nature of the nonattainment problem, the types of sources contributing
to PM2.5 levels in the area, and the ability to perform
timely implementation of control measures). For a Serious area, the EPA
requires that the state must include in its RFP analysis the
anticipated emissions reductions expected to be achieved through the
implementation of control measures required by the control strategy
described in Section VI.D of this preamble (BACM and BACT, additional
feasible measures and MSM, if applicable). Similar to Moderate areas,
the optional air quality analysis discussed in Section IV.F of this
preamble is also available for use by a state preparing a Serious area
RFP plan.
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    \181\ As noted in Section V.B of this preamble, depending upon
when the area is reclassified from Moderate to Serious, this base
year inventory may need to be more recent than the inventory
submitted with the Moderate area attainment plan.
---------------------------------------------------------------------------

    Additionally, the EPA requires that motor vehicle emissions budgets
must also be established for direct PM2.5 and
PM2.5 plan precursors using the latest planning assumptions
and the latest approved motor vehicle emissions model available at the
time that the Serious area attainment plan is developed.\182\ See 40
CFR 51.1012(a).
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    \182\ If an area includes re-entrained road dust in the motor
vehicle emissions budget, the latest approved version of AP-42
should be used unless the EPA has approved an alternative model for
the area.
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    Finally, similar to Moderate areas, Serious areas that are multi-
state or multi-jurisdictional shall provide RFP plans for each state
represented in the nonattainment area that demonstrate RFP on the basis
of common multi-state inventories. The states or jurisdictions within
which the area is located must provide a coordinated RFP plan. For
further information, see Section IV.F.5 of this preamble. See 40 CFR
51.1012(b).
    c. Comments and Responses. Any additional comments received related
to RFP are addressed Section IV.F of this preamble or in the Response
to Comments document found in the docket for this action.

G. Quantitative Milestones

1. Summary of the Proposal
    The EPA proposed that a Serious area plan for an area that can
demonstrate attainment by the statutory Serious area attainment date
must also include quantitative milestones to be reached 7.5 and 10.5
years from designation, to help assess the state's progress toward
attaining the PM2.5 NAAQS in the event the area fails to
attain by the applicable attainment date. For a Serious area that
cannot demonstrate attainment by the statutory Serious area attainment
date, the EPA proposed that the state must include in the Serious area
attainment plan quantitative milestones to be achieved at 7.5, 10.5 and
13.5 years from the area's date of designation.
    The EPA proposed that the general approach to selecting
quantitative milestones outlined in the Moderate nonattainment area
section of the proposal should apply to any attainment plan for a
PM2.5 nonattainment area, independent of its classification.
Specifically, the EPA proposed that states be allowed to select the
quantitative milestones that they identify as appropriate and
quantifiable and that will provide for objective evaluation of progress
toward attainment in their Serious PM2.5 nonattainment area,
and that the EPA, in its attainment plan approval process, will
determine if they satisfy the statutory requirements of CAA section
189(c). Additionally, the EPA proposed to require that, at a minimum,
states must include in all attainment plans for Serious
PM2.5 nonattainment areas a measure to confirm that some
specific portion of BACM and BACT for the area has been implemented as
appropriate in order to comply with the statutory requirement at CAA
section 189(b)(1)(B).
2. Final Rule
    The final rule provisions for Serious area quantitative milestones
are similar to such provisions for Moderate areas discussed in Section
IV.G of this preamble. As required for Moderate areas, Serious area
attainment plans must include quantitative milestones that demonstrate
RFP towards attainment to be achieved every 3 years until the area is
redesignated to attainment. To account for variations in the timing of
possible additional plans that may be required beyond the Serious area
attainment plan (such as a plan revision under CAA section 189(d) for a
Serious area that fails to attain) the EPA is also clarifying,
consistent with the requirements discussed in Section IV.G of this
preamble for Moderate areas, that all Serious area attainment plans
must contain one additional quantitative milestone to be met in the 3-
year period beyond the applicable Serious area attainment date. This
will provide the EPA with appropriate tools necessary to continue to
monitor the area's continued progress toward attainment in the event
that the area fails to attain and develops a new attainment plan.
    For an area that is discretionarily reclassified to Serious under
the provisions of CAA section 188(b)(1), the Serious area plan must
contain quantitative milestones to be achieved by 7.5 years from the
area's date of designation as nonattainment. In this case, the 7.5 year
quantitative milestone that was submitted with the Moderate area plan
may still be sufficient to demonstrate RFP or may have to be adjusted
to reflect the difference in actual progress from the projections of
the Moderate area plan. For an area that is reclassified to Serious
under CAA section 188(b)(2) due to failure to attain, the 7.5 year
quantitative milestones that were submitted with the Moderate area plan
are still required and would be sufficient for the EPA to evaluate the
area's progress toward attaining the NAAQS while the Serious area plan
is being developed. All Serious area plans must also include
quantitative milestones to be achieved 10.5 years from designation, to
help assess the state's progress toward attaining the

PM2.5 NAAQS in the event the area fails to attain by the
applicable attainment date. Finally, for a Serious area that cannot
demonstrate attainment by the statutory Serious area attainment date,
the state must include quantitative milestones to be achieved every 3
years, such that the final milestone falls within the 3 years after the
applicable Serious area attainment date. For example, if a state
requests an attainment date extension to 14 years after designation
pursuant to CAA section 188(e), the attainment plan should contain not
only the 7.5 and 10.5 year milestones, but also milestones to be
achieved 13.5 and 16.5 years from designation.
    The Addendum included guidance that recommended milestones ``should
be addressed by quantifying and comparing the annual incremental
emissions reductions which result from implementation of BACM and BACT
(required within 4 years after the area is reclassified as serious) and
from additional measures included in the final serious area SIP to
those reductions which were identified in the SIP as quantitative
milestones necessary to achieve the NAAQS by the applicable attainment
date.'' \183\ The final rule does not specify that the milestones must
be expressed in terms of emissions reductions. While the EPA notes that
the Addendum contains this fundamental concept, it is impractical to
expect that a state will always be able to quantify and compare real
and projected emissions reductions, and submit a report to the EPA
within 90 days of a given milestone, as required under CAA section
189(c)(2). Therefore, the final rule requires that states selecting
quantitative milestones for a Serious area plan should use the approach
outlined for Moderate areas, as described in Section IV.G of this
preamble. This approach applies to any attainment plan for a
PM2.5 nonattainment area, independent of its classification.
Specifically, the final rule requires that states be allowed to select
the quantitative milestones that they identify as appropriate and
quantifiable and that will provide for objective evaluation of progress
toward attainment in their Serious PM2.5 nonattainment area,
and that the EPA, in its attainment plan approval process, will
determine if they satisfy the statutory requirements of CAA section
189(c). See 40 CFR 51.1013(a)(2).
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    \183\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), at page 42016.
---------------------------------------------------------------------------

    In addition to this general approach for selecting quantitative
milestones and similar to what the final rule requires for Moderate
area attainment plans, the final rule requires that, at a minimum,
states must ensure that the quantitative milestones for Serious
PM2.5 nonattainment areas assure RFP is being met by
demonstrating that BACM and BACT have been implemented, as appropriate
considering the timing of the milestone report, in order to comply with
the statutory requirement at CAA section 189(b)(1)(B). The agency is
further finalizing a corresponding requirement for Serious
PM2.5 nonattainment areas that receive an attainment date
extension. For these areas, the quantitative milestone should assure
that RFP is being met by demonstrating that MSM for the area has been
implemented as required pursuant to CAA section 188(e). This
requirement was not specifically outlined in the proposal. However,
while considering the requirements that were proposed for Serious
areas, the EPA determined that including this additional provision
within quantitative milestones would enable the agency to better
evaluate progress toward attainment in areas that receive a Serious
area extension. The EPA acknowledges that the precise quantifiable
metric for a quantitative milestone (e.g., 50 percent of BACM and BACT
measures implemented by milestone date 7.5 years from designation)
would need to be determined on a case-by-case basis, as it would depend
upon the date of reclassification of the area, which quantitative
milestone (i.e., 7.5 or 10.5 years from designation), and the
anticipated implementation timing and nature of the BACM and BACT
controls themselves. Nonetheless, the EPA believes it is appropriate to
include confirmation that such control measures and technologies are
implemented as a metric that any state with a Serious nonattainment
area must adopt as a quantitative milestone to demonstrate RFP (and
thus must demonstrate compliance with when they submit their milestone
report), as it derives from a statutory provision that applies to all
Serious areas and thus represents a milestone that all Serious
nonattainment areas must meet.
    Additional provisions discussed in the Moderate area quantitative
milestones requirements in Section IV.G of the preamble also apply to
Serious areas. Specifically, if a Serious area submitted the optional
air quality targets with the RFP plan then an air quality based
milestone (i.e., one that is expressed in terms of an ambient
PM2.5 level) is strongly recommended to be included in order
to confirm that the air quality target has been met for the
quantitative milestone year. If used, this milestone will be compared
to the most recently certified monitored ambient air data as part of
the milestone report due after the area reaches each quantitative
milestone date. For additional details on this optional provision,
refer to Section IV.G of this preamble.
    Finally, the quantitative milestone report requirements outlined in
Section IV.G of this preamble apply to Serious areas as well.
Specifically, the requirements associated with the timing and contents
of the quantitative milestone report submission for a Moderate area
also requirements in a Serious area. For additional details on these
requirements, refer to Section IV.G of this preamble. See 40 CFR
51.1013(b).
3. Comments and Responses
    Any additional comments received on this section are addressed in
Section IV.G of this preamble or in the Response to Comments document
found in the docket for this action.

H. Contingency Measures

1. Summary of the Proposal
    In the proposal, the EPA proposed that the criteria for identifying
and selecting contingency measures for a Serious area attainment plan
should be the same as those for Moderate area plans. The EPA also
proposed that, as with Moderate areas, a state may elect to rely on
contingency measures that achieve emissions reductions not only from
sources within the nonattainment area, but also from sources located
outside the nonattainment area but within the state, provided that the
measures on sources outside the designated nonattainment area are
demonstrated to produce the appropriate air quality impact within the
nonattainment area. As with contingency measures for Moderate area
attainment plans, the EPA proposed that the emissions reductions
associated with contingency measures for Serious area plans must be
equal to approximately 1 year's worth of emissions reductions necessary
to achieve RFP for the area, unless the state adequately demonstrates
that some smaller amount of reductions is appropriate while the state
is revising its attainment plan for the area. The agency also proposed
options for submission deadlines for Serious area contingency measures.
2. Final Rule
    As noted in Section IV.G of this preamble, all PM2.5
nonattainment areas must include in their attainment plans contingency
measures consistent with

CAA section 172(c)(9). Contingency measures are additional control
measures to be implemented in the event that an area fails to meet RFP
requirements, fails to meet any quantitative milestone, fails to submit
a quantitative milestone report or fails to attain the PM2.5
standard by the applicable attainment date. These measures must be
fully adopted rules or control measures that are ready to be
implemented quickly upon a determination by the EPA that a failure
occurred, and such measures are required to take effect without
significant further action by the state or the EPA.
    The statutory contingency measure requirement at CAA section
172(c)(9) is not superseded or subsumed by any requirement under
subpart 4, nor does it apply only to Moderate area attainment plans.
Thus, contingency measures are required for Serious PM2.5
nonattainment areas as part of a state's Serious area attainment plan
submission. Accordingly, the final rule requires the criteria for
identifying and selecting contingency measures for a Serious area
attainment plan that are the same as those for Moderate area plans.
Specifically, the EPA is finalizing that the following requirements
must be met in order for contingency measures to be approvable as part
of a state's Serious area attainment plan submission:
    (1) Contingency measures must be fully adopted rules or control
measures that are ready to be implemented quickly upon a determination
by the Administrator of the nonattainment area's failure to meet RFP,
failure to meet any quantitative milestone, failure to submit a
quantitative milestone report or failure to meet the standard by the
applicable attainment date.
    (2) The SIP must contain trigger mechanisms for the contingency
measures, specify a schedule for implementation, and indicate that the
measures will be implemented without significant further action by the
state or by the EPA.
    (3) Contingency measures should consist of control measures that
are not otherwise included in the control strategy for the SIP, or that
achieve emissions reductions not otherwise relied upon in the control
strategy for the area.
    (4) Contingency measures should provide for emissions reductions
equivalent to 1 year's share of reductions needed to demonstrate
attainment (i.e., the overall needed reductions divided by the number
of years from the base year to the attainment year), or approximately
equivalent to 1 year's worth of air quality improvement or emissions
reductions proportional to the overall amount of air quality
improvement or emissions reductions to be achieved by the area's
attainment plan.
    The EPA is also finalizing its proposal to allow a state to rely on
contingency measures that achieve emissions reductions on sources
located outside the nonattainment area, but within the state provided
that the measures on sources outside the designated nonattainment area
are demonstrated to produce the appropriate air quality impact within
the nonattainment area.
    As with contingency measures for Moderate nonattainment areas, the
EPA allows a state under these circumstances to rely on additional
reductions from federal or local measures already scheduled for
implementation as part or all of their contingency measures. The EPA
could consider such measures as meeting the contingency measure
requirement as long as they produce emissions reductions in excess of
those required to meet other statutory nonattainment provisions (such
as to meet BACM/BACT requirements) and they can be relied on to achieve
a sufficient portion of the actual emissions reductions necessary to
reduce emissions in the area while the state develops a new plan to
bring the area into attainment.\184\ As with contingency measures for
Moderate area attainment plans, the EPA requires that the emissions
reductions associated with contingency measures for Serious area plans
should be approximately equivalent to 1 year's worth of emissions
reductions necessary to achieve RFP for the area, unless the state
adequately demonstrates that some smaller amount of reductions is
appropriate while the state is revising its attainment plan for the
area. See 40 CFR 51.1014(b)(2).
---------------------------------------------------------------------------

    \184\ See LEAN v. EPA, 382 F.3d 575 (5th Cir. 2004).
---------------------------------------------------------------------------

    The Addendum provided guidance related specifically to the
selection and implementation of contingency measures for Serious
nonattainment areas. First, the guidance indicated that ``for those
moderate areas reclassified as serious, if all or part of the moderate
area plan contingency measures become part of the required serious area
control measures (i.e., BACM), then additional contingency measures
must be submitted whether or not the previously submitted contingency
measures had already been implemented. Further, the affected states
must ensure that serious areas have adequate contingency measures
considering, among other things, new information about the potential
attainment shortfall for the newly reclassified serious area.'' \185\
The EPA continues to believe that this approach to the statutory
contingency measure requirement is appropriate and is finalizing it for
purposes of implementing the PM2.5 NAAQS in Serious
nonattainment areas. See 40 CFR 51.1014.
---------------------------------------------------------------------------

    \185\ Addendum to General Preamble, 59 FR 41988 (August 16,
1994), at 42015.
---------------------------------------------------------------------------

    With regard to the timing for implementing contingency measures,
the EPA reiterates that the purpose of contingency measures is to
ensure that corrective measures are put in place automatically at the
time that the EPA makes a determination that an area has failed to meet
RFP, failed to meet any quantitative milestone, failed to submit a
quantitative milestone report or failed to meet the NAAQS by the
applicable attainment date. For any nonattainment area, the EPA is
required to determine within 90 days after receiving a state's RFP
demonstration, and within 6 months after the attainment date for an
area, whether the state has met their statutory obligations for
demonstrating RFP or attaining the standard, as appropriate. As with
Moderate areas, the EPA expects that contingency measures should become
effective for Serious areas within 60 days of the EPA making its
determination that the area failed to meet RFP or attain the NAAQS.
3. Comments and Responses
    Comment: One commenter supported the proposal that contingency
measures may be approved if they will result in the equivalent air
quality improvement as would be obtained by implementing measures
obtaining 1 year's worth of emissions reductions needed to demonstrate
attainment.
    Response: In the case where a state selected the optional RFP
analysis that includes air quality targets, the EPA expects that an
area contingency measures may be approved if they will result in
approximately 1 year's worth of air quality improvement.

I. Attainment Dates

1. Summary of Proposal
    Section 188(c) of the CAA states that the attainment date for a
Serious area is to be the end of the tenth calendar year after
designation. The EPA proposed to interpret the reference to
``designation'' in section 188(c) as meaning the ``effective date of
designation.''
2. Final Rule
    As explained earlier, section 188 establishes the attainment dates
for both Moderate and Serious areas. For a

Serious area, CAA section 188(c)(2) provides that ``the attainment date
shall be as expeditiously as practicable but no later than the end of
the tenth calendar year beginning after the area's designation as
nonattainment.'' \186\ For example, for an area initially designated as
a Moderate nonattainment area effective in April 2015 that is
reclassified to Serious at some future date, the Serious area
attainment date, absent any approved Serious area attainment date
extension, would be no later than December 31, 2025 (the end of the
tenth calendar year after designation). As discussed in Section IV.I of
this preamble, the EPA interprets the references to ``designation'' in
CAA section 188(c) as meaning ``effective date of designation,''
consistent with the agency's prior approach for implementing the
previous PM2.5 NAAQS under subpart 1 and other NAAQS.
---------------------------------------------------------------------------

    \186\ The EPA believes that there is no real effect on
attainment date determinations due to the small difference in
statutory language in CAA section 188(c) basing the Moderate area
attainment date on the ``sixth calendar year after the area's
designation'' and the Serious area attainment date on the ``tenth
calendar year beginning after the area's designation,'' (emphasis
added).
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3. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.

J. Attainment Date Extensions

    Background. Section 188(e) of the CAA provides that the EPA may
grant a Serious area one attainment date extension of no more than 5
years ``upon application by any state . . . if attainment by the
[original Serious area attainment date] would be impracticable, the
state has complied with all requirements and commitments pertaining to
that area in the implementation plan, and the state demonstrates to the
satisfaction of the Administrator that the plan for that area includes
the most stringent measures that are included in the implementation
plan of any state or are achieved in practice in any state, and can
feasibly be implemented in the area.''
    The statute also includes factors that the EPA may consider in
determining whether to grant the extension and the length of the
extension, including ``the nature and extent of nonattainment, the
types and numbers of sources or other emitting activities in the area
(including the influence of uncontrollable natural sources and
transboundary emissions from foreign countries), the population exposed
to concentrations in excess of the standard, the presence and
concentrations of potentially toxic substances in the mix of
particulate emissions in the area, and the technological and economic
feasibility of various control measures.'' \187\
---------------------------------------------------------------------------

    \187\ Notably, these statutory criteria do not include specific
ambient air quality criteria like the criteria that need to be met
in the year prior to a Moderate area attainment date in order for
the area to qualify for an attainment date extension under CAA
section 188(d).
---------------------------------------------------------------------------

    The proposal described the four main elements the state must submit
when requesting a Serious area attainment date extension: (1) A
demonstration that attainment by the statutory Serious area attainment
date is impracticable; (2) a demonstration that the area is complying
with all requirements and commitments in the applicable attainment
plan; (3) a demonstration that the plan includes the MSM that are
included in the implementation plan of any state, or are achieved in
practice in any state; and (4) a demonstration of attainment by the
most expeditious alternative date practicable. The proposal also
included a discussion about the timing of extension request
submissions, and how to interpret the second element in cases where the
extension request is submitted after the state has already submitted an
initial Serious area attainment plan. These topics are addressed in the
following sections.
1. Demonstration That Attainment by the Statutory Serious Area
Attainment Date is Impracticable
    a. Summary of Proposal. The proposed rule discussed the
requirements for a demonstration to show that it is impracticable for a
Serious area to attain by the attainment date. This demonstration
involves evaluating through air quality modeling whether all best
available control measures will enable the area to attain the standard
by the attainment date.
    b. Final Rule. This section remains relatively unchanged from the
proposal. In order to demonstrate that it is impracticable for an area
to attain by the attainment date, the state would have to show that the
implementation of all BACM/BACT (and additional feasible measures) will
not bring the area into attainment by the statutory Serious area
attainment date (i.e., by no later than the end of the tenth calendar
year after designation).\188\ The statutory provision for demonstrating
that it is impracticable to attain by the Serious area attainment date
requires that the demonstration be based on air quality modeling (see
CAA section 189(b)(1)(A)). Additional guidance on this demonstration is
provided in Section VI.E of this preamble.
---------------------------------------------------------------------------

    \188\ This proposed approach parallels the EPA's proposed
approach, described earlier in this preamble, for the
impracticability option for Moderate areas under CAA section
189(a)(1)(B) in which all measures that qualify as RACM and RACT and
all additional reasonable measures are required before a Moderate
area plan could show impracticability of attainment by the statutory
Moderate area attainment date (the end of the sixth calendar year
after designation).
---------------------------------------------------------------------------

    c. Comments and Responses. Any additional comments received on this
section are addressed in the Response to Comments document found in the
docket for this action.
2. Demonstration That the Area is Complying With all Requirements and
Commitments in the Applicable Implementation Plan
a. Extension Request Submitted at the Same Time as the Serious Area
Attainment Plan
i. Summary of Proposal
    The EPA proposed to interpret the criterion under CAA section
188(e) that requires a state to have ``complied with all requirements
and commitments pertaining to that area in the implementation plan''
simply to mean that the state has implemented the control measures in
the SIP revisions it has submitted to address the applicable
requirements in CAA sections 172 and 189. For a Serious area attainment
date extension request being submitted contemporaneously with the
``original'' Serious area attainment plan for the area, the EPA
proposed to read CAA section 188(e) not to require the area to have a
fully approved attainment plan that meets the CAA's requirements for
Moderate areas. The EPA also proposed to read this provision not to bar
an extension if all or part of an area's Moderate area plan is
disapproved or has been promulgated as a FIP, provided the area has
complied with all of the requirements in the applicable FIP, or in the
applicable SIP and FIP.\189\
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    \189\ In Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d
826 (9th Cir. 2004), the court indicated that an area that had
previously failed to meet a requirement of the CAA could still be
eligible to receive an attainment date extension: ``Nowhere does the
provision limit extensions to those states that never made a misstep
in their efforts to comply with the Act.''
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ii. Final Rule
    Some commenters stated that an area should only be able to receive
an extension if the Moderate area plan had been fully approved by the
EPA. Other commenters agreed with the EPA's proposed approach. They
suggested that if a part of the Moderate plan had been disapproved, but
it was clear that the

area could not practicably attain by the Serious area attainment date,
then the area should be able to receive an extension. Other commenters
suggested that an area should not be deprived an extension if the
approval of all or part of the Moderate area attainment plan is delayed
due to logistical reasons or the EPA's inability to take final action
in a timely manner.
    The final rule does not require the area to have a fully approved
Moderate area plan when the attainment date extension request is
submitted at the same time as the Serious area plan. An extension is
allowed if the area is complying with all Moderate area requirements
and commitments pertaining to that area in the state's submitted
Moderate area implementation plan, but the plan does not need to be
fully approved by EPA. The EPA considers this to be a reasonable
interpretation of the statute because, as noted by commenters, there
may be various reasons why an area may not have a fully approved
Moderate area SIP by the time an extension request may be granted.
iii. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.
b. Extension Request Submitted After Submission of an ``Original''
Serious Area Attainment Plan
i. Summary of Proposal
    For a Serious area extension request that was submitted after
submission of an ``original'' Serious area attainment plan that
contained an attainment demonstration meeting the requirements of CAA
section 189(b)(1)(A)(i), the EPA proposed to read CAA section 188(e)
not to require the area to have a fully approved attainment plan that
meets the CAA's requirements for Serious areas, but to have a fully
approved Moderate area attainment plan. The EPA stated that this
proposed interpretation of this criterion would apply whether the area
was reclassified to Serious under the EPA's discretionary authority
(CAA section 188(b)(1)) or by operation of law upon failing to attain
by the Moderate area attainment date (CAA section 188(b)(2)).
    The proposal also requested comment on an ``alternative
interpretation'' that, as pointed out by some commenters, appears to
also have mistakenly required the same thing as the first option: That
the state would need to have a fully approved Moderate area attainment
plan in order to receive an extension.
    The EPA notes that Section VI.C of this preamble, Timing of
Extension Request Submission, also discusses this issue. It requested
comment on whether, for areas that had already submitted Serious area
attainment plans, it would be appropriate that the state must have
complied with all requirements and commitments in the area's initial
Serious area plan (the EPA's preferred option), or in the Moderate area
plan.
ii. Final Rule
    After considering the comments received on this issue, the EPA is
finalizing an approach that requires that, where a Serious area
attainment date extension is being submitted after the initial Serious
area attainment plan has been submitted, the state would need to
demonstrate that it was complying with all Serious area requirements
and commitments pertaining to the area in the plan it had initially
submitted. However, it would not need a fully approved Serious area
attainment plan. The EPA believes the state should not be prevented
from obtaining an attainment date extension in the event the EPA is
unable to take final action on a submitted plan in a timely manner. The
original proposal did not specify Serious area provisions implementing
this approach, but commenters noted the proposed analogous provisions
for Moderate areas seeking 1-year extensions, and suggested that EPA
should adopt a similar approach for Serious areas. Under this approach,
the state would not need a fully approved Serious area plan; it would
be able to receive an extension if it had already submitted the Serious
area plan but had not received EPA approval yet, and if it was
complying with all Serious area requirements and commitments pertaining
to the area in the state's implementation plan. The EPA also considered
an alternative option wherein the state would be able to receive an
extension only if it had a fully approved Serious area attainment plan.
The commenters did not favor this option, nor does the EPA.
iii. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.
3. Demonstration That the Plan Includes the MSM That Are Included in
the Implementation Plan of Any State, or Are Achieved in Practice in
Any State
    To qualify for any extension of a Serious area attainment date, CAA
section 188(e) requires a state to ``demonstrate to the satisfaction of
the Administrator that the plan for the area includes the most
stringent measures that are included in the implementation plan of any
state, or are achieved in practice in any state, and can feasibly be
implemented in the area.'' In its prior guidance in the Addendum, the
EPA interpreted the term ``most stringent measures'' (MSM) to mean the
maximum degree of emission reduction that has been required or achieved
from a source or source category in any other attainment plans or in
practice in any other states and that can feasibly be implemented in
the area seeking the extension, such as what LAER represents for new or
modified sources under the NNSR permit program.\190\
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    \190\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), at page 42010.
---------------------------------------------------------------------------

    a. Summary of Proposal. The proposal suggested that a state would
need to follow a process for determining MSM for a Serious
nonattainment area that is generally similar to proposed Option 2 for
BACM/BACT described in Section VI.D of this preamble, which would
include exemptions from MSM for sources in de minimis source categories
if such measures did not collectively advance the attainment date for
the area by at least 1 year. The EPA also proposed an alternative
approach for determining MSM for a Serious nonattainment area that
would provide for de minimis source category exemptions for MSM only
for those source categories that do not contribute significantly to
ambient PM2.5 concentrations in the Serious nonattainment
area, an approach more closely aligned with proposed Option 1 for
determining BACM/BACT.
    For each approach, the proposal described a five step process for
determining MSM: (1) Update the emissions inventories for the
nonattainment area; (2) identify de minimis source categories through
modeling; (3) identify potential MSM; (4) compare MSM to control
measures already adopted in the SIP for the nonattainment area; and (5)
adopt and implement any MSM that are more stringent than any measures
that are already approved into the SIP. The proposal requested comment
on whether the two proposed approaches are sufficiently consistent with
the agency's respective proposed

approaches to BACM/BACT determinations.
    b. Final Rule. Almost all comments received on this section
involved the issue of whether the rule should allow for de minimis
source categories to be exempted in the process of determining MSM. A
few commenters supported the identification of de minimis source
categories and their exemption from the MSM requirement. These
commenters were split in terms of their preference for the two de
minimis approaches that were presented. Some commenters suggested that
under any approach, an area could still exclude a measure from MSM
based on the inability to feasibly implement the measure in the area.
Some commenters stated that it would be too burdensome to require a
state to evaluate whether a particular source category had a
``significant'' or de minimis impact on air quality, while others
supported the approach. One group of commenters disagreed with the
notion that a Serious area could exempt de minimis sources from the MSM
requirement in the first place. They stated that de minimis exemptions
would not be appropriate for MSM, for which the CAA has expansive
language requiring the most stringent measures required in any SIP or
achieved in practice in any state.
    After considering the comments received on the de minimis source
category issue, the EPA is adopting a final rule that does not include
an explicit de minimis source category exemption in determining MSM.
The agency's reasons for not allowing a de minimis source category or
de minimis impact concept, articulated in prior sections on determining
RACM/RACT (Section IV.D) and BACM/BACT (Section VI.D), apply equally
here. Moreover, the EPA believes it would be particularly inappropriate
to allow for a de minimis source category approach for MSM. The statute
requires MSM to be implemented because the area is unable to attain the
standard within 10 years of designation and has a more severe air
quality problem. Congress clearly intended for such areas to more
widely explore potential control measure possibilities, and a de
minimis source category exclusion would be contrary to that intent.
    The EPA believes the rule provides sufficient flexibility in the
MSM area control measure analysis and attainment demonstration process
enabling states to identify sources that should not be subject to
control measures, including the ability to develop precursor
demonstrations to exclude precursors from control requirements, and to
consider case-specific factors in determining technological and
economic feasibility of potential control measures. If the final rule
were to include an explicit step to conduct a de minimis source
category analysis on the entire inventory early in MSM process, the EPA
also believes that there is a risk that such an analysis may bring
about investment of scarce time and analytical resources on analysis of
categories to exclude rather than on the identification of the most
stringent control measures necessary to attain the standard. As noted
in Section IV.D of this preamble on Moderate areas, and again in
[serious area section] the EPA also finds that from a technical
perspective, it would be very challenging to implement a de minimis
source category process in a consistent manner nationally without clear
guidelines describing how narrowly or how broadly a de minimis
exemption could apply to a ``source category,'' or how the technical
analysis would need to be performed. For all of these reasons, a de
minimis source category concept is not included in the final rule for
MSM.
    Process for determining MSM. The following sections describe the
process for determining MSM that is finalized in this rule: (a) Update
emissions inventories; (b) identify potential MSM; (c) compare MSM to
control measures already adopted in the SIP for the nonattainment area;
and (d) adopt and implement any MSM that are more stringent than any
measures that are already approved into the SIP. (See 40 CFR
51.1010(b)(1)-(4).)
i. Update Emissions Inventories
    The first step would be for the state to update as needed the
emissions inventory of direct PM2.5 and PM2.5
precursor sources and source categories in the Serious nonattainment
area required under CAA section 172(c)(3) for any attainment plan
submission. The EPA expects that the state would meet this inventory
requirement as part of its Serious area attainment plan submission
without any additional work if the state submits the Serious area
attainment date extension request simultaneously with the plan itself.
However, in the event the attainment date extension request is
submitted after the ``original'' Serious area attainment plan for the
area (i.e., toward the end of the Serious area attainment period), then
the state must submit a more recent, complete and accurate emissions
inventory that meets the same emissions inventory requirements for
Moderate and Serious PM2.5 nonattainment areas pursuant to
CAA section 172(c)(3), as well as an attainment projected inventory as
part of the new Serious area attainment plan for the area. The
inventories submitted to support a Serious area attainment plan must
also include point sources meeting the lower major stationary source
threshold in 40 CFR part 51, subpart A.
ii. Identify Potential MSM
    The second step in determining MSM involves identifying the
potentially MSM in other state implementation plans for
PM2.5 or other NAAQS, or that are used in practice in other
states for controlling emissions from sources similar to those listed
in the emissions inventory. This information can be obtained from a
number of sources, including state regulations on the books, state
summaries of control measures, state permitting databases, the RACT/
BACT/LAER Clearinghouse, and control measure compilations developed by
regional or state/local organizations. Elsewhere in this preamble, the
EPA recommends that a state identify potential measures for
consideration as RACM/RACT or BACM/BACT by evaluating control measures
implemented by other states to meet PM2.5 NAAQS or other
NAAQS. Thus, a state seeking to identify MSM should be able to start
its process using the work already undertaken for the nonattainment
area's RACM and BACM determinations and to make updates to the list of
potential control measures accordingly.
    For each measure, the state is required to determine its
technological and economic feasibility for sources in the area. States
should apply more stringent criteria for determining the feasibility of
potential MSM than that described for BACM and BACT in Section VI.D of
this preamble. In some situations, MSM could involve increasing the
coverage of measures that were already adopted and implemented as BACM
and BACT (for example, changing out an even greater percentage of
woodstoves in an area, if such sources were major contributors to the
air quality problem in the nonattainment area).
    However, because BACM and BACT represent the ``best'' level of
control feasible for an area, in some cases it may be possible for the
MSM requirement to result in no more controls and no more emissions
reductions in an area than result from the implementation of BACM and
BACT. Stated another way, there may be sources or categories for which
no other feasible controls exist beyond what a state has already
adopted as BACM or BACT. Given the strategy in the nonattainment
provisions of the CAA to offset longer attainment timeframes with more
stringent control requirements, the EPA therefore

interprets the MSM provision so as to increase the potential that it
will result in additional controls beyond the set of measures adopted
as BACM and BACT. In the MSM analysis, in addition to identifying
additional candidate MSM, the state is required to reanalyze any
measures that were rejected during the state's BACM and BACT analysis
for the area to see if they are now feasible for the area given the
potentially longer attainment date (up to 5 years after the statutory
Serious area attainment date), or given the changes that have occurred
in the interim that improve the feasibility of previously rejected
measures.
iii. Compare MSM to Control Measures Already Adopted in the SIP for the
Nonattainment Area
    The third step requires the state to compare the potential MSM that
have been identified for each source type or source category against
the measures, if any, already adopted into the Serious area SIP for
that source category to determine if such MSM would provide any
additional reductions. This comparison will be used in determining what
measures to adopt in the next step.
iv. Adopt and Implement Any MSM That are More Stringent Than Any
Measures That Are Already Approved Into the SIP
    The fourth step requires the adoption of any MSM that are more
stringent than existing measures as a regulation, and requires
submission of the regulation as part of the SIP, as well as expeditious
implementation of the regulation. For any measures that the state
determines cannot be feasibly implemented in the area, it should
provide a reasoned justification for rejecting the potential MSM.
    The EPA notes that CAA section 188(e) does not identify a deadline
for a state to implement MSM, whereas elsewhere the statute establishes
a deadline for implementing RACM and RACT and BACM and BACT [see CAA
sections 189(a)(1)(C) and 189(b)(1)(A)], respectively). However,
because the clear intent of CAA section 188(e) is to minimize the
length of a Serious area attainment date extension, the EPA requires
that the implementation of MSM must be as expeditious as practicable
but no later than 1 year prior to the alternate Serious area attainment
date identified by the state in its extension request.
    c. Comments and Responses. Any additional comments received on this
section are addressed in the Response to Comments document found in the
docket for this action.
4. Demonstration of Attainment by the Most Expeditious Alternative Date
Practicable
    Section 189(b)(1)(A) of the CAA requires that a Serious area plan
demonstrate attainment, using air quality modeling, by the most
expeditious date practicable after the statutory Serious area
attainment date. This demonstration is the final criterion that must be
met before the EPA may consider granting an extension. The agency's
determination of whether the plan provides for attainment by the most
expeditious date practicable would depend on whether the plan provides
for implementation of BACM and BACT by the statutory implementation
deadline and MSM as expeditiously as practicable. In no case would a
state be able to seek an extension of a Serious area attainment date to
a date more than 5 years past the statutory attainment date for Serious
areas. Section VI.E of this preamble describes the EPA's proposed
requirements for attainment demonstration modeling for Serious area
attainment plans.
5. Apply for an Attainment Date Extension
    The state would have to apply to the EPA for any extension of a
Serious area attainment date. The request would have to accompany an
attainment plan submission containing an attainment demonstration
showing attainment by the most expeditious alternative date
practicable, and the state would need to submit modeling as part of the
attainment demonstration in accordance with Section VI.E of this
preamble. Furthermore, the state would have to provide the public
reasonable notice and a public hearing on the attainment date extension
request before submitting it to the EPA, as the EPA would consider it
an integral part of the attainment demonstration and part of the
revised SIP submission which is subject to the requirements of the CAA
and federal regulations for public notice and hearing on SIP revisions.
6. Timing of Extension Request Submission
    The EPA has identified two potential Serious area attainment date
extension scenarios: (1) The more straightforward scenario where the
attainment date extension is included with the initial Serious area
plan, and (2) the scenario where a state may prepare and fully
implement a timely Serious area plan that includes a modeling analysis
that demonstrates the area would attain no later than the statutory
Serious area attainment date (the end of the tenth calendar year
following designation), and yet the state may see as the attainment
date nears that the Serious area will in fact fail to attain by its
projected attainment date. While the statute provides a remedy to be
instituted immediately upon failure of a Serious area to attain the
standard (through contingency measures and other measures stipulated in
CAA section 189(d)), the EPA also believes that the criteria of CAA
section 188(e) could be applied after a state submits a Serious area
attainment plan but prior to the area failing to attain (as long as the
area had not already been granted a prior Serious area attainment date
extension under CAA section 188(e)).
    In the first scenario, there is no need to specify any further
timing requirements beyond those previously described for Serious area
plan submission. However, for the second scenario the final rule needs
to specify a due date for the request. The EPA believes that it would
be acceptable for a state to submit a Serious area attainment date
extension request (as described earlier) together with a new Serious
area attainment plan meeting all of the statutory requirements that
apply to such plans. The state should submit the extension request and
new implementation plan to EPA as early as possible, but the final rule
requires that it must be submitted no later than 60 days prior to the
approved attainment date for the area or, in the absence of an approved
attainment date, no later than 60 days prior to the applicable
statutory attainment date for Serious areas (i.e., the end of the tenth
year after designation). See 40 CFR 51.1005(b)(6). The EPA believes
that this deadline is necessary due to its statutory obligation to
determine whether the area attained by the attainment date. In order to
preserve the possibility that EPA could review and take action on the
new attainment plan for the area and the accompanying attainment date
extension request prior to its deadline for making the attainment
determination the EPA estimates that the 60-day deadline provides the
minimum amount of necessary time. The EPA notes that during this time,
it would have to ascertain the status of compliance with all
requirements and commitments in the Moderate and initial Serious area
attainment plans for the area, evaluate the state's justification for
the selection of the alternate attainment date (including modeling),
and review provisions for the implementation of MSM).

VII. Requirements Under CAA Section 189(d) for PM2.5 Serious
Areas That Fail To Attain the NAAQS by the Applicable Attainment Date

    Background. In the event that a Serious area fails to attain the
PM2.5 NAAQS by the applicable attainment date, CAA section
189(d) requires that ``the state in which such area is located shall,
after notice and opportunity for public comment, submit within 12
months after the applicable attainment date, plan revisions which
provide for attainment of the . . . standard and, from the date of such
submission until attainment, for an annual reduction in PM10
or PM10 precursor emissions within the area of not less than
5 percent of the amount of such emissions as reported in the most
recent inventory prepared for such area.''
    In addition to the requirement for the submission of control
measures providing for a 5 percent reduction in emissions of certain
pollutants on an annual basis, the EPA interprets CAA section 189(d) as
requiring the State to submit an attainment plan that includes the same
basic statutory plan elements that are required for other attainment
plans. Because section 189(d) does not include a specific provision
specifying a new attainment date, the EPA relies on sections 179(d)(3)
and 172(a)(2) of the CAA to establish the attainment date for such
plans to be as expeditiously as practicable, and no later than five
years from the effective date of the EPA's determination that the area
failed to attain. Pursuant to those provisions, the Administrator may
also extend the attainment date to the extent the Administrator deems
appropriate, for a period no greater than 10 years from the effective
date of the EPA's determination that the area failed to attain,
considering the severity of nonattainment and the availability and
feasibility of pollution control measures. The state must submit as
part of the new attainment plan a justification explaining that it
represents an attainment date that is as expeditious as practicable.
    A state must submit to the EPA its plan to meet the requirements of
CAA section 189(d) in the form of a complete attainment plan submission
that includes the following elements: (i) Base year and attainment
projection year emissions inventory requirements; (ii) additional
attainment plan control strategy requirements, including control
measures and a demonstration that each year the area will achieve at
least a 5 percent reduction in emissions of direct PM2.5 or
a 5 percent reduction in emissions of a PM2.5 plan precursor
based on the most recent emissions inventory for the area; (iii)
attainment demonstration and modeling; (iv) RFP plan and quantitative
milestones; and (v) contingency measures. A state with a Serious
PM2.5 nonattainment area that fails to attain the NAAQS by
the applicable Serious area attainment date must also address any
statutory requirements relevant to Moderate nonattainment areas and
Serious nonattainment areas under CAA sections 172 and 189 of the CAA
that have not already been satisfied. These elements are discussed in
more detail in the following sections.

A. Plan Due Dates

1. Summary of Proposal
    The proposed rule indicated that under CAA section 189(d), the
state would be required to submit the attainment plan for a Serious
area that failed to attain the NAAQS by the Serious area attainment
date within 12 months after the applicable attainment date.
2. Final Rule
    The final rule remains unchanged from the proposal. Section 189(d)
of the CAA requires a state with a Serious PM10
nonattainment area that failed to attain the NAAQS by the applicable
Serious area attainment date to submit a new attainment plan submission
for the area within 12 months after the missed ``applicable attainment
date.'' The EPA finds that the most straightforward interpretation of
the statutory language is that the state must submit a new attainment
plan for the area--with all required elements--within 12 months after
the missed applicable attainment date. Although the EPA may take up to
6 months to make a determination that the area failed to attain, the
text of the statute ties the 12-month SIP due date to the missed
attainment date, not to the date that the EPA determines that the area
failed to attain. Because all attainment dates for implementation of
the PM2.5 NAAQS under subpart 4 are expressed in terms of
the end of a calendar year, the new due date for a SIP required under
CAA section 189(d) also would be due on December 31--of the year
following the area's Serious area attainment date. This requirement is
consistent with the manner in which the CAA section 189(d) SIP
submission date has been interpreted for implementation of the
PM10 NAAQS in the past. The EPA recognizes that this
statutory timeline is shorter than for Moderate or Serious area
attainment plans, but expects that, given the prior planning history
for such areas, much of the analyses to support these new attainment
plan submissions will be based on updates to previous analyses, which
would require less time than generating new analyses. In any event, it
is clear from the face of the statute that Congress intended that
states with areas that fail to attain the NAAQS by the outermost
statutory attainment date for Serious areas must proceed more quickly
to revise their SIPs to provide for attainment of the NAAQS.
3. Comments and Responses
    Any comments received on this section are addressed in the Response
to Comments document found in the docket for this action.

B. Emissions Inventory Requirements

1. Summary of Proposal
    The EPA also proposed that the inventory requirements under section
189(d) for Serious areas that fail to attain by the attainment date
should be the same as those for Moderate and Serious areas, but with a
change to the appropriate year for the inventory. The EPA proposed that
for these areas, the inventory year must be one of the 3 years from
which monitored data was used to determine that the area failed to
attain the PM2.5 NAAQS by the applicable Serious area
attainment date. In addition, the EPA proposed an alternative approach
that would allow the state to use an earlier year than one of the 3
years used to determine that the area failed to attain. As proposed,
this alternative approach would require written justification that
included an explanation of how the inventory modifications adequately
incorporate emissions reductions projected to be achieved through the
implementation of BACM and BACT, and additional feasible control
measures submitted with the original Serious area attainment plan for
the area, and through implementation of MSM if appropriate.
2. Final Rule
    The statute requires states to use an emissions inventory that
meets the requirements of section 172(c)(3). The final rule recommends
using an inventory for one of the 3 years for which air quality data
were used to determine that the area failed to attain in order to meet
this requirement. However it also allows the state to use an earlier
inventory year under certain circumstances.
    As with all other attainment plan submissions required for Moderate
and Serious PM2.5 nonattainment areas, a

state must develop its submission to meet CAA section 189(d) based on
``the most recent inventory prepared for such [nonattainment] area.''
This inventory must meet the same requirements that would apply to any
other emissions inventory submitted for a PM2.5
nonattainment area to meet the requirements of CAA section 172(c)(3),
which requires ``a comprehensive, accurate, current inventory of actual
emissions of the relevant pollutants'' in the nonattainment area.
Therefore this rule requires that the inventory submitted with an
attainment plan to meet CAA section 189(d) requirements must also meet
the EPA's regulatory requirements for such emissions inventories as
described earlier in this preamble under Section IV.B of this preamble
(for Moderate area attainment plans) and Section VI.B of this preamble
(for Serious area attainment plans).
    One important aspect of the emissions inventory required to be
submitted with an attainment plan under CAA section 189(d) is its role
as the basis for calculating the emissions reductions of direct
PM2.5 or any PM2.5 plan precursor necessary to
satisfy the 5 percent annual reduction criterion of CAA section 189(d).
For this reason, the ``most recent inventory'' for the area must not
only meet the criteria described for a base year inventory submitted
pursuant to CAA section 172(c)(3) and in Section VI.B of this preamble,
but it also must fully account for emissions reductions achieved to
date through the implementation of all RACM and RACT, BACM and BACT,
additional reasonable and feasible measures, and MSM (as applicable)
submitted with the Moderate and original Serious area attainment plans
for the area. In this way, the state will calculate the additional
reductions that the nonattainment area will need beyond those already
required in order to fulfill the requirements of CAA section 189(d) and
bring the area into attainment as expeditiously as practicable.
    To ensure that the inventory is representative of the nonattainment
problem in the area current at the time of the CAA section 189(d)
submission, the EPA strongly recommends that the inventory year be one
of the 3 years from which monitored air quality data were used to
determine that the area failed to attain the PM2.5 NAAQS by
the applicable Serious area attainment date. The EPA believes that
associating the inventory with one of these 3 years is reasonable in
light of the fact that some control measures (e.g., BACM and BACT
controls and additional feasible measures) for sources in the area may
not be implemented until the beginning of the attainment year. Thus,
using an emissions inventory for one of those 3 years will help ensure
that the inventory adequately captures the emissions reductions already
achieved through the prior implementation of control measures for
Moderate and Serious areas.
    The EPA recognizes that the timing and resource requirements for
inventory preparation may make it challenging in some cases for a state
to use an inventory for a year that is one of the 3 years from which
monitored data were used to determine that the area failed to attain
the NAAQS by the applicable attainment date. To address such cases, the
final rule allows states to use an earlier inventory year in the plan,
provided that (1) the year is selected in consultation with the
appropriate EPA Regional Office, and (2) the state provides a written
justification for selecting the earlier year in its SIP submission. See
51.1008(c)(1). At a minimum, the inventory must adequately incorporate
emissions reductions projected to be achieved through the
implementation of BACM and BACT, and additional feasible control
measures submitted with the original Serious area attainment plan for
the area, and MSM if appropriate. Because these emissions reductions
may have occurred after the inventory year the state intends to use,
adjustments to the original inventory for that year would need to be
made to reflect those reductions. The written justification must also
include an explanation of how those reductions have been incorporated
into the inventory. In considering use of an ``older'' inventory, the
EPA recommends that states weigh the possible impact of using an older
inventory that could have higher emissions than a more current
inventory. The state may be obligated to achieve a larger annual
emissions reduction to satisfy the 5 percent annual reduction criteria
of CAA section 189(d) than would otherwise be required if a newer
inventory were used with lower emissions.
3. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.

C. Pollutants To Be Addressed in the Plan

1. Summary of Proposal
    The proposed rule indicated that to determine what pollutants need
to be addressed in the attainment plan and 5 percent requirement in CAA
section 189(d), the state could provide a demonstration to the EPA
showing that a particular precursor does not significantly contribute
to PM2.5 levels that exceed the standard. The proposal
suggested that if the precursor demonstration is approved by the EPA,
then the state would not be required to evaluate or adopt control
measures for that precursor, nor would the state need to address the
precursor in meeting the 5 percent annual emissions reduction
requirement in section 189(d). The proposal indicated that Section III
of the preamble further discussed options describing optional precursor
demonstrations.
2. Final Rule
    The final rule remains relatively unchanged with respect to this
issue. Section 189(d) of the CAA requires states to develop a new
attainment plan for an area that failed to attain by the applicable
Serious area attainment date that provides for ``an annual reduction in
PM10 or PM10 precursor emissions within the area
of not less than 5 percent of the amount of such emissions'' reported
in the latest emissions inventory for the area. In Section III of this
preamble, the EPA describes optional approaches by which a state could
demonstrate that a PM2.5 precursor does not contribute
significantly to PM2.5 levels that exceed the standard in
the area, and thereby would not need to adopt control measures for that
precursor in the area. The EPA also interprets the CAA generally to
allow a state to provide such a ``precursor demonstration'' for the
attainment plan required under section 189(d), even if the area has
previously failed to attain the relevant NAAQS by the applicable
Serious area attainment date. If the state has provided a demonstration
with the previous Serious area attainment plan to establish that a
precursor does not significantly contribute to PM2.5 levels
for purposes of the attainment plan for the area, and it seeks to
maintain the status of that precursor as not significantly contributing
to PM2.5 levels in the area, the state would still need to
provide an updated precursor demonstration for the new section 189(d)
SIP because emissions and atmospheric conditions will have changed
since the previous demonstration was submitted, and the conclusions
from any previous precursor demonstration may no longer be appropriate.
See Section III of this preamble for more information about potential
precursor demonstrations that could be conducted to show that a
particular precursor does not contribute

significantly to PM2.5 levels that exceed the standard.
3. Comments and Responses
    Any comments received on this section are addressed in the Response
to Comments document found in the docket for this action.

D. Attainment Plan Control Strategy

1. Background
    As for other PM2.5 NAAQS attainment demonstrations, the
overarching requirement for the CAA section 189(d) control strategy is
that it needs to provide for attainment of the standard as
expeditiously as practicable. The strategy must include any additional
measures (beyond those already adopted in previous SIPs for the area as
RACM/RACT, BACM/BACT, MSM (if applicable), for example) that are needed
for the area to attain expeditiously. The plan must also demonstrate
that the new attainment plan will at a minimum achieve an annual 5
percent reduction in emissions of direct PM2.5 or any
PM2.5 plan precursor from sources in the area, based on the
most recent emissions inventory for the area. However, it is important
to emphasize that a CAA section 189(d) plan must require other control
measures (even if beyond those sufficient to meet the annual 5 percent
reduction requirement) that are needed in order to meet the overarching
goal of attaining the standard as expeditiously as practicable.
2. 5 Percent Annual Reduction in Direct PM2.5 or Any
PM2.5 Plan Precursor
    a. Summary of Proposal. Section 189(d) of the CAA requires an
``annual reduction in PM10 or PM10 precursor
emissions within the area of not less than 5 percent of the amount of
such emissions as reported in the most recent inventory prepared for
such area.'' Because the statute is ambiguous with regard to how this
language should apply for the PM2.5 NAAQS, the EPA proposed
two options for interpreting this provision. One option interpreted
this language to require a 5 percent annual reduction in all pollutants
that contribute to PM2.5, meaning direct PM2.5
and the four precursors (SO2, NOX, VOC, and
ammonia), or those precursors that are necessary to control in the
area. A second option interpreted the language more literally, meaning
that it required a 5 percent annual reduction of either direct
PM2.5 or PM2.5 precursor emissions on an annual
basis, and that a state could elect to control either direct
PM2.5 or PM2.5 precursor emissions in a given
year. (Note that under either proposed option, a precursor still could
be excluded from control requirements if the state submitted a new
precursor demonstration as part of the revised CAA section 189(d)
implementation plan showing that the precursor does not contribute
significantly to levels that exceed the relevant PM2.5
NAAQS, and such demonstration is approved by the EPA).
    b. Final Rule. One group of commenters supported the inclusion of
direct PM2.5 and all precursors in the calculation of the
annual emission reduction requirement because precursors typically play
a significant role in PM2.5 formation, and they believed
that allowing states to be able to pick and choose which pollutants to
reduce would undermine efforts to attain most expeditiously. Other
commenters supported the second option because they believe it follows
a plain reading of the statute (i.e., it uses the word ``or''), and
because it would allow a state to devote resources toward achieving
emissions reductions in those pollutants that are most effective in
reducing PM2.5 concentrations and thus in attaining the
NAAQS most expeditiously.
    After considering comments on this issue, the EPA agrees that the
second option is the more appropriate reading of the statute. When
paired with the overarching requirement for the area to reach
attainment of the NAAQS as expeditiously as practicable, and with
provisions in the rule allowing a state to demonstrate that a precursor
does not provide a significant contribution to PM2.5 levels,
the EPA believes that such an interpretation is reasonable and would
authorize states to focus emission reduction efforts on those
pollutants that will be most effective for purposes of attainment in a
given area. For example, interpreting the statutory provision to
require emissions reductions in a specific precursor merely for
purposes of meeting a 5 percent requirement, without regard to whether
the reductions would be effective for purposes of attainment, could be
counterproductive to reducing the emissions of other pollutants that
could result in earlier attainment. This interpretation of CAA section
189(d) is also consistent with past EPA actions for an area that failed
to attain the PM10 Serious area attainment date.\191\
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    \191\ For example, see 69 FR 30006 (May 26, 2004). Approval and
Promulgation of Implementation Plans for California-San Joaquin
Valley PM-10 Nonattainment Area; Serious Area Plan for Attainment of
the 24-Hour and Annual PM-10 Standards.
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    Thus, in applying the statutory language to implementation of the
PM2.5 NAAQS in the final rule, the EPA interprets an
``annual reduction in PM10 or PM10 precursor
emissions within the area of not less than 5 percent of the amount of
such emissions'' to mean that an attainment demonstration for a Serious
area that failed to attain by the attainment date must include control
measures providing for a 5 percent annual reduction in direct
PM2.5 emissions or in the emissions of any PM2.5
plan precursor. The EPA considered whether the statutory phrase
``precursor emissions'' requires a 5 percent reduction of each
individual plan precursor in each year, but determined that such an
interpretation was unnecessarily restrictive in light of the
overarching requirement for states to adopt the control measures that
will result in attainment as expeditiously as practicable, and is not
compelled by the wording of the 5 percent requirement in the statute.
Accordingly, the final rule requires an annual reduction of either
direct PM2.5 or any single PM2.5 precursor.
    Because this requirement is an annual one, the final rule also
authorizes the state to meet the 5 percent requirement to vary between
direct PM2.5 and PM2.5 precursors, or among
precursors, from year to year throughout the duration of the section
189(d) attainment plan, so long as the attainment plan provides for
expeditious attainment and meets the other applicable attainment plan
requirements. For example, in year 1 a state could provide for a 5
percent reduction of direct PM2.5, and in year 2 could
provide for a 5 percent reduction in a precursor, and so on.
    c. Comments and Responses. Comment: Some commenters suggested that
a more appropriate approach would be to require a 5 percent annual
reduction in PM2.5 ambient concentrations (rather than in
pollutant emissions), and allow the state to meet this air quality
target with any combination of emissions reductions.
    Response: The EPA does not find that this approach would be
consistent with the statutory language in CAA section 189(d), which
clearly expresses the requirement in terms of emissions reductions
(i.e., ``annual reduction in PM10 or PM10
precursor emissions within the area of not less than 5 percent of the
amount of such emissions as reported in the most recent inventory
prepared for such area.'') Moreover, the EPA is concerned that this
approach would necessitate, on an annual basis, a complex modeling
analysis or at the very least some other analytical approach to
translate emissions to

ambient concentrations. The burdens of such analysis could be
significant, and it is unclear what benefit would be realized from such
an approach. States are already obligated to provide a modeled
attainment demonstration as part of the new SIP submission to meet the
requirements of section 189(d), and the 5 percent requirement is a
separate requirement that the statute explicitly imposes in addition to
that modeled attainment demonstration. For these reasons, the EPA is
not adopting the commenter's suggested air quality approach in the
final rule.
3. Calculating the 5 Percent Annual Reductions
    a. Summary of Proposal. The proposed rule provided an example of
how annual reductions would be tracked under this provision, and it
also provided another example describing how reductions in excess of
the 5 percent requirement in 1 year could be ``carried forward'' to
help meet the requirement in a future year.
    b. Final Rule. The previous section 2 explains that the EPA
interprets the statute to require a 5 percent annual reduction in
direct PM2.5 emissions or in the emissions of any one
PM2.5 plan precursor in each year, until attainment. The
requisite minimum 5 percent emissions reduction level for any pollutant
must be calculated from the total emissions of the pollutant contained
in the most recent inventory for the area, as described earlier in this
section. The requirement for a 5 percent annual reduction in any one
pollutant, calculated based on the emissions levels in the most recent
inventory, must then be achieved every year between the CAA section
189(d) plan submission date and the new projected attainment date for
the area.
    For example, assume it is 2026, and based on monitoring data from
years 2023-2025, a Serious area has failed to attain the 2012
PM2.5 NAAQS within 10 years of designation. Assume also that
the most recent inventory available for an area subject to CAA section
189(d) is for the year 2023. This inventory would serve as the base
inventory for determining the 5 percent emissions reduction requirement
under CAA section 189(d). If the state elects to reduce direct
PM2.5 emissions each year of the plan (i.e., instead of
choosing to reduce a precursor), and the most recent inventory (``base
inventory'') indicates that emissions of direct PM2.5 from
all sources in the area are 10,000 tons/year, then the area at a
minimum would need to reduce emissions of direct PM2.5 by 5
percent of the 2023 base inventory, or 500 tons, each year until the
area attains the NAAQS. Thus, in the first year following submission of
the CAA section 189(d) plan for the area, emissions of direct
PM2.5 could not exceed 9500 tons/year; in the second year,
emissions could not exceed 9000 tons/year; and so forth. Note that if
the area needs emissions reductions beyond this amount (i.e., in direct
PM2.5 or in PM2.5 plan precursors) in order to
meet the overarching requirement of attaining the standard as
expeditiously as practicable, then it must adopt and implement such
control measures.\192\
---------------------------------------------------------------------------

    \192\ See Section IV.D.3 of this preamble for a discussion on
sources of information for control measures.
---------------------------------------------------------------------------

    Although CAA section 189(d) requires that a state develop measures
that will obtain annual emissions reductions of ``not less than 5
percent'' from the most recent inventory, the EPA interprets this
language to authorize states to maximize emissions reductions in
earlier years and still meet the 5 percent per year requirement for
subsequent years. The EPA notes that interpreting the statute in this
way will encourage states to implement measures earlier, where
possible, rather than delay implementation of measures merely to assure
that the 5 percent requirement can be met in later years. Thus, using
the example described earlier, the annual reduction requirement for the
area would be 500 tons/year from a base year emissions level of 10,000
tons/year. The required level after year 1 would be 9500 tons/year,
after year 2 the level would be 9000 tons/year, and so on. If the area
reached a level of 8100 tons/year by the end of year 3, then by the end
of year 4 it would only need to reduce emissions by 100 tons/year to
yield an emissions level of 8000 tons/year. Thus, this approach will
allow states to carry forward any emissions reductions beyond the
required minimum 5 percent in a given year to the next year as a means
to encourage states to achieve emissions reductions as quickly as
possible, as long as those emissions reductions are realized after the
Serious area attainment date.\193\
---------------------------------------------------------------------------

    \193\ 69 FR 30006 (May 26, 2004).
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    The previous example addresses a situation where the state chooses
to reduce only direct PM2.5. In that example, the 5 percent
annual reduction amount for any year would be 5 percent of the 2023
PM2.5 emission inventory amount of 10,000 tons. The final
rule allows the state to meet its 5 percent reduction each year in
terms of reducing direct PM2.5 or any PM2.5 plan
precursor. Thus, if the area had a 2023 emission inventory that
included 5000 tons of each of the four PM2.5 precursors, and
if the state chose to meet its ``5% reduction'' obligation in a
particular year by reducing SO2, it would need to achieve
emissions reductions of 250 tons of SO2 in that year.
    The EPA is also clarifying its interpretation of the statutory
language under CAA section 189(d) that requires a state to submit a new
attainment plan to achieve annual reductions ``from the date of such
submission until attainment,'' to mean annual reductions beginning from
the due date of such submission until the new projected attainment date
for the area based on the new or additional control measures identified
to achieve at least 5 percent emissions reductions annually. This
clarification is intended to make clear that even if a state is late in
submitting its CAA section 189(d) plan, the area must still achieve its
annual 5 percent emissions reductions beginning from the date by which
the state is required to make its CAA section 189(d) plan submission,
not by some later date. Because attainment dates for PM2.5
nonattainment areas established under subpart 4 occur at the end of the
calendar year, any CAA section 189(d) plan, which is required within 12
months of the missed attainment date for the area, would also be due by
the end of the calendar year.
    c. Comments and Responses. Any additional comments received on this
section are addressed in the Response to Comments document found in the
docket for this action.
4. Additional Guidance on CAA Section 189(d) Control Measures
    The EPA believes that an appropriate starting point for a state to
identify measures to provide for attainment and to meet the requisite
minimum 5 percent annual emissions reductions of direct
PM2.5 and PM2.5 precursors is the list of
potential control measures initially required to be identified as part
of the RACM and RACT determination process, the BACM and BACT
determination process, or the MSM determination process (if
appropriate) for the area. The EPA anticipates that a state should be
able to rely on much of the work it previously undertook to develop
this list of potential control measures and analyze their technological
and economic feasibility, and the time required to implement them.
Control measures that the state identified but did not previously adopt
may be likely measures for inclusion in an attainment plan to meet the
requirements of section 189(d). However, for purposes of meeting the
requirements of CAA section 189(d), the

EPA recommends that the state first identify any additional potential
measures not previously identified for the area, and then analyze any
new or additional measures that the state has not already adopted in a
previous attainment plan for the area.
    In addition, a state may include in the CAA section 189(d) plan
control strategy for the area any control measures triggered as
contingency measures after the area failed to attain the
PM2.5 NAAQS by the applicable attainment date. In order to
be included as control measures that will help the area meet its
requisite minimum 5 percent reductions in direct PM2.5
emissions or in emissions of any one PM2.5 plan precursor,
such measures would have to meet the same requirements as all other
approvable control measures for being quantifiable, enforceable,
replicable and accountable. The EPA believes that reliance on triggered
contingency measures may be appropriate given the short timeline
provided for in the statute for states to revise and submit their SIP
revisions (12 months from the missed attainment date) and the fact that
the contingency measures included in the prior attainment plan for the
area under CAA section 172(c)(9) must be activated once the EPA
publishes its finding of the area's failure to attain the NAAQS by the
applicable attainment date. As explained previously, however, the EPA
interprets the statute to require that any new 189(d) submission must
meet all the statutory requirements applicable to all submissions,
including the requirement to identify contingency measures. Thus, if
contingency measures from the Serious area attainment plan are relied
on in the new attainment demonstration as part of the control strategy,
then the state must submit additional contingency measures for the CAA
section 189(d) attainment plan. See 40 CFR 51.1003(c)(1)(vii).
5. Control Strategy Submission Requirements
    To ensure that attainment plan submissions contain the necessary
supporting information for the EPA to review and approve the state's
new control strategy to achieve at least 5 percent annual reductions in
emissions of direct PM2.5 or any PM2.5 plan
precursor, the final rule requires that a state must submit information
about the new control strategy for an area subject to section 189(d) in
a manner consistent with the requirements described in section VI.D.3.
    As with other PM2.5 attainment plan submissions, the EPA
believes that it is incumbent on the state to ensure that the
information needed for the EPA to evaluate the state's analysis of new
control measures--which in the case of 189(d) plans is also needed to
achieve annual 5 percent reductions--is presented separately as part of
the control strategy analysis, and in a format that provides
transparency, consistency and the ability for another party to evaluate
the state's analysis effectively and to duplicate the state's results.
For this reason, the EPA is including the CAA section 189(d) plan base
year emissions inventory information as a necessary part of the control
strategy submission and as one element of the state's CAA section
189(d) plan due 12 months after the missed attainment date for the
area. In addition, the state must provide information as part of any
attainment plan submitted to meet the requirements of CAA section
189(d) consistent with the criteria described in Section VI.D.5 of this
preamble to ensure that a state adopts effective regulations to
implement the control measures identified as being needed to meet those
requirements. Specifically, all control measures must be quantifiable,
enforceable, replicable and accountable.

E. Modeling for Attainment Demonstrations

    Section 189(d) of the CAA requires a state with a Serious
nonattainment area that failed to attain the relevant NAAQS by the
applicable Serious area attainment date to submit a new attainment plan
for such area within 12 months after the missed attainment date. The
same general requirements for attainment demonstrations and modeling
that apply to Moderate area plans and Serious area plans due under CAA
sections 189(a) and 189(b) should also apply to CAA section 189(d)
attainment plans. However, the EPA is including additional requirements
in the final rule specific to plans submitted pursuant to CAA section
189(d), as described in the following sections.
1. Attainment Demonstrations for Serious Areas That Fail To Attain the
NAAQS by the Applicable Attainment Date
    a. Summary of Proposal. The EPA proposed attainment demonstration
modeling requirements for Serious areas that fail to attain the NAAQS
by the applicable attainment date. See Section VI.E of this preamble,
for more details on Serious area attainment demonstrations.
    b. Final Rule. The final rule requirements are unchanged from the
proposal with respect to this requirement. Attainment demonstrations
for Serious areas subject to CAA section 189(d) requirements must
consist of: (i) Technical analyses such as base year and future year
modeling of emissions that identify sources and quantify their
emissions that are contributing to violations of the PM2.5
NAAQS; (ii) analyses of future year projected emissions reductions and
air quality improvement resulting from national, regional and local
programs already implemented as part of previous Moderate and/or
Serious area attainment plans for the area (including reasonable
control measures, BACM and BACT and additional feasible measures), and
(iii) additional measures needed for expeditious attainment, including
measures needed to achieve 5 percent emissions reductions on an annual
basis. Each state with a nonattainment area subject to the requirements
of CAA section 189(d) must submit an attainment plan with an attainment
demonstration that includes analyses supporting the state's
determination of its proposed new attainment date. In all cases, the
state must show that the area will attain the NAAQS as expeditiously as
practicable.
    c. Comments and Responses. Any comments received on this section
are addressed in the Response to Comments document found in the docket
for this action.
2. Air Quality Modeling Required for Serious Areas Subject to the
Requirements of CAA Section 189(d)
    a. Summary of Proposal. The EPA proposed that states are required
to submit air quality modeling in support of an attainment
demonstration for a nonattainment area subject to the requirements of
CAA section 189(d).
    b. Final Rule. The final rule requirements are unchanged from the
proposal with respect to this issue. States are required to submit air
quality modeling in support of an attainment demonstration for a
Serious nonattainment area subject to the requirements of CAA section
189(d). The modeling demonstration must show how and when the area will
attain the NAAQS. Other than the timing of plan submissions and
requirement to achieve 5 percent emissions reductions in direct
PM2.5 or any PM2.5 plan precursor, the relevant
air quality modeling procedures and guidance for all PM2.5
nonattainment area plans are the same. See Sections IV.E. and VI.E of
this preamble for more details on proposed modeling requirements and
guidance for Moderate and Serious PM2.5 nonattainment areas,
respectively.
    c. Comments and Responses. Any comments received on this section
are

addressed in the Response to Comments document found in the docket for
this action.
3. Future Year(s) To Be Modeled in Attainment Demonstrations
    a. Summary of Proposal. The EPA proposed that a state performing a
modeling analysis for a plan submitted under CAA section 189(d) must
select a future modeling year such that all emissions control measures
relied on for attainment will have been implemented by the beginning of
that calendar year. To demonstrate attainment, the modeling results for
the nonattainment area must predict that emissions reductions
implemented by the beginning of the last calendar year preceding the
attainment date will result in PM2.5 concentrations that
meet the level of the standard.
    b. Final Rule. As discussed more fully in Section VII.I of this
preamble, the EPA must establish a new attainment date for a
PM2.5 nonattainment area subject to CAA section 189(d) and
must do so according to the provisions of CAA sections 179(d)(3) and
172(a)(2), which require that the new attainment date must be as
expeditious as practicable, but no later than 5 years from the date of
publication in the Federal Register of the EPA's determination that the
area failed to attain the relevant NAAQS. In addition, the EPA may
extend the attainment date by up to 5 additional years (thus up to 10
years from the date of publication of the notice of finding of failure
to attain by the applicable attainment date for the area) if the EPA
deems it appropriate ``considering the severity of nonattainment and
the availability and feasibility of pollution control measures.''
    For purposes of determining the attainment date that is as
expeditious as practicable, the state must conduct future year modeling
that takes into account emissions growth, known controls (including any
controls that were previously determined to be RACM and RACT, BACM and
BACT, and MSM if appropriate, for the area), the 5 percent per year
emissions reductions required by CAA section 189(d), plus any other
emissions controls that are needed for expeditious attainment of the
NAAQS. A state performing a modeling analysis for a plan submitted
under CAA section 189(d) must select a future modeling year such that
all emissions control measures relied on for attainment will have been
implemented by the beginning of that year. To demonstrate attainment,
the modeling results for the nonattainment area must predict that
emissions reductions implemented by the beginning of the last calendar
year preceding the attainment date will result in PM2.5
concentrations that meet the level of the standard.\194\
---------------------------------------------------------------------------

    \194\ Note that for purposes of the PM2.5 NAAQS, a
determination of attainment (or failure to attain), which the EPA is
required to make after the attainment date has passed, is based on
an average of the most recent 3 years of ambient data prior to the
area's attainment date.
---------------------------------------------------------------------------

    For a PM2.5 nonattainment area subject to CAA section
189(d), the state must adopt any control measures necessary to
demonstrate expeditious attainment within 5 years of the area failing
to attain the NAAQS by the applicable Serious area attainment date.
    c. Comments and Responses. Any comments received on this section
are addressed in the Response to Comments document found in the docket
for this action.
4. Attainment Year Motor Vehicle Emissions Budgets
    As with all other PM2.5 NAAQS attainment plans, the
transportation conformity rule requires that attainment plans for areas
subject to CAA section 189(d) establish motor vehicle emissions budgets
for the area's attainment year. Therefore, for such an area, the state
would first determine the new attainment date as described in Section
VII.I of this preamble. Once an area's attainment date has been
established, the state would establish motor vehicle emissions budgets
for direct PM2.5 and any relevant PM2.5 precursor
for the attainment year.\195\ A motor vehicle emissions budget for the
purposes of a PM2.5 attainment plan is that portion of the
total allowable emissions within the nonattainment area allocated to
on-road sources as defined in the submitted attainment plan.\196\ Such
motor vehicle emissions budgets would be calculated using the latest
planning assumptions and the latest approved motor vehicle emissions
model available at the time that the attainment plan is developed,
unless the EPA approves the state's use of an alternative model.\197\
---------------------------------------------------------------------------

    \195\ For more information on PM2.5 precursor
requirements, see CAA section 93.102(b)(2)(iv) and (v) of the
transportation conformity rule. See also the May 6, 2005, final
transportation conformity rule that addressed requirements for
PM2.5 precursors. (70 FR 24280).
    \196\ A state would also establish motor vehicle emissions
budgets for an area's attainment year. Those budgets would be the
motor vehicle emissions that the SIP establishes as being necessary
to attain the NAAQS.
    \197\ If an area includes re-entrained road dust in the motor
vehicle emissions budget, the latest approved version of AP-42
should be used unless the EPA has approved an alternative model for
the area.
---------------------------------------------------------------------------

F. RFP Requirements

1. Specific Requirements
    a. Summary of the Proposal. The EPA proposed to determine that a
state has satisfied the RFP requirement if the state submits an
approvable control strategy under CAA section 189(d) that demonstrates
that the state will achieve at least 5 percent reductions in direct
PM2.5 or PM2.5 precursor emissions from sources
in the area annually until attainment. Additionally, the EPA proposed
that motor vehicle emissions budgets must also be established as part
of any RFP plan for direct PM2.5 and for any relevant
PM2.5 plan precursor using the latest planning assumptions
and the latest approved motor vehicle emissions model available at the
time that the plan is developed for a Serious area subject to
189(d).\198\
---------------------------------------------------------------------------

    \198\ Ibid.
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing RFP requirements for
attainment plans required pursuant to CAA section 189(d) that are
similar to other Serious area RFP requirements discussed in section
VI.F of this preamble. The EPA is providing similar guidance regarding
how to prepare an RFP analysis, RFP projected emissions, geographic
coverage of emission sources for RFP, and RFP requirements for multi-
state nonattainment areas.
    The RFP analysis must contain appropriate information to
demonstrate that the state will achieve the emissions reductions from
the control strategy necessary to result in generally linear reductions
in emissions and provide for expeditious attainment as discussed in
Section VII.D of this preamble. As with other Serious area RFP
analyses, the state may consider PM2.5 plan precursor
emissions reductions in the aggregate for RFP purposes in a 189(d)
area.
    The state's RFP analysis must include three components: (1) An
implementation schedule for control measures on sources in the
nonattainment area, (2) RFP projected emissions for each applicable
quantitative milestone year (discussed in Section VII.G of this
preamble), based on the anticipated control measure implementation
schedule; and (3) an analysis that demonstrates that this schedule of
aggregate emissions reductions achieves sufficient progress toward
attainment between the applicable baseline year to the attainment year.
For additional discussion of each of the components of the RFP
analysis, refer to Section IV.F of this preamble. See 40 CFR
51.1012(a).
    In the proposal, the EPA proposed an option to require at least 5
percent

emissions reductions in direct PM2.5 and all
PM2.5 plan precursor from sources in the area annually until
attainment to meet the separate RFP requirement for attainment plans.
However, some commenters did not agree that EPA should consider an area
meeting the 5 percent requirement under CAA section 189(d) to
automatically have satisfied the RFP requirement. The EPA agrees with
this comment and is therefore not finalizing an approach to the RFP
requirement that is tied to the 5 percent requirement. Instead, the
final RFP requirement will be tied to progress toward expeditious
attainment (which the EPA recommends should be generally linear but may
also be stepwise with appropriate justification), just as it is for all
other types of Moderate and Serious area plans for PM2.5 as
summarized in the previous paragraph. The emissions reductions that a
state achieves for purposes of meeting the 5 percent requirement may
also be counted towards meeting the separate RFP requirement, but the
EPA does not believe that meeting the 5 percent requirement would
automatically equate to meeting the RFP requirement. That determination
requires the separate evaluations required for the RFP analysis.
    The EPA requires that the applicable baseline year for the RFP
analysis must be the same year as that represented by the latest base
year inventory for the Serious area. The projected attainment date
should be as expeditiously as practicable and is discussed further in
Section VII.I of this preamble. The RFP analysis must clearly convey
how the schedule for implementing the control strategy will provide for
generally linear or stepwise progress towards attainment. If stepwise
progress is more appropriate for the specific nonattainment area, the
state is required to submit a clear rationale and supporting
information to explain why generally linear progress towards attainment
in the area is not appropriate (e.g., due to the nature of the
nonattainment problem, the types of sources contributing to
PM2.5 levels in the area, and the ability to perform timely
implementation of control measures). Further, if a stepwise approach is
needed, this does not relieve the state of the requirements of CAA
section 189(d). As stated earlier, the EPA requires that a section
189(d) plan must include in its RFP analysis the anticipated emissions
reductions expected to be achieved through the implementation of
control measures required by the control strategy described in Section
VII.D of this preamble. Further, the optional air quality analysis
discussed in Section IV.F of this preamble is also available for use by
a state preparing a section 189(d) plan.
    Additionally, the EPA requires states to establish motor vehicle
emissions budgets for direct PM2.5 and PM2.5 plan
precursors using the latest planning assumptions and the latest
approved motor vehicle emissions model available at the time that the
189(d) plan is developed.\199\ See 40 CFR 51.1012(a).It is also
important to note that if a section 189(d) area is multi-state or
multi-jurisdictional, the states or jurisdictions comprising the area
must provide a coordinated approach to meeting the RFP requirement for
the shared area. For further information, see Section IV.F.5 of this
preamble. See 40 CFR 51.1012(b).
---------------------------------------------------------------------------

    \199\ If an area includes re-entrained road dust in the motor
vehicle emissions budget, the latest approved version of AP-42
should be used unless the EPA has approved an alternative model for
the area.
---------------------------------------------------------------------------

    c. Comments and Responses. Any additional comments received on RFP
are addressed in the Response to Comments document found in the docket
for this action.

G. Quantitative Milestones

1. Specific Requirements
    a. Summary of the Proposal. The proposal indicated that
quantitative milestones would need to be achieved every 3 years until
the area attains the relevant NAAQS, similar to proposed requirements
for Moderate area plans and other types of Serious area plans. In the
proposal, the EPA stated that, at a minimum, quantitative milestones
selected for an attainment plan submitted under CAA section 189(d)
would need to demonstrate a reduction of at least 15 percent (i.e., 5
percent for each year in the 3-year period) in emissions of direct
PM2.5 and PM2.5 plan precursors below those
emissions reported in the most recent inventory for the area. The
proposal identified requirements for direct PM2.5 and
precursors, to be consistent with the RFP proposal. The EPA proposed
that attainment plans developed pursuant to CAA section 189(d) would
have to contain quantitative milestones beginning at 13.5 years or 16.5
years from designation (depending on whether the section 189(d) plan
would be due before or after the 13.5 year mark), and every 3 years
thereafter until the attainment date for the area.
    The EPA also proposed that the requirements for quantitative
milestones, described in Section VI.G of this preamble, should also
apply to quantitative milestones submitted with any revised Serious
area attainment plan pursuant to CAA section 189(d).
    b. Final Rule. The revised attainment plan for any Serious
nonattainment area that fails to attain the relevant PM2.5
NAAQS by the applicable attainment date must include quantitative
milestones pursuant to CAA section 189(c). These quantitative
milestones should track the progress being made in the nonattainment
area in the implementation of specific control measures in the SIP, and
may potentially be in the form of metrics for tracking air quality
improvement or emissions reductions over time. The EPA wishes to
clarify that the quantitative milestones for a section 189(d) plan are
designed to track RFP, not solely to track progress in achieving the
minimum 5 percent annual emission reduction requirement in this section
of the CAA. The RFP discussion in the previous section noted that in
some cases, the state may need to adopt additional emission reduction
measures (beyond those existing or new measures that will meet the 5
percent emission reduction requirement) in order for the plan to meet
the overarching requirement to attain the standard as expeditiously as
practicable. Thus, the RFP plan and quantitative milestones must be
designed to track progress based on the overall set of control measures
needed for expeditious attainment.
    The quantitative milestones need to be achieved every 3 years until
the area attains the relevant NAAQS. Therefore, at a minimum, the final
rule requires that quantitative milestones selected for an attainment
plan submitted under CAA section 189(d) need to track progress in the
implementation of control measures required to achieve RFP in emissions
reductions of direct PM2.5 and/or all PM2.5 plan
precursors described in the previous section. The CAA section 189(d)
plan must contain quantitative milestones to be achieved every 3 years,
beginning with a milestone at either 13.5 years or 16.5 years from the
area's date of designation. If the attainment plan is due prior to a
date 13.5 years from designation of the area, then the plan shall
contain milestones to be achieved by no later than a milestone date of
13.5 years from the date of designation of the area, and every 3 years
thereafter, with the final milestone being the first 3-year milestone
date falling after the applicable attainment date. If the attainment
plan is due later than a date 13.5 years from designation of the area,
then the plan shall contain milestones to be achieved by no later than
a

milestone date of 16.5 years from the date of designation of the area,
and every 3 years thereafter, with the final milestone being the first
3-year milestone date falling after the applicable attainment date. See
40 CFR 51.1013(a)(3).
    The EPA is also finalizing that the requirements for quantitative
milestones described in Section VI.G of this preamble shall also apply
to quantitative milestones submitted with any revised attainment plan
pursuant to CAA section 189(d), including but not limited to, the
construction, content, reporting requirements and a quantitative
milestone that specifically tracks implementation of control measures
identified in the plan to attach the standard as expeditiously as
practicable. See 40 CFR 51.1013(a)(3).
    c. Comments and Responses. Any additional comments received on
quantitative milestones are addressed in the Response to Comments
document found in the docket for this action.

H. Contingency Measures

1. Summary of the Proposal
    The EPA proposed that contingency measures for attainment plans
under CAA section 189(d) for Serious areas that fail to attain the
NAAQS by the applicable attainment date must meet the same criteria as
contingency measures for a Serious area attainment plan outlined in
Section VI.H of this preamble. The EPA also proposed that the
contingency measures should achieve approximately 1 year's worth of
emissions reductions.
2. Final Rule
    All PM2.5 attainment plans, including plans for areas
subject to CAA section 189(d), must contain contingency measures that
are consistent with CAA section 172(c)(9). Section VI.H of this
preamble describes the EPA's criteria for contingency measures for a
Serious area attainment plan, and contingency measures for a section
189(d) plan must meet the same criteria. The final rule reiterates the
EPA's longstanding policy that contingency measures should provide for
emissions reductions approximately equivalent to 1 year's worth of
reductions needed for RFP.
    The statutory contingency measure requirement at CAA section
172(c)(9) is not superseded or subsumed by any requirement under
subpart 4. Thus, contingency measures are required as part of a state's
attainment plan submission under section 189(d). Accordingly, the final
rule requires the criteria for identifying and selecting contingency
measures for a section 189(d) submission that are the same as for
Moderate or Serious area attainment plans.
    Specifically, the EPA is finalizing that the following requirements
must be met in order for contingency measures to be approvable as part
of a state's attainment plan submission for purposes of section 189(d):
    (1) Contingency measures must be fully adopted rules or control
measures that are ready to be implemented quickly upon a determination
by the Administrator of the nonattainment area's failure to meet RFP,
failure to meet any quantitative milestone, failure to submit a
quantitative milestone report or failure to meet the standard by the
applicable attainment date.
    (2) The SIP must contain trigger mechanisms for the contingency
measures, specify a schedule for implementation, and indicate that the
measures will be implemented without significant further action by the
state or by the EPA.
    (3) Contingency measures should consist of control measures that
are not otherwise included in the control strategy for the SIP, or that
achieve emissions reductions not otherwise relied upon in the control
strategy for the area.
    (4) Contingency measures should provide for emissions reductions
equivalent to 1 year's share of reductions needed to demonstrate
attainment (i.e., the overall needed reductions divided by the number
of years from the base year to the attainment year), or approximately
equivalent to 1 year's worth of air quality improvement or emissions
reductions proportional to the overall amount of air quality
improvement or emissions reductions to be achieved by the area's
attainment plan.
    The EPA is also finalizing its proposal to allow a state to rely on
contingency measures that achieve emissions reductions on sources
located outside the nonattainment area, but within the state provided
that the measures on sources outside the designated nonattainment area
are demonstrated to produce the appropriate air quality impact within
the nonattainment area.
    As with contingency measures for Moderate or Serious areas, the EPA
allows a state under these circumstances to rely on additional
reductions from federal or local measures already scheduled for
implementation as part or all of their contingency measures. The EPA
could consider such measures as meeting the contingency measure
requirement as long as they produce emissions reductions in excess of
those required to meet other statutory nonattainment provisions (e.g.,
such as to meet BACM/BACT requirements) and they can be relied on to
achieve a sufficient portion of the actual emissions reductions
necessary to reduce emissions in the area while the state develops a
new plan to bring the area into attainment.\200\ As with contingency
measures for Moderate area or Serious area attainment plans, the EPA
requires that the emissions reductions associated with contingency
measures for attainment plans under section 189(d) should be
approximately equivalent to 1 year's worth of emissions reductions
necessary to achieve RFP for the area, unless the state adequately
demonstrates that some smaller amount of reductions is appropriate
while the state is revising its attainment plan for the area. See 40
CFR 51.1014(b)(2).
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    \200\ See LEAN v. EPA, 382 F.3d 575 (5th Cir. 2004).
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    The EPA recognizes that identifying contingency measures for a
Serious PM2.5 nonattainment area that failed to attain the
relevant NAAQS by the applicable attainment date may be challenging for
a state that should already have fully implemented all control measures
identified as ``reasonable'' and ``best,'' and potentially ``most
stringent,'' in addition to any new control measures to achieve the
requisite minimum 5 percent reductions in direct PM2.5 or
PM2.5 plan precursor emissions necessary for expeditious
attainment. However, for an area that has not implemented MSM, states
could identify potential contingency measures by reviewing attainment
plans for other nonattainment areas. The state should also reevaluate
control measures that were identified previously as technologically or
economically infeasible for the area, or otherwise removed from
consideration as part of the RACM/RACT or BACM/BACT process.
Additionally, states can review other sources of control measure
information, such as the RBLC (a central database of air pollution
control technology information) and the EPA's Menu of Control Measures
document available at http://www3.epa.gov/ttn/naaqs/pdfs/MenuOfControlMeasures.pdf. See 40 CFR 51.1014.
3. Comments and Responses
    Comment: Commenters stated that because 189(d) requires annual
emissions reductions of not less than 5 percent, then the EPA cannot
assume that 1 year's worth of emissions reductions will be no greater
than 5

percent. The commenter stated that only if an area shows that the 5
percent reduction requirement of CAA section 189(d) is greater than
what would be necessary to demonstrate RFP annually may an area assume
that contingency measures must achieve only the 5 percent target.
    Response: The EPA agrees with the commenters. As discussed earlier
and in Sections IV.H and VI.H of this preamble, contingency measures
should equal approximately 1 year's worth of emissions reductions
necessary to achieve RFP for the area. The EPA notes that RFP might
require more than the 5 percent emissions reductions required by CAA
section 189(d). Therefore, if contingency measures should equal
approximately 1 year's worth of emissions reductions necessary to
achieve RFP, then those contingency measures should provide more than 5
percent of emissions reductions in direct PM2.5 or aggregate
PM2.5 plan precursors.
    Comment: Commenters suggested that, similar to the ozone program,
the EPA should consider whether the contingency measures for an area
that failed to attain by the deadline for Serious areas could
anticipate the development of proven new technology, with a requirement
to add further contingency measures if such technology does not develop
as anticipated.
    Response: The EPA disagrees with the commenters, noting that CAA
section 182(e)(5) provides this flexibility for Extreme areas that are
nonattainment for the ozone NAAQS. That section of the Act falls within
subpart 2 of part D, which identifies additional contingency measure
provisions applicable only in ozone nonattainment areas. Subpart 4 does
not contain a provision similar to that in subpart 2. Therefore, CAA
section 172(c)(9) applies and, as explained earlier, that provision
requires contingency measures be included in the attainment plan.
    Comment: Commenters requested the EPA to allow a state to
demonstrate, in the alternative, that its contingency measures will
achieve a 5 percent reduction in PM2.5 ambient
concentrations, and that such reductions can be obtained by reducing
direct PM2.5 emissions, emissions of one or more precursors,
or both.
    Response: The EPA is finalizing the optional air quality analysis
as an additional component of the RFP plan, as previously discussed in
Section IV.F of the preamble. Therefore, although the state could
demonstrate that its contingency measures will achieve a 5 percent
reduction in PM2.5 ambient concentrations, the EPA notes
that this optional analysis does not relieve the requirements of
189(d). Specifically, the area remains required to achieve an emissions
reduction of not less than 5 percent of direct PM2.5 or any
PM2.5 plan precursor.

I. Attainment Dates

1. Summary of the Proposal
    The proposed rule indicated that the new attainment date for an
area that failed to attain by the Serious area attainment date would be
governed by sections 172(a)(2) and 179(d)(3) of the CAA. Under the
proposal, the attainment date would be as expeditiously as practicable,
but no later than 5 years from the date of publication in the Federal
Register of the EPA's determination that the area failed to attain the
relevant NAAQS. The EPA may extend the attainment date by up to 5
additional years based on certain criteria.
2. Final Rule
    As described in the proposal, the final rule includes the
overarching requirement for a Serious area that failed to attain by the
previous attainment date to establish a new date for attaining the
standard as expeditiously as practicable. However, neither CAA section
189(d) nor other sections in subpart 4 explicitly establish or provide
the authority to establish a new attainment date for the area.
Therefore, once an area is beyond the attainment dates that Congress
specified in subpart 4 for the PM10 NAAQS, the EPA must look
to other provisions of part D of the CAA to provide authority for a new
attainment date. Sections 179(d)(3) and 172(a)(2) of the CAA provide
generally applicable attainment dates that fill the gap in the statute
left for areas subject to the requirements of CAA section 189(d). Thus,
for a PM2.5 nonattainment area subject to CAA section 189(d)
requirements, the EPA must establish a new attainment date according to
the provisions of CAA section 179(d)(3) and 172(a)(2). The EPA has
followed this same approach in the past for PM10
nonattainment areas governed by subpart 4 nonattainment
requirements.\201\
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    \201\ For example, see the Federal Register notice from June 6,
2007 (72 FR 31183) in which the EPA found that the Phoenix
PM10 Serious nonattainment area failed to attain the
standard by the 2006 attainment date.
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    Applying these provisions, the final rule therefore provides that
the new attainment date in a CAA section 189(d) plan must be as
expeditious as practicable, but no later than 5 years from the date of
publication in the Federal Register of the EPA's determination that the
area failed to attain the relevant NAAQS. The EPA may extend the
attainment date by up to 5 additional years (thus to 10 years from the
date of publication of the notice of finding of failure to attain by
the applicable attainment date for the area) if the agency deems it
appropriate ``considering the severity of nonattainment and the
availability and feasibility of pollution control measures.'' For a
PM2.5 nonattainment area subject to CAA section 189(d), the
EPA expects that the state will adopt any control measures necessary to
demonstrate expeditious attainment within 5 years of the area failing
to attain the NAAQS by the applicable Serious area attainment date. The
EPA will consider the state's proposed attainment date for the area
based on its revised attainment demonstration and modeling of its
updated control strategy, and other relevant facts and circumstances
for the area, in order to identify the most expeditious attainment date
practicable for the area.
3. Comments and Responses
    Comment: Some commenters stated that the EPA should set a date that
is as expeditious as practicable, but if it takes longer than 10 more
years to attain, the EPA may approve such a plan, as long as the
minimum 5 percent reduction requirement is met. The commenter stated
that this is the plain meaning of CAA section 189(d)'s reference that
the plan shall provide for at least 5 percent reductions ``from the
date of such submission until attainment.''
    Response: The EPA does not agree with the commenter. As indicated
earlier, the EPA's longstanding interpretation is that the statutory
provisions of CAA sections 172(c)(2) and 179(d)(3) govern the
attainment date for new plans required under CAA section 189(d) for
Serious areas that previously fail to attain by the Serious area
attainment date. Under certain circumstances, these provisions would
allow for an attainment date up to 10 years from the effective date of
a finding of failure to attain, but would not allow for an attainment
date longer than that.

VIII. NNSR Requirements for PM2.5 Nonattainment Areas

A. Background

1. Statutory Requirements for NSR
    Section 110(a)(2)(C) of the CAA requires states to include in their
SIPs a preconstruction review permitting program that regulates the
construction and modification of stationary sources

as necessary to ensure that NAAQS are achieved. To address the
regulation of the larger pollutant-emitting sources (defined as major
stationary sources), Congress provided specific permitting requirements
in the CAA in parts C and D of title I. The requirements for
preconstruction permits under parts C and D of the CAA are commonly
known collectively as the major NSR program because they apply
specifically to the preconstruction review and permitting of new major
stationary sources and major modifications at existing sources. As
explained in Sections VIII.A.1.a and b of this preamble, the
preconstruction review of each proposed new major stationary source and
major modification generally is carried out on a pollutant-specific
basis and the permitting requirements with regard to each pollutant
apply based on whether the area in which the proposed major source or
major modification would locate is designated attainment (or
unclassifiable) or nonattainment for that pollutant at the time the
permit is issued.
    a. Prevention of Significant Deterioration. Part C of title I of
the CAA (hereafter referred to simply as part C) contains
implementation plan requirements that apply to new major stationary
sources and major modifications locating in areas designated attainment
or unclassifiable for any NAAQS. These requirements constitute the
Prevention of Significant Deterioration (PSD) program. Pursuant to part
C, the EPA has adopted PSD regulations at 40 CFR 51.166 (minimum
requirements for an approvable state PSD program in the SIP) and 40 CFR
52.21 (the federal PSD program, applicable in areas where the state
does not have an EPA-approved PSD program in its SIP).\202\ The EPA
last amended the PSD regulations for PM2.5 on January 15,
2013, in the final rule revising the PM2.5 NAAQS.\203\ This
final rule does not relate to the PSD program, nor does it amend the
PSD regulations.
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    \202\ The federal PSD program enables the EPA or a state that
has been delegated authority by the EPA to issue PSD permits.
    \203\ More information on the PSD requirements for
PM2.5 as well as the public comments and the EPA's
responses to those comments is contained in the January 15, 2013
Federal Register document (78 FR 3086, beginning at page 3251).
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    b. Nonattainment New Source Review. Part D of title I of the CAA
(hereafter referred to as part D) contains implementation plan
requirements for nonattainment areas, which include the requirements
for permitting new major stationary sources and major modifications
locating in designated nonattainment areas, referred to as the
Nonattainment New Source Review (NNSR) program. As noted earlier, part
D contains several subparts that include various requirements for
addressing nonattainment areas. Subpart 1 addresses plan requirements
for nonattainment areas generally, including CAA section 172(c)(5),
which requires preconstruction and operating permits for new major
stationary sources and major modifications locating in nonattainment
areas. Section 173 of the CAA outlines the minimum statutory
requirements for a state's NNSR permit program and serves as the basis
for the EPA's NNSR regulations for PM2.5 as promulgated in
the 2008 PM2.5 NSR Rule published at 73 FR 28321, May 16,
2008. Subpart 4 was added to part D as part of the 1990 CAA Amendments
and includes additional plan provisions for designated PM10
nonattainment areas. Relevant here, CAA section 189(a)(1)(A) of subpart
4 requires states to include in their implementation plan a permit
program addressing major stationary sources of PM10 that
meets the requirements under CAA section 173 of subpart 1. Subpart 4
also includes some additional preconstruction review requirements,
which, until the court's decision in NRDC v. EPA, the EPA has only
applied to major sources of PM10 located in PM10
nonattainment areas. The specific NNSR requirements contained in both
subparts 1 and 4 are described later, including the changes that we are
making in this final rule to the NNSR regulations to address these
requirements with respect to PM2.5.
2. Federal NNSR Regulations
    The EPA has adopted numerous NNSR regulations in 40 CFR parts 51
and 52, including Sec.  51.165; part 51 Appendix S; and Sec.  52.24. An
approvable NNSR program in a state's implementation plan must, at a
minimum, meet the applicable program requirements set forth in the
federal NNSR provisions at 40 CFR 51.165, which for PM2.5
have been based on changes to that section made by the 2008
PM2.5 NSR Rule. States with designated nonattainment areas
for a particular pollutant are required to adopt regulations consistent
with those applicable plan requirements, including any subsequent rule
changes that the EPA may make, and submit them to the EPA for approval
as part of their SIP within a period of time consistent with the
schedule prescribed by the CAA or the EPA, as appropriate.
    The EPA interprets the requirement established under section
110(a)(2)(C) of the CAA that states regulate the construction and
modification of sources to apply as of the effective date of an area's
designation to nonattainment for a given pollutant.\204\ Although CAA
section 110(a)(2)(C) does not contain specific requirements a state
must follow for issuing major source permits during the interim period
between effective date of designation and the date when the EPA
approves a state's NNSR program to address a given pollutant, the EPA
regulations at 40 CFR 52.24(k) authorize states to apply 40 CFR part
51, Appendix S, known as the Emission Offset Interpretative Ruling or
simply the Offset Ruling, during the interim period.205 206
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    \204\ See the EPA's final rule to implement certain aspects of
the 1990 CAA Amendments relating to NSR and PSD, published in the
Federal Register on November 29, 2005 (70 FR 71612, 71677 and
71678).
    \205\ States with designated PM2.5 nonattainment
areas for the 1997 and 2006 PM2.5 standards were required
to submit SIPs, including a NNSR program satisfying the requirements
of the 2008 PM2.5 NSR Rule, by May 16, 2011, 3 years from
the date of publication of that 2008 rule. See 73 FR 28321 (May 16,
2008), at page 28342. States must continue to implement those
approved state programs to issue permits to new major stationary
sources and major modifications until the state's revised program
containing the subpart 4 NNSR provisions promulgated in this
rulemaking is approved under the applicable SIP.
    \206\ Appendix S was originally promulgated in 1976 to address
whether, and to what extent, new and modified sources would be
allowed to construct in nonattainment areas whose attainment
deadlines had already passed, in light of the regulatory requirement
that applications for construction permits for new or modified
sources be disapproved where the source would interfere with
attainment of the NAAQS, see 41 FR 55524 (December 21, 1976). When
Congress added the part D provisions in the 1977 CAA Amendments, it