```

[Federal Register Volume 76, Number 75 (Tuesday, April 19, 2011)]
[Proposed Rules]
[Pages 21835-21847]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-9451]

=======================================================================
-----------------------------------------------------------------------

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.

-----------------------------------------------------------------------

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: clark.adam@epa.gov.
     Fax: (303) 312-6064 (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

[[Page 21836]]

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, (303) 312-7104, 
clark.adam@epa.gov.

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

[[Page 21837]]

respect to the 1997 PM2.5 and 8-hour ozone NAAQS.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \3\ ``Federal Implementation Plans To Reduce Interstate 
Transport of Fine Particulate Matter and Ozone,'' 75 FR 45210 (Aug. 
2, 2010).

---------------------------------------------------------------------------

[[Page 21838]]

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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \5\ See, 70 FR 25162 (May 12, 2005).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \6\ 2006 Guidance at 5.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \7\ See, North Carolina v. EPA, 531 F.3d 896 (DC Cir. 2008).
    \8\ Id. at 909.
    \9\ 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)(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

[[Page 21839]]

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.
---------------------------------------------------------------------------

    \10\ 75 FR 45210 (Aug. 2, 2010).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \12\ Transport Rule Proposal, 75 FR at 45246-51. Additional 
information concerning these weighted averages is provided in the 
Western States Design Values Memo.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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

[[Page 21840]]

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

[[Page 21841]]

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

[[Page 21842]]

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

[[Page 21843]]

(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

[[Page 21844]]

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.
--------------------------------------------------------------------------------------------------------------------------------------------------------

[[Page 21845]]

    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

[[Page 21846]]

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

[[Page 21847]]

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]
BILLING CODE 6560-50-P
```