Agency on a case-by-case basis, and such evaluation is dependent upon
the specific facts and circumstances present in a specific SIP action
and would follow the process described in the proposal.
    2. Comments that opposed the EPA's interpretation of the CAA to
allow reliance on interpretive letters to clarify ambiguities in state
SIP submissions.
    Comment: Other commenters disagreed with the EPA's proposed
response to the Petition on this issue. One commenter opposed the
Agency's reliance on interpretive letters under any circumstances and
did not draw any factual or procedural distinctions between situations
in which this approach might or might not be appropriate or correctly
processed. This commenter argued that citizens should not be required
``to sift through a large and complex rulemaking docket in order to
figure out the meaning and operation of state regulations.'' The
commenter asserted that simply as a matter of ``good government,'' all
state regulations approved as SIP provisions should be clear and
unambiguous on their face. This commenter also expressed concern that
courts could not or would not accord legal weight to interpretive
letters created after state regulations were adopted and submitted to
the EPA, or after the EPA's approval of the SIP submission occurred,
and would view such letters as post hoc interpretations of no probative
value. Another commenter added its view that reliance on interpretive
letters is appropriate only when affected parties have the right to
comment on the interpretive letters and the EPA's proposed use of them
during the rulemaking in which the EPA relies on such letters to
resolve ambiguities and before the Agency finally approves the SIP
revision.
    Response: As a general matter, the commenter opposing the EPA's
reliance on interpretive letters in any circumstances because citizens
would be required ``to sift through'' the docket did not provide
specific arguments regarding the EPA's interpretation of the statute as
stated in the February 2013 proposal. Consistent with the EPA's
interpretation of the CAA, and as explained earlier in this document,
the EPA agrees with the core principle that the language of regulations
in SIPs that pertain to SSM events should be clear and unambiguous. A
commenter argued that ``a fundamental principle of good government is
making sure that all people know what the applicable law is. Having the
applicable law manifest in a letter sitting in a filing cabinet in one
office clearly does not qualify as good government.'' The EPA generally
agrees on this point as well. As explained earlier in this document,
the EPA allows the use of interpretive letters to clarify perceived
ambiguity in the provisions of a SIP submission only when used
correctly, with adequate documentation in both the Federal Register and
the docket for the underlying rulemaking action. Section VI.B of this
document explains how interested parties can use the list or table of
actions that appears in the CFR and that reflects the various
components of the approved SIP, to identify the Federal Register
document wherein the EPA has explained the basis for its decision on
any individual SIP provision. As such, the EPA does not envision a
scenario whereby a citizen or a court would be unable to determine how
the air agency and the EPA interpreted a specific SIP provision at the
time of its approval into the SIP. Assuming there is any ambiguity in
the provision, the mutual understanding of the state and the EPA as to
the proper interpretation of that provision would be clear at the time
of the approval of the SIP revision, as reflected in the Federal
Register document for the final rule and the docket supporting that
rule, which should answer any question about the correct interpretation
of the term.
    The same commenter also questioned whether ``courts can or will
give any

legal weight to interpretative letters created after state regulations
are adopted or SIP approvals occurred, in the face of industry
defendant arguments that the SIP provisions do not accord with those
post hoc interpretive letters.'' This commenter asserted that by not
requiring all interpretations of the SSM provisions in the
``unambiguous language of the SIPs,'' the EPA is accepting ``great
legal uncertainty'' as to whether judges will consider interpretive
letters in enforcement actions. As a preliminary matter, as explained
earlier in this document, this action does not apply to ``post hoc''
interpretive letters, i.e., to situations where a state would submit an
interpretive letter after the EPA's approval of the SIP. Through this
action the EPA is confirming its view that it may use interpretive
letters to clarify ambiguous SIP provisions only when those letters
were submitted to the EPA during the evaluation of the SIP submission
and before final approval of the SIP revision and were included in the
final rulemaking docket and explicitly discussed in the Federal
Register document announcing such final action.
    In addition, as explained earlier in this document, once the EPA
approves a SIP revision, it becomes part of the state's SIP identified
in the CFR and thus becomes a federally enforceable regulation. In
cases where the substance of the interpretive letter is provided in the
CFR itself, either by copying the interpretation verbatim into the
regulatory text or by incorporating the letter by reference, courts
need not look further for the state and the Agency's agreed upon
interpretation. The EPA's interpretation will be clearly reflected in
the CFR. The EPA recognizes that actual or perceived regulatory
ambiguity may become an issue in instances where the interpretive
letter is reflected in the preamble to the final rulemaking but is not
copied or incorporated by reference in the CFR text itself. It is
important to note, however, that once included in the preamble to the
final rule, the air agency's interpretation of the SIP provision, as
reflected in the interpretive letter, becomes the EPA's promulgated
interpretation as well. While the EPA recognizes that an agency's
preamble guidance generally does not have the binding force of an
agency's regulations, courts do view it as informative in understanding
an agency's interpretation of its own regulation,\133\ and courts
accord an agency's interpretation of its own regulations a `` `high
level of deference,' accepting it `unless it is plainly wrong.' ''
\134\ When reviewing a purportedly ambiguous agency regulation, courts
have found that the agency's interpretation of its own regulation is
``controlling unless `plainly erroneous or inconsistent with the
regulation.' '' \135\ Based on these settled legal principles, the EPA
would expect a court in an enforcement action to look not only to the
text of the regulation at issue but also to the preamble to the final
rule. The preamble would contain an explanation of any interpretive
letter from the state upon which the EPA relied in order to interpret
any ambiguous SIP provisions.\136\ As such, the EPA disagrees that it
is ``accepting an unreasonable amount of legal uncertainty'' in future
enforcement actions by allowing the use of interpretive letters to
clarify SIP provisions where such letters are specifically discussed in
the final rulemaking. The EPA reiterates that reliance on such
interpretive letters is not appropriate in all circumstances, such as
instances in which the state's SIP submission is so significantly
ambiguous that it is necessary to request that the state revise the
regulatory text before the EPA can approve it into the SIP.
---------------------------------------------------------------------------

    \133\ See, e.g., Howmet Corp. v. EPA, 614 F.3d 544, 552 (D.C.
Cir. 2010) (using preamble guidance to interpret an ambiguous
regulatory provision); Wyo. Outdoor Council v. U.S. Forest Serv.,
165 F.3d 43, 53 (D.C. Cir. 1999) (``Although the preamble does not
`control' the meaning of the regulation, it may serve as a source of
evidence concerning contemporaneous agency intent.'').
    \134\ Howmet at 549 (quoting Gen Elec. Co. v. EPA, 53 F.3d 1324,
1327 (D.C. Cir. 1990)).
    \135\ Auer v. Robbins, 519 U.S. 452, 461 (1997) (quoting
Robertson v. Methow Valley Citizens Council, 490 U.S. 332, 359
(1989)).
    \136\ Indeed, the APA requires agencies to ``incorporate in the
rules adopted a concise general statement of their basis and
purpose,'' 5 U.S.C. 553(c), often referred to as the regulatory
preamble. It would not make sense for a court to attempt to
interpret the text of a regulation independently from its
statutorily mandated statement of basis and purpose.
---------------------------------------------------------------------------

    Finally, a commenter stated its view that reliance on interpretive
letters may be appropriate, but only when affected parties have the
right to comment on the letter and the EPA's reliance on it during the
rulemaking in which the letter is relied upon. The EPA has explained
earlier in this document the proper circumstances under which such
reliance may be appropriate and the proper process to be followed when
reliance upon such letters is appropriate, but the EPA also notes that
the process does not require that the letters always be made available
for public comment. As explained earlier in this document, the EPA
makes every attempt to identify ambiguities in state-submitted SIPs and
requests states to submit interpretive letters to explain any
ambiguities, before putting the proposed action on the SIP submission
out for public notice and comment. On occasion, however, ambiguous
provisions may inadvertently remain and are not identified until the
notice-and-comment period has begun. As explained earlier in this
document, sometimes these ambiguities are so significant that the EPA
requires the state to resubmit its SIP submission altogether, which
would entail another notice-and-comment period. When the EPA does not
deem the ambiguity to be so significant as to warrant a revision to the
state's regulatory text in the SIP submission, the Agency believes that
resolution of the ambiguity through the submission of an interpretive
letter, which then is incorporated into the EPA's action, reflected in
the administrative record and memorialized as the proper intended
reading of the provision, is appropriate.
    This approach comports with well-established principles applicable
to notice-and-comment rulemaking generally. One purpose of giving
interested parties the opportunity to comment is to provide these
parties the opportunity to bring areas of potential ambiguity in the
proposal to an agency's attention so that the concerns may be addressed
before the agency takes final action. If the APA did not allow the
agency to consider comments and provide clarification when issuing its
final action as necessary, this purpose would be defeated. Courts have
held that so long as a final rule is a ``logical outgrowth'' of the
proposed rule, adequate notice has been provided.\137\ It is the EPA's
practice to neither require a state to resubmit a SIP submission nor
repropose action on the submission, so long as the clarification
provided in the interpretive letter is a logical outgrowth of the
proposed SIP provision. If an interested party believes that the EPA is
incorrect in not requiring the state to revise its SIP submission or
that the EPA should repropose action on a submission, including the
clarification provided by the interpretive letter in the plain language
of the SIP submission itself, that party does have recourse. The APA
gives that party the opportunity to petition the EPA for rulemaking to
reconsider the decision under 5 U.S.C. 553(e). For these reasons, the
EPA believes that its process for using interpretive letters to clarify
SIP

provisions, as articulated in this rulemaking, is appropriate.
---------------------------------------------------------------------------

    \137\ See, e.g., Shell Oil Co., 950 F.2d 741; NRDC v. Thomas,
838 F.2d 1224 (D.C. Cir. 1988); South Terminal Corp. v. EPA, 504
F.2d 646.
---------------------------------------------------------------------------

VII. Clarifications, Reiterations and Revisions to the EPA's SSM Policy

A. Applicability of Emission Limitations During Periods of SSM

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 excess emissions during SSM events. This
has been the EPA's explicitly stated interpretation of the CAA with
respect to SIP provisions since the 1982 SSM Guidance, and the Agency
has reiterated this important point in the 1983 SSM Guidance, the 1999
SSM Guidance and the 2001 SSM Guidance. In accordance with CAA section
302(k), SIPs must contain emission limitations that ``limit the
quantity, rate, or concentration of emissions of air pollutants on a
continuous basis.'' Court decisions confirm that this requirement for
continuous compliance prohibits exemptions for excess emissions during
SSM events.\138\
---------------------------------------------------------------------------

    \138\ See, e.g., Sierra Club v. Johnson, 551 F.3d 1019, 1021
(D.C. Cir. 2008) (interpreting the definition of emission limitation
in section 302(k) and section 112); Mich. Dep't of Envtl. Quality v.
Browner, 230 F.3d 181 (6th Cir. 2000) (upholding disapproval of SIP
provisions because they contained exemptions applicable to SSM
events); US Magnesium, LLC v. EPA, 690 F.3d 1157, 1170 (10th Cir.
2012) (upholding the EPA's issuance of a SIP call to a state to
correct SSM-related deficiencies).
---------------------------------------------------------------------------

2. What Is Being Finalized in This Action
    For the reasons explained in the February 2013 proposal, in the
background memorandum supporting that proposal and in the EPA's
responses to comments in this document, the EPA interprets the CAA to
prohibit exemptions for excess emissions during SSM events in SIP
provisions. This interpretation has long been reflected in the SSM
Policy. The EPA acknowledges, however, that both states and the Agency
have failed to adhere to the CAA consistently with respect to this
issue in some instances in the past, and thus the need for this SIP
call action to correct the existing deficiencies in SIPs. In order to
be clear about this important point on a going-forward basis, the EPA
is reiterating that emission limitations in SIP provisions cannot
contain exemptions for emissions during SSM events.
    Many commenters wrongly asserted that the EPA declared in the
February 2013 proposal that all emission limitations in SIPs must be
established as numerical limitations, or must be set at the same
numerical level at all times. The EPA did not take this position. In
the case of section 110(a)(2)(A), the statute does not include an
explicit requirement that all SIP emission limitations must be
expressed numerically. In practice, it may be that numerical emission
limitations are the most appropriate from a regulatory perspective
(e.g., to be legally and practically enforceable) and thus the
limitation would need to be established in this form to meet CAA
requirements. The EPA did not, however, adopt the position ascribed to
it by commenters, i.e., that SIP emission limitations must always be
expressed only numerically and must always be set at the same numerical
level during all modes of source operation.
    The EPA notes that some provisions of the CAA that govern standard-
setting limit the EPA's own ability to set non-numerical
standards.\139\ Section 110(a)(2)(A) does not contain comparable
explicit limits on non-numerical forms of emission limitation.
Presumably, however, some commenters misunderstood the explicit
statutory requirement for emission limitations to be ``continuous'' as
a requirement that states must literally establish SIP emission
limitations that would apply the same precise numerical level at all
times. Evidently these commenters did not consider the explicit
recommendations that the EPA made in the February 2013 proposal
concerning creation of alternative emission limitations in SIP
provisions that states may elect to apply to sources during startup,
shutdown or other specifically defined modes of source operation.\140\
As many of the commenters acknowledged, the EPA itself has recently
promulgated emission limitations in NSPS and NESHAP regulations that
impose different numerical levels during different modes of source
operation or impose emission limitations that are composed of a
combination of a numerical limitation during some modes of operation
and a specific technological control requirement or work practice
requirement during other modes of operation. In light of the court's
decision in Sierra Club v. Johnson, the EPA has been taking steps to
assure that its own regulations impose emission limitations that apply
continuously, including during startup and shutdown, as required.\141\
---------------------------------------------------------------------------

    \139\ See, e.g., CAA section 112(h)(1) (authorizing design,
equipment, work practice, or other operational emission limitations
under certain conditions); 40 CFR 51.308(e)(1)(iii) (regulations
applicable to regional haze plans).
    \140\ See February 2013 proposal, 78 FR 12459 at 12478 (February
22, 2013) (the recommended criteria for consideration in creation of
SIP provisions that apply during startup and shutdown).
    \141\ 551 F.3d 1019 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    Regardless of the reason for the commenters' apparent
misunderstanding on this point, many of the commenters used this
incorrect premise as a basis to argue that ``continuous'' SIP emission
limitations may contain total exemptions for all emissions during SSM
events. Therefore, in this final action the EPA wishes to be very clear
on this important point, which 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. It is important to emphasize,
however, that regardless of how the air agency structures or expresses
a SIP emission limitation--whether solely as one numerical limitation,
as a combination of different numerical limitations or as a combination
of numerical limitations, specific technological control requirements
and/or work practice requirements that apply during certain modes of
operation such as startup and shutdown--the emission limitation as a
whole must be continuous, must meet applicable CAA stringency
requirements and must be legally and practically enforceable.\142\
---------------------------------------------------------------------------

    \142\ The EPA notes that CAA section 123 explicitly prohibits
certain intermittent or supplemental controls on sources. In a
situation where an emission limitation is continuous, by virtue of
the fact that it has components applicable during all modes of
source operation, the EPA would not interpret the components that
applied only during certain modes of operation, e.g., startup and
shutdown, to be prohibited intermittent or supplemental controls.
---------------------------------------------------------------------------

    Another apparent common misconception of commenters was that SIP
provisions may contain exemptions for emissions during SSM events, so
long as there is some other generic regulatory requirement of some kind
somewhere else in the SIP that coincidentally applies during those
exempt periods. The other generic regulatory requirements most
frequently referred to by commenters are ``general duty'' type
requirements, such as a general duty to minimize emissions at all
times, a general duty to use good engineering judgment at all times, or
a

general duty not to cause a violation of the NAAQS at any time. To the
extent that such other general-duty requirement is properly established
and legally and practically enforceable, the EPA would agree that it
may be an appropriate separate requirement to impose upon sources in
addition to the (continuous) emission limitation. The EPA itself
imposes separate general duties of this type in appropriate
circumstances.\143\ The existence of these generic provisions does not,
however, legitimize exemptions for emissions during SSM events in a SIP
provision that imposes an emission limitation.
---------------------------------------------------------------------------

    \143\ See, e.g., ``Oil and Natural Gas Sector: New Source
Performance Standards and National Emission Standards for Hazardous
Air Pollutants Reviews; Final rule,'' 77 FR 49489 at 49570, 49586
(August 16, 2012) (added general standards to apply at all times).
---------------------------------------------------------------------------

    In accordance with the definition of section 302(k), SIP emission
limitations must be continuous and apply at all times. SIP provisions
may be composed of a combination of numerical limitations, specific
technological control requirements and/or work practice requirements,
but those must be components of a continuously applicable SIP emission
limitation. In addition, the SIP emission limitation must meet
applicable stringency requirements during all modes of source operation
(e.g., be RACT for stationary sources located in a nonattainment area)
and be legally and practically enforceable. General-duty requirements
that are not clearly part of or explicitly cross-referenced in a SIP
emission limitation cannot be viewed as a component of a continuous
emission limitation. Even if clearly part of or explicitly cross-
referenced in the SIP emission limitation, however, a given general-
duty requirement may not be consistent with the applicable stringency
requirements for that type of SIP provision during startup and
shutdown. The EPA's recommendations for developing appropriate
alternative emission limitations applicable during certain modes of
source operation are discussed in section VII.B.2 of this document. In
general, the EPA believes that a legally and practically enforceable
alternative emission limitation applicable during startup and shutdown
should be expressed as a numerical limitation, a specific technological
control requirement or a specific work practice requirement applicable
to affected sources during specifically defined periods or modes of
operation.
3. Response to Comments
    The EPA received a substantial number of comments, both supportive
and adverse, concerning the issue of exemptions in SIP provisions for
excess emissions during SSM events. Many of these comments raised the
same core issues, albeit using slight variations on the arguments or
variations on the combination and sequence of arguments. 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 the EPA's proposed action on the Petition is
incorrect because some of the Agency's own regulations contain
exemptions for emissions during SSM events.
    Comment: Many commenters argued that the EPA is misinterpreting the
CAA to preclude SIP provisions with exemptions for emissions during SSM
events because some of the Agency's own existing NSPS and NESHAP rules
contain such exemptions. Some commenters provided a list of existing
NSPS or NESHAP standards that they claimed currently contain exemptions
for emissions during SSM events. Commenters also noted that the NSPS
general provisions at 40 CFR 60.11(d) excuse noncompliance with many
NSPS during periods of startup and shutdown. Other commenters asserted
that the EPA's interpretations in the February 2013 proposal are
inconsistent with its longstanding interpretation of the Act because
the EPA itself has a long history of adopting exceptions to numerical
emission limitations for emissions during SSM events, citing to the
NSPS general provisions at 40 CFR 60.8, the NSPS for Fossil-Fuel-Fired
Steam Generators and for Electric Utility Steam Generating Units (40
CFR part 60, respectively subparts D and Da) and the NSPS for
Industrial-Commercial-Institutional Steam Generating Units and for
Small Industrial-Commercial-Institutional Steam Generating Units (40
CFR part 60, respectively subparts Db and Dc). Commenters claimed that
recent revisions to 40 CFR part 60, subpart Da excluded periods of
startup and shutdown from new PM standards. The commenters pointed to
these facts or alleged facts as evidence that the EPA is interpreting
the term ``emission limitation'' or other provisions of the statute
inconsistently to preclude SSM exemptions in SIP provisions.
    Response: Commenters are correct that many of the EPA's existing
NSPS and NESHAP standards still contain exemptions from emission
limitations during periods of SSM. The exemptions in these EPA
regulations, however, predated the 2008 issuance of the D.C. Circuit
decision in Sierra Club v. Johnson, in which the court held that
emission limitations must be continuous and thus cannot contain
exemptions for emissions during SSM events. Likewise, the NSPS general
provisions in 40 CFR 60.8 that commenters identified as inconsistent
also predate that 2008 court decision. Although these other EPA
regulations that include exemptions for emissions during SSM events
were not before the court in the Sierra Club case, the EPA's view is
that the legal reasoning of the Sierra Club decision applies equally to
these exemptions and that the exemptions are thus inconsistent with the
CAA.
    Consequently, since the Sierra Club decision, the EPA has
eliminated exemptions in many existing federal emission limitations as
these standards are revised or reviewed pursuant to CAA requirements,
such as CAA sections 111(b)(1)(B), 112(d)(6) and 112(f)(2).\144\
Similarly, the EPA has established emission standards that apply at all
times, including during SSM events, when promulgating new NSPS and
NESHAP standards to be consistent with the Sierra Club decision.\145\
The EPA recognizes that the NSPS general provisions regulations also
include exemptions for emissions during SSM events, but in promulgating
new NSPS since the Sierra Club decision, the EPA has established
emission limitations in the new NSPS that apply at all times thereby
superseding those general provisions. Therefore, the EPA's action in
this rulemaking is consistent with other actions that the EPA has taken
since the Sierra Club decision concerning the issue of SSM exemptions.
---------------------------------------------------------------------------

    \144\ See, e.g., ``New Source Performance Standards Review for
Nitric Acid Plants; Final rule,'' 77 FR 48433 (August 14, 2012)
(example of NSPS emission limitation that no longer includes
exemption for periods of startup or shutdown).
    \145\ See, e.g., ``Oil and Natural Gas Sector: New Source
Performance Standards and National Emission Standards for Hazardous
Air Pollutants Reviews; Final rule,'' 77 FR 49489 (August 16, 2012)
(consistent with Sierra Club v. Johnson, the EPA has established
standards in both rules that apply at all times).
---------------------------------------------------------------------------

    The fact that the EPA has not completed the process of updating its
own regulations to bring them into compliance with respect to CAA
requirements concerning proper treatment of emissions during SSM events
does not render this SIP call action arbitrary or capricious. The
existence of a deficiency in an existing EPA regulation that has not
yet been corrected does not alter the legal requirements imposed by the
CAA upon states with respect to SIP provisions. Thus, for example, the
EPA does not agree with commenters that the continued existence of SSM
exemptions

in the general provisions applicable to the emission limitations in the
Agency's own NSPS for Fossil-Fuel-Fired Steam Generators in 40 CFR part
60, subpart D, is evidence that exemptions for emissions during SSM
events are permitted by the CAA.
    The EPA acknowledges that correction of longstanding regulatory
deficiencies by proper rulemaking procedures requires time and
resources, not only for the EPA but also for states and affected
sources. Hence, the EPA has elected to proceed via its authority under
section 110(k)(5) and to provide states with the full 18 months allowed
by statute for compliance with this action. This SIP call is intended
to help assure that state SIP provisions are brought into line with CAA
requirements for emission limitations, just as the EPA is undertaking a
process to update its own regulations.
    The EPA also specifically disagrees with the commenters'
implication that 40 CFR 60.11(d) completely excuses noncompliance
during periods of startup and shutdown. Rather, that provision imposes
a separate affirmative obligation to maintain and operate the affected
facility, including associated air pollution control equipment, in a
manner consistent with good air pollution control practices at all
times. The existence of this separate duty to minimize emissions,
however, does not justify or excuse the existence of an exemption for
emissions during SSM events from the emission limitations of an EPA
NSPS. It is a separate obligation that sources must also meet at all
times.
    The EPA also disagrees with the commenters who argued that the
Agency has recently created new exemptions for PM emissions during
startup and shutdown events in the NSPS for Electric Utility Steam
Generating Units in 40 CFR part 60, subpart Da. The EPA has not created
new exemptions for emissions during startup and shutdown. To the
contrary, the EPA has taken steps to assure that these regulations are
consistent with the statutory definition of emission limitation and
with the logic of the Sierra Club decision on a going-forward basis. In
accordance with that decision, the revised emission limitations in
subpart Da NSPS apply continuously. In revising subpart Da to establish
requirements for sources on which construction, modification or
reconstruction commenced after May 3, 2011, the EPA determined that it
was appropriate to provide that the exemptions for emissions during SSM
events in the General Provisions do not apply.\146\ Although the Sierra
Club v. Johnson decision specifically addressed the validity of SSM
exemptions in NESHAP regulations, the EPA concluded that the court's
focus on the definition of ``emission limitation'' in section 302(k)
applied equally to any such SSM exemptions in NSPS regulations. Thus,
for affected sources on which construction, modification or
reconstruction starts after May 3, 2011, the General Provisions do not
provide an exemption to compliance with the applicable emission
limitations during SSM events.
---------------------------------------------------------------------------

    \146\ See 40 CFR 60.48Da(a). For affected facilities for which
construction, modification, or reconstruction commenced after May 3,
2011, the applicable SO2 emissions limit under Sec.
60.43Da, NOX emissions limit under Sec.  60.44Da, and
NOX plus CO emissions limit under Sec.  60.45Da apply at
all times.
---------------------------------------------------------------------------

    For such sources, the emission limitation for PM in 40 CFR
60.42Da(a) imposes a numerical level of 0.03 lb/MMBtu that applies at
all times except during startup and shutdown and specific work
practices that apply during startup and shutdown.\147\ The related
emission limitation for opacity from such sources in 40 CFR 60.42Da(b)
is 20 percent opacity at all times, except for one 6-minute period per
hour of not more than 27 percent, and it applies at all times except
during periods of startup and shutdown when the work practices for PM
limit opacity. Commenters alleged that the EPA created an ``exemption''
from the PM emission limitations in subpart Da applicable to post-May
3, 2011, affected sources. That is simply incorrect. The revised
regulations in subpart Da impose a numerical emission limitation that
applies at all times except during startup and shutdown and impose
specific work practice requirements that apply during startup and
shutdown as a component of the emission limitation. Specifically, 40
CFR 60.42Da(e)(2) explicitly requires post-May 3, 2011, affected
sources to comply with specific work practice standards in part 63,
subpart UUUUU. The numerical emission limitation and the work practice
requirement together comprise a continuous emission limitation and
there is no exemption for emissions during startup and shutdown. The
fact that the EPA has established different requirements for different
periods of operation does not constitute creation of an exemption.
These emission limitations have numerical limitations that apply during
most periods and specific technological control requirements or work
practice requirements that apply during startup and shutdown, but all
periods of operation are subject to controls and no periods of
operation are exempt from regulation. States are similarly able to
alter their regulations, in response to this SIP call, to provide for
emission limitations with different types of controls applicable during
different modes of source operation, so long as those controls apply at
all times and no periods are exempt from controls. As explained in
section VII.A of this document, the EPA interprets section 110(a)(2)(A)
to permit SIP provisions that are composed of a combination of
numerical limitations, specific technological control requirements and/
or work practice requirements, so long as the resulting emission
limitations are continuous, meet applicable stringency requirements
(e.g., are RACT for sources in nonattainment areas) and are legally and
practically enforceable.
---------------------------------------------------------------------------

    \147\ The EPA notes that the emission standards for
SO2 in 40 CFR 60.43Da and for NOX in 40 CFR
60.44Da, applicable to sources on which construction, modification
or reconstruction commenced after May 3, 2011, also apply
continuously and contain no exemptions for emissions during SSM
events.
---------------------------------------------------------------------------

    The EPA also notes that the provisions of 40 CFR 60.42Da(b)(1) do
not provide an ``exemption'' from the opacity standard. That section
merely provides that the affected sources do not need to meet the
opacity standard of the NSPS (at any time), if they have installed a PM
continuous emission monitoring system (PM CEMS) to measure PM emissions
continuously instead of relying on periodic stack tests to assure
compliance with the PM emission limitation. One reason for the
imposition of opacity standards on sources is to provide an effective
means of monitoring for purposes of assuring source compliance with PM
emission limitations and proper operation of PM emission controls on a
continuous basis. If a source is subject to a sufficiently stringent PM
limitation and has opted to install, calibrate, maintain and operate a
PM CEMS to measure PM emissions, then it is reasonable for the EPA to
conclude that an opacity emission limitation is not needed for that
particular source for those purposes.\148\ The direct measurement of
PM, in conjunction with an appropriately stringent PM emission
limitation that

applies continuously, is an appropriate means to assure adequate
control of PM emissions on a continuous basis. States evaluating how
best to replace impermissible SSM exemptions from opacity standards may
wish to consider a similar approach, conditioned upon the use of PM
CEMS and a sufficiently stringent PM emission limitation.
---------------------------------------------------------------------------

    \148\ For example, for NSPS regulations under subparts D, Da, Db
and Dc of 40 CFR part 60, the EPA has deemed 0.030 lb/MMBtu to be a
sufficiently stringent PM limitation for certain sources operating
PM CEMS to conclude that an opacity emission limitation is not
needed, on the basis that the contribution of filterable PM to
opacity at PM levels of 0.030 lb/MMBtu or less is generally
negligible, and sources with mass limits at this level or less will
operate with little or no visible emissions (i.e., less than 5
percent opacity). See 74 FR 5072 at 5073 (January 28, 2009).
---------------------------------------------------------------------------

    Finally, the EPA emphasizes that what is at issue in this action is
the question of whether emission limitations in SIP provisions can
include exemptions for emissions during SSM events. The EPA is
reiterating its longstanding interpretation of the CAA with respect to
this question, in the process of responding to the Petition, updating
its SSM Policy and applying its current interpretations of the CAA to
the specific SIP provisions at issue in this SIP call action. To the
extent that commenters intend to point out that the EPA needs to
address exemptions for emissions during SSM events in its own existing
regulations, the Agency is already aware of that need due to recent
judicial decisions and is proceeding to correct those regulations in
due course.
    b. Comments that the EPA's proposed action on the Petition is
incorrect because the Agency has previously allowed the inclusion of
exemptions for emissions during SSM events through approval of NSPS or
NESHAP requirements into SIPs.
    Comment: Commenters asserted that the EPA is being inconsistent
because it has previously approved SIP submissions that rely on NSPS
rules, including the SSM exemptions in those existing rules. The
commenters argued that the EPA's current interpretation of the CAA to
preclude SSM exemptions in SIP provisions is thus at odds with past
guidance and practice.
    Response: The EPA disagrees with the argument that past approval of
SIP submissions that relied upon an NSPS or NESHAP with an SSM
exemption is evidence that such exemptions should be permissible in SIP
provisions in the future. In the 1999 SSM Guidance, the EPA addressed
the related issue of whether states could create affirmative defenses
in SIP provisions that would alter or add to the requirements of an
existing EPA NSPS or NESHAP.\149\ At that time, the EPA clearly stated
that it would be inappropriate for a state to seek to ``deviate'' from
the specific requirements of an NSPS or NESHAP when adopting that
standard as a SIP provision, stating that ``[b]ecause EPA set these
standards taking into account technological limitations, additional
exemptions would be inappropriate.'' Thus, so long as a state did not
alter the requirements of the existing NSPS or NESHAP by including
additional affirmative defenses or exemptions, the EPA indicated that
it would approve a SIP submission that included an NSPS or NESHAP.
---------------------------------------------------------------------------

    \149\ See 1999 SSM Guidance at Attachment p. 3.
---------------------------------------------------------------------------

    The commenters' argument has brought to the EPA's attention that
past guidance on this issue is in fact inconsistent with more recent
legal developments. At the time of the 1999 SSM Guidance, the EPA was
still of the belief that its own NSPS and NESHAP regulations could
legitimately include exemptions for emissions during SSM events. In
that light, recommending to states that they could rely on an EPA NSPS
or NESHAP as an emission limitation in a SIP provision so long as they
did not alter the NSPS or NESHAP in any fashion was logical. At that
time, the reasoning was that NSPS and NESHAP standards were technology-
based standards that, although neither designed nor intended to meet
the separate legal requirements for SIP provisions, could be used to
provide emission reductions creditable in SIPs. Since the 2008 D.C.
Circuit decision in Sierra Club v. Johnson, however, it has been clear
that NSPS and NESHAP standards themselves cannot contain such
exemptions. The reasoning of the court was that exemptions for SSM
events are impermissible because they contradict the requirement that
emission limitations be ``continuous'' in accordance with the
definition of that term in section 302(k). Although the court evaluated
this issue in the context of EPA regulations under section 112, the EPA
believes that this same logic extends to SIP provisions under section
110, which similarly must contain emission limitations as defined in
the CAA. Section 110(a)(2)(A) requires states to have emission
limitations in their SIPs to meet other CAA requirements, and any such
emission limitations would similarly be subject to the definition of
that term in section 302(k).
    Accordingly, the EPA concludes that, prospectively, a state should
not submit an NSPS or NESHAP for inclusion into its SIP as an emission
limitation (whether through incorporation by reference or otherwise),
unless that NSPS or NESHAP does not include an exemption for SSM events
or unless the state otherwise takes action to exclude the SSM exemption
from the standard as part of the SIP submission. Because SIP provisions
must apply continuously, including during SSM events, the EPA can no
longer approve SIP submissions that include any emission limitations
with such exemptions, even if those emission limitations are NSPS or
NESHAP regulations that the EPA has not yet revised to make consistent
with CAA requirements. Alternatively, states may elect to adopt an
existing NSPS or NESHAP as a SIP provision, so long as the state
provision excludes the SSM exemption.\150\ States may also wish to
replace the SSM exemption with appropriately developed alternative
emission limitations that apply during startup and shutdown in lieu of
the SSM exemption. Otherwise, the EPA's approval of the deficient SSM
exemption provisions into the SIP would contravene CAA requirements for
SIP provisions and would potentially result in misinterpretation or
misapplication of the standards by regulators, regulated entities,
courts and members of the public. The EPA emphasizes that the inclusion
of an NSPS or NESHAP as an emission limitation in a state's SIP (which
approach, as noted in section VII.B.3 of this document, would be at the
state's option) is different and distinct from reliance on such
standards indirectly, such as sources of emission reductions that may
be taken into account for SIP planning purposes in emissions
inventories or attainment demonstrations. For these uses (i.e., other
than as direct emission limitations), states may continue to rely on
EPA NSPS and NESHAP regulations, even those that have not yet been
revised to remove inappropriate exemptions, in accordance with the
requirements applicable to those SIP planning functions.
---------------------------------------------------------------------------

    \150\ Under CAA section 116, states have the explicit general
authority to regulate more stringently than the EPA. Indeed, under
section 116 states can regulate sources subject to EPA regulations
promulgated under section 111 or section 112 so long as they do not
regulate them less stringently. Accordingly, the EPA believes that
states may elect to adopt EPA regulations under section 111 or
section 112 as SIP provisions and expressly eliminate the exemptions
for emissions during SSM events.
---------------------------------------------------------------------------

    c. Comments that the EPA is misinterpreting the Sierra Club case
because it applies only to MACT regulations and not to SIP provisions.
    Comment: Many commenters claimed that the EPA incorrectly applies
the holding in the Sierra Club decision to preclude exemptions for
emissions during SSM events in SIP provisions and that the Sierra Club
decision does not apply in this context. The commenters argued that the
Sierra Club decision was directly dependent on the structure of CAA
section 112 and cannot be extended to the different regulatory

structure that governs SIPs under CAA section 110.
    The commenters further contended that in the SIP context, the
underlying air quality pollution control requirement for SIPs is to
attain NAAQS and no specific level of stringency is required, unlike
section 112, and Congress gave states broad discretion in the design of
their SIPs. Commenters asserted that the Sierra Club decision held only
that the general-duty requirement in the section 112 regulations did
not meet the stringency requirements of CAA section 112 and that this
holding does not apply in the SIP context because in the SIP context no
specific level of stringency is required.
    Commenters also asserted that a general-duty requirement is an
appropriate alternative standard for SSM events in the SIP context
because CAA sections 302(k) and 110(a)(2)(A) give states broad
authority to develop the mix of controls necessary and appropriate to
implement the NAAQS. Other commenters contended that the Sierra Club
decision does not preclude states from constructing a compliance regime
that uses multiple methods to limit emissions as long as the overall
compliance regime to minimize emissions is enforceable.
    Commenters also suggested that the decision in Kamp v. Hernandez
relied upon in the Sierra Club case affirmed EPA's approval of a state
emission limitation in a SIP that specifically allowed and even
expected a certain number of annual exceedances of the emission
limit.\151\ Some commenters argued that the Sierra Club decision should
not be read to impose a ``continuous emissions limitation'' requirement
and that to the extent it does, it was incorrectly decided.
---------------------------------------------------------------------------

    \151\ 752 F.2d 1444 (9th Cir. 1985).
---------------------------------------------------------------------------

    Response: The EPA disagrees that the court's decision in Sierra
Club v. Johnson has no relevance to this action. Of course that
decision specifically addressed the validity of exemptions for
emissions during SSM events in the Agency's own regulations promulgated
under section 112. Naturally, that decision turned, in part, on the
specific provisions of section 112 and the specific arguments that each
of the litigants raised in that case. However, the decision also turned
in large part on the explicit statutory definition of the term
``emission limitation'' in section 302(k), which requires such
limitations to be ``continuous.''
    In that litigation, the EPA itself had argued that the exemptions
from the otherwise applicable MACT standards during SSM events were
consistent with CAA requirements because the MACT standards and the
separate ``general duty'' requirements ``together form an
uninterrupted, i.e., continuous'' emission limitation, because either
the numerical limitation or the general duty applied at all times.\152\
The Sierra Club court rejected this argument, in part because the
general duty that EPA required sources to meet during SSM events was
not itself consistent with section 112(d) and the EPA did not purport
to act under section 112(h). Thus, the EPA agrees that the court in
Sierra Club explicitly found that the SSM exemption in EPA's NESHAP
general provision rules violated the CAA because the general duty to
minimize emissions was not a section 112(d)-compliant standard and had
not been justified by the EPA as a 112(h)-compliant standard. The court
reasoned that when sections 112 and 302(k) are read together, there
must be a continuous section 112-compliant standard. It is important to
note that if the otherwise applicable numerical MACT standards had
themselves applied at all times consistent with section 302(k), then
there would have been no question that they were in fact continuous.
---------------------------------------------------------------------------

    \152\ See 551 F.3d 1019, 1026 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    The EPA has concluded that the reasoning of the Sierra Club
decision is correct and further supports the Agency's interpretations
of the CAA with respect to SIP provisions. As explained in the February
2013 proposal, the EPA's longstanding SSM guidance has interpreted the
CAA to prohibit exemptions for emissions during SSM events since at
least 1982. The EPA has long explained that exemptions for emissions
during SSM events are not permissible in SIP provisions, because they
interfere with attainment and maintenance of the NAAQS, protection of
PSD increments and improvement of visibility, and because they are
inconsistent with the enforcement structure of the CAA. The EPA also
noted that the definition of emission limitation in section 302(k) was
part of the basis for its interpretation concerning SIP
provisions.\153\ In the February 2013 proposal, the EPA explained that
the Sierra Club court's emphasis on the definition of the term emission
limitation in section 302(k) further bolsters the Agency's basis for
interpreting the CAA to preclude such exemptions in SIP provisions. In
other words, under the CAA and the court's decision, emission
limitations in SIP provisions as well as in NSPS and NESHAP regulations
must be continuous, although they can impose different levels or forms
of control during different modes of source operation.
---------------------------------------------------------------------------

    \153\ See 1999 SSM Guidance at 2, footnote 1 (citing the section
302(k) definition of emission limitations and emission standards).
---------------------------------------------------------------------------

    The EPA also disagrees with the argument that the Sierra Club
decision does not apply because section 110, unlike section 112, does
not impose any specific level of ``stringency'' for SIP provisions. In
accordance with section 110(a)(1), states are required to have SIPs
that provide for attainment, maintenance and enforcement of the NAAQS
in general. Pursuant to section 110(a)(2), states are required to have
SIP provisions that meet many specific procedural and substantive
requirements, including but not limited to, the explicit requirements
of section 110(a)(2)(A) for emission limitations necessary to meet
other substantive CAA requirements. In addition, however, states must
have SIP provisions that collectively meet a host of other statutory
requirements that also impose more specific stringency requirements.
Merely by way of example, section 110(a)(2)(I) requires states with
nonattainment areas to have SIP provisions that collectively meet part
D requirements.\154\ In turn, the different subparts of part D
applicable to each NAAQS impose many requirements that require emission
limitations in SIPs that meet various levels of stringency. Again,
merely by way of example, states with nonattainment areas for PM under
part D subpart 4 must have SIPs that include emission limitations that
meet either the RACM and RACT level of stringency (if the nonattainment
area is classified Moderate) or meet the BACM and BACT level of
stringency (if the area is classified Serious).\155\ There are similar
requirements for states to impose emission limitations that must meet
various levels of stringency for each of the NAAQS. Likewise, states
must impose SIP emission limitations that meet BART and reasonable
progress levels of stringency for regional haze program purposes \156\
and must ensure that emission limitations meet BACT or LAER levels of
stringency for PSD or nonattainment NSR permitting program

purposes.\157\ The EPA agrees that states have broad discretion in how
to devise SIP provisions under section 110, but states nevertheless are
required to devise SIP provisions that meet applicable statutory
stringency requirements. In short, the argument that the Sierra Club
decision is not germane because there are no comparable ``stringency''
requirements applicable to SIP provisions is simply in error. While it
is true that SIP provisions do not need to meet section 112 levels of
stringency, they must still be continuous under section 302(k) and meet
applicable NAAQS, PSD and visibility requirements and stringency
levels. In short, they cannot contain exemptions for emissions during
SSM events.
---------------------------------------------------------------------------

    \154\ Sections 171-193 of CAA title I comprise part D.
    \155\ See CAA section 172(c)(2) (generally applicable attainment
plan requirements including RACM and RACT); CAA section 189(a)(1)
(requirements for areas classified Moderate); section 189(b)
(requirements for areas classified Serious).
    \156\ See CAA section 169A(b)(2)(A).
    \157\ See CAA section 165(a)(4) and CAA section 173(a)(2).
---------------------------------------------------------------------------

    Finally, the EPA does not agree with the commenters' view of the
significance of the reference to the Kamp v. Hernandez decision by the
court in the Sierra Club decision. The Kamp decision upheld the EPA's
approval of a SIP provision that imposed an SO2 emission
limitation on a specific stationary source.\158\ To the extent that the
commenters believe that the Kamp decision stands for the principle that
SIP emission limitations can be ``continuous'' even if they do not
restrict emissions to the same numerical limitation at all times, this
point is not in dispute. As explained in section VII.A of this
document, the EPA agrees with this principle. If, however, the
commenters believe that the Kamp decision instead indicates that SIP
emission limitations may contain exemptions, such that no emission
standard applies during some mode of source operation, then that is
simply incorrect. The EPA-approved SIP provision at issue in Kamp did
not itself allow for a certain number of ``exceedances'' of the
emission limitation each year. The state emission limitation rule in
that case was developed to ensure attainment and maintenance of the
then applicable SO2 NAAQS and the approved emission
limitation for the source fluctuated but was continuous. It was the
specifications of the SO2 NAAQS standard that allowed for a
certain number of ``exceedances'' each year. The NAAQS themselves are
not ``emission limitations'' governed by section 302(k) and commonly
have a statistical ``form'' that authorizes a set number of
``exceedances'' of the numerical level of the NAAQS before there is a
``violation'' of the NAAQS.\159\ Thus, the EPA believes that the court
in the Sierra Club decision properly cited the Kamp case as support for
the fundamental proposition that emission limitations must be
``continuous.'' Moreover, the EPA notes that commenters did not address
other reported decisions in which courts have upheld the Agency's
disapproval of SIP submissions containing SSM exemptions.\160\
---------------------------------------------------------------------------

    \158\ 753 F.3d 1444, 1452-53 (9th Cir. 1985).
    \159\ See, e.g., 40 CFR 50.18 (24-hour PM2.5 NAAQS
met when 98th-percentile monitored value is less than or equal to 35
ug/m\3\).
    \160\ See, e.g., Mich. Dep't of Envtl. Quality v. Browner, 230
F.3d 181 (6th Cir. 2000) (upholding disapproval of SIP provisions
because they contained exemptions applicable to SSM events); US
Magnesium, LLC v. EPA, 690 F.3d 1157, 1170 (10th Cir. 2012)
(upholding the EPA's issuance of a SIP call to a state to correct
SSM-related deficiencies).
---------------------------------------------------------------------------

    d. Comments that the EPA's proposed action contradicts a 2009
guidance document concerning the effect of the Sierra Club decision on
SSM exemptions in existing standards.
    Comment: A number of commenters suggested that the EPA's February
2013 proposal is inconsistent with a memorandum (in fact a public
letter) issued by the Agency following the Sierra Club decision in
which the D.C. Circuit vacated two EPA provisions that exempt sources
from section 112(d) emission standards during periods of SSM (Kushner
letter).\161\ The commenters noted that the Kushner letter explained
that many MACT standards have SSM exemptions that were not affected by
the Sierra Club decision. They argued that the Kushner letter should be
read to mean that no emission limitations other than the ones
explicitly discussed within that letter would be affected by the
court's holding that emission limitations under the CAA must be
continuous.
---------------------------------------------------------------------------

    \161\ See Letter from A. Kushner, Director, Office of Civil
Enforcement, EPA/OECA, regarding ``Vacatur of Startup, Shutdown, and
Malfunction (SSM) Exemption (40 CFR 63.6(f)(1) and 63.6(h)(1)),''
July 22, 2009, in the rulemaking docket.
---------------------------------------------------------------------------

    Response: The EPA disagrees with these comments for several
reasons. First, the commenters misinterpret the Kushner letter. The
purpose of the Kushner letter was to explain the direct and immediate
impact of the Sierra Club decision, which vacated the SSM exemption in
EPA's NESHAP general provisions regulations. The Kushner letter
explained that the vacatur would ``immediately and directly'' affect
only the subset of NESHAP source category standards that incorporated
the general provisions' exemption by reference, and that contain no
other regulatory text exempting or excusing, in any way, compliance
during SSM events, because only the general provisions' exemption was
challenged and before the court in the Sierra Club case. However, the
Kushner letter clearly stated that the legality of all NESHAP SSM
exemption provisions was in question and that EPA would examine such
provisions in light of the court's decision. Therefore, the commenters'
suggestion that the Kushner letter supports a limited reading of the
legal reasoning of the Sierra Club case is incorrect.
    Second, the Kushner letter did not explicitly or implicitly address
the issue of whether the CAA allows exemptions for emissions during SSM
events in SIP provisions. That fact is unsurprising, in that at the
time of the Kushner letter the EPA already had guidance in the SSM
Policy (issued and reiterated in 1982, 1983, 1999 and 2001) that
clearly stated the Agency's view that such exemptions are not
permissible in SIP provisions, consistent with CAA requirements. It
would also have been unnecessary for the Kushner letter discussing the
impact of the Sierra Club decision on NESHAP standards to have
mentioned that the statutory definition of emission limitation also
precludes exemptions for SSM provisions in SIPs. The EPA had already
made this point explicitly in the 1999 SSM Guidance, when it explained
the reasons why such provisions would be contrary to CAA requirements
for SIPs.\162\ Thus, the EPA's guidance for SIP provisions concerning
emissions during SSM events had already explicitly articulated that
provisions with exemptions for SSM events could not be approved
pursuant to CAA section 110(l), because that would interfere with a
fundamental requirement of the CAA, i.e., the definition of ``emission
limitation'' in section 302(k).
---------------------------------------------------------------------------

    \162\ See 1999 SSM Guidance at 2, footnote 1.
---------------------------------------------------------------------------

    Finally, the EPA disagrees that the Kushner letter could override
the applicability of the logic of the Sierra Club decision to SIP
provisions, even if the Agency had any such intentions. The D.C.
Circuit's evaluation of the issue with respect to the EPA's own
regulations was premised not solely upon the particular requirements of
section 112 but also more broadly on the meaning and specific
definition of the term ``emission limitation'' under the CAA. That
definition applies to SIP provisions as well as to the EPA's own
regulations. Because the SSM Policy in effect at the time of the Sierra
Club decision and the time of the Kushner letter already stated that
EPA interpreted the CAA to prohibit SIP provisions that exempt
emissions during SSM events, there would have

been no need for the Kushner letter to speak to this issue.\163\
---------------------------------------------------------------------------

    \163\ See, e.g., 1999 SSM Guidance, Attachment at 1 (``any
provision that allows for an automatic exemption for excess
emissions is prohibited'').
---------------------------------------------------------------------------

    e. Comments that the EPA's proposed action on the Petition is
incorrect because the Agency's recent MATS rule and Area Source Boiler
rule regulations contain exemptions for emissions during SSM events.
    Comment: Many commenters asserted that the EPA's February 2013
proposed action to find SIP provisions with exemptions for emissions
during SSM events to be substantially inadequate is arbitrary and
capricious because recent Agency NESHAP regulations under section 112
contain similar exemptions. Commenters pointed to recently promulgated
rules such as the MATS rule \164\ and the Area Source Boiler rule \165\
as examples of NESHAP regulations that they claim contain similar
exemptions. According to commenters, the emission limitations in EPA's
own MATS rule ``allow excess emissions during SSM events,'' suggesting
that the Agency created exemptions for such emissions.\166\ Other
commenters similarly argued that the EPA created emission limitations
in the Area Source Boiler rule that do not apply ``continuously''
because the numerical limitations do not apply during startup and
shutdown.\167\ In short, these commenters argued that the EPA is being
arbitrary and capricious because it is holding emission limitations in
SIPs to a different and higher standard than emission limitations under
its own NSPS and NESHAP regulations.
---------------------------------------------------------------------------

    \164\ The mercury and air toxics standards (MATS) rule for power
plants regulates emissions from new and existing coal- and oil-fired
electric utility steam generating units (EGUs) under 40 CFR part 63,
subpart UUUUU.
    \165\ The Area Source Boiler rule regulates industrial,
commercial and institutional boilers at area sources under 40 CFR
part 63, subpart JJJJJJ.
    \166\ See MATS rule, requirements during startup, shutdown and
malfunction, 77 FR 9304 at 9370 (February 16, 2012).
    \167\ See Area Source Boiler rule, notice of final action on
reconsideration, periods of startup and shutdown, 78 FR 7487 at 7496
(February 1, 2013).
---------------------------------------------------------------------------

    Response: The EPA disagrees with these commenters. The recent EPA
rulemaking efforts that commenters claim are at odds with EPA's SIP
call are completely consistent with the Agency's action today. First,
as explained in the February 2013 proposal, the EPA has not taken the
position that sources must be subject to SIP emission limitations that
are set at the same numerical level at all times, or that are expressed
as numerical limitations at all times. As the EPA stated, ``[i]f
justified, the state can develop special emission limitations or
control measures that apply during startup or shutdown if the source
cannot meet the otherwise applicable emission limitation in the SIP.''
\168\ The EPA's 1999 SSM Guidance articulated that SIP provisions may
include alternative emission limitations applicable during startup and
shutdown as part of a continuously applicable emission limitation when
properly developed and otherwise consistent with CAA requirements.
Moreover, the EPA recommended specific criteria relevant to the
creation of such alternative emission limitations. The EPA reiterated
that guidance in the February 2013 proposal and is providing a
clarified version of the guidance in this final action. This issue is
addressed in more detail in section VII.B.2 of this document.
---------------------------------------------------------------------------

    \168\ See February 2013 proposal, 78 FR 12459 at 12488 (February
22, 2013).
---------------------------------------------------------------------------

    The EPA also disagrees with the assertion that it is holding state
SIP provisions to a different standard than its own NSPS and NESHAP
regulations. The EPA notes that SIP emission limitations and NSPS and
NESHAP emission limitations are, of course, designed for different
purposes (e.g., to meet the NAAQS versus to reduce emissions of HAPs)
and have to meet some different statutory requirements (e.g., to be
RACM versus be standards that are compliant with section 112). However,
the EPA understands the commenters' claim to be more specifically that
the Agency is applying a different interpretation of the term
``emission limitation'' and taking a different approach to the
treatment of emissions during SSM events in its own regulations, even
in recent regulations developed subsequent to the Sierra Club decision.
The EPA believes that this argument reflects a misunderstanding of both
the February 2013 proposal and what the Agency's own new regulations
contain.
    The MATS rule and the Area Source Boiler rule in fact illustrate
how the EPA is creating emission limitations that apply continuously,
with numerical limitations or combinations of numerical limitations and
other specific technological control requirements or work practice
requirements applicable during startup and shutdown, depending upon
what is appropriate for the source category and the pollutants at
issue. For example, in the MATS rule the EPA has promulgated
regulations that impose emission limitations on various subcategories
of sources to address HAP emissions. To do so, the EPA developed
emission limitations to address the relevant pollutants using a
combination of numerical emission limitations and work practices. The
work practice requirements specifically apply to sources during startup
and shutdown and are thus components of the continuously applicable
emission limitations.\169\
---------------------------------------------------------------------------

    \169\ The EPA took final action on a petition for
reconsideration concerning the MATS rule and the Utility NSPS that
made certain revisions related to the emission limitations and work
practices applicable during startup and shutdown. Those revisions
did not, however, alter the basic structure of the emission
limitations as numerical limitations, or numerical limitations with
work practice components during startup and shutdown, depending upon
the source category and the pollutants at issue. See 79 FR 68777
(November 19, 2014).
---------------------------------------------------------------------------

    Similarly, in the Area Source Boiler rule \170\ the EPA has imposed
emission limitations on affected sources for PM, mercury and CO. The
specific emission limitations that apply vary depending upon the
subcategory of boiler. The emission limitations include a combination
of numerical emission limitations and work practice requirements that
together apply during all modes of source operation. For some
subcategories, the standards that apply during startup and shutdown
differ from the standards that apply during other periods of operation.
This illustrates what the EPA considers the correct approach to
creating emission limitations: (i) The emission limitation contains no
exemption for emissions during SSM events; (ii) the component of the
emission limitation that applies during startup and shutdown is clearly
stated and obviously is an emission limitation that applies to the
source; (iii) the component of the emission limitation that applies
during startup and shutdown meets the applicable stringency level for
this type of emission limitation (in this case section 112); and (iv)
the emission limitation contains requirements to make it legally and
practically enforceable. In short, the Area Source Boiler rule
established emission limitations that apply continuously, in accordance
with the requirements of the CAA, and consistent with the court's
decision in the Sierra Club decision. States with SIP provisions that
are deficient because they contain automatic or discretionary
exemptions for emissions during SSM events may wish to consider the
Agency's own approach when they develop SIP revisions in response to
this SIP call.
---------------------------------------------------------------------------

    \170\ 78 FR 7487 (February 1, 2013).
---------------------------------------------------------------------------

    f. Comments that section 110(a)(2)(A) authorizes states to have SIP
provisions with exemptions for emissions during SSM events because they
are not ``emission limitations'' and are not

subject to the requirement to be ``continuous.''
    Comment: Section 110(a)(2)(A) requires states to have SIPs that
include emission limitations for purposes of imposing restrictions on
sources of emissions in order to attain and maintain the NAAQS and to
meet other CAA requirements. Some commenters noted that, in addition to
``emission limitations,'' section 110(a)(2)(A) also explicitly refers
to ``other control measures, means, or techniques.'' Unlike the term
``emission limitation,'' which is defined in section 302(k), commenters
contended that these ``other control[s]'' need not be continuous.
Accordingly, these commenters argued that emission controls in SIP
provisions that either contain, or are subject to, SSM exemptions can
be viewed merely as examples of these ``other control measures, means,
or techniques'' that are validly included in SIPs and that do not have
to limit emissions from sources on a continuous basis. Specifically,
these commenters asserted that the plain text of section 110(a)(2)(A)
does not require SIPs to include only emission limitations but rather
requires that SIPs include ``emission limitations,'' ``other control
measures, means, or techniques,'' or a mixture thereof. Furthermore,
according to some of these commenters, an interpretation of section
110(a)(2)(A) that requires all SIP provisions to be ``emission
limitations,'' and thus subject to the requirement that they be
continuous, would render the ``other control'' language in the statute
superfluous.
    Response: The EPA agrees with the commenters that SIPs do not have
to be composed solely of numerical emission limitations, that SIPs can
contain other forms of controls in addition to emission limitations and
that certain forms of controls other than emission limitations may not
need to apply to sources continuously. However, the EPA disagrees with
the commenters' conclusion that the mere act of labeling certain SIP
provisions as ``control measures, means, or techniques'' rather than as
``emission limitations'' can be a means to circumvent the requirement
that emission limitations must regulate sources continuously. To the
extent that there is any ambiguity in the requirements of section
110(a)(2), it is not reasonable to interpret the statute to allow the
explicit requirement that emission limitations must be continuous to be
negated in this fashion.
    As an initial matter, the SIP provisions that contain automatic or
discretionary exemptions during SSM events at issue in this SIP call
excuse compliance with requirements that presumably were submitted to
the EPA as emission limitations, were intended to limit emissions on a
continuous basis or were otherwise included to ensure that the SIP
contained continuous emission limitations. All of the SIP provisions at
issue in this action provide automatic or discretionary exemptions from
emission limitations that are formulated as restrictions on the
``quantity, rate, or concentration'' of emissions from affected
sources, just as section 302(k) describes the purpose of an emission
limitation. Longstanding EPA regulations applicable to SIPs require
that states have a control strategy to provide for attainment and
maintenance of the NAAQS.\171\ The required ``control strategy'' is
defined to be the combination of measures including, but not limited
to, ``emission limitations,'' ``emission control measures applicable to
in use motor vehicles'' and ``transportation control measures'' listed
in section 108(f).\172\ The regulatory definition of ``emission
limitation'' applicable to SIP provisions tracks the statutory
definition of section 302(k) and notably also does not define the term
to allow exemptions for emissions during SSM events.\173\ To the EPA's
knowledge, none of the specific SIP provisions that contain or that are
subject to the automatic or discretionary exemptions at issue in this
SIP call action were developed by the states with the intention or
expectation that absent the exemption they would not apply at all times
when the source is in operation; i.e., they impose restrictions on
emissions that were intended to apply continuously when the source is
emitting pollutants. Logically, the states intended the emission
limitations to impose limits that apply continuously at all times when
the affected sources are emitting pollutants or else there would have
been no impetus to include any exemptions for emissions during SSM
events.
---------------------------------------------------------------------------

    \171\ See, e.g., 40 CFR 51.100.
    \172\ See, e.g., 40 CFR 51.100(n).
    \173\ See 40 CFR 51.100(z).
---------------------------------------------------------------------------

    However, even if the EPA were to accept the commenters' premise
arguendo--that inclusion of an SSM exemption in a given SIP provision
turns ``emission limitations'' into ``other control measures, means, or
techniques,'' this would not be a reasonable reading of the
requirements of section 110(a)(2)(A) and section 302(k) for several
reasons. To the extent that either section 110(a)(2)(A) or section
302(k) is ambiguous with respect to this point, the EPA does not
interpret the CAA to allow exemptions for emissions during SSM events
in SIP provisions in the way advocated by the commenters.
    First, section 110(a)(2)(A) explicitly requires that SIPs must
contain emission limitations as necessary to meet various CAA
requirements. Section 302(k) requires that such emission limitations
must limit ``the quantity, rate, or concentrations of emissions of air
pollutants on a continuous basis.'' Moreover, section 302(k) reiterates
that the term ``continuous emission limitation'' also specifically
includes ``any requirement relating to the operation or maintenance of
a source to assure continuous emission reduction.'' Lest there be
doubt, section 302(m) provides a definition for the related term
``means of emission limitation'' as ``a system of continuous emissions
reduction (including the use of specific technology or fuels with
specified pollution characteristics).'' In the Sierra Club v. Johnson
decision, the D.C. Circuit concluded that the statutory definition of
``emission limitation'' in section 302(k) precludes exemptions for
emissions during SSM events because such exemptions are inconsistent
with the requirement for continuous controls.\174\ Given the emphasis
that the statute places on the requirement that sources be subject to
continuous emission controls, and given the emphasis that courts have
placed on the requirement that sources be subject to continuous
controls on their emissions, the EPA believes that it is illogical that
the statutory requirement for continuous controls on sources could be
subverted merely by the act of labeling a given SIP provision a
``control measure'' rather than an ``emission limitation.'' The
commenters' argument that if a given SIP provision contains an SSM
exemption, it is merely a ``control measure[ ], mean[ ], or technique[
]'' reduces the explicit requirement for continuous controls on
emissions to a semantic exercise.
---------------------------------------------------------------------------

    \174\ See Sierra Club v. Johnson, 551 F.3d 1019, 1027-28 (citing
CAA sections 112(d)(2), 302(k)).
---------------------------------------------------------------------------

    Second, the EPA believes that the commenters' reading of the
statute to permit SIP provisions to contain an SSM exemption by virtue
of what it is labeled is incorrect if taken to its logical extreme. The
commenters' interpretation of section 110(a)(2)(A) would theoretically
allow a SIP to contain no emission limitations whatsoever, merely a
collection of requirements labeled ``control measures'' so that sources
can be excused from having to limit emissions on a continuous basis.
This result is contrary to judicially approved EPA

interpretations of prior versions of the CAA as requiring all SIPs to
include continuously applicable emission limitations and only requiring
``other'' additional controls ``as may be necessary'' to satisfy the
NAAQS.\175\ Additionally, this result is contrary to legislative
history of the 1990 Clean Air Act Amendments, which indicates that in
slightly revising this portion of section 110(a)(2)(A), Congress
intended to merely ``combine and streamline'' previously existing SIP
requirements into a single provision, not to vitiate statutory
requirements concerning emission limitations.\176\
---------------------------------------------------------------------------

    \175\ See, e.g., Kennecott Copper Corp. v. Train, 526 F.2d 1149,
1153 (9th Cir. 1975). The current version of section 110(a)(2)(A) is
admittedly worded differently than the 1970 version. However, for
purposes of these commenters the critical distinction is not that
Congress changed the location of the word ``necessary'' but rather
that Congress changed the subject that ``necessary'' modifies--and
thus the entire scope of 110(a)(2)(A)--from satisfying the NAAQS to
meeting ``applicable requirements'' of the entire CAA.
    \176\ See, e.g., S. Rept. 101-228, at 20 (noting that the
structure of section 110(a)(2)(A) as it appears today reflects
congressional intent to ``combine and streamline'' previously
existing SIP requirements into a single provision).
---------------------------------------------------------------------------

    Finally, the EPA's interpretation of the requirements of section
110(a)(2) does not render the ``other control'' language in the statute
superfluous as claimed by the commenters. In addition to emission
limitations, the EPA interprets that section to allow other ``control
measures, means or techniques'' as contemplated by the statute. For
example, the EPA's regulations implementing SIP requirements explicitly
enumerate nine separate types of measures that states may include in
SIPs.\177\ This list of nine different forms of potential SIP
provisions to reduce emissions varies broadly, from measures that
``impose emission charges or taxes or other economic incentives or
disincentives'' to ``changes in schedules or methods of operation of
commercial or industrial facilities'' to ``any transportation control
measure including those transportation measures listed in section
108(f).'' The EPA made clear that this list is not all-inclusive. In
addition, the EPA has, when appropriate, approved SIP provisions that
impose various forms of emissions controls that are not, by definition,
emission limitations.\178\ Thus, the commenters are in error in their
belief that the EPA's reading of the statute to require that SIPs
contain emission limitations that apply continuously ignores the other
forms of potential measures that section 110(a)(2)(A) authorizes.
---------------------------------------------------------------------------

    \177\ See 40 CFR 51.100(n).
    \178\ See, e.g., 71 FR 7683 (February 14, 2006) (approving as
BACM the use of ``conservation management practices'' to control
fugitive dust emissions from agricultural sources, including
techniques that limit emissions only during certain activities or
times); 68 FR 56181 (September 30, 2003) (approving as BACM an
``episodic wood burning curtailment'' program that restricts the use
of wood-burning stoves based on predicted particulate matter
concentrations).
---------------------------------------------------------------------------

    Section 110(a)(2) requires SIPs to include enforceable emission
limitations and other controls ``as necessary or appropriate to meet
the applicable requirements'' of the CAA. Regardless of whether
commenters' semantic labeling arguments are valid in the abstract, they
are not correct with respect to the fundamental CAA requirements for
SIPs relating to continuous emission limitations. The automatic or
discretionary exemptions for emissions during SSM events in the SIP
provisions at issue in this SIP call authorize exemptions from
statutorily required emission limitations. To the extent that such a
SIP provision would functionally or legally exempt sources from
regulation during SSM events, the SIP provision fails to be a
continuously applicable enforceable emission limitation as required by
the CAA. The fact that a SIP may also contain ``other control[s]'' as
advocated by the commenters does not negate the statutory requirement
that emission limitations must apply continuously.
    g. Comments that the definition of ``emission limitation'' in
section 302(k) does not require that all forms of emission limitations
must apply continuously.
    Comment: Section 110(a)(2)(A) requires that SIPs must contain
emission limitations, and section 302(k) defines the term ``emission
limitation'' to mean a limit on emissions from a source that applies
continuously. A number of commenters disagreed that section 302(k)
requires that all ``emission limitations'' have to be ``continuous.''
The commenters argued that section 302(k) establishes two distinct
categories of emission limitations: (1) Requirements that ``limit[ ]
the quantity, rate, or concentration of emissions of air pollutants on
a continuous basis, including any requirement relating to the operation
or maintenance of a source to assure continuous emission reduction,''
and (2) requirements constituting a ``design, equipment, work practice
or operational standard promulgated under this chapter.'' These
commenters claimed that only the first purported category is emission
limitations that must be continuous and that the second purported
category is emission limitations that do not need to apply
continuously. Accordingly, these commenters asserted that SIP
provisions that are rendered noncontinuous by inclusion of exemptions
for emissions during SSM events are still legally valid ``emission
limitations'' because they fall within the second category. Other
commenters separately contended that under section 302(k), SIP
provisions imposing requirements ``relating to the operation or
maintenance of sources'' do not need to be continuous, unlike those
imposing requirements that limit ``the quantity, rate, or concentration
of emissions or air pollutants.''
    Response: The EPA disagrees with the commenters' view that section
302(k) establishes two discrete categories of emission limitations,
only one of which must reduce continuous emissions on a continuous
basis. The EPA acknowledges that the text of section 302(k) is
ambiguous with respect to this point, but the Agency does not agree
with the commenters' interpretation of the statute. The statutory text
of section 302(k) begins with a catch-all definition of the term
``emission limitation'' as ``a requirement established by the State or
the Administrator which limits the quantity, rate, or concentration of
emissions of air pollutants on a continuous basis . . . .'' \179\ The
EPA believes that the rest of the first sentence in section 302(k),
beginning with the word ``including,'' is best read as a list of
examples of types of measures that satisfy this general definition. In
other words, the remainder of the sentence provide examples of types of
SIP provisions that could be used to limit emissions on a continuous
basis, including any design standard, equipment standard, work practice
standard or operational standard promulgated under the CAA, as well as
``any requirement relating to the operation or maintenance of a source
to assure continuous emission reduction.'' However, each of these forms
of emission limitation would be required to apply at all times, or be
required to apply in combination at all times, in order to meet the
fundamental requirement that the emission limitation serves to limit
emissions from the affected sources continuously. Thus, the EPA
interprets the term ``emission limitation'' to permit emission
limitations that are composed of a combination of numerical
limitations, technological control requirements and/or work practice
requirements, so long as they are components of an emission limitation
that applies continuously. This interpretation accords with

statutory context,\180\ the legislative history regarding the
definition of ``emission limitation,'' \181\ judicial interpretations
of section 302(k) \182\ and the EPA's definition of ``emission
limitation'' in its SIP regulations.\183\ Accordingly, the EPA's
interpretation of section 302(k) is reasonable.
---------------------------------------------------------------------------

    \179\ CAA section 302(k).
    \180\ See, e.g., CAA section 302(m) (defining ``means of
emission limitation'' as a ``system of continuous emission
reduction'').
    \181\ See e.g., H.R. Rep. 95-294, at 92 (1977) (explaining that
the definition of ``emission limitation,'' like the definition of
``standard of performance,'' was intended to ``ma[ke] clear that
constant or continuous means of reducing emissions must be used to
meet th[ose] requirements''); S. Rep. 95-127, at 94 (explaining that
the definition of ``emission limitation'' was intended to ``clarify
the committee's view that the only acceptable basic strategy is one
based on continuous emission control,'' rather than ``unacceptable''
``[i]ntermittent controls or dispersion techniques . . . .'').
    \182\ See, e.g., Sierra Club v. Johnson, 551 F.3d 1019, 1027-28
(D.C. Cir. 2008).
    \183\ See 40 CFR 51.100(n) (defining ``emission limitation'' as
a requirement that limits emissions on a continuous basis).
---------------------------------------------------------------------------

    The EPA also disagrees with the commenters who contended that the
third clause of section 302(k) authorizes exemptions for emissions
during SSM events in emission limitations. The commenters argued that
requirements ``relating to the operation or maintenance of sources'' do
not have to be continuous. The EPA believes that this reading of the
statute is simply in error, because section 302(k) on its face provides
that these requirements must ``assure continuous emission reduction.''
\184\
---------------------------------------------------------------------------

    \184\ See CAA section 302(k).
---------------------------------------------------------------------------

    h. Comments that exemptions or affirmative defenses are not only
not prohibited, but are actually required by the CAA because they are
necessary to make an emission limitation ``reasonable'' or
``achievable'' for sources that cannot comply during SSM events.
    Comment: Commenters argued that some emission limitations currently
in SIPs are only ``reasonable'' or technologically ``achievable''
because they include exemptions or affirmative defenses applicable to
emissions during SSM events. According to these commenters, without
exemptions or affirmative defenses to excuse sources from compliance
with the limits during SSM events, these emission limitations would not
be reasonable or achievable as required by law. To support these
contentions, commenters cited case law from the early 1970s to argue
that the CAA requires emission limitations in SIP provisions to include
exemptions or affirmative defenses for SSM events.
    Response: The EPA agrees that SIP provisions should impose emission
limitations that are reasonable and achievable by sources, so long as
they are also consistent with the applicable legal requirements for
that type of provision. The EPA acknowledges that in some cases,
emission limitations may need to include alternative numerical
limitations, technological controls or work practices during some modes
of operation, such as startup and shutdown. As explained in detail in
the February 2013 proposal and in this action, the EPA interprets the
CAA to allow SIP provisions to include different numerical limitations
or other control requirements as components of a continuously
applicable emission limitation, so long as the SIP provision meets all
other applicable requirements. However, the EPA disagrees with these
commenters' conclusions that the need for ``reasonable'' and
``achievable'' emission limitations provides a legal justification for
exemptions or affirmative defenses for excess emissions during SSM
events.
    First, many of the commenters erroneously presupposed that an
emission limitation must continuously control emissions at the same
rate, quantity, or concentration at all times. For sources or source
categories that cannot comply with otherwise applicable emission
limitations during certain modes of operation, such as startup and
shutdown, the state may elect to develop alternative emission
limitations applicable during those events as a component of the SIP
provision. The EPA has provided recommended criteria for states to use
in developing appropriate alternative emission limitations. Appropriate
alternative emission limitations would ensure the existence of
requirements that limit the quantity, rate or concentration of
pollutants from the affected sources on a continuous basis, while also
providing differing limitations tailored specifically to limit
emissions during specified modes of source operation. As long as those
differing limitations are components of a continuously applicable
emission limitation that meets other applicable substantive
requirements (e.g., is RACT for stationary sources in nonattainment
areas) and that is legally and practically enforceable, then such
alternative emission limitations are valid. States are not required to
create such alternative emission limitations, but to do so is an
acceptable approach.
    Second, these commenters pointed to no provision of the CAA
requiring or allowing exemptions or affirmative defenses for SSM
events. Instead, they contend that D.C. Circuit opinions in Portland
Cement Association v. Ruckelshaus \185\ and Essex Chemical Corp. v.
Ruckelshaus \186\ require SIPs to include exemptions for emissions
during SSM events. As an initial matter, these cases predate amendments
to the CAA that expressly defined ``emission limitation'' as a
requirement that continuously limits emissions. Furthermore, even
accepting these commenters' interpretations of those cases (which as
explained below, EPA does not), any purported holdings to that effect
have been further eroded by more recent case law from the D.C. Circuit
and other courts. Most importantly, the Sierra Club v. Johnson decision
has reiterated that emission limitations must apply continuously in
order to comply with section 302(k), and the logic of NRDC v. EPA
decision indicates that affirmative defense provisions are not
appropriate because they purport to alter the jurisdiction of the
courts.\187\
---------------------------------------------------------------------------

    \185\ 486 F.2d 375 (D.C. Cir. 1973).
    \186\ 486 F.2d 427 (D.C. Cir. 1973).
    \187\ See Sierra Club v. Johnson, 551 F.3d 1019 (D.C. Cir.
2008); NRDC v. EPA, 749 F.3d 1055 (D.C. Cir. 2014).
---------------------------------------------------------------------------

    In addition to these more recent legal developments, however, the
two earlier D.C. Circuit cases highlighted by commenters simply did not
hold what commenters claim that they held. With respect to the Portland
Cement Association decision, commenters selectively quoted from the
case for the proposition that the D.C. Circuit had ``acknowledged''
that malfunctions are an inescapable aspect of industrial life and that
EPA must make allowances for malfunctions when promulgating standards.
The full sentence from the opinion, however, makes clear that the D.C.
Circuit was merely summarizing the ``concern of manufacturers,'' not
stating the court's own position.\188\ To the contrary, the EPA
believes that Portland Cement stands for the broader proposition that a
system incorporating flexibility is reasonable and consistent with the
overall intent of the CAA, and the EPA merely ``may'' take such
flexibility into account.\189\ As relevant to this action, the
flexibility provided states to ensure continuous controls by developing
alternative emission limitations is fully consistent with that view of
the CAA. SIP provisions that include alternative emission limitations
provide the sort of ``limited safety valve'' contemplated by the courts
that can serve to make SIP emission limitations more achievable without
authorizing complete exemptions for

emissions during SSM events in violation of statutory
requirements.\190\
---------------------------------------------------------------------------

    \188\ Portland Cement Ass'n, 486 F.2d at 398.
    \189\ Id. at 399.
    \190\ Id. (citing International Harvester, 478 F.2d 615, 641
(D.C. Cir. 1973)).
---------------------------------------------------------------------------

    Commenters also cited Essex Chemical Corp. for the proposition that
SSM exemptions are necessary to ensure that standards are reasonable.
This court decision, however, also did not hold that emission
limitations must provide exemptions or affirmative defenses for excess
emissions during SSM events. To the contrary, the petitioners'
complaint in Essex Chemical Corp. was that EPA had ``fail[ed] to
provide that lesser standards, or no standards at all, should apply
when the stationary source is experiencing startup, shutdown, or
mechanical malfunctions through no fault of the manufacturer.'' \191\
It was these variant provisions that, in the court's opinion,
``appear[ed] necessary'' to ensure that the standards before it were
reasonable.\192\ Again, the EPA believes that emission limitations in
SIP provisions may include alternative emission limitations that can
provide those ``lesser standards'' that apply during startup and
shutdown events consistent with the court's opinion but also ensure
that emissions are continuously limited as required by the 1977 CAA
Amendments defining ``emission limitation.''
---------------------------------------------------------------------------

    \191\ Essex Chem. Corp v. Ruckelshaus, 486 F.2d at 433 (emphasis
added).
    \192\ See id.
---------------------------------------------------------------------------

    As a legal matter, the court in Essex Chemical was reviewing a
specific ``never to be exceeded'' standard for new and modified sources
and addressed only whether the EPA's failure to provide some form of
flexibility during SSM events was supported by the record; \193\ the
court was not interpreting whether the CAA inherently required such
exemptions (rather than alternative limits) regardless of future
developments in technology. Accordingly, the D.C. Circuit ultimately
remanded the challenged standards to the EPA for reconsideration, not
because SSM exemptions are mandatory but rather because of comments
made by the EPA Acting Administrator and deficiencies identified in the
administrative record with respect to ``never to be exceeded'' limits
for those specific standards. In short, the Essex Chemical court did
not hold that the CAA ``requires'' emission limitations to include
exemptions for emissions during SSM events as suggested by commenters.
---------------------------------------------------------------------------

    \193\ Id. (``the record does not support the `never to be
exceeded' standard currently in force'').
---------------------------------------------------------------------------

    Furthermore, the EPA notes that the most salient legal holding of
Essex Chemical with respect to achievability is not what the court said
about the circumstances peculiar to the EPA's development of those
specific standards but rather is the court's holding that standards of
performance can be ``achievable'' even if there is no facility
``currently in operation which can at all times and under all
circumstances meet the standards . . . .'' \194\ Thus, the decision
supports the EPA's conclusion that the CAA requires appropriately drawn
emission limitations that apply on a continuous basis. As explained in
section IV of this document, SIP provisions also cannot include the
affirmative defenses advocated by commenters, because those are
inconsistent with CAA provisions concerning the jurisdiction of the
courts.
---------------------------------------------------------------------------

    \194\ Essex Chem. Corp v. Ruckelshaus, 486 F.2d 427, 433 (D.C.
Cir. 1973).
---------------------------------------------------------------------------

    i. Comments that the EPA is requiring that all SIP emission
limitations must be ``numerical'' at all times and set at the same
numerical level at all times.
    Comment: Many commenters on the February 2013 proposal evidently
believed that the EPA was proposing an interpretation of the term
``emission limitation'' under section 302(k) that would requires all
SIP provisions to impose numerical emission limits, and that such
limits must be set at the same numerical level at all times. These
commenters argued that numerical emission limitations are not required
by the text of section 302(k). For example, commenters pointed to
section 302(k)'s use of ``work practice or operational standard[s]'' as
evidence that an emission limitation may be composed of more than
merely numerical criteria. These commenters also reiterated their view
that section 302(k) allows for or requires alternative limits during
periods of SSM, including non-numerical alternative limits such as work
practice or operational standards.
    Response: At the outset, the EPA notes that it did not intend to
imply that all emission limitations in SIP provisions must be expressed
numerically, or that they must be set at the same numerical level for
all modes of source operation. To the contrary, the EPA intended to
indicate that states may elect to create emission limitations that
include alternative emission limitations that apply during certain
modes of source operation, such as startup and shutdown. This was the
reason for inclusion of the recommended criteria for states to develop
appropriate alternative emission limitations applicable during startup
and shutdown in section VII.A of the February 2013 proposal. The EPA
has provided similar recommended criteria in this final action (see
section VII.B.2 of this document). The EPA agrees that neither section
110(a)(2)(A) nor section 302(k) inherently requires that SIP emission
limitations must be expressed numerically. Furthermore, section 302(k)
does not itself require imposition of numerical limitations or
foreclose the use of higher numerical levels, specific technological
controls or work practices during certain modes of operation.
    Although some CAA programs may require or impose a presumption that
emission limitations be expressed numerically, the text of section
110(a)(2)(A) and section 302(k) does not expressly state a preference
for emission limitations that are in all cases numerical in form.\195\
Rather, as many commenters pointed out, the critical aspect of an
emission limitation in general is that it be a ``requirement . . .
which limits the quantity, rate, or concentration of emissions of air
pollutants on a continuous basis . . . .'' \196\ Accordingly, although
other regulatory requirements may also apply, a non-numerical design
standard, equipment standard, work practice standard or operational
standard could theoretically meet the definition of ``emission
limitation'' for purposes of section 302(k) if it continuously limited
the quantity, rate or concentration of air pollutants.\197\ By
contrast, if a non-numerical requirement does not itself (or in
combination with other components of the emission limitation) limit the
quantity, rate or concentration of air pollutants on a continuous
basis, then the non-numerical standard (or overarching requirement)
does not meet the statutory definition of an emission limitation under
section 302(k).
---------------------------------------------------------------------------

    \195\ Numerical requirements or preferences for some emission
limitations flow from substantive requirements of specific CAA
programs, which are incorporated into section 110(a)(2)(A) by the
requirement that SIPs ``include enforceable emission limitations . .
. as may be necessary or appropriate to meet the applicable
requirements of'' the CAA. CAA section 110(a)(2)(A).
    \196\ See, e.g., id., section 112(h)(4).
    \197\ For example, emission limitations must meet the
requirements of various substantive provisions of the CAA and must
be legally and practically enforceable.
---------------------------------------------------------------------------

    Finally, the EPA does not believe that section 110(a)(2)(A) or
section 302(k) mandates that an emission limitation be composed of a
single, uniformly applicable numerical emission limitation. As the EPA
stated in the February 2013 proposal, ``[i]f sources in fact cannot
meet the otherwise applicable emission limitations during planned
events such as startup and shutdown, then an air agency can develop
specific alternative

requirements that apply during such periods, so long as they meet other
applicable CAA requirements.'' \198\ As explained in the EPA's response
in section VII.A.3 of this document regarding the meaning of the
statutory term ``continuous,'' the critical aspect for purposes of
section 302(k) is not whether the emission limitation is expressed as a
static versus variable numerical limitation but rather whether as a
whole it constitutes a requirement that limits emissions on a
continuous basis. Furthermore, any emission limitation must also meet
all other applicable CAA requirements concerning stringency and
enforceability.
---------------------------------------------------------------------------

    \198\ 78 FR 12459 at 12471.
---------------------------------------------------------------------------

    j. Comments that an emission limitation can be ``continuous'' even
if it has different numerical limitations applicable during some modes
of source operation or has a combination of numerical emission
limitations and specific control technologies or work practices
applicable during other modes of operation.
    Comment: Several commenters argued that an emission limitation can
be ``continuous'' under section 302(k) even if it provides different
substantive requirements applicable during SSM events. One commenter
illustrated this position with a hypothetical:

    [W]hile Section 302 requires ``emission limits'' to be
``continuous,'' it does not specify . . . that the same ``emission
limit'' must apply at all times. That is, if a state chooses to
require sources to comply with a 40% opacity limit during steady-
state operations, the Act does not then require the state to apply
that 40% limit at all times, including startup, shutdown and
malfunction events.

    Commenters pointed to a number of sources as justification for this
position, including the text of section 302(k), relevant case law,
legislative history of the 1977 CAA Amendments, prior EPA
interpretations, and practical concerns.
    Response: The EPA agrees with these commenters' conclusion that an
``emission limitation'' under section 302(k) does not need to be
expressed as a static, inflexible limit on emissions. Rather, a SIP
provision qualifying as an ``emission limitation'' consistent with
section 302(k) must merely limit ``the quantity, rate, or
concentration'' of emissions, and must do so ``on a continuous basis.''
The critical aspect for purposes of section 302(k) is that the SIP
provision impose limits on emissions on a continuous basis, regardless
of whether the emission limitation as a whole is expressed numerically
or as a combination of numerical limitations, specific control
technology requirements and/or work practice requirements, and
regardless of whether the emission limitation is static or variable.
For example, so long as the SIP provision meets other applicable
requirements, it may impose different numerical limitations for startup
and shutdown.
    The EPA also agrees that the text of section 302(k) does not
require states to impose emission limitations that include a static,
inflexible standard. Rather, the term ``emission limitation'' is merely
defined as a ``requirement established by the State or the
Administrator which limits the quantity, rate, or concentration of
emissions of air pollutants on a continuous basis. . . .'' The
continuous limits imposed by emission limitations are a fundamental
distinction between emission limitations and the other control
measures, means or techniques that may also limit emissions.\199\ The
text of section 302(k), however, does not distinguish between a
variable or static ``requirement'' that continuously limits emissions--
all that is required is that the emissions are limited on a continuous
basis.
---------------------------------------------------------------------------

    \199\ See CAA section 110(a)(2)(A).
---------------------------------------------------------------------------

    This interpretation is consistent with prior EPA interpretations of
section 302(k), as well as relevant case law. In Kamp v. Hernandez, the
U.S. Court of Appeals for the Ninth Circuit (Ninth Circuit) upheld the
EPA's interpretation of ``continuous'' in section 302(k), as requiring
that ``some limitation on emissions, although not necessarily the same
limitation, is always imposed'' on the source.\200\ More recently, the
D.C. Circuit favorably cited Kamp when holding that section 302(k)
requires emission standards to limit emissions on a continuous basis
and precludes exemptions for emissions during SSM events.\201\
---------------------------------------------------------------------------

    \200\ Kamp v. Hernandez, 752 F.2d 1444, 1452-53 (9th Cir. 1985)
(citing Chevron, U.S.A., Inc. v. Natural Res. Def. Council, 467 U.S.
837 (1984)) (upholding EPA's ``broader definition of `continuous' ''
under section 302(k)).
    \201\ Sierra Club v. Johnson, 551 F.3d 1019, 1027-28 (D.C. Cir.
2008) (quoting Kamp, 752 F.2d at 1452).
---------------------------------------------------------------------------

    Legislative history confirms that Congress was primarily concerned
that there be constant or continuous means of reducing emissions--not
that the nature of those controls could not be different during
different modes of operation.\202\ For example, legislative history
from the 1977 CAA Amendments states that Congress added section
302(k)'s definition of ``emission limitation'' to:
---------------------------------------------------------------------------

    \202\ See, e.g., H.R. Rep. 95-294, at 92 (1977) (explaining that
the definition of ``emission limitation,'' like the definition of
``standard of performance,'' was intended to ``ma[ke] clear that
constant or continuous means of reducing emissions must be used to
meet th[ose] requirements''); S. Rep. 95-127, at 94 (explaining that
the definition of ``emission limitation'' was intended to ``clarify
the committee's view that the only acceptable basic strategy is one
based on continuous emission control,'' rather than ``unacceptable''
``[i]ntermittent controls or dispersion techniques . . . .'').

. . . ma[ke] clear that constant or continuous means of reducing
emissions must be used to meet these requirements. By the same
token, intermittent or supplemental controls or other temporary,
periodic, or limited systems of control would not be permitted as a
final means of compliance.\203\
---------------------------------------------------------------------------

    \203\ H.R. Rep. 95-294, at 92 (1977), as reprinted in 1977
U.S.C.C.A.N. 1077, 1170); Sierra Club v. Johnson, 551 F.3d at 1027
(quoting the same); Kamp v. Hernandez, 752 F.2d at 1453-54 (quoting
the same).

    Although this legislative history demonstrates congressional intent
that any ``emission limitation'' would require limits on emissions at
all times, this history does not necessarily indicate that the emission
limitation must consist of a single static numerical limitation.
Accordingly, this legislative history is consistent with the EPA's view
that section 302(k) requires continuous limits on emissions and that
variable (albeit still continuous) limits on emissions can qualify as
an emission limitation for purposes of section 302(k).
    Finally, although the EPA agrees with these commenters' conclusion,
the EPA does not agree with these commenters' view that practical
concerns require states in all cases to establish alternative emission
limitations for modes of operation such as startup and shutdown within
any continuously applicable emission limitation. Principles of
cooperative federalism incorporated into section 110 allow states great
leeway in developing SIP emission limitations, provided those
limitations comply with applicable legal requirements.\204\ States are
thus not required to establish alternative emission limitations for any
sources during startup and shutdown, but they may elect to do so.
Neither the definition of ``emission limitation'' in section 302(k) nor
the requirements of section 110(a)(2)(A) explicitly require states to
develop emission limitations that include alternative emission
limitations for periods of SSM, just as they do not explicitly preclude
states from doing so.
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    \204\ As discussed above and elsewhere in this document, those
requirements include satisfying the definition of ``emission
limitation'' under CAA section 302(k), and being ``enforceable'' in
accordance with section 110(a)(2)(A).

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    k. Comments that an emission limitation can be ``continuous'' even
if it includes periods of exemptions from the emission limitation.
    Comment: Commenters asserted that a requirement limiting emissions
can be ``continuous'' even if a SIP provision includes periods of
exemption from that limit. For example, some commenters contended that
SSM exemptions only excuse compliance with emission limitations for a
``short duration,'' or ``brief'' period of time, and that these
purportedly ephemeral interruptions should not be viewed as rendering
the requirement noncontinuous. Other commenters contended that the EPA
misinterpreted portions of the D.C. Circuit's opinion in Sierra Club v.
Johnson,\205\ interpreting section 302(k). Specifically, this group of
commenters claimed that because the holding of that case was based on a
combined reading of sections 112 and 302(k), the court's interpretation
of the word ``continuous'' in section 302(k) does not extend outside
the context of section 112. This included one commenter who suggested,
in a one-sentence footnote, that ``[i]n the cooperative-federalism
context''--presumably of section 110--``the standard of flexibility
that Congress gave the States with respect to selecting the elements of
their SIPs is not necessarily the same standard Congress set to govern
EPA's responsibility to establish the NAAQS or section 112 standards.''
Still other commenters further argued that the EPA mischaracterized
legislative history discussing ``continuous'' in section 302(k).
According to these commenters, the context of legislative history on
section 302(k) indicates that Congress did not intend for the word
``continuous'' to be given its plain meaning but rather intended to use
``continuous'' in relation only to specific types of intermittent
controls.
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    \205\ 551 F.3d 1019 (D.C. Cir. 2008).
---------------------------------------------------------------------------

    Response: The EPA disagrees with these commenters. First,
commenters' interpretation would contravene the plain meaning of
``continuous.'' Section 302(k) defines ``emission limitation'' as a
requirement that ``limits the quantity, rate, or concentration of
emissions of air pollutants on a continuous basis. . . .'' \206\
Although the word ``continuous'' is not separately defined in the Act,
its plain and unambiguous meaning is ``uninterrupted.'' \207\
Accordingly, to the extent that a SIP provision provides for any period
of time when a source is not subject to any requirement that limits
emissions, the requirements limiting the source's emissions by
definition cannot do so ``on a continuous basis.'' Such a source would
not be subject to an ``emission limitation,'' as that term is defined
under section 302(k). The same principle applies even for ``brief''
exemptions from limits on emissions, because such exemptions
nevertheless render the emission limitation noncontinuous.
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    \206\ CAA section 302(k).
    \207\ See Webster's Third New International Dictionary 493-94
(Phillip Babcock Gove ed., Merriam-Webster 1993) (defining
``continuous'').
---------------------------------------------------------------------------

    Second, the EPA disagrees with commenters' interpretation of the
D.C. Circuit's opinion in Sierra Club. While the court's ultimate
decision was based on ``sections 112 and 302(k) . . . read together,''
\208\ the court's analysis of what makes a standard ``continuous'' was
based on section 302(k) alone.\209\ Although the precise components of
an emission limitation or standard may expand depending on which other
provisions of the CAA are applicable, the bedrock definition for what
it means to be an ``emission limitation'' under section 302(k) does
not. Congress appeared to share the EPA's view that section 302(k)
provides a bedrock definition of ``emission limitation'' applicable
``to all emission limitations under the act, not just to limitations
under sections 110, 111, or 112 of the act.'' \210\ Accordingly, the
D.C. Circuit's interpretation of section 302(k) applies equally in the
context of SIP provisions developed by states as in the context of MACT
standards developed by the EPA, even if additional requirements may be
different.\211\
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    \208\ Sierra Club, 551 F.3d at 1027.
    \209\ See id. (quoting H.R. Rep. 95-294, at 92 (1977), as
reprinted in 1977 U.S.C.C.A.N. 1077, 1170); see also Kamp v.
Hernandez, 752 F.2d at 1453-54 (quoting the same and coming to the
same conclusion).
    \210\ See H.R. 95-294, at 92 (1977); see also section 302
(stating that the definitions appearing therein apply ``[w]hen used
in this chapter'').
    \211\ The fact that CAA section 110 incorporates principles of
cooperative federalism does not inevitably mean that the definition
of ``emission limitation'' under section 302(k) changes depending on
whether it is applied in the context of section 110 versus section
112. Accordingly, in the context of judicial interpretation of a
statute, the U.S. Supreme Court has held that judges cannot ``give
the same statutory text different meanings in different cases.''
Clark v. Martinez, 543 U.S. 371, 386 (2005). The EPA believes that
the text and legislative history of section 302(k) evince
congressional intent to consistently apply the definition of
``emission limitation'' under section 302(k) rather than to develop
an inconsistent interpretation peculiar to section 110.
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    Finally, the EPA rejects commenters' contention that section
302(k)'s legislative history indicates that use of the word
``continuous'' in the definition of ``emission limitation'' was merely
intended to prevent the use of intermittent controls or, even more
narrowly, only dispersion techniques. While legislative history of the
1977 Amendments discusses at length the concerns associated with these
types of controls, section 302(k) was not intended to merely prevent
the narrow problem of intermittent controls. To the contrary, the House
Report states that under section 302(k)'s definition of emission
limitation, ``intermittent or supplemental controls or other temporary,
periodic, or limited systems of control would not be permitted as a
final means of compliance.'' \212\
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    \212\ H.R. 95-294, at 92 (emphasis added).
---------------------------------------------------------------------------

    In explaining congressional intent behind adopting a statutory
definition of ``emission limitation,'' the House Report articulated a
rationale broader than would apply if Congress had merely intended to
prohibit the tall stacks and dispersion techniques that commenters
claim were targeted: ``Each source's prescribed emission limitation is
the fundamental tool for assuring that ambient standards are attained
and maintained. Without an enforceable emission limitation which will
be complied with at all times, there can be no assurance that ambient
standards will be attained and maintained.'' \213\ By contrast,
Congress criticized limitations structured in ways that could not
``provide assurances that the emission limitation will be met at all
times,'' or that would sometimes allow the ``emission limitation [to]
be exceeded, perhaps by a wide margin . . . .'' \214\ Such flaws
``would defeat the remedy provision provided by section 304 of the act
which allows citizens to assure compliance with emission limitations
and other requirements of the act.'' \215\ Exemptions for emissions
during SSM events have the same effects.\216\
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    \213\ Id. (emphasis added). The Senate Report expressed a
similar sentiment. See S. Rep. No. 95-127, at 94-95 (1977)
(explaining that the definition of ``emission limitation'' was
intended ``to clarify the committee's view that the only acceptable
basic strategy [for emission limitations in SIPs] is one based on
continuous emission control'').
    \214\ See H.R. 95-294, at 92.
    \215\ See id.
    \216\ See, e.g., NRDC v. EPA, 749 F.3d 1055, 1064 (D.C. Cir.
2014) (holding that an affirmative defense for excess emissions
during malfunctions contradicts the requirement that an emission
limitation be ``continuous'').
---------------------------------------------------------------------------

    In adopting section 302(k)'s definition of ``emission limitation,''
Congress did not merely intend to prohibit the use of intermittent
controls as final compliance strategies--much less intermittent
controls as narrowly defined by commenters to mean only dispersion
techniques and certain ``tall stacks.'' Rather, Congress intended to
eliminate the fundamental problems

that were illustrated by use of those controls.\217\ SSM exemptions and
affirmative defenses raise many of the same problems, and addressing
those problems through this action fully accords with section 302(k)'s
legislative history.
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    \217\ See, e.g., H.R. 95-294, at 94 (noting that the provision
was intended to overcome ``objections'' to such measures, not merely
the measures themselves); id. at 92 (indicating that the problems
arise from ``temporary, periodic, or limited systems of control''
generally, not merely dispersion techniques or tall stacks).
---------------------------------------------------------------------------

    l. Comments that the ``as may be necessary or appropriate''
language in section 110(a)(2)(A) per se authorizes states to create
exemptions in SIP emission limitations.
    Comment: Some commenters contended that section 110(a)(2)(A) merely
requires states to include emission limitations and other control
measures in their SIPs ``as may be necessary or appropriate.'' These
commenters interpreted that language as a broad delegation of
discretion to states to develop SIP provisions that are necessary or
appropriate to satisfy the particular needs of a state, as judged
solely by that state. Some of the commenters argued that the EPA's
interpretation of ``as may be necessary or appropriate'' would, in all
circumstances, improperly substitute the EPA's judgment for that of the
state concerning what emission limitations are necessary or
appropriate. One commenter highlighted the EPA's proposal to deny the
Petition with respect to a specific SIP provision of the South Carolina
SIP that entirely exempts a source category from regulation.\218\
According to this commenter, if the ``as may be necessary or
appropriate'' language grants states the authority to exempt a source
category from regulation entirely, then it must allow states to exempt
sources selectively during SSM events.
---------------------------------------------------------------------------

    \218\ See 78 FR 12459 at 12512 (citing S.C. Code Ann. Regs. 61-
62.5 St 5.2(I)(b)(14)).
---------------------------------------------------------------------------

    Some commenters further argued that regardless of what the terms
``emission limitations'' or ``other control measures, means, or
techniques'' mean, section 110(a)(2)(A) only requires states to include
such emission controls in SIPs ``as may be necessary or appropriate''
to meet the NAAQS, or some requirement germane to attainment of the
NAAQS, such as various technology-based standards or general principles
of enforceability. Commenters also disagreed with the EPA's purported
interpretation that the statutory phrase ``as may be necessary'' only
qualifies what ``other control[s]'' are required, rather than also
qualifying what emission limitations are required. According to these
commenters, that interpretation is a vestige of the 1970 CAA and was
foreclosed by textual changes in the 1977 CAA Amendments or,
alternatively, the 1990 CAA Amendments.
    Response: The EPA disagrees with the commenters' interpretation of
the ``as may be necessary or appropriate'' language of section
110(a)(2)(A). As an initial matter, those commenters contending that
section 110(a)(2)(A) is only concerned with what is ``necessary or
appropriate'' to attain and maintain the NAAQS (or some requirement
germane to the NAAQS) ignore the plain language of section
110(a)(2)(A). While the predecessor provisions to section 110(a)(2)(A)
prior to the 1990 CAA Amendments did indeed speak in terms of emissions
controls ``necessary to insure attainment and maintenance of [the
NAAQS],'' \219\ the statute in effect today requires controls
``necessary or appropriate to meet the applicable requirements of this
chapter,'' \220\--i.e., to meet the requirements of the CAA as a whole.
Thus, at a minimum, the EPA interprets the phrase ``as may be necessary
or appropriate'' to include what is necessary or appropriate to meet
legal requirements of the CAA, including the requirement that emission
limitations must apply on a continuous basis.
---------------------------------------------------------------------------

    \219\ See, e.g., Clean Air Act of 1970, Public Law 91-604,
section 4(a), 84 Stat. 1676, 1680 (December 31, 1970).
    \220\ Section 110(a)(2)(A).
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    Regardless of whether all SIPs must always contain emission
limitations, the text of the CAA is clear that the EPA is at a minimum
tasked with determining whether SIPs include all emission limitations
that are ``necessary'' (i.e., required) ``to meet the applicable
requirements of'' that CAA. Broadly speaking, this requires that the
EPA determine whether the SIP meets the basic legal requirements
applicable to all SIPs (e.g., the requirements of section 110(a)(2)(A)
through (M)), whether the SIP contains emission limitations necessary
to meet substantive requirements of the Act (e.g., RACT-level controls
in nonattainment areas) and whether all emission limitations and other
controls, as well as the schedules and timetables for compliance, are
legally and functionally enforceable.
    In every state subject to this SIP call, the EPA has previously
concluded in approving the existing SIP provisions that the emission
limitations are necessary to comply with legal requirements of the CAA.
The states in question would not have developed and submitted them, and
the EPA would not have approved them, unless the state and the EPA
considered those emission limitations fulfilled a CAA requirement in
the first instance. However, the automatic and discretionary exemptions
for emissions during SSM events in the SIP provisions at issue in this
action render those necessary emission limitations noncontinuous, and
thus not meeting the statutory definition of ``emission limitations''
as defined in section 302(k). Accordingly, regardless of whether all
SIPs must always include emission limitations, these specific SIP
provisions fail to meet a fundamental requirement of the CAA because
they do not impose the continuous emission limitations required by the
Act.
    The EPA also disagrees with the argument raised by commenters that
its denial of the Petition with respect to a South Carolina SIP