its requirements and commitments) since the 14.9 ambient air quality
value in the third year (2009) met the test of being at or below 15.0.
Section 51.1005(a) of the proposed regulation addresses the initial 1-
year attainment date extension.
    The air quality measured in 2010 in conjunction with prior data
will determine if the area attains the standard, qualifies for a second
1-year extension, or does not attain the standard. For example, if the
area's annual average for 2010 is 14.3, then its 3-year average for
2008-2010 would be 14.9 and it would have met the annual standard.
    If the area's annual average for 2010 is 14.9, however, then its 3-
year average for 2008-2010 would be 15.1. In this situation the area
would not have attained the standard, but the area would meet the air
quality test for the second of the 1-year extensions allowed under
section 172(a)(2)(C), because the 2010 annual average was at or below
15.0. Section 51.1005(b) of the proposed rule addresses the second 1-
year attainment date extension. After obtaining a second 1-year
extension, the State would evaluate whether the air quality values in
2011, in conjunction with 2009 and 2010 data, bring the area into
attainment.
    Pursuant to section 172(a)(2)(C), States must submit additional
information to EPA to demonstrate that they have complied with
applicable requirements, commitments, and milestones in the
implementation plan. This information is needed in order for EPA to
make a decision on whether to grant a 1-year attainment date extension.
The EPA will not be inclined to grant a 1-year attainment date
extension to an area unless the State can demonstrate that it has met
important requirements contained in the area's implementation plan.
States must demonstrate that: (1) Control measures have been submitted
in the form of a SIP revision and substantially implemented to satisfy
the requirements of RACT and RACM for the area, (2) the area has made
emissions reductions progress that

represents reasonable further progress (RFP) toward attainment of the
NAAQS, and (3) trends related to recent air quality data for the area
indicate that the area is in fact making progress toward attainment of
the standard. Any decision made by EPA to extend the attainment date
for an area will be based on facts specific to the nonattainment area
at issue, and will only be made after providing notice in the Federal
Register and an opportunity for the public to comment.
    If an area fails to attain the standard by the attainment date, EPA
would publish a finding to this effect in accordance with section 179
of the CAA. The area then would be required, within 1 year of
publication of this finding, to develop a revised SIP containing
additional emission reduction measures needed to attain the standard as
expeditiously as practicable.
b. Final Rule
    The final rule retains the proposed criteria for states to receive
a 1-year attainment date extension for a nonattainment area.
c. Comments and Responses
    Comment: A number of commenters supported EPA's ability to grant a
1-year attainment date extension if monitoring data indicate that the
PM2.5 levels during the most recent year were below 15.05
[mu]g/m\3\.
    Response: The EPA agrees with these comments.
    Comment: Some commenters recommended that a 1-year extension be
provided if the trend line of the area's emissions levels or air
quality data projects attainment in the extension year.
    Response: The EPA believes that 1-year extensions should be based
on air quality data, which can be assessed quickly after the end of the
year. Basing such extensions solely on emissions trends would be
impractical due to the longer turnaround time needed to evaluate
emissions changes affecting a monitor.
    Comment: One commenter believes the current requirement is overly
stringent and inconsistent with the statute. The commenter believes
that EPA's proposed approach incorrectly defines the statutory language
referring to a ``minimal number of exceedances'' of the standard in the
previous year as ``zero'' exceedances. Alternatively, the commenter
suggests EPA could withdraw this provision and provide more detailed
guidance giving the Agency and states some flexibility to demonstrate
that exceedances were minimal in a given case since nothing in the
statute requires the rigid definition of minimal that EPA proposes.
    Response: The EPA believes the policy in the final rule is a
reasonable application of the statutory language to a standard not
based on exceedances. The EPA does not believe it would be appropriate
to provide a 1-year extension to an area with air quality data showing
it violating the standard over the 3 years prior to the attainment
year.
4. Achieving ``Clean Data''
a. Background
    Section III.D of the preamble to the proposed rule describes the
incentives for attaining the standards prior to April 2008, when SIP
submittals are due, or prior to an area's approved attainment date.
Areas with design values just over the level of the standard may be
able to achieve reductions in the local area or in the State so that,
when their effect is considered in combination with reductions achieved
under national programs, they may be sufficient to attain the standards
before SIPs are due in 2008. For example, if monitoring in a
nonattainment area shows that the air quality for 2004-2006 meets the
standards, then the area may be subject to reduced regulatory
requirements and be redesignated as ``attainment.''
    The EPA issued a ``Clean Data'' policy memorandum in December 2004
describing possible reduced regulatory requirements for areas that
attain the standards, but have not yet been redesignated as
attainment.\16\
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    \16\ Memorandum of December 14, 2004, from Steve Page, Director,
EPA Office of Air Quality Planning and Standards to EPA Air Division
Directors, ``Clean Data Policy for the Fine Particle National
Ambient Air Quality Standards.'' This document is available at:
http://www.epa.gov/pmdesignations/guidance.htm.

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b. Final Rule
    In the proposed rule, EPA indicated that it had issued this ``Clean
Data'' policy to apply for purposes of the PM2.5 standards.
In this action EPA is finalizing as a rule the statutory interpretation
that is embodied in the policy. Section 51.1004(c). The text of the
final rule encapsulates the statutory interpretation set forth in the
policy. Determinations as to whether individual areas have attained the
PM2.5 standard and thus qualify for application of the new
clean data rule will be made in the context of rulemakings for those
individual areas.
    The preamble to the proposed rule mistakenly stated that if an area
achieved ``clean data,'' it would be ``relieved of the requirements to
implement the nonattainment NSR program otherwise required for
nonattainment areas, and instead would implement the PSD program.'' The
EPA wishes to clarify that the Clean Data Policy does not provide for
suspension of the requirements for NSR nor for RACT. The provisions at
issue in the Clean Data Policy include the requirements for an
attainment demonstration and other related requirements, reasonable
further progress, and contingency measures.
c. Comments and Responses
    Comment: One commenter stated that EPA has absolutely no authority
to waive NSR or any of the CAA's other requirements for nonattainment
areas merely because a nonattainment area has 3 years of clean data,
nor does EPA have authority to waive mandatory requirements of the CAA
such as NSR, RACT, and RFP merely because EPA or the State claims they
are not needed for attainment. The commenter believes that the only way
that a nonattainment area can cease implementing controls and
requirements mandated for such areas is to seek and obtain
redesignation to attainment, and demonstrate in the process that the
controls and requirements are not needed for maintenance of standards.
The CAA has explicit procedures and prerequisites for redesignating
nonattainment areas to attainment (CAA sections 107(d)(3)(E) and 175A).
The EPA's ``clean data'' proposal would illegally circumvent those
requirements.
    Response: The Clean Data policy does not waive requirements for NSR
nor for RACT. However, EPA believes that ``clean data'' policies for
the ozone and fine particle programs are based on a reasonable
interpretation of the CAA. The Clean Data Policy is the subject of two
EPA memoranda setting forth our interpretation of the provisions of the
Act as they apply to areas that have attained the relevant NAAQS. The
EPA also finalized the statutory interpretation set forth in the policy
in a final rule, 40 CFR 51.918, as part of its Final Rule to Implement
the 8-Hour Ozone National Ambient Air Quality Standard--Phase 2 (Phase
2 Final Rule). See discussion in the preamble to the rule at 70 FR
71645-71646 (November 29, 2005). The legal rationale for the Clean Data
policy is explained in our Phase 2 Final Rule, in our December 14, 2004
memorandum from Stephen D. Page entitled ``Clean Data Policy for the
Fine Particle National Ambient Air Quality Standards'' (Page Memo), and
in our May 10, 1995 memorandum from John S. Seitz, entitled
``Reasonable Further Progress, Attainment

Demonstration, and Related Requirements for Ozone Nonattainment Areas
Meeting the Ozone National Ambient Air Quality Standard'' (Seitz memo).
We adopt and reiterate those explications here.
    The EPA has also explained its rationale for applying the Clean
Data policy in rulemaking actions associated with nonattainment areas
for the PM10 and 1-hour ozone standards. For rulemaking
actions applying the Clean Data policy to the PM10
standards, see 71 FR 27440 (May 11, 2006) (Weirton, WVA), 71 FR 13021
(March 14, 2006) (Yuma, AZ), 71 FR 6352 (February 8, 2006) (Ajo, AZ).
For a discussion of the legal rationale supporting rulemaking actions
applying the Clean Data policy to the 1-hour ozone standards, see, for
example, 67 FR 49600 (July 31, 2002); 65 FR 37879 (June 19, 2000)
Cincinnati-Hamilton, Ohio-Kentucky); 61 FR 20458 (May 7, 1996)
(Cleveland Akron-Lorain, Ohio); 66 FR 53094 (October 19, 2001)
(Pittsburgh-Beaver Valley, Pennsylvania); 61 FR 31832 (June 21, 1996
(Grand Rapids, Michigan); 60 FR 36723 (July 18, 1995) (Salt Lake and
Davis Counties, Utah); 68 FR 25418 (May 12, 2003) (St Louis, Missouri);
69 FR 21717 (April 22, 2004) (San Francisco Bay Area).
    The EPA has further elaborated on its legal rationale for the Clean
Data Policy in briefs filed in the 10th, 7th, and 9th Circuits, and
hereby incorporates those briefs insofar as relevant here. See Sierra
Club v. EPA, No. 95-9541 (10th Cir.), Sierra Club v. EPA, No. 03-2839,
03-3329 (7th Cir.), Our Children's Earth Foundation v. EPA, No. 04-
73032 (9th Cir.). As stated in the policy, the attainment
demonstration, RFP requirements, and contingency measure requirement
are designed to bring an area into attainment. Once this goal has been
achieved, it is appropriate to suspend the obligation that States
submit plans to meet these goals, so long as the area continues to
attain the relevant standard. The Tenth, Seventh and Ninth Circuits
have all upheld EPA rulemakings applying the Clean Data Policy. See
Sierra Club v. EPA, 99 F. 3d 1551 (10th Cir. 1996); Sierra Club v. EPA,
375 F. 3d 537 (7th Cir. 2004); Our Children's Earth Foundation v. EPA,
No. 04-73032 (9th Cir. June 28, 2005 (Memorandum Opinion).
    The EPA has explained in its memoranda on the Clean Data Policy for
PM2.5 and for ozone that it is reasonable to interpret the
provisions regarding RFP and attainment demonstrations, along with
certain other related provisions, as not requiring further submissions
to achieve attainment for so long as the area is in fact attaining the
standard. Under the policy, EPA is not granting an exemption from any
applicable requirement under Part D. Rather, EPA has interpreted these
requirements as not applying for so long as the area remains in
attainment with the standard. This is not a waiver of requirements that
by their terms apply; it is a determination that certain requirements
are written so as to be operative only if the area is not attaining the
standard.
    CAA section 172(c)(2) provides that SIP provisions in nonattainment
areas must require ``reasonable further progress.'' The term
``reasonable further progress'' is defined in section 171(1) as ``such
annual incremental reductions in emissions of the relevant air
pollutant as are required by this part or may reasonably be required by
the Administrator for the purpose of ensuring attainment of the
applicable NAAQS by the applicable date.'' Thus, by definition, the
``reasonable further progress'' provision requires only such reductions
in emissions as are necessary to attain the NAAQS. If an area has
attained the NAAQS, the purpose of the RFP requirement will have been
fulfilled, and since the area has already attained, showing that the
State will make RFP towards attainment will ``have no meaning at that
point.'' The EPA's General Preamble for the Implementation of Title I
of the Clean Air Act Amendments of 1990 (General Preamble) 57 FR 13498,
13564 (April 16, 1992).
    CAA section 172(c)(1), the requirement for an attainment
demonstration, provides in relevant part that SIPs ``shall provide for
attainment of the [NAAQS].'' The EPA has interpreted this requirement
as not applying to areas that have reached attainment. If an area has
attained the standard, there is no need to submit a plan demonstrating
how the area will reach attainment. In the General Preamble (57 FR
13564), EPA stated that no other measures to provide for attainment
would be needed by areas seeking redesignation to attainment since
``attainment will have been reached.'' See also Memorandum from John
Calcagni, ``Procedures for Processing Requests to Redesignate Areas to
Attainment,'' September 4, 1992, at page 6.
    CAA section 172(c)(9) provides that SIPs in nonattainment areas
``[S]hall provide for the implementation of specific measures to be
undertaken if the area fails to make reasonable further progress, or to
attain the [NAAQS] by the attainment date applicable under this part.
Such measures shall be included in the plan revision as contingency
measures to take effect in any such case without further action by the
State or [EPA].''
    This contingency measure requirement is inextricably tied to the
reasonable further progress and attainment demonstration requirements.
Contingency measures are implemented if reasonable further progress
targets are not achieved, or if attainment is not realized by the
attainment date. Where an area has already achieved attainment by the
attainment date, it has no need to rely on contingency measures to come
into attainment or to make further progress to attainment. As EPA
stated in the General Preamble:

    ``The section 172(c)(9) requirements for contingency measures
are directed at ensuring RFP and attainment by the applicable
date.'' 57 FR 13564. Thus these requirements no longer apply when an
area has attained the standard.

It is important to note that should an area attain the PM2.5
standards based on three years of data, its obligation to submit an
attainment demonstration is not waived but is only suspended. If the
area then has air quality concentrations in the following year such
that the area exceeds the standard for years 2 through 4, then the
area's obligation to submit an attainment demonstration is back in
effect.
    The determination of attainment contemplated by the Clean Data
Policy does not purport to be a redesignation, and thus the
requirements for redesignation under section 107(d) are not applicable.
Nor does the Clean Data Policy avoid or illegally circumvent the
redesignation requirements of section 107 of the CAA. All of the
requirements for redesignation remain in effect and must be satisfied
for an area to be redesignated. Sierra Club v. EPA, 99 F.3d at 1557-
1558. The Clean Data Policy is simply an interpretation of certain
provisions of the CAA, whose express purpose is to achieve attainment
of the standard, as not requiring SIP revisions to be made by the State
for so long as the area continues to attain the standard. The policy
does not purport to exempt areas from requirements that are
inapplicable only if an area is redesignated to attainment. It
interprets certain provisions which are written in such a way as to
impose requirements only upon areas that are not attaining the NAAQS,
regardless of whether they have been redesignated to attainment. The
EPA has not provided for any waiver from statutory requirements that
was not provided by Congress. The area at issue remains designated
nonattainment, and is subject to the risk that if a violation occurs it
will have to

adopt and implement reasonable further progress requirements,
contingency measures, and an attainment demonstration, unless it is
redesignated to attainment. In order to be redesignated to attainment,
however, the area will have to satisfy all of the requirements of
section 107(d)(3)(E), including the requirement for a long-term
maintenance plan.
    While a determination of attainment is not equivalent to a
redesignation to attainment, nothing in the Act compels EPA to wait
until an area meets all the requirements for redesignation before EPA
makes a determination that the area is in attainment with the standard,
thereby suspending the requirements for certain provisions related to
attainment. Indeed, section 179(c) of the Act requires EPA to make an
attainment determination within six months after an area's applicable
attainment date whether or not the EPA has made a finding with respect
to redesignation. The EPA's interpretation of the Act's provisions not
to require, once attainment has been reached, certain plan submissions
whose purpose is to assure attainment, is not at odds with the
requirements for redesignation. Nor does EPA's construction of the
statute adversely impact planning for maintenance. An area that is
monitoring attainment, but is still designated as a nonattainment area,
retains strong incentives to seek redesignation to attainment, and
remains subject to the requirement to demonstrate maintenance in order
to be redesignated. For a detailed discussion of the relationship of
redesignation requirements and attainment determinations, see the
discussions in the EPA briefs in Our Children's Earth Foundation v.
EPA, supra at pp. 43-60., Sierra Club v. EPA No. 95-9541 (10th Cir.) at
29-43, and Sierra Club v. EPA Nos. 03-2839, 03-3329 (7th Cir.) at 33-44
which are contained in the docket for this rulemaking.
    Comment: A commenter noted that EPA's proposal suggested that areas
attaining the standard would be subject to reduced regulatory
requirements. The commenter believed that EPA's interpretation should
be codified in regulatory form, in order to assure that areas legally
meeting the current PM2.5 standard and those requesting
redesignation be enabled to be redesignated and to benefit from the
interpretation through regulation, rather than by guidance or policy.
    Response: The EPA has adopted the commenter's suggested approach of
codifying its Clean Data Policy interpretation for PM2.5 in
regulatory form. Section 51.1004(c). As it did for ozone in its Phase
II Ozone Implementation Rule, EPA is including in this rulemaking a
regulation that encapsulates the statutory interpretation that is
embodied in its Clean Data Policy for PM2.5, set forth
above. As noted in the response to comment above, determinations as to
whether individual areas have attained the PM2.5 standard
and thus qualify for application of the rule will be made in the
context of rulemakings for those individual areas. The EPA believes,
however, that encapsulating its interpretation in regulatory form will
lend clarity and consistency to the process of applying its
interpretation.

E. Modeling and Attainment Demonstrations

1. Background
    [Section III.F.1 of November 1, 2005 proposed rule (70 FR 66007);
sec 51.1007 in draft and final regulatory text]
    As noted in the proposal, Section 172(c) requires States with
nonattainment areas to submit an attainment demonstration. An
attainment demonstration consists of: (1) Technical analyses that
locate, identify, and quantify sources of emissions that are
contributing to violations of the PM2.5 NAAQS; (2) analyses
of future year emissions reductions and air quality improvement
resulting from already-adopted national and local programs, and from
potential new local measures to meet the RACT, RACM, and RFP
requirements in the area; (3) adopted emission reduction measures with
schedules for implementation; and (4) contingency measures required
under section 172(c)(9) of the CAA.
a. Final Rule
    The requirements from the proposal are unchanged. Each State with a
nonattainment area will be required to submit a SIP with an attainment
demonstration that includes analyses supporting the State's proposed
attainment date. States must show that the area will attain the
standards as expeditiously as practicable and it must include an
analysis of whether implementation of reasonably available measures
will advance the attainment date.
2. Areas That Need To Conduct Modeling
    [Section III.F.2 of November 1, 2005 proposed rule (70 FR 66007)]
a. Background
    All nonattainment areas need to submit an attainment demonstration,
but in some cases, States may not need new, local-scale modeling
analyses. In the proposed rule, EPA proposed that States may use in a
PM2.5 attainment demonstration certain local, regional and/
or national modeling analyses that have been developed to support
Federal or local emission reduction programs, provided the modeling
meets the attainment modeling criteria set forth in EPA's modeling
guidance. The proposal also stated that nonattainment areas for which
local, regional, or national scale modeling demonstrates the area will
not attain the standard within 5 years of designation would be required
to submit an attainment demonstration SIP that includes new modeling
showing attainment of the standards as expeditiously as practicable.
b. Final Rule
    In the final rule, EPA is reaffirming the potential use of national
and/or regional modeling as part of an attainment demonstration. We are
also clarifying the types of modeling analyses that may be useful as a
``primary'' modeling analysis and as a ``supplemental'' analysis. The
proposal suggested that it may be appropriate, in certain
circumstances, for a State to submit regional or national modeling as
the sole (primary) modeling analysis in its attainment demonstration.
This implies that the State would not need to conduct local modeling
analyses. We wish to further define the differences between
``national'', ``regional'', and ``local'' modeling analyses. In this
context, national analyses are generally those conducted by EPA in
support of national or regional rules. Regional and local modeling
analyses are generally those conducted by the RPOs and/or States for
the purpose of developing State Implementation Plans (SIPs). EPA has
conducted national scale modeling for a variety of rules and analyses.
Additionally, the RPOs and many States are conducting regional and/or
local scale modeling of PM2.5 and regional haze across the
country. The national scale of the EPA modeling analyses requires basic
assumptions concerning local model inputs. Compared to regional or
local modeling done by the States and/or RPOs, EPA modeling may, in
some cases, use coarser grid resolution, use inventories that are not
as refined, and model performance may be highly variable from area to
area. For these reasons, national scale modeling may not always be
appropriate for local area attainment demonstrations.
    Therefore, we believe that regional or local modeling conducted by
the States or RPOs is best suited as the primary modeling analysis for
a modeled

attainment demonstration. The local modeling is more likely to meet the
recommendations contained in EPA's modeling guidance. However, some
areas having design values close to the standard may be projected to
come into attainment within five years based on modeling analyses of
national and regional emission control measures (e.g. CAIR) that are
scheduled to occur through 2009. Regional scale modeling for national
rules such as the Tier II motor vehicle standards, the Heavy-duty
Engine standards, the Nonroad Engine standards, and CAIR indicate major
reductions in PM2.5 by 2010. A portion of these benefits
will occur in the 2006-2009 PM2.5 attainment timeframe.
    Experience with past ozone attainment demonstrations has shown that
the process of performing detailed photochemical grid modeling to
develop an attainment demonstration can be very resource intensive for
States. The EPA believes that it would be appropriate for States to
leverage resources by collaborating on modeling analyses to support SIP
submittals, or by making use of recent modeling analyses that are
completed prior to the SIP submittal date. For this reason, EPA
recognizes that States may use in a PM2.5 attainment
demonstration certain local, regional and/or national modeling analyses
that have been developed to support Federal or local emission reduction
programs, provided the modeling meets the attainment modeling criteria
set forth in EPA's modeling guidance (described below). As with all
SIPs under subpart 1, the State must demonstrate that the area will
attain the PM2.5 standards as expeditiously as practicable.
The judgment of whether the modeling is appropriate for an area should
be made by the State(s) and their respective EPA regional office on a
case-by-case basis.
c. Comments and Responses
    Comment: There were many commenters that agreed that States should
be able to use EPA modeling or other national or regional modeling as a
modeled attainment demonstration. One commenter recommended that the
final rule require States to show that the existing modeling
incorporates realistic assumptions, accurately reflects local emissions
and trends, and provides adequate model performance for the local
nonattainment area.
    Response: We agree that national and regional modeling may be used
as part of an attainment demonstration as long as it is shown to be
applicable to the local area. This is consistent with the proposal
where we said that existing modeling should ``meet the attainment
modeling criteria set forth in EPA's modeling guidance.'' Part of the
analysis to determine if existing modeling meets the criteria in the
modeling guidance is to assess whether the modeling incorporates
realistic assumptions, accurately reflects local emissions and trends,
and provides adequate model performance for the local nonattainment
area.
    Comment: Some commenters thought States should be able to use EPA
modeling in the absence of an analysis of the applicability of the
modeling for a local nonattainment area. One commenter said that EPA
should determine that States should not have to do any additional
modeling analyses if the CAIR modeling showed they were expected to
attain the NAAQS by 2010.
    Response: While we acknowledge there may be some circumstances in
which national or regional modeling would be appropriate to use without
local modeling and allow for such use, we disagree that national
modeling should be used in support of an attainment demonstration
without further analysis of the modeling assumptions for a particular
area. National scale modeling may not always be appropriate for local
areas. Most often, national scale EPA modeling is best suited for use
as a supplemental analysis or as part of a ``weight of evidence''
demonstration. The modeling guidance recommends supplemental analyses
for all attainment demonstrations. The guidance specifically recommends
the examination of other modeling studies as a supplemental analysis.
The EPA modeling as well as other ``non-local'' modeling can be used
for this purpose. The ``weight'' of this alternative modeling in an
attainment demonstration should be guided by how well the modeling
system is suited for the local nonattainment area. States should
consult with their EPA regional offices for further guidance and
recommendations. As such, we do not believe it to be appropriate to
determine a priori that CAIR or any other modeling analyses are
appropriate to use in a local attainment demonstration for any or all
nonattainment areas.
    Comment: Several commenters believe that States should be able to
use existing EPA modeling (such as CAIR), as the basis for an extension
of the area's attainment date, if it shows that the nonattainment area
may not be able to attain the NAAQS by 2010. They believe that the
State should not have to do additional modeling to show that they need
an attainment date extension.
    Response: We disagree with this comment. The CAIR modeling included
national controls that are expected to be in place by 2010 (including
the CAIR rule itself), as well as existing state and local controls
reflected in the inventory used in the CAIR analysis. It did not
include any additional local controls that could be implemented under
RACT and RACM requirements for the 1997 standards that may bring the
area into attainment sooner. Nonattainment areas are required to attain
the NAAQS as expeditiously as practicable. Therefore, updated modeling
of existing controls as well as additional local controls is needed
before an attainment date extension can be granted. Additional
information on attainment dates and extensions is contained in the
preamble to the final rule, section II.D., and additional information
on RACT and RACM requirements is contained in section II.F.
    Comment: Several commenters noted an apparent inconsistency in the
language concerning who would be required to perform ``new'' local-
scale modeling. First, there are potentially conflicting statements in
the proposal when EPA states that areas with an attainment date of 2010
will need to conduct local-scale modeling to project the estimated
level of air quality improvement in accordance with EPA's modeling
guidance. This conflicts with the proposed ability for States to use
existing national or regional modeling as their modeled attainment
demonstration. Second, a portion of a sentence was removed from the
Federal Register version of the notice which differs from the pre-
Federal Register version. The published version implies that all
nonattainment areas would be required to submit new modeling.
    Response: We agree that there are inconsistencies in the proposal
preamble text. To clarify, new local-scale modeling is required for
areas that are not expected to come into attainment by 2010. For other
areas, there may be national or regional modeling which may be
applicable to the area which shows they are likely to come into
attainment. As noted earlier, national scale modeling is best suited
for use as a supplemental analysis, but in some cases may be acceptable
evidence that an area will attain by 2010.
    Additionally, the preamble language in the Federal Register
contained an error. A portion of a sentence was mistakenly removed,
which led to some confusion. The language in the FR notice (FR page
66008) stated ``Nonattainment areas would be required to submit an
attainment demonstration SIP that includes new modeling showing
attainment of the

standards as expeditiously as practicable. The new modeling will need
to include additional emissions controls or measures in order to
demonstrate attainment.'' The language should have read,
``Nonattainment areas for which local, regional, or national scale
modeling demonstrates the area will not be in attainment of the NAAQS
within 5 years of designation would be required to submit an attainment
demonstration SIP that includes new modeling showing attainment of the
standards as expeditiously as practicable. The new modeling will need
to include additional emissions controls or measures in order to
demonstrate attainment.'' This should clarify that States that cannot
show attainment within 5 years will need to develop new modeling
analyses which contain additional control strategies which show how and
when they expect to attain the PM2.5 NAAQS.
    Comment: One commenter maintained that relying on large-scale
regional modeling alone may allow for PM2.5 hot spots (i.e.
small unmonitored areas projected to exceed the standard) to exist past
the attainment date.
    Response: We agree that nonattainment areas with potential hotspot
issues (relatively high concentrations and/or gradients of primary
PM2.5) should not rely exclusively on regional modeling. The
EPA's attainment demonstration modeling guidance attempts to address
several aspects of hotspot issues in both monitored and unmonitored
areas \17\. The modeled attainment tests contained in EPA's modeling
guidance are primarily monitor based tests. Ambient data is combined
with the model predicted relative change in PM components to determine
if attainment of the standards is likely in the future. There are
several aspects of the attainment test. In most cases, States will run
a photochemical grid model to determine the future year predicted
PM2.5 concentrations at monitors. The modeling guidance
generally recommends that for urban scale PM2.5 modeling,
the State performs modeling analyses at 12 kilometer grid resolution or
finer. There is an additional component to the attainment test for
areas that have measured relatively high concentrations and/or
gradients of primary PM2.5 at monitors. In these cases, we
recommend running a Gaussian dispersion model for potential primary PM
sources, to determine the local impact of changes in primary PM
emissions (from the modeled sources) on predicted concentrations at the
monitor(s).
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    \17\ The recommendations contained in the modeled attainment
demonstration guidance are separate from the Agency's future hot-
spot modeling guidance for transportation conformity purposes.
---------------------------------------------------------------------------

    In addition, we describe an ``unmonitored area analysis'' which
uses interpolated ambient data combined with gridded model outputs to
examine whether potential violations of the NAAQS may occur in
unmonitored areas. If potential violations are indicated, we recommend
further analysis of the problem through additional local modeling.
Options for State action to address such a situation could include
imposition of reasonably available control technology to reduce
emissions, or the deployment of an air quality monitor to further
characterize the problem.
    We believe that the combination of these model-based tests will
adequately determine whether attainment of the standards is likely by
the attainment date. We also believe that these tests address the issue
of hotspots by recommending a combination of photochemical modeling,
dispersion modeling of local sources, and additional monitoring and/or
emissions controls.
3. Modeling Guidance
    [Section III.F.3 of November 1, 2005 proposed rule (70 FR 66008)]
a. Background
    Section 110(a)(2)(K)(i) states that SIPs must contain air quality
modeling as prescribed by the Administrator for the purpose of
predicting the effect of emissions on ambient air quality. The
procedures for modeling PM2.5 as part of an attainment SIP
are contained in EPA's ``Guidance for Demonstrating Attainment of Air
Quality Goals for PM2.5 and Regional Haze.'' The proposal
summarized several of the chapters in a draft version of the modeling
guidance.
b. Final Rule
    A draft of the PM2.5 attainment demonstration and
regional haze modeling guidance has now been revised (September 2006)
and is available at http://www.epa.gov/ttn/scram/guidance_sip.htm. The

draft PM2.5 attainment demonstration and regional haze
guidance has been incorporated into the ozone modeling guidance and is
now called ``Guidance on the Use of Models and Other Analyses for
Demonstrating Attainment of Air Quality Goals for the 8-Hour Ozone and
PM2.5 NAAQS and Regional Haze''. The final version of the
modeling guidance will be available at the same location in the near
future.
    The revised draft PM2.5 modeling guidance document is
very similar to the previous draft version, although there were several
changes and updates. Among them are new methods in treating
PM2.5 species components as part of the PM2.5
attainment test; new methods for determining potential future year
violations in unmonitored areas; new procedures for handling potential
PM2.5 ``hotspots''; and an increased reliance on
supplemental analyses, including ``weight of evidence'' analyses. The
EPA notes that the PM2.5 attainment demonstration modeling
guidance that we have released is separate from the Agency's future
hot-spot modeling guidance for transportation conformity purposes.\18\
---------------------------------------------------------------------------

    \18\ In the March 10, 2006, final transportation conformity rule
(71 FR 12468), EPA committed to develop PM2.5 and
PM10 quantitative hot-spot modeling guidance for
transportation conformity determinations for highway and transit
projects of local air quality concern.
---------------------------------------------------------------------------

    The modeling guidance describes how to estimate whether a control
strategy to reduce emissions of particulate matter and its precursors
will lead to attainment of the annual and 24-hour PM2.5
NAAQS. Part I of the guidance describes a ``modeled attainment test''
for the annual and 24-hour PM2.5 NAAQS. Both tests are
similar. The output of each is an estimated future design value
consistent with the respective forms of the NAAQS. If the future design
value does not exceed the concentration of PM2.5 specified
in the NAAQS, then the primary modeled test is passed. The modeled
attainment test applies to locations with monitored data.
    A separate test is recommended to examine projected future year
PM2.5 concentrations in unmonitored locations.\19\
Interpolated PM2.5 ambient data, combined with modeling
data, is used to predict PM2.5 concentrations in unmonitored
areas. The goal of this analysis is to identify areas without monitors
that may be violating the PM2.5 NAAQS, often due to high
levels of primary PM2.5 (both now and in the future). The
details of the analysis are contained in the final modeling guidance.
---------------------------------------------------------------------------

    \19\ Application of the unmonitored area analysis is limited to
locations which are appropriate to allow the comparison of predicted
PM2.5 concentrations to the NAAQS, based on
PM2.5 monitor siting requirements and recommendations.
---------------------------------------------------------------------------

    The guidance also discusses modeling PM2.5 at monitors
where high concentrations of primary PM2.5 are measured. In
these cases, it may be beneficial to model the primary component of the
PM2.5 with a Gaussian dispersion model. Dispersion models
are better able to capture the influence

of primary PM sources where large concentration gradients may exist.
Grid models spread out the PM emissions to the size of the grid
(typically 4 or 12 km). This makes it difficult to judge the benefits
of control strategies that may affect primary PM sources. The final
modeling guidance recommends procedures for applying dispersion models
in these situations.
    The guidance also recommends the submittal of supplemental analyses
as part of all attainment demonstrations. Supplemental analyses are
modeling, emissions, and/or ambient data analyses that are submitted as
part of a SIP, in addition to the primary modeled attainment test. The
evaluation of supplemental analyses when the predicted concentrations
in the primary attainment test are close to the NAAQS (slightly above
or slightly below) is called a weight-of-evidence (WOE) analysis. This
is simply a collection of evidence that aims to show that attainment of
the standard is likely. The final version of the modeling guidance puts
more emphasis on the submittal of supplemental analyses than in
previous versions.
    Part II of the guidance describes how to apply air quality models
to generate results needed by the modeled tests for attainment. This
includes developing a conceptual description of the problem to be
addressed; developing a modeling/analysis protocol; selecting an
appropriate model to support the demonstration; selecting appropriate
meteorological episodes or time periods to model; choosing an
appropriate area to model with appropriate horizontal/vertical
resolution; generating meteorological and air quality inputs to the air
quality model; generating emissions inputs to the air quality model;
evaluating performance of the air quality model; and performing
diagnostic tests. After these steps are completed, the model is used to
simulate the effects of candidate control strategies.
    Comment: Several commenters were supportive of the weight of
evidence concept. They said that PM2.5 modeling is
inherently more uncertain than previous ozone modeling and the modeling
guidance should reflect that. One commenter noted that weight of
evidence demonstrations should be ``unbiased'', meaning that States
should use all relevant analyses and not only information that helps
their case.
    Response: The EPA agrees with these comments. The final modeling
guidance recommends supplemental analyses (including weight of
evidence) for all attainment demonstrations. All States should submit
modeling, ambient data, and emissions analyses in addition to the
primary modeling demonstration. A weight of evidence analysis is needed
if the predicted future year PM2.5 concentrations are
slightly higher or slightly lower than the NAAQS.
    We also agree that a weight of evidence demonstration should
include all relevant information, including analyses which support
attainment and those that do not. The idea of the analysis is to
``weigh'' the evidence, both good and bad. That cannot be fairly done
if some evidence is not presented.
    Comment: Several commenters suggested that a modeled attainment
demonstration should not be specifically required. Instead they suggest
that all demonstrations should be weight of evidence demonstrations.
This would include different analyses of ambient data, trends, and
modeling. But due to the uncertainties in the current PM2.5
models and emissions data, modeling would be but one part of a broader
weight of evidence approach.
    Response: We disagree with this comment. Model results should be
the primary analysis of an attainment demonstration. Regardless of
current uncertainties in the PM2.5 models and emissions,
models are the only tool that can predict future concentrations of
PM2.5. The uncertainties in the model inputs and formulation
should be taken into account when evaluating the results. We agree that
a broad analysis of modeling, ambient data and emissions trends should
be part of the attainment demonstration. This is reflected in the final
modeling guidance.
4. Modeled Attainment Test
    [Section III.F.4 of November 1, 2005 proposed rule (70 FR 66008)]
a. Background
    The proposal described the nature of the attainment tests for the
annual average and 24-hour average PM2.5 NAAQS contained
within the modeling guidance. Both tests use monitored data to estimate
current air quality. The attainment test for a given standard is
applied at each monitor location within or near a designated
nonattainment area for that standard. There is also an additional
attainment test to be performed in unmonitored areas. Models are used
in a relative sense to estimate the response of measured air quality to
future changes in emissions. Future air quality is estimated by
multiplying current monitored values times modeled responses to changes
in emissions. Because PM2.5 is a mixture of chemical
components, the guidance recommends using current observations and
modeled responses of major components of PM2.5 to estimate
future concentrations of each component. The predicted future
concentration of PM2.5 is the sum of the predicted component
concentrations.
b. Final Rule
    The nature of the PM2.5 attainment tests is unchanged.
The final modeling guidance recommends refinements to the test and
discusses the treatment of individual PM2.5 species. The
speciated modeled attainment test (SMAT) that was used to estimate
future PM2.5 concentrations for CAIR has been (mostly)
implemented in the final guidance. Among the new recommendations is to
better account for the known differences between the PM2.5
Federal Reference Method (FRM) measurements and the PM2.5
speciation measurements. For example, it is recommended to account for
the volatilization of nitrate from the FRM filters and to account for
uncertainties in organic carbon measurements by employing an ``organic
carbon by mass balance'' technique. This assumes that all remaining
mass not accounted for by other species is organic carbon mass.
Additional details are contained in the modeling guidance.
    The guidance also recommends, where necessary, to spatially
interpolate PM2.5 species data to estimate the species
concentrations at FRM sites. It is necessary to estimate species
concentrations when there are no species measurements at FRM sites.
Several techniques can be used to estimate species concentrations.
Spatial interpolation techniques may be useful in many areas. In other
cases, it may be adequate to assume that data from a speciation monitor
may be representative of multiple FRM monitors. It is particularly
important to develop credible techniques to estimate species
concentrations at the locations of the highest FRM monitors.
    The guidance lists several techniques that can be used. The EPA
will provide software which will apply the modeled attainment test,
using ambient data and model outputs. Additionally, the software will
interpolate the PM2.5 species data to allow application of
SMAT for all FRM monitors. The software will be available at the same
location as the final modeling guidance (http://www.epa.gov/scram001/guidance_sip.htm
).

    Ultimately, it is up to the States to determine the best method to
represent the PM2.5 species concentrations, subject to EPA's
review and approval. These estimates are needed to perform the modeled
attainment test.

c. Comments and Responses
    Comment: Several commenters were concerned that interpolation of
PM2.5 species concentrations may not be appropriate in
certain areas or situations. The concentrations can vary significantly
between urban and rural areas and even between nearby urban areas. One
commenter suggested that it might be useful to use older field study
measurements to derive current species concentrations. Another
commenter suggested that it might be reasonable to assume that
speciation measurements were representative of nearby FRM sites.
    Response: We agree that interpolations of species data may not
always be the best way to estimate species concentrations at FRM sites.
The modeling guidance lists several different possible techniques.
States should review their data and situation and choose the most
reasonable methodology to estimate species concentrations.
Nonattainment areas that don't have speciation measurements at the
highest FRM site(s) need to be especially careful. The result of the
speciated attainment test can be heavily influenced by the assumed
species concentrations at the highest FRM sites. The attainment test
will be more straightforward in areas with speciation monitors at the
highest FRM sites. States are also encouraged to place speciation
monitors at the highest FRM sites. This will aid in future assessments
of attainment and ambient trends.
5. Multi-Pollutant Assessments
    [Section III.F.5 of November 1, 2005 proposed rule (70 FR 66009)]
a. Background
    The formation and transport of PM2.5 is in many cases
closely related to the formation of both regional haze and ozone. There
is often a positive correlation between measured ozone and secondary
particulate matter. Many of the same factors affecting concentrations
of ozone also affect concentrations of secondary particulate matter.
For example, similarities exist in sources of precursors for ozone and
secondary particulate matter. Emissions of NOX may lead to
formation of nitrates as well as ozone. Sources of VOC may be sources
or precursors for both ozone and organic particles. Presence of ozone
itself may be an important factor affecting secondary particulate
formation. The proposal recommended multi-pollutant assessments for
PM2.5 attainment demonstrations. A multi-pollutant
assessment, or one-atmosphere modeling, is conducted with a single air
quality model that is capable of simulating transport and formation of
multiple pollutants simultaneously. This type of model simulates the
formation and deposition of PM2.5, ozone, and regional haze
components, and it includes algorithms simulating gas phase chemistry,
aqueous phase chemistry, aerosol formation, and acid deposition.
b. Final Rule
    The recommendation to conduct multi-pollutant assessments remains
unchanged. It is recommended to model the impacts of future year
control strategies on PM2.5, ozone, and regional haze. It
may not always be possible or convenient to do so, but it can be
beneficial to the strategy development process.
    PM2.5 control strategies will have an impact on regional
haze, and will possibly impact ozone. Even if high ozone and high
PM2.5 concentrations don't typically occur during the same
time of the year, controls that affect precursors to PM2.5
may also affect ozone (e.g. NOX). The SIP submittal dates
for PM2.5, ozone, and regional haze do not currently line
up. The PM2.5 SIPs are due almost 1 year later than ozone.
But States can still do modeling analyses that can provide information
for multiple pollutants. States can use one-atmosphere models that are
capable of simulating both ozone and PM2.5. They can also
try to use consistent meteorological fields and emissions inventories
so that the same control strategies are relatively easy to evaluate for
both ozone and PM2.5. Modeling the same future year(s) for
PM2.5 and ozone can also make it easier to evaluate the
impacts of controls on both pollutants.
    It should be noted that there are no specific modeling requirements
other than the recommendation to try to harmonize the ozone,
PM2.5, and regional haze analyses whenever possible.
c. Comments and Responses
    Comment: One commenter suggests that multi-pollutant assessments
may not be beneficial because their area experiences winter
PM2.5 exceedances and summer ozone exceedances.
    Response: We disagree with the comment. Even in situations where
high PM2.5 and ozone don't occur during the same time of
year, multi-pollutant assessments may be helpful. NOX
controls that may be needed to reduce nitrates in the winter are likely
to have an impact on ozone in the summer. As well, changes in VOCs may
have an impact on both PM2.5 and ozone. Running potential
control strategies through the same modeling platform for ozone,
PM2.5, and regional haze may allow the development of
optimized strategies.
6. Which Future Year(s) Should Be Modeled?
    [Section III.F.6 of November 1, 2005 proposed rule (70 FR 66009)]
a. Background
    Modeling analyses consist of base year modeling and future year
modeling. The attainment test examines the change in air quality
between the base and future years. The proposal recommended, where
possible, future modeling years should be coordinated so that a single
year can be used for both PM2.5 and ozone modeling. This
coordination will help to reduce resources expended for individual
modeling applications for PM2.5 and ozone and will
facilitate simultaneous evaluation of ozone and PM impacts.
    Although there is some flexibility in choosing the future year
modeling time periods, unless the State believes it cannot attain the
standards within 5 years of the date of designation and must request an
attainment date extension, the choice of modeling years for
PM2.5 cannot go beyond the initial 5 attainment period.
Attainment date extensions will only be granted under certain
circumstances. Among other things, the State must submit an attainment
demonstration showing that attainment within 5 years of the designation
date is impracticable.
b. Final Rule
    Further information is now known concerning the modeling years for
ozone. Moderate nonattainment areas are presumed to be modeling 2009.
This is consistent with the last year of the 5 year period allowed
under Subpart I for PM2.5. Therefore, it is logical to
presume that areas that are able to attain the PM2.5 NAAQS
within 5 years will model a future year of 2009. Areas that won't be
able to attain the standard in 5 years will need to request an
attainment date extension (of up to 5 additional years).
    The NAAQS must be attained as expeditiously as practicable.
Therefore, attainment date extensions must contain modeling analyses to
justify the extension. Details of the required analyses are contained
in the RACT and RACM sections of the final rule. See section F for more
details.

F. Reasonably Available Control Technology and Reasonably Available
Control Measures

    This section of the preamble discusses the final rule requirements
for RACT and RACM. In order to explain EPA's

approach in the final rule more clearly, we first discuss the statutory
and regulatory background for the RACT and RACM requirements, and we
then explain the key options and interpretations upon which we took
comment in the proposal. Thereafter, we discuss significant comments we
received on the proposal and provide brief responses to those comments.
[Additional comments and responses appear in the RTC for this final
rule located in the docket.] Most of the comments received on this
topic addressed the three options EPA proposed for the RACT
requirement, the relationship between the RACT requirement and EPA's
Clean Air Interstate Rule (CAIR), and the control measures to be
required or considered for RACT and RACM.
1. Background on Statutory Requirements for RACT and RACM
    Subpart 1 of Part D of the CAA (sections 171-179B) applies to all
designated nonattainment areas. Section 172 of this subpart includes
general requirements for all attainment plans.
    Notably, Congress provided EPA and States a great deal of deference
for determining what measures to include in an attainment plan.
Specifically, Section 172(c)(1) requires that each attainment plan
``provide for the implementation of all reasonably available control
measures as expeditiously as practicable (including such reductions in
emissions from existing sources in the area as may be obtained through
the adoption, at a minimum, of reasonably available control
technology), and shall provide for attainment of the national primary
ambient air quality standards.'' By including language in Section
172(c)(1) that only ``reasonably available'' measures be considered for
RACT/RACM, and that implementation of these measures need be applied
only ``as expeditiously as practicable,'' Congress clearly intended
that the RACT/RACM requirement be driven by an overall requirement that
the measure be ``reasonable.'' Thus, the rule of ``reason'' drives the
decisions on what controls to apply, what should be controlled, by when
emissions must be reduced, and finally, the rigor required in a State's
RACT/RACM analysis. For example, we previously stated that the Act
``does not require measures that are absurd, unenforceable, or
impractical'' or result in ``severely disruptive socioeconomic
impacts'' 55 FR 38327. Moreover, we interpret the term ``reasonably
available'' to allow States to consider both the costs and benefits of
applying the measure, and whether the measure can be readily and
effectively implemented without undue administrative burden. 66 FR
26969.
    We also interpret the ``reasonably available control measures'' in
these provisions as referring to measures of any type that may be
applicable to a wide range of sources, whereas the parenthetical
reference to ``reasonably available control technology'' refers to
measures applicable to stationary sources. RACM can apply to mobile
sources, areas sources and stationary sources not already subject to
PM2.5 RACT requirements. Thus, RACT is a type of RACM
specifically designed for stationary sources. As noted above, States
are required to implement RACM and RACT ``as expeditiously as
practicable'' as part of attainment plans designed to attain the
standards.\20\
---------------------------------------------------------------------------

    \20\ Under the Tribal Air Rule (TAR), requirements for RACT and
RACM may be considered to be severable elements of implementation
plan requirements for Tribes.
---------------------------------------------------------------------------

    Section 172 does not include any specific applicability thresholds
to identify the size of sources that States and EPA must consider in
the RACT and RACM analysis. Nor, does Section 172 specifically indicate
which pollutant(s) or precursor(s) must be subject to RACM or RACT
measures to attain the NAAQS. Other pollutant-specific provisions of
the CAA do include applicability thresholds pertaining to attainment
plan requirements for NAAQS and precursor pollutants. For example,
subpart 2 of part D, which establishes additional requirements for
ozone nonattainment areas, establishes thresholds ranging from 100 to
10 tons per year for requirements applicable to ``major sources'' or
``major stationary sources,'' depending on the area's classification or
level of nonattainment. Subpart 4 of part D, which provides additional
plan requirements for PM10 nonattainment areas, establishes
thresholds of 100 and 70 tons per year for requirements applicable to a
``major source'' or ``major stationary source.''
    Moreover, subpart 1, unlike subparts 2 and 4, does not identify
specific source categories for which EPA must issue control technology
documents or guidelines, or identify specific source categories for
State and EPA evaluation during attainment plan development. For ozone,
subpart 2 contains a list of specific requirements for control
techniques guidelines (CTGs) and alternative control techniques (ACT)
documents. For PM10, section 190 of the CAA (in subpart 4)
places particular emphasis on specific sources of area emissions, but
does not identify specific stationary source categories for which RACT
guidance must be issued. Section 190 requires EPA to develop RACM
guidance documents for residential wood combustion, silvacultural and
agricultural burning, and for urban fugitive dust control.
2. What Is the Overall Approach To Implementing RACT and RACM in the
Final Rule?
a. Background for RACT
    Since the 1970s, EPA has interpreted RACT to mean ``the lowest
emissions limitation that a particular source is capable of meeting by
the application of control technology that is reasonably available
considering technological and economic feasibility'' as well as other
considerations.\21\ Presumptive RACT has been described as the norm
achievable by the source category.\22\
---------------------------------------------------------------------------

    \21\ See, 44 FR 53782, September 17, 1979, and 1976 memorandum
from Roger Strelow, Assistant Administrator for Air and Waste
Management to Regional Administrators, ``Guidance for Determining
Acceptability of SIP Regulations in Non-attainment Areas'' (Dec. 9,
1976).
    \22\ See e.g. Workshop on Requirements for Non-attainment Area
Plans--Compilation of Presentations (OAQPS No. 1.2-103, revised
edition April 1978).
---------------------------------------------------------------------------

    Section 110 of the 1970 Clean Air Act required States to develop
SIPs providing for attainment of the NAAQS by 1975 or 1977. A number of
areas were having difficulty with developing attainment plans,
particularly for the ozone standard. In response to the implementation
needs of this time period, EPA introduced the term ``RACT'' in a 1976
memorandum from Roger Strelow, Assistant Administrator for Air and
Waste Management to Regional Administrators, ``Guidance for Determining
Acceptability of SIP Regulations in Non-attainment Areas'' (Dec. 9,
1976). In this early guidance relating to the acceptability of SIP
regulations, we indicated that our overriding concern in approving SIPs
was attaining the particular NAAQS as expeditiously as practicable
through reasonably available control technology and other reasonably
available control measures. ``The basis for fully approving state-
submitted SIP regulations continues to be demonstrated attainment and
maintenance of all national ambient air quality standards as
expeditiously as practicable,'' the memo stated.
    The 1977 Clean Air Act amendments added Part D to Title I of the
Act, and for the first time the Act specifically called for EPA to
designate nonattainment areas and for SIPs to require RACT and RACM in
those nonattainment areas. In a 1979 Federal

Register notice, EPA noted its view that Congress adopted EPA's pre-
existing conception of RACT in the 1977 amendments. (44 FR 53782,
September 17, 1979). Also during the late 1970s, EPA developed a number
of new control techniques guideline (CTG) documents as directed in the
1977 amendments. These CTGs provided States with information on
controls for a number of categories of sources emitting VOCs, and
recommended a ``presumptive norm'' for State RACT determinations based
on the control levels achievable by sources in a given industry. CTGs
reduced the burden on States by eliminating the need for each State to
develop its own technical support for implementing the RACT
requirement. Since the CTG-recommended controls were based on general
capabilities of an industry, EPA in the 1979 guidance (44 FR 53782)
urged States in setting RACT to judge the feasibility of the
recommended controls on particular sources, and to adjust accordingly.
    As noted above, EPA's early guidance related to the RACT
requirement indicated that our overriding concern in approving State
RACT requirements was attaining the particular NAAQS. We initially
required States to apply RACT to qualify for attainment extensions, and
in some cases, for plans that could not demonstrate attainment.
    During the 1980s, EPA implemented the RACT requirements with a
number of CTGs and guidance documents. These materials were aimed at
addressing the attainment deadlines of 1982 and 1987 under the 1977
Clean Air Act amendments. During this time, EPA, for pollutants other
than ozone, considered RACT to be dependent upon reductions needed for
attainment as expeditiously as practicable. For ozone, where the State
performed photochemical grid modeling, the approach was the same, but
where the State used less sophisticated tools, we considered RACT to be
independent of whether the controls were needed to reach attainment as
expeditiously as practicable. We took this alternate approach because
of concerns related to the precision of modeling techniques. In other
words, in those cases, we required that a stationary source of the
requisite type and size be subject to RACT, whether or not such
controls were actually demonstrated to be necessary for the area to
attain by its specified date. (44 FR 20375-20376, April 4, 1979)
    Congress followed a similar approach in the 1990 amendments to the
CAA for purposes of the ozone NAAQS in the subpart 2 provisions added
at that time. For example, section 182(b)(2) requires the imposition of
RACT controls for all VOC source categories covered by a CTG and for
all other major stationary sources of VOC located within certain
nonattainment areas. Thus, Congress required these controls without
allowing for an area-specific demonstration by the State that the area
needed the controls for attainment as expeditiously as practicable.
Extensive discussion of this requirement appeared in the 1992 general
preamble (57 FR 13541), in which EPA provided guidance for
implementation of the ozone NAAQS.
    Notably, Congress did not significantly amend the generally
applicable provisions for nonattainment areas that appear in subpart 1
of Part D in 1990. This indicates that Congress intended that the
Agency retain the authority to interpret the generally applicable
nonattainment area plan requirements of section 172(c), including the
RACT and RACM requirements, in the way that is most appropriate for new
NAAQS that are subject to subpart 1. As discussed below, EPA has
determined that an approach to the RACT requirement in which RACT
varies in different nonattainment areas based on the reductions needed
for attainment as expeditiously as practicable, is appropriate for
implementation of the PM2.5 NAAQS. We believe that the
improved ability to model air quality impacts of emissions controls
allows for this approach.
b. Proposed Options for RACT
    The EPA proposed and requested comment on three alternative
approaches for interpretation of the RACT requirement of section
172(c)(1) for implementation of the PM2.5 NAAQS. The EPA
proposed these approaches in order to evaluate which method would best
ensure that States consider and adopt RACT measures for stationary
sources in a way that is consistent with the overarching requirement to
attain the standards as expeditiously as practicable, while providing
flexibility for States to focus regulatory resources on those sources
of emissions that contribute most to local PM2.5
nonattainment.
    Under the first proposed alternative, EPA would require States to
conduct a RACT analysis and to identify and require reasonably
available controls for all affected stationary sources in the
nonattainment area, comparable to the implementation of RACT provided
in subpart 2 governing implementation of the 1-hour ozone NAAQS. Under
this option, covered sources would be required to apply reasonable
available controls considering technical and economic feasibility, and
there would be no opportunity for States to excuse stationary sources
from control on the basis that the emissions reductions from those
controls would not be necessary to meet RFP requirements or to reach
attainment. Under this alternative, EPA proposed to limit the universe
of sources for which States must conduct a RACT analysis and impose
RACT controls, by providing an applicability threshold based upon the
amount of emissions potentially emitted by the sources. Under this
first option, EPA requested comment on a number of alternative
emissions applicability thresholds.
    Under the second proposed alternative, EPA would require States to
conduct a RACT analysis and to identify reasonably available controls
for all affected stationary sources. Under this option, however, States
could thereafter determine that RACT does not include controls that
would not otherwise be necessary to meet RFP requirements or to attain
the PM2.5 NAAQS as expeditiously as practicable.\23\ Under
this approach, RACT would be determined as part of the broader RACM
analysis and identification of all measures--for stationary, mobile,
and area sources--that are technically and economically feasible, and
that would collectively contribute to advancing the attainment
date.\24\ Because RACT and RACM are considered together under this
alternative, we did not propose emissions threshold options for
evaluation of stationary source RACT. In addition, consistent with
existing policies, States would be required to evaluate the combined
effect of reasonably available measures to determine whether
application of such measures could advance the attainment date by at
least one year.\25\
---------------------------------------------------------------------------

    \23\ Under the Tribal Air Rule (TAR), requirements for RACT and
RACM may be considered to be severable elements of implementation
plan requirements for Tribes.
    \24\ In Sierra Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002), the
court stated in upholding EPA's statutory interpretation of RACM
that the Act does not compel a state to consider a measure without
regard to whether it would expedite attainment.
    \25\ In this notice, where we use the shorthand phrase ``advance
the attainment date,'' it means ``advance the attainment date by one
year or more.''
---------------------------------------------------------------------------

    The third proposed alternative, EPA's preferred option in the
proposal, combined the first two options and is similar to the RACT
approach adopted in the final implementation rule for the 8-hour ozone
program. Under the third option, EPA would require States to conduct a
RACT analysis and to require reasonably available controls for all
affected stationary sources in

nonattainment areas with attainment dates more than 5 years from the
date of designation. For areas with an attainment date within 5 years
of designation (e.g. by April 5, 2010 for areas with an effective date
for designation of April 5, 2005), EPA would require RACT as under the
second proposed alternative, in which RACT would be determined as part
of the broader RACM analysis. For these areas, States could determine
that RACT does not include controls that would not otherwise be
necessary to meet RFP requirements or to attain the PM2.5
NAAQS as expeditiously as practicable. The same proposed suboptions
with respect to the size of sources for consideration under the first
alternative were also included under this alternative.
c. Proposed Approach for RACM
    The EPA proposed and asked for comment on one approach for
interpreting the RACM requirement for PM2.5. The EPA based
the proposal on the approach that we adopted for other NAAQS
implementation programs. Under this approach, a State provides a
demonstration in its SIP that it adopted all reasonably available
measures needed to meet RFP requirements and to attain the standard as
expeditiously as practicable and that no reasonably available
additional measures would advance the advance the attainment date by at
least 1 year or would be necessary to meet the RFP requirement for the
area.\26\
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    \26\ In the context of the PM10 NAAQS, EPA has
concluded that ``advancement of the attainment date'' should mean an
advancement of at least one calendar year. See State Implementation
Plans; General Preamble for the Implementation of Title I of the CAA
Amendments of 1990, 57 FR 12498 (April 16, 1992). See also Sierra
Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002).
---------------------------------------------------------------------------

    Under section 172(a)(2), the state implementation plan must provide
for a nonattainment area to attain as expeditiously as practicable, but
no later than 5 years after the effective date of designation of the
area (e.g., no later than April 2010 for the final designations
effective April 2005). The statute thus creates a presumption for
attainment within 5 years of designation unless certain statutory
criteria are met for an extension of the attainment date. Under the
proposed approach to RACM for PM2.5, each State would
evaluate available measures for sources of PM2.5 or its
regulatory precursors in the area to determine if reasonable measures
were needed to meet the RFP requirement or to achieve attainment as
expeditiously as practicable. If modeling of all RACM and other state,
regional and federal measures indicates that the State will not be able
to demonstrate attainment within 5 years after designation based upon
the severity of nonattainment in that area or the availability or
feasibility of implementing controls in that area, then the State may
request an attainment date extension. We proposed that under these
circumstances, the EPA could extend the attainment date for a period of
1 to 5 years, when the State shows that it will implement all RACT and
RACM as expeditiously as practicable, has met its obligation to address
intrastate pollution transport from sources within its jurisdiction,
and still needs additional time to attain.
    In the proposed rule, the EPA also took comment on the following
overall steps for implementing the statutory requirement for RACM.
    (1) Identification of measures. The State would begin the process
of determining RACM by identifying all available control measures for
all sources of PM2.5 and its precursors in the nonattainment
area. The RACM can apply to mobile sources, area sources, and
stationary sources.
    (2) Evaluation of measures. After the State identifies the universe
of available measures for the sources in the area, the State would
evaluate them to determine whether implementation of such measures is
technically and economically feasible, and whether the measure will
contribute to advancing the attainment date.
    (3) Adoption of measures. The State would adopt all reasonably
available measures for the area consistent with meeting the applicable
RFP requirements and attaining the NAAQS as expeditiously as
practicable, in accordance with applicable policy and guidance for
attainment demonstrations. We would then approve or disapprove the
State's plan through notice and comment rulemaking. We also noted that
in reviewing the State's selection of measures for RACM, or determining
that certain measures are not RACM, EPA may independently supplement
the rationale of the State or provide an alternative reason for
reaching the same conclusion as the State.
c. Final Rule
    The EPA carefully considered our interpretation of section
172(c)(1) for the PM2.5 NAAQS. Because of the variable
nature of the PM2.5 problem in different nonattainment
areas, which may require States to develop attainment plans that
address widely disparate circumstances (e.g., different source types
and mixes, different precursors and mixes of precursors, and different
meteorological conditions), we determined that the regulations
implementing the PM2.5 NAAQS should provide for a great
degree of flexibility with respect to the RACT and RACM controls.
    Selected approach to RACT and RACM. The final rule reflects EPA's
decision to select option 2 for RACT and to require a combined approach
to RACT and RACM. Under this approach, RACT and RACM are those measures
that a State finds are both reasonably available and contribute to
attainment as expeditiously as practical in the specific nonattainment
area.
    By definition, measures that are not necessary either to meet the
RFP requirement, or to help the area attain the NAAQS as expeditiously
as practicable, are not required RACT or RACM for such area. The EPA
believes that this approach provides the greatest flexibility to a
State to tailor its SIP control strategy to the needs of a particular
PM2.5 nonattainment area, but it may require the State to
conduct a more detailed analysis to identify the most effective RACT/
RACM strategy to attain the NAAQS.
    During the comment period, commenters raised concerns that this
approach may be overly burdensome on States because of the number of
potential control measures a State would need to consider. Today, we
clarify that although the State must conduct a thorough analysis of
reasonably available measures, States need not analyze every
conceivable measure, as explained in the guidance below. Instead,
``reason'' should drive States identification of potential measures,
but States should remain mindful of the public health risks of
PM2.5. As long as a State's analysis is sufficiently robust
in considering potential measures to ensure selection of all
appropriate RACT and RACM, and the State provides a reasoned
justification for its analytical approach, we will consider approving
that State's RACT/RACM strategy.
    Guidance on State analysis to identify RACT, RACM and appropriate
attainment date. A State must consider RACT and RACM for all of its
nonattainment areas. However, EPA believes that if the State projects
that an area will attain the standard within 5 years of designation as
a result of existing national measures (i.e. projected to have a design
value of 14.5 or lower), then the State may conduct a limited RACT and
RACM analysis that does not involve additional air quality modeling. A
limited analysis of this type would involve the review of reasonably
available measures, the estimation of potential emissions

reductions, and the evaluation of the time needed to implement these
measures. If the State could not achieve significant emissions
reductions during 2008 due to time needed to implement the potential
measures or other relevant factors, then the State and EPA could
conclude that there are no further reasonably available control
measures for that area that would advance the attainment date by one
year or more relative to the presumptive outer limit for attainment
dates, i.e., 5 years from designation. In lieu of conducting air
quality modeling to assess the impact of potential RACT and RACM
measures, States may consider existing modeling information to
determine the magnitude of emissions reductions that could
significantly affect air quality and potentially result in attaining
prior to 2010 (e.g. in 2009 based on 2006-8 air quality data). If the
State, in consultation with EPA, determines from this initial, limited
RACT and RACM analysis that the area may be able to advance its
attainment date through implementation of reasonable measures, then the
State would conduct a more detailed RACT and RACM analysis, including
appropriate air quality modeling analyses, to assess whether it can
advance the attainment date.
    In general, the combined approach to RACT and RACM in the final
rule includes the following steps: (1) Identification of potential
measures that are reasonable; (2) modeling to identify the attainment
date that is as expeditious as practicable; and (3) selection of RACT
and RACM.
    Identification of potential measures. The State's review of
potential measures must be sufficient to identify all appropriate RACT
and RACM. As stated previously, inherent to RACT/RACM is the basic
requirement that the measure be ``reasonable.'' A State need not
evaluate measures in its RACM/RACT analysis that it determines are
unreasonable such as measures that are ``absurd, unenforceable, or
impractical'' or that would cause ``severely disruptive socioeconomic
impacts, (e.g. gas rationing and mandatory source shutdowns); such
measures are not required by the Act. 55 FR 38327.
    As we also stated earlier, a State's RACT/RACM analysis not only
involves an assessment about what emissions sources to control and to
what level, but also a judgment as to when it is reasonable to require
a sector to comply with a given measure. Accordingly, if the State or
Federal rules already heavily regulate a given sector, it is reasonable
for the State to first look to unregulated parts of the sector for
RACT/RACM measures, especially, in light of costs already realized by
the regulated sector. A State may conclude that it is unreasonable to
further regulate the industry, or that it is only reasonable to impose
measures in the latter years of the attainment plan.
    Finally, the State should use reason in the extent of its efforts
to identify potential control measures. For example, if a review of
monitoring data and modeling studies indicates that reductions in
SO2 are much more effective in reducing ambient
PM2.5 than reductions in other pollutants, we expect that
the State will more vigorously identify RACT/RACM measures for
SO2 than for other pollutants. Conversely, if reductions in
a given pollutant, even in large quantities, would have trivial impacts
on PM2.5, less rigor is needed in the State's assessment of
controls for that pollutant, because such controls could not contribute
to advancing the attainment date. Likewise, where reducing emissions of
a pollutant is effective in reducing ambient PM2.5, if the
emissions inventory for that pollutant is dominated by a given type of
emissions source, then it would be appropriate to focus the analysis on
measures for that segment of the inventory. No RACT/RACM analysis is
needed for pollutants that are not attainment plan precursors for a
particular PM2.5 nonattainment area.
    As supporting information for identification of RACT and RACM, the
State ordinarily provides data on technologically feasible control
measures:

--A list of all emissions source categories, sources and activities in
the nonattainment area (for multi-State nonattainment areas, this would
include source categories, sources and activities from all states which
make up the area)
--For each source category, source, or activity, an inventory of direct
PM2.5 and precursor emissions;
--For each source category, source, or activity, a list of
technologically feasible emission control technologies and/or measures
\27\
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    \27\ The EPA believes that it is not necessary to identify every
possible variation of every type of control measure, or all possible
combinations of technologies and measures that would apply to a
given source or activity if the State has properly characterized the
potentially available emissions reductions and their costs. For
example, EPA believes that the State can conduct a thorough analysis
of VMT reduction measures without including every possible level or
stringency of implementation of certain possible measures or
combinations of measures for reducing VMT, so long as those measures
would not affect the overall assessment of VMT reduction
capabilities and the associated costs.
---------------------------------------------------------------------------

--For each technologically feasible emission control technology or
measure, the State should provide the following information: (1) The
control efficiency by pollutant; (2) the possible emission reductions
by pollutant; (3) the estimated cost per ton of pollutant reduced; and
(4) the date by which the technology or measure could be reasonably
implemented.

    Based on this and other relevant information, the State will
identify the reasonable measures (potential RACT and RACM) to be
included in air quality modeling. (At its option, the State may prefer
not to make a judgment on whether certain measures are technically and
economically feasible, if it believes they will not contribute to
earlier attainment. In that case, the State could include those
measures in the modeling, and later exclude them from RACT and RACM by
showing that all the excluded measures together would not advance the
attainment date by at least 1 year.) As previously mentioned, in
determining the attainment date that is as expeditious as practicable,
the State should consider impacts on the nonattainment area of
intrastate transport of pollution from sources within its jurisdiction,
and potential reasonable measures to reduce emissions from those
sources.
    Modeling to determine the attainment date that is as expeditious as
practicable. Second, for purposes of determining the attainment date
that is as expeditious as practicable, the State will need to conduct
modeling to show the combined air quality impact of all of the
potential measures identified in the first step with a modeling
analysis for the year 2009. A base case scenario for the year 2009
would project future air quality given implementation of existing
measures (Federal, State and local). If this base case scenario
demonstrates attainment by 2010, then the State must demonstrate why
attainment could not be achieved in an earlier year. (As noted above,
given the April 2008 due date for SIP submissions, it may be difficult
to achieve earlier attainment in many cases).
    If the base case scenario does not demonstrate attainment, then a
control case scenario (described below) is needed to examine whether
the reasonable, technically and economically feasible measures
identified by the State would result in attainment in 2009. The control
case scenario would add potential SIP measures--e.g. potential RACT/
RACM, plus any candidate intrastate transport measures that the State
has identified

and would be feasible to implement by that year. States in multi-State
nonattainment areas are strongly encouraged to collaborate on their
modeling analyses. This modeling, along with other information known as
weight of evidence considerations, would inform a judgment as to
whether reasonable measures could lead to attainment of the standards
within 5 years after designation. If the analysis does not demonstrate
attainment by April 2010 (2009 analysis year), then the analysis would
serve as the technical basis for the State to seek an extension of the
attainment date for that area. Further analysis would then be necessary
and is required to identify the specific attainment date.
    The choice of future years to model beyond 2010 may vary from area
to area. Often, modeling potential controls in two different future
years may be necessary to support a judgment that a projected
attainment year is as expeditious as practicable. If the area is
projected to remain over the standard in the early projection year
(e.g., 2009) despite the emission reductions from the modeled control
measures, but is projected to be well below the standard in the later
projection year (e.g., 2012), interpolation and emission inventory
analysis could identify an intermediate year as the appropriate
attainment date. There may be cases in which modeling a single year is
sufficient because modeling of all technically and economically
feasible controls results in attainment by a narrow margin in that
year.
    For many areas, EPA modeling analysis for CAIR and other modeling
analyses that have been performed suggest a number of nonattainment
areas will have a modest amount (in some cases only a few tenths of a
microgram) of needed reductions in ambient levels after 2010 to reach
attainment. For any such area, and for areas otherwise expected to
attain relatively soon after 2010 (for example, due to substantial
reductions in a dominant local source), EPA believes that this analysis
should be for a year no later than 2012. A later date (e.g., 2014) may
be appropriate for areas with very high PM2.5 levels that
face difficulty attaining within 10 years.
    The EPA believes that it is not reasonable to require States to
model each and every year between 2009 and 2014 to determine the
appropriate attainment date. Modeling future year inventories is a time
consuming and resource intensive process. Multiple models and pre-
processors are needed in order to generate year specific emissions for
the various emissions sectors (e.g. mobile, non-road, non-EGU point,
EGU point, etc.). Because it is not reasonable to model every year, a
logical choice often may be to model a year in the middle of the
period. As such, we recommend modeling an emissions year no later than
2012 as the initial extension date (which translates to a 2013
attainment date). If this modeling indicates that the area can reach
attainment by 2012, then the State can further analyze emissions and
strategies to determine if the attainment date can be advanced to an
earlier year. If the modeling indicates that the area cannot reach
attainment by 2012, then the modeling will serve as further
justification for granting a longer attainment date extension (e.g.,
attainment date of 2015 with modeling for 2014). In that case,
additional modeling of 2014 with further emissions controls would be
required in order to show attainment. Again, the State should then
further analyze emissions and strategies to determine if the attainment
date can be advanced to an earlier year between 2012 and 2015.
    Additionally, in the discussion of air quality modeling issues in
section II.E above, we discuss the benefits of addressing control
strategies for multiple pollutants. Part of the challenge of multi-
pollutant modeling is coordinating the future modeling years for
different pollutants in order to minimize the number of required future
year model runs. As part of the requirements of the 8-hour ozone
implementation rule, States are currently working on modeling analyses
for 2009 and in some cases for 2012 (serious nonattainment areas). For
an area that cannot attain the PM2.5 NAAQS by 2010, this may
be reason to select 2012 as the year to model, so that the State could
conduct the modeling for both ozone and PM2.5 in tandem.
This would, in some cases, allow the pooling of resources (e.g.,
inventories, model runs, etc.) and provide for faster development of a
PM2.5 attainment demonstration.
    It may also be possible for the State to look at 2009 and 2014
only. In this instance, the State may find sufficient data to
interpolate results for the years in between based on estimated changes
in emissions.
    We emphasize that when a State models later years, that this
analysis must take into account potential controls that the State may
have determined would not be RACT or RACM for an earlier year. For
example, some measures that are impractical to implement by 2009 could
be reasonable if implemented by 2010, 2011 or 2012. Thus, when the
State models later years, the list of potential controls should be
expanded to include technically and economically feasible measures that
can be implemented by the analysis year.
    Selection of RACT & RACM. Based on this analysis, the State should
make decisions on RACT, RACM, intrastate measures, and the attainment
date that is as expeditious as practicable. Because EPA is defining
RACT and RACM as only those reasonable, technically and economically
feasible measures that are necessary for attainment as expeditiously as
practicable, the State need not adopt all feasible, reasonable
measures. The State may exclude those reasonable measures that,
considered collectively, would not advance the attainment date.

Comments and Responses

    Comment: A number of commenters generally supported EPA's second
proposed alternative to RACT (option 2). Most of these commenters
expressed concern that the other options would require the imposition
of controls whether or not they were needed to attain the
PM2.5 standards as expeditiously as practicable. Some State
and local commenters also urged EPA to select option 2 as the best
interpretation of the RACT requirement for PM2.5 because
they believe that it will be the most appropriate approach for
designing attainment strategies for their particular nonattainment area
or areas.
    Response: The EPA agrees that these two points are important
considerations. After carefully considering the options, we concluded
that Option 2 was the most suitable approach for the PM2.5
NAAQS. Options 1 and 3 do not reduce the States' burden to analyze
potential control measures as the States would still be required to
look beyond the mandated RACT for reasonably available control measures
(RACM). Moreover, Options 1 and 3 could require imposition of controls
on some sources that would not strictly be necessary to attain the
NAAQS as expeditiously as practicable. Given the nature of the
PM2.5 nonattainment problem, EPA concluded that an
interpretation that provides the maximum flexibility is a better
approach.
    Comment: Some commenters recommended that EPA modify proposed
option 2 to include a tons-per-year threshold. Under such an approach,
the States and EPA would only require RACT for sources whose emissions
were above the threshold. Most of these comments recommended a RACT
threshold of 100 tons per year. These commenters expressed concern that
if option 2 were implemented

without such a threshold, States would be burdened with conducting RACT
analyses for very small sources or source categories with low
emissions.
    Response: The EPA believes that under the approach chosen for the
final rule in which RACT is considered to be a part of the overall RACM
process, it would be difficult to define a threshold that would apply
for all types of sources and for all types of control measures in all
nonattainment areas. It has not been common practice under past EPA
policy to establish or use an emissions threshold when considering
sources for possible emission reductions as part of a RACM analysis to
show attainment as expeditiously as practicable. Indeed, many of the
control technique guidelines for VOC RACT do not recommend an emissions
threshold. A state needing significant emission reductions to attain
the standards in a given area even by 2015 would likely conclude that
controls should be considered on smaller sources. In contrast, a State
with an area that exceeds the standard by only a few tenths of a
microgram per cubic meter may not need to consider controls on smaller
source to reach attainment as expeditiously as practicable. The EPA has
selected option 2 for interpretation of the RACT requirement for
PM2.5, in part, specifically because that approach
contemplates that States will conduct an appropriate analysis of the
spectrum of source categories and potential controls available. To cut
off such analysis at a set emissions-based cut point for all sources
and all areas would undermine one of the key benefits of the approach.
Accordingly, EPA disagrees with comments that option 2 should include a
nationally-defined threshold for the size of sources or source
categories that require RACT analyses.
    Comment: A number of commenters supported EPA's first and third
proposed alternative approaches to RACT (option 1 and option 3).
Commenters supporting these two options used similar reasoning.
Commenters cited the statutory language in section 172(c)(1) requiring
that the attainment plan provide for ``at a minimum'' the adoption of
RACT. Accordingly, these commenters argued that RACT is an independent,
minimum requirement of attainment plans irrespective of the attainment
demonstration and that option 2, which would not require the adoption
of RACT for all sources, has no policy or legal justification. Other
commenters noted that option 1 would be much easier to implement,
because RACT would be defined according to technical reasonableness and
would not hinge on complicated determinations involving attainment
demonstrations. Some commenters argued that option 1 provides for
greater equity, because similar measures would be required for similar
sources for all nonattainment areas. Finally, some commenters believed
that it is inherently inconsistent to assert that plans have met the
requirement for attainment ``as expeditiously as practicable'' without
applying RACT to all major sources.
    Response: The EPA disagrees with these comments. The EPA believes
that option 2 is fully consistent with section 172(c)(1). Section
172(c)(1) requires that attainment plans must provide for the
implementation of RACM as expeditiously as practicable (including such
reductions in emissions from existing sources in the area as may be
obtained through the adoption, at a minimum, of RACT). Contrary to the
commenters' assertions, this language does not demonstrate that RACT is
required for all sources, independent of RACM and attainment
demonstrations. Moreover, this provision does not require RACT whether
or not imposition of technology would advance the attainment date.
Instead, section 172(c)(1) explicitly provides that RACT is included
within the definition of RACM, and EPA has previously determined that
the CAA only requires such RACM as will provide for attainment as
expeditiously as practicable. (See 57 FR 13498, 13560). The courts have
deferred to this interpretation and concluded that EPA interprets RACM
as a collection of reasonable measures that would advance the
attainment date. See Sierra Club v. EPA, 294 F.3d 155, 162 (D.C. Cir.
2002); see also Sierra Club v. EPA, 314 F.3d 735, 744 (5th Cir. 2002).
The CAA does not ``compel [ ] a State to consider whether any measure
is `reasonably available' without regard to whether it would expedite
attainment in the relevant area.'' Sierra Club v. EPA, 294 F.3d at 162.
The EPA concludes that because section 172(c)(1) establishes that RACT
is a part of RACM, EPA is reasonably applying the same interpretation
to the RACT requirement for PM2.5. The RACT is a part of the
collection of measures that are necessary to reach attainment as
expeditiously as practicable. It is thus directly related to what a
specific area needs to attain the NAAQS, and States need not implement
reasonably available measures that would not advance the attainment
date as part of the PM2.5 RACT requirement.
    The EPA also finds that option 2 is consistent with the statutory
language providing that a State must apply RACT to existing sources,
``at a minimum,'' to meet its requirement to apply RACM. We interpret
the ``at a minimum'' clause to mean that when a State determines that
control of a specified existing stationary source(s) is necessary to
attain, the State must apply RACT to that source. Further, EPA believes
this requirement for RACT applies to stationary sources as a group, and
not to each stationary source.
    The EPA finds sound policy reasons for choosing option 2. While an
approach that provided for application of the same controls in all
areas would provide for more equity across areas, EPA emphasizes that
equity is only one of many factors considered by EPA when deciding
between options 1, 2 and 3. The EPA believes that it is also important
to ensure that control strategies focus on the most effective measures
with the greatest possibility for significant air quality improvements.
In addition, while EPA agrees that options 1 and 3 could provide for
greater ease of implementation, this is also only one of the factors
EPA considered when deciding between the proposed options. Under option
2, States have a greater burden and responsibility to identify the
local strategy that is tailored to their particular air quality
problem. At the same time, the States have the ability to identify the
sources with the greatest impact on nonattainment and to identify a
sound strategy that achieves attainment in the most sensible manner.
The EPA believes that approaching RACT and RACM in this manner is
consistent with the overall philosophy imbedded in the SIP program
since its inception in the late 1960s and early 1970s.
    Comment: Some commenters believed that the proposed RACM
requirement was too broad. These commenters believed that the
requirement to analyze the entire ``universe'' of possible measures was
too burdensome for States. Commenters felt this was especially true in
light of the lack of federally issued CTG and ACT documents for
PM2.5 and its precursors for all potential source
categories.
    Response: As explained earlier, States should apply ``reason'' in
identifying measures to evaluate as potential RACM/RACT. We recognize
that States are implementing the PM2.5 standard for the
first time, and do not have the long history and experience in
implementing PM2.5 as they have in implementing the
PM10 and ozone standards. Accordingly, we expect that both
the States and EPA will expend extra effort in developing and
evaluating attainment plans that contain appropriate controls. A number

of resources exist to provide States with information on potential
control measure costs and emissions reductions. We intend to facilitate
the sharing of information through a control measure website and other
efforts, and expect that States will develop screening methods to
reduce the burden of analysis.
    Comment: One commenter asserted that EPA should not require the
analysis for, or implementation of, RACT and RACM for sources
throughout the entire nonattainment area, and should permit States to
focus only on sources located in smaller specific ``problem areas''
within the nonattainment area.
    Response: The EPA designated areas nonattainment based upon
analysis of the geographic area with sources that ``contribute'' to the
violation of the NAAQS in the area, in accordance with section 107(d).
These designations are based upon, among other things, a network of
monitors that the State and EPA previously agreed represented the
ambient air concentrations throughout the area. Additional analysis of
information during the designation process indicated those areas that
contributed to the violations at the violating monitor because of,
among other things, the amount of emissions in such adjoining areas.
Accordingly, the State in which a nonattainment area is located must
evaluate the full range of sources of PM2.5 and its
precursors throughout the designated nonattainment area during the
development of the SIP. The EPA agrees that there are some
nonattainment areas where one or a few large emissions sources may be
causing localized concentrations at a monitor that are much higher than
those within the remainder of the nonattainment area. For such areas,
the nonattainment strategy will likely not succeed without addressing
those sources. The EPA does not, however, believe it is acceptable that
the nonattainment strategy focus only on those sources, because
additional reductions within the nonattainment area would still have
the potential to advance the attainment date. Exempting portions of the
nonattainment area could expose a portion of the public residing
downwind in the area to exposure to levels of PM2.5 that
exceed the NAAQS for longer than necessary, and the health detriments
from such exposure, merely to minimize the impact of having to impose
control strategies on sources upwind. Moreover, to the extent that
monitoring in one portion of a nonattainment area indicates violations
in multiple portions of the area, a strategy that solely focused upon
the sources in the immediate vicinity of the monitor might fail to
assure that the NAAQS is achieved throughout the area. Because NAAQS
violations generally reflect a combination of regional scale,
metropolitan scale, and local scale impacts, and all three scales must
be addressed, EPA requires RACT/RACM submittals to address sources
throughout the nonattainment area.
    Comment: Some commenters agreed with EPA's view that State's RACM
analysis must address those measures that a State declines to adopt and
must show whether the combined measures would cumulatively advance the
attainment date by at least 1 year. One commenter questioned the legal
basis for EPA's determination that the only controls necessary to
attain the PM2.5 NAAQS as expeditiously as practicable are
those that would cumulatively advance an area's projected attainment
date by at least one calendar year. The commenter suggested that
control measures that would advance attainment by a smaller increment
``would meet the criteria endorsed in Sierra Club [Sierra Club v. EPA,
294 F.3d 155 (D.C. Cir 2002)] by `expedit[ing] attainment in the
relevant area.' ''
    Response: The EPA has consistently interpreted RACM as a collection
of measures that would advance the attainment date by at least 1 year,
and the courts have determined that the statutory RACM requirement is
ambiguous and deferred to EPA's interpretation of the requirement. See
Sierra Club v. EPA, 314 F.3d 735, 744 (5th Cir. 2002); see also Sierra
Club v. EPA, 294 F.3d, 155 162 (D.C. Cir. 2002). Contrary to the
commenter's suggestion, the court in Sierra Club v. EPA, did not
endorse specific criteria for identifying control measures that
expedite attainment, but instead deferred to EPA's interpretation of an
ambiguous statutory term. The courts deferred to EPA's interpretation
after reviewing EPA's approval of State SIP submissions. The EPA
conducts such reviews consistent with its determination that the CAA
only requires such RACM as will provide for attainment as expeditiously
as practicable, and its belief that it would be unreasonable to require
implementation of measures that would not in fact advance attainment.
See 57 FR 13498, 13560 (April 15, 1992); see also 44 FR 20372, 20374
(April 4, 1979). In considering whether a collection of measures would
advance the attainment date of an area, EPA has previously interpreted
the phrase ``advance the attainment date'' as meaning that the
attainment date would be advanced by at least 1 year. See e.g., 66 FR
57160, 57182 (Nov. 14, 2001) (approval of Houston SIP); 66 FR 586 (Jan
3. 2001) (approval of DC area SIP). Further, EPA's use of a one-year
increment in determining whether a collection of measures would advance
the attainment date is reasonable and consistent with the fact that all
areas will be designing attainment demonstrations for the annual
PM2.5 standard. Section 172(a)(2)(C) statute uses 1 year as
the increment by which attainment date extensions can be granted. Thus,
requiring evaluation of whether control measures would advance
attainment by an increment of 1 year is a reasonable approach for the
PM2.5 NAAQS.
    Comment: Some commenters recommended that EPA consider not
requiring a RACM analysis for areas projected to attain the standards
within 5 years of designation, i.e., by April 2010 for the areas
currently designated nonattainment. One commenter suggested that
practical considerations would make it impossible for any State
projected to attain by 2010 to advance the attainment date by a year.
This commenter noted that because measures to provide for attainment by
2010 must be implemented by the beginning of 2009, and SIPs are not
submitted until April 2008, it would impossible to advance the
implementation of measures by 1 year (that is, the beginning of 2008).
    Response: The EPA generally agrees that given the time constraints
it will be difficult for States with areas currently designated
nonattainment to devise, adopt, and implement RACM measures to advance
the attainment date before 2010. At the same time, however, we note
that nothing precludes States from taking early action and we encourage
States to take actions to reduce PM2.5 concentrations where
feasible even before the SIPs are submitted. RACM is required by the
CAA and thus EPA cannot waive the requirement for the analysis. At the
same time, EPA recognizes that a streamlined analysis may be
appropriate given the short time periods involved.
3. Observations and Considerations in Determining RACT and RACM
a. Background
    The preamble to the proposed rule included a discussion of general
considerations for RACT (70 FR 66020 and 66021, latter part of section
III.I.6) and RACM (70 FR 66028, section III.1.15). The preamble to the
final rule retains this discussion with some modifications and
restructuring to

reflect the combined approach to RACT and RACM
b. Final Rule
    General considerations. Once the State has identified measures and
technologies that are available for implementation in the nonattainment
area, then it must evaluate those measures to determine whether
implementation of such measures are reasonable, and would collectively
advance attainment. Many of the factors that the State should take into
consideration in determining whether a measure is ``reasonable'' are
related to the measure's technical and economic feasibility. Since RACM
applies to area and mobile sources as well as stationary sources, the
State should consider other factors as well in conducting its RACM
analysis. For example, in many cases obtaining emissions reductions
from area and mobile sources is achieved not by adding control
technology to a specific emissions source, but by reducing the level of
activity of a fleet of vehicles or by modifying a type of commercial
process. In these situations, the State should also consider local
circumstances such as infrastructure, population, or workforce and the
time needed to implement the measure in light of the attainment date.
    The EPA believes that while areas projected to attain within 5
years of designation as a result of existing national measures should
still be required to conduct a RACT and RACM analysis, such areas may
be able to conduct a limited RACT and RACM analysis that does not
involve additional air quality modeling. A limited analysis of this
type could involve the review of available reasonable measures, the
estimation of potential emissions reductions, and the evaluation of the
time needed to implement these measures. If the State could not achieve
significant emissions reductions by the beginning of 2008 due to time
needed to implement reasonable measures or other factors, then it could
be concluded that reasonably available local measures would not advance
the attainment date. In lieu of conducting air quality modeling to
assess the impact of potential RACT and RACM measures, existing
modeling information could be considered in determining the magnitude
of emissions reductions that could significantly affect air quality and
potentially result in earlier attainment. If the State, in consultation
with EPA, determines from this initial, more limited RACT and RACM
analysis that the area may be able to advance its attainment date
through implementation of reasonable measures, then the State would
conduct a more detailed RACT and RACM analysis.
    Observations on control opportunities. The implementation of the
PM2.5 NAAQS is in its initial stages, and many of the
designated PM2.5 nonattainment areas are not current or
former PM10 nonattainment areas. Thus, some existing
stationary sources in these areas may currently be uncontrolled or
undercontrolled for PM2.5 or PM2.5 precursors.
Further, to this point in time, emissions controls for existing sources
in these areas may have focused primarily on particulate matter that is
filterable at stack temperatures and thus may not adequately control
condensable emissions. In addition, States should bear in mind that the
controlled sources may have installed emission controls 15 years ago or
more, and there may now be cost-effective opportunities available to
reduce emissions further through more comprehensive and improved
emissions control technologies, or through production process changes
that are inherently lower in emissions.
    Moreover, improved monitoring methods may enhance the ability of
sources to maintain the effectiveness of installed emissions controls
and to reduce emissions by detecting equipment failures more quickly.
For example, State imposition of requirements for more frequent
monitoring (e.g., continuous opacity monitors, PM continuous emissions
monitors, etc.) may provide greater assurance of source compliance and
quicker correction of inadvertent upset emissions conditions than
existing approaches.
    Even in former or current PM10 nonattainment areas,
existing requirements for controlling direct PM emissions (e.g., with a
baghouse or electrostatic precipitator) may not have been revised
significantly since the 1970's. When EPA established the
PM10 standards in 1987, we stated in the preamble that it
was reasonable to assume that control technology that represented RACT
and RACM for total suspended particulates (TSP) should satisfy the
requirement for RACT and RACM for PM10. 52 FR 24672 (July 1,
1987). The basis for EPA's belief was that controls for PM10
and TSP would both focus on reducing coarse particulate matter, and
specifically that fraction of particulate matter that is solid (rather
than gaseous or condensable) at typical stack temperatures. However,
emission controls to capture coarse particles in some cases may be less
effective in controlling PM2.5. For this reason, there may
be significant opportunities for sources to upgrade existing control
technologies \28\ and compliance monitoring methods to address direct
PM emissions contributing to fine particulate matter levels with
technologies that have advanced significantly over the past 15 years.
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    \28\ For example, see past EPA guidance on PM2.5
control technologies: Stationary Source Control Techniques Document
for Fine Particulate Matter (EPA-452/R-97-001), EPA Office of Air
Quality Planning and Standards, October 1998.
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    Precursor Controls. It will be important for States to conduct RACT
and RACM determinations for stationary sources of PM2.5
precursors as well as direct PM2.5 emissions although, as
noted above, the known atmospheric chemistry of the area may dictate
the necessary rigor of this analysis. A significant fraction of
PM2.5 mass in most areas violating the standards is
attributed to secondarily-formed components such as sulfate, nitrate,
and some organic PM, and EPA believes that certain stationary sources
of precursors of these components in nonattainment areas currently may
be poorly controlled. Accordingly, to address these precursors, States
should review existing sources for emission controls or process changes
that could be reasonably implemented to reduce emissions from
activities such as fuel combustion, industrial processes, and solvent
usage.
    Multi-State Nonattainment Areas. States in multi-State
nonattainment areas will need to consult with each other on appropriate
level of RACT and RACM for that area. We anticipate that States may
decide upon RACT and RACM controls that differ from State to State,
based upon the State's determination of the most effective strategies
given the relevant mixture of sources and potential controls in the
relevant nonattainment areas. So long as each State can adequately
demonstrate that its chosen RACT and RACM approach will provide for
meeting RFP requirements and for attainment of the NAAQS as
expeditiously as practicable for the nonattainment area at issue, we
anticipate approving plans that may elect to control a somewhat
different mix of sources or to implement somewhat different controls as
RACT and RACM. Nevertheless, States should consider RACT and RACM
measures developed for other areas or other States. EPA may consider
such measures in assessing the approvability of a State's SIP.
c. Comments and Responses
    Comment: In the proposed rule, EPA indicated that States could
consider the ``social acceptability'' of measures as a

factor in the determination of what constitutes RACM in a given area. A
number of commenters recommended that EPA eliminate use of this factor.
Some commenters questioned whether States or EPA had the legal
authority to exclude measures from consideration based on social
acceptability or popularity, if the measures are technically and
economically available, and are needed to attain the NAAQS for
protection of public health. Others expressed concerns that inclusion
of such a factor would inevitably result in the elimination of controls
for area and mobile sources and for this reason would unfairly focus
emissions reduction strategies on industrial sources of
PM2.5 and precursors.
    Response: The EPA believes that in developing RACM measures, it is
important that States not rely unduly on measures that would be very
difficult to enforce in practice. We discourage States from relying on
measures that on paper may seem reasonably available but in practice
might fail to achieve benefits due to the problems and costs of
effectively enforcing these measures. However, we recognize that the
CAA does not identify ``social acceptability'' as a factor in the
definition of what may constitute RACT or RACM, and more generally the
CAA does not establish a preference for measures that affect industrial
sources instead of the general public and are therefore more likely to
be ``socially acceptable.'' Therefore, given the concerns raised by
commenters that establishment of ``social acceptability'' as a factor
in the RACM analysis is without basis in the CAA and might result in
inappropriate skewing of control strategies, we have removed this term
from the final rule. We reiterate, however, that capability of
effective implementation and enforcement are relevant considerations in
the RACM analysis, even though public ``unpopularity'' is not.
Moreover, in assessing the efficacy of measures and the credit they
should be given in the context of attainment demonstrations or RFP
calculations, EPA believes that such considerations are important.
4. What Factors Should States Consider in Determining Whether an
Available Control Technology or Measure Is Technically Feasible?
a. Background
    The following provides guidance for States to consider in
determining whether an available control technology is technologically
feasible.
b. Final Rule
    The technological feasibility of applying an emission reduction
method to a particular source should consider factors such as the
source's process and operating procedures, raw materials, physical
plant layout, and any other environmental impacts such as water
pollution, waste disposal, and energy requirements. For example, the
process, operating procedures, and raw materials used by a source can
affect the feasibility of implementing process changes that reduce
emissions and the selection of add-on emission control equipment. The
operation and longevity of control equipment can be significantly
influenced by the raw materials used and the process to which it is
applied. The feasibility of modifying processes or applying control
equipment also can be influenced by the physical layout of the
particular plant. The space available in which to implement such
changes may limit the choices and will also affect the costs of
control.
    Reducing air emissions may not justify adversely affecting other
resources by increasing pollution in bodies of water, creating
additional solid waste disposal problems or creating excessive energy
demands. An otherwise available control technology may not be
reasonable if these other environmental impacts cannot reasonably be
mitigated. For analytic purposes, a State may consider a
PM2.5 control measure technologically infeasible if,
considering the availability (and cost) of mitigating adverse impacts
of that control on other pollution media, the control would not, in the
State's reasoned judgment, provide a net benefit to public health and
the environment. However, in many past situations, States and owners of
existing sources have adopted PM2.5 control technologies
with known energy penalties and some adverse effects on other media,
based on the reasoned judgment that installation of such technology
would result in a net benefit to public health and the environment.
States should consider this in determining technical feasibility. The
costs of preventing adverse water, solid waste and energy impacts
should be included in assessing the economic feasibility of the
PM2.5 control technology.
    One particular cross-media issue relates to concentrated animal
feeding operations (CAFOs). Should a State determine that reductions of
direct PM2.5 or PM2.5 precursors from CAFOs are
necessary for attainment in a nonattainment area, EPA strongly suggests
that the State address these reductions from a cross-media perspective.
Since 2003, EPA and many stakeholders have been interested in
developing a framework to enable CAFOs to pursue superior environmental
performance across all media. We are aware that today some CAFOs
voluntarily conduct whole-farm audits to evaluate releases of
pollutants to all media through Environmental Management Systems, self-
assessment tools, performance track, ISO 14001 certification, and
State-approved trade offs in meeting regulatory thresholds between air
and water that accomplish the best overall level of environmental
protection given State and local conditions. The EPA continues to
believe the development of new and emerging technologies offers the
potential to achieve equivalent or greater pollutant reductions than
achieved solely by effluent guidelines and standards. Many of these are
superior from a multimedia perspective, and EPA would like to encourage
superior multimedia solutions. SIPs which need to address ammonia may
provide a unique opportunity to encourage multimedia approaches at
CAFOs. For example, the addition of animal by-products provides a
valuable source of nutrients for crops, improves soil structure which
enhances soil permeability, and adds valuable organic matter that
improves soil health. However, inappropriate application can lead to
air and water quality concerns or the improvement of one media at the
cost of another. Optimal application technologies and rates reduce
potential air and water quality standards violations. The EPA does not
want to discourage approaches that are superior from a cross media
perspective.
    The EPA recommends that States evaluate alternative approaches to
reducing emissions of particulate matter by reviewing existing EPA
guidance \29\ and other sources of control technology information. The
EPA's 1998 guidance presents information on topics such as the design,
operation and maintenance of general particulate matter control systems
such as electrostatic precipitators, fabric filters, and wet scrubbers.
The filterable particulate matter collection efficiency of each system
is discussed as a function of particle size. The guidance document also
provides information concerning

other relevant considerations such as energy and environmental
considerations, procedures for estimating costs of particulate matter
control equipment, and evaluation of secondary environmental impacts.
Because control technologies and monitoring approaches are constantly
being improved, the State should also consider more updated or advanced
technologies not referenced in this 1998 guidance when conducting a
RACT determination. Emissions reductions may also be achieved through
the application of monitoring and maintenance programs that use
critical process and control parameters to verify that emission
controls are operated and maintained so that they more continuously
achieve the level of control that they were designed to achieve.\30\
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    \29\ Stationary Source Control Techniques Document for Fine
Particulate Matter (EPA-452/R-97-001), EPA Office of Air Quality
Planning and Standards, October 1998. See also: Controlling
SO2 Emissions: A Review of Technologies (EPA/600/R-00/
093), EPA Office of Research and Development, November 2000.
    \30\ See EPA's Web site for more information: http://www.epa.gov/ttn/emc/monitor.html
.

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c. Comments and Responses
    Comment: One commenter noted that the guidance for ``technical
feasibility'' implies that States look at individual sources with a
BACT-like case-by-case analysis. The commenter recommended that source
owners conduct such a site-specific analysis and submit the analysis to
the State through the permitting process.
    Response: While the analytical analysis to identify RACT is similar
to BACT, as noted above, EPA in the past has issued CTGs that describe
the presumptive norm for RACT controls for a given industry, but that
allow for case-by-case considerations for a given source. Where States
wished to require source owners to conduct such a site-specific
analysis as part of the control technology review, EPA supports this
type of process. On the other hand, EPA does not believe it would be
appropriate to require all RACT-eligible sources to conduct such an
analysis, given that States have the primary responsibility for
identifying and analyzing measures for such sources.
5. What Factors Should States Consider in Determining Whether an
Available Control Technology or Measure Is Economically Feasible?
a. Background
    The follow provides guidance for States to consider in determining
whether an available control technology is economically feasible for
purposes of identifying reasonably available control measures. This
guidance is slightly modified from our proposal.
b. Final Rule
    Economic feasibility encompasses considerations such as whether the
cost of a potential measure is reasonable considering attainment needs
of the area and the costs of other measures, and whether the cost of a
measure is reasonable for the regulated entity to bear, in light of
benefits.
    While many States generally establish RACT requirements for a
category of sources, the Act does not require the same level of control
on all sources in a category, nor does the Act require that each source
be controlled individually. Similar sources may have different marginal
costs, profit margins and abilities to pass costs through to the
consumer. These factors are appropriate to consider in determining
whether a given level of control is appropriate for an individual
source or category of sources. Accordingly, there is no presumption
that a given source must bear a cost similar to any other source.
    States should consider the capital costs, annualized costs, cost
effectiveness of an emissions reduction technology, and effects on the
local economy in determining whether a potential control measure is
reasonable for an area or State. One available reference for
calculating costs is the EPA Air Pollution Control Cost Manual,\31\
which describes the procedures EPA uses for determining these costs for
stationary sources. The above costs should be determined for all
technologically feasible emission reduction options if such measure is
inherently ``reasonably available'' (e.g., not absurd or clearly
impractical). States may give substantial weight to cost effectiveness
in evaluating the economic feasibility of an emission reduction
technology. The cost effectiveness of a technology is its annualized
cost ($/year) divided by the emissions reduced (i.e., tons/year) which