provision supports the validity of SSM exemptions in SIP emission
limitations.\221\ In that situation, the state determined that
regulating the source category at issue was not a necessary or
appropriate means of meeting the requirements of the CAA. The EPA's
approval of that provision indicates that the Agency agreed with that
determination. This factual scenario is not the same as one in which
the state has determined that regulation of the source category is
necessary or appropriate to meet CAA requirements. Once the
determination is made that the source category must or should be
regulated, then the SIP provisions developed by the state to regulate
the source must meet applicable requirements. These include that any
limits on emissions must be consistent with CAA requirements, including
the requirement that any emission limitation limit emissions on a
continuous basis. The EPA agrees that a state can validly determine
that regulation of a source category is not necessary, so long as this
is consistent with CAA requirements. This is not the same as allowing
impermissible exemptions for emissions from a source category that must
be regulated.
---------------------------------------------------------------------------

    \221\ See 78 FR 12459 at 12512 (citing S.C. Code Ann. Regs. 61-
62.5 St 5.2(I)(b)(14)).
---------------------------------------------------------------------------

    Finally, the EPA does not agree with commenters' allegations that
that the EPA's interpretation of section 110(a)(2)(A) eliminates the
states' discretion to take local concerns into account when developing
their SIP provisions. Rather, for reasons discussed in more detail in
the EPA's response in section V.D.2 of this document regarding
cooperative federalism, the EPA's interpretation is

fully consistent with the principles of cooperative federalism codified
in the CAA. As courts have concluded, although Congress provided states
with ``considerable latitude in fashioning SIPs, the CAA `nonetheless
subjects the States to strict minimum compliance requirements' and
gives EPA the authority to determine a state's compliance with the
requirements.'' \222\ This interpretation is also consistent with
congressional intent that the EPA exercise supervisory responsibility
to ensure that, inter alia, SIPs satisfy the broad requirements that
section 110(a)(2) mandates that SIPs ``shall'' satisfy.\223\ Where the
EPA determines that a SIP provision does not satisfy legal
requirements, the EPA is not substituting its judgment for that of the
state but rather is determining whether the state's judgment falls
within the wide boundaries of the CAA.
---------------------------------------------------------------------------

    \222\ Michigan v. EPA, 213 F.3d 663, 687 (D.C. Cir. 2000)
(quoting Union Elec. Co. v. EPA, 427 U.S. 246, 256-57 (1976)).
    \223\ With respect to section 110(a)(2)(A), this means that a
SIP must at least contain legitimate, enforceable emission
limitations to the extent they are necessary or appropriate ``to
meet the applicable requirements'' of the Act. Likewise, SIPs cannot
have enforcement discretion provisions or affirmative defense
provisions that contravene the fundamental requirements concerning
the enforcement of SIP provisions.
---------------------------------------------------------------------------

    m. Comments that a ``general duty'' provision--or comparable
generic provisions that require sources to ``exercise good engineering
judgment,'' to ``minimize emissions'' or to ``not cause a violation of
the NAAQS''--inoculate or make up for exemptions in specific emission
limitations that apply to the source.
    Comment: Numerous commenters argued that even if some of the SIP
provisions with SSM exemptions identified in this SIP call are not
themselves emission limitations, they are nevertheless components of
valid emission limitations. According to these commenters, some SIPs
contain separate ``general duty'' provisions that are not affected by
SSM exemptions and thus have the effect of limiting emissions from
sources during SSM events that are explicitly exempted from the
emission limitations in the SIP. These general-duty provisions vary,
but most of them: (1) Instruct sources to ``minimize emissions''
consistent with good air pollution control practices, (2) prohibit
sources from emitting pollutants that cause a violation of the NAAQS,
or (3) prohibit source operators from ``improperly operating or
maintaining'' their facilities.
    Commenters contended that these general-duty provisions are
requirements that--either alone or in combination with other
requirements--have the effect of limiting emissions on a continuous
basis. In other words, the commenter asserted that these general-duty
provisions impose limits on emissions during SSM events, when the
otherwise applicable controls no longer apply. According to these
commenters, SSM exemptions that excuse noncompliance with typical
controls do not interrupt the continuous application of an ``emission
limitation,'' because these general-duty provisions elsewhere in the
SIP or in a separate permit are part of the emission limitation and
apply even during SSM events.
    Some commenters further argued that some SSM exemptions themselves
demonstrate that sources remain subject to general-duty provisions
during SSM events. These SSM exemptions require sources seeking to
qualify for the exemption to demonstrate that, inter alia, they were at
the time complying with certain general duties. Accordingly, these
commenters contended that the SSM exemption itself demonstrates that
sources remain subject to requirements that limit their emissions
during SSM events, even when the source is excused from complying with
other components of the overarching emission limitation.
    Finally, as evidence that these general-duty clauses must be
permissible under the CAA, some commenters pointed to similar federal
requirements established by the EPA under the NSPS and NESHAP
programs.\224\ These commenters argued that the D.C. Circuit's decision
in Sierra Club v. Johnson \225\ was limited to circumstances unique to
section 112 and does not support a per se prohibition on general-duty
clauses operating as ``emission limitations.''
---------------------------------------------------------------------------

    \224\ See, e.g., 40 CFR 63.6(e)(3).
    \225\ 551 F.3d 1019, 1027-28 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    Response: The EPA disagrees with these comments. As described
elsewhere in this response to comments, all ``emission limitations''
must limit emissions of air pollutants on a continuous basis.\226\ The
specific requirements of a SIP emission limitation must be discernible
on the face of the provision, must meet the applicable substantive and
stringency requirements of the CAA and must be legally and practically
enforceable. The general-duty clauses identified by these commenters
are not part of the putative emission limitations contained in these
SIP provisions. To the contrary, these general-duty clauses are often
located in different parts of the SIP and are often not cross-
referenced or otherwise identified as part of the putative continuously
applicable emission limitation.
---------------------------------------------------------------------------

    \226\ CAA section 302(k).
---------------------------------------------------------------------------

    Furthermore, the fact that a SIP provision includes prerequisites
to qualifying for an SSM exemption does not mean those prerequisites
are themselves an ``alternative emission limitation'' applicable during
SSM events. The text and context of the SIP provisions at issue in this
SIP call action make clear that the conditions under which sources
qualify for an SSM exemption are not themselves components of an
overarching emission limitation--i.e., a requirement that limits
emissions of air pollutants from the affected source on a continuous
basis. Rather, these provisions merely identify the circumstances when
sources are exempt from emission limitations.
    Reviewing an example of the SIP provisions cited by commenters is
illustrative of this point. For example, several commenters pointed to
provisions in Alabama's SIP that excuse a source from complying with an
otherwise applicable emission limitation only when the permittee ``took
all reasonable steps to minimize emissions'' and the ``permitted
facility was at the time being properly operated.'' According to
commenters, the general duties in this provision--to take reasonable
steps to minimize emissions, and to properly operate the facility--
ensure that even during SSM events, the permittee remains subject to
requirements limiting emissions.
    However, a review of the provisions themselves in context--not
selectively quoted--reveals that these general-duty provisions were
included in the SIP not as components of an emission limitation but
rather as components of an exception to that emission limitation. In
order to qualify, the SIP requires the permittee to have taken ``all
reasonable steps to minimize levels of emissions that exceeded the
emission standard'' \227\--an acknowledgement that the emissions to be
``minimize[d]'' are those that ``exceed[]'' (i.e., go beyond) the
required limits of ``the emission standard.'' In case there were any
doubt that the general-duty provisions identified are elements of an
exemption from an emission limitation, rather than components of the
emission limitation itself, the provisions apply during what the
Alabama SIP calls ``[e]xceedances of emission limitations'' \228\ and
are found within a

broader section addressing ``Exceptions to violations of emission
limitations.'' \229\ By exempting sources from compliance with ``the
emission standard,'' these exemptions render the SIP emission
limitation noncontinuous, contrary to section 302(k).\230\
---------------------------------------------------------------------------

    \227\ Ala. Admin. Code Rule 335-3-14-.03(h)(2)(ii)(III)
(emphasis added).
    \228\ Id. at 335-3-14-.03(h)(2)(ii) (emphasis added).
    \229\ Id. at 335-3-14-.03(h) (emphasis added).
    \230\ See CAA section 302(k) (defining ``emission limitation''
and ``emission standard'').
---------------------------------------------------------------------------

    The consequences for failing to satisfy the preconditions for an
exemption further bolster the conclusion that these preconditions are
not themselves part of an emission limitation. Failure to meet the
``general duty'' preconditions for an SSM exemption means that the
source remains subject to the otherwise applicable emission limitation
during the SSM event and is thus liable for violating the emission
limitation. If those general duties were independent parts of an
emission limitation (rather than merely preconditions for an
exemption), then one would expect that periods of time could exist when
the source was liable for violating those general duties rather than
the default emission limitation.
    The general-duty provisions that apply as part of the SSM exemption
are not alternative emission limitations; they merely define an
unlawful exemption to an emission limitation. States have discretion to
fix this issue in a number of ways, including by removing the
exceptions entirely, by replacing these exceptions with alternative
emission limitations including specific control technologies or work
practices that do ensure continuous limits on emissions or by
reformulating the entire emission limitation.
    In addition to the EPA's fundamental disagreement with commenters
that these general-duty provisions are actually components of emission
limitations, the EPA has additional concerns about whether many of
these provisions could operate as stand-alone emission limitations even
if they were properly identified as portions of the overall emissions
limitations in the SIP.\231\ Furthermore, some of these general-duty
provisions do not meet the level of stringency required to be an
``emission limitation'' compliant with specific substantive provisions
of the CAA applicable to SIP provisions.\232\ Accordingly, while states
are free to include general-duty provisions in their SIPs as separate
additional requirements, for example, to ensure that owners and
operators act consistent with reasonable standards of care, the EPA
does not recommend using these background standards to bridge unlawful
interruptions in an emission limitation.\233\
---------------------------------------------------------------------------

    \231\ See Sierra Club, 551 F.3d at 1026 (discussing the EPA's
prior determinations that ``compliance with the general duty on its
own was insufficient to prevent the SSM exemption from becoming a
`blanket' exemption'').
    \232\ See, e.g., Sierra Club v. Johnson, 551 F.3d at 1027-28 (so
holding with respect to section 112).
    \233\ For example, the EPA has concerns the some of these
general-duty provisions, if at any point relied upon as the sole
requirement purportedly limiting emissions, could undermine the
ability to ensure compliance with SIP emission limitations relied on
to achieve the NAAQS and other relevant CAA requirements at all
times. See section 110(a)(2)(A), (C); US Magnesium, LLC v. EPA, 690
F.3d 1157, 1161-62 (10th Cir. 2012).
---------------------------------------------------------------------------

    The NSPS and NESHAP emission standards and limitations that the EPA
has issued since Sierra Club demonstrate the distinct roles played by
emission limitations and general-duty provisions. The emission
limitations themselves are clear and legally and functionally
enforceable, and they are composed of obviously integrated requirements
that limit emissions on a continuous basis during all modes of source
operation. Crucially, the general-duty provisions in these post-Sierra
Club regulations merely supplement the integrated emission limitation;
they do not supplant the emission limitation, which independently
requires continuous limits on emissions. As discussed elsewhere in this
document, the fact that the EPA is in the process of updating its own
regulations to comply with CAA requirements does not alter the legal
requirements applicable to SIPs.
    n. Comments that EPA's action on the petition is a ``change of
policy.''
    Comment: A number of commenters claimed that the EPA's action on
the Petition is illegitimate because it is based upon a ``change of
policy.'' Some commenters claimed that the EPA's reliance on the
definition of ``emission limitation'' in section 302(k) and the
requirements for SIP provisions in section 110(a)(2) as barring
automatic exemptions are ``new.'' These commenters claimed that the EPA
has historically relied on the fact that NAAQS are ambient-standard-
based and that the EPA has relied also on the fact that SSM exemptions
had potential adverse air quality impacts as the basis for interpreting
the CAA to preclude exemptions. The commenters argued that this basis
for the SSM Policy is evidenced by the fact that EPA itself
historically included SSM exemptions in NSPS and NESHAP rules, which
establish emission limitations that should be governed by section
302(k) as well.
    Other commenters claimed that the EPA is changing its SSM Policy by
seeking to revoke ``enforcement discretion'' exercised on the part of
states, which the EPA specifically recognized as an acceptable approach
in the 1983 SSM Guidance. A commenter asserted that ``fairness
principles'' mean that the EPA cannot require a state to modify its SIP
without substantial justification. The commenter further contended that
the EPA's claim that it has a longstanding interpretation of the CAA
that automatic exemptions are not allowed in SIP provisions is false;
otherwise, the commenter argued, the EPA would not have approved some
of the provisions at issue in the SIP call long after 1982. As evidence
for this argument, the commenter pointed to the West Virginia
regulations that provide an automatic exemption.
    Finally, other commenters argued that the EPA's changed
interpretation of the CAA requires an acknowledgement that the SSM
Policy is being changed and a rational explanation for such change.
These commenters noted that the EPA previously argued in a brief for
the type of exemption provisions that it is now claiming are deficient,
citing Sierra Club v. Johnson, No. 02-1135 (D.C. Cir. March 14, 2008).
The commenters claimed that the EPA has provided no rational basis for
its change in interpretation of the CAA concerning exemptions for
emissions during SSM events.
    Response: The EPA's longstanding position, at least since issuance
of the 1982 SSM Guidance, is that SIP provisions providing an exemption
from emission limitations for emissions during SSM events are
prohibited by the CAA. The EPA's guidance documents issued in 1982 and
1983 expressly recognized that in place of exemptions, states should
exercise enforcement discretion in determining whether to pursue a
violation of an emission limitation. In the 1983 SSM Guidance, the EPA
made recommendations for states that elected to adopt specific SIP
provisions affecting their own exercise of enforcement discretion, so
long as those provisions do not apply to enforcement discretion of the
EPA or other parties under the citizen suit provision of the CAA. More
than 15 years ago, in the 1999 SSM Guidance, the EPA reiterated its
longstanding position that it is inappropriate for SIPs to exempt SSM
emissions from compliance with emission limitations and repeated that
instead of incorporating exemptions, enforcement discretion could be an
appropriate tool. In addition, EPA clarified at that time that a
narrowly tailored affirmative

defense might also be an appropriate tool for addressing excess
emissions in a SIP provision. However, in response to recent court
decisions, and as discussed in detail in section IV of this document,
the EPA no longer interprets the CAA to permit affirmative defense
provisions in SIPs.
    Although the EPA did not expressly rely on the definition of
``emission limitation'' in section 302(k) as the basis for its SSM
Policy in each of these guidance documents, it did rely on the purpose
of the NAAQS program and the underlying statutory provisions (including
section 110) governing that program. In the 1999 SSM Guidance, however,
the EPA indicated that the definition of emission limitation in section
302(k) was part of the basis for its position concerning SIP
provisions.\234\ After the EPA issued the 1999 SSM Guidance, the D.C.
Circuit issued a decision holding that the definition of emission
limitation in section 302(k) does not allow for periods when sources
are not subject to emissions standards.\235\ While the court's decision
concerned the section 112 program addressing hazardous air pollutants,
the EPA believes that the court's ruling concerning section 302(k)
applies equally in the context of SIP provisions because the definition
of emission limitation also applies to SIP requirements. That court's
decision is consistent with and provides support for the EPA's
longstanding position in the SSM Policy that exemptions from compliance
with SIP emission limitations are not appropriate under the CAA.
---------------------------------------------------------------------------

    \234\ See 1999 SSM Guidance at 2, footnote 1. The EPA included
section 302(k) among the statutory provisions that formed the basis
for its interpretations of the CAA in that document.
    \235\ Sierra Club, 551 F.3d 1019 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    Commenters claimed that by interpreting the CAA to prohibit
exemptions for emissions during SSM events the EPA is revoking
``enforcement discretion'' exercised by the state. This is not true. As
part of state programs governing enforcement, states can include
regulatory provisions or may adopt policies setting forth criteria for
how they plan to exercise their own enforcement authority. Under
section 110(a)(2), states must have adequate authority to enforce
provisions adopted into the SIP, but states can establish criteria for
how they plan to exercise that authority. Such enforcement discretion
provisions cannot, however, impinge upon the enforcement authority of
the EPA or of others pursuant to the citizen suit provision of the CAA.
The EPA notes that the requirement for adequate enforcement authority
to enforce CAA requirements is likewise a bar to automatic exemptions
from compliance during SSM events.
    Commenters confused the EPA's evolution in describing the basis for
its longstanding SSM Policy as a change in the SSM Policy itself. The
EPA's interpretation of the CAA in the SSM Policy has not changed with
respect to exemptions for emissions during SSM events. The EPA's
discussion of the basis for its longstanding interpretation has evolved
and become more robust over time as the EPA has responded to comments
in rulemakings and in response to court decisions. In support of its
interpretation of the CAA that exemptions for periods of SSM are not
acceptable in SIPs, the EPA has long relied on its view that NAAQS are
health-based standards and that exemptions undermine the ability of
SIPs to attain and maintain the NAAQS, to protect PSD increments, to
improve visibility and to meet other CAA requirements. By contrast, the
EPA historically took the position that SSM exemptions were acceptable
for certain technology-based standards, such as NSPS and NESHAP
standards, and argued that position in the Sierra Club case cited by
commenters. However, in that case, the court explicitly ruled against
the EPA's interpretation, holding that exemptions for emissions during
SSM events are precluded by the definition of ``emission limitation''
in CAA section 302(k). The Sierra Club court's rationale thus provided
additional support for the EPA's longstanding position with respect to
SSM exemptions in SIP provisions, and in more recent actions the EPA
has relied on the reasoning from the court's decision as further
support for its current SSM Policy. Thus, even if the EPA were
proceeding under a ``change of policy'' here as the commenters claimed,
the EPA has adequately explained the basis for its current SSM Policy,
including the basis for any actual ``change'' in that guidance (e.g.,
the actual change in the SSM Policy with respect to affirmative defense
provisions in SIPs). Courts have upheld an agency's authority to revise
its interpretation of a statute, so long as that change of
interpretation is explained.\236\
---------------------------------------------------------------------------

    \236\ The EPA emphasized this important point in the SNPR. See
79 FR 55919 at 55931.
---------------------------------------------------------------------------

    o. Comments that the EPA's proposed action on the petition is based
on a ``changed interpretation'' of the definition of ``emission
limitation.''
    Comment: Commenters claimed that the EPA's action on the Petition
is based on a changed interpretation of the term ``emission
limitation'' and that the Agency cannot apply that changed
interpretation ``retroactively.'' One commenter cited several cases for
the proposition that retroactivity is disfavored and that the EPA is
applying this new interpretation retroactively to existing SIP
provisions. The commenter claimed that the EPA approved the existing
SIP provisions with full knowledge of what those provisions were and
``consistent with the provisions EPA itself adopted and courts
required.'' The commenter characterized the SIP provisions for which
the EPA is issuing a SIP call as ``enforcement discretion'' provisions
and ``affirmative defense'' provisions for startup and shutdown. The
commenter contended that the EPA does not have authority to issue a SIP
call on the premise that the CAA is less flexible than the Agency
previously thought. The commenter concluded that ``[t]he factors of
repose, reasonable reliance, and settled expectations favor not
imposing EPA's new interpretations.''
    Response: The EPA disagrees that this SIP call action has
``retroactive'' effect. As recognized by the commenter, this SIP call
action does not automatically change the terms of the existing SIP or
of any existing SIP provision, nor does it mean that affected sources
could be held liable in an enforcement case for past emissions that
occurred when the deficient SIP provisions still applied. Rather, the
EPA is exercising its clear statutory authority to call for the
affected states to revise specific deficient SIP provisions so that the
SIP provisions will comply with the requirements of the CAA
prospectively and so that affected sources will be required to comply
with the revised SIP provisions prospectively.
    To the extent that a SIP provision complied with previous EPA
interpretations of the CAA that the Agency has since determined are
flawed, or to the extent that the EPA erroneously approved a SIP
provision that was inconsistent with the terms of the CAA, the EPA
disagrees that it is precluded from requiring the state to modify its
SIP now so that it is consistent with the Act. In fact, that is
precisely the type of situation that the SIP call provision of the CAA
is designed to address. Specifically, section 110(k)(5) begins,
``[w]henever'' the EPA determines that an applicable implementation
plan is inadequate to attain or maintain the NAAQS, to mitigate
adequately interstate pollutant transport, or ``to otherwise comply
with

any requirement'' of the Act, the EPA must call for the SIP to be
revised. The commenter does not question that sections 110(a)(2) and
302(k) are requirements of the Act. Thus, the EPA has authority under
section 110(k)(5) to call on states to revise their SIP provisions to
be consistent with those requirements.
    The EPA disagrees that the doctrines of ``repose,'' ``reasonable
reliance'' and ``settled expectations'' preclude such an action. The
CAA is clear that ``whenever'' the EPA determines that a SIP provision
is inconsistent with the statute, ``the Administrator shall'' notify
the state of the inadequacies and establish a schedule for correction.
This language does not provide the Agency with discretion to consider
the factors cited by the commenter in deciding whether to call for a
SIP revision once it is determined to be flawed. Here, the EPA has
determined that the SIP provisions at issue are flawed and thus the
Agency was required to notify the states to correct the inadequacies.
    p. Comments that the EPA should not encourage states to rely on
enforcement discretion because this will inevitably lead to states'
creating emission limitations that some sources cannot meet.
    Comment: Commenters claimed that it is not appropriate for the EPA
to encourage states to exercise enforcement discretion rather than to
encourage them either to define periods when numerical emission
limitations do not apply or to develop alternative emission limitations
or other control measures. The commenters contended that inclusion of
an enforcement discretion provision in a SIP is superfluous. The
commenter cited to Portland Cement, where the D.C. Circuit court stated
that ``an excessively broad theory of enforcement discretion might
endanger securing compliance with promulgated standards.'' \237\ The
commenter also cited the Marathon Oil case in the Ninth Circuit in
which the court rejected an approach that relied heavily on enforcement
discretion. The commenter then asserted that sources are liable for
violations and that ``[s]ources should not be required to litigate
remedy for violations they cannot avoid.'' \238\ The commenter
concluded that it is ``unreasonable for EPA to subject itself to claims
that it must exercise its federal enforcement authority in the event a
state refuses to enforce unachievable standards, or for states to put
source owners and operators in jeopardy of criminal prosecution for
starting up a source with knowledge that a numerical emission
limitation might be exceeded. In summary, the commenter appeared to
argue that the EPA should require states to establish alternative
numerical emission limitations or other control requirements during SSM
events, rather than merely eliminating SSM exemptions and relying on
enforcement discretion to address SSM emissions.
---------------------------------------------------------------------------

    \237\ 486 F.2d at 399 n.91.
    \238\ Marathon Oil Co. v. Environmental Protection Agency, 564
F.2d 1253 (9th Cir. 1977).
---------------------------------------------------------------------------

    Response: The EPA disagrees with the commenter's suggestion that
the EPA should discourage states from relying on enforcement
discretion. Enforcement discretion is a valid state prerogative, long
recognized by courts. However, the EPA agrees with the commenter that
states should not adopt overly broad enforcement discretion provisions
for inclusion in their SIPs. Section 110(a)(2) requires states to have
adequate enforcement authority, and overly broad enforcement discretion
provisions would run afoul of this requirement if they have the effect
of precluding adequate state authority to enforce SIP requirements. The
EPA also agrees that states may elect to include alternative emission
limitations, whether expressed numerically or otherwise, for certain
periods of normal operations, including startup and shutdown.
    It is unclear precisely what the commenters are advocating when
they suggest that sources should not be subject to litigating a remedy
for violations they cannot avoid. The likely interpretation is that the
commenters believe that excess emissions during unavoidable events
should be automatically exempted (i.e., not considered a violation).
This approach was rejected by the court in Sierra Club v. Johnson,
because it was not consistent with the definition of emission
limitation in section 302(k).\239\ As previously explained in the
February 2013 proposal and in this document, the EPA believes that
definition, and thus the court's holding in Sierra Club, is equally
relevant for the SIP program.
---------------------------------------------------------------------------

    \239\ 551 F.3d 1019 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    With respect to a commenter's concerns about criminal enforcement,
the EPA disagrees that sources will be unable to start operations
because they will automatically be subject to criminal prosecution if
an emission limitation is exceeded during a malfunction. Under CAA
section 113(c), criminal enforcement for violation of a SIP can occur
when a person knowingly violates a requirement or prohibition of an
implementation plan ``during any period of federally assumed
enforcement or more than 30 days after having been notified'' under the
provisions governing notification that the person is violating that
specific requirement of the SIP. The EPA is unaware of any
jurisdictions where federally assumed enforcement is in force, and the
EPA does not anticipate that this situation would arise often. Thus, in
almost every case, criminal enforcement would not occur in the absence
of a pending notification of a civil enforcement case and could then
apply only for repeated violation of the activity at issue in that
civil action. Moreover, the concern raised by the commenter is one that
would exist if there is any requirement that applies during a period of
malfunction beyond the owner's control. The commenter's preferred way
to address this concern would be to exempt these periods from
compliance with any requirements, an approach rejected by the Sierra
Club court as inconsistent with the definition of ``emission
limitation'' and an approach that the EPA's longstanding SSM Policy has
explained is inconsistent with the purpose of the NAAQS program, which
is to ensure public health is protected through attainment and
maintenance of the NAAQS, protection of PSD increments, improvement of
visibility and compliance with other requirements of the CAA.
    Finally, to the extent that the commenter was advocating that the
EPA should require states to develop SIP provisions that impose
alternative emission limitations during certain modes of source
operation such as startup and shutdown to replace SSM exemptions, the
EPA notes that to require states to do so would not be consistent with
the principles of cooperative federalism and could be misconstrued as
the Agency's imposing a specific control requirement in contravention
of the Virginia decision.\240\ As the commenter elsewhere itself
argued, states have broad discretion in how to develop SIP provisions
to meet the objectives of the CAA, so long as those provisions also
meet the legal requirements of the CAA. To the extent that a state
would prefer to have emission limitations that apply continuously,
without higher numerical levels or specific technological controls or
work practice standards applicable during modes of operation such as
startup and shutdown, that is the prerogative of the state, so long as
the revised SIP provision otherwise meets

CAA requirements. If a state determines that it is reasonable to
require a source to meet a specific emission limitation on a continuous
basis and also decides to rely on its own enforcement discretion to
determine whether a violation of that emission limit should be subject
to enforcement, then the EPA believes that to do so is within the
discretion of the state.
---------------------------------------------------------------------------

    \240\ See Virginia v. EPA, 108 F.3d 1397 (D.C. Cir. 1997) (SIP
call remanded and vacated because, inter alia, the EPA had issued a
SIP call that required states to adopt a particular control measure
for mobile sources).
---------------------------------------------------------------------------

    q. Comments that the EPA's action on the Petition is inconsistent
with the Credible Evidence Rule.
    Comment: A number of commenters raised concerns based upon how the
EPA's statements in the February 2013 proposal relate to the Credible
Evidence Rule issued in 1997.\241\ For example, one commenter argued
that throughout the February 2013 proposal, when the EPA stated that
excess emissions during SSM events should be treated as ``violations''
of the applicable SIP emission limitations, the Agency was
contradicting the Credible Evidence Rule and other provisions of law.
The commenter emphasized that the determination of whether excess
emissions during an SSM event are in fact a ``violation'' of the
applicable SIP provisions must be made using the appropriate reference
test method. In addition, the commenter asserted that whether any other
form of information may be used as ``credible evidence'' of a violation
must be evaluated by the trier of fact in a specific enforcement
action. Another commenter raised a different argument based on the
Credible Evidence Rule, claiming that the EPA's statements in the
preamble to that rulemaking contradict the EPA's statements in the
February 2013 proposal and support the need for exemptions for
emissions during SSM events. The implication of the commenter is that
any such EPA statements in connection with the Credible Evidence Rule
would negate the Agency's interpretation of the statutory requirements
for SIP provisions as interpreted in the SSM Policy since at least
1982, the decision of the court in the Sierra Club case or any other
actions such as the recent issuance of EPA regulations with no such SSM
exemptions.
---------------------------------------------------------------------------

    \241\ See ``Credible Evidence Revisions; Final rule,'' 62 FR
8314 (February 24, 1997).
---------------------------------------------------------------------------

    Response: The EPA agrees, in part, with the commenters who
expressed concern that the Agency's statements in the February 2013
proposal could be misconstrued as a definitive determination that the
excess emissions during any and all SSM events are automatically a
violation of the applicable emission limitation, without factual proof
of that violation, and without the existence and scope of that
violation being decided by the appropriate trier of fact. The EPA
agrees that the alleged violation of the applicable SIP emission
limitation, if not conceded by the source, must be established by the
party bearing the burden of proof in a legal proceeding. The degree to
which evidence of an alleged violation may derive from a specific
reference method or any other credible evidence must be determined
based upon the facts and circumstances of the exceedance of the
emission limitations at issue.\242\ This is a basic principle of
enforcement actions under the CAA, but the EPA wishes to make this
point clearly in this final action to avoid any unintended confusion
between the legal standard creating the enforceable obligation and the
evidentiary standard for proving a violation of that obligation.
---------------------------------------------------------------------------

    \242\ For example, the degree to which data from continuous
opacity monitoring systems (COMS) is evidence of violations of SIP
opacity or PM mass emission limitations is a factual question that
must be resolved on the facts and circumstances in the context of an
enforcement action. See, e.g., Sierra Club v. Pub. Ser v. Co. of
Colorado, Inc., 894 F.Supp. 1455 (D. Colo. 1995) (allowing use of
COMS data to prove opacity limit violations).
---------------------------------------------------------------------------

    The EPA's general statements in the February 2013 proposal, the
SNPR and this final action about treatment of SSM emissions as a
violation pertain to another basic principle, i.e., that SIP provisions
cannot treat emissions during SSM events as exempt, because this is
inconsistent with CAA requirements. Thus, when the EPA explains that
these emissions must be treated as ``violations'' in SIP provisions,
this is meant in the sense that states with SSM exemptions need to
remove them, replace them with alternative emission limitations that
apply during startup and shutdown or eliminate them by revising the
emission limitation as a whole. Once impermissible SSM exemptions are
removed from the SIP, then any excess emissions during such events may
be the subject of an enforcement action, in which the parties may use
any appropriate evidence to prove or disprove the existence and scope
of the alleged violation and the appropriate remedy for an established
violation. To be clear, the fact that these emissions are currently
exempt through inappropriate SIP provisions is a deficiency that the
EPA is addressing in this action. Thus, the EPA disagrees with the
commenters' suggestion that these emissions are never to be treated as
violations simply because a deficient SIP provision currently includes
an SSM exemption. Once the SIP provisions are corrected, the excess
emissions may be addressed through the legal structure for establishing
an enforceable violation, which then may be proven using appropriate
evidence, including test method evidence or other credible evidence.
This means that excess emissions that occur during an SSM event will be
treated for enforcement purposes in exactly the same manner as excess
emissions that occur outside of SSM events. The EPA acknowledges that
the limitation that applies during a startup or shutdown event might
ultimately be different (whether higher or lower) than the limitation
that applies at other times, if the state elects to replace the SSM
exemption with an appropriate alternative emission limitation in
response to this SIP call action.
    The EPA also disagrees with commenters who claimed that statements
by the Agency in the Credible Evidence Rule final rule preamble support
the inclusion of exemptions for SSM events in SIP provisions. The
commenter is correct that at that time, the EPA held the view that
emission limitations in its own NSPS could be considered
``continuous,'' notwithstanding the fact that they contained
``specifically excused periods of noncompliance'' (i.e., exemptions
from emission limitations during SSM events).\243\ Similarly, at that
time the EPA relied on a number of reported court decisions discussed
in the preamble for the Credible Evidence Rule for determining at that
time that NSPS could contain such exemptions in order to make the
emission limitations ``reasonable.'' However, after the court's
decision in the Sierra Club case interpreting the definition of
emission limitation in section 302(k), these EPA statements in the
preamble for the Credible Evidence Rule are no longer correct and thus
do not apply to the EPA's action in this document.
---------------------------------------------------------------------------

    \243\ Id., 62 FR 8314, 8323-24.
---------------------------------------------------------------------------

    First, the EPA notes that these prior statements related to the
Credible Evidence Rule specifically addressed not SIP provisions but
rather the provisions of the Agency's own technologically based NSPS.
The statements in the document make no reference to SIP provisions,
which is unsurprising given that EPA's SSM Policy at the time indicated
that no such SSM exemptions are appropriate in SIP provisions. Second,
the EPA's justification for exemptions from emission limitations during
SSM events in NSPS was made prior to the 2008

decision of the court in the Sierra Club case. The EPA's interpretation
of the statute and the case law to justify exemptions for emissions
during SSM events in that 1997 document is no longer correct. Finally,
the EPA in its own new NESHAP and NSPS regulations is now providing no
exemptions for emissions during SSM events and is imposing specific
numerical limitations or other control requirements on sources that
apply to affected sources at all times, including during SSM
events.\244\ Thus, the statements in the 1997 Credible Evidence Rule
preamble relied upon by commenters do not render the EPA's
interpretation of the CAA with respect to SSM exemptions in SIP
provisions in this action incorrect.
---------------------------------------------------------------------------

    \244\ See, e.g., 40 CFR 60.42Da, where paragraph (e)(1) applies
a numerical PM emission limitation at all times except during
periods of startup and shutdown, and paragraph (e)(2) applies work
practice standards during periods of startup and shutdown.
---------------------------------------------------------------------------

    For clarity, the EPA emphasizes that it is in no way reopening,
revising or otherwise amending the Credible Evidence Rule in this
action. The EPA is merely responding to commenters who characterized
the relationship between Agency statements in that rulemaking action
and this SIP call action. The EPA also emphasizes that no changes to
the Credible Evidence Rule should be necessary as a result of this
rulemaking.
    r. Comments that exemptions in opacity standards should be
permissible because opacity is not a NAAQS pollutant.
    Comment: Many state and industry commenters argued that the EPA
should interpret the CAA to allow SIP provisions that impose opacity
emission limitations to contain exemptions for SSM events or for other
modes of source operation. The reasons given by commenters ranged
broadly, but they included assertions that opacity is not a criteria
pollutant, that opacity limitations serve no purpose other than as a
tool to monitor PM control device performance, that there is no
reliable correlation between opacity and PM mass, that there are
circumstances during which sources may not be capable of meeting the
otherwise applicable SIP opacity standards and that opacity is not an
``air pollutant.'' Commenters also argued that because SIP opacity
standards were originally established when the NAAQS applied to ``total
suspended particles'' (TSP), rather than the current PM10
and PM2.5, this alone should be a reason to allow SSM
exemptions now that the NAAQS have been revised and the indicator
species changed. Some of the commenters acknowledged that their
underlying concern is that requirements for COMS on certain sources
have rendered it much easier to monitor exceedances of SIP opacity
limits and to bring enforcement actions for alleged violations.
    Response: The EPA agrees with many of the points made by commenters
but not with the conclusion that the commenters drew from these points,
i.e., that exemptions for SSM events are appropriate in SIP provisions
that impose opacity emission limitations.
    First, although the EPA agrees that opacity itself is not a
criteria pollutant and that there is thus no NAAQS for opacity, this
does not mean that SIP opacity limitations are not ``emission
limitations'' subject to the requirements of section 110(a)(2)(A) and
do not need to be continuous. As the commenters often conceded, opacity
is a surrogate for PM emissions for which there are NAAQS, and opacity
has served this purpose since the beginning of the SIP program in the
1970s. SIP provisions that impose opacity emission limitations often
date back to the earliest phases of the SIP program. From the outset,
such opacity limitations have provided an important regulatory tool for
implementing the PM NAAQS and for limiting PM emissions from sources.
To this day, states continue to use opacity limitations in SIP
provisions and the EPA continues to use opacity limitations in its own
NSPS and NESHAP regulations, as necessary, for specific source
categories.\245\ EPA regulations applicable to SIPs explicitly define
the term ``emission limitation'' to include opacity limits.\246\ It is
also important to note that these SIP provisions impose opacity
emission limitations that sources must meet independently; i.e.,
opacity limitations are independent ``emission limitations'' under
section 110(a)(2)(A) that must, consistent with section 302(k),
``limit[ ] the quantity, rate, or concentration of emissions of air
pollutants on a continuous basis.'' These opacity emission limitations
in SIP provisions are not stated conditionally as opacity limits that
sources do not need to meet if they are otherwise in compliance with PM
mass emission limitations or with any other CAA requirements. Thus, the
fact that opacity is not itself a criteria pollutant is irrelevant.
---------------------------------------------------------------------------

    \245\ See, e.g., 40 CFR 60.42Da(b). The EPA's revised NSPS for
this category imposes an opacity limit of 20 percent at all times,
except for one 6-minute period per hour when the opacity may rise to
27 percent. Notably, as an option, sources may elect to install PM
CEMS and be subject only to the revised particulate matter emission
limitation.
    \246\ See 40 CFR 51.100(z) (defining the term ``emission
limitation'' as limits on ``the quantity, rate, or concentration of
emissions of air pollutants on a continuous basis, including any
requirements which limit the level of opacity'').
---------------------------------------------------------------------------

    Second, although the EPA agrees that SIP opacity limitations also
provide an important means of monitoring control device performance and
thus indirectly provide a means to monitor compliance with PM emission
limitations as well, this does not mean that opacity limits do not need
to meet the statutory requirements for SIP emission limitations.
Historically, opacity limits have been an important tool for
implementation of the PM NAAQS, and in particular for the
implementation and enforcement of PM mass limitations on sources to
help attain and maintain the PM NAAQS. The EPA agrees that opacity is a
useful tool to indicate overall operation and maintenance of a source
and its emission control devices, such as electrostatic precipitators
or baghouses. SIP opacity limitations provided this tool even before
modern instruments that measure PM emissions on a direct, continuous
basis existed. At a minimum, elevated opacity indicates potential
problems with source design, operation or maintenance, or potential
problems with incorrect operation of pollution control devices,
especially at the elevated levels of many existing opacity standards.
Well-run sources should be in compliance with typical SIP opacity
limits. Opacity exceeding the applicable limitations can be indicative
of problems that justify further investigation by sources and
regulators, such as conducting a stack test to determine compliance
with PM mass emission limitations. Not all sources have or will have PM
CEMS, or have PM CEMS at all emission points, to monitor PM emissions
directly, nor do PM CEMS necessarily obviate the need for opacity
standards to regulate condensables, and thus there is a continued need
for opacity emission limitations in SIPs. The continued need for SIP
opacity limitations for this and other purposes contradicts the
commenters' arguments concerning the validity of SSM exemptions.
    Third, the EPA agrees that the precise correlation between opacity
and PM mass emissions is not always known for a specific source under
all operating conditions, unless there is parallel testing and
measurement of the opacity and the PM emissions to determine the
correlation at that particular source. Similarly, parametric monitoring
can be used to establish such a correlation. Nevertheless, there is
commonly a positive correlation between PM and opacity and thus
elevated opacity is often indicative of additional PM

emissions from a source. Even in those instances where a precise
correlation is not available, however, the use of opacity as a means to
assure the reduction of PM emissions and to monitor source compliance
remains a valid approach to regulation of PM from sources. In any
event, the absence of a precise correlation between opacity and PM does
not justify the complete exemptions from SIP opacity limitations during
SSM events that the commenters advocate and instead suggests that it
may be appropriate to replace such exemptions with valid and
enforceable alternative numerical limitations or other control
requirements as a component of the SIP opacity emission limitation that
applies during startup and shutdown. Opacity emission limitations in
SIPs must meet the statutory requirements for emission limitations.
    Fourth, the EPA agrees with commenters that for some sources some
PM controls cannot operate, or operate at full effectiveness and ideal
efficiency, during startup and shutdown. Accordingly, as the commenters
implicitly recognized, the resulting increases in PM emissions can
result in elevated opacity and thus exceedances of the applicable SIP
opacity emission limitations. In those situations where it is true that
no additional emissions controls are available or would function more
effectively to reduce PM emissions, and hence to reduce opacity, it may
be appropriate for states to consider imposing an alternative opacity
emission limitation applicable during startup and shutdown. As
discussed in section VII.B.2 of this document, the EPA provides
recommendations to states concerning how to develop such alternative
emission limitations. To the extent that sources believe that a SIP
provision with a higher opacity level for startup and shutdown may be
justified, they may seek these alternative limitations from the state
and they can presumably advocate for opacity standards that are
tailored to reflect the correlation between PM mass and opacity at a
specific source. Significantly, however, even if it is appropriate to
impose a somewhat higher opacity limitation for some sources during
specifically defined modes of operation such as startup and shutdown,
that does not justify the total exemptions from SIP opacity emission
limitations during SSM events that the commenters advocated. To provide
total exemptions from SIP opacity emission limitations during SSM
events does not provide any incentive for sources to be better
designed, operated, maintained and controlled to reduce emissions, nor
does it comply with the most basic requirement that SIP emission
limitations be continuous in accordance with section 302(k). As
explained in section X.B of this document, the SIP revisions in
response to this SIP call action will need to be consistent with the
requirements of sections 110(k)(3), 110(l) and 193 as well as any other
applicable requirements.
    Fifth, the EPA notes that few commenters seriously argued that SIP
provisions for opacity do not fit within the plain language of section
110(a)(2)(A) or the definition of ``emission limitation'' in section
302(k) or in EPA regulations applicable to SIP provisions. Section
110(a)(2)(A) requires SIPs to contain such enforceable emission
limitations ``as may be necessary and appropriate to meet the
applicable requirements of'' the CAA. Opacity limitations in SIP
provisions are necessary and appropriate for a variety of reasons
already described, including as a means to reduce PM emissions, as a
means to monitor source compliance and to provide for more effective
enforcement. Opacity limitations in SIP provisions also easily fit
within the concept of a limit on the ``quantity, rate or concentration
of air pollutants'' that relates to the ``operation or maintenance of a
source to assure continuous emission reduction and any design,
equipment, work practice or operational standard'' under the CAA, as
provided in section 302(k). The term ``air pollutant'' is defined
broadly in section 302(g) to mean ``any air pollution agent or
combination of such agents, including any physical, chemical,
biological, radioactive . . . substance or matter which is emitted into
or otherwise enters the ambient air.'' Even if opacity is not itself an
air pollutant, it is clearly a means of monitoring and limiting
emissions of PM from sources and is thus encompassed within the
definition of ``emission limitation'' in section 302(k).\247\
Significantly, existing EPA regulations applicable to SIP provisions
already explicitly define the term ``emission limitation'' to include
opacity limitations.\248\
---------------------------------------------------------------------------

    \247\ See Sierra Club v. TVA, 430 F.3d 1337, 1340 (11th Cir.
2005).
    \248\ See 40 CFR 51.100(z).
---------------------------------------------------------------------------

    Finally, the EPA does not agree with commenters who argued that
because SIP opacity limitations were often originally imposed when the
PM NAAQS was for TSP, it is legally acceptable to have exemptions for
emissions during SSM events now that the PM NAAQS use PM10
and PM2.5 as the indicator species. On a factual level, it
is obvious that SIP provisions for opacity limitations are expressed in
terms of percentage ``opacity'' unrelated to the size of the particles.
Opacity represents the degree to which emissions reduce the
transmission of light and obscures the view of an object in the
background. In general, the more particles which scatter or absorb
light that passes through an emissions point, the more light will be
blocked, thus increasing the opacity percentage of the emissions plume.
The EPA agrees that variables such as the size, number and composition
of the particles in the emissions can result in variations in the
percentage of opacity. Notwithstanding the changes in the NAAQS,
however, both states and the EPA have continued to rely on opacity
limitations because they serve the same purposes for the current
PM10 and PM2.5 NAAQS (and other purposes such as
the regulation of HAPs under section 112) that they previously did for
the TSP NAAQS. Indeed, as the PM NAAQS have been revised to provide
better protection of public health, the need for such opacity
limitations continues unless there is a better means to monitor source
compliance, such as PM CEMS. As with other SIP emission limitations,
the EPA interprets the CAA to preclude SSM exemptions in opacity
standards.
    s. Comments that exemptions from SIP opacity limitations for excess
emissions during SSM events should be allowed because such emissions
are difficult to monitor or to control.
    Comment: Several commenters argued that the EPA's proposal of a SIP
call for SIP opacity emission limitations that include an SSM exemption
is arbitrary and capricious because it is difficult or impossible to
monitor or measure opacity during SSM events. According to commenters,
there is no compliance methodology to determine whether opacity
limitations are met during SSM events and this is the reason that the
EPA's own general provisions for NSPS and NESHAP exclude emissions
during SSM events as ``not representative'' of source operation. In the
absence of a specific methodology to demonstrate compliance, the
commenters argued that expecting sources to comply with any opacity
emission limitations during SSM events is arbitrary and capricious. The
commenters asserted that in light of this, the EPA must interpret the
CAA to allow exemptions for SSM events in SIP opacity provisions.
    A number of commenters also argued that because emission controls
for PM do not function, or do not function as effectively or
efficiently, during certain

modes of source operation, the EPA should interpret the CAA to permit
exemptions for SSM events in opacity emission limitations. Many
commenters explained that certain types of emission controls at certain
types of sources only operate at specific temperatures or under
specific conditions. For example, many commenters stated that existing
pollution control devices on certain categories of stationary sources
do not operate, or do not operate as effectively or efficiently, during
startup and shutdown. Based upon this assertion, the commenters argued
that the EPA should interpret the CAA to allow total exemptions from
SIP opacity emission limitations during such periods.
    Commenters also characterized the EPA's February 2013 proposal as
``particularly unreasonable'' with respect to SSM exemptions in SIP
opacity limitations, because those limitations should be allowed to
exclude elevated opacity during periods when PM emissions controls
devices are ``not expected to operate correctly.'' According to
commenters, treating the higher opacity during SSM events ``as a
violation simply because it is indicating something that is expected is
ridiculous.'' As an example, the commenters specifically mentioned
occurrences such as when a source's electrostatic precipitator (ESP) is
not functioning or is not functioning properly as periods during which
there should be an exemption from SIP opacity emission limitations.
    Response: The EPA agrees with some of the points made by commenters
but does not agree with the conclusions that the commenters drew from
these points, i.e., that alleged difficulties in monitoring, measuring
or controlling opacity during some modes of source operation in general
justify complete exemptions from opacity emission limitations during
SSM events.
    First, the EPA does not agree with the argument that there is no
``compliance methodology'' available for purposes of verifying
compliance with SIP opacity limitations. Since the earliest phases of
the SIP program, Reference Method 9 has been available as a means of
verifying a source's compliance with applicable SIP opacity emission
limitations. Whatever concerns the commenters may have with this test
method, it is a valid method and it continues to be used as a means of
verifying source compliance with opacity limitations and a source of
evidence for determining whether there are violations of such emission
limitations.\249\ Sources routinely monitor and certify to their
compliance with SIP opacity limitations based upon Method 9. In
addition, COMS have been available, and in some cases are required, as
another means of monitoring emissions and verifying compliance with
opacity emission limitations. With respect to COMS, commenters
expressed concerns that they are not always accurate, are not always
properly calibrated or are not always the reference test method for SIP
opacity emission limitations, and other similar arguments. In this
rulemaking, the EPA is not addressing these allegations concerning COMS
but merely noting that COMS are an available means of monitoring
opacity from sources and in appropriate circumstances can provide data
meeting the EPA's criteria as credible evidence to be used to determine
compliance with emission limitations.
---------------------------------------------------------------------------

    \249\ The EPA notes that one commenter characterized SIP opacity
limits as ``archaic'' and suggested that the Agency should issue a
SIP call requiring their removal from SIPs entirely. Unless and
until regulators and sources have a better means of monitoring
compliance with PM emission limitations on a continuous basis, such
as through installation of PM CEMS, the EPA believes that opacity
limits will continue to be a necessary part of emission limitations.
There will continue to be sources of emissions for which it will not
be cost-effective or technologically viable to require the
installation of PM CEMS or for which opacity standards will be
needed as a means of regulating condensables.
---------------------------------------------------------------------------

    Second, the EPA does not agree that the fact that its regulations
concerning performance tests in 40 CFR 63.7(e) for NESHAP and in 40 CFR
60.8(c) for NSPS exclude SSM emissions for purposes of evaluation of
emissions under normal operating conditions provides a justification
for SSM exemptions from opacity emission limitations in SIP provisions.
The D.C. Circuit decision in Sierra Club has already indicated that
such exemptions are not permissible in emission limitations and vacated
the general provisions applicable to NESHAP. In the case of the
exemption language in 40 CFR 60.8(c) relevant to NSPS, the EPA
acknowledges that it has not yet taken action to revise the language to
eliminate that exemption. However, in promulgating new NSPS regulations
subsequent to the Sierra Club decision, the EPA is including emission
limitations for newly constructed, reconstructed and modified sources
that apply continuously and including provisions expressly stating that
the SSM exemptions in the General Provisions do not apply. The EPA
notes that the commenter is also in error because the performance tests
are intended to be a means of evaluating emissions from sources during
periods that are representative of source operation.
    Third, the EPA does not agree with the premise that because certain
forms or types of emission controls do not work, or do not work as
effectively or efficiently, during certain modes of operation at some
sources, it necessarily follows that sources should be totally exempt
from emission limitations during such periods. The EPA interprets the
CAA to require that SIP emission limitations be continuous. As
explained in section VII.A of this document, emission limitations do
not necessarily need to be expressed numerically, can have higher
numerical levels during certain modes of operation, and may be composed
of a combination of numerical limitations, specific technological
control requirements and/or work practice requirements during certain
modes of operation, so long as these emission limitations meet
applicable CAA stringency requirements and are legally and practically
enforceable. If it is factually accurate that a given source category
requires a higher opacity limit during periods such as startup and
shutdown, then the state may elect to develop one consistent with other
CAA requirements. The EPA has provided guidance to states with criteria
to consider in revising their SIP provisions to replace exemptions with
an appropriate alternative emission limitation for such purposes. The
EPA emphasizes that even if it is the case that existing control
measures cannot operate, or cannot operate as effectively or
efficiently, during startup and shutdown at a particular source, this
does not legally justify a complete exemption from SIP emission
limitations and may merely indicate that additional emission controls
or work practices are necessary when the existing control measures are
insufficient to meet the applicable SIP emission limitation. The EPA is
taking this approach with its own recent NSPS and NESHAP regulations,
when appropriate, in order to ensure that its own emission limitations
are consistent with CAA requirements.
    Finally, the EPA also disagrees with the logic of commenters that
argued in favor of exemptions from SIP opacity limitations during
periods when a source is most likely to violate them, e.g., when the
source's control devices are not functioning. Even if exemptions from
SIP opacity emission limitations were legally permissible under the
CAA, which they are not, it would be illogical to excuse compliance
with the standards during the precise periods when opacity standards
are most

needed to monitor source compliance with SIP emission limitations and
provide incentives to avoid and promptly correct malfunctions; i.e., it
would be illogical to require no legal restriction on emissions when
the sources are most likely to be emitting the most air pollutants.
Inclusion of exemptions for exceedances of SIP opacity limitations
during such periods would remove incentives to design, maintain and
operate the source correctly, and to promptly correct malfunctions, in
order to assure that it meets the applicable SIP emission limitations.
By exempting excess emissions during such events, the provision would
undermine the enforcement structure of the CAA in section 113 and
section 304, through which the air agency, the EPA and citizens are
authorized to assure that sources meet their obligations. The EPA
emphasizes that while exemptions from SIP limitations are not
permissible in SIP provisions, states may elect to impose appropriate
alternative emission limitations. They may include alternative
numerical limitations, control technologies or work practices that
apply during modes of operation such as startup and shutdown, so long
as all components of the SIP emission limitation meet all applicable
CAA requirements.
    t. Comments that exemptions in SIP opacity limitations should be
permissible for ``maintenance,'' ``soot-blowing'' or other normal modes
of source operation.
    Comment: A number of industry commenters argued that the EPA should
interpret the CAA to allow exemptions from SIP opacity limitations for
``maintenance.'' The commenters stated that during maintenance, sources
must shut down operations and control devices while the source is
cleaned or repaired. During such periods, the commenters explained, a
ventilation system operated to protect workers at the source could
result in monitored exceedances of a SIP opacity limitation. Commenters
specifically argued that although COMS data may suggest violations of
opacity standards during such periods, the fact that the source is not
combusting fuel during maintenance should mean that the opacity
emission limitation does not apply at such times. According to
commenters, opacity limitations are only intended to reflect the
performance of pollution control equipment while the source is
operating and thus have no relevance during periods of maintenance.
Other commenters made comparable arguments with respect to soot-
blowing, asserting that the high opacity levels during this activity
are ``indicative of normal ESP operation, not poor performance.'' In
other words, the commenters argued that opacity limitations should
contain complete exemptions for opacity emitted during soot-blowing on
the theory that the elevated emissions during this mode of operation
show that the control measure on a source is functioning properly. The
commenters further argued that considering emissions during soot-
blowing for purposes of PM limitations is appropriate, but not for
purposes of opacity limitations, because of the way in which regulators
developed the respective emission limitations.
    Response: The EPA does not agree that exemptions from SIP opacity
limitations are appropriate for any mode of source operation, whether
during SSM events or during other normal, predictable modes of source
operation. To the extent that there are legitimate technological
reasons why sources are able to meet only a higher opacity limitation
during certain modes of operation, it does not follow that this
constraint justifies complete exemption from any standard or any
alternative technological control or work practice in order to reduce
opacity during such periods. Providing a complete exemption for opacity
during these modes of source operation, and no specific alternative
emission limitation during such periods, removes incentives for sources
to be properly designed, maintained and operated to reduce emissions
during such periods.
    With respect to maintenance, the EPA does not agree with commenters
that total exemptions from opacity emission limitations during such
activities are consistent with CAA requirements for SIP provisions. As
the EPA has stated repeatedly in its interpretation of the CAA in the
SSM Policy, maintenance activities are predictable and planned
activities during which sources should be expected to comply with
applicable emission limitations.\250\ The premise of the commenters
advocating for such exemptions for all emissions during maintenance is
evidently that nothing can be done to limit PM emissions and thus limit
opacity during maintenance activities, and the EPA disagrees with that
general premise. To the extent appropriate, however, states may elect
to create alternative emission limitations applicable to opacity during
maintenance periods, so long as they are consistent with CAA
requirements. The EPA provides recommendations for alternative emission
limitations in section VII.B.2 of this document.
---------------------------------------------------------------------------

    \250\ See 1982 SSM Guidance at Attachment p. 2; 1983 SSM
Guidance at Attachment p. 3. The EPA notes that it also did not
interpret the CAA to permit affirmative defense provisions for
planned events under its prior 1999 SSM Guidance on the grounds that
sources should be expected to operate in accordance with applicable
SIP emission limitations during maintenance. This interpretation was
upheld in Luminant Generation v. EPA, 714 F.3d 841 (5th Cir. 2013).
---------------------------------------------------------------------------

    With respect to soot-blowing, the EPA likewise does not agree that
total exemptions from opacity limitations during such periods are
consistent with CAA requirements. As with maintenance in general, soot-
blowing is an intentional, predictable event within the control of the
source. The commenters' implication is that nothing whatsoever could be
done to limit opacity during such activities, and the EPA believes that
this is both inaccurate and not a justification for sources' being
subject to no standards whatsoever during soot-blowing. In addition,
the EPA disagrees with the commenters' claim that exemptions from
opacity emission limitations during soot-blowing are legally
permissible because this allegedly shows that the control devices for
opacity and PM are in fact performing correctly. This argument
incorrectly presupposes that the sole reason for SIP opacity emission
limitations is as a means of better evaluating control measure
performance. This is but one reason for SIP opacity limitations.
Moreover, the EPA notes, excusing opacity during soot-blowing has the
diametrically opposite effect of the actual purpose of the control
devices and can result in much higher emissions as opposed to
encouraging limiting these emission with other forms of controls.
    Finally, the EPA notes, the commenters' argument that whether
opacity limitations should apply during soot-blowing depends upon
whether the emissions were or were not accounted for in the applicable
PM emissions is also based upon an incorrect premise. Even if the PM
emission limitation applicable to a source was developed to include the
emissions during soot-blowing specifically, it does not follow that
sources should be completely exempted from opacity limitations during
such periods. As the commenters themselves frequently acknowledged,
when compared to other enforcement tools, SIP opacity provisions often
provide a much more effective and continuous means of determining
source compliance with SIP PM limitations and control measure
performance. A typical SIP opacity provision imposes an emission
limitation such as 20 percent opacity at all times, except for 6
minutes per hour when those emissions may rise to 40 percent opacity.
Well-maintained and

well-operated sources should be able to meet such SIP opacity
limitations. Given that properly designed, maintained and operated
sources should typically have opacity substantially below these levels,
elevated opacity at a source is a good indication that the source may
not be in compliance with its applicable PM limitations.
    u. Comments that elimination of exemptions from SIP opacity
emission limitations during SSM events will compel states to alter the
averaging period of opacity limitations so as to allow sources to have
elevated emissions during SSM events.
    Comment: Commenters argued that if exemptions for excess emissions
during SSM events are not legally permissible in SIP opacity emission
limitations, then states will have no option but to alter the existing
opacity limitations. The commenters argued that if the SSM exemptions
are removed, then the averaging time should be ``greatly extended'' and
the numerical limits ``should be significantly increased.''
    Response: The EPA agrees that SIP provisions for opacity that
contain exemptions for SSM events at issue in this action must be
revised to eliminate the exemptions. States may elect to do this by
merely removing the exemptions, by replacing the exemptions with
appropriate alternative emission limitations that apply in place of the
exemptions or, as the commenters evidently advocate, by a total
overhaul of the emission limitation. The EPA disagrees, however, with
the commenters' contentions that removal of the SSM exemptions would
necessarily result in extensions of the averaging time or increases of
the numerical levels in the existing SIP opacity emission limitations.
In some cases, extension of the averaging period and elevation of the
numerical limitations may in fact be appropriate. In other cases,
however, it may instead be appropriate to reduce the existing numerical
opacity limitations, given improvements in control technology since the
original imposition of the limits and the need for additional PM
emission reductions from the affected sources due to more recent
revisions to the PM NAAQS. Thus, the EPA notes, a total revision of
some of the SIP opacity limitations at issue in this action may indeed
be the proper course for states to consider. The implications of the
commenters' argument, however, are that existing opacity limitations
will automatically need to be revised in order to allow sources to
continue to emit as usual and that states and sources may ignore
improvements that have been made in source design, operation,
maintenance or controls to reduce emissions. The EPA emphasizes that
the removal of impermissible SSM exemptions should not be perceived as
an opportunity to provide new de facto exemptions for these emissions
by manipulation of the averaging time and the numerical level of
existing opacity emission limitations.
    In any event, the EPA is not in this final action deciding how
states must revise SIP opacity emission limitations but is merely
issuing a SIP call directing the affected states to eliminate existing
automatic and discretionary exemptions for excess emissions during SSM
events. The affected states will elect how best to respond to this SIP
call, whether by simply removing the exemptions, by replacing the
exemptions with appropriate alternative emission limitations applicable
to startup and shutdown or other normal modes of operation or by a
complete overhaul of the SIP provision in question. In particular,
where the affected sources are located in designated nonattainment
areas, there may be a need to evaluate additional controls that are
needed for attainment planning purposes that were not necessary when
the emission limitation was first adopted. Whichever approach a state
determines to be most appropriate, the resulting SIP submission to
revise the existing deficient provisions will be subject to review by
the EPA pursuant to sections 110(k)(3), 110(l) and 193. Considerations
relevant to this issue are discussed in section X.B of this document.

B. Alternative Emission Limitations During Periods of Startup and
Shutdown

1. What the EPA Proposed
    In the February 2013 proposal, the EPA reiterated its longstanding
interpretation of the CAA that SIP provisions cannot include exemptions
from emission limitations for emissions during SSM events but may
include different requirements that apply to affected sources during
startup and shutdown. Since the 1982 SSM Guidance, the EPA has clearly
stated that startup and shutdown are part of the normal operation of a
source and should be accounted for in the design and operation of the
source. Thus, the EPA has long concluded that sources should be
required to meet the applicable SIP emission limitations during normal
modes of operation including startup and shutdown.\251\ In the 1983 SSM
Guidance, the EPA explained that it may be appropriate to exercise
enforcement discretion for violations that occur during startup and
shutdown under proper circumstances. In the 1999 SSM Guidance, the EPA
further explained that it interprets the CAA to permit SIP emission
limitations that include alternative emission limitations specifically
applicable during startup and shutdown. In the context of making
recommendations to states for how to address emissions during startup
and shutdown, the EPA provided seven criteria for states to evaluate in
establishing appropriate alternative emission limitations. The specific
purpose for these recommendations was to take into account
technological limitations that might prevent compliance with the
otherwise applicable emission limitations. As explained in detail in
the February 2013 proposal, the EPA did not intend these criteria to be
the basis for the creation of exemptions from SIP emission limitations
during startup and shutdown, because the Agency interprets the CAA to
prohibit such exemptions.
---------------------------------------------------------------------------

    \251\ Some commenters on the February 2013 proposal focused
great attention on whether startup and shutdown are modes of
``normal'' source operation. The EPA assumes that every source is
designed, maintained and operated with the expectation that the
source will at least occasionally start up and shut down, and thus
these modes of operation are ``normal'' in the sense that they are
to be expected. The EPA used this term in the ordinary sense of the
word to distinguish between such predictable modes of source
operation and genuine ``malfunctions,'' which are by definition
supposed to be unpredictable and unforeseen events that could not
have been precluded by proper source design, maintenance and
operation.
---------------------------------------------------------------------------

    In the February 2013 proposal, the EPA also repeated its guidance
concerning establishment of alternative emission limitations that apply
to sources during startup and shutdown, in those situations where the
sources cannot meet the otherwise applicable SIP emission limitations.
As explained in section VII.A of the February 2013 proposal, the EPA
interprets the CAA to require that SIP emission limitations must be
continuous and thus to prohibit exemptions for emissions during startup
and shutdown. This does not, however, mean that every SIP emission
limitation must be expressed as a numerical limitation or that it must
impose the same limitations during all modes of source operation. The
EPA's interpretation of the CAA with respect to SIP provisions is that
SIP emission limitations: (i) Do not need to be numerical in format;
(ii) do not have to apply the same limitation (e.g., numerical level)
at all times; and (iii) may be composed of a combination of numerical
limitations, specific technological control requirements and/

or work practice requirements, with each component of the emission
limitation applicable during a defined mode of source operation.
Regardless of how an air agency elects to express the emission
limitation, however, the emission limitation must limit emissions from
the affected sources on a continuous basis. Thus, if there are
different numerical limitations or other control requirements that
apply during startup and shutdown, those must be clearly stated
components of the emission limitation, must meet the applicable level
of control required for the type of SIP provision (e.g., be RACT for
sources located in nonattainment areas) and must be legally and
practicably enforceable.
2. What Is Being Finalized in This Action
    The EPA is reiterating its interpretation of the CAA to allow SIP
emission limitations to include components that apply during specific
modes of source operation, such as startup and shutdown, so long as
those components together create a continuously applicable emission
limitation that meets the relevant substantive requirements and
requisite level of stringency for the type of SIP provision at issue
and is legally and practically enforceable. In addition, the EPA is
updating the specific recommendations to states for developing such
alternative emission limitations described in the February 2013
proposal, by providing in this document some additional explanation and
revisions to the text of its recommended criteria regarding alternative
emission limitations.
    The EPA's longstanding position is that the CAA does not allow SIP
provisions that include exemptions from emission limitations for excess
emissions that occur during startup and shutdown. The EPA reiterates
that exemptions from SIP emission limitations are also not permissible
for excess emissions that occur during other periods of normal source
operation. A number of SIP provisions identified in the Petition create
automatic or discretionary exemptions from otherwise applicable
emission limitations during periods such as ``maintenance,'' ``load
change,'' ``soot-blowing,'' ``on-line operating changes'' or other
similar normal modes of operation. Like startup and shutdown, the EPA
considers all of these to be modes of normal operation at a source, for
which the source can be designed, operated and maintained in order to
meet the applicable emission limitations and during which the source
should be expected to control and minimize emissions. Accordingly,
exemptions for emissions during these periods of normal source
operation are not consistent with CAA requirements. Excess emissions
that occur during planned and predicted periods should be treated as
violations of any applicable emission limitations.
    However, the EPA interprets the CAA to allow SIPs to include
alternative emission limitations for modes of operation during which an
otherwise applicable emission limitation cannot be met, such as may be
the case during startup or shutdown. The alternative emission
limitation, whether a numerical limitation, technological control
requirement or work practice requirement, would apply during a specific
mode of operation as a component of the continuously applicable
emission limitation. For example, an air agency might elect to create
an emission limitation with different levels of control applicable
during specifically defined periods of startup and shutdown than during
other normal modes of operation. All components of the resulting
emission limitation must meet the substantive requirements applicable
to the type of SIP provision at issue, must meet the applicable level
of stringency for that type of emission limitation and must be legally
and practically enforceable. The EPA will evaluate a SIP submission
that establishes a SIP emission limitation that includes alternative
emission limitations applicable to sources during startup and shutdown
consistent with its authority and responsibility pursuant to sections
110(k)(3), 110(l) and 193 and any other CAA provision substantively
germane to the SIP revision. Absent a properly established alternative
emission limitation for these modes of operation, a source should be
required to comply with the otherwise applicable emission limitation.
    In addition, the EPA is providing in this document some additional
explanation and clarifications to its recommended criteria for
developing alternative emission limitations applicable during startup
and shutdown. The EPA continues to recommend that, in order to be
approvable (i.e., meet CAA requirements), alternative requirements
applicable to the source during startup and shutdown should be narrowly
tailored and take into account considerations such as the technological
limitations of the specific source category and the control technology
that is feasible during startup and shutdown. Accordingly, the EPA
continues to recommend the seven specific criteria enumerated in
section III.A of the Attachment to the 1999 SSM Guidance as appropriate
considerations for SIP provisions that establish alternative emission
limitations that apply to startup and shutdown. The EPA repeated those
criteria in the February 2013 proposal as guidance to states for
developing components of emission limitations that apply to sources
during startup, shutdown or other specific modes of source operation to
meet CAA requirements for SIP provisions.
    Comments received on the February 2013 proposal suggested that the
purpose of the recommended criteria may have been misunderstood by some
commenters. The criteria were phrased in such a way that commenters may
have misinterpreted them to be criteria to be applied by a state
retrospectively (i.e., after the fact) to an individual instance of
emissions from a source during an SSM period, in order to establish
whether the source had exceeded the applicable emission limitation.
This was not the intended purpose of the recommended criteria at the
time of the 1999 SSM Guidance, nor is it the intended purpose now.
    The EPA seeks to make clear in this document that the recommended
criteria are intended as guidance to states developing SIP provisions
that include emission limitations with alternative emission limitations
applicable to specifically defined modes of source operation such as
startup and shutdown. A state may choose to consider these criteria in
developing such a SIP provision. The EPA will use these criteria when
evaluating whether a particular alternative emission limitation
component of an emission limitation meets CAA requirements for SIP
provisions. Any SIP revision establishing an alternative emission
limitation that applies during startup and shutdown would be subject to
the same procedural and substantive review requirements as any other
SIP submission.
    Based on comment on the February 2013 proposal, the EPA is updating
the criteria to make clear that they are recommendations relevant for
development of appropriate alternative emission limitations in SIP
provisions. Thus, in this document, the EPA is providing a restatement
of its recommended criteria that reflects clarifying but not
substantive changes to the text of those criteria. One clarifying
change is removal of the word ``must'' from the criteria, to better
convey that these are recommendations to states concerning how to
develop an approvable SIP provision with alternative requirements
applicable to

startup and shutdown and to make clear that other approaches might also
be consistent with the CAA in particular circumstances.
    The clarified criteria for developing and evaluating alternative
emission limitations applicable during startup and shutdown are as
follows:
    (1) The revision is limited to specific, narrowly defined source
categories using specific control strategies (e.g., cogeneration
facilities burning natural gas and using selective catalytic
reduction);
    (2) Use of the control strategy for this source category is
technically infeasible during startup or shutdown periods;
    (3) The alternative emission limitation requires that the frequency
and duration of operation in startup or shutdown mode are minimized to
the greatest extent practicable;
    (4) As part of its justification of the SIP revision, the state
analyzes the potential worst-case emissions that could occur during
startup and shutdown based on the applicable alternative emission
limitation;
    (5) The alternative emission limitation requires that all possible
steps are taken to minimize the impact of emissions during startup and
shutdown on ambient air quality;
    (6) The alternative emission limitation requires that, at all
times, the facility is operated in a manner consistent with good
practice for minimizing emissions and the source uses best efforts
regarding planning, design, and operating procedures; and
    (7) The alternative emission limitation requires that the owner or
operator's actions during startup and shutdown periods are documented
by properly signed, contemporaneous operating logs or other relevant
evidence.
    It may be appropriate for an air agency to establish alternative
emission limitations that apply during modes of source operation other
than during startup and shutdown, but any such alternative emission
limitations should be developed using the same criteria that the EPA
recommends for those applicable during startup and shutdown.
3. Response to Comments
    The EPA received a number of comments, both supportive and adverse,
concerning the issue of how air agencies may replace existing
exemptions for emissions during SSM events with alternative emission
limitations that apply during startup, shutdown or other normal modes
of source operation. The majority of these comments were critical of
the EPA's position but did not base this criticism on an interpretation
of specific CAA provisions. For clarity and ease of discussion, the EPA
is responding to these comments, grouped by issue, in this section of
this document.
    a. Comments that as a technical matter sources cannot meet emission
limitations (or cannot be accurately monitored) during startup and
shutdown.
    Comment: Several commenters claimed that as a technical matter, SIP
emission limitations cannot be met or that monitoring to ensure
compliance with emission limitations cannot occur during startup and
shutdown. Commenters raised ``practical concerns'' with the EPA's
proposal as it applies to emissions during SSM at electric generating
units (EGUs). The commenters claimed that it is incorrect to treat
periods of startup and shutdown as part of ``normal source operation''
and claimed that it is fundamentally incorrect to characterize all
periods of startup and shutdown as planned events. The commenters
claimed that many air pollution control devices (APCDs) are subject to
technical, operational or safety constraints that prevent use or
optimization during startup and shutdown periods. The commenters
requested the EPA to continue the practice of allowing states to
provide ``protection'' from enforcement for excess emissions during
startup and shutdown. The commenters claimed that the EPA's premise for
this action is that startup and shutdown events are planned and sources
should be able to meet limits applicable during these normal
operations. The commenters asserted that the proposal does not
recognize technical and operational limits and that it conflicts with
the EPA's own acknowledgement in the proposal that there are sometimes
technical, operational and safety limits that may prevent compliance
with emission limitations during startup and shutdown. The commenters
also noted that the type of equipment that a control device is attached
to may affect the time it takes for a control device to reach
optimization. Further, the commenters identified control technologies
that cannot achieve reductions until specific temperatures are reached
and other technologies that cannot be used during startup and/or
shutdown because of technical limitations or safety concerns. Finally,
the commenters noted that the geographical location and/or weather can
have an effect on the operation of a source and control devices during
startup and shutdown.
    Commenters raised specific concerns regarding pollution controls
for EGUs. The commenters claimed that startup and shutdown events are
unavoidable at EGUs even though they may be planned. The commenters
also attached appendices providing an explanation of why emissions are
higher for startup and shutdown for certain types of EGUs. The
commenters claimed that the ``EPA's proposal to eliminate the States'
SSM provisions, and prohibit them from adopting any provisions for
startups and shutdowns, could force sources to comply with emission
limitations during periods when they were never meant to apply, thus
rendering those emissions limitations unachievable.'' The commenters
also noted that the permits for their sources all require that the
sources minimize the magnitude and duration of emissions during SSM.
The implication of this latter comment is that a general duty to
minimize emissions is sufficient to justify the exemption of all
emissions during SSM events in the underlying SIP provisions.
    Response: Although intended as criticism of the EPA's proposed
action, these comments in fact support the Agency's position that
states should consider startup and shutdown events as they promulgate
standards for specific industries or even for specific sources. The
commenters seem to suggest that because some equipment or sources
cannot during startup and shutdown meet the emission limits that apply
during ``regular'' operation, no limit or standards should apply during
startup and shutdown. The EPA disagrees. As the court in Sierra Club
held, emission limitations must apply at ``all times.'' That is not to
say that the emission limitation must impose the same numerical
limitation or impose the same other control requirement at all times.
As explained at length in section VII.A of this document, the EPA
interprets the CAA to allow SIP emission limitations that may be a
combination of numerical limitations, technological control measures
and/or work practice requirements, so long as the resulting emission
limitations are properly developed to meet CAA requirements and are
legally and practically enforceable. As the commenters noted, the EPA
does recognize that some control equipment cannot be operated at all or
in the same manner during every mode of normal operations.
    In its 1999 SSM Guidance, the EPA expressly recognized that an
appropriate way for a state to address such technological limitations
is to set alternative emission limitations that apply during periods of
startup and shutdown as part of the SIP emission

limitation.\252\ In these cases the state should consider how the
control equipment works in determining what standards should apply
during startup and shutdown. In addition, as noted by commenters, such
standards may vary based on location (e.g., standards in a hot and
humid area may differ from those adopted for a cool and dry area). Some
equipment during startup and shutdown may be unable to meet the same
emission limitation that applies during steady-state operations and so
alternative limitations for startup and shutdown may be
appropriate.\253\ However, for many sources, it should be feasible to
meet the same emission limitation that applies during steady-state
operations also during startup and shutdown.\254\ These are issues for
the state to consider in developing specific regulations as they revise
the deficient SIP provisions identified in this action. The EPA
emphasizes that the state has discretion to determine the best means by
which to revise a deficient provision to eliminate an automatic or
discretionary SSM exemption, so long as that revision is consistent
with CAA requirements. The EPA will work with the states as they
consider possible revisions to deficient provisions.
---------------------------------------------------------------------------

    \252\ See 1999 SSM Guidance, Attachment at 4-5.
    \253\ The EPA notes that it has taken this approach in its own
recent actions establishing emission limitations for sources. See,
e.g., ``National Emission Standards for Hazardous Air Pollutants for
Major Sources: Industrial, Commercial, and Institutional Boilers and
Process Heaters; Final rule; notice of final action on
reconsideration,'' 78 FR 7137 (January 31, 2013) (example of work
practice requirement for startup as a component of a continuous
emission limitation).
    \254\ The EPA notes that it has taken this approach in its own
recent actions establishing emission limitations for sources. See,
e.g., ``National Emission Standards for Hazardous Air Pollutants
Residual Risk and Technology Review for Flexible Polyurethane Foam
Production; Final rule,'' 79 FR 48073 (August 15, 2014) (example of
NESHAP emission limitation that is continuous and does not include a
different component for periods of startup or shutdown).
---------------------------------------------------------------------------

    The EPA recognizes that a malfunction may cause a source to shut
down in a manner different than in a planned shutdown, and in that
case, such a shutdown would typically be considered part of the
malfunction event. However, as part of the normal operation of a
facility, sources typically will also have periodic or otherwise
scheduled startup and shutdown of equipment, and steps to limit
emissions during this type of event are or can be planned for. The EPA
disagrees with the suggestion of commenters that because some startup
or shutdown events may be unplanned, all startup and shutdown events
should be exempt from compliance with any requirements. For those
events that are planned, the state should be able to establish
requirements to regulate emissions, such as a numerical limitation,
technological control measure or work practice standard that will apply
as a part of the revised emission limitation. When unplanned startup or
shutdown events are part of a malfunction, they should be treated the
same as a malfunction; however, as with malfunctions, startup and
shutdown events cannot be exempted from compliance with SIP
requirements. Questions of liability and remedy for violations that
result from malfunctions are to be resolved in the context of an
enforcement action, if such an action occurs.
    b. Comments that it is impossible, unreasonable or impractical for
states to develop emission limitations that apply during startup and
shutdown to replace existing exemptions.
    Comment: A number of commenters suggested that it will be difficult
for states to develop emission limits that apply during startup and
shutdown. One state commenter reasoned that alternative emission limits
are applied to facilities in that state through individual permits on a
case-by-case basis and claimed that there are 500 permitted facilities
in the state. The commenter contended that ``non-steady-state'' limits
would need to be set for startup and shutdown for all 500 permitted
facilities and that such an effort would be ``time, resource, and data
intensive.'' The state commenter further contended that it would be
unreasonable to require the state to include such limits ``for every
source'' in the SIP because ``permit modifications would need to occur
every time there is a new emission source, a source ceases to operate,
or an emission-related regulation is changed.''
    A local government commenter stated that to establish limits for
startup and shutdown that also demonstrate compliance with the NSR
regulations (including protection of the NAAQS and PSD increments and
maintenance of BACT or LAER) would be a difficult, time-consuming task
that was mostly impractical.
    An industry commenter claimed that the EPA is encouraging states to
adopt numerical alternative emission limitations in their SIP
provisions that would apply during startup and shutdown. The commenter
claimed that adequate and accurate emissions data are necessary to do
so and that such information is not generally available for existing
equipment or, in many cases, for new equipment. Furthermore, the
commenter asserted, even if an emission limit could be established for
startup and shutdown, there are no current approved test measures to
verify compliance during such modes of operation. Even where data are
available, the commenter alleged, the data may not be representative of
actual conditions because of limitations related to low-load
conditions. If a state lacks information to conclude that a limit can
be met, the commenter argued, the state should not be required to
establish numerical limits but should instead be allowed ``to specify
that numerical standards do not apply to those conditions or that those
conditions are exempt, or should be allowed to establish work practice
standards.''
    Response: The comments of the state commenter seem to be based on
the premise that all sources will be unable to meet otherwise
applicable SIP emission limitations during periods of startup and
shutdown. The EPA anticipates that many types of sources should be able
during startup and shutdown to meet the same emission limitation that
applies during full operation. Additionally, even where a specific type
of operation may not during startup and/or shutdown be able to meet an
emission limitation that applies during full operation, the state
should be able to develop appropriate limitations that would apply to
those types of operations at all similar types of facilities. The EPA
believes that there will be limited, if any, cases where it may be
necessary to develop source-specific emission requirements for startup
and/or shutdown. In any event, this is a question that is best
addressed by each state in the context of the revisions to the SIP
provisions at issue in this action. To the extent that there are
appropriate reasons to establish an emission limitation with
alternative numerical, technological control and/or work practice
requirements during startup or shutdown for certain categories of
sources, this SIP call action provides the state with the opportunity
to do so.
    As to the commenter's concern that such alternative emission
limitations should not be included in a state's SIP, the EPA disagrees.
The SIP needs to reflect the control obligations of sources, and any
revision or modification of those obligations should not be occurring
through a separate process, such as a permit process, which would not
ensure that ``alternative'' compliance options do not weaken the SIP.
The SIP is a combination of state statutes, regulations and other
requirements that the EPA approves for demonstrating attainment and
maintenance of the NAAQS, protection of PSD increments, improvement of
visibility and compliance with other

CAA requirements. As discussed in section X.B of this document, any
revisions to obligations in the SIP need to occur through the SIP
revision process and must comply with sections 110(k)(3), 110(l) and
193 and any other applicable substantive requirements of the CAA.
    As to concerns that a SIP revision will be necessary every time a
new source comes into existence, an existing source is permanently
retired or a new regulation is promulgated, the EPA does not see these
as significant concerns. Unless the startup or shutdown process for an
individual source is truly unique to that source, then existing SIP
provisions for sources within the same industrial category should be
able to apply to any new source. Moreover, assuming any new source is
subject to permitting obligations, then any applicable startup and
shutdown issues should already be resolved in developing the permit for
such source. The state could choose to incorporate that permit by
reference into the SIP at the time it next modifies its SIP. Further,
assuming that there is a source-specific regulation for a source in the
SIP (a circumstance that the EPA believes would occur only rarely), the
state is not obligated to remove such provision when the source is
retired. Rather, the state could leave the provision in its rules or
remove such a provision the next time it submits another SIP revision
or when it chooses to do a ``cleanup'' of the SIP, an activity that
numerous states have taken from time to time. Finally, whenever a new
regulation is promulgated is precisely the time that a state should be
considering the appropriate provisions that would apply during startup
and shutdown, as that is the time when the state is considering what is
necessary to comply with the CAA and what is necessary to meet
attainment, maintenance or other requirements of the CAA.
    The local government commenter contended that establishing limits
for startup and shutdown that also demonstrate compliance with the NSR
regulations (including protection of the NAAQS and PSD increments and
imposition of BACT- or LAER-level controls) would be a difficult, time-
consuming task that was impractical. The commenter did not provide an
explanation of how this would be difficult. The implication of the
comment is that a SIP provision that provides an exemption or an
affirmative defense for emissions during startup and shutdown would be
compliant with the statutory requirements and NSR regulations
(including attainment of the NAAQS and protecting PSD increments). That
is incorrect because the EPA does not interpret the CAA to allow such
exemptions or affirmative defenses for purposes of NSR regulations. The
suggestion that a SIP provision that does not regulate emissions during
startup and shutdown would be more likely to address NAAQS attainment
and to protect PSD increments than would a SIP provision that does
regulate such emissions is illogical. The EPA further notes that the
Agency's interpretation of the CAA, explicitly set forth in a 1993
guidance document, has been that periods of startup and shutdown must
be addressed in any new source permit.\255\ Moreover, the EPA explained
in the February 2013 proposal, in the SNPR and in the background
memorandum accompanying the February 2013 proposal concerning the legal
basis for this action why exemptions and affirmative defenses
applicable to emissions during SSM events are not consistent with CAA
requirements for SIP provisions.
---------------------------------------------------------------------------

    \255\ See Memorandum from John B. Rasnic, EPA/OAQPS, January 28,
1993, in the rulemaking docket at EPA-HQ-OAR-2012-0322-0022.
---------------------------------------------------------------------------

    c. Comments that the EPA should ``authorize'' states to replace SSM
exemptions with ``work practice'' standards developed by the EPA in its
own recent NESHAP and NSPS rules.
    Comment: Commenters suggested that the EPA should allow states to
use work practice standards to address emissions during startup and
shutdown. The NESHAP rules cited by commenters included the Industrial
Boiler MACT rule \256\ and the MATS rule, and the NSPS rules cited by
the commenters included the NSPS for Electric Utility Steam Generating
Units (40 CFR part 60, subpart Da) and the gas turbine NSPS as examples
of where the EPA itself has established work practice standards rather
than numerical emission limitations for periods of startup and
shutdown. The commenters suggested that where these work practice
standards are already in place, states should be able to rely on the
work practice standards rather than having to create new SIP
provisions.
---------------------------------------------------------------------------

    \256\ The Industrial Boiler MACT rule regulates industrial,
commercial and institutional boilers and process heaters at major
sources under 40 CFR part 63, subpart DDDDD.
---------------------------------------------------------------------------

    Response: The EPA agrees that states may adopt work practice
standards to address periods of startup and shutdown as a component of
a SIP emission limitation that applies continuously. Adoption of work
practice standards from a NESHAP or NSPS as a component of an emission
limitation to satisfy SIP requirements is addressed in this document
not as a requirement or even as a recommendation but rather as an
approach that a state may use at its option. The EPA cannot foretell
the extent to which this optional approach of adopting other existing
standards to satisfy SIP requirements may benefit an individual state.
For a state choosing to use this approach, such work practice standards
must meet the otherwise applicable CAA requirements (e.g., be a RACT-
level control for the source as part of an attainment plan requirement)
and the necessary parameters to make it legally and practically
enforceable (e.g., have adequate recordkeeping, reporting and/or
monitoring requirements to assure compliance). However, it cannot
automatically be assumed that emission limitation requirements in
recent NESHAP and NSPS are appropriate for all sources regulated by
SIPs. The universe of sources regulated under the federal NSPS and
NESHAP programs is not identical to the universe of sources regulated
by states for purposes of the NAAQS. Moreover, the pollutants regulated
under the NESHAP (i.e., HAPs) are in many cases different than those
that would be regulated for purposes of attaining and maintaining the
NAAQS, protecting PSD increments, improving visibility and meeting
other CAA requirements.\257\ Thus, the EPA cannot say as a matter of
law that those federal regulations establish emission limitation
requirements appropriate for all of the sources that states are
regulating in their SIPs or for the purpose for which they are being
regulated. The EPA believes, however, that those federal regulations
and the technical materials in the public record for those rules may
provide assistance for states as they develop and consider regulations
for sources in their states and may be appropriate for adoption by the
state in certain circumstances. In particular, the NSPS regulations
should provide very relevant information for sources of the same type,
size and control equipment type, even if the sources were not
constructed or modified within a date range that would make them
subject to the NSPS. The EPA therefore encourages states to explore
these approaches, as well as any other relevant information available,
in

determining what is appropriate for revised SIP provisions.
---------------------------------------------------------------------------

    \257\ While some HAPs are also VOCs or particulate matter, many
HAPs are not. Moreover, there are many VOCs and types of particulate
matter that are not HAPs and thus are not regulated under the MACT
standards. The MACT standards also do not address other criteria
pollutants or pollutant precursors from sources that may be relevant
for SIP purposes.
---------------------------------------------------------------------------

    d. Comments that if states remove existing SSM exemptions and
replace them with alternative emission limitations that apply during
startup and shutdown events, this would automatically be consistent
with the requirements of CAA section 193.
    Comment: Commenters stated that section 193 was included in the CAA
to prohibit states from modifying regulations in place prior to
November 15, 1990, unless the modification ensures equivalent or
greater reductions of the pollutant. The commenters asserted that to
the extent a state replaces ``general excess emissions exclusions and/
or affirmative defense provisions'' such amendments would per se be
more stringent than the provisions they replace. The commenters also
contended that any replacement SIP provision that spells out more
clearly how a source will operate ensures equivalent or greater
emission reductions. The commenters urged the EPA to clarify that any
revisions pursuant to a final SIP call would not be considered
``backsliding.''
    Response: The EPA agrees with the commenters that any SIP
submission made by a state in response to this SIP call action will
need to comply with the requirements of section 193 of the CAA, if that
section applies to the SIP provision at issue. In addition, such SIP
provision will also need to comply with section 110(l), which requires
that SIP revisions do not interfere with attainment, reasonable
progress or any other applicable requirement of the CAA. However, it is
premature to draw the conclusion that any SIP revision made by a state
in response to this SIP call will automatically meet the requirements
of section 110(l) and section 193. Such a conclusion could only be made
in the context of reviewing the actual SIP revision. The EPA will
address this issue, for each SIP revision in response to this SIP call
action, at the time that it proposes and finalizes action on the SIP
revision, and any comments on this issue can be raised during those
individual rulemaking actions. The EPA provides additional guidance to
states on the analysis needed to comply with section 110(l) and section
193 in section X.B of this document.

C. Director's Discretion Provisions Pertaining to SSM Events

1. What the EPA Proposed
    In the February 2013 proposal, the EPA stated and explained in
detail the reasons for its belief that the CAA prohibits unbounded
director's discretion provisions in SIPs, including those provisions
that purport to authorize unilateral revisions to, or exemptions from,
SIP emission limitations for emissions during SSM events.\258\
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    \258\ See February 2013 proposal, 78 FR 12459 at 12485-86.
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2. What Is Being Finalized in This Action
    The EPA is reiterating its interpretation of the CAA with respect
to unbounded director's discretion provisions applicable to emissions
during SSM events, which is that SIP provisions cannot contain
director's discretion to alter SIP requirements, including those that
allow for variances or outright exemptions for emissions during SSM
events. This interpretation has been clear with respect to emissions
during SSM events in the SSM Policy since at least 1999. In the 1999
SSM Guidance, the EPA stated that it would not approve SIP revisions
``that would enable a State director's decision to bar EPA's or
citizens' ability to enforce applicable requirements.'' \259\
Director's discretion provisions operate to allow air agency personnel
to make just such unilateral decisions on an ad hoc basis, up to and
including the granting of complete exemptions for emissions during SSM
events, thereby negating any possibility of enforcement for what would
be violations of the otherwise applicable emission limitation. Given
that the EPA interprets the CAA to bar exemptions from SIP emission
limitations for emissions during SSM events in the first instance, the
fact that director's discretion provisions operate to authorize these
exemptions on an ad hoc basis compounds the problem. The EPA
acknowledges, however, that both states and the Agency have, in some
instances, failed to adhere to the requirements of the CAA with respect
to this issue consistently in the past, and thus the need for this SIP
call to correct existing deficiencies in SIPs.\260\ In order to be
clear about its interpretation of the CAA with respect to this point on
a going-forward basis, the EPA is reiterating in this action that SIP
provisions cannot contain unbounded director's discretion provisions,
including those that operate to allow for variances or outright
exemptions from SIP emission limitations for excess emissions during
SSM events.
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    \259\ See 1999 SSM Guidance at 3.
    \260\ In this action, the EPA is addressing the specific SIP
provisions with director's discretion provisions that the Petitioner
listed in the Petition. In the event that there are other such
impermissible director's discretion provisions in existing SIPs, the
EPA will address those provisions in a later action.
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    Many commenters on the February 2013 proposal opposed the EPA's
interpretation of the CAA with respect to director's discretion
provisions simply on the grounds that states are per se entitled to
have unfettered discretion with respect to the content of their SIP
provisions. Other commenters argued that any director's discretion
provision is merely a manifestation of an air agency's general
``enforcement discretion.'' Some commenters simply asserted that recent
court decisions by the Fifth Circuit definitively establish that the
CAA does not prohibit SIP provisions that include director's
discretion, regardless of whether those provisions contain any
limitations whatsoever on the exercise of that discretion.\261\ The
commenters did not, however, address the specific statutory
interpretations that the EPA set forth in the February 2013 proposal to
explain why SIP provisions that authorize unlimited director's
discretion are prohibited by CAA provisions applicable to SIP
revisions.
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    \261\ For example, commenters on the February 2013 proposal
cited two decisions of the Fifth Circuit within which the court
cited a prior EPA approval of a SIP revision in Georgia that
contained director's discretion provisions supposedly comparable to
those at issue in the Fifth Circuit cases. These provisions were not
included in the Petition and the EPA is not reexamining those
provisions as part of this action.
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    As explained in detail in the February 2013 proposal and in section
VII.C of this document, the EPA interprets the CAA to prohibit SIP
provisions that include unlimited director's discretion to alter the
SIP emission limitations applicable to sources, including those that
operate to allow exemptions for emissions from sources during SSM
events. The EPA believes that such provisions that operate to authorize
total exemptions from emission limitations on an ad hoc basis are
especially problematic. Given that the EPA interprets section
110(a)(2)(A) and section 302(k) to preclude exemptions for emissions
during SSM events in emission limitations in the first instance, it is
also impermissible for states to have SIP provisions that authorize
such exemptions on an ad hoc basis. These provisions functionally allow
the air agency to impose its own enforcement discretion decisions on
the EPA and other parties by granting exemptions for emissions that
should be treated as violations of the applicable SIP emission
limitations. Provisions that functionally allow such exemptions are
also inconsistent with requirements of the CAA related to enforcement

including: (i) The general requirements of section 110(a)(1) that SIPs
provide for enforcement; (ii) the section 110(a)(2)(A) requirement that
the specific emission limitations and other contents of SIPs be
enforceable; and (iii) the section 110(a)(2)(C) requirement that SIPs
contain a program to provide for enforcement. Moreover, these
provisions operate to interfere with the enforcement structure of the
CAA provided in section 113 and section 304, through which the EPA and
other parties have authority to seek enforcement for violations of CAA
requirements, including SIP emission limitations.
    There are two ways in which such a provision can be consistent with
CAA requirements: (1) When the exercise of director's discretion by the
state agency to alter or eliminate the SIP emission limitation can have
no effect for purposes of federal law unless and until the EPA ratifies
that state action with a SIP revision; or (2) when the director's
discretion authority is adequately bounded such that the EPA can
ascertain in advance, at the time of approving the SIP provision, how
the exercise of that discretion to alter the SIP emission limitations
for a source could affect compliance with other CAA requirements. If
the provision includes director's discretion that could result in
violation of any other CAA requirement for SIPs, then the EPA cannot
approve the provision consistent with the requirements of section
110(k)(3) and section 110(l). For example, a director's discretion
provision that authorizes state personnel to excuse source compliance
with SIP emission limitations during SSM events could not be approved
because the provision would run afoul of the requirement that sources
be subject to emission limitations that apply continuously, consistent
with section 302(k).
3. Response to Comments
    The EPA received a number of comments, both supportive and adverse,
concerning the issue of director's discretion provisions in SIPs. The
majority of these comments were critical of the EPA's position but did
not base this criticism on an interpretation of specific CAA
provisions. For clarity and ease of discussion, the EPA is responding
to these comments, grouped by issue, in this section of this document.
    a. Comments that broad state discretion in how to develop SIP
provisions includes the authority to create provisions that include
director's discretion variances or exemptions for excess emission
during SSM events.
    Comment: A number of state and industry commenters argued that
because states have great discretion when developing SIP provisions in
general, this necessarily includes the ability to create director's
discretion provisions in SIPs that authorize state personnel to grant
unilateral variances or exemptions for emissions during SSM events.
According to commenters, the overarching principle of ``cooperative
federalism'' and court decisions concerning the division of regulatory
responsibilities between the states and the EPA support their view that
states can create SIP provisions that provide authority to alter the
SIP emission limitations or other requirements via director's
discretion provisions without restriction.
    Response: The EPA disagrees with the commenters' view that
director's discretion provisions in SIPs are per se permissible because
of the principles of cooperative federalism. As explained in more
detail in section V.D.2 of this document, states and the EPA each have
authorities and responsibilities under the CAA. With respect to SIPs,
under section 107(a) the states have primary responsibility for
assuring attainment of the NAAQS within their borders. Under section
110(a) the states have a statutory duty to develop and submit a SIP
that provides for the attainment, maintenance and enforcement of the
NAAQS, as well as meeting many other CAA requirements and objectives.
The specific procedural and substantive requirements that states must
meet for SIPs are set forth in section 110(a)(1) and section 110(a)(2)
and in other more specific requirements throughout the CAA (e.g., the
attainment plan requirements for each of the NAAQS as specified in part
D). By contrast, the EPA has its own statutory authorities and
responsibilities, including the obligation to review new SIP
submissions for compliance with CAA procedural and substantive
requirements pursuant to sections 110(k)(3), 110(l) and 193. In
addition, the EPA has authority to assure that previously approved SIP
provisions continue to meet CAA requirements, whether through the SIP
call authority of section 110(k)(5) or the error correction authority
of section 110(k)(6).
    As the EPA explained in detail in the February 2013 proposal, SIP
provisions that include unbounded director's discretion to alter the
otherwise applicable emission limitations are inconsistent with CAA
requirements. Such provisions purport to authorize air agency personnel
unilaterally to change or to eliminate the applicable SIP emission
limitations for a source without meeting the requirements for a SIP
revision. Pursuant to the EPA's own responsibilities under sections
110(k)(3), 110(l) and 193 and any other CAA provision substantively
germane to the specific SIP provision at issue, it would be
inappropriate for the Agency to approve a SIP provision that
automatically preauthorized the state unilaterally to revise the SIP
emission limitation without meeting the applicable procedural and
substantive statutory requirements for a SIP revision. Section 110(i)
prohibits modification of SIP requirements for stationary sources by
either the state or the EPA, except through specified processes. The
EPA's implementing regulations applicable to SIP provisions likewise
impose requirements for a specific process for the approval of SIP
revisions.\262\ In addition, section 116 explicitly prohibits a state
from adopting or enforcing regulations for sources that are less
stringent than what is required by the emission limitations in its SIP,
i.e., the emission limitation previously approved by the EPA as meeting
the requirements of the CAA applicable to that specific SIP provision.
It is a fundamental tenet of the CAA that states cannot unilaterally