPA considers: (a) Projected annual PM2.5
nonattainment receptor locations; (b) projected statewide
SO2 and NOX emission data for Colorado and
three states east of Colorado (Kansas, Nebraska, and Oklahoma); and
(c) projected downwind contributions to annual PM2.5
nonattainment receptors for Kansas, Nebraska, and Oklahoma.
    \18\ Memorandum from Brian Timin, EPA Office of Air Quality
Planning and Standards, ``Documentation of Future Year Ozone and
Annual PM2.5 Design Values for Western States,'' (Aug.
23, 2010) (``Western States Design Values Memo''), available in the
docket for this action.
---------------------------------------------------------------------------

    As described in detail above, in the Transport Rule Proposal, EPA
projected future concentrations of PM2.5 to identify
receptors that are expected to be violating the 1997 PM2.5
NAAQS in 2012. For the 1997 annual PM2.5 NAAQS, the
receptors EPA identified in the Transport Rule Proposal nearest to
Colorado are located in Chicago, IL to the northeast, East St. Louis,
IL to the east, and Birmingham, AL to the southeast.\19\ No monitoring
sites within the geographic region addressed in the Transport Rule
Proposal analysis were projected to be violating the 1997 24-hour
PM2.5 NAAQS.\20\
---------------------------------------------------------------------------

    \19\ Transport Rule Proposal, 75 FR at 45247-48 (Table IV.C-7).
    \20\ Id. at 45249-51 (Table IV.C-9).
---------------------------------------------------------------------------

    Available information indicates that emissions from Colorado are
unlikely to contribute significantly to violations of the 1997 annual
PM2.5 NAAQS in Chicago, IL, in East St. Louis, IL, or in
Birmingham, AL. In our rulemaking process for CAIR, EPA modeled the
contribution from individual states to counties in the eastern U.S.
projected to be nonattainment for the 1997 annual PM2.5
NAAQS in 2010. According to this modeling, EPA projected annual
PM2.5 contributions from Colorado sources to Cook County
(Chicago), IL in 2010 to be 0.03 [mu]g/m3,\21\ which is well
below the significance threshold of one percent of the NAAQS (0.15
[mu]g/m3 for the 1997 annual PM2.5 NAAQS) used in
the Transport Rule Proposal. Contributions from Colorado to annual
PM2.5 emissions in Saint Clair County (East St. Louis), IL
in 2010 were modeled to be 0.04 [mu]g/m3. Finally, projected
contributions from Colorado to annual PM2.5 emissions in
Jefferson County (Birmingham), AL were modeled to be 0.03 [mu]g/
m3, also far below the significance threshold. The CAIR
Proposal modeling used a 2010 future year assessment versus the 2012
year used in the Transport Rule Proposal, so it is not determinative of
significant contribution from Colorado to these receptors, but it does
provide an initial piece of evidence for EPA's weight-of-evidence
analysis.
---------------------------------------------------------------------------

    \21\ ``Technical Support Document for the Interstate Air Quality
Rule Air Quality Modeling Analyses Appendix H, PM2.5
Contributions to Downwind Nonattainment Counties in 2010'' (Jan. 30,
2004), available in the docket for this action.
---------------------------------------------------------------------------

    Certain portions of the Transport Rule Proposal modeling analysis
provide more evidence that emissions of PM2.5 or its
precursors from Colorado sources are not likely to contribute
significantly to the nonattainment receptors (identified above) in
Illinois and Alabama, or to any nonattainment receptors located in
states further east.\22\ EPA did not model the impacts of emissions
from Colorado sources on receptors in other states as part of the
Transport Rule Proposal. However, Kansas, Nebraska and Oklahoma were
among the states whose interstate contribution to annual
PM2.5 nonattainment receptors in other states EPA did model
for the Transport Rule Proposal.\23\ None of these three states
(Kansas, Oklahoma and Nebraska) was projected to contribute more than
0.09 [mu]g/m3 (60% of the significance threshold) to any
annual PM2.5 nonattainment receptor inside the

Transport Rule Proposal domain in 2012.\24\
---------------------------------------------------------------------------

    \22\ Transport Rule Proposal, 75 FR at 45247-48 (Table IV.C-7).
    \23\ As technical support for the Transport Rule Proposal, all
48 contiguous states were modeled using a horizontal grid resolution
of 36 x 36 km. States in the eastern U.S. modeled for contribution
in the Transport Rule Proposal, including Kansas, Nebraska and
Oklahoma, were also modeled using a finer horizontal grid resolution
of 12 x 12 km. Contribution was determined using zero-out modeling.
    \24\ Transport Rule Proposal, 75 FR at 45255 (Table IV.C-13).
---------------------------------------------------------------------------

    For the Transport Rule Proposal, EPA projected total emissions for
NOX and SO2, the two major precursors for
PM2.5, for each of the 48 contiguous states in 2012 and
2014. Colorado's NOX and SO2 emissions were
generally less than or similar to those in Kansas, Oklahoma and
Nebraska.\25\ Under prevailing meteorological conditions, all three
states are typically downwind from Colorado and upwind of the
nonattainment receptors in the eastern U.S. Furthermore, emissions from
Colorado must travel a greater distance (compared to these three
states) to reach nonattainment receptors in the eastern U.S.\26\ Though
distance by itself is not an obstacle to long range transport of
PM2.5 and/or its precursors, and therefore by itself not
determinative of significant contribution, greater distance provides
greater opportunities for PM2.5 and precursor dispersion
and/or removal from the atmosphere due to the effect of winds or
chemical sink processes. In summary, EPA-projected PM2.5
precursor emissions from Colorado are lower or similar to those in
Kansas, Nebraska or Oklahoma, and, based on geography and meteorology,
emissions from these three states are more likely to reach
nonattainment receptors in the eastern U.S. than are emissions from
Colorado. Therefore, because Kansas, Nebraska and Oklahoma are each
well below the significance threshold for contribution for the annual
PM2.5 NAAQS in the Transport Rule Proposal, Colorado is
likely to be even further below the significance threshold. This
consideration, along with the 2004 CAIR Proposal modeling, when taken
into account under the weight-of-evidence approach, shows that Colorado
emissions are very unlikely to contribute significantly to violations
of the 1997 annual PM2.5 standard at nonattainment receptors
in Illinois, Alabama or any states further east.
---------------------------------------------------------------------------

    \25\ See ``Technical Support Document (TSD) for the Transport
Rule Docket ID No. EPA-HQ-OAR-2009-0491. Emission Inventories'' at
40-43 (June 2010). Based on these projections, in 2012, Kansas will
have higher NOX (~24%) and SO2 (~35%)
emissions than Colorado, Oklahoma will have higher NOX
(~54%) and SO2 (~147%) emissions than Colorado, and
Nebraska will have lower NOX (~23%) and higher
SO2 (~94%) emissions than Colorado.
    \26\ At the shortest possible distance for each measurement, the
eastern Colorado border is approximately 320 miles west of the
eastern Nebraska border, 370 miles west of the eastern Kansas
border, and 410 miles west of the eastern Oklahoma border. It should
be noted that the measured distance represents that of the straight
(and shortest) path, which does not reflect the more circuitous
paths typically followed by air parcels.
---------------------------------------------------------------------------

    To assist in the evaluation of whether emissions from a state's
sources contribute significantly to nonattainment of the NAAQS in
western states, EPA has also developed an analysis identifying monitors
projected to be in nonattainment or at risk for maintenance of the
NAAQS within a modeling domain that includes the western states. The
analysis presented in the memo, ``Documentation of Future Year Ozone
and Annual PM2.5 Design Values for Western States,'' \27\
(``Western State Design Values Memo'') uses model results from the
Transport Rule Proposal based on a continental U.S. 36 km grid, which
is coarser than the final 12 km grid used in the Transport Rule for the
eastern states. Though the 36 km grid is more coarse, EPA considers
these modeling results sufficient to determine the appropriate
nonattainment and maintenance receptors for analysis of interstate
transport from Colorado to other western states. In identifying these
receptors, the Western States Design Values Memo takes the same
approach as the Transport Rule Proposal (5 year weighted average design
values to project 2012 concentrations).\28\ For the 1997 annual
PM2.5 NAAQS, the nonattainment receptors identified in the
Memo are all located in southern and central California, and the
nonattainment receptor nearest to Colorado is located in San
Bernardino, CA.
---------------------------------------------------------------------------

    \27\ Supra n. 18.
    \28\ Id. at 5.
---------------------------------------------------------------------------

    In the Western States Design Values Memo, EPA did not calculate
interstate PM2.5 contributions to or from western states.
Therefore, EPA is using a weight-of-evidence approach to determine if
the emissions from Colorado sources contribute significantly to
nonattainment for receptors in San Bernardino, CA, or other
nonattainment receptors in California further west. Distance and
topography, although not determinative by themselves, indicate that
PM2.5 transport from Colorado to California is unlikely. The
southwestern corner of Colorado is approximately 500 miles from San
Bernardino, making distance an obstacle for PM2.5 emissions
transport. Moreover, the mountainous topography between Colorado's
sources and California's nearest nonattainment receptors presents a
large obstacle to PM2.5 transport. The prevailing wind
orientation also provides evidence that Colorado's emissions are
unlikely to contribute significantly to nonattainment of the 1997
annual PM2.5 NAAQS in California. West of the Continental
Divide the prevailing winds generally move from south-westerly,
westerly, or north-westerly directions, as indicated by the typical
movement of weather systems.
    Finally, projected design values presented in the Western States
Design Values Memo provide some evidence that significant contribution
from Colorado sources to annual PM2.5 nonattainment
receptors in California is unlikely. The highest projected average
PM2.5 design value for 2012 in Colorado is 9.36 [mu]g/
m3, or 64% of the 1997 annual PM2.5 NAAQS.\29\
The highest projected average PM2.5 design value for 2012
throughout Utah, Arizona and Nevada, the states between Colorado and
California, is 12.7 [mu]g/m3, or 84.6% of the NAAQS.\30\
Given the distance between Colorado sources and California
nonattainment receptors, the intervening mountainous topography, the
general west-to-east direction of transport winds in the western U.S.,
and the low projected PM2.5 design values in Colorado and
intervening states, the weight-of-evidence makes it reasonable to
conclude that Colorado sources are very unlikely to contribute
significantly to nonattainment of the 1997 annual PM2.5
NAAQS in California.
---------------------------------------------------------------------------

    \29\ Western States Design Values Memo, Appendix A.
    \30\ Id.
---------------------------------------------------------------------------

    EPA did not project 2012 design values for the 1997 24-hour
PM2.5 NAAQS in the Western States Design Values Memo. EPA
therefore used the most recent AQS monitoring data to determine the
monitor nearest to Colorado with a design value above the 1997 24-hour
PM2.5 NAAQS. Based on recent monitoring data (2009 design
values), the highest 24-hour PM2.5 design value in 47 of the
48 states of the continental U.S. (not including California) is 50
[mu]g/m3, which is well below the level of the 1997 24-hour
PM2.5 NAAQS of 65 [mu]g/m3.\31\ In California,
the most recent (2009) 24-hour PM2.5 design values show that
the monitor nearest Colorado that might be violating the 1997 24-hour
PM2.5 NAAQS is in Bakersfield.\32\ Transport of emissions
from Colorado sources to PM2.5 receptors in Bakersfield is
very unlikely, based on a similar weight-of-evidence analysis as for
San Bernardino above. Bakersfield is roughly 570 miles from the nearest
Colorado border. The topography between Colorado sources and California
monitors is largely

mountainous, presenting an obstacle to transport of emissions. Winds
typically travel west to east in the western United States, making
transport of emissions from Colorado to California unlikely. Under the
weight-of-evidence approach, these factors combined lead EPA to the
conclusion that significant contribution from Colorado sources to 24-
hour PM2.5 nonattainment monitors in California is very
unlikely.
---------------------------------------------------------------------------

    \31\ Data from EPA's Air Quality System, which is EPA's
repository of ambient air quality data. (See http://www.epa.gov/ttn/airs/airsaqs/).
    \32\ The AQS design value data shows 2009 design values in
Bakersfield of roughly 70 [mu]g/m3.
---------------------------------------------------------------------------

    In conclusion, our analysis indicates that emissions of
PM2.5 and/or its precursors from the sources in Colorado are
unlikely to contribute significantly to nonattainment of the 1997 24-
hour and annual PM2.5 NAAQS in any other state.

C. EPA's Evaluation of Colorado's Interference With Maintenance

    As discussed above, following the 2006 Guidance and consistent with
EPA's approach in CAIR, Colorado's submission for section
110(a)(2)(D)(i) for the 1997 PM2.5 NAAQS did not evaluate
whether emissions from the sources in the state interfere with
maintenance of these NAAQS by other states, separately from evaluation
of significant contribution to nonattainment in other states. Instead,
the State presumed that if Colorado sources did not significantly
contribute to violations of the NAAQS in other states, then no further
specific evaluation was necessary for purposes of the interference with
maintenance element of section 110(a)(2)(D)(i)(I). As explained above,
however, CAIR was remanded to EPA, in part because the court found that
EPA had failed to give independent meaning to the ``interfere with
maintenance'' requirement, a concern that EPA has addressed in the
Transport Rule Proposal. However, Colorado submitted its Interstate
Transport SIP without the benefit of EPA's new approach. Accordingly,
we are evaluating the state's submission using additional information
to address the issue of interference with maintenance.
    In particular, EPA has developed an approach to identify those
monitors for PM2.5 that are located in areas appropriate for
consideration as receptors for evaluating the potential for inference
with maintenance of the 1997 PM2.5 NAAQS. As discussed in
more detail above in section A, EPA has examined data from existing
monitors for three overlapping three year periods to predict what areas
may have difficultly attaining the NAAQS in 2012. By identifying these
monitors, EPA can then use available analytical tools to determine
whether emissions from sources in a state are having an impact on other
states, and the degree of that impact.
    EPA did not model the contribution of emissions from Colorado
sources (because Colorado and other western states are not fully inside
the Transport Rule Proposal's modeling domain) to PM2.5
maintenance receptors in other states. Therefore, EPA's assessment of
whether emissions from Colorado sources interfere with maintenance in
other states relies on a weight-of-evidence approach that considers
relevant information (such as identification of maintenance receptors
and estimates of PM2.5 contributions) from the Transport
Rule Proposal pertaining to states within its modeling domain, modeling
analysis results from other studies, additional material such as
geographical, topographical and meteorological factors, and back
trajectory analyses. While conclusions reached for each of the factors
considered in the following analysis are not themselves determinative,
consideration of these factors together provides a reliable qualitative
conclusion that emissions from Colorado are not likely to interfere
with maintenance of the 1997 PM2.5 NAAQS at monitors in
other states.
    It should be noted that the maintenance receptors analyzed are
separate from the nonattainment receptors analyzed for purposes of
significant contribution to nonattainment. EPA is evaluating impacts on
these monitors specifically to address the independent interference
with maintenance requirement of section 110(a)(2)(D)(i)(I). However,
the maintenance receptors in Cook County, IL are geographically close
to the nonattainment receptors in that same county, especially relative
to the distance from Colorado. The following analysis therefore uses
similar evidence to evaluate interference with maintenance as that used
for the evaluation of the potential for significant contribution to
nonattainment. EPA uses similar evidence only because these
nonattainment and maintenance receptors are in similar locations, and
recognizes that the two types of receptors are analytically distinct.
    In connection with the Transport Rule Proposal, EPA evaluated
monitor data for states within the geographic scope of that rulemaking
to project future concentrations of PM2.5 to identify
receptors that are expected to have difficulty maintaining compliance
with the NAAQS in 2012, referred to as maintenance receptors. For the
1997 annual PM2.5 NAAQS, this analysis identified 16
maintenance receptors in its modeling analysis domain (i.e. states east
of the Rocky Mountains). The maintenance receptors for the 1997
PM2.5 NAAQS nearest to Colorado are two monitoring sites
located in Cook County, Illinois in the Chicago area, and a monitoring
site in Harris County, Texas, in the Houston-Galveston-Brazoria area.
For the 1997 24-hour PM2.5 NAAQS, EPA did not evaluate
maintenance receptors because there were no violations of these
standards in the 37 states east of the Rockies.\33\
---------------------------------------------------------------------------

    \33\ Areas east of the Rockies were modeled for the Transport
Rule Proposal using a 12km grid. Areas west of the Rockies were
modeled using a 36km grid. EPA did not model projections for the 24-
hour PM2.5 NAAQS in the 36km grid modeling domain. For
the states included in the eastern domain, see Table IV.C-13,
Transport Rule Proposal, 75 FR at 45255-56.
---------------------------------------------------------------------------

    EPA analyzed contribution of annual PM2.5 emissions from
Colorado sources to maintenance receptors in Cook County, Illinois
using the same evidence as was used in Section B of this action to
determine the potential impact of Colorado sources on the projected
nonattainment receptor in the same county. As noted in that section,
modeling conducted for the 2004 CAIR Proposal projected 2010 emissions
from Colorado sources to contribute 0.03 [mu]g/m3 annual
PM2.5 emissions to Cook County, just 20% of the significance
threshold (0.15 [mu]g/m3) for interference with maintenance
used in the Transport Rule Proposal for the 1997 annual
PM2.5 NAAQS. The CAIR Proposal modeling therefore provides
the initial evidence--not determinative by itself--that emissions from
Colorado sources are not likely to interfere with maintenance of the
annual PM2.5 NAAQS in Cook County, IL.
    Portions of the modeling analysis and projected emission levels
calculated for the Transport Rule Proposal provide further evidence for
the conclusion that emissions from Colorado sources are unlikely to
interfere with maintenance at the Cook County, IL receptors. As noted
above, in the Transport Rule Proposal, EPA did not directly model the
impacts of emissions from Colorado, but EPA did model the impacts of
emissions from other states that are within the modeling domain for the
Transport Rule Proposal. Kansas and Nebraska were among the states
whose interstate contribution to annual PM2.5 maintenance
receptors in other states EPA did model for the Transport Rule
Proposal.\34\ Neither of these two states

(Kansas or Nebraska) was projected to contribute more than 0.06 [mu]g/
m3,\35\ or 40% of the significance threshold, to any
maintenance receptor covered by the Transport Rule Proposal, which
included the Cook County, IL monitors.
---------------------------------------------------------------------------

    \34\ As technical support for the Transport Rule Proposal, all
48 contiguous states were modeled using a horizontal grid resolution
of 36 x 36 km. States in the eastern U.S. modeled for contribution
in the Transport Rule Proposal, including Kansas and Nebraska, were
also modeled using a finer horizontal grid resolution of 12 x 12 km.
Contribution was determined using zero-out modeling.
    \35\ Transport Rule Proposal, 75 FR at 47255 (Table IV.C-13).
---------------------------------------------------------------------------

    For the Transport Rule Proposal, EPA projected total emissions for
NOX and SO2, the two major precursors for
PM2.5, for each of the 48 contiguous states in 2012 and
2014. Nebraska and Kansas were each projected to have similar amounts
of PM2.5 precursor emissions (NOX and
SO2) to those of Colorado.\36\ Both states are also upwind
of Cook County, IL, but are much closer to the Cook County maintenance
receptors than is Colorado.\37\ Distance by itself is not an obstacle
to long range transport of PM2.5 and/or its precursors, and
is therefore not determinative of interference with maintenance.
However, with increasing distance there are greater opportunities for
PM2.5 or precursor dispersion and/or removal from the
atmosphere due to the effect of winds or chemical sink processes. In
summary, EPA-projected PM2.5 precursor emissions from
Colorado are lower or similar to those in Kansas or Nebraska, and,
based on geography and meteorology, emissions from each of these states
are more likely to reach maintenance receptors in the eastern U.S. than
are emissions from Colorado. Therefore, because Kansas and Nebraska are
each well below the significance threshold for interference with
maintenance for the annual PM2.5 NAAQS in the Transport Rule
Proposal, Colorado is likely to be even further below the significance
threshold. Based on the modeling analysis from the CAIR Proposal and
the Transport Rule Proposal, the weight of evidence shows that it is
very unlikely that emissions from Colorado sources would interfere with
maintenance of the 1997 annual PM2.5 NAAQS at any monitor in
Cook County, IL.
---------------------------------------------------------------------------

    \36\ See ``Technical Support Document (TSD) for the Transport
Rule Docket ID No. EPA-HQ-OAR-2009-0491. Emission Inventories'' at
40-43 (June 2010). Based on these projections, in 2012, Kansas will
have higher NOX (~24%) and SO2 (~35%)
emissions than Colorado, and Nebraska will have lower NOX
(~23%) and higher SO2 (~94%) emissions than Colorado.
    \37\ At the shortest possible distance for each measurement, the
eastern Colorado border is approximately 320 miles west of the
eastern Nebraska border and 370 miles west of the eastern Kansas
border.
---------------------------------------------------------------------------

    EPA did not calculate the impact of Colorado's emissions on the
Houston area as part of the CAIR modeling analysis or the Transport
Rule Proposal modeling analysis. EPA is therefore using other evidence
in a weight-of-evidence assessment to determine if Colorado emissions
interfere with maintenance of the 1997 annual PM2.5 NAAQS at
the Harris County monitor. Our assessment considers modeling analysis
from the Transport Rule Proposal, geographical and meteorological
factors, and back trajectory analyses.
    Oklahoma was among the states EPA modeled for the Transport Rule
Proposal to estimate their interstate contribution of annual
PM2.5 emissions to nonattainment and maintenance monitors in
other states. Oklahoma's estimated maximum contribution to any
maintenance monitor covered by the Transport Rule Proposal, which
included the Harris County, TX monitor, was 0.05 [mu]g/
m3,\38\ or 33% of the significance threshold.
---------------------------------------------------------------------------

    \38\ Transport Rule Proposal, 75 FR at 45255 (Table IV.C-13).
---------------------------------------------------------------------------

    Back trajectory analysis indicates that air parcel pathways that
reach Houston will pass through Oklahoma more frequently than they will
pass through Colorado.\39\ Because back trajectory analysis results map
pathways of air parcels that may or may not transport pollutants, they
cannot be considered determinative as to the transport of
PM2.5 and its precursors, or of the absence of such
transport, from Colorado sources. However, this back trajectory
analysis provides evidence that PM2.5 emissions and
PM2.5 precursor emissions from Oklahoma are more likely to
reach Houston than Colorado emissions, based simply on wind patterns.
In addition, emissions from Oklahoma sources travel a much shorter
distance to the Houston area than emissions from Colorado sources.\40\
Furthermore, the emissions of SO2 and NOX, the
two major PM2.5 precursors, are significantly lower in
Colorado than in Oklahoma.\41\ The weight of evidence from these
factors combined shows that emissions from Oklahoma sources are much
more likely to reach the Houston area than are emissions from Colorado
sources. Given that Oklahoma is far below the Transport Rule Proposal
threshold for interference with maintenance at annual PM2.5
maintenance receptors, including the Harris County receptor, the weight
of evidence shows it is highly unlikely that Colorado sources will
interfere with maintenance of the 1997 annual PM2.5 NAAQS at
the Harris County receptor.
---------------------------------------------------------------------------

    \39\ See ``Eight-Site SA Speciation Trends Final Report.
Appendix G: Graphical Representation of the Source Apportionment
Results for Houston, Texas,'' (September 24, 2003), available in the
docket for this action.
    \40\ The Houston area is approximately 270 miles from the
nearest Oklahoma border. The Houston area is approximately 630 miles
from the nearest Colorado border.
    \41\ See ``Technical Support Document (TSD) for the Transport
Rule Docket ID No. EPA-HQ-OAR-2009-0491. Emission Inventories'' at
40-43 (June 2010). Based on these projections, Oklahoma will have
higher NOX (~54%) and SO2 (~147%) emissions
than Colorado in 2012.
---------------------------------------------------------------------------

    As discussed above in section B, EPA developed the Western States
Design Values Memo to identify nonattainment and maintenance receptors
within a modeling domain that includes the western states.\42\ The
Western States Design Values Memo analysis uses the same general
approach as the Transport Rule Proposal (5 year weighted average design
values to project 2012 concentrations) to project nonattainment and
maintenance receptors.\43\ For the 1997 annual PM2.5 NAAQS,
the two maintenance receptors identified in the Western States Design
Values Memo are in Orange and Los Angeles counties in California.
---------------------------------------------------------------------------

    \42\ Western States Design Values Memo.
    \43\ Id. at 5.
---------------------------------------------------------------------------

    Distance and topography, while not determinative in of themselves,
indicate that PM2.5 and precursor transport from Colorado to
California is unlikely. The southwestern corner of the Colorado border
is approximately 545 miles from Anaheim, the city with the nearest
maintenance receptor for these NAAQS. The mountainous topography
between Colorado sources and California maintenance receptors also
presents a large obstacle to PM2.5 transport. Thus,
geography and topography significantly reduce the likelihood of
transport from Colorado to California's maintenance receptors.
    Prevailing wind orientation also provides strong evidence that
Colorado's emissions are unlikely to interfere with maintenance of the
1997 annual PM2.5 standards in California. West of the
Continental Divide the prevailing winds generally move from south-
westerly, westerly, or north-westerly directions, as indicated by the
typical movement of weather systems. In addition, projected design
values presented in the Western States Design Values Memo provide some
evidence that interference with maintenance by emissions from Colorado
sources to maintenance receptors for the 1997 annual PM2.5
NAAQS in California is unlikely. The highest projected average
PM2.5 design value for 2012 in Colorado is 9.36 [mu]g/
m3, or 64% of the 1997 annual PM2.5 NAAQS.\44\
The highest

projected average PM2.5 design value for 2012 throughout
Utah, Arizona and Nevada, the states between Colorado and California,
is 12.7 [mu]g/m3, or 84.6% of the NAAQS.\45\ Given the
distance between Colorado sources and California maintenance receptors,
the intervening mountainous topography, the general west-to-east
direction of transport winds in the western U.S., and the low level of
emissions from Colorado sources, EPA concludes that Colorado sources
are not likely to interfere with maintenance of the 1997 annual
PM2.5 NAAQS in California.
---------------------------------------------------------------------------

    \44\ Western States Design Values Memo, Appendix A.
    \45\ Id.
---------------------------------------------------------------------------

    EPA did not project 2012 design values for the 1997 24-hour
PM2.5 NAAQS in the Western States Design Values Memo. Based
on recent monitoring data (2009 design values), the highest 24-hour
PM2.5 design value in 47 of the 48 states of the continental
U.S. (not including California) is 50 [mu]g/m3, which is
well below the level of the 1997 24-hour PM2.5 NAAQS of 65
[mu]g/m3.\46\ Therefore, outside of California, there are no
areas that we would expect to have difficulty in maintaining the 1997
24-hour PM2.5 NAAQS. In California, the most recent (2009)
24-hour PM2.5 design values show that the only monitors that
might be at risk for maintenance of the 1997 24-hour PM2.5
NAAQS are in Turlock, Fresno, and Bakersfield, in the northern, central
and southern sections of the San Joaquin Valley.\47\ Of these, the
monitor located in Bakersfield is nearest Colorado.
---------------------------------------------------------------------------

    \46\ Data from EPA's Air Quality System, which is EPA's
repository of ambient air quality data. (See http://www.epa.gov/ttn/airs/airsaqs/).
    \47\ The AQS design value data shows that in 2009 design values
at monitors in these locations ranged from 60 [mu]g/m3 in
Fresno and Turlock, to 70 [mu]g/m3 in Bakersfield.
---------------------------------------------------------------------------

    Transport of emissions from Colorado sources to potential
PM2.5 maintenance receptors in Bakersfield, or any monitors
in California further west, is very unlikely, based on a weight-of-
evidence analysis. Bakersfield is roughly 570 miles from the nearest
Colorado border. The topography between Colorado sources and California
monitors is largely mountainous, presenting an obstacle to transport of
emissions. Transport winds typically travel west to east in the western
United States, making transport of emissions from Colorado to
California unlikely. These factors combined lead EPA to the conclusion
that interference with maintenance by Colorado sources at 1997
PM2.5 NAAQS maintenance receptors in California is very
unlikely.
    In conclusion, our analysis of the weight of evidence indicates
that emissions of PM2.5 and/or its precursors from the
sources in Colorado are unlikely to interfere with maintenance of the
1997 24-hour and the annual PM2.5 NAAQS by any other state.

 D. EPA's Evaluation of Colorado's Prevention of Significant
Deterioration (PSD)

    The third element of section 110(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 (CAA section 110(a)(2)(D)(i)(II)).
EPA's 2006 Guidance made recommendations to states for making SIP
submissions to meet this requirement with respect to both the 1997 8-
hour ozone and PM2.5 NAAQS.
    The 2006 Guidance states that the PSD requirement of section
110(a)(2)(D)(i)(II) may be met by the State's confirmation in a SIP
submission that new major sources and major modifications in the State
are subject to PSD and (if the State contains a nonattainment area for
the relevant pollutant) Nonattainment New Source Review (NNSR) programs
that implement the relevant standards.\48\ The Guidance explains that
the requirements for PSD and NNSR programs include provisions that
protect air quality in other states. Specifically, a PSD permit may not
be issued unless the new or modified source demonstrates that emissions
from the construction or operation of the facility will not cause or
contribute to air pollution in any area--including areas in other
States--that exceeds any NAAQS or any maximum allowable increase (i.e.,
PSD increment).\49\ An NNSR permit may not be issued unless the new or
modified source shows it has obtained sufficient emissions reductions
to offset increases in emissions of the pollutants for which an area is
designated nonattainment, consistent with reasonable further progress
toward attainment.\50\ Because the PSD and NNSR permitting programs
currently applicable in each area require a demonstration that new or
modified sources will not cause or contribute to air pollution in
excess of the NAAQS in neighboring states or that sources in
nonattainment areas procure offsets, States may satisfy the requirement
of section 110(a)(2)(D)(i)(II) regarding other States' required
measures to prevent significant deterioration of air quality by
submitting SIPs confirming that new major sources and major
modifications in the State are subject to PSD and (if applicable) NNSR
programs that implement the relevant standards.
---------------------------------------------------------------------------

    \48\ 2006 Guidance at 6.
    \49\ 42 U.S.C. 7475(a)(3); 40 CFR 51.166(k).
    \50\ 42 U.S.C. 7503(a)(1); 40 CFR 51.165(a)(3).
---------------------------------------------------------------------------

1. PSD and NNSR SIP Requirements for the 1997 8-Hour Ozone NAAQS
    On November 29, 2005, EPA published the Phase 2 implementation rule
for the 1997 8-hour ozone NAAQS (``Phase 2 Rule'').\51\ For ozone
nonattainment areas, the Phase 2 Rule requires revisions to States'
NNSR SIPs to implement the requirements of the CAA Amendments of 1990,
as applicable based on each area's classification for the ozone
standard.\52\ Specifically, the Phase 2 Rule requires that NNSR SIPs
apply all NNSR requirements that apply to major sources of volatile
organic compounds (VOCs) to major NOX emissions sources,
except where a NOX waiver applies under section 182(f) of
the Act.\53\ In addition, NNSR SIPs must include provisions
establishing the applicable major stationary source thresholds,
significant emissions rates, and offset ratios for VOCs and
NOX based on each area's classification, as listed in Table
1.\54\
---------------------------------------------------------------------------

    \51\ 70 FR 71612.
    \52\ See 70 FR at 71675, 71698-99.
    \53\ 40 CFR 51.165(a)(8).
    \54\ 40 CFR 51.165(a)(1)(iv), (a)(1)(v), (a)(1)(x), (a)(8),
(a)(9).

                                        Table 1--VOC and NOX Thresholds and Offset Ratios by Ozone Classification
--------------------------------------------------------------------------------------------------------------------------------------------------------
         Classification             Subpart 1 \55\         Marginal            Moderate             Serious             Severe              Extreme
--------------------------------------------------------------------------------------------------------------------------------------------------------
Major Source (tons per year      100................  100...............  100...............  25................  25................  10.
 (tpy)).
Significant Emissions Rate       40.................  40................  40................  25................  25................  0.
 (tpy).
Offset Ratio \56\..............  1 to 1.............  1.1 to 1..........  1.15 to 1.........  1.2 to 1..........  1.3 to 1..........  1.5 to 1.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    For areas  designated  unclassifiable/attainment for the 1997 ozone
NAAQS, the Phase 2 Rule requires revisions to PSD SIPs to require
explicit identification of NOx as an ozone precursor.\57\ States were
required to submit the relevant PSD and NNSR SIP revisions to address
the 1997 8-hour ozone NAAQS by June 15, 2007.\58\ In the 2006 Guidance,
issued before the deadline for States to submit the SIP revisions
described above, EPA recommended States make a submission confirming
they were on track to meet this deadline. At that point, Colorado had
no areas designated nonattainment for ozone. However, on November 20,
2007, the Denver Metropolitan Area/North Front Range (``DMA/NFR'') area
was designated nonattainment for the 1997 8-hour ozone standard and,
consistent with the approach taken in the Phase 1 ozone implementation
rule,\59\ was made subject solely to the requirements of subpart 1
discussed above. Subsequently, the D.C. Circuit Court of Appeals
vacated those elements of EPA's Phase 1 ozone implementation rule that
placed areas solely under the implementation requirements of subpart
1.\60\ As a result, areas such as the DMA/NFR are now referred to as
``former subpart 1 areas.'' EPA has proposed to classify the DMA/NFR
under subpart 2 of part D, title I of the Act as a ``marginal'' area
but has not yet finalized this rulemaking.\61\ In the interim, the DMA/
NFR area is still subject to the subpart 1 requirements discussed
above.
---------------------------------------------------------------------------

    \55\ Although the ``subpart 1'' category is not a
classification, the general requirements of subpart 1, part D of
title I of the CAA apply in all ozone nonattainment areas (to the
extent they are not superseded by the more specific requirements of
subpart 2), including those areas now referred to as ``former
subpart 1 areas'' under the DC Circuit Court of Appeals' vacatur of
certain elements of EPA's Phase 1 ozone implementation rule. See S.
Coast Air Quality Mgmt. Dist. v. EPA, 472 F.3d 882 (DC Cir. 2006),
reh'g denied, 489 F.3d 1245 (clarifying that the vacatur was limited
to the issues on which the court granted the petitions for review).
    \56\ For any nonattainment area classified as severe or extreme,
if the approved plan requires all existing major sources in such an
area to use BACT to control VOC and NOX, then the ratio
must be at least 1.2 to 1. CAA sections 182(d)(2), (e)(1) and
182(f).
    \57\ See 70 FR at 71679, 71699-700; 40 CFR 51.166(b)(1)(ii),
(b)(2)(ii), (b)(23)(i).
    \58\ 70 FR at 71683.
    \59\ See 69 FR at 23951 (Apr. 30, 2004).
    \60\ See S. Coast Air Quality Mgmt. Dist. v. EPA, 472 F.3d 882
(DC Cir. 2006), reh'g denied, 489 F.3d 1245.
    \61\ 74 FR 2936, 2944 (Jan. 16, 2009).
---------------------------------------------------------------------------

    In Colorado's March 31, 2010 submission, the State cites August 17,
2006 revisions to Colorado Regulation No. 3 Part D to assert that they
are on track to meet the requirements of the Phase 2 Rule within three
years of the DMA/NFR November 20, 2007 nonattainment designation. In
this action, EPA proposes to approve portions of the August 17, 2006
revisions, submitted to EPA August 1, 2007, that implement the Phase 2
Rule. Specifically, we propose approval of the sections that adopt
language to treat nitrogen oxides as an ozone precursor. Other portions
of the August 17, 2006 revisions are being acted upon separately. The
sections that we propose to approve are set out in the table below.

----------------------------------------------------------------------------------------------------------------
                                        Description of provision--
                                         language adopted August
Provision location in  Colorado's 8/17/   17, 2006 to conform to
           06 Reg 3 Revision                the Phase II Ozone       Corresponding provision in  40 CFR 51.166
                                          Implementation Rule is
                                                underlined
----------------------------------------------------------------------------------------------------------------
D--II.A.22.a..........................  Significant Emissions      40 CFR 51.166(b)(2)(ii).
                                         Increase or Net
                                         Emissions Increase (at a
                                         major source) that is
                                         significant for VOCs or
                                         NOX is significant for
                                         ozone.
D--II.A.24.d..........................  Major source that is       40 CFR 51.166(b)(1)(ii).
                                         major for VOCs or NOX is
                                         major for ozone.
D--II.A.38.c..........................  VOCs and NOX are           40 CFR 51.166(b)(49)(i).
                                         precursors for ozone.
D--II.A.42.a..........................  Significant rate of        40 CFR 51.166(b)(23)(i).
                                         emissions for ozone
                                         means 40 tons per year
                                         of VOCs or NOX.
----------------------------------------------------------------------------------------------------------------

    These revisions are contained with Colorado's rules for its SIP-
approved PSD program. Colorado also has a generic SIP-approved NNSR
program that applies in any nonattainment area and that relies on the
definitions provided in the PSD program, but separately imposes
requirements that sources achieve the lowest achievable emission rate
(``LAER'') and obtain offsets in a ratio greater than one to one. As a
result of the structure of Colorado's NNSR program, the revisions to
the PSD program discussed above also apply to it. Under these
revisions, the State's SIP-approved NNSR program meets the currently
applicable requirements of the Phase 2 Rule (prior to reclassification
of the DMA/NFR nonattainment area) and satisfies the requirements for
the PSD element of 110(a)(2)(D)(i) for the 1997 8-hour ozone NAAQS.
    Colorado's March 31, 2010 Interstate Transport SIP submission is
consistent with the 2006 Guidance, when considered in conjunction with
the Colorado PSD program revisions that EPA is also proposing to
approve in this action. EPA's proposed approval of Colorado's
Interstate Transport SIP for the purposes of meeting the third element
of section 110(a)(2)(D)(i) is contingent upon the final approval of the
PSD program revisions in the form specified in EPA's proposed approval,
referenced above. Colorado's SIP regulations for its PSD program were
federally-approved and made part of the SIP on September 2, 1986.\62\
EPA is proposing to approve, concurrent with this action, Colorado's
PSD rule revisions incorporating into the State's regulations the
provisions of EPA's November 29, 2005 Phase 2 rule that treat
NOX as a precursor for ozone for the 1997 8-hour ozone
NAAQS.\63\
---------------------------------------------------------------------------

    \62\ 51 FR 31125.
    \63\ 70 FR at 71698-700.
---------------------------------------------------------------------------

2. PSD SIP Requirements for the 1997 PM2.5 NAAQS
    Colorado has no areas designated nonattainment for PM2.5
and correspondingly no NNSR program for PM2.5. EPA thus
considers only whether Colorado's SIP-approved PSD program satisfies
the requirements of the PSD element of 110(a)(2)(D)(i) for the 1997
PM2.5 NAAQS. First, the 2006 Guidance noted that EPA had not
yet established PSD increments for PM2.5 and therefore, at
that point it was difficult for states to determine if additional
measures were needed to satisfy the requirements of the PSD element of
section 110(a)(2)(D)(i). However, in a final rule published October 20,
2010, EPA established PM2.5 increments.\64\ EPA set an
applicability date of October 20, 2011 for the new increments and
required States with SIP-approved PSD programs to submit updates
incorporating these increments by July 20, 2012.\65\ At this point,
though, incorporation of the PM2.5 increments is not
required to satisfy the PSD element of section 110(a)(2)(D)(i).
---------------------------------------------------------------------------

    \64\ 75 FR 64864.
    \65\ Id. at 64887-88, 64898.
---------------------------------------------------------------------------

    The 2006 Guidance also discusses the use of PM10 as a
surrogate for PM2.5 in PSD programs. As recommended in the
2006 Guidance, Colorado's SIP declares

that the State will follow EPA's interim guidance on use of
PM10 as a surrogate for PM2.5.\66\ In response to
EPA's request of December 1, 2010, the Colorado Air Pollution Control
Division, in a January 13, 2011 letter to the EPA Region 8 Air Program,
has clarified an ambiguity in its interpretation of the interim
guidance.\67\ The letter states that, until the guidance is ended or
replaced, Colorado will apply it consistent with EPA's interpretation
of the federal case law relevant to the use of the PM10
Surrogate Policy.\68\ The State will also take into account the limits
provided in the policy itself, such as the need to identify the
technical difficulties that justify the application of the policy in
each specific case.\69\ With that clarification, the Colorado
Interstate Transport SIP satisfies the requirements of the third
element of section 110(a)(2)(D)(i) for the 1997 PM2.5 NAAQS.
---------------------------------------------------------------------------

    \66\ See 2006 Guidance at 7.
    \67\ Letter from Paul Tourangeau, Director, Colorado APCD,
Clarifying use of PM10 Surrogacy Policy (Jan 13, 2011), available in
the docket for this action.
    \68\ See 75 FR 6827, 6831-32 (Feb. 11, 2010).
    \69\ Id. at 6834.
---------------------------------------------------------------------------

3. PSD SIP Requirements for Greenhouse Gases
    EPA notes a potential inconsistency between Colorado's Interstate
Transport SIP submission and EPA's recently promulgated rule,
``Limitation of Approval of Prevention of Significant Deterioration
Provisions Concerning Greenhouse Gas Emitting-Sources in State
Implementation Plans'' (``PSD SIP Narrowing Rule'').\70\ In the PSD SIP
Narrowing Rule, EPA withdrew its previous approval of Colorado's PSD
program to the extent that it applied PSD permitting to greenhouse gas
(GHG) emissions increases from GHG-emitting sources below thresholds
set in EPA's June 3, 2010 ``Prevention of Significant Deterioration and
Title V Greenhouse Gas Tailoring Rule'' (``Tailoring Rule'').\71\ EPA
withdrew its approval on the basis that the State lacked sufficient
resources to issue PSD permits to such sources at the statutory
thresholds in effect in the previously-approved PSD program. After the
PSD SIP Narrowing Rule, the portion of Colorado's PSD SIP from which
EPA withdrew its approval had the status of having been submitted to
EPA but not yet acted upon. In Colorado's March 31, 2010 submission,
Colorado relied on its PSD program as approved at that date--which was
before December 30, 2010, the effective date of the PSD SIP Narrowing
Rule--to satisfy the ``interference with PSD'' requirements of
110(a)(2)(D)(i). Given EPA's basis for the PSD SIP Narrowing Rule, EPA
proposes approval of the Colorado Interstate Transport SIP submission
in its entirety if either the State clarifies (or modifies) its
submission to make clear that the State relies only on the portion of
the PSD program that remains approved after the PSD SIP Narrowing Rule
issued on December 30, 2010, and for which the State has sufficient
resources to implement, or the State acts to withdraw from EPA
consideration the remaining portion of its PSD program submission that
would have applied PSD permitting to GHG sources below the Tailoring
Rule thresholds.\72\ In the alternative, if Colorado does not take
either action, EPA proposes to disapprove the Interstate Transport SIP
to the extent it incorporates that portion of the previously-approved
PSD program from which EPA withdrew its approval in the PSD SIP
Narrowing Rule, which is the portion which would have applied PSD
permitting requirements to GHG emissions increases from GHG-emitting
sources below the Tailoring Rule thresholds. Such disapproval, if
finalized, would not result in a need for Colorado to resubmit a SIP
revision, sanctions, or a federal implementation plan (FIP).\73\
---------------------------------------------------------------------------

    \70\ 75 FR 82536 (Dec. 30, 2010).
    \71\ 75 FR 31514.
    \72\ EPA specified how to accomplish this in the PSD SIP
Narrowing Rule, 75 FR at 82538, 82540.
    \73\ Id.
---------------------------------------------------------------------------

VI. Summary of Proposed Action

    In light of the data and the weight-of-evidence analysis presented
above, EPA is proposing approval of portions of the Colorado Interstate
Transport SIP addressing the requirements of CAA section
110(a)(2)(D)(i) for the 1997 PM2.5 and 8-hour ozone NAAQS.
On January 13, 2010, the Colorado AQCC adopted interstate transport SIP
revisions addressing requirements (3) and (4) of CAA section
110(a)(2)(D)(i) for the 1997 8-hour ozone NAAQS, and all four
requirements of CAA section 110(a)(2)(D)(i) for the 1997
PM2.5 NAAQS. Colorado submitted these revisions to EPA on
March 31, 2010. Specifically, EPA is proposing to approve the language
and demonstration of the March 31, 2010 submission that addresses three
requirements of section 110(a)(2)(D)(i) with respect to the 1997
PM2.5 NAAQS: (1) Prohibition of significant contribution to
nonattainment of the NAAQS in any other state, (2) prohibition of
interference with maintenance of the NAAQS by any other state, and (3)
prohibition of interference with other states' required measures to
prevent significant deterioration of air quality. EPA is also proposing
to approve the language and demonstration that addresses requirement
(3) of section 110(a)(2)(D)(i)--prohibition of interference with other
states' required measures to prevent significant deterioration of air
quality--with respect to the 1997 8-hour ozone NAAQS.

VII. Statutory and Executive Order Review

    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 approves 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.);
     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 (Pub. L. 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 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.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Nitrogen dioxide, Ozone,
Particulate matter, Reporting and recordkeeping requirements, Volatile
Organic Compounds.

    Authority: 42 U.S.C. 7401 et seq.

    Dated: April 12, 2011.
Carol Rushin,
Acting Regional Administrator, Region 8.
[FR Doc. 2011-9451 Filed 4-18-11; 8:45 am]
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