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

    \90\ Id. at 2-3 to 2-4.
---------------------------------------------------------------------------

    Another commenter contended that the EPA's proposed revisions
failed to include a necessary step where states evaluate the control
measures identified as necessary to make reasonable progress in light
of the RPGs themselves. This commenter requested a mechanism whereby a
state could determine that some of the initially evaluated control
measures were unnecessary in light of the RPGs themselves. In
particular, this commenter suggested that a state should be able to
reject ``costly'' control measures if (1) the RPG for the most impaired
days is on or below the URP line or (2) the RPGs are not
``meaningfully'' different than current visibility conditions.
    We disagree that the states should be able to reevaluate whether a
control measure is necessary to make reasonable progress based on the
RPGs. The CAA requires states to determine what emission limitations,
compliance schedules and other measures are necessary to make
reasonable progress by considering the four factors. The CAA does not
provide that states may then reject some control measures already
determined to be reasonable if, in the aggregate, the controls are
projected to result in too much or too little progress. Rather, the
rate of progress that will be achieved by the emission reductions
resulting from all reasonable control measures is, by definition, a
reasonable rate of progress.
    In regards to the commenter's first suggestion, if a state has
reasonably selected a set of sources for analysis and has reasonably
considered the four factors in determining what additional control
measures are necessary to make reasonable progress, then the state's
analytical obligations are complete if the resulting RPG for the most
impaired days is below the URP line. The URP is not a safe harbor,
however, and states may not subsequently reject control measures that
they have already determined are reasonable. If a state's RPG for the
most impaired days is above the URP line, then the state has an
additional analytical obligation to ensure that no reasonable controls
were left off the table.
    The commenter's second suggestion, that states should be able to
reject ``costly'' control measures if the RPG for the most impaired
days is not ``meaningfully'' different than current visibility
conditions, is counterintuitive and at odds with the purpose of the
visibility program. In this situation, the state should take a second
look to see whether more effective controls or additional measures are
available and reasonable. Whether the state takes this second look or
not, it may not abandon the controls it has already determined are
reasonable based on the four factors. Regional haze is visibility
impairment that is caused by the emission of air pollutants from
numerous sources located over a wide geographic area. At any given
Class I area, hundreds or even thousands of individual sources may
contribute to regional haze. Thus, it would not be appropriate for a
state to reject a control measure (or measures) because its effect on
the RPG is subjectively assessed as not ``meaningful.'' Also, for Class
I areas where visibility conditions are considerably worse than natural
conditions because of continuing anthropogenic impairment from numerous
sources, the logarithmic nature of the deciview index makes the effect
of a control measure on the value of the RPG less than its effect would
be if visibility conditions at the Class I area were better. Thus, if a
state could reject a control measure based on its individual effect on
the RPG, the state would be more likely to reject those measures that
are necessary to make reasonable progress at the dirtiest Class I
areas, which would thwart Congress' national goal.
    One commenter contended that the proposed revisions would lead to
disagreements among states because states might set different RPGs
instead of working jointly toward the downwind state's goals. We
disagree. Only downwind states set RPGs for their mandatory Class I
Federal areas, so there is no situation in which there would be
different goals for the same area.
    Another commenter contended that the proposed revisions would force
states to require controls even where visibility at a Class I area is
already equivalent to or better than the visibility that represents the
URP at the end of the implementation period. We agree that some states
may end up establishing RPGs that exceed the URP, but as we explained
previously in this document, the URP was never intended to be a safe
harbor. In the 1999 RHR, we explained that ``[i]f the State determines
that the amount of progress identified through the analysis is
reasonable based upon the statutory factors, the State should identify
this amount of progress as its reasonable progress goal for the first
long-term strategy, unless it determines that additional progress
beyond this

amount is also reasonable. If the State determines that additional
progress is reasonable based on the statutory factors, the State should
adopt that amount of progress as its goal for the first long-term
strategy.'' \91\ This approach is consistent with and advances the
ultimate goal of section 169A: Remedying existing and preventing future
visibility impairment. Congress required the EPA to promulgate
regulations requiring reasonable progress toward that goal, and it
would be antithetical to allow states to avoid implementing reasonable
measures until and unless that goal is achieved.
---------------------------------------------------------------------------

    \91\ 64 FR 35732.
---------------------------------------------------------------------------

    Other commenters were supportive of the proposed structural
revisions intended to clarify the relationship between RPGs and long-
term strategies. They explained that by reorienting these provisions to
reflect the EPA's long-standing interpretation, the EPA was providing a
clearer blueprint for states to follow in future implementation
periods. These commenters also provided specific suggestions for how
the EPA could further revise the proposed regulatory text for 40 CFR
51.308(f). Among other things, these commenters requested that the EPA
include language in the regulations that would make it clear that a
state's long-term strategy can include emission limits and other
measures that cannot be installed by the end of an implementation
period. As discussed earlier in Section IV.A of this document, we are
modifying the language in 40 CFR 51.308(f)(2(i) and 51.308(f)(3)(i) to
make this point clear. We have reviewed the other suggestions made by
these commenters and do not believe that they are necessary, as
discussed more fully in the RTC document available in the docket for
this rulemaking.
    We also received several comments regarding the obligations of
upwind and downwind states. Some commenters supported the revisions
that were intended to clarify that all states must conduct a four-
factor analysis to determine what control measures are necessary to
make reasonable progress at each mandatory Class I Federal area
affected by emissions from the state. They explained that any other
interpretation of the CAA's requirements would allow an upwind state to
continue impairing downwind visibility without consequence, regardless
of whether there were reasonable, cost-effective measures that would
improve downwind visibility. Other commenters argued that upwind states
should not have the same obligations as downwind states. One commenter
asserted that, under the proposal, all states would be subject to the
RHR for the very first time, regardless of whether they have a
mandatory Class I Federal area or not. Another commenter contended that
requiring upwind states to conduct four-factor analyses for downwind
Class I areas was a new requirement that was not part of the 1999 RHR.
This commenter acknowledged that upwind states must address downwind
Class I areas where their emissions ``may reasonably be anticipated to
cause or contribute to any impairment of visibility'' at the downwind
area, but suggested that the proposed revisions use the language ``may
affect'' instead. This commenter stated that the EPA's proposal did not
define or quantify what the term ``may affect'' means.

    Section 169A(b)(2) states that the EPA's regulations must:
Require each applicable implementation plan for a State in which any
[mandatory Class I Federal] area . . . is located (or a for a State
the emissions from which may reasonably be anticipated to cause or
contribute to any impairment of visibility in any such area) to
contain such emission limits, schedules of compliance and other
measures as may be necessary to make reasonable progress toward
meeting the national goal.

Section 169A(g)(1) thus requires states to determine the measures
necessary to make reasonable progress by considering the four factors,
while section 169A(a)(1) defines Congress's national goal as preventing
future and remedying existing anthropogenic visibility impairment in
all Class I areas. Thus, Congress was clear that both downwind states
(i.e., ``a State in which any [mandatory Class I Federal] area . . . is
located) and upwind states (i.e., ``a State the emissions from which
may reasonably be anticipated to cause or contribute to any impairment
of visibility in any such area'') must revise their SIPs to include
measures that will make reasonable progress at all affected Class I
areas. Congress was also clear that states must determine the necessary
measures and rate of progress that are reasonable by considering the
four factors. Our proposed revisions to 40 CFR 51.308(f)(2) are in
accord with this congressional mandate.
    The commenter who suggested that our proposed revisions are
expanding the scope of the RHR to all states for the first time is
incorrect. The 1999 RHR applies to all states,\92\ and all states
submitted regional haze SIPs (or asked the EPA to promulgate a regional
haze FIP on its behalf) during the first implementation period. As
discussed later in this preamble, we are expanding the scope of the
1980 reasonably attributable visibility impairment regulations to all
states for the first time, but the new reasonably attributable
visibility impairment provisions only require state action upon receipt
of a certification by a FLM. Historically, there have been very few FLM
certifications requesting states to assess controls for a particular
source or small group of sources.
---------------------------------------------------------------------------

    \92\ 40 CFR 51.300(b)(1)(i).
---------------------------------------------------------------------------

    Finally, we note that the language ``may affect'' in 40 CFR
51.308(f)(2) was adapted from the 1999 RHR, which used the same
term.\93\ On July 8, 2016, we released draft guidance that discusses
how states can determine which Class I areas they ``may affect'' and
therefore must consider when selecting sources for inclusion in a four-
factor analysis.\94\ The draft guidance discusses various approaches
that states used during the first implementation period, provides
states with the flexibility to choose from among these approaches in
the second implementation period, and recommends that states adopt ``a
conservative . . . approach to determining whether their sources may
affect visibility at out-of-state Class I areas.'' \95\ We plan to
finalize the draft guidance in the near future.
---------------------------------------------------------------------------

    \93\ See 40 CFR 51.308(d)(3).
    \94\ 81 FR 44608 (July 8, 2016).
    \95\ Draft Guidance on Progress Tracking Metrics, Long-term
Strategies, Reasonable Progress Goals and Other Requirements for
Regional Haze State Implementation Plans for the Second
Implementation Period, at 57-58 (2016).
---------------------------------------------------------------------------

    We also received comments on the proposed interstate consultation
provisions in 40 CFR 51.308(f). A few commenters inquired whether
proposed 40 CFR 51.308(f)(2)(iii) \96\ would affect a substantive
change from the existing consultation provisions in 40 CFR 51.308(d).
One commenter stated that proposed 40 CFR 51.308(f)(2)(ii) would
apparently require states to consider how other states calculated the
URP, adopted emission reduction measures for sources and adopted any
additional measures that may be needed to address state contributions.
This commenter also argued that proposed 40 CFR 51.308(f)(2)(iii) would
incentivize states not to agree with other states on coordinated
emission management strategies because an agreement would create an
enforceable obligation against the state. Another commenter stated that
the EPA would need to coordinate and

mediate interstate consultations in order for them to prove successful.
---------------------------------------------------------------------------

    \96\ As explained later in this document, the final rule
includes a consolidation and resulting renumbering of some of the
proposed provisions of 40 CFR 51.308(f)(2). This discussion refers
specifically to either proposed or final section numbers to avoid
confusion.
---------------------------------------------------------------------------

    With one exception, we did not intend the proposed interstate
consultation provisions to affect a substantive change from the
existing provisions in the 1999 RHR. Under the proposed provisions, as
under the 1999 RHR, states must consult to develop coordinated emission
management strategies, demonstrate that their SIPs contain all agreed-
upon emission reduction measures, and document disagreements so that
the EPA can properly evaluate whether each state's implementation plan
provides for reasonable progress toward the national goal. We also
proposed a new requirement, in 40 CFR 51.308(f)(2)(ii), that states
must consider the control strategies being adopted by other states when
conducting their own four-factor analyses. The purpose of this
provision was to ensure that if one state had identified a control
measure as being reasonable for a source or group of sources to improve
visibility at a Class I area, then other states that affect that Class
I area would be required to consider that control measure for their own
sources, to the extent that the sources share similar characteristics.
However, in reviewing proposed 40 CFR 51.308(f)(2)(ii), we realized
that it contains extraneous language that has led to confusion among
some of the commenters. We discuss this issue in more depth, and other
changes being made to the consultation provisions, in the following
section.
    In regard to the commenter's concern that the consultation
provisions will incentivize states to avoid entering into agreements
with each other to avoid enforceable obligations, we disagree. States
largely worked cooperatively to develop coordinated emission management
strategies during the first implementation period, and we expect that
they will do so again. If a state believes that additional controls
from sources in another state or states are necessary to make
reasonable progress at a Class I area, then the state should document
the disagreement to assist the EPA in determining whether the other
state's SIP is inadequate. Moreover, even if states were to avoid
entering into agreements for the purpose of avoiding enforceable
obligations under 40 CFR 51.308(f)(iii), this would not absolve the
states of their independent obligation to include in their SIPs
enforceable emission limits and other measures that are necessary to
make reasonable progress at all affected Class I areas, as determined
by considering the four factors. Finally, we do not believe that the
EPA needs to coordinate or mediate interstate consultations. During the
first implementation period, states consulted one-on-one and through
the RPO process without EPA oversight, and we expect this process to
work going forward as well.
3. Final Rule
    We are finalizing the revisions to 40 CFR 51.308(f) that were
intended to clarify the relationship between RPGs and long-term
strategies and the obligations of upwind and downwind states largely as
proposed. However, we are making several changes to the provisions in
40 CFR 51.308(f)(2) governing long-term strategies to simplify these
provisions, enhance clarity and eliminate superfluous regulatory text.
    In 40 CFR 51.308(f)(2), we are revising the requirement that states
must include in their long-term strategies ``the enforceable emissions
limitations, compliance schedules, and other measures that are
necessary to achieve reasonable progress'' to read ``make reasonable
progress'' instead. This change is to maintain consistency with the
language in CAA section 169A(b)(2).
    In 40 CFR 51.308(f)(2)(i), we are making two minor changes. First,
we are revising the beginning of the first sentence to read, ``[t]he
State must evaluate and determine the emission reduction measures that
are necessary to make reasonable progress by considering'' the four
factors. We believe that this formulation is clearer than the language
in the proposal and more consistent with the language of the CAA.
Second, we are revising the second sentence, and splitting it into two
separate sentences, to make it clear that states must consider
anthropogenic sources of visibility impairment when conducting their
four-factor analyses, not natural sources, and that anthropogenic
sources can include mobile and area sources in addition to major and
minor stationary sources. As mentioned earlier, we are also adding a
sentence to 40 CFR 51.308(f)(2)(i) regarding the consideration of
emission controls that cannot reasonably be installed prior to the end
of the implementation period.
    We are removing proposed 40 CFR 51.308(f)(2)(ii) in these final
revisions, which required states to consider the URP, the emission
reduction measures identified under 40 CFR 51.308(f)(2)(i), and
measures being adopted by contributing states under 40 CFR
51.308(f)(2)(iii) when developing their long-term strategies. States
are already required to consider the URP under 40 CFR 51.308(f)(3)(ii)
when establishing their RPGs. Moreover, it is duplicative to require
states to consider the emission reduction measures identified under 40
CFR 51.308(f)(2)(i) a second time. As discussed in the following
paragraph, we are moving the third requirement in proposed 40 CFR
51.308(f)(2)(ii) to the interstate consultation provisions.
    We are changing proposed 40 CFR 51.308(f)(2)(iii), regarding
interstate consultations, to be 40 CFR 51.308(f)(2)(ii) and making
several changes. First, we are removing the distinction between
contributing states and states affected by contributing states because
the substance of the two provisions was essentially the same. The final
revisions include a single provision requiring each state to consult
with the other states that are reasonably anticipated to contribute to
visibility impairment in a mandatory Class I Federal area to develop
coordinated emission management strategies. Identification of the other
states should occur as part of a regional planning process. Second, we
are revising the language that required states to obtain either their
``share of the emission reductions needed to provide for reasonable
progress'' or ``all measures needed to achieve its apportionment of
emission reduction obligations'' depending on whether the state was a
contributing state or a state affected by contributing states. Most
states are both contributing states and states affected by contributing
states, so these variations in wording could be viewed as creating two
distinct obligations. Now, each state must demonstrate that it has
included in its long-term strategy ``all measures agreed to during
state-to-state consultations or a regional planning process, or
measures that will provide equivalent visibility improvement.'' Third,
as discussed previously, we have moved the requirement that states
consider the emission reduction measures other states have identified
as being necessary to make reasonable progress from proposed 40 CFR
51.308(f)(2)(ii), which accordingly has been eliminated, to the
interstate consultation provisions (now numbered as 40 CFR
51.308(f)(2)(ii)) because it is a more logical place for it. We have
also revised the wording of this provision to eliminate the ambiguity
in the proposed language noted by commenters regarding ``additional
measures being adopted'' by other states. Under this provision, states
must consider whether the emission reduction measures other states have
identified by other States for their sources as being necessary to make
reasonable progress in the mandatory Class I Federal area. This
consideration

is appropriate especially when the sources are of a similar type and
have similar emissions profiles and visibility impacts.
    We are changing proposed 40 CFR 51.308(f)(2)(iv), regarding
documentation requirements, to be 40 CFR 51.308(f)(2)(iii) and making a
few minor changes. First, we are revising the first sentence to require
the states to ``document the technical basis, including modeling,
monitoring, cost, engineering, and emissions information, on which the
State is relying to determine the emission reduction measures that are
necessary to make reasonable progress in each mandatory Class I area it
affects.'' The proposed language referred to ``information on the
factors listed in (f)(2)(i) and modeling, monitoring, and emissions
information,'' but we believe this language was confusing because it
suggested that information on the four factors was something distinct
from modeling, monitoring and emissions information. The purpose of
this provision is to require states to document all of the information
on which they rely to develop their long-term strategies, which will
primarily be information used to conduct the four-factor analysis.
Therefore, in addition to modeling, monitoring and emissions
information, we are making it explicit that states must also submit the
cost and engineering information on which they are relying to evaluate
the costs of compliance, the time necessary for compliance, the energy
and non-air quality impacts of compliance and the remaining useful
lives of sources.
    We are removing proposed 40 CFR 51.308(f)(2)(v), which required
states to identify the anthropogenic sources of visibility impairment
analyzed using the four factors and the criteria used to select sources
for analysis, because 40 CFR 51.308(f)(2)(i) as finalized already
includes these requirements.
    Finally, we are changing proposed 40 CFR 51.308(f)(2)(vi) to be 40
CFR 51.308(f)(2)(iv) and making a few changes. We are revising the
first sentence of this provision to clarify that the enumerated factors
are additional to the factors states must consider in 40 CFR
51.308(f)(2)(i). We are also removing proposed 40 CFR
51.308(f)(2)(vi)(C) and (F) because they are duplicative requirements.
These provisions required states to consider the emission limitations
and schedules for compliance to achieve the RPG and the enforceability
of emission limitations and control measures. Section 40 CFR
51.308(f)(2) already requires states to include enforceable emission
limitations, compliance schedules, and other measures that are
necessary to make reasonable progress in their long-term strategies.
Section IV.G of this document discusses revisions we are making to the
additional factor regarding basic smoke management practices and smoke
management programs.

D. Other Clarifications and Changes to Requirements for Periodic
Comprehensive Revisions of Implementation Plans

    The following clarifications and changes were also proposed to be
included in the revised 40 CFR 51.308(f). A summary of each proposed
clarifying change, a synopsis of the final rule, and a discussion of
comments received and EPA's responses are given later.
    The URP line starts at 2000-2004, for every implementation period.
1. Summary of Proposal
    The 1999 RHR's text of 40 CFR 51.308(d)(1)(i)(B) contains a
discussion of how states must analyze and determine ``the rate of
progress needed to attain natural visibility conditions by the year
2064.'' This rate has commonly been called the ``uniform rate of
progress'' or URP as well as ``the glidepath.'' The 1999 RHR's text of
40 CFR 51.308(f), which indicates that states must evaluate and
reassess all elements required by 40 CFR 51.308(d), requires states to
evaluate and reassess the URP in the second and subsequent
implementation periods. We explained in the proposal that 40 CFR
51.308(d) is not perfectly clear as to whether the URP line for the
second or later implementation periods must always start in the
baseline period of 2000-2004, or whether the state must (or may)
recalculate the starting point of the URP line based on data from the
most recent 5-year period during each successive regional haze SIP
revision.\97\ We also explained that although the regulations make
clear that the endpoint of the URP line should be set based on
attainment of the natural visibility condition for the 20 percent most
impaired days in 2064, the 1999 RHR does not specify an exact date in
2064 for this element.
---------------------------------------------------------------------------

    \97\ The preamble to the 1999 RHR provides an example explaining
how a state would determine the 2028 point on the URP line. 64 FR at
35746, n. 113. In this example, the URP line for the second
implementation period starts at 2000-2004.
---------------------------------------------------------------------------

    To ensure consistent understanding of how the URP analysis must be
done, the EPA proposed rule revisions in 40 CFR 51.308(f)(1)(i) and
(vi) that would make it explicit that in every implementation period,
the URP line for each Class I area is to be drawn starting on December
31, 2004, at the value of the 2000-2004 baseline visibility conditions
for the 20 percent most impaired days, and ending at the value of
natural visibility conditions on December 31, 2064. Specifying that the
5-year average baseline visibility conditions are associated with the
date of December 31, 2004, and that natural visibility conditions are
associated with the date of December 31, 2064, also clarifies that the
period of time between the baseline period and natural visibility
conditions, which is needed for determining the URP (deciviews/year) is
60 years.
    Along with the clarification that the baseline period remains 2000-
2004 for subsequent implementation periods, the EPA also proposed
clarifications in 40 CFR 51.308(f)(1)(i) regarding how states treat
Class I areas without available monitoring data or Class I areas with
incomplete monitoring data, as follows: If Class I areas do not have
monitoring data for the baseline period, data from representative sites
should be used; if baseline monitoring data are incomplete, states
should use the 5 complete years closest to the baseline period. We
proposed to add this provision to remove any uncertainty about how an
issue of data incompleteness should be addressed in a SIP.
    Finally, we proposed language in 40 CFR 51.308(f)(3)(i) and an
accompanying definition of ``end of the applicable implementation
period'' in 40 CFR 51.301 to make clear that RPGs are to address the
period extending to the end of the year of the due date of the next
periodic comprehensive SIP revision.
2. Comments and Responses
    Some commenters were supportive of EPA's proposal to have the URP
line start at 2000-2004 for every implementation period, although some
asked for the option of recalculating the URP for the start of each
implementation period based on how much further progress is needed to
reach natural conditions given the progress already achieved. Other
commenters did not agree with EPA's proposal and instead supported a
revision to the regulations that would require states to reset the URP
at current visibility conditions during each periodic review, provided
those visibility conditions are better than during the baseline. Taking
into account past improvements in visibility that were in excess of the
URP in this way would result in a lower-lying URP line for successive
planning periods. This could change the comparison of the RPG to the
URP line, and trigger the

requirement of 40 CFR 51.308(f)(3)(ii) to show that there are no
additional measures that would be reasonable to include in the long-
term strategy, when it would not be triggered if the start of the URP
line had been kept at the 2000-2004 period.
    As explained in the 1999 RHR, the consideration of the improvement
in visibility represented by the URP and the measures necessary to
attain that level of improvement is an analytical requirement. In the
1999 RHR, EPA adopted this required analysis in lieu of establishing
presumptive reasonable progress targets, in part to provide equity
between the goals set for the Class I areas in the more impaired
eastern portion of the country as compared to the areas in the western
portion. The URP analysis also helps to provide transparency to the
overall regional haze SIP planning process, in part by requiring states
to compare their RPGs to the rate of progress represented by the URP at
each Class I areas. Neither of these goals would be served by allowing
states to adopt differing approaches to the calculation of the URP.
    We have considered the comments suggesting that the URP be redrawn
during each successive planning period. Although such an approach is
apparently intended by commenters to maintain pressure on the states to
adopt more comprehensive and effective reasonable progress strategies,
it is not clear that this approach would in fact achieve that outcome
because it may create disincentives for states to take aggressive
action during the first few planning periods. This is because resetting
the URP would make it more likely that a state that has taken early and
aggressive action to improve visibility would become subject to the
enhanced analytical requirement of 40 CFR 51.308(f)(3)(ii), thus
generating a possible disincentive for continued progress.
    Because we have concluded that our proposed approach of starting
the URP for every implementation period at 2000-2004 will result in the
most equitable and transparent process and provide the strongest
incentive for continued progress toward achieving natural visibility
conditions, we are finalizing that approach with no changes to 40 CFR
51.308(f)(1)(i) or (vi).
3. Final Rule
    The EPA is finalizing all of the previously described rule text
without any changes from the proposal.
    The long-term strategy and the RPGs must provide for an improvement
in visibility for the most impaired days and ensure no degradation for
the clearest days.
1. Summary of Proposal
    Section 169A of the CAA requires a SIP to not only reduce existing
visibility impairment but also to prevent future impairment. As part of
meeting the goal of preventing future visibility impairment, 40 CFR
51.308(d)(1) of the 1999 RHR requires a state to establish RPGs that
ensure no degradation in visibility for the least impaired days over
the period of the implementation plan. This text is ambiguous, however,
as to whether ``the period of the implementation plan'' refers to the
entire period since the baseline period of 2000-2004 or to the specific
implementation period addressed by the periodic SIP revision. The
proposal noted that a table in the preamble to the 1999 RHR summarizing
certain requirements indicated that the 2000-2004 period would be used
for ``tracking visibility improvement.'' \98\ To provide further
clarity on this issue, we proposed new rule text in revised 40 CFR
51.308(f)(3)(i) that would make clear that the requirement is for a
state to establish an RPG for the 20 percent clearest days in each
periodic review that ensures that there is no deterioration in
visibility on the 20 percent clearest days as compared to the baseline
period of 2000-2004. We note that while 40 CFR 308(d)(1) of the 1999
RHR expresses the requirement of no degradation in visibility in terms
of the RPG for the 20 percent clearest days, this requirement comes
into play as a factor in what emission sources are subject to
additional control measures in the long-term strategy, because this RPG
is the projected result of implementing the long-term strategy. In
other words, a state must adopt a long-term strategy that includes the
necessary measures to ensure that the expected visibility on the 20
percent clearest days at the end of the planning period, as represented
by the RPG for these days, will not deteriorate as compared to the
visibility condition for these days in 2000-2004.The rule text we
proposed for 40 CFR 308(f)(3)(i) made this connection explicit by
saying that the long-term strategy and the RPG must provide for no
degradation.
---------------------------------------------------------------------------

    \98\ 64 FR 35730.
---------------------------------------------------------------------------

2. Comments and Responses
    The EPA received comments both in support of, and raising concerns
with, the proposed changes. The commenters opposed to our proposal
preferred that when a state documents that the RPG for the 20 percent
clearest days (i.e., the projected visibility condition on the clearest
days as of the end of the given implementation period) shows no
degradation, the benchmark for that comparison should be the lowest
measured impairment of either the baseline period or current conditions
reported in any progress report or comprehensive periodic revision for
the clearest days. The approach recommended by the commenter would mean
that the benchmark for the no degradation comparison would ratchet down
over time.
    One commenter pointed out that as proposed, 40 CFR 308(f)(3)(i)
addressed not just the requirement for no degradation for the clearest
days but also the requirement that there be an improvement for the most
impaired days. This commenter noted that the relevant sentence of 40
CFR 308(f)(3)(i) could be interpreted to mean that the baseline period
of 2000-2004 is the benchmark for determining if the long-term strategy
and RPG for the most impaired days provides for an improvement.\99\ The
commenter said that the final rule should provide that the benchmark
for the improvement requirement should be the lowest measured
impairment of either the baseline period or current conditions reported
in any progress report or comprehensive periodic revision for the most
impaired days. The approach recommended by the commenter would mean
that the benchmark for the improvement comparison would ratchet down
over time.
---------------------------------------------------------------------------

    \99\ The relevant sentence in the rule reads, ``The long-term
strategy and reasonable progress goals must provide for an
improvement in visibility for the most impaired days and ensure no
degradation in visibility for the clearest days since the baseline
period.'' The concluding phrase ``since the baseline period'' can be
taken to apply to only the clearest days, or to both the most
impaired days and the clearest days.
---------------------------------------------------------------------------

    We are finalizing our proposal to clarify that the benchmark for
the requirement for no degradation on the 20 percent clearest days is
the 2000-2004 baseline visibility condition. Further, we are clarifying
that the baseline visibility condition for the 20 percent most impaired
days is also the benchmark for the requirement that the long-term
strategy and RPGs provide for an improvement for the most impaired
days. We are taking this approach in the final rule for several
reasons.
    Visibility on the clearest days has been improving since the 2000-
2004 period in most Class I areas, generally tracking the improvements
seen on the 20 percent haziest and 20 percent most

impaired days.\100\ We expect that it will continue to be the case that
emission reduction measures that provide for reasonable progress on the
20 percent most impaired days will also have benefits on the clearest
days. Thus, we expect that there will be a continuing improvement on
the clearest days regardless of the benchmark selected, even if the
rule did not contain any requirement for no degradation on the clearest
days. Even so, we believe that the no degradation requirement with the
2000-2004 visibility condition as the benchmark is an appropriate
backstop in the rule that will continue to require states to consider
additional measures in the event that measures adopted to improve
visibility on the most impaired days are insufficient to protect
visibility on the clearest days.
---------------------------------------------------------------------------

    \100\ The RTC contains graphics illustrating these improvement
trends. The only situations in which there has been degradation
since 2000-2004 are at a few Class I areas in the Virgin Islands and
Alaska where sea salt particles significantly contribute to light
extinction on the clearest days and concentrations of such particles
on those days have increased over this period.
---------------------------------------------------------------------------

    We are not adopting the approach of ratcheting down the benchmark
for the no degradation requirement. If we were to do this, it might
lead to unreasonable outcomes in some cases. Available air quality
modeling approaches for forecasting visibility conditions are at
present more uncertain when predicting low concentrations of
visibility-impairing pollution than when predicting higher
concentrations, making comparisons of two ``clean'' scenarios more
uncertain. Such comparisons could become required for many areas and
have critical implications for SIP approvals. Errors in such
comparisons due to modeling system errors might lead to inappropriate
SIP disapprovals if the benchmark for the no degradation requirement
continually ratcheted down as progress is made. Another consideration
is that even with a 5-year averaging approach, transient natural
phenomena might cause a temporary improvement in visibility on the
clearest days entirely unrelated to the content and implementation of
states' long term strategies, which would permanently reduce the
benchmark if the ratcheting approach were followed. It might then be
very difficult or unreasonable for a state in subsequent periods to
show no degradation relative to this lower benchmark given that on the
clearest days influences from anthropogenic sources will be relatively
small. Finally, we believe that consistency between the benchmark for
the no degradation test and the starting point for the URP, across
Class I areas in a given implementation period and across
implementation periods, will aid public understanding and participation
in SIP development. For these reasons, we are finalizing our proposal
on this aspect of the RHR.
    In addition, we are finalizing wording in 40 CFR 308(f)(3)(i) that
makes it clear that the baseline condition in 2000-2004 is also the
benchmark for determining whether the long-term strategy and RPGs
provide for an improvement in visibility for the most impaired days,
but repeating the reference to this baseline so that it links
unambiguously to that requirement as well as to the no degradation
requirement. We recognize that since 2000-2004 there have been
widespread improvements in visibility on the most impaired days and
that this already accomplished improvement has created a ``cushion''
for a comparison to check that the RPG for the end of a future
implementation period shows improvement. However, we disagree with the
commenter's suggestion that the benchmark for the improvement
requirement should ratchet down over time, for similar but not entirely
identical reasons that we disagree regarding the no degradation
requirement. The advantage of consistency to public understanding
applies to the improvement requirement as well as to the no degradation
requirement. While the problem of modeling uncertainty applies less to
the most impaired days at this stage of the regional haze program, in
later periods the most impaired days will be clearer than they are now
and the difficulty of distinguishing differences may apply more
strongly. Also, we are mindful of the potential for reducing incentives
for states to take action during the first few planning periods. With
the 2000-2004 period as the benchmark for the no degradation
requirement, a state has an incentive to take early action to improve
the clearest days because this will create a safety margin in case
later developments outside the state's control cause an increase in
impairment on these days. Ratcheting down the baseline for the no
degradation requirement would remove this incentive for continued
progress because it would never be possible for a state to create a
safety margin.
    However, the use of the baseline period as the benchmark for the no
degradation and improvement requirements does not mean that states are
free to simply allow visibility levels to return to what they were in
the baseline period, or to allow for degradation in visibility as
compared to current conditions. If a state were to set an RPG that
reflects a forecast of degradation during a particular period, the
adequacy of the SIP would need to be carefully assessed. In this
situation, additional measures may be necessary to ensure reasonable
progress, depending on the underlying explanation for the forecasted
degradation. It may be that a state would be able to show that any
forecasted degradation is attributable to causes other than
deficiencies in its long-term strategy, but such a demonstration would
need to be carefully assessed. We note that for at least the next
planning period or two, the requirement to consider the four statutory
factors for a reasonably selected set of sources should result in the
adoption of additional control measures that provide an improvement,
especially for a state with sources that contribute to impairment at a
Class I area with an RPG above the URP line.
3. Final Rule
    Upon careful consideration of public comments received on this
issue, the EPA is finalizing the proposed rule with a clarifying edit
to the proposed language to make it clear that the baseline visibility
condition is also the benchmark for determining whether the long-term
strategy and RPGs provide for an improvement in visibility on the most
impaired days.
    The sentences of the final version of 40 CFR 51.308(f)(1)(i),
regarding the calculation of the baseline visibility conditions, have
been slightly reordered and reworded from the proposed version for
clarity. In addition, the final sentence of this paragraph, regarding
Class I areas that did not have IMPROVE monitoring stations installed
in time to provide complete monitoring data for 2000-2004, has been re-
worded to clarify that ``closest'' means closest in time to 2000-2004
and does not refer to another Class I area that is nearest in distance.
In the final version of 40 CFR 51.308(f)(1)(ii), an occurrence of
``or'' has been corrected to ``and'' to indicate that natural
visibility conditions for both the most impaired days and the clearest
days must be based on available monitoring information. Minor edits for
clarity have also been included in the final versions of 40 CFR
51.308(f)(1)(iii) and (iv).
    Analytical Obligation When the Reasonable Progress Goal for the 20
Percent Most Impaired Days Is Not On or Below the URP Line.
1. Summary of Proposal
    The EPA proposed 40 CFR 51.308(f)(3)(ii) in order to clarify the

relationship between the RPG for the 20 percent most impaired days and
the URP line. This relationship determines the content of the
demonstration a state must submit to show that its long-term strategy
provides for reasonable progress. This clarification was based upon the
1999 RHR's text of 40 CFR 51.308(d)(1)(ii). That provision addresses
required actions of a state containing a Class I area that has adopted
an RPG for the area that provides for a slower rate of visibility
improvement than that needed to attain natural conditions by 2064
(i.e., an RPG for the 20 percent most impaired days that is above the
URP line). The proposed text of 40 CFR 51.308(f)(3)(ii)(A) stated that
if the RPG for a Class I area is above the URP line, the state
containing the Class I area must demonstrate, based on the four
reasonable progress factors, that there are no additional emission
reduction measures for anthropogenic sources or groups of sources in
the state that may be reasonably anticipated to contribute to
visibility impairment that would be reasonable to include in the long-
term strategy, and that such a demonstration is required to be
``robust.'' Specifically, this demonstration must include documentation
of the criteria used to determine which sources or groups of sources
were evaluated and of how the four factors were taken into
consideration in selecting the measures for inclusion in its long-term
strategy.
    In addition, in comparison with the 1999 RHR's 40 CFR
51.308(d)(2)(iv) and 40 CFR 51.308(d)(3)(i) and (ii), the proposed 40
CFR 51.308(f)(2)(iii) more clearly spelled out the respective
consultation responsibilities of states containing Class I areas as
well as states with sources that may reasonably be anticipated to cause
or contribute to visibility impairment in those areas. To further
clarify the obligations of what we are referring to as contributing
states, we proposed 40 CFR 51.308(f)(3)(ii)(B) to specify that in a
situation where the RPG for the most impaired days is set above the
glidepath, a contributing state must make the same demonstration with
respect to its own long-term strategy that is required of the state
containing the Class I area, namely that there are no other measures
needed to provide for reasonable progress. The intent of this proposal
was to ensure that states perform rigorous analyses, and adopt measures
necessary for reasonable progress, with respect to Class I areas that
their sources contribute to, regardless of whether such areas are
located within their borders. This proposed change clarifies that the
RPG for the most impaired days in the SIP of the state containing the
Class I area does not ``set the bar'' for the contributing state's
long-term strategy.
2. Comments and Responses
    The EPA received comments both in support of, and opposed to, the
proposed changes. Comments opposing these provisions stated that this
additional requirement goes beyond the CAA's requirement to consider
the four statutory factors. The EPA disagrees with this assertion.
Congress declared a national goal of preventing any future and
remedying any existing visibility impairment in Class I areas resulting
from manmade air pollution and delegated to EPA the authority to
promulgate regulations assuring reasonable progress toward meeting that
goal. CAA section 169A(a)(1), (a)(4). The analytical obligations
contained in 40 CFR 51.308(f)(3)(ii) are a mechanism to ensure that
states are, in fact, making reasonable progress by requiring states in
certain circumstances to demonstrate the reasonableness of their four-
factor analyses. In addition, some commenters suggested that the term
``robust demonstration'' is overly vague and expressed concern that,
essentially, the EPA could take advantage of this vagueness in order to
form its own criteria for disapproval of a SIP. Most commenters did not
supply any specific suggestions, simply stating either that the term
should be clarified or that this provision should not be finalized,
although one commenter suggested states be allowed to refer to
information already submitted or contained in an applicable docket for
purposes of such a demonstration. We disagree that the requirement of a
``robust demonstration'' is vague. The provision requires the
demonstration to be based on the analysis in 40 CFR 51.308(f)(2)(i),
and further clarifies that the demonstration must document the criteria
used to determine which sources or groups of sources were evaluated and
how the four reasonable progress factors were considered. The purpose
of this demonstration is to show that a state conducted its analysis in
a reasonable manner and that there are no additional measures that
would be reasonable to implement in a particular planning period. A
state may refer to its own experience, past EPA actions, the preamble
to this rule as proposed and this final rule preamble, and existing
guidance documents for direction on what constitutes a reasoned
determination. Additionally, the EPA recently issued a draft guidance
document that addresses, among other things, the reasonable progress
analysis, which we expect to finalize in the near future. This guidance
can provide further direction regarding the types of information and
analyses a state may provide in its demonstration under 40 CFR
51.308(f)(3)(ii). The EPA is therefore finalizing this provision as
proposed. In addition, one commenter stated that the ``robust
demonstration'' language of the proposed 40 CFR 51.308(f)(3)(ii)(A) was
missing from the proposed 40 CFR 51.308(f)(3)(ii)(B). The EPA agrees
the necessary text was missing from proposal, as states with Class I
areas should be subject to the same type of demonstration as those
contributing states without Class I areas. Therefore, the final rule
includes in the requirements for a contributing state in 40 CFR
51.308(f)(3)(ii)(B) the same requirement for a robust demonstration
that appeared only in 40 CFR 51.308(f)(3)(ii)(A) at proposal.
    Some commenters stated a desire for corresponding rule text dealing
with situations where RPGs are equal to (``on'') or better than
(``below'') the URP or glidepath. Several commenters stated that the
URP or glidepath should be a ``safe harbor,'' opining that states
should be permitted to analyze whether projected visibility conditions
for the end of the implementation period will be on or below the
glidepath based on on-the-books or on-the-way control measures, and
that in such cases a four-factor analysis should not be required. Other
commenters suggested a somewhat narrower entrance to a ``safe harbor,''
by suggesting that if current visibility conditions are already below
the end-of-planning-period point on the URP line, a four-factor
analysis should not be required. We do not agree with either of these
recommendations. The CAA requires that each SIP revision contain long-
term strategies for making reasonable progress, and that in determining
reasonable progress states must consider the four statutory
factors.\101\ Treating the URP as a safe harbor would be inconsistent
with the statutory requirement that states assess the potential to make
further reasonable progress towards natural visibility goal in every
implementation period. Even if a state is currently on or below the
URP, there may be sources contributing to visibility impairment for
which it would be reasonable to apply additional control measures in
light of the four factors. Although it may conversely be the case that
no such sources or control measures exist in a particular state with
respect to a particular Class I area and implementation period, this
should be determined based on a four-factor

analysis for a reasonable set of in-state sources that are contributing
the most to the visibility impairment that is still occurring at the
Class I area.\102\ It would bypass the four statutory factors and
undermine the fundamental structure and purpose of the reasonable
progress analysis to treat the URP as a safe harbor, or as a rigid
requirement.
---------------------------------------------------------------------------

    \101\ CAA section 169A(b)(2)(B), (g)(1).
    \102\ The point that having a RPG that is on or below the URP
line is not a safe harbor has been articulated in past actions such
as the disapproval of the reasonable progress element of Arkansas'
SIP (see fn 32). Our approval of the reasonable progress element of
South Dakota's SIP is an example in which we approved the state's
RPGs even though the RPG for the most impaired days for two Class I
areas were above the respective URP lines, based on the state having
adequately considered the four statutory factors for important
contributing sources. 76 FR 76646 (December 8, 2011) (proposed
action) and 77 FR 24845 (April 26, 2012) (final action).
---------------------------------------------------------------------------

3. Final Rule

    The EPA is finalizing all of the previously described rule text
without any changes from the proposal, with the exception of including
in 40 CFR 51.308(f)(3)(ii)(B) the same requirement for a robust
demonstration that appeared only in 40 CFR 51.308(f)(3)(ii)(A) at
proposal.
    Emission inventories.
1. Summary of Proposal
    The EPA proposed language in 40 CFR 51.308(f)(2)(iv) regarding the
``baseline emissions inventory'' to be used by a state in developing
the technical basis for the state's long-term strategy. This was done
in order to reconcile this section with changes that have occurred to
40 CFR part 51, subpart A, Air Emissions Reporting Requirements, since
the RHR was originally promulgated in 1999. The proposed changes were
also intended to provide flexibility in the base inventory year the
state chooses to use, as the EPA has always intended if there is good
reason to use another inventory year.
2. Comments and Responses
    Commenters were split on whether to support the flexibility
afforded by the proposed rule text for selecting a year other than the
most recent NEI year as the year of the inventory to be used as the
basis for developing the long-term strategy. Some commenters supported
the proposal, while others preferred that EPA require or definitively
endorse that the 2011 NEI can be used as the base year for modeling for
the next periodic comprehensive SIP revisions. The latter view
generally resulted from concerns that while additional NEI versions,
such as the 2014 and 2017 NEI versions, should be available by the time
periodic comprehensive SIP revisions are due in 2021, there would not
be adequate time after release of these inventories to complete all the
modeling and analysis work required.
    Consideration of these comments uncovered significant ambiguity in
the text of 40 CFR 51.308(d)(3)(iii) of the 1999 RHR and ambiguity in
the proposed new 40 CFR 51.308(f)(2)(iv) that would reflect 40 CFR
51.308(d)(3)(iii). Specifically, the term ``the baseline inventory on
which [the state's] strategies are based'' in the 1999 RHR can be taken
to refer to the inventory that is used to assess the contribution that
sources make to visibility impairment (and the visibility benefits of
additional control measures, when such benefits are considered) for
individual sources or groups of sources. That information is critical
to the development of the long-term strategy and, in that sense, is the
information on which a state's strategies are to be based. However, we
believe that some commenters have taken the term to refer to the
inventory that is used as the expected starting point for the
photochemical modeling that they (and we) expect will be used to
project the RPG that quantifies the projected effect of all the
measures in the long-term strategy and other influences on visibility
at the end of the implementation period. The two bodies of information
are not necessarily the same, and they do not necessarily even need to
be for the same year in order to develop a SIP that provides for
reasonable progress. In fact, the modeled RPGs that are eventually
included in a SIP revision do not directly affect the development of
the long-term strategy, but rather they reflect that strategy. We are
revising the proposed regulatory text to make this clear. The final
regulations use the ``emissions information on which the State's
strategies are based'' to refer to the inventory that is used to assess
the contribution that sources make to visibility impairment and not to
the base year inventory used to model the RPGs.
    The requirement in the final version of 40 CFR 51.308(f)(2)(iv) is
that the emissions information on which the state is relying to
determine the emission reduction measures that are necessary to make
reasonable progress must include, but need not be limited to,
information on emissions in a year at least as recent as the most
recent year for which the State has submitted emission inventory
information to the Administrator under the Air Emissions Reporting
Requirements. To allow time for this information to be used in SIP
development, the rule provides for a 12-month ``grace period'' such
that a submission to the NEI in the period 12 months prior to the due
date of the SIP does not trigger this requirement. We agree with the
comments to the effect that there is no reason why a state should not
make at least some information for the year of its most recent
submission to the NEI part of the basis for its determination of the
emission reduction measures that are necessary to make reasonable
progress. The state is not required to use the same information as was
submitted to the NEI, and it should not if it has developed or received
better information for that year since its NEI submission. A state may
also consider information for a more recent year if it is available and
is of sufficient quality. Therefore, we do not believe it is necessary
or appropriate for the RHR to provide for an exception to the
requirement as it is stated in this section of the rule text and
interpreted here. A state that plans to use information other than what
is in the most recent NEI version released by the EPA to develop its
long-term strategy should consult with its EPA regional office to
obtain the EPA's preliminary perspective on whether there is a
reasonable basis for its planned approach. This should also be a topic
of the ongoing consultation with affected FLMs.
    The final version of 40 CFR 51.308(f)(2)(iv) does not address the
question of the year to be used as the base year for emissions modeling
of the RPGs. The EPA generally recommends that this be the year of the
most recent NEI version that has been developed and validated enough to
be appropriate for air quality modeling to support policy development.
The final rule provides the EPA flexibility to approve a SIP based on
another year if there are good reasons. States that believe that
another year is more suitable should consult with the EPA Regional
office about their reasons.
3. Final Rule
    For the reasons described previously, and also here, the final
language for 40 CFR 51.308(f)(2)(iv) differs somewhat from the wording
we proposed with respect to the terminology used to refer to emissions
inventories. The final version of this subsection of the rule refers to
the ``emissions information on which the state's strategies are
based,'' rather than to a ``baseline'' emissions inventory. The final
version also does not include a provision for EPA approval for
selecting a year other than the year of the most recent submission
under the Air Emissions Reporting Requirements as the year of the

inventory to be used as the basis for developing the long-term
strategy. However, the final rule provides a 12-month grace period for
the use of the year of the most recent submission under the Air
Emissions Reporting Requirements. The rule does not address the
selection of a year as the base year for emissions modeling of the RPGs
for the end of the implementation period.
    EPA action on RPGs.
1. Summary of Proposal
    The proposed language of 40 CFR 51.308(f)(3)(iv) was intended to
make clear that in approving a state's RPGs, the EPA will consider the
controls and technical demonstration provided by a contributing state
with respect to its long-term strategy, in addition to those developed
by the state containing the Class I area with respect to its long-term
strategy. This clarification was proposed in light of the 1999 RHR's 40
CFR 51.308(d)(1)(iii), which only explicitly mentions the demonstration
provided by the state containing the Class I area.
2. Comments and Responses
    No comments were received that specifically addressed this proposed
rule text.
3. Final Rule
    The EPA is finalizing this rule text as proposed.
    Progress report elements of periodic comprehensive SIP revisions.
1. Summary of Proposal
    The proposed language in 40 CFR 51.308(f)(5) complemented proposed
changes regarding progress reports and the proposal to eliminate
separate progress reports being due simultaneously with periodic
comprehensive SIP revisions by requiring periodic comprehensive SIP
revisions to include certain information that would have been addressed
in the progress reports. While the proposed language would expand the
scope of periodic comprehensive SIP revisions, the same information
would still be covered and states would no longer need to prepare and
submit two separate documents (potentially containing overlapping
content) at the same time.
2. Comments and Responses
    Few comments were received that specifically addressed this
proposed rule text. Those that did address these provisions supported
the proposed changes, with one comment additionally suggesting use of
the terminology ``the most recent progress report'' instead of ``the
past progress report,'' which EPA is incorporating into the final text
(this is discussed later). In addition, one commenter noted that states
should also be required to address the requirements of proposed 40 CFR
51.308(g)(8) in periodic comprehensive SIP revisions. Proposed 40 CFR
51.308(g)(6), renumbered in the final rule as 40 CFR 51.308(g)(8),
requires progress reports to include a summary of the most recent
assessment of smoke management programs operating within the state if
such assessments are an element of the program. (As background, this is
not a requirement of the 1999 RHR for either progress reports or
periodic SIP revisions.) We agree that the provisions of 40 CFR
51.308(f)(5) do not contain a requirement similar to the requirement in
proposed 40 CFR 51.308(g)(6) or final 40 CFR 51.308(g)(8). However, for
any state where smoke from prescribed fires is a significant
contributor to visibility impairment, the analysis that it will perform
under 40 CFR 51.308(f)(3)(iv)(D) as finalized (the requirement for a
state to consider basic smoke management practices and smoke management
programs) will serve the same purpose as would requiring periodic SIP
revisions to summarize the conclusions of the most recent assessment of
an existing smoke management program.
3. Final Rule
    The EPA is finalizing this rule text as proposed with only minor
wording changes for clarity including a small change in wording in
response to a public comment indicating confusion with the terminology
``past progress report.'' The EPA agrees that this should instead refer
to the ``most recent progress report'' and is finalizing revised text
accordingly.

E. Changes to Definitions and Terminology Related to How Days Are
Selected for Tracking Progress

1. Summary of Proposal
    The 1999 RHR's 40 CFR 51.308(d) required states to determine the
visibility conditions (in deciviews) for the average of the 20 percent
least impaired and 20 percent most impaired visibility days over a
specified time period at each of their Class I areas. As discussed in
detail in the preamble of the proposed rule, the definition of
visibility impairment included in 40 CFR 51.301 of the 1999 RHR
suggests that only visibility impacts from anthropogenic sources should
be included when considering the degree of visibility impairment.
However, the approach followed for the first implementation period
involved selecting the least and most impaired days as the monitored
days with the lowest and highest actual deciview levels regardless of
the source of the particulate matter causing the visibility impairment.
While the EPA approved SIPs using this approach for the first
implementation period, experience now indicates that for the most
impaired days an approach focusing on anthropogenic impairment is more
appropriate because it will more effectively track whether states are
making progress in controlling anthropogenic sources. Our proposed
approach is also more consistent with the definition of visibility
impairment in 40 CFR 51.301. Because the 1999 RHR rule text already
refers to the 20 percent most impaired days, we did not propose to
change that wording. In the preamble to the proposal, we made clear
that going forward, we would interpret ``most impaired days'' to mean
those with the greatest anthropogenic visibility impairment, as opposed
to the 20 percent haziest days. We did not propose to change the
approach of using the 20 percent of days with the best visibility to
represent good visibility conditions for RPG and tracking purposes, but
we did propose a rule text change to refer to them as the 20 percent
clearest days rather than the 20 percent least impaired days.
    The proposal included changes to a number of the definitions in 40
CFR 51.301 as well as added definitions for some previously undefined
terms, including clearest days, the deciview index, natural visibility
conditions and visibility.
    The EPA solicited comment on requiring all states to use the new
meaning of ``most impaired days'' as referring to the days with the
most anthropogenic impairment, as well as on a second proposed
approach. In the second proposed rule alternative, states would be
allowed to choose between selecting the 20 percent of days with the
highest overall haze (i.e., the approach used in the first
implementation period) and selecting the 20 percent of days with the
most impairment from anthropogenic sources (the proposed new meaning).
The EPA also solicited comment on any additional approaches.
2. Comments and Responses
    We received some comments favoring the first proposed rule
alternative that expressed support for a single, consistent approach to
selecting the 20 percent most impaired days for all states. However,
the majority of comments from states favored the second proposed rule
alternative due to

the flexibility it offered. Some comments on the second proposed rule
alternative expressed concerns about, and requested guidance for,
consultation between states in situations where two states use
different approaches. Some comments favoring the second proposed rule
alternative said that they anticipated that using the 20 percent most
anthropogenically impaired days would mean an additional workload that
would consume state resources during the planning process, and cited
this as the reason they did not support the first proposed rule
alternative. One commenter suggested that the final rule could allow
states submitting their SIPs for the second implementation period by
the 1999 RHR's deadline of July 31, 2018, to choose between using the
20 percent most anthropogenically impaired days or the 20 percent
haziest days, with states submitting later required to use the latter
approach.
    After considering these comments and other considerations as
described here, we are finalizing the first proposed alternative for
the final rule (i.e., that ``most impaired days'' means those with the
most anthropogenic impairment). The EPA often provides states
flexibility when it may help achieve the objectives of SIP development
and does not negatively implicate a program's objectives. In this
particular situation, however, the flexibility of the second proposed
rule approach would not significantly assist in developing efficient
and effective SIPs and would likely result in confusion among
stakeholders. For example, if two states with Class I areas in close
proximity choose different approaches to the selection of days, the
public might misunderstand how past and projected progress in improving
visibility compares between the two areas. Also, allowing the state
with a Class I area to unilaterally choose the selection approach for
that area would raise the prospect that a contributing state might
disagree with that choice, because the choice could make a difference
in whether both states are subject to the enhanced analysis requirement
of 40 CFR 51.308(f)(3)(ii), therefore complicating consultation among
states. It would be possible for a state to choose a given approach
simply because it would result in the best comparison of RPGs to the
glidepath or URP for the implementation period being addressed by a SIP
revision, and a state could conceivably switch back and forth between
the two approaches from one period to another to get the best
comparison for each period, causing additional confusion. In addition,
we believe the approach of using anthropogenic impairment to select the
20 percent worst days is more consistent with the intent of the
original RHR, namely to reduce the aggregate effect that anthropogenic
sources have on the visual experience of visitors to Class I areas.
    The EPA disagrees that concerns regarding additional workload and
lack of resources preclude adopting the first proposed alternative. The
EPA and IMPROVE program will work together to provide datasets that
identify the most anthropogenically impaired days in each year of
IMPROVE data and that contain the statistical summaries of these days
need as part of a SIP revision or progress report. These datasets will
be based on a specific method the EPA intends to recommend in a future
guidance document. We expect that these datasets will avoid any
increase in the workload and resources required of states relative to
continued use of the haziest days. We will also work with any state or
states interested in a different specific method for identifying the
most impaired days than the one we will recommend, to avoid an increase
in workload that would interfere with other aspects of SIP development.
    The final rule revisions requiring states to use the 20 percent of
days with the greatest anthropogenic impairment do not have any direct
implications for how states develop their long-term strategies. While
these revisions may affect whether a state has to demonstrate that
there are no additional measures that would be reasonable to include in
the long-term strategy under the requirement of 40 CFR
51.308(f)(3)(ii), these revisions do not prescribe how a state may make
this demonstration. Thus, we believe that this requirement will not
impair states' flexibility to appropriately analyze and address the
sources of visibility impairment at Class I areas in and near their
states.
    We are not making any changes in response to the comment suggesting
that the final rule provide flexibility in the approach to the
selection of the worst days only for areas that submit their SIP
revisions by July 31, 2018. It is our understanding that only some
eastern states may be submitting SIP revisions this early and that the
states involved have not been experiencing erratic impacts from
wildfires and dust storms. Therefore, we do not believe the special
flexibility the commenter suggests is needed. As mentioned, any state
may choose to include in its SIP a second summary of visibility data
using the 20 percent haziest days approach, for public information
purposes.
    Regarding the proposed changes to definitions, commenters
recommended adding language to the definitions of most impaired days,
regional haze, and visibility impairment to further clarify that these
terms refer to impairment due to anthropogenic sources. The EPA agrees
that some of the suggestions provided by commenters further clarify
that visibility impairment is due to anthropogenic sources and does not
include emissions from natural sources. Therefore, in response to these
comments, we have finalized additional changes to the definitions of
most impaired days, regional haze, and visibility impairment to also
include the concept that impairment is anthropogenic.
    We also received comments on the proposed change to the definition
of natural conditions and the proposed definition of natural visibility
conditions. The commenters asked the EPA to further revise these
definitions to reflect the reality that natural conditions have changed
over time and will continue to change in the future; to make clear the
timeframe of natural visibility conditions we intend to be captured by
the definition; that natural visibility conditions may reflect poor
visibility conditions; and to more explicitly include the factors
contributing to natural visibility conditions (e.g., fire and dust
events, volcanic activity, etc.). As a result of these comments, we are
finalizing additional changes to these two definitions and adding
definitions for two additional terms used in the rule. We are also
providing further explanation of the role of natural visibility
conditions in the SIP development process as follows.
    The EPA is finalizing the definition of natural conditions to
include a list of example phenomena considered to be a part of natural
conditions. The list provided is not intended to be exhaustive, but
provides examples of some of the types of natural impacts that may
affect Class I areas. We are also finalizing the definition of natural
conditions to reflect the EPA's understanding that natural conditions
not only will vary with time, but that they also may have long-term
trends due to changes in the Earth's climate system. We have also
clarified in this definition that natural phenomena both near to and
far from a Class I area may impact visibility in the Class I area.
    To reduce confusion between the natural visibility that would exist
on a single day and the average of a set of natural visibility values
for a set of days, we are finalizing separate definitions of natural
visibility and natural visibility

condition. Natural visibility will refer to visibility on a single day.
The natural visibility definition includes language that recognizes
natural visibility does vary daily and may contain long-term trends.
Natural visibility condition will refer to the average of a set of
values on an indicated set of days.
    In practice, the natural visibility condition for the 20 percent
most impaired days is used by a state when developing the most
appropriate 2064 endpoint for the URP line. Then the RPG for the 20
percent most impaired days is to be compared with the point on the URP
line corresponding to the end date of the implementation period, which
will in effect be adjusted by a portion of the adjustment made to the
2064 endpoint. The EPA invited comment on draft guidance \103\ to the
states on how to determine the value of the 2064 natural visibility
condition for the 20 percent most impaired days for each Class I area
for purposes of calculating the URP, and we intend to provide final
guidance on this topic separately from this action on revisions to the
RHR.
---------------------------------------------------------------------------

    \103\ Draft Guidance on Progress Tracking Metrics, Long-Term
Strategies, Reasonable Progress Goals and Other Requirements for
Regional Haze State Implementation Plans for the Second
Implementation Period. 81 FR 44608 (July 8, 2016).
---------------------------------------------------------------------------

    The need for clarity about the distinction between visibility on
one day and the average of the visibility values for a set of days also
applies to baseline visibility conditions and to current visibility
conditions. To achieve this clarity, the final rule text includes new
definitions of the terms baseline visibility condition and current
visibility condition. These definitions are consistent with the way
these terms are used in 40 CFR 51.308, but having these explicit
definitions will improve understanding by participants in the regional
haze program.
3. Final Rule
    The EPA is finalizing the requirement that all states select the 20
percent most impaired days, i.e., the days with the most impairment
from anthropogenic sources, as the ``worst'' days for purposes of
calculating baseline visibility conditions, current visibility
conditions, natural visibility conditions and the URP in SIPs and, as
applicable, in progress reports. Under the final rule revisions, states
retain the option to also present visibility data using the days with
the highest overall deciview index values (i.e., the 20 percent haziest
days), for public information purposes. Including this information in
the SIP may help communicate to the public the magnitude of impacts
from natural sources including wildland wildfires and dust storms. The
RPGs and URP line that are calculated using anthropogenic impairment to
select the most impaired days constitute the glidepath representing the
state's determination of reasonable progress and, if appropriate, may
trigger the requirement for a state to show that there are no
additional emission reductions measures that would be reasonable to
include in the long-term strategy (see Section IV.D of this document).
Since the 20 percent most anthropogenically impaired days will, going
forward, be used to estimate natural visibility conditions, current
visibility conditions and the URP, they must also be used in setting
RPGs and in progress reports. Conforming edits that were proposed to
the provisions related to each of these calculations are likewise being
finalized. As described at proposal, the revised approach will apply
starting with the second and subsequent periodic comprehensive SIP
revisions and will apply to progress reports starting with those
submitted after the second SIP revision. EPA will continue to use the
previous approach of considering the 20 percent haziest days with
respect to SIP revisions submitted to satisfy the requirements of the
first implementation period or initial progress reports.
    The EPA did not propose to require any particular method for
determining the natural versus anthropogenic contributions to daily
haze and thus the degree of visibility impairment for each monitored
day. The EPA issued draft guidance \104\ describing a recommended
approach along with a process for routinely providing relevant datasets
for use by states when they develop their SIPs and progress reports. No
particular method is being prescribed by the final rule nor will the
final version of the guidance contain any binding requirements; states
can therefore develop, justify and use another method of discerning
natural and anthropogenic contributions to visibility impairment in
their SIPs. The EPA intends to include more information on this subject
in the final guidance.
---------------------------------------------------------------------------

    \104\ 81 FR 44608 (July 8, 2016).
---------------------------------------------------------------------------

    As described in the summary of comments on this topic, the EPA is
finalizing the proposed changes to the definitions of clearest days,
deciview, deciview index, least impaired days, and visibility along
with additional changes we have determined are needed to further
clarify the definitions of most impaired days, visibility impairment,
regional haze, natural conditions, and natural visibility condition.
The additional changes to these proposed definitions are intended to
more clearly explain that impairment is from anthropogenic sources and
that natural sources and their contributions to visibility vary over
time. Additionally, the EPA is finalizing definitions for natural
visibility, baseline visibility condition, and current visibility
condition that we determined are needed to fully clarify the meanings
of these terms.
    We are not finalizing the proposed change to the definition of a
Federal Class I area that would have stated that non-mandatory Federal
Class I areas are identified in 40 CFR part 52. There currently are no
non-mandatory Federal Class I areas and the reference to 40 CFR part 52
could have created confusion. The final definition of a mandatory Class
I Federal area correctly indicates that the mandatory areas are
identified in 40 CFR part 81 subpart D.

F. Impacts on Visibility From Anthropogenic Sources Outside the U.S.

1. Summary of Proposal
    In the proposal, the EPA acknowledged that emissions (natural and
anthropogenic) from other countries and marine vessel activity in
waters outside the U.S. may impact Class I areas, especially those
areas near borders and coastlines. Prior to our proposal, several
states with such Class I areas requested that they be allowed to adjust
their URP line, visibility tracking metrics and RPGs to account for
international anthropogenic impacts when preparing SIPs and progress
reports.\105\ We therefore solicited comment on a proposed provision
that would allow states with Class I areas significantly impacted by
international anthropogenic emissions to adjust their URPs with
approval from the Administrator.\106\ The proposed

adjustment would consist of adding to the value of the natural
visibility condition for the 20 percent most impaired days in 2064 an
estimate of the average impact from international anthropogenic sources
on such days,\107\ for the sole purpose of calculating the URP.\108\ We
also solicited comment on another possible approach to accounting for
international anthropogenic impacts, in which the influence of
emissions from anthropogenic sources outside the U.S. would be removed
from estimates of 2000-2004 baseline visibility conditions, current
visibility conditions and the RPG for the end of an implementation
period.
---------------------------------------------------------------------------

    \105\ The impacts from natural sources located outside the U.S.
can be large in certain Class I areas, but because the RHR treats
impacts from all natural sources equally, those impacts are
inherently properly included in the 2000-2004 baseline condition
used as the starting point for the URP line and the natural
visibility condition used as the 2064 endpoint of the URP line.
Thus, the logical interest of these states was in a special
adjustment for the impacts of anthropogenic sources outside the U.S.
We note for clarity that under the final rule, prescribed fires
outside of the U.S. are considered anthropogenic sources and thus
the discussion in this section is relevant to such prescribed fires.
Prescribed fires in wildland are also addressed in Section IV.G of
this document.
    \106\ The 1999 RHR provided that if a state found that
international emissions sources were affecting visibility conditions
in a Class I area or interfering with plan implementation, that
state could submit a technical demonstration in support of its
finding. If EPA agreed with the finding, it would ``take appropriate
action to address the international emissions through available
mechanisms.'' 64 FR 35714, 35747 (July 1, 1999).
    \107\ The URP line is expressed in deciview units, so the value
added to the natural visibility condition would also be in
deciviews. However, that added deciview value would be based on the
light extinction increments caused by the indicated sources.
    \108\ This proposed extra step in determining the URP was not
intended to have the effect of defining international anthropogenic
sources as natural, or to change any other aspect of SIP
development.
---------------------------------------------------------------------------

    The proposal reflected the EPA's position that it may be
appropriate to allow a state to adjust the RPG framework, including in
its progress reports, to avoid any perception that a state should be
aiming to compensate for impacts from international anthropogenic
sources and to avoid requiring a state to undertake the additional
analytical requirement under 40 CFR 51.308(f)(3)(ii) based solely on
visibility impairment due to international anthropogenic sources.
However, we proposed that an adjustment to compensate for such impacts
would be available only when and if these impacts can be estimated with
sufficient accuracy. In the proposal we stated that we do not expect
that explicit consideration of impacts from anthropogenic sources
outside the U.S. should or would actually affect the conclusions that
states make about what emission controls for their own sources are
necessary for reasonable progress. However, we explained that explicit
quantification of international anthropogenic impacts, if accurate,
could improve public understanding and effective participation in the
development of regional haze SIPs. We also indicated that while we had
not yet, at the time of the proposal, seen an approach that would allow
states to adjust their visibility tracking metrics with sufficient
accuracy, we expected that by the time some future periodic
comprehensive SIP revisions are to be prepared, methods and data for
estimating international anthropogenic impacts will be substantially
more robust. Our proposal did not include any statement about whether
EPA would provide estimates on international impacts or guidance on how
states can estimate such impacts.
2. Comments and Responses
    Some commenters opposed allowing any adjustment to the URP, while
others supported some sort of adjustment based on the impacts of
international anthropogenic sources. Several commenters stated that the
EPA or other federal entities should provide an approach to estimating
international anthropogenic impacts, or actual estimates of such
impacts, that are presumptively approvable, or that the EPA should give
deference to any estimate a state develops. Some commenters inferred
that the EPA's statements in the proposal regarding the current state
of the art for estimating international anthropogenic impacts meant
that no state would be able to obtain EPA approval for an adjustment in
the SIP due in 2021. Several commenters objected to their understanding
that the proposed rule would require a state to obtain EPA approval for
a particular adjustment approach before including such an approach in
its SIP submission. Finally, at least one commenter requested that EPA
also provide rule language allowing for adjustment of the 20 percent
clearest days framework to reflect the impacts of international
anthropogenic sources.
    The EPA does not have a near-term plan to develop guidance on
estimating international anthropogenic impacts or to provide such
estimates specifically for the purpose of regional haze SIPs. However,
the EPA is an active participant in research in this area and will
continue to share its work with interested states and with others.\109\
To clarify, the statements in the preamble regarding the state of the
art method refer to our assessment of the estimates and models for
estimating international impacts available in the scientific literature
at the time of this rulemaking. We did not intend to preclude or
prejudge consideration of estimates that states may include in SIPs for
the second implementation period or subsequent periods based on newer
and more refined methodologies and/or information. Although we do not
believe such estimates and models are currently able to adequately
represent the impacts of international anthropogenic sources on
visibility, we acknowledge that this is an area of active research and
development that may lead to adequate estimates in time for the
development of SIPs for the second implementation period. Additionally,
the final rule text includes a small change to clarify that the
Administrator's approval for an adjustment will be part of the
Administrator's review of the full SIP submission for an implementation
period, and not a separate action in advance of SIP submission. In this
way, the Administrator's decision to approve or not approve the
adjustment will be made in the context of the complete SIP submission,
with public notice and an opportunity to comment. As with any SIP
element, states are encouraged to consult with EPA Regional offices
during the development of any proposed adjustment approach.
---------------------------------------------------------------------------

    \109\ For example, the EPA held a 2-day workshop in February
2016 to advance the collective understanding of technical and policy
issues associated with background ozone, which includes impacts from
anthropogenic sources outside the U.S., as part of the agency's
ongoing efforts to engage with states and stakeholders on
implementation of the 2015 ozone NAAQS. While this workshop focused
on ozone, the modeling issues and approaches for ozone are similar
to those for visibility-impairing pollutants. More information on
the EPA's activities and current understanding of this area can be
found in the white paper available at https://www.epa.gov/ozone-pollution/background-ozone-workshop-and-information and other
documents available in EPA number EPA-HQ-OAR-2016-0097 at https://www.regulations.gov.
---------------------------------------------------------------------------

    Because the EPA is not providing estimates of international
anthropogenic impacts or guidance for calculating those impacts at this
time, we are not specifying that any such estimates or methodologies
are presumptively approvable. We further disagree with comments that
states have inherent discretion to adjust their URP and RPG frameworks
to account for impacts of international anthropogenic sources and that
the EPA lacks the authority to review such adjustments. As explained in
Section IV.B of this notice, the CAA mandates that the EPA promulgate
regulations requiring that states' SIP submittals contain, among other
things, ``measures as may be necessary to make reasonable progress
toward meeting the national goal.'' \110\ Furthermore, the EPA is
required to ensure that states' submittals meet the basic legal
requirements and objectives of the CAA, including any regulations the
agency promulgates for the purpose of ensuring that states make
reasonable progress towards achieving natural visibility. A proposed
adjustment to a state's RPG framework to address the impacts of
international anthropogenic sources has the potential to affect that
state's assessment of what constitutes reasonable progress. Thus, the
EPA not only has the authority to review a state's

proposed adjustment, it has an obligation to do so.
---------------------------------------------------------------------------

    \110\ CAA section 169A(b)(2).
---------------------------------------------------------------------------

    Finally, we disagree with the comment that we should provide rule
language for states to adjust their frameworks for assessing visibility
on the 20 percent clearest days to account for any impacts of
international anthropogenic sources. First, particular days on which
international anthropogenic sources have particularly strong impacts
due to unusual source events or transport conditions are unlikely to be
among the 20 percent clearest days in their respective years. The
commenter presented no basis for anticipating that increasing impacts
from anthropogenic sources on the clearest days might cause a state to
be unable to satisfy the no degradation requirement without employing
unreasonable measures for domestic sources. Second, our analysis
indicates that such an adjustment would not have been necessary in the
first implementation period, in that nearly all Class I areas in fact
have had no degradation during this period so far, and the few that
have experienced degradation have not done so because of impacts
attributable to international anthropogenic sources. Improvements in
visibility on the 20 percent clearest days have been significant enough
so that we expect that states impacted by increased emissions from
international anthropogenic sources in the second implementation period
will still be able to comply with the requirement that visibility on
those days show no degradation compared to 2000-2004 baseline
conditions. The RTC contains more information on this improvement
trend. The EPA will continue to assess this relationship throughout the
second and subsequent implementation periods. Third, on clear days when
there is relatively little visibility-impairing air pollution, it is
difficult with our current tools to discern the portion of that air
pollution originating from international anthropogenic sources, as
opposed to domestic anthropogenic or natural sources and as compared to
the assessment of the impact of international anthropogenic sources on
the most impaired days. It would thus be unlikely that a state could
estimate international anthropogenic impacts on the 20 percent clearest
days with the requisite degree of accuracy at this time or when
developing a SIP for the second implementation period.
3. Final Rule
    The EPA is finalizing the provision to allow an adjustment of the
URP by adding an estimate for international anthropogenic impacts to
2064 natural visibility conditions. We are not finalizing the
alternative approach to accounting for international anthropogenic
impacts that would have involved removing the influence of emissions
from anthropogenic sources outside the U.S. when developing the
estimates of 2000-2004 baseline visibility conditions, current
visibility conditions and the RPGs. We are finalizing only one approach
to provide consistency and transparency, as the alternative approach
would have been more complicated and involved presenting numerous
counterfactual values of visibility levels that could be mistaken as
actual measured values.
    Because this adjustment is permitted only if the Administrator
determines that a state has estimated the international impacts from
anthropogenic sources outside the U.S. using scientifically valid data
and methods, we are finalizing the rule text of 40 CFR
51.308(f)(1)(vi)(B) as proposed, with a small change to clarify
singular versus plural,\111\ as well as the aforementioned change to
clarify that the Administrator's approval for an adjustment will be
part of the Administrator's review of the full SIP submission for an
implementation period, and not a separate action in advance of SIP
submission.
---------------------------------------------------------------------------

    \111\ Our proposed rule text used the phrase ``the State must
add the estimated impacts [of international anthropogenic sources
(or certain prescribed fires)] to natural visibility conditions and
compare the resulting value to baseline visibility conditions.'' For
consistency with our final definitions, this part of the final rule
text instead refers to the natural visibility condition and the
baseline visibility condition. The use of the plural form for
``natural visibility conditions'' and ``baseline visibility
conditions'' could give the impression that multiple values of
impacts are to be added to multiple values of natural visibility
conditions, when actually a single value reflecting impacts from
international anthropogenic sources (or certain prescribed fires) is
to be added to the single value of the ``natural visibility
condition'' for the 20 percent most impaired days. The final rule
text does not specify that the average of estimates of daily
international impacts be used in this addition step, so that states
can propose and the Administrator can approve another statistic to
represent the distribution of daily values, for example the median
value, if more appropriate.
---------------------------------------------------------------------------

    In addition, we are finalizing the proposed rule text changes in 40
CFR 51.308(f)(1)(i) and 40 CFR 51.308(f)(1)(vi) to remove ``needed to
attain natural visibility conditions'' from the reference to ``uniform
rate of progress,'' because when adjusted to reflect international
impacts the ``uniform rate of progress'' would not be the rate of
progress that would reach true natural visibility conditions.
    Because the manner in which a state with a Class I area calculates
the URP may affect other states with sources that contribute to
visibility impairment at the Class I area,\112\ we recommend that a
state seeking approval for such an adjustment first consult with
contributing states. Such an adjustment should also be a topic for the
required consultation with the FLM for the Class I area at issue.
---------------------------------------------------------------------------

    \112\ Contributing states may be affected because under the
final version of 40 CFR 51.308(f)(3)(iv)(B), a contributing state
will have an additional analytical requirement if the RPG does not
provide for the URP at an affected Class I area in another state.
---------------------------------------------------------------------------

G. Impacts on Visibility From Wildland Fires

1. Summary of Proposal
    Fires on wildlands within and outside the U.S. can significantly
impact visibility in some Class I areas on some days but have little to
no impact in other Class I areas. And even in those Class I areas
significantly impacted by fires on wildlands on some days, there are a
greater number of days where fires do not have such impacts. The EPA
presented an extensive discussion of wildland fire concepts, including
actions that the manager of a prescribed fire can take to reduce the
amount of smoke generated by a prescribed fire and/or to reduce public
exposure to the smoke that is generated (i.e., basic smoke management
practices), in the proposed and recently finalized revisions to the
Exceptional Events Rule.\113\ That discussion is not repeated here.
---------------------------------------------------------------------------

    \113\ 80 FR 72840 (November 20, 2015); 81 FR 68216 (October 3,
2016). Both the preamble and final rule of the Exceptional Events
Rule listed six basic smoke management practices with an important
footnote which recognizes that those listed are not intended to be
all-inclusive for the purpose of the Exceptional Events Rule.
Section IV.G.2 of this document discusses the term ``basic smoke
management practices'' in the context of the Regional Haze Rule.
---------------------------------------------------------------------------

    The preamble for our proposed action discussed at length how the
RHR relates to the management of wildland wildfires and wildland
prescribed fires. The information presented there is applicable to
states as guidance under these final RHR revisions, except as revised
or supplemented as follows. There were many public comments on the
subject of wildland fires, some of which are addressed in this section.
We address the remaining comments in the RTC document for this action.
    We proposed new definitions for wildland, wildfire and prescribed
fire. These proposed definitions were consistent with the definitions
we had recently proposed be added to the Exceptional Events Rule. We
said in the proposal for the Exceptional Events Rule that wildland can
include

forestland, shrubland, grassland and wetlands, and that the proposed
definition of wildland includes lands that are predominantly wildland,
such as land in the wildland-urban interface. The proposed definition
for wildfire included a provision that a wildfire that occurs
predominantly on wildland is a natural event.
    We also proposed language for new 40 CFR 51.308(f)(2)(vi)(E) based
on the provisions of the 1999 RHR's 40 CFR 51.308(d)(3)(v)(E), with
updates to reflect terminology used within the air quality and land
management communities. Specifically, we proposed to use the term
``basic smoke management practices'' to better align with current usage
of ``smoke management practices'' in the fire management community to
refer to steps that a burn manager can take to reduce emissions during
a prescribed fire. We also proposed to use the term ``wildland
vegetation management purposes'' in lieu of ``forestry management
purposes.'' This latter change was proposed in recognition of the fact
that not all wildland for which fire and smoke are issues is forested.
We also proposed to replace the phrase ``including plans as currently
exist within the State for these purposes'' with ``and smoke management
programs for prescribed fire as currently exist within the State.'' The
term ``smoke management program'' is used within the fire management
community to refer to a multi-participant program that seeks to
influence or regulate both whether and when prescribed fires are
conducted and, typically, the smoke management practices employed
during a prescribed fire. We stated in the preamble of the proposal
that this required consideration of smoke management programs only
applies if the existing smoke management program has six key features:
(i) Authorization to burn, (ii) minimizing air pollutant emissions,
(iii) smoke management components of burn plans, (iv) public education
and awareness, (v) surveillance and enforcement and (vi) program
evaluation.
    We proposed that for a state with a long-term strategy that
includes a smoke management program for prescribed fires on wildland,
each required progress report must include a summary of the most recent
periodic assessment of the smoke management program including
conclusions the managers of the smoke management program or other
reviewing body reached in the assessment as to whether the program is
meeting its goals regarding improving ecosystem health and reducing the
damaging effects of catastrophic wildfires. (Comments on this proposal
are summarized in Section IV.H of this document.)
    We proposed that the Administrator may approve a state's proposal
to adjust the URP to avoid subjecting a state to the additional
analytical requirement of 40 CFR 51.308(f)(3)(ii) due to the impacts of
wildland fire conducted with the objective to establish, restore and/or
maintain sustainable and resilient wildland ecosystems, to reduce the
risk of catastrophic wildfires, and/or to preserve endangered or
threatened species for purposes of ecosystem health (objectives that we
refer to here as ``wildland ecosystem health'') and public safety
during which appropriate basic smoke management practices were applied.
This aspect of the proposal did not address and did not apply to fires
of any type on lands other than wildland or to burning on wildland that
is for purposes of commercial logging slash disposal rather than
wildland ecosystem health and public safety. This aspect of the
proposal was not restricted to prescribed fires within the U.S.
    We proposed to revise the definition of ``fire'' to remove the
phrase ``prescribed natural fire.'' However, we stated that the
definition of ``fire'' that would be revised appears in 40 CFR 51.301,
when it actually appears in 40 CFR 51.309(b)(4) and applies only to 40
CFR 51.309. We inadvertently did not make any change to 40 CFR
51.309(b)(4) in our proposed rule text. We proposed this revision to
remove ``prescribed natural fire'' from the ``fire'' definition because
the concept of a ``prescribed natural fire'' is inconsistent with our
proposal that all prescribed fires be considered anthropogenic sources.
We recognize that some prescribed fires are intended to emulate and/or
mitigate natural wildfires that would otherwise occur at some point in
time. We also recognize that some wildfires are appropriately allowed
to proceed for some time over an area without suppression in order to
help achieve land management objectives. However, to use the term
``natural'' and ``prescribed'' in one definition would cause confusion.
    While the direction of these proposals was towards providing states
considerable flexibility regarding measures to limit emissions from
wildland prescribed fire after having given reasonable consideration to
their options, it was not and is not our intention to in any way
discourage federal, state, local or tribal agencies or private land
owners from taking situation-appropriate steps to minimize emissions
from prescribed fires on wildland or prescribed fires on other types of
land.
2. Comments and Responses
    With regard to the definitions of prescribed fire and wildfire and
the related question of whether each type of wildland fire should be
considered as an anthropogenic versus non-anthropogenic event or
source, some commenters said that all wildland prescribed fires, or at
least all prescribed fires conducted under a smoke management program,
should be treated as non-anthropogenic. Other commenters said that all
or some wildfires should be treated as anthropogenic, noting that the
occurrence of wildfires is not purely natural in that past human
actions have affected fire risks and that current actions by humans
initiate some wildfires. We disagree with these and similar comments.
We recognize that prescribed fires in many cases are conducted because
natural wildfires have been previously suppressed, or as a substitute
for waiting for a wildfire to take place because conditions are such
that a wildfire would pose high risks. We also recognize that human
actions, in particular the suppression of wildfires in the past, have
affected the propensity of some wildlands to experience wildfires from
natural ignition sources such as lightning and that human actions such
as arson or careless smoking, fireworks, target practice or backyard
burning are the sources of the ignition of many wildland wildfires.
Thus, there is some basis for the perspective that prescribed fires
merit being treated somewhat like natural sources, as well as for the
opposite view that wildfires merit being treated somewhat as
anthropogenic sources. However, by declaring in section 169A(a) of the
CAA a national goal of remedying visibility impairment in Class I areas
``which impairment results from man-made air pollution,'' Congress
established a bifurcation between anthropogenic and non-anthropogenic
sources of air pollution. Given that prescribed fires involve conscious
planning by humans, it would be unreasonable for the rule to
categorically consider them to be natural events and natural sources of
air pollution.\114\ We consider wildfires

having natural causes of ignition to be natural sources of air
pollution. The provision that a wildfire that occurs predominantly on
wildland is a natural event also encompasses wildfires initiated by
human action because it is not always possible to determine the cause
of ignition for some wildfires, and because once ignited the progress
of these wildfires is largely determined by factors beyond human
control at the time. Therefore, it is appropriate to treat both
wildland wildfires with natural sources of ignition and the other types
of wildfires encompassed by the definition in 40 CFR 51.301 as natural
events and natural sources of air pollution.
---------------------------------------------------------------------------

    \114\ As explained in footnote 95, the rationale for allowing an
adjustment of the URP framework to address the impacts of wildland
prescribed fires does not stem from the fact that we are treating
these fires as natural sources of air pollution, as this is not the
case. Rather, we are providing for an adjustment because we
acknowledge that anthropogenic prescribed fire conducted for
purposes of ecosystem health and public safety during which
appropriate basic smoke management practices have been applied can
be consistent with the goal of making reasonable progress towards
natural visibility.
---------------------------------------------------------------------------

    These categorizations do not mean that prescribed fires necessarily
should or can be regulated in a manner similar to sources that are more
purely anthropogenic, such as industrial sources, or that no
consideration should be given to how human actions affect wildfire
occurrence. For the regional haze program, an implication of these
categorizations is that states are not required to consider additional
measures to reduce visibility impacts from wildfires when they develop
their regional haze SIP submissions. However, we believe that it is in
the public interest for states, and all managers of wildland, to
consider such measures to limit wildfire impacts on visibility on an
ongoing basis. We encourage them to do so, to help improve visitor
experiences in Class I areas, to protect public safety and health and
to protect ecosystems from the impacts of catastrophic wildfires. We
also believe that it is in the public interest for states, and all land
managers using prescribed fire, to consider measures that can reduce
the impact of prescribed fires on visibility in Class I areas and other
air quality objectives. As they consider measures to reduce the impacts
of prescribed fires on visibility, states may consider the benefits of
wildland prescribed fire use (including benefits to ecosystem health
and reduction in the risk of catastrophic wildfires) and the
opportunity provided by the final rule for a state to make an
adjustment to the URP to account for the impact of certain prescribed
fires.
    Regarding the proposal that would allow the Administrator to
approve an adjustment to the URP for impacts from at least some
wildland prescribed fires, some comments were in favor of this
provision while others suggested minor changes to the proposed
approach. Many comments did not support all the specifics of our
proposal for adjustment of the URP. Many commenters also said that the
EPA or the FLMs should provide guidance on how to estimate prescribed
fire impacts for the purposes of this adjustment and/or provide the
adjustment values themselves.
    Of those commenters who did not support all the specifics of our
proposal, one commenter said that states should be required to apply
the four statutory factors to prescribed fire in order to be eligible
to make any adjustment to the URP for prescribed fire impacts. Other
commenters said that adjustment should be allowed only for prescribed
fires conducted in accordance with any applicable smoke management
program. However, other commenters said that an adjustment should be
allowed to reflect the impacts of all types of prescribed fire and not
merely those that met the conditions proposed by the EPA based on
ecosystem or public health protection and use of basic smoke management
practices.
    We disagree with commenters that the adjustment of the URP should
be based on the impact of all prescribed fires, or all wildland
prescribed fires, rather than only wildland prescribed fire conducted
for purposes of ecosystem health and public safety during which
appropriate basic smoke management practices have been applied. The
fires that meet these conditions are fires conducted for purposes and
in accordance with practices that are consistent with the goal of
making reasonable progress towards natural visibility. We note,
however, that the availability of an adjustment to the URP for the
impacts of these particular prescribed fires does not in any way
restrict a state from considering additional measures or management
programs to address their impacts on visibility. We recommend that as a
state considers such measures, it should consult with managers of
federal, state and private lands that would be subject to such
measures; this may include federal agencies in addition to the federal
land manager of the Class I areas affected by sources in the state,
with whom consultation on the development of the SIP is a requirement
of the final rule. Furthermore, it is appropriate that for prescribed
fires conducted on lands other than wildlands, wildland fires conducted
for other purposes and wildland fires conducted without application of
basic smoke management practices, the URP should assume their impacts
will diminish to zero by 2064, just as the URP effectively assumes with
respect to other types of anthropogenic sources within the U.S.\115\
This will focus public and state attention on whether there are any
reasonable measures for reducing impacts from these other types of
prescribed fires. We also disagree with other commenters who
recommended that the adjustment be more restrictive and apply only to
prescribed fires conducted in compliance with a smoke management
program, because this would make the adjustment unavailable to some
states where it would be consistent with the goal of making reasonable
progress and where an adjustment would be an appropriate efficiency and
public communication approach.
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    \115\ If there is no adjustment of the 2064 endpoint of the URP
line for impacts from international anthropogenic sources, the URP
effectively assumes that emissions from these sources will be zero
in 2064. If there is an adjustment, the URP effectively assumes that
these sources continue to have emissions in 2064.
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    We also disagree with commenters that states should be required to
conduct a four-factor analysis for prescribed fire before being
eligible to adjust their URPs for the impacts of such fires. As we
explained earlier, we are limiting the availability of an adjustment to
only those wildland prescribed fires conducted for the purposes of
ecosystem health and public safety and in accordance with basic smoke
management practices. These particular types of fires are generally
consistent with the goal of making reasonable progress because they are
most often conducted to improve ecosystem health and to reduce the risk
of catastrophic wildfires, both of which can result in net beneficial
impacts on visibility.\116\ Therefore, as

long as these fires are conducted in accordance with basic smoke
management practices, an additional four-factor analysis in this
specific case might serve no purpose. States may consider additional
measures to address the impacts of these and other types of prescribed
fires, on the basis of a formal four-factor analysis if they choose or
after another form of consideration.\117\
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    \116\ There is similarity and a difference in the rationales for
an adjustment of the URP related to impacts from anthropogenic
sources outside the U.S. and an adjustment related to impacts from
wildland prescribed fire conducted for reasons of ecosystem health
and public safety with appropriate basic smoke management practices
applied. Because states cannot control and should not be expected to
compensate for impacts from international anthropogenic sources,
such international impacts should not be the sole reason that the
RPG is above the URP line. In contrast, states generally have
authority to regulate wildland prescribed fires within their
borders. However, because it is generally reasonable for wildland
prescribed fires of the type described to be conducted as determined
to be needed through appropriate planning processes, with
appropriate basic smoke management practices to reduce smoke impacts
on the public, states should have the flexibility to determine that
limiting the number of such wildland prescribed fires is not
necessary for reasonable progress. SIP development can be more
efficient and the public will better understand the progress being
made to control other types of sources if the URP is adjusted to
remove the influence of any projected increase in application of
this type of wildland prescribed fire. Also, as with international
anthropogenic impacts, this will avoid such fire impacts from being
a critical factor in whether the RPG is above the URP line.
    \117\ Another way of considering whether measures in addition to
BSMP are appropriate for prescribed fires conducted to improve
ecosystem health and to reduce the risk of catastrophic wildfires,
and/or considering what measures are appropriate for other types of
prescribed fires, could be to assess and conclude that a particular
subcategory of prescribed fires does not meaningfully impact
visibility at any Class I area. Such a conclusion could support a
decision not to require additional measures for that subcategory in
the LTS even though a formal four-factor analysis has not been
completed. A state might also include in its LTS measures aimed at
reducing impacts from a subcategory of prescribed fire because those
measures are already in effect in the state due to another CAA
requirement or due to state-only considerations. If so, a new formal
four-factor analysis of those measures would not be useful.
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    One commenter suggested that an adjustment for the impacts of
prescribed fires also be allowed as part of the demonstration that the
long-term strategy and RPGs ensure no degradation on the clearest days.
We disagree with this suggestion. First, the impacts from prescribed
fires will necessarily be small on the clearest days. The commenter
presented no basis for anticipating that increasing impacts from
prescribed fire on the clearest days might cause a state to be unable
to satisfy the no degradation requirement without employing
unreasonable measures for other source types. Second, our analysis
indicates that such an adjustment would not have been necessary in the
first implementation period, in that nearly all Class I areas in fact
have had no degradation during this period so far, and the few that
have experienced degradation have not done so because of impacts
attributable to prescribed fire. Improvements in visibility on the 20
percent clearest days have been significant enough so that we expect
that states impacted by increased emissions from prescribed fire in the
second implementation period will still be able to comply with the
requirement that visibility on those days show no degradation compared
to 2000-2004 baseline conditions. The RTC contains more information on
this improvement trend. The EPA will continue to assess this
relationship throughout the second and subsequent implementation
periods. Finally, on clear days when there is relatively little
visibility-impairing air pollution, it is difficult with our current
tools to discern the portion of that air pollution originating from
prescribed fire, as opposed to the assessment of the impact of
prescribed fire on the most impaired days. It would thus be unlikely
that a state could estimate prescribed fire impacts on the 20 percent
clearest days with the requisite degree of accuracy at this time or
when developing a SIP for the second implementation period.
    Regarding our proposal to use updated terminology in proposed 40
CFR 51.308(f)(2)(vi)(E), some commenters said that ``basic smoke
management practices'' was not the appropriate update of the term
``smoke management techniques'' because the latter term is not
explicitly restricted to ``basic'' techniques. We disagree with the
commenter that the phrase ``basic smoke management practices'' could be
interpreted as requiring a state to consider a narrower set of
practices than the phrase ``smoke management techniques.'' The EPA
listed six basic smoke management practices in both the preamble and
final rule of the Exceptional Events Rule with an important footnote
which recognizes that those listed are not intended to be all-inclusive
for the purposes of the Exceptional Events Rule. We similarly consider
the term ``basic smoke management practices'' in the context of the
Regional Haze Rule as allowing for additional basic smoke management
practices to be developed to address Class 1 visibility impacts. In
addition, this paragraph of the Regional Haze Rule specifies what a
state at a minimum must consider, and a state may consider other
measures as well. Accordingly, the final rule text in 308(f)(2)(iv)(D)
contains the phrase ``basic smoke management practices.''
    No commenters opposed the use of ``and smoke management programs''
in proposed 40 CFR 51.308(f)(2)(vi)(E) in place of ``including plans''
in 40 CFR 51.308(d)(3)(v)(E). However, there were other comments on
proposed 40 CFR 51.308(f)(2)(vi)(E) that concern the proposed retention
and meaning of the phrase ``as currently exist within the State for
these purposes.'' One commenter supported the concept that only states
with existing smoke management programs should be subject to this
specific requirement to consider smoke management programs. Another
commenter said that even with this restricted applicability, the
requirement to consider smoke management programs was too prescriptive
and states should be allowed to apply the same consideration to
prescribed fires as generally apply for all sources. One group of
commenters opposed the restriction to only states with existing smoke
management programs, and further suggested that listing only smoke
management practices and smoke management programs was insufficient and
that the rule should also require all states to consider other measures
to mitigate the impact of fire.
    After consideration of these comments and a review of how the EPA
and the states have applied 40 CFR 51.308(d)(3)(v)(E) during the first
implementation period, we decided that finalization of the phase ``as
currently exist with the State for these purposes'' cannot be said to
clearly be only a preservation of the existing requirement of the 1999
RHR, particularly when combined with the replacement of ``including
plans'' with ``and smoke management programs.'' In the first
implementation period the EPA never relied on a narrow interpretation
of the applicability of this part of 40 CFR 51.308(d)(3)(v)(E) in
reviewing a SIP. The final rule does not include the phrase ``as
currently exist with the State for these purposes'' because we have
decided that there is no rational basis for the restriction.\118\
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    \118\ Given the removal of the phrase ``as currently exist
within the state,'' the interpretation we articulated in the
proposal that this phrase refers only to smoke management programs
with the six listed features listed in the proposal is no longer
relevant.
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    The final version of 40 CFR 51.308(f)(2)(iv)(D) (renumbered)
requires that states consider basic smoke management practices and
smoke management programs when developing their long-term strategies.
As discussed in the preamble to our proposed action,\119\ these
requirements do not require a state to adopt basic smoke management
practices or programs into its regional haze SIP.\120\ As states
consider whether to adopt new measures that might affect the ability of
land managers to use prescribed fire, they may newly consider both the
effectiveness of their smoke management programs in protecting
visibility and the benefits of wildland prescribed fire for ecosystem
health and public safety. There are many ways that a state can give new
consideration to such practices and programs. For example, a state can
consider the need for including such measures in its SIP without
shoehorning them into a formal four-factor analysis. A state can also
consider them by determining based on analysis of IMPROVE data that
fires in general, and thus prescribed fires in

particular, are not a significant contributor to reduced visibility at
the Class I areas in the state (or impacted by the state). Therefore,
this requirement of the final rule will not impose a difficult
analytical burden on states or require them to adopt unreasonable
measures. However, a state cannot unreasonably determine that a
requirement for burn managers to use certain basic smoke management
practices is not necessary to make reasonable progress. If a state
determines that a requirement for burn managers to use certain smoke
management practices is necessary to make reasonable progress, the
long-term strategy must include such measure(s) in enforceable form.
The same applies to consideration of a smoke management program. One
possible outcome may be that a state reasonably does not make such a
formal determination, but nevertheless decides to revise its current
program regarding prescribed fires without incorporating the program
(or the program enhancements) into the SIP. Such an action could
indicate that the state has satisfied the requirement to consider basic
smoke management practices and smoke management programs.
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    \119\ See 81 FR 26958-59.
    \120\ Also, the EPA is not recommending that all states adopt
any particular measures for wildland fire because situations vary
too much from state to state and within states for any general
recommendation to be appropriate.
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    States also have the flexibility to allow reasonable use of
prescribed fire. As previously noted, one approach to reducing the
occurrence of wildland wildfires, and the risk of wildfires having
catastrophic impacts, is appropriate use of prescribed fire. The EPA
and the federal land management agencies will continue to work with the
states as they consider how use of prescribed fire may reduce the
frequency, geographic scale and intensity of natural wildfires, such
that vistas in Class I areas will be clearer on more days of the year,
to the enjoyment of visitors. States may also consider how the use of
prescribed fire on wildland can benefit ecosystem health, protect
public health from the air quality impacts of catastrophic wildfires
and protect against other risks from catastrophic wildfires. These
final rule revisions give states that have considered these factors,
and other relevant factors, the flexibility to provide and plan for the
use of prescribed fire, with basic smoke management practices applied,