Document ID: EPA-R06-OAR-2017-0435-0019
Agency: epa
Document Type: Rule
Title: AR026.19 Approval and Promulgation of Implementation Plans; Arkansas; Revisions to Minor New Source Review Program, Final rule, 18 pages. The Final rule documents for this action are in documents EPA-R06-OAR-2017-0435-0019 [AR026.19] to EPA-R06-OAR-2017-0435-0022 [AR026.22]. The Proposed rule documents are in documents EPA-R06-OAR-2017-0435-0001 [AR026.01] to EPA-R06-OAR-2017-0435-0010 [AR026.10].
Posted Date: 2018-06-29T04:00Z

[Federal Register Volume 83, Number 126 (Friday, June 29, 2018)]
[Rules and Regulations]
[Pages 30553-30570]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-13942]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R06-OAR-2017-0435; FRL-9979-15--Region 6]

Approval and Promulgation of Implementation Plans; Arkansas; 
Revisions to Minor New Source Review Program

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: Pursuant to the Federal Clean Air Act (CAA or the Act), the 
Environmental Protection Agency (EPA) is approving revisions to the 
Arkansas State Implementation Plan (SIP) minor New Source Review (NSR) 
program submitted on July 26, 2010, and March 24, 2017, including 
supplemental information provided on November 30, 2015, May 26, 2016, 
July 5, 2017, July 27, 2017, and March 16, 2018. Specifically, we are 
proposing to approve revisions that revise the minor NSR permitting 
thresholds and de minimis levels, as well as, additional non-
substantive revisions contained in those submittals. This final action 
is consistent with the requirements of section 110 of the CAA.

DATES: This rule is effective on July 30, 2018.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-R06-OAR-2017-0435. All documents in the docket are 
listed on the http://www.regulations.gov website. Although listed in 
the index, some information is not publicly available, e.g., 
Confidential Business Information or other information whose disclosure 
is restricted by statute. Certain other material, such as copyrighted 
material, is not placed on the internet and will be publicly available 
only in hard copy form. Publicly available docket materials are 
available either electronically through http://www.regulations.gov or 
in hard copy at the EPA Region 6, 1445 Ross Avenue, Suite 700, Dallas, 
Texas 75202-2733.

[[Page 30554]]

FOR FURTHER INFORMATION CONTACT: Ashley Mohr, 214-665-7289, 
[email protected].

SUPPLEMENTARY INFORMATION: Throughout this document ``we,'' ``us,'' and 
``our'' means the EPA.

I. Background

    The background for this action is discussed in detail in our 
September 18, 2017 proposal (82 FR 43506). In that document we proposed 
to approve revisions to the Arkansas SIP submitted on July 26, 2010, 
and March 24, 2017, including supplemental information submitted on 
November 30, 2015, May 26, 2016, July 5, 2017, July 27, 2017, and March 
16, 2018. The revisions addressed in our proposal included revisions to 
the Arkansas minor NSR permitting thresholds and de minimis levels, as 
well as, additional revisions to the minor NSR provisions that are 
considered to be non-substantive.
    We received one set of comments on the proposal. The full text of 
the comment letter received during the public comment period, which 
closed on October 18, 2017, is included in the publicly posted docket 
associated with this action at www.regulations.gov. Below the EPA 
provides a summary of the comments received and corresponding 
responses.

II. Response to Comments

    Comment: The commenter stated that the revised minor NSR rule fails 
to provide legally enforceable procedures to ensure new sources that 
could interfere with NAAQS attainment or maintenance or violate the 
control strategy won't be allowed to construct. More specifically, they 
stated that the minor NSR program does not explain how ``actual 
emissions'' are to be determined for a new source with no operational 
history. To the extent that Arkansas Department of Environmental 
Quality (ADEQ) determined applicability for new sources based on 
projected actual emissions, then the rule could ultimately allow 
sources with emissions greater than the permitting thresholds to 
construct without a permit and without evaluation of air quality 
impacts by a new source underestimating emission factors and/or 
operating parameters and exceeding those projected emissions after its 
construction. Therefore, the commenter stated it is unclear what size 
of sources could ultimately end up exempt from Arkansas' minor NSR 
program. The commenter claims that because of the noted deficiencies 
there is a problem with any attempt to determine whether the revised 
minor NSR rule's applicability thresholds are set to the appropriate 
level to ensure the state meets the applicable federal requirements 
found in CAA section 110(a)(2)(C) and 40 CFR 51.160(b).
    Response: This comment is not relevant to our current rulemaking. 
As shown in Section IV of the Technical Support Document that 
accompanied our proposed approval action, our rulemaking only addresses 
revisions to the permitting thresholds values contained in Reg. 19.401. 
The applicability determination for the minor NSR program and its 
reliance on ``actual emissions'' was not revised by Arkansas as part of 
the July 26, 2010, or May 24, 2017 SIP revision submittals. Therefore, 
the applicability determination as originally SIP-approved October 16, 
2000 (65 FR 61103) remains unchanged, is not a part of this rulemaking, 
and any comment on it is not relevant to the current rulemaking.
    While the comments regarding the applicability determination basis 
are not relevant to this rulemaking, we will respond to the commenter's 
assertion that any attempt to determine if the revised minor NSR 
permitting thresholds meet the referenced federal requirements is 
problematic. We do not agree with this statement. As outlined in our 
proposed rulemaking, we evaluated several analyses submitted by 
Arkansas in support of the revised thresholds, including an emissions 
inventory analysis, a monitoring trends analysis, and a modeling 
analysis. Based on our evaluation of those analyses along with the SIP 
revisions submittals documentation (found in the Technical Support 
Document (TSD)), we find that the proposed thresholds will meet 
applicable federal requirements and not interfere with NAAQS attainment 
or maintenance or violate the control strategy. As required by Reg. 
19.401, a source with actual emissions greater than the applicability 
thresholds would be required to obtain a permit and is subject to 
enforcement action if the source fails to do so. The emissions from a 
new source to be compared with the permitting thresholds would be based 
on controlled emission factors and projected operations (hours of 
operation and/or amounts of material processed). This approach allows 
permitting applicability to be based on emissions that are close to 
actual emissions. The regulation specifically does not allow 
construction and operation of sources with actual emissions in excess 
of the thresholds, and any source that did underestimate their 
emissions and exceed the emissions thresholds would be in violation of 
the regulations and beyond the scope of the analyses conducted to 
demonstrate the regulation's compliance with applicable federal 
requirements for minor NSR programs.
    Comment: The commenter stated that the rule exempting de minimis 
changes at existing sources from permitting fails to provide legally 
enforceable procedures to ensure that modified sources that could 
interfere with NAAQS attainment or maintenance or violate the control 
strategy won't be allowed to construct. More specifically, they stated 
a physical change or change in the method of operation at a source with 
no existing permit has no existing ``permitted rates'' to compare 
``proposed permitted rates'' to, and the rule does not explain how 
applicability is determined in such cases and the rule does not clearly 
say that it applies only to sources with existing permits. In addition, 
the commenter stated that Reg. 19 does not clearly require a permit 
application for de minimis changes. Therefore, they claim that de 
minimis exemptions rule does not meet the requirements of 40 CFR 
51.160(a) of providing legally enforceable procedures.
    Response: We do not agree that the applicability of the de minimis 
changes rule to existing sources with no permits is unclear. The de 
minimis change provisions are found in paragraph C of Reg. 19.407 of 
Arkansas' ``Minor Source Review'' regulation (Reg. 19, Chapter 4). Reg. 
19.407 is titled ``Permit Amendments'' and as stated in our original 
2000 approval of Reg. 19.407 (65 FR 26795; finalized at 65 FR 61103), 
this section describes the procedures for amending a permit. Because 
Reg. 19.407 describes permit amendments, including de minimis changes, 
these provisions are not applicable to a source that does not have a 
permit. Existing sources with no existing permit would be subject to 
the minor NSR permitting thresholds found in Reg. 19.401 under the 
``General Applicability'' section to determine if the source was 
subject to minor NSR permitting requirements. In addition to the 
clarity provided in the rule itself, the current ``Air Application 
Instructions for Registrations, Minor Source Permits, or Title V 
Permits'' made available on ADEQ's air permitting website also 
indicates that de minimis applications are for ``small modifications to 
a permit.'' (Pg. 5) \1\ Page 12 of the application instructions 
reiterates the applicability of the de

[[Page 30555]]

minimis rule and states that a de minimis application ``applies to 
facilities having a current air permits [sic].'' Much like the de 
minimis change provisions in the rule, it is clear based on ADEQ's 
current air permit application guidance that the de minimis change rule 
only applies to existing permitted facilities and not new facilities.
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    \1\ Air Application Instructions available online at: https://www.adeq.state.ar.us/downloads/WebDatabases/Air/PermitData/Forms%20and%20Instructions/Form%20and%20Instructions/Air_Permit_Application_Forms_Instructions.pdf.
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    The portion of the comment raised regarding permit application 
requirements for de minimis changes is not relevant to our current 
rulemaking. As shown in Section IV of the Technical Support Document 
that accompanied our proposed action, our rulemaking only addresses 
revisions related to de minimis changes that are found in Reg. 
19.407(C)(2)(a) and (b). Permit application requirements, which are 
found in Reg. 19.404, are currently SIP-approved and were not revised 
as part of the July 26, 2010, or May 24, 2017 SIP revision submittals 
under review in this rulemaking. Similarly, Reg. 19.407(C)(7) was not 
revised in the 2010 or 2017 SIP revision submittals. Therefore, the 
SIP-approved Reg. 19.404 and Reg. 19.407(C)(7) provisions as most-
recently approved on October 16, 2000 (65 FR 61103) and April 12, 2007 
(72 FR 18394), respectively, remain unchanged and are not part of this 
rulemaking and any comment on those provisions is not relevant.
    Comment: The commenter claims that Arkansas has failed to 
adequately justify the basis for its revised emission thresholds for 
exempting new sources and de minimis changes from its minor NSR 
program. They state that 40 CFR 51.160(e) requires states to identify 
the types and sizes of sources subject to its minor NSR program and to 
explain the basis for determining which facilities are subject to 
review. ADEQ's justification for the emission thresholds adopted in its 
minor NSR program for Reg. 19, Chapter 4, was essentially that these 
tons per year thresholds were the same thresholds identified as ``de 
minimis'' under major NSR permitting programs. However, there has been 
no analysis with current modeling techniques that the major NSR 
significance levels are adequate to ensure a modified source won't 
interfere with the attainment or maintenance of all of the various 
current NAAQS, which differ in stringency from the NAAQS applicable at 
the time the PSD significant emission rates were developed. The 
commenter also stated that the AERMOD (dispersion) modeling results, 
which they believe underestimate actual impacts, indicate that the 
pollutant concentrations resulting from the emissions exempt from 
permitting based on the revised thresholds are significantly higher 
than 4% of the NAAQS, which was a threshold for the EPA's analyses from 
1980, 1987, and 2008 for demonstrating that the significant emission 
levels were de minimis to the PSD program.
    Response: We do not agree with this comment. Although ADEQ did 
include the data referenced by the commenter in their initial 2010 SIP 
revision submittal, the basis for ADEQ's findings regarding the 
appropriateness of the revised thresholds was different and they also 
provided additional analyses to demonstrate the scope of the exempt 
sources and modifications resulting from the revised minor NSR 
permitting thresholds and de minimis change levels and to demonstrate 
that the revised thresholds will not interfere with attainment or 
maintenance of the NAAQS. These analyses were included in their 
entirety in the March 24, 2017 SIP revision submittal and included: (1) 
An emissions inventory analysis that determined the percentage of the 
total statewide emissions that were to be exempt under the revised 
minor NSR permitting thresholds and de minimis change levels; (2) a 
monitoring trends analysis that included a review of the current status 
of ambient air quality, as well as, the impacts of the revised 
thresholds on ambient concentration monitoring trends in the state of 
Arkansas; and (3) a modeling analysis that included photochemical and 
dispersion modeling analyses that evaluated the impacts of the revised 
thresholds through model predicted results. The air quality modeling 
analysis report included in Appendix D of the March 24, 2017 SIP 
submittal describes the modeling approach used by ADEQ as part of the 
demonstration showing that the revised minor NSR permitting thresholds 
and de minimis change levels will not adversely impact the current 
NAAQS. Based on our review of the modeling analysis, which did use 
current air quality modeling techniques, and the other analyses 
completed by ADEQ, we found that the impacts resulting from the revised 
minor NSR permitting thresholds and de minimis levels would not 
interfere with the state's ability to maintain compliance with the 
NAAQS.
    As discussed in the Technical Support Document accompanying our 
proposed action, ADEQ conducted both regional scale photochemical 
modeling using CMAQ and local-scale dispersion modeling using AERMOD to 
examine the predicted impacts from sources or de minimis changes that 
would be exempt from minor NSR permitting based on the revised 
thresholds.\2\ ADEQ employed this combined modeling approach in an 
effort to look at both regional and local scale impacts from emissions 
equal to the revised thresholds for VOC, NOX, 
SO2, CO, PM10, and PM2.5. In both the 
regional- and local-scale modeling analyses, ADEQ modeled hypothetical 
sources with emissions equal to the minor NSR permitting and de minimis 
change thresholds and stack parameters set equal to median values based 
on the 2011 National Emissions Inventory (NEI) for Arkansas sources. As 
part of photochemical modeling, the maximum CMAQ-derived impacts on 
daily maximum 8-hour ozone, 24-hour PM2.5, annual average 
PM2.5, 1-hour NO2, 1-hour SO2, and 24-
hour PM10 were calculated. The statewide maximum impacts for 
each day resulting from the hypothetical sources was added to the 
unmodified future year concentration for each day and grid cell. The 
resulting concentrations represented the worst-case ambient 
concentrations including impacts from the threshold emission increases 
at any location in Arkansas. These worst-case ambient concentrations 
were then used to calculate relative response factors (RRFs) to 
estimate future design values (FDVs) at both monitored and unmonitored 
locations throughout Arkansas.\3\ \4\ The FDVs were compared with FDVs 
without the thresholds increase impacts, as well as, the NAAQS in an 
effort to determine whether emissions increases less than the minor NSR 
thresholds would cause or

[[Page 30556]]

contribute to NAAQS violations or potentially interfere with NAAQS 
maintenance. Similar to the regional-scale photochemical modeling, the 
hypothetical sources modeling in the near-field dispersion modeling 
analysis were modeled with emission rates equal to the minor NSR 
permitting thresholds and de minimis levels and stack parameters were 
set equal to median stack parameter based on the 2011 NEI data. The 
maximum AERMOD-derived impacts on daily maximum 1-hr NO2, 
annual average NO2, daily maximum 1-hour SO2, 
daily maximum 1-hour CO, daily maximum 8-hour average CO, and 24-hour 
average PM10 were calculated for each air quality control 
region. The daily AERMOD-derived concentrations were added to the CMAQ-
derived concentrations for the same location, using the CMAQ values as 
``background.'' ADEQ stated that the values determined for the 
statewide daily maximum impacts are expected to represent the near-
field concentrations assuming worst-case impacts from threshold 
emission increases at a range of locations through Arkansas. The daily 
maximum worst case AERMOD impacts were added to the unmodified future 
year concentration for each day and grid cell. The resulting 
concentrations represented the worst-case ambient concentrations 
including impacts from the threshold emission increases at any location 
in Arkansas. Similar to the CMAQ-only modeling analysis, the worse-case 
modeled impacts were used to calculate RRFs and FDVs. The calculated 
FDVs were compared with the original unmodified FDVs and the NAAQS in 
order to examine the potential impacts of the proposed minor NSR 
threshold emissions on NAAQS attainment and maintenance. The modeling 
conducted by Arkansas utilized current air quality modeling techniques 
to demonstrate that the predicted impacts resulting from emissions at 
or below the revised minor NSR permitting thresholds and de minimis 
change levels, which happen to be equal in magnitude to the major NSR 
significance levels, will not interfere with the attainment or 
maintenance of the NAAQS current in effect at the time of the 
analysis--including those that were not applicable at the time the PSD 
significant emission rates were developed.
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    \2\ See Pages 31-32 of the EPA's Technical Support Document 
dated August 24, 2017, which discusses the air quality modeling 
analyses that were completed by ADEQ in support of the submitted SIP 
revisions. In addition to the TSD, additional details regarding the 
modeling analyses are located in the modeling report submitted as 
part of the March 24, 2017 SIP revisions submittal, which outlines 
modeling tools and techniques utilized by Arkansas along with the 
results from the modeling analyses. (ADEQ's modeling report located 
in the ``ADEQ 2010 Minor NSR Permitting Thresholds and De Minimis 
Levels SIP Revision--Technical Support Document'' dated November 
2015,)
    \3\ A RRF is the ratio of future case modeled concentrations to 
base case modeled concentrations, which is used to quantify the 
relative impacts of the emissions added to the model. In the 
photochemical modeling conducted by ADEQ, the base case modeled 
concentrations are taken from the 2015 modeling without the 
hypothetical sources added while the future case modeling results 
are taken from the 2015 modeling plus the 8 modeled hypothetical 
sources. Therefore, the RRFs calculated in this modeling analysis 
quantify the relative impacts from the additional emissions from the 
hypothetical sources that would be exempt from permitting based on 
the new thresholds/de minimis levels.
    \4\ RRFs can be used to estimate FDVs, which are determined by 
applying the RRF ratios to monitored design values from the base 
year taken from ambient monitoring data.
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    Further, the entirety of the additional analyses provided by ADEQ 
in the March 24, 2017 SIP revision submittal, including the NAAQS non-
interference modeling demonstration, was the basis of the EPA's finding 
that the revised thresholds were approvable. As such, a linkage to the 
PSD significant emission rate values and/or comparison of modeled 
impacts to percentage thresholds relied upon during the EPA's 
development of the significant emission rates in 1980, 1987, and 2008 
for the PSD program was not applicable to our proposed approval of the 
revised minor NSR permitting thresholds and de minimis levels. 
Elsewhere in this final rulemaking, we have addressed the comments 
specifically made regarding the modeling techniques used by Arkansas 
and restated our finding that those techniques were reasonable and 
appropriate for the NAAQS non-interference demonstration required by 
CAA section 110(l).
    Comment: The commenter stated that modified major sources exempted 
from major source permitting under the PSD program will also be exempt 
from minor source permitting under Arkansas' de minimis changes rule 
and that the revised minor NSR program will not pick up the slack and 
ensure protection of the NAAQS as was intended when EPA promulgated the 
2002 revisions to the major source NSR rules.
    Response: The commenter is incorrect that modifications to existing 
PSD major sources, which are exempt from PSD permitting, would be 
exempt from minor source permitting under the de minimis change rule. 
As discussed below, any change at an existing major NSR source (PSD 
source) is prohibited from using the de minimis change process because 
the de minimis change rule at Reg. 19.407(C) is located in Chapter 4 of 
Reg. 19, which does not apply to PSD sources or any modifications at 
those sources.
    The SIP-approved Arkansas NSR program is comprised of two types of 
review: ``Minor Source Review'' and ``Major Source Review''. Arkansas 
operates a so-called ``merged, one permit'' system, which is divided 
into these two types of review based on whether a source is required to 
obtain a title V operating permit. As such, ``Minor Source Review'', 
which is contained in Reg. 19, Chapter 4, applies only to those sources 
that are not subject to title V permitting and require only a title I 
NSR authorization.\5\ All sources that are subject to title V, which 
would include PSD sources, are subject to ``Major Source Review'' under 
Reg. 26 provisions incorporated by reference in Reg. 19, Chapter 11. 
Therefore, all permitting at PSD sources, including all modifications, 
would be subject to Reg. 19, Chapter 11 ``Major Source Review'' under 
the Arkansas NSR permitting program and cannot use the de minimis 
change provisions, which are limited to ``Minor Source Review'' in 
Chapter 4. Only those non-title V sources that are minor under the SIP-
approved definition of minor source may qualify for the de minimis 
change exemption found in Reg. 19.407(C). As discussed in our proposed 
rulemaking and the accompanying TSD, the emissions inventory analysis 
for the de minimis changes found that the scope of changes expected to 
qualify for the de minimis change exemption is very small with 
emissions associated with those exempted changes making up a fraction 
of a percent of statewide emissions. The range of percentage of 
statewide emissions for the pollutants determined in the emissions 
inventory analysis for de minimis changes was 0.0005% to 0.019%. At 
these levels it would require over 50 times the NOX 
emissions authorized in 2016 to approach 1% of the statewide emissions 
and over 300 times the emissions for the other pollutants.
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    \5\ As stated in our original SIP approval of Chapter 4, ``[a] 
minor source is any source which does not meet the requirements of a 
major source. The Act in section 302(j) defines the terms ``major 
stationary source'' and ``major emitting facility'' as ``any 
stationary facility of source of air pollutants which directly 
emits, or has the potential to emit, one hundred tons per year of 
more of any air pollutant (including any major emitting facility or 
source of fugitive emissions of any such pollutant, as determined by 
rule by the Administrator).''
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    The state did not rely solely on the emissions inventory analysis 
to demonstrate NAAQS compliance. This emissions inventory analysis was 
coupled with additional analyses specifically looking at ambient 
concentrations (monitoring trends analysis) and potential ambient 
impacts (modeling analysis) that were completed by ADEQ as part of the 
110(l) demonstration. The results from the modeling analysis indicate 
that while the addition of the exempt emissions did result in slight 
increases in the model predicted impacts, it did not violate the NAAQS. 
As such, the modeling analysis portion of the 110(l) demonstration 
shows that revised minor NSR program will continue to ensure NAAQS 
protection.
    EPA's intent at the time of promulgation of the 2002 revisions to 
the major source NSR rules is not relevant here. What is relevant here 
is the approvability of these revisions in the context of the current 
regulatory framework as promulgated. The commenter has not cited any 
ambiguous regulatory language in order to justify an examination of 
EPA's intent. In the absence of any ambiguity in regulatory language it 
is not necessary to address EPA's intent here as there is no dispute 
regarding interpretation on the applicable rules.

[[Page 30557]]

    Comment: The commenter stated that EPA has previously required 
minor NSR programs to use much smaller emission thresholds than the 
major modification significant impact levels and gave the example of 
the Montana minor NSR program includes a de minimis increase exemption 
threshold of 5 TPY, which was approved by EPA, after a 15 TPY threshold 
that was initially set by Montana was not approved by EPA into the SIP.
    Response: In the case of Montana, which was referenced by the 
commenter, the state did not provide an adequate demonstration to 
support the approval of the 15 TPY exemption threshold that was 
initially established by the state into the SIP. The state later 
revised the threshold to 5 TPY and submitted this threshold for SIP 
approval along with an analysis to show that the 5 TPY exemption would 
not interfere with NAAQS attainment or maintenance or violate the 
control strategy. Based on the revised submittal and supporting 
information, EPA approved the lower threshold of 5 TPY into the Montana 
SIP. Our proposed approval of the de minimis change levels in Arkansas 
does not contradict the previous Montana approval. In fact, our 
proposed approval mirrors the Montana SIP approval in that we requested 
analyses from Arkansas as part of the 110(l) demonstration for the 
revised de minimis change levels and our approval is based on those 
analyses as documented in the proposed rulemaking. Specifically, we 
found that Arkansas' documentation adequately demonstrates that these 
revised thresholds will not interfere with NAAQS compliance. Our 
approval of one de minimis exemption threshold level in one state does 
not preclude the approval of a different threshold in another state. 
Each state's universe of minor NSR sources, meteorology, and ambient 
air quality conditions are unique and influence the types of exemptions 
that would not interfere with the minor NSR program's ability to meet 
the applicable federal requirements.
    Comment: The commenter stated that the de minimis change rule 
contradicts with how applicability is determined under PSD permitting 
requirements and thus fails to ensure projects that should be required 
to obtain a PSD permit will not be instead considered a de minimis 
change under Reg. 19.407(C). They also state that EPA must disapprove 
the current submittal and require Arkansas to revise its de minimis 
rule and relevant definitions rule to clearly state that changes that 
are considered major modifications under the PSD permitting regulations 
cannot be considered as de minimis changes. Without such language 
clearly stated, the Arkansas minor NSR program could allow sources that 
would otherwise be subject to PSD permitting to improperly avoid major 
source PSD permitting requirements for a major modification. The 
commenter also states that EPA must disapprove the version of Reg. 
19.407(C) currently approved into the SIP which EPA has reopened with 
this action to the extent the provisions could interfere with 
compliance with the PSD permitting regulations.
    Response: We agree with the commenter that changes that are 
considered major modifications under the PSD permitting regulations 
cannot be considered as de minimis changes. However, the commenter is 
incorrect that the revisions to the de minimis change provisions will 
interfere with proper implementation of the PSD permitting 
requirements. As previously stated in our responses, the de minimis 
change rules contained in Chapter 4 of Reg. 19 cannot be used for any 
changes at PSD sources/modifications. Therefore, our proposed approval 
of revisions to Chapter 4, including the de minimis change rule, will 
not impact PSD permitting implementation. Changes that are considered 
major would be subject to permitting under Reg. 26 is incorporated by 
reference in Chapter 11, which utilizes an actual-to-projected actual 
test for modifications to existing units and an actual-to-potential 
test for new units, are not exempted from the requirements of Chapter 
11 by the provisions we are approving in this rulemaking. As noted in 
Section IV of the TSD, we are not taking action on any portion of 
Chapter 11 and the requirements of that chapter, which mainly 
incorporate by reference the requirements of the federal PSD program at 
40 CFR 52.21, remain in effect.
    Regarding the commenter's statement that EPA should take action to 
disapprove Reg. 19.407(C) as it is currently approved into the SIP, 
aside from the revisions to 407(C)(2)(a) and 407(C)(2)(b) which are 
clearly annotated in Section IV of the TSD, the other portions of Reg. 
19.407 are not being revised by our current rulemaking.\6\ Therefore, 
the other SIP-approved portions of Reg. 19.407 will remain unchanged by 
our rulemaking. As previously stated in our responses, any comment on 
provisions that are not being revised as part of our rulemaking is 
irrelevant to this action. Further, our current rulemaking does not 
reopen the current SIP-approved and unchanged provisions for any 
action, including disapproval.
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    \6\ Reg. 407(C)(2)(a) and (b) contain the de minimis change 
emissions and air quality impacts thresholds.
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    Comment: The commenter stated that because the minor NSR revisions 
could allow for increased deterioration in air quality over PSD 
baseline concentration the EPA cannot approve such a SIP revision 
without a demonstration that it will not cause or contribute to a 
violation of the applicable PSD increment. The commenter listed the 
following as chances for increased deterioration resulting from the SIP 
revision: (1) The minor NSR SIP revisions submitted by ADEQ allow for 
an increase in allowable emission rates to occur under the de minimis 
provisions of Reg. 19.407(C)(7); (2) Reg. 19.417 allows sources 
currently holding permits pursuant to Reg. 19 but whose emissions are 
below the permitting thresholds to submit a registration request under 
Reg. 18.315, which is a state-only rule and not part of the SIP, and 
request that their permit containing federally enforceable requirements 
be terminated; and (3) to the extent ADEQ ensures compliance with the 
PSD increment as part of its minor NSR program, the relaxation in the 
sizes of sources and modifications subject to minor NSR permitting also 
could allow increased deterioration of air quality above baseline 
concentration. The commenter also stated that the modeling analysis 
provided by ADEQ to support approval of the minor NSR relaxations 
included violations of the Class I and Class II PM10 
increments that were predicted due to the increased emissions 
thresholds that would exempt from minor NSR review under the proposed 
SIP revision, which indicates that an unpermitted source pursuant to 
the expanded exemptions from Arkansas' minor NSR could cause an 
exceedance of the PM10 increment. The commenter also stated 
that pursuant to CAA section 110(l) and 40 CFR 51.166(a)(2), EPA cannot 
approve a SIP submittal which admittedly allows a violation of the PSD 
increments.
    Response: We agree with the commenter that the revisions to the 
Arkansas minor NSR program do allow larger increases in allowable 
emissions to be authorized via the de minimis change rule by increasing 
the de minimis change thresholds. We also agree that the revisions 
allow currently permitted sources with emissions that fall between the 
old minor NSR permitting thresholds and the revised permitting 
thresholds to submit a registration under Reg. 18.315 and request that 
their Reg. 19 permit be

[[Page 30558]]

terminated. However, the applicable legal test for determining 
approvability of these revisions, which revise the minor NSR program so 
that it becomes less stringent, is the requirement of CAA section 
110(l), EPA cannot approve a revision to the SIP if it interferes with 
applicable requirements of the Act. The PSD increment requirement found 
at 40 CFR 51.166(a)(2) is inapplicable here because it is required to 
be met by a major source/major modification application, not a minor 
NSR permitting application. The major source/major modification 
application must show that the PSD increment is not violated and the 
applicant's modeling must include the emissions from all of the nearby 
minor sources, as well as any other nearby major sources. If the major 
source/major modification modeling shows the PSD increment will be 
violated by the proposed construction/modification, then the major 
source/major modification must reduce its requested emissions or obtain 
reductions from the other sources impacting the increment. Because the 
burden of not violating the PSD increment is placed on the source 
subject to PSD, the PSD increment requirement does not apply to a minor 
NSR permitting SIP. As stated previously in our responses to the 
commenter, the PSD increment requirements are contained in the PSD 
rules under 40 CFR 51.166 and apply only to sources subject to PSD. 
They do not apply to minor sources. Therefore, an increment analysis 
would only be required to be completed as part of a PSD permitting 
action (Reg. 19, Chapter 9) and would be a separate analysis than that 
completed as part of the NAAQS demonstration. Further, the air quality 
modeling that was conducted by Arkansas was conducted for NAAQS 
compliance demonstration purposes as part of the 110(l) non-
interference demonstration. (See the March 24, 2017 SIP Revision 
Submittal, Appendix D--Air Quality Modeling Analysis of Minor Source 
Permit Thresholds.) Because the PSD increment analysis and NAAQS 
analysis serve separate and distinct purposes, these analyses use 
different modeling approaches and often different model inputs. 
Therefore, a modeling demonstration conducted for NAAQS compliance 
cannot be relied upon to make a modeled PSD increment analysis 
determination, such as if a PSD increment violation exists. Therefore, 
we do not agree with the commenter that the NAAQS modeling indicates 
that the proposed SIP revision allows a violation of the PSD 
increments. We also do not agree that the modeled PM10 
impacts exceed the referenced increments because the state's modeling 
analysis did not include a PSD increment analysis for comparison with 
the PSD increments to determine if a predicted exceedance occurred. In 
addition, we reiterate that a PSD increment analysis is not necessary 
as part of a 110(l) analysis to support revisions to a minor NSR 
permitting program, since the federal PSD increment analysis 
requirement at 40 CFR 51.166(a)(2) is not applicable to minor NSR 
programs.
    Comment: The commenter stated that a comparison of emissions that 
could be exempt from the relaxed minor NSR with total statewide 
emissions across the state of more than 53,000 square miles does not 
give any indication of whether the exempted emissions would interfere 
with attainment or maintenance of the NAAQS or increments. As such, the 
commenter stated that the emissions comparison analysis does not 
provide information relevant to whether the relaxations to Arkansas' 
minor NSR program will interfere with attainment or maintenance of the 
NAAQS or any other CAA requirement.
    Response: We do not agree with the commenter that the emissions 
inventory analysis for the emissions exempt from minor NSR permitting 
based on the revised permitting thresholds does not provide information 
that is relevant to the 110(l) analysis. This analysis serves to 
determine the scope, or portion of emissions that would not undergo 
minor NSR permitting requirements relative to the statewide emissions. 
The approach to determine the scope is independent of the physical size 
of the state since the emissions inventory analysis was conducted to 
compare exempt emissions with the statewide emissions inventory. As 
detailed in our proposed rulemaking the scope of emissions anticipated 
to be exempt from minor NSR permitting by the revised permitting 
thresholds was minimal. The pollutant-based emissions inventory 
analysis showed that the scope of emissions exempt from permitting 
based on the revised permitting thresholds ranged from 0.006% to 0.125% 
of the total statewide emissions. This analysis clearly demonstrates 
that the magnitude of emissions that would be exempt from minor NSR 
permitting program makes up an extremely small portion of the statewide 
emissions. The state did not rely solely on the emissions inventory 
analysis to demonstrate NAAQS compliance. This emissions inventory 
analysis was coupled with additional analyses specifically looking at 
ambient concentrations (monitoring trends analysis) and potential 
ambient impacts (modeling analysis) that were completed by ADEQ as part 
of the 110(l) demonstration. The modeling trends analysis looked 
specifically at the current status of ambient air quality and the 
trends in ambient concentrations since the 2008 state adoption and on-
going implementation of the revised minor NSR permitting thresholds. 
The modeling analysis examined the potential impacts of the exempt 
emissions on ambient air quality via local and regional air quality 
modeling. (See the March 24, 2017 SIP Revisions Submittal Appendix C--
2010 Minor NSR Permitting Thresholds and De Minimis Levels SIP 
Technical Support Document and Appendix D--Air Quality Modeling 
Analysis of Minor Source Permitting Thresholds. Monitoring analysis is 
discussed on pages 3-17 of Appendix C. Modeling analysis is discussed 
on pages 17-25 of Appendix C and pages 1-35 of Appendix D.) Regarding 
interference with increments, we previously responded regarding the 
non-applicability of PSD increment requirements to the 110(l) analysis 
completed for this rulemaking.
    Comment: The commenter stated that ADEQ's emissions analysis was 
incomplete because it analyzed sources with allowable emissions less 
than the emission thresholds of Reg. 19.401 when the exemptions for new 
sources are not based on ``allowable emissions,'' but instead are based 
on ``actual emissions.'' The commenter also claimed the analysis was 
incomplete because it does not project total emissions that might be 
exempt from minor NSR in the future and instead reflects on sources 
that may request permits to be revoked because they are no longer 
subject to minor NSR permitting requirements found in Reg. 19, Chapter 
4.
    Response: We do not agree with the commenter that the emissions 
inventory analysis conducted for the permitting thresholds exemptions 
was incomplete. In their analysis, ADEQ compiled a complete list of all 
currently permitted minor NSR sources and determined which currently 
permitted sources would not be required to obtain a permit based on the 
revised permitting thresholds. It is important to note that this 
analysis included the review of all currently permitted facilities in 
the minor NSR program which spanned the entirety of the program--
meaning all active minor NSR permits that had been issued by ADEQ. EPA 
originally SIP-approved the Arkansas construction permitting 
requirements in October

[[Page 30559]]

1976 (effective November 1976).\7\ This means that ADEQ looked at all 
minor NSR permits that had ever been issued and were still active. To 
determine the percentage of emissions exempt from permitting, the 
permitted emission rates were totaled for each pollutant and compared 
with the total emissions from the statewide emissions inventory. The 
state's analysis based on the permitted allowable emissions is more 
conservative than the use of actual emissions for those permitted 
sources since they represent the maximum permit allowable emissions for 
the particular source. In most cases, the actual emissions would be 
less than the allowable emissions because of actual operations at less 
than maximum levels during a given calendar year and because of non-
operational periods that may have taken place. If the state had further 
refined their analysis to determine the historical actual emissions 
emitted by the currently permitted sources which would not be required 
to be permitted under the new thresholds and compared the total actual 
emissions with the total statewide emissions inventory, the actual 
emissions would be expected to make up an even smaller fraction of the 
total statewide emissions.
---------------------------------------------------------------------------

    \7\ EPA originally approved the Arkansas requirements for 
permitting the construction of new and modified sources, which were 
contained in the Regulation of Plan (ROP) Section 4--Permits, on 
October 5, 1976, effective November 4, 1976. (41 FR 43904) EPA later 
approved the recodification of the permitting requirements for minor 
sources from ROP Section 4 into Regulation 19, Chapter 4--Minor 
Source Review on October 26, 2000, effective November 15, 2000. (65 
FR 61103)
---------------------------------------------------------------------------

    As stated above, Arkansas conducted the emissions review as a part 
of the 110(l) demonstration to determine the scope of emissions that 
were previously subject to minor NSR permitting that would be exempt 
from permitting under the revised thresholds. As stated above, Arkansas 
reviewed their entire minor NSR permitting universe, which included all 
active permits that had historically been issued by ADEQ, to determine 
the currently permitted emissions that would be exempt from minor NSR 
permitting under the revised permitting thresholds.\8\ They found that 
the magnitude of currently permitted emissions that would be exempt 
from minor NSR permitting was a fraction of a percent of the total 
emissions in the statewide emissions inventory. (The range of 
calculated percentages by pollutant was 0.006% to 0.125%.) While 
emissions will be exempt in the future, the emissions inventory 
analysis shows the percentage of statewide emissions that were exempt 
from permitting for the entire minor NSR program based on the revised 
permitting thresholds indicates that the magnitude of emissions exempt 
from minor NSR permitting in the future will continue to make up a 
small fraction of the total statewide emissions. In addition, the 
state's regulations require that a source exempt from minor NSR 
permitting based on the new revised permitting thresholds but with 
emissions greater than the previous thresholds obtain a registration in 
accordance with Reg. 18.315, which allows ADEQ to keep track of the 
sources exempt as a result of the new thresholds. In addition to the 
emissions inventory analysis, Arkansas provided additional analyses, 
both monitoring and modeling, to further show the limited potential 
impacts of the revised minor NSR permitting thresholds. The monitoring 
analysis examined statewide ambient air quality data since the adoption 
of the revised minor NSR permitting thresholds in 2008 for CO, 
NOX, SO2, VOC, and PM10, including the 
examination of trends in design values (DVs). Since adoption of the 
revised thresholds, the DVs remain unchanged or show downward 
thresholds since the 2008 adoption of revised thresholds.\9\ The 
modeling analysis included regional-scale photochemical and local-scale 
air dispersion modeling to examine the potential impacts from emissions 
exempt from minor NSR permitting based on the revised thresholds. (See 
the March 24, 2017 SIP Revision Submittal, Appendix D--Air Quality 
Modeling Analysis of Minor Source Permit Thresholds.) As expected, both 
the regional and local modeling indicated some increases in model 
predicted concentration as a result of adding the exempt emissions into 
the modeled emissions inventory. However, for all pollutants and 
averaging period, the resulting ambient concentrations were less than 
the corresponding NAAQS. As stated in our proposed rulemaking, we find 
that the analyses submitted by Arkansas as part of the 110(l) 
demonstration show that the revised thresholds will not interfere with 
attainment or maintenance of the NAAQS.\10\
---------------------------------------------------------------------------

    \8\ Ibid.
    \9\ The Springdale ozone monitor was the only exception and 
showed increased DVs since 2008. ADEQ did further evaluation of the 
Springdale monitor and determined that the increase in the monitored 
ozone DVs at this monitor are likely due to the increase in mobile 
emissions in the Fayetteville-Springdale-Rogers MSA as a result of 
rapid population growth in that area (population grew by over 65,000 
people in the 2007-2014 timeframe. The monitoring trends analysis 
included in the March 24, 2017 SIP submittal indicated that the 
2012-2014 DV at the Springdale monitor was 67 ppb (as compared with 
the 2008 and 2015 O3 NAAQS of 75 and 70 ppb, 
respectively).
    \10\ EPA's review of the monitoring and modeling analyses is 
detailed in Pages 27-33 of the Technical Support Document that 
accompanied our proposed rulemaking and if available in the docket.
---------------------------------------------------------------------------

    Comment: The commenter stated that the emissions inventory analysis 
of the de minimis increases allowed (based on the 2016 de minimis 
approvals) is not persuasive because, the increased de minimis 
thresholds have not yet been approved as part of the SIP, and thus it 
is not reasonable to assume that all sources that might take advantage 
of this rule did take advantage of this rule in 2016. The commenter 
also states that because the revised minor NSR permitting thresholds 
and de minimis levels have not been approved as part of the SIP, the 
state cannot infer anything in the monitoring trends analysis regarding 
the impacts of the revised minor NSR rules on air pollutant 
concentrations from reviewing past monitoring data and trends since it 
is likely that sources would be unwilling to rely on the revised values 
prior to SIP approval.
    Response: We do agree with the commenter's claims that the SIP 
approval status of the revised minor NSR permitting thresholds and de 
minimis change levels impacts the validity or persuasiveness of the 
data included in the emissions inventory and monitoring trends 
analyses. While the revised de minimis change rule provisions are not 
approved into the current Arkansas SIP, they are adopted by the state 
into the state regulations and thereby state law. The CAA requires 
states to adopt, after reasonable notice and public hearings, revised 
regulations for submission to EPA as SIP revisions. (See CAA 
110(a)(1)). Since adoption of the revised permitting thresholds and de 
minimis change levels into their states regulations, Arkansas has been 
implementing those revised levels through the issuance of Reg. 18 
registrations and de minimis change approvals. Lookback information 
regarding the historical de minimis change approvals was specifically 
cited in the emissions inventory analysis portion of the 110(l) 
demonstration. The calendar year (CY2016) de minimis change approvals 
included approval issued based on the revised thresholds that were 
adopted as state law December 2008 (effective January 2009). ADEQ has 
subsequently provided more information regarding the number of Reg. 18 
registrations (issued to those sources exempt from minor NSR permitting 
with emissions that fall within the old and revised permitting

[[Page 30560]]

thresholds) submitted and de minimis change approvals issued since the 
adoption of the revised regulations. This additional lookback 
information clearly indicates that sources have been utilizing the 
revised thresholds--75 registrations have been submitted since the 
permitting thresholds were revised and 476 de minimis change actions 
have taken place since 2010.\11\ Because state law requires that if a 
source used either the minor NSR permitting thresholds or de minimis 
changes levels to avoid minor NSR permitting the source must submit the 
required registration (in accordance with Reg. 19.417 and Reg. 18.315) 
or obtain the required approval (in accordance with Reg. 19.407(C)(6)), 
a source not accounted for in the lookback information provided by ADEQ 
would have been, and still is, in violation of state law. Furthermore, 
ADEQ has indicated that since the adoption of the revised minor NSR 
permitting thresholds and de minimis change levels, they are not aware 
of any instance where a source has been unwilling to utilize the 
revised thresholds because of the status of the revisions with respect 
to the SIP.\12\ Based on the historical information provided, we find 
that the data included in the emissions inventory and monitoring trends 
analyses is valid and reflects the reality and do not agree with the 
commenter that nothing can be inferred from those analyses regarding 
the impacts of the revised minor NSR permitting thresholds and de 
minimis levels. Following adoption of the revised permitting thresholds 
and de minimis change levels in 2008, Arkansas began implementing the 
revised provisions (at the owner or operator's own risk of federal 
enforcement) to exempt qualifying sources from minor NSR permitting 
requirements. The persuasiveness of data used in the monitoring trends 
analysis is not dependent on the SIP approval status.
---------------------------------------------------------------------------

    \11\ The number of Reg. 18 registrations submitted and de 
minimis change actions provided via emails received from Ms. Tricia 
Treece, ADEQ, on July 5, 2017.
    \12\ Information regarding source inquiries to utilize SIP-
approved thresholds instead of revised thresholds provided during 
telephone discussion between Ms. Ashley Mohr, EPA, and Mr. Thomas 
Rheaume and Ms. Tricia Treece, ADEQ, on March 16, 2018.
---------------------------------------------------------------------------

    Comment: The commenter stated that the de minimis exemption is 
based on a comparison of allowable emissions increases, thus it could 
allow larger increases in actual emissions than the tpy emissions 
thresholds in Reg. 19.407(C). Thus, the commenter states that any 
analysis, including the emissions inventory analysis, presented by ADEQ 
about the thresholds is not sufficient to ensure that the actual 
emissions increases allowed by the de minimis exemption will not 
threaten NAAQS attainment or maintenance or otherwise interfere with 
the control strategy. Similarly, the commenter also stated that the 
photochemical modeling also did not model the true increase in 
emissions that could be allowed--the actual emissions increases 
resulting from a de minimis change could be significantly higher than 
the de minimis levels and the actual emissions from a new source could 
exceed projected actuals that were used as a basis to exempt the source 
from permitting.
    Response: We do not agree with the commenter that the emissions 
inventory analysis and modeling analysis provided by ADEQ is not 
sufficient to support the proposed revisions to the de minimis change 
levels. Also, we do not agree with the commenters that the analysis 
provided by Arkansas did not model the true increase in emissions that 
could be allowed under Arkansas' relaxed minor NSR program (i.e., those 
emissions exempt from minor NSR permitting requirements based on the 
revised permitting thresholds and de minimis change levels) under the 
revised minor NSR program. As stated in our proposed rulemaking, the de 
minimis change levels listed in Reg. 19.407(C)(2)(a) are the maximum 
increases in permitted emission rates that can be exempt from minor NSR 
permitting requirements via the de minimis change rule. As such, to 
demonstrate that the proposed SIP revision resulting in revised de 
minimis change levels will not interfere with NAAQS compliance, it is 
reasonable that the 110(l) demonstration should evaluate the projected 
impacts resulting from the maximum emission increases allowed by the 
revised rule (i.e., the de minimis change levels). As documented in the 
modeling report submitted as part of the March 24, 2017 SIP revision 
submittal, Arkansas did follow this approach in their 110(l) 
demonstration and evaluated the impacts resulting from emission rates 
equal to the de minimis change levels. (See the March 24, 2017 SIP 
Revision Submittal, Appendix D--Air Quality Modeling Analysis of Minor 
Source Permit Thresholds.) When a source seeks authorization for a 
proposed change at a facility via the de minimis change provision, they 
are requesting authorization specifically for the increase in the 
permitting emission rates. The previously permitted emission rates 
underwent a previous minor NSR permitting review and were demonstrated 
to be in compliance with the NAAQS. Evaluation of emissions accounted 
for in the pre-de minimis change permitted emission rates, which were 
previously authorized and evaluated for NAAQS compliance under an 
existing permit, are beyond the scope of the 110(l) analysis for the 
revised de minimis change levels. Therefore, a NAAQS demonstration 
associated with the potential impacts from a de minimis change should 
be based on the magnitude of increases in the permitted emission rates, 
which are being authorized via the de minimis change rule. With respect 
to the photochemical modeling, the purpose of the modeling analysis 
submitted by Arkansas was to demonstrate that those emissions exempt 
from permitting based on the revised thresholds would not cause a NAAQS 
violation.
    In the case of a new source that has actual emissions in excess of 
the minor NSR permitting thresholds without an issued permit 
authorizing those emissions, the source would be in violation of the 
minor NSR permitting requirements contained in Reg. 19, Chapter 4, and 
they could be subject to an enforcement action. For example, if a 
source was initially constructed as a seasonal source with emission 
below the de minimis levels, it is exempt from permitting. However, if 
the source's actual emissions rise above those levels without first 
obtaining a permit, it would be in violation of minor NSR. It is 
reasonable (for the purposes of demonstrating compliance with 110(l)) 
to assume a new source would be required to obtain a permit to 
authorize the emissions and demonstrate they will not cause or 
contribute to a violation of a NAAQS if they have actual emissions 
above the minor NSR permitting thresholds. Therefore, the scenarios 
involving potentially violating sources are not a reasonable scenario 
to be included in an analysis conducted to support the minor NSR 
permitting thresholds.
    In the case of a de minimis change, the emissions exempt from minor 
NSR permitting by the de minimis change rule are the increases in the 
permitted emission rates. For the de minimis revisions to be approvable 
the analysis should demonstrate that the increases in the permitted 
emissions will not cause a NAAQS violation. By modeling the minor NSR 
permitting thresholds and de minimis change levels for each pollutant, 
Arkansas did evaluate the prospective impacts associated with the 
emission levels that could qualify for exemption from minor NSR 
permitting requirements under the revised rule.

[[Page 30561]]

    Comment: The commenter stated that the analysis of the de minimis 
increases allowed (based on the 2016 de minimis approvals) is not 
persuasive because 2016 only reflects one year of implementation and 
this rule will be in effect for the foreseeable future.
    Response: We do not agree with the commenter that the emissions 
inventory analysis for the de minimis changes is not persuasive because 
it is limited to 2016. CY2016 provides a portion of time when the 
revised thresholds were being relied upon by owners and operators in 
Arkansas. The review of emissions associated with de minimis changes 
limited to CY2016 found that the 2016 emissions inventory analysis 
shows the percentage of statewide emissions exempt by the de minimis 
change levels in the range of 0.0005 to 0.019%. While the analysis was 
limited to one calendar year, as discussed in our proposal, at these 
percentage levels it would require over 50 times the NOX 
emissions authorized in 2016 to approach 1% of the statewide emissions 
and over 300 times the emissions for the other pollutants. In addition, 
this analysis conservatively did not account for any emissions 
decreases occurring as part of the approved de minimis changes. In 
addition, the analysis for 2016 was conservative in that it did not 
account for emissions decreases that did occur as part of the de 
minimis changes. We believe that additional analysis beyond one 
calendar year is unnecessary because the CY2016 data, that did not 
account for any associated emissions decreases, shows that exempt 
emissions makes up such a small fraction (much less than 1% for all 
pollutants) of the total statewide emissions.
    Comment: The commenter restates that a comparison of emissions that 
could be exempt from minor NSR permitting based on the revised de 
minimis change levels with total statewide emissions does not give any 
indication of whether the exempt emissions would interfere with 
attainment or maintenance of the NAAQS because of the various factors 
(such as: Stack parameters, operational stages, topography, and 
meteorology) that dictate ambient impacts. Because of the variability 
of these factors between sources, the commenter stated that the fact 
that two sources have similar annual emissions is not a rational basis 
to claim that they have similar ambient impacts.
    Response: We do agree with the commenter that a variety of factors 
may dictate ambient impacts, and that reliance on the state's emissions 
inventory analysis does not demonstrate non-interference with the 
NAAQS. Instead, the emissions inventory analysis serves to determine 
the scope, or portion, of emissions that would not undergo minor NSR 
permitting based on the revised thresholds. However, the state did not 
only rely upon the emissions inventory analysis to demonstrate NAAQS 
compliance. The state addressed ambient concentrations and potential 
ambient impacts by looking specifically at the current status of 
ambient air quality, the historical ambient air quality trends since 
adoption in 2008 and the on-going implementation of the revised de 
minimis levels, and the potential impacts of the exempt emissions on 
ambient air quality via local dispersion (AERMOD) and regional 
photochemical (CMAQ) air quality modeling. As previously discussed in 
our responses, the monitoring analysis shows that since the adoption 
and implementation of the revised permitting thresholds and de minimis 
change levels the overall trends in DVs are either unchanged or 
decreasing. Meanwhile, the local and regional modeling analyses show 
that model predicted concentrations resulting from the addition of the 
emissions exempt from permitting remain less than the NAAQS. (See the 
March 24, 2017 SIP Revision Submittal, Appendix D--Air Quality Modeling 
Analysis of Minor Source Permit Thresholds.) While the emissions 
inventory analysis served to determine the scope, or portion of 
emissions that would not undergo minor NSR permitting requirements 
based on the revised de minimis change levels relative to the statewide 
emissions, the monitoring and modeling analyses completed as part of 
the 110(l) analysis accounted for the various factors cited by the 
commenter in evaluating the impacts of the revised de minimis levels. 
Specifically, the results from the air quality modeling analyses were 
impacted by the following factors, which are included as air quality 
model inputs: Emissions, stack parameters, topography and meteorology.
    Comment: The commenter stated that there are numerous other factors 
that came into play during the same timeframe that could cause 
pollutant concentrations to decrease in the timeframe right after the 
December 2008 adoption of the minor NSR rule relaxations, including: 
The Great Recession began in 2007 and continued through 2009; natural 
gas prices dropped significantly and renewable sources of power 
generation became more competitive, reducing demand for coal-fired 
power plants which was replaced by gas turbines and renewables; various 
vehicle emission and liquid fuel standards came into effect; and less 
fuel efficient vehicles were replaced with more fuel efficient 
vehicles. The commenter stated that these factors make it very 
difficult for ADEQ to infer anything regarding the relaxations to its 
minor NSR program through the review of how air monitoring design 
values have changed over time.
    Response: We agree that the monitoring data reflects not only the 
impacts of the revised thresholds and de minimis levels, but other 
factors such as those cited by the commenter as well. However, the 
monitoring analysis does show that since Arkansas' adoption in 2008 and 
ongoing implementation of the revised values, the monitored ambient 
concentration data shows no NAAQS issues along with overall decreasing 
trends in DVs for some pollutants indicative of improved air quality 
since 2008. The monitoring analysis submitted by Arkansas spanned eight 
years of ambient data (2007-2014, which includes and extends beyond the 
time period referenced as ``the Great Recession'' by the commenter). 
The 8-year period covered in the ambient monitoring study is a 
reasonable and representative period of time to examine the impacts of 
the revised thresholds while also accounting for the variability in the 
other factors that may contribute to ambient concentrations. Further, 
we would like to point out that a NAAQS demonstration, including 
demonstrations of non-interference with attainment or maintenance of 
the NAAQS under section 110(l), should reflect ambient air quality as a 
whole, which would take into account the impacts on ambient 
concentrations resulting from the revised minor NSR regulations, as 
well as, the other factors mentioned by the commenter. As shown in the 
referenced monitoring analysis, the resulting ambient concentrations 
including the impacts from the minor NSR program revisions do not 
indicate NAAQS compliance issues. As stated in our proposal, the 
monitoring trends analysis is one part of the demonstration provided by 
Arkansas that supports the finding that the revised permitting 
thresholds and de minimis levels will not adversely impact NAAQS 
attainment or maintenance. In addition to the monitoring analysis, the 
modeling analysis is an important element of the NAAQS compliance 
demonstration and as discussed in our proposed rulemaking and previous 
responses, the modeling results indicate that the addition of the 
emissions exempt from minor NSR permitting requirements will

[[Page 30562]]

not interfere with NAAQS compliance. (See the March 24, 2017 SIP 
Revision Submittal, Appendix D--Air Quality Modeling Analysis of Minor 
Source Permit Thresholds.)
    Comment: The commenter stated that because the state does not have 
a monitoring network that covers all pollutants and all areas of the 
state where industrial sources are constructing and operating, a review 
of the monitoring data from Arkansas monitors provides an incomplete 
picture of the NAAQS attainment status around the state.
    Response: We do not agree that Arkansas' submittal provided an 
incomplete picture of NAAQS attainment around the state. The ambient 
monitoring analysis was one part of the demonstration provided by the 
state to meet the 110(l) requirement. The monitoring trends analysis 
discussion included in Appendix C of the March 24, 2017 SIP revision 
submittal includes a figure showing the Arkansas Ambient Air Monitoring 
Network. This network includes ambient monitoring for the NAAQS \13\ at 
monitoring sites located throughout the state in accordance with 
federal requirements.\14\ The State of Arkansas' ambient air monitoring 
network is reviewed each year to ensure the air quality surveillance 
system continues to meet applicable requirements. The most recent 
review of the ambient air monitoring network for Arkansas, the 2017 
Annual Monitoring Network Plan, was reviewed and approved by EPA on 
October 3, 2017, as meeting the requirements of 40 CFR and its 
appendices. The analysis of the available monitoring data does provide 
valuable information about the current ambient air quality in the 
state, and the historical trends analysis of the data shows that since 
the adoption in 2008 and the ongoing implementation of the revised 
exemption thresholds, ambient air quality has not been adversely 
impacted. In fact, as discussed in our proposed rulemaking, for several 
pollutants the ambient air quality has shown continued improvements 
since the state adoption and implementation of the revised thresholds. 
This information was supplemented by the additional analyses conducted 
by Arkansas, one of which specifically addresses the comment regarding 
the completeness of the picture of attainment status around the state. 
As discussed in our proposed rulemaking, Arkansas completed a modeling 
analysis to determine the potential impacts from sources exempt from 
permitting based on the revised minor NSR permitting thresholds and de 
minimis change levels, which included statewide modeling. (See the 
March 24, 2017 SIP Revision Submittal, Appendix D--Air Quality Modeling 
Analysis of Minor Source Permit Thresholds.) Arkansas conducted 
photochemical modeling to support the revised thresholds based on a 
previous statewide modeling effort conducted for the 2008 base year and 
the 2008/2015 future year scenarios. For the minor NSR thresholds 
analysis, the future year (2015) emissions inventory was modified to 
include eight hypothetical point sources that were distributed 
throughout the state's Air Quality Control Regions. The emission rates 
for each of the hypothetical sources were set equal to the revised 
minor NSR permitting thresholds and de minimis levels. The statewide 
maximum impacts for each day resulting from the hypothetical sources 
was added to the unmodified future year concentration for each day and 
grid cell. The resulting concentrations represented the maximum ambient 
concentrations including impacts from the threshold emission increases 
at any location located throughout Arkansas. While the results from the 
photochemical modeling showed that while the addition of the 
hypothetical source emissions may increase the predicted concentrations 
within most grid cells, the calculated FDVs were still less than each 
of the NAAQS at each monitoring site. (See the March 24, 2017 SIP 
Revision Submittal, Appendix D--Air Quality Modeling Analysis of Minor 
Source Permit Thresholds.)
---------------------------------------------------------------------------

    \13\ EPA has set National Ambient Air Quality Standards for six 
principal pollutants, called criteria pollutants: Carbon Monoxide 
(CO), Lead (Pb), Nitrogen Dioxide (NO2), Ozone 
(O3), Particulate Matter (PM), and Sulfur Dioxide 
(SO2), as indicated in 40 CFR part 50 and appendices.
    \14\ See 40 CFR part 58 and its appendices for federal 
requirements related to measuring ambient air quality and for 
reporting ambient air quality data and related information.
---------------------------------------------------------------------------

    Comment: The commenter stated that it is not appropriate to rely on 
a modeling assessment intended to estimate future pollutant 
concentrations out to 2015 to assess whether Arkansas' relaxed minor 
NSR program will interfere with attainment or maintenance of the NAAQS. 
The commenter based their statement on the possibility that some of the 
rules that were relied on for the 2015 emission inventories could go 
away, the possibility of an economic boom in the state, the possibility 
of growth in a certain type of industry, or a combination of these 
events, which in turn could result in the approval of this SIP 
relaxation interfering with attainment or maintenance of the NAAQS in 
the future despite the CMAQ (photochemical) modeling predictions for 
2015.
    Response: We do not agree with the commenter that the use of the 
future year (FY) modeling for 2015 is not appropriate.\15\ Arkansas 
submitted several analyses as part of the 110(l) demonstration, with 
the modeling assessment being one part of the demonstration submitted 
to support the proposed revisions to the Arkansas SIP. As such, our 
determination regarding the approvability of the SIP revisions relied 
on the combined demonstration and not just one element. Regarding the 
use of the future year modeling, Arkansas used this modeling in 
combination with the baseline modeling to determine RRFs both with and 
without the hypothetical exempt sources to calculate FDVs) \16\ \17\ 
\18\ These FDVs were used to compare and contrast those DVs and 
determine the potential impacts of the exempt sources. This approach 
allowed for a quantitative comparison to determine what potential 
impacts would be expected from the

[[Page 30563]]

additional emissions associated with sources and/or de minimis changes 
that would be exempt from minor NSR permitting requirements based on 
the revised thresholds. The quantitative comparison provided 
information regarding relative difference in impacts both with and 
without the newly exempt emissions compared with the NAAQS. When 
conducting future year modeling, informed assumptions must be made and 
some of these assumptions may differ from the actual real world 
conditions present when the future year becomes the present.\19\ 
However, it is important to note that the future year modeling approach 
was conducted in order to quantify the relative change in ambient 
concentrations resulting from the added potential impacts from the 
newly exempt sources using RRFs. Specifically, this analysis results in 
the calculation of FDVs both with and without the hypothetical source 
emissions and the difference between the FDVs represents the modeled 
predicted impacts from those emissions on ambient concentrations. The 
results of this quantitative comparison of ambient impacts with and 
without the newly exempt sources are not expected to deviate 
significantly, even with actual real world conditions potentially being 
different than the assumed modeled conditions, since the analysis 
focused on the relative impacts of the addition of the hypothetical 
source emissions. We believe that the future year modeling approach 
used by Arkansas that focused on the quantitative difference in the 
relative ambient impacts with and without the hypothetical sources is 
reasonable and informative for a 110(l) demonstration in that it 
specifically evaluated the impacts from newly exempt emissions based on 
revised minor NSR permitting thresholds and de minimis levels. The 
concerns raised by the commenter regarding the state's ability to 
predict the exact conditions of a future year do not change our 
determination that this approach is reasonable. In fact, the inclusion 
of informed assumptions in a future year modeling analysis is not only 
reasonable, but also necessary, since neither we nor Arkansas can know 
with any certainty what emissions and/or sources may change in the 
future. The inclusion of informed assumptions in the modeling analysis 
provides a reasonable estimate of future levels, given the inability to 
foresee the future. If ADEQ modified or removed any SIP-approved 
regulations (as relied upon to make these assumptions) and relax the 
SIP and render them substantially inadequate to attain or maintain the 
relevant NAAQ's standard, EPA has the authority to publish a SIP call 
Federal Register notice requiring the state to adopt and submit a 
110(l) justification for the relaxation. Regarding the commenter's 
concern with potential boom in industrial growth, those sources seeking 
a construction permit, such as a PSD permit, would have to demonstrate 
NAAQS compliance as part of their permit application modeling. As such, 
we find that the state's analysis based on future year photochemical 
modeling, along with the additional modeling, monitoring, and emissions 
inventory analyses, demonstrate that the revised thresholds are not 
expected to adversely impact the state's ability to attain and maintain 
the NAAQS.
---------------------------------------------------------------------------

    \15\ Arkansas's initial statewide criteria pollutant modeling 
was conducted prior to 2015 using base case years of 2005 and 2008 
and a future year of 2015. The final modeling report detailing this 
initial modeling entitled ``Criteria Pollutant Modeling Analysis for 
Arkansas'' dated July 28, 2014 was included in the March 24, 2017 
SIP revision submittal. Arkansas relied upon the 2015 modeling 
scenario from this statewide modeling as the baseline scenario in 
the minor NSR permitting thresholds and de minimis change levels 
modeling. They modified the 2015 emissions inventory to include the 
hypothetical source to represent the addition of emissions from a 
newly exempt emissions source based on the revised thresholds in 
order to examine the potential impacts and sensitivity of model 
predicted ambient concentrations to the exempt emissions.
    \16\ A RRF is the ratio of future case modeled concentrations to 
base case modeled concentrations, which is used to quantify the 
relative impacts of the emissions added to the model. In the 
photochemical modeling conducted by ADEQ, the base case modeled 
concentrations are taken from the 2015 modeling without the 
hypothetical sources added while the future case modeling results 
are taken from the 2015 modeling plus the 8 modeled hypothetical 
sources. Therefore, the RRFs calculated in this modeling analysis 
quantify the relative impacts from the additional emissions from the 
hypothetical sources that would be exempt from permitting based on 
the new thresholds/de minimis levels.
    \17\ RRFs can be used to estimate FDVs, which are determined by 
applying the RRF ratios to monitored design values from the base 
year taken from ambient monitoring data.
    \18\ Arkansas applied the RRFs derived from the 2015 baseline 
and 2015 baseline with hypothetical sources modeling analyses to 
calculated FDVs at all ambient monitoring locations for each 
pollutant. The difference between these FDVs represents the impacts 
from the hypothetical source emissions on ambient air quality. 
Appendix D of the March 24, 2017 SIP revision submittal contains the 
details of this analysis including the calculated RRFs and FDVs.
    \19\ The methodology used by Arkansas to develop the modeled 
future year 2015 emissions inventory is detailed in Section 3.6 of 
the ``Criteria Pollutant Modeling Analysis for Arkansas'' report 
provided in Appendix D of the March 24, 2017 SIP revision submittal. 
The 2015 emissions inventory was assumed equal to the 2014 emissions 
inventory with no further adjustments that were prepared based on as 
part of the EPA's 2005-based platform, which included future year 
cases developed from it, that was used in the Final Transport Rule 
modeling (available at ftp://ftp.epa.gov/EmisInventory/2005v4_2/). 
Arkansas did adjust the emissions inventory to include a new 
facility (AEP Service Corporations' John W. Turk, Jr. facility 
located in southwestern Arkansas.
---------------------------------------------------------------------------

    Comment: The commenter stated that photochemical modeling submitted 
by Arkansas in support of the SIP revisions does not give a rational 
picture of the effect the SIP relaxations could have on air quality in 
Arkansas. The commenter stated that first, there could clearly be more 
than 8 sources, which was the number of sources included in the 
photochemical modeling, exempt from permitting under the revised minor 
NSR rules. The commenter also stated that the photochemical modeling 
did not model the worst case conditions such as terrain, stack height, 
stack temperature and velocity.
    Response: While we agree with the commenters that the potential 
number of exemptions resulting from the revised rule may not be limited 
to 8 sources, we do not agree with their assessment that the modeling 
analysis was limited to the impacts from only those 8 sources. Arkansas 
submitted statewide modeling that accounted for cumulative impacts from 
the 8 hypothetical sources along with the emissions contained in the 
statewide emissions inventory. (See the March 24, 2017 SIP Revision 
Submittal, Appendix D--Air Quality Modeling Analysis of Minor Source 
Permit Thresholds.) The 8 modeled sources were distributed throughout 
the state's Air Quality Control Regions. The modeling results showed 
the impacts of the addition of these eight hypothetical sources to the 
predicted ambient concentrations. In addition, the modeling 
extrapolated for the maximum modeled impacts from the hypothetical 
sources applied at each modeled grid cell throughout the state. In 
addition to examining the modeled impacts from these 8 hypothetical 
sources in their chosen locations in the Air Quality Control Regions, 
the modeling analysis conducted by Arkansas also looked at the impacts 
of sources with emissions equal to the revised thresholds throughout 
the state. This analysis was accomplished by determining the statewide 
maximum modeled impacts in the photochemical modeling for each day 
resulting from the hypothetical sources and adding those impacts to the 
unmodified future year concentration for each day and grid cell. This 
approach allowed the examination of the maximum predicted hypothetical 
source impacts combined at different geographic/topographic locations 
along with looking at those impacts combined with a variety of 
cumulative source inventory impacts throughout the state. It is 
impossible for the state to project each source that may be exempt 
under the revised rule and unreasonable to expect the inclusion of 
every potentially exempt source within an air quality modeling 
analysis. We determined that the approach used by Arkansas to include a 
number of hypothetical sources throughout the state and to examine the 
combined impacts of these sources with background emissions sources at 
each modeled grid cell in Arkansas provides information and a rational 
picture regarding the potential impacts of newly exempt emissions 
throughout the state. By modeling these 8 hypothetical sources with 
emission rates equal to the revised thresholds, the state's approach 
provided for the examination of the actual model predicted impacts at 
locations within each Air Quality Control Region from the maximum level 
of emissions that could be exempt from permitting for a source based on 
the revised minor NSR permitting thresholds and de minimis change 
levels. As a second step, the approach to apply the daily maximum 
modeled impacts from the hypothetical sources to each grid cell for 
each day in the modeled period provided for the examination of the 
impacts of the exempt emissions at each grid cell throughout the state. 
In the case of the minor NSR program revisions proposed by Arkansas, 
the state developed a 110(l) demonstration comprised of air quality 
modeling, as well as an emissions inventory analysis and a monitoring 
trends analysis. As stated in our proposed rulemaking, we found in

[[Page 30564]]

combination that the modeling analysis along with the other analyses 
submitted by the state demonstrated that the proposed revisions would 
not interfere with NAAQS attainment or maintenance. Based on our 
review, we find the analysis conducted and the methods used to be 
appropriate and sufficient to support the proposed SIP revisions, 
especially for exemptions from minor NSR permitting requirements that 
are expected to make up fractional percentages (<1% for all pollutants) 
of the total emissions in the statewide emissions inventory--as 
documented in the state supplied emissions inventory analysis.
    Regarding the commenter's statement regarding the modeling of 
worst-case conditions, we do not agree with the commenter. The modeling 
of the worst case conditions such as terrain, stack height, stack 
temperature and velocity is inappropriate for assessing whether the 
relaxed applicability to Arkansas' minor NSR rule would violate the 
NAAQs. The hypothetical sources included in the 110(l) demonstration 
modeling were meant to represent the exempt emissions that could occur 
from a variety of sources and were being modeled to examine the 
potential impacts from exempt emissions as part of the demonstration of 
non-interference with attainment or maintenance of the NAAQS under CAA 
section 110(l). Arkansas determined representative values to be used as 
model inputs for the hypothetical sources by reviewing real world stack 
parameters available through their emissions inventory data. Based on 
their review, the state chose the average stack conditions from the 
emissions inventory data as the representative inputs for the modeled 
hypothetical sources. As stated in the modeling report included in the 
March 24, 2017 SIP revision submittal and in our proposed rulemaking, 
the state modeled the hypothetical sources with the maximum emissions 
exempt by the rule (i.e., emissions equal to the thresholds values), 
even though not all exempt sources would have those emissions levels.
    The use of the worst case conditions (as referenced by the 
commenter) is typically applied in modeling for an existing source or a 
proposed source of known type/size and location as part of a case-by-
case NSR modeling analysis, such as a modeling analysis completed as 
part of a PSD permit action. In the case of the modeling analysis 
conducted by Arkansas to support the proposed SIP revisions, the state 
was examining the potential impacts of emissions exempt from minor NSR 
permitting by adding hypothetical exempt sources to represent those 
added emissions in the modeled emissions inventory. The modeling 
conducted by Arkansas as part of the 110(l) demonstration modeling 
serves a different purpose, and therefore is inherently different than 
PSD permit modeling. PSD permit modeling is conducted as part of the 
source analysis PSD requirement (40 CFR 51.21(k)) to examine the 
impacts from the construction or major modification of a specific, 
known PSD source where model inputs are based on the actual design and 
operational parameters of the emission points located at the source. 
That said, we do not agree that the modeling analysis conducted by 
Arkansas did not take terrain into account. As discussed previously in 
this response, at least one of the modeled hypothetical sources was 
located in each of the AQCRs. This allowed the examination of model 
predicted impacts across the different geographic and topographic areas 
in the state, including those areas in NW Arkansas with more elevated/
complex terrain (1 source located in AQCR 17 and 2 sources located in 
AQCR 21), which are expected to have higher impacts. As discussed in 
our evaluation of the photochemical modeling conducted by Arkansas, the 
model predicted impacts from the hypothetical sources did not indicate 
any model predicted violations of the NAAQS for any pollutant or 
averaging period. The photochemical modeling approach was one element 
of the 110(l) demonstration provided by the state to support the 
proposed SIP revisions. The approaches used by Arkansas in their 
modeling demonstration to determine the potential impacts from the 
newly exempt emissions were reasonable and appropriate for 110(l) 
analysis being conducted to demonstrate non-interference, especially 
considering the small amounts of emissions expected to be exempt from 
minor NSR permitting based on the revised rule relative to the current 
statewide emissions.
    Comment: The commenter stated that the photochemical modeling gave 
no justification for where it located the sources within the state and 
it is not clear if the sources were located in areas where the source's 
plume could cause high concentrations due to nearby elevated terrain or 
in areas where there are other significant sources of air pollutants to 
determine the cumulative impacts.
    Response: We do not agree with the commenter that no justification 
was provided for the location of the hypothetical sources within the 
photochemical modeling. Arkansas did state that they placed at least 
one source in each of their Air Quality Control Regions. They also 
stated that the sources were typically located in or near more urban 
areas of the state. A figure was included in the modeling report 
showing the location of the modeled sources relative to the populated 
areas in the state, which are also more likely to have larger 
``background'' emissions within the modeled emissions inventory. (See 
the March 24, 2017 SIP Revision Submittal, Appendix C--2010 Minor NSR 
Permitting Thresholds and De Minimis Levels SIP Technical Support 
Document, Figure 19.) The chosen locations allowed for the examination 
of impacts throughout the various regions of the state, focused on the 
more populated areas. As stated in our previous response, two of the 
modeled hypothetical sources were included in the areas in NW Arkansas 
with more elevated/complex terrain (1 source located in AQCR 17 and 2 
sources located in AQCR 21). Additionally, the modeling approach used 
by the state in their 110(l) demonstration included a separate analysis 
to specifically examine the model predicted concentrations at each grid 
cell throughput the state when the maximum modeled impacts from the 
hypothetical sources were applied. This approach allowed the 
examination of the maximum hypothetical source impacts combined at 
different geographic locations along with looking at those impacts 
combined with a variety of cumulative source inventory impacts 
throughout the state.
    Comment: The commenter stated that the photochemical modeling did 
not attempt to take into account the cumulative impacts of exempt 
sources or modifications, and it did not include the possibility of 
multiple exempt sources locating nearby each other, nor did the 
modeling attempt to model more than one exemption at a single or 
multiple sources over time.
    Response: As discussed previously in our responses, we do not agree 
that cumulative impacts analysis was not conducted as part of the 
state's modeling analysis. The photochemical modeling analysis combined 
the impacts from the hypothetical sources with the impacts of 
background emissions inventory sources via emissions inventory model 
inputs.\20\ Further, this cumulative impacts analysis was conducted in 
such a way

[[Page 30565]]

as to examine the maximum modeled impacts from the hypothetical sources 
with the impacts from the background emissions inventory sources at 
each grid cell in the state. Regarding the cumulative impacts from 
multiple exempt sources potentially located nearby each other, the 
modeling report included in the March 24, 2017 SIP revision submittal 
stated that ``since the modeled impacts occur within or nearby the 
source location, cumulative effects from multiple sources in multiple 
grid cells are expected to be small.'' Based on the 110(l) 
demonstration provided by Arkansas, which included modeling that looked 
at cumulative impacts from hypothetical exempt sources and the 
background emissions sources inventory, we do not find the revised 
thresholds to adversely impact the NAAQS.
---------------------------------------------------------------------------

    \20\ As discussed in Arkansas's ``2010 Minor NSR Permitting 
Thresholds and De Minimis Levels SIP Technical Support Document'' 
(Appendix C to March 24, 2017 SIP revision submittal), the CMAQ 
photochemical modeling requires as input, hourly, gridded pollutant 
emissions from both anthropogenic and biogenic sources.
---------------------------------------------------------------------------

    Comment: The commenter stated that there is no indication that the 
modeling took into account variability of emission rates over time to 
account for the very likely possibility that an exempt source could 
emit at higher rates over shorter periods of time rather than emitting 
at a consistent level.
    Response: It is unreasonable to expect the type of modeling 
conducted by Arkansas to examine the potential impacts of a small 
subset of minor sources that make up much less than 1% of the total 
emissions in the statewide emissions inventory (less than or equal to 
0.125% of the statewide emissions for minor NSR permitting thresholds; 
less than or equal to 0.019% of the statewide emissions for de minimis 
change levels) to include variable emissions modeling. The evaluation 
of impacts from variable emission rates is typically associated with 
modeling an existing source or a proposed source of known type/size and 
operation as part of a case-by-case NSR modeling analysis (such as the 
modeling conducted for PSD permitting). As stated in our previous 
responses, the modeling analysis conducted by Arkansas as part of the 
SIP revision submittal was completed as part of a 110(l) demonstration 
for the purposes of determining the potential impacts of the revised 
missions exempt from minor NSR permitting by adding hypothetical exempt 
sources to represent those added emissions in the modeled emissions 
inventory. Modeling conducted as part of the 110(l) demonstration is 
conducted to determine whether a SIP revision will interfere with 
attainment or maintenance of the NAAQS, any required milestone, or any 
other requirement of the Act. Because the modeled sources were 
hypothetical in nature, source-specific information including emission 
rates and their potential variability, cannot be available, nor does it 
need to be. As stated in the modeling report included in the March 24, 
2017 SIP revision submittal and in our proposed rulemaking, in the 
modeling analysis the hypothetical source emission rates were set equal 
to the revised minor NSR permitting thresholds and de minimis change 
levels to examine the potential impacts resulting from the newly exempt 
emissions. (See the March 24, 2017 SIP Revision Submittal, Appendix D--
Air Quality Modeling Analysis of Minor Source Permit Thresholds.) The 
approaches used by Arkansas in their modeling demonstration to 
determine the potential impacts from the newly exempt emissions were 
reasonable and appropriate for the type of analysis being conducted, 
especially considering the relatively small amount of emissions 
expected to be exempt from minor NSR permitting based on the revised 
rule compared to statewide emissions.
    Comment: The commenter stated that because presumably the same 
emission rates, stack parameters, and sources locations were modeled 
with AERMOD (dispersion model) as were modeled in the CMAQ 
photochemical modeling. Therefore, they stated that all of the prior 
comments raised with the CMAQ (photochemical) modeling also apply to 
the AERMOD (dispersion) modeling results. The commenter also stated 
that there is no indication that the air dispersion modeling accounted 
for impacts from startup, shutdown and malfunction emissions.
    Response: The comments raised on the CMAQ photochemical modeling 
were addressed above. Those responses would also apply to the AERMOD 
dispersion modeling, with some slight clarifications due to the 
inherent differences between photochemical and dispersion modeling 
analyses. We provide the following clarification related to the 
comments raised on cumulative impacts analyses since the CMAQ 
photochemical modeling and AERMOD dispersion modeling have different 
approaches to account for cumulative impacts because the models differ 
on how off-site background sources emissions inventories are 
represented and how impacts are determined. As discussed in the 
modeling report included in the March 24, 2017 SIP revisions submittal, 
the CMAQ photochemical modeled concentrations/impacts from the 
background emissions inventory sources were included as background 
values in the AERMOD dispersion modeling and added to the AERMOD 
dispersion modeled concentrations from the hypothetical sources to 
determine cumulative impacts from the exempt emissions and the off-site 
emissions. (See the March 24, 2017 SIP Revision Submittal, Appendix D--
Air Quality Modeling Analysis of Minor Source Permit Thresholds.) 
Although these approaches differ because of the nature of the modeling 
system used, both the CMAQ photochemical and AERMOD dispersion modeling 
analyses include the cumulative impacts of the hypothetical sources 
plus the background emissions inventory sources.
    Regarding the modeling of impacts from startup, shutdown and 
malfunction emissions, the evaluation of impacts from routine and/or 
predictable startup and shutdown emissions would be associated with 
modeling an existing source or a proposed source of known type/size and 
operation as part of a case-by-case NSR modeling analysis, such as PSD 
permit modeling.\21\ The routine and predictable startups and shutdowns 
are permitted emissions which are accounted for in the emissions 
inventory. As stated in our previous responses, the hypothetical 
sources included in the 110(l) demonstration modeling were meant to 
represent the exempt emissions that could occur from a variety of 
sources and were being modeled to examine the potential impacts from 
exempt emissions. Because the modeled sources were hypothetical in 
nature, information regarding source inputs including a small subset of 
their emissions such as source-specific startup, shutdown and 
malfunction emissions, was not available, nor should it be. Further, 
the emissions expected to be exempt from minor NSR permitting based on 
the revised permitting thresholds and de minimis levels made up much 
less than 1% of the total statewide emissions (less than or equal to 
0.125% of the statewide emissions for minor NSR permitting thresholds; 
less than or equal to 0.019% of the statewide emissions for de minimis 
change levels) meaning that the startup, shutdown and malfunctions 
being a small subset of total emissions would make up an even smaller 
fraction of the statewide emissions. The commenter's expectation for 
this type of analysis is unreasonable on the basis that these emissions 
make up such a small fraction of the statewide emissions (that is, a 
small subset of the total exempt emissions that are

[[Page 30566]]

anticipated to make up much less than 1% of the statewide emissions). 
As stated in the modeling report included in the March 24, 2017 SIP 
revision submittal and in our proposed rulemaking, the hypothetical 
source emission rates were set equal to the revised minor NSR 
permitting thresholds and de minimis change levels to examine the 
potential impacts resulting from the newly exempt emissions. The 
approaches used by Arkansas in their modeling demonstration to 
determine the potential impacts from the newly exempt emissions were 
reasonable and appropriate for the type of analysis being conducted, 
especially considering the relatively small amount of emissions 
expected to be exempt from minor NSR permitting based on the revised 
rule compared to statewide emissions.
---------------------------------------------------------------------------

    \21\ Any emissions resulting from unplanned startup or shutdown 
activities or from malfunctions, and therefore not accounted for in 
the NSR permit authorization, would be considered violations of the 
SIP unless these emissions limits are reflected in a NSR SIP or a 
SIP rule.
---------------------------------------------------------------------------

    Comment: The commenter stated that the dispersion modeling did not 
include the modeling of line sources and that fugitive PM10 
emissions often cause increment and NAAQS violations. Therefore, the 
commenter claims that the AERMOD (dispersion) modeling does not reflect 
reasonable worst case impacts that could occur due to the sources and 
de minimis changes exempt from minor NSR based on the SIP revisions.
    Response: As discussed in our previous responses, the worst case 
impacts conditions (or potential worst case source type in the case of 
this comment) referenced by the commenter are typically associated with 
case-by-case NSR modeling of an existing source or a proposed source 
with known stack/emission characteristics (such as, modeling associated 
with a PSD permit action). This would also be the case for the modeling 
of line sources mentioned by the commenter. The 110(l) demonstration 
modeling conducted by Arkansas in support of the SIP revisions has a 
different purpose and associated requirements than case-by-case NSR 
modeling. As discussed in our earlier response to the comment raised 
regarding worst case stack parameters, Arkansas relied on real world 
stack parameters available in their emissions inventory data to 
determine representative stack parameters to represent emissions newly 
exempt from minor NSR permitting via the inclusion of hypothetical 
sources in their modeling analyses. Specifically, they reviewed the 
stack parameters and determined the average stack parameters included 
as hypothetical point sources with emissions set equal to the minor NSR 
permitting thresholds and de minimis change levels. Because the modeled 
sources were hypothetical in nature, source-specific information 
including whether or not any portion of the emissions were fugitive in 
nature (such as road emissions) versus stack emissions, cannot be 
available, nor does it need to be. Modeling of hypothetical sources 
with emissions rates set equal to the revised minor NSR permitting and 
de minimis change thresholds ensures that the analysis accounts for the 
maximum amount of emissions that would be exempt from minor NSR 
permitting based on the revisions. The approaches used by Arkansas in 
their modeling demonstration and their reliance on representative stack 
parameters to determine the potential impacts from the newly exempt 
emissions were reasonable and appropriate for the type of analysis 
being conducted, especially considering the relatively small fraction 
of emissions expected to be exempt from minor NSR permitting based on 
the revised rule compared with statewide emissions.
    Comment: The commenter stated that the revised Arkansas NSR program 
conflicts with the requirements of section 110(2)(C). More 
specifically, the commenter stated that the de minimis change 
exemptions will exempt most if not all modifications at existing major 
stationary sources from minor NSR permitting. They indicate that this 
is in direct contrast with the intention for the new source review 
program required by CAA section 110(a)(2)(C) and 40 CFR 51.160 to be a 
backstop on threats to attainment or maintenance of the NAAQS posed by 
new source growth that is not planned for in existing SIP rules.
    Response: We do not agree with the commenter that the de minimis 
exemptions will exempt most if not all modifications at existing major 
stationary sources from minor NSR permitting. As previously stated in 
our responses, the SIP-approved Arkansas NSR program is comprised of 
two types of review: ``Minor Source Review'' and ``Major Source 
Review''. Arkansas operates a so-called ``merged, one permit'' system, 
which is divided into these two types of review based on whether a 
source is required to obtain a title V operating permit. As such, 
``Minor Source Review'', which is contained in Reg. 19, Chapter 4, 
applies only to those sources that are not subject to title V 
permitting and require only a title I minor NSR authorization.\22\ Any 
source that would be a major source for purposes of PSD review would 
also be a major source subject to title V permitting. Compare 40 CFR 
52.21(b)(1) (establishing major source thresholds of 100 and 250 tons 
per year) with Reg. 26, Chapter 2 (defining major sources to include, 
inter alia, any source with the potential to emit 100 tons per year). 
Therefore, any source subject to title V, which would include any new 
PSD major source and/or any modification to an existing PSD major 
source, cannot utilize the de minimis change exemption found at Reg. 
19.407(C). Instead, all modifications at title V sources that are not 
be subject to Reg. 19, Chapter 9 would instead be subject to the 
``Major Source Review'' requirements found in Reg. 26 and incorporated 
by reference in Reg. 19, Chapter 11 and cannot use the de minimis 
change provisions, which are limited to ``Minor Source Review'' in 
Chapter 4 of Reg. 19. The revisions addressed in our proposed 
rulemaking are limited to ``Minor Source Review'' under Chapter 4 of 
Reg. 19 and do not impact ``Major Source Review'' in Chapter 11, which 
has already been approved into the SIP as part of Arkansas' minor NSR 
program, most recent approval on March 4, 2015 (See 80 FR 11573), and 
which contains the permitting requirement provisions applicable to the 
modifications not subject to Reg. 19, Chapter 9 at all title V sources, 
including all of the sources referenced by the commenter.
---------------------------------------------------------------------------

    \22\ As stated in our original SIP approval of Chapter 4, ``[a] 
minor source is any source which does not meet the requirements of a 
major source. The Act in section 302(j) defines the terms ``major 
stationary source'' and ``major emitting facility'' as ``any 
stationary facility of source of air pollutants which directly 
emits, or has the potential to emit, one hundred tons per year of 
more of any air pollutant (including any major emitting facility or 
source of fugitive emissions of any such pollutant, as determined by 
rule by the Administrator).'' ''
---------------------------------------------------------------------------

    Comment: The commenter stated that the NSR program required by CAA 
section 110(a)(2)(C) and 40 CFR 51.160 is intended to be a backstop on 
threats to attainment or maintenance of the NAAQS posed by new sources 
growth that is not planned for in existing SIP rules. Because of the 
commenter's assessment that NSR program is an important part of the 
SIP, they stated that EPA cannot approve exemptions from a minor NSR 
program unless it is shown that the exemptions are truly de minimis to 
the purposes of the program.
    Response: We agree that the NSR program is an important part of the 
SIP but this does not mean that under the CAA and the minor NSR SIP 
rules, EPA cannot approve exemptions from a minor NSR program. 
Consequently, what is relevant is whether or not the revisions to the 
Arkansas minor NSR program are approvable under the plain reading of 
the applicable statute and rules. There is no regulatory or statutory

[[Page 30567]]

prohibition that prohibits the types and/or sizes of sources that could 
be exempt from the minor NSR program. In fact, the minor NSR SIP rules 
at 40 CFR 51.160(e) only require that the minor NSR program include 
procedures that ``identify types and sizes of facilities, buildings, 
structures, or installations which will be subject to review under this 
section. [and] The plan must discuss the basis for determining which 
facilities will be subject to review.'' These rules furthermore require 
that the plan must ensure that the issuance of minor NSR permits not 
result in a violation of the control strategy or interfere with the 
attainment or maintenance of a national standard. The CAA at section 
110((a)(2)((C) requires regulation of the modification or construction 
of any stationary source within the area as necessary (emphasis added) 
to assure that the standards are achieved. As such, the CAA at section 
110((a)(2)(C) and the minor NSR SIP rules found at 40 CFR 51.160-165, 
as well as case law,\23\ allow exemptions from a minor NSR permitting 
program. In cases such as this, where the minor NSR SIP is being 
revised, the state must also demonstrate that the revisions meet the 
requirements of CAA section 110(l). Similar to the provisions of the 
Act and rules discussed above, section 110(l) requires that EPA cannot 
approve revisions to the Arkansas minor NSR SIP unless EPA finds that 
the changes would not interfere with any applicable requirement 
concerning attainment and reasonable further progress, as well as any 
other applicable statutory requirement. The clear reading of the Act 
and the EPA rules are that EPA can approve exemptions to the Arkansas 
minor NSR SIP program as long as it finds these exemptions will not 
interfere with attainment or maintenance of a NAAQS or other control 
strategy. Consistent with what is allowed, Arkansas has identified 
revised permitting thresholds and de minimis change levels to serve as 
the exemption thresholds for their minor NSR permitting program. To 
support the revised exemption thresholds, Arkansas provided analyses to 
define the scope of the exemptions and to demonstrate that these 
revised thresholds will not adversely impact NAAQS maintenance or 
attainment. The analyses, which were submitted as part of the March 24, 
2017 SIP revision submittal, included: (1) An emissions inventory 
analysis that determined the percentage of the statewide total 
emissions inventory that would be newly exempt by the revised 
thresholds; (2) a monitoring analysis that included a review of the 
current status of ambient air quality in the state along with a review 
of the trends in monitoring data since the state adopted and 
implemented the revised thresholds; and (3) a modeling analysis that 
examined the impacts of the exempt emissions on ambient concentrations. 
The analyses provided by Arkansas in the SIP revision submittals show 
that the minor NSR permitting exemptions resulting from the revised 
rule were limited in scope and comprised much less than 1% of the total 
emissions in the statewide emissions inventory and that the impacts 
from the newly exempt emissions would not adversely impact NAAQS 
maintenance or attainment, as part of their 110(l) demonstration. The 
EPA's review of these analyses and our finding that the proposed SIP 
revisions were approvable were detailed in the proposed rulemaking and 
the Technical Support Document accompanying the rulemaking.
---------------------------------------------------------------------------

    \23\ Alabama Power Company, et al., Petitioners,* v. Douglas M. 
Costle, As Administrator, Environmental Protection Agency, et al., 
Respondents,* Sierra Club, et al., Intervenors.*, 636 F.2d 323 (D.C. 
Cir. 1980).
---------------------------------------------------------------------------

    Comment: The commenter stated that the results from the state's 
AERMOD (dispersion) modeling show that the exemptions are not ``de 
minimis.'' The commenter also states that the EPA must not approve the 
revised program because it will interfere with the requirements that 
SIPs include programs to ensure that new and modified sources not be 
allowed to construct or modify if they would interfere with attainment 
or maintenance of the NAAQS.
    Response: Our proposed rulemaking specifically addressed the scope 
of the exemptions resulting from the revised minor NSR permitting 
thresholds and de minimis levels. As discussed in our proposal, 
Arkansas provided an analysis to quantify the amount of emissions that 
would be expected to be exempt from minor NSR permitting requirements 
relative to total emissions from the statewide emissions inventories. 
For all pollutants, the exempt emissions for both the permitting 
thresholds and de minimis levels made up a fraction of 1% of the 
statewide emissions. Therefore, we find that the scope of emissions 
expected to be exempt from minor NSR permitting as a result of the 
revised minor NSR program thresholds and de minimis change levels is 
extremely limited. Regarding the commenter's claim that the revised 
program will interfere with NAAQS attainment or maintenance, the 110(l) 
demonstration submitted by Arkansas in support of the proposed 
revisions to the SIP specifically addressed the anticipated impacts on 
the NAAQS through both a review of the current status of ambient air 
quality in Arkansas and an evaluation the impacts of the revised 
thresholds on ambient air quality via air monitoring and air modeling 
data. As discussed in our proposed rulemaking, based on the ambient 
monitoring trend analysis, the implementation of the revised minor NSR 
permitting thresholds and de minimis levels following state adoption of 
the revisions in 2008 and ongoing implementation have not negatively 
impacted ambient air quality or interfered with the attainment of the 
NAAQS. In fact, for several pollutants the ambient air quality has 
shown continued improvements via decreases in monitored DVs during this 
period; and currently Arkansas does not have any areas classified as 
nonattainment for any NAAQS. Our proposal also summarized the air 
quality modeling results that Arkansas submitted as part of the SIP 
revisions. The modeling analysis included an evaluation of both 
statewide regional-scale (photochemical) and local-scale impacts. (See 
the March 24, 2017 SIP Revision Submittal, Appendix D--Air Quality 
Modeling Analysis of Minor Source Permit Thresholds.) The photochemical 
modeling was designed to specifically examine ozone and 
PM2.5, the model also simulates NO2, 
SO2, and PM10 so the results for those pollutants 
were also examined. The maximum photochemical modeling derived impacts 
including the hypothetical source emissions on daily maximum 8-hr 
ozone, 24-hr PM2.5, and annual average PM2.5 for 
any location in Arkansas was calculated. The maximum impacts including 
hypothetical source emissions on daily maximum 1-hr NO2 and 
SO2 and 24-hr average PM10 was also calculated. 
These maximum impacts were added to the baseline modeled predicted 
concentrations for each day and grid cell for the future year 
simulation. The resultant model predicted concentrations represented 
the future year concentrations assuming the worst-case impacts from the 
threshold emission increases at any location within the modeling grid. 
These model results were used in conjunction with the baseline modeling 
results to calculate the RRFs necessary to estimate FDVs. The FDVs were 
used to examine whether emission increases less than or equal to the 
revised thresholds will cause or contribute to a NAAQS violation or 
interfere with NAAQS maintenance. To further examine the potential 
near-field impacts

[[Page 30568]]

from new or existing sources with emission increases less than or equal 
to the revised permitting and de minimis change thresholds, a 
dispersion modeling analysis was conducted. The dispersion model was 
applied for the same hypothetical sources used in the photochemical 
modeling with emissions set to the revised thresholds. The dispersion 
model was applied for one year for NOX, SO2, CO, 
and PM10. For each source location, daily concentrations 
(for the receptor with the maximum annual average value) taken from the 
dispersion modeling were added to the photochemical model -derived 
concentrations for that same location. In this manner, the 
photochemical modeling values were used as ``background''. The 
statewide daily maximum impact (maximum over all locations/AQCRs) 
obtained were expected to represent the near-field future-year 
concentrations assuming worst-case impacts from threshold emission 
increases at a range of locations throughout the state. Similar to the 
photochemical modeling, these maximum impacts were added to the 
baseline modeled predicted concentrations for each day and grid cell 
for the future year simulation. The resultant model predicted 
concentrations represented the future year concentrations assuming the 
worst-case impacts from the threshold emission increases at any 
location within the modeling grid. The resultant concentrations were 
used in conjunction with the baseline modeling results to calculate the 
RRFs necessary to estimate FDVs. Once again, the FDVs were used to 
examine if the emissions under the revised threshold values would 
cause/contribute to a NAAQS violation and/or interfere with NAAQS 
attainment. Both the photochemical and dispersion modeling results did 
show that the addition of exempt emissions via modeled hypothetical 
sources may result in some increases in ambient concentrations. 
However, as discussed in the TSD accompanying our proposed rulemaking, 
the FDVs calculated as part of the regional-scale modeling analysis 
that were based on the maximum modeled impacts from the hypothetical 
source were less than the NAAQS for each pollutant and averaging 
period.\24\ Similarly, the results from the near-field dispersion 
modeling also showed the modeled impacts from the hypothetical sources 
combined with background concentrations were all less than their 
corresponding NAAQS.\25\ Based on our evaluation of these analyses 
conducted by ADEQ to support the revised minor NSR permitting 
thresholds and de minimis levels, we find that the increased levels 
will not interfere with attainment or maintenance of the NAAQS.
---------------------------------------------------------------------------

    \24\ For more detailed discussion regarding the regional-scale 
photochemical modeling results see Pages 29-31 of EPA's Technical 
Support Document dated August 24, 2017, available in the electronic 
docket for this rulemaking.
    \25\ For more detailed discussion regarding the near-field 
dispersion modeling results see Pages 31-32 of the EPA's Technical 
Support Document dated August 24, 2017, including Table V.5 which 
contains the maximum and average AERMOD concentrations both with and 
without the CMAQ-derived background concentrations that were 
determined in ADEQ's nearfield hypothetical source analysis.
---------------------------------------------------------------------------

    Comment: The commenter stated that EPA does not cite to the 
specific rule that states that ``de minimis changes are still required 
to meet minor NSR requirements contained in Reg. 19, Chapter 4 
including a demonstration that the proposed modification will not 
interfere with the NAAQS on a case-by-case basis'' and that the EPA's 
claim that this requirement remains is without merit. The commenter 
stated that EPA may be assuming that Reg. 19.402 applies since a permit 
revision is implied by Reg. 19.407(C)(6), it is not clear that this 
requirement applies to what appears to be an administrative amendment 
to a source's permit if it makes a de minimis change. The commenter 
also states that ADEQ made it clear that it does not plan to require or 
base any decision for de minimis changes on air quality modeling, and 
without conducting modeling, they will not be able to ensure that the 
proposed modification will not interfere with attainment or maintenance 
of a NAAQS on a case-by-case basis. So, the commenter stated that it is 
unlikely that ADEQ considered Reg. 19.402 as applying to de minimis 
permit changes.
    Response: We do not agree that our proposed rulemaking did not 
include a citation to the specific rule related to a case-by-case 
demonstration of non-interference with the NAAQS that is applicable to 
de minimis changes. We also do not agree that our statement that de 
minimis changes must still meet minor NSR requirements is without 
merit. Our position that de minimis changes must include a 
demonstration that the proposed modification will not interfere with 
the NAAQS on a case-by-case basis is based on the applicability of Reg. 
19.405(A)(1) to these changes. Further, the provisions in the de 
minimis change rule indicate that de minimis changes include an 
application submittal/review process at Reg. 19.407(C)(5) at it 
references applications for de minimis changes. In addition to the rule 
language, the current ``Air Application Instructions for Registrations, 
Minor Source Permits, or Title V Permits'' made available on ADEQ's air 
permitting website indicate that the forms are to be used for de 
minimis changes.\26\ As such, we do not agree with the commenter that 
EPA assuming the de minimis changes include an application process 
without a basis. Further we do not agree with the commenter, that our 
proposed rulemaking did not clearly state the specific rule regarding 
the referenced technical review requirement to demonstrate NAAQS 
compliance for a de minimis change. In our proposed rulemaking, we 
specifically stated that the requirement found at Reg. 19.405(A)(1) 
requires ADEQ must ensure as part of their technical review of de 
minimis change applications that the source will be modified to operate 
without interfering with NAAQS attainment or maintenance.\27\ The de 
minimis change rule found at Reg. 19.407(C)(2) of the current Arkansas 
SIP exempts qualified proposed changes at an existing source from minor 
NSR permitting requirements, including public notice. The exemption 
only exempts the de minimis change from minor NSR permitting 
requirements and not all applicable minor NSR requirements. Therefore, 
the exemption does not exempt the change from the technical review 
requirements found at Reg. 19.405(A). Reg. 19.405(A) applies to the 
review of applications submitted under Chapter 4 of Reg. 19, where the 
de minimis change rule is located, and requires that on an application-
by-application basis ADEQ must ensure as part of their technical review 
that the source will be modified to operate without interfering with 
NAAQS attainment or maintenance. Our approval of the de minimis change 
level revisions does not revise or in any way change the applicability 
of the SIP-approved technical review requirements found in Reg. 
19.405(A), or any other applicable minor NSR requirements, to de 
minimis changes. It is important to note that the Reg. 19.405(A) 
technical review requirements do not specify that modeling be completed 
to demonstrate that the source will be constructed/modified without 
interfering with attainment or maintenance of the NAAQS. The EPA minor 
NSR SIP rules found in 40 CFR 51.160-165 do not

[[Page 30569]]

require modeling either. We do not agree with the commenter that 
without conducting modeling, ADEQ cannot ensure that a de minimis 
change will not interfere with attainment or maintenance of a NAAQS on 
a case-by-case basis. Case-by-case modeling, such as air dispersion 
modeling, is one of the methods that is commonly used to meet NAAQS 
requirements, but it is not the only method. Depending on the source 
and the proposed de minimis change, as part of their technical review 
ADEQ could alternatively utilize past modeling analyses, such as the 
statewide modeling that was included as part of the 110(l) 
demonstration in the March 24, 2017 SIP revision submittal, or existing 
ambient monitoring data or emissions inventory data relevant to the 
proposed change to make a determination regarding NAAQS compliance. In 
addition, the SIP-approved provision found at Reg. 19.407(C)(1)(b) 
specifies that ``a proposed change to a facility will be considered De 
Minimis if: . . . the change will result in a trivial environmental 
impact.'' Our rulemaking does not revise or in any way change this 
provision.
---------------------------------------------------------------------------

    \26\ Air Application Instructions available online at: https://www.adeq.state.ar.us/downloads/WebDatabases/Air/PermitData/Forms%20and%20Instructions/Form%20and%20Instructions/Air_Permit_Application_Forms_Instructions.pdf.
    \27\ See 82 FR 43508.
---------------------------------------------------------------------------

    Comment: The commenter stated that EPA has not evaluated whether 
the SIP revision satisfies CAA section 193. They state that because the 
revisions allow ADEQ to relax emission limits via de minimis changes 
and for previously permitting sources to terminate the existing permit 
and replace with a registration, EPA's review should include an 
evaluation pursuant to CAA section 193 of whether these relaxations 
would allow for the relaxation of any control requirements in effect 
before November 15, 1990, in any nonattainment area, in which case 
equivalent or greater emissions reductions.
    Response: We do not agree with the commenter that this rulemaking 
is subject to CAA section 193. Section 193 applies to nonattainment 
areas only and provides that ``[n]o control requirement in effect, or 
required to be adopted by an order, settlement agreement, or plan in 
effect before the date of the enactment of the Clean Air Act Amendments 
of 1990 in area for any air pollutant may be modified after such 
enactment in any manner unless the modifications insures equivalent or 
greater emission reductions of such air pollutant.'' The proposed rule 
does not change control requirements in nonattainment areas, of which 
Arkansas currently has none. Therefore, EPA did not address section 193 
in the proposed approval action, since it does not apply. In the 
future, should an area become designated as nonattainment, Arkansas 
when developing the required nonattainment NSR permitting program would 
have to ensure that this program applied the Act's thresholds, which 
might require Arkansas to revise its minor NSR SIP program.

III. Final Action

    In this action, EPA is approving revisions to the minor NSR 
permitting program as submitted as revisions to the Arkansas SIP on 
July 26, 2010, and March 24, 2017, including supplemental information 
submitted on November 30, 2015, May 26, 2016, July 5, 2017, July 27, 
2017, and March 16, 2018. Our approval includes the following revisions 
to the Arkansas SIP:
     Revisions to Reg. 19.401 (submitted 07/26/2010 and 03/24/
2017);
     Revisions to Reg. 19.407(C)(2)(a) and (b) (submitted 07/
26/2010 and 03/24/2017); and
     Revisions to Reg. 19.417(A) and (B) (submitted 07/26/
2010).
    As previously stated in our proposed rulemaking, this final action 
does not remove or modify the existing federal and state requirements 
that each NSR permit action issued by ADEQ include an analysis 
completed by the Department and their determination that the proposed 
construction or modification authorized by the permit action will not 
interfere with attainment or maintenance of a national ambient air 
quality standard.

IV. Incorporation by Reference

    In this rule, the EPA is finalizing regulatory text that includes 
incorporation by reference. In accordance with requirements of 1 CFR 
51.5, the EPA is finalizing the incorporation by reference of the 
revisions to the Arkansas regulations as described in the Final Action 
section above. The EPA has made, and will continue to make, these 
materials generally available through www.regulations.gov and at the 
EPA Region 6 Office (please contact Ashley Mohr for more information). 
Therefore, these materials have been approved by EPA for inclusion in 
the SIP, have been incorporated by reference by EPA into that plan, are 
fully federally enforceable under sections 110 and 113 of the CAA as of 
the effective date of the final rulemaking of EPA's approval, and will 
be incorporated by reference in the next update to the SIP compilation.

V. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Act and 
applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, the EPA's role is to approve state 
choices, provided that they meet the criteria of the Clean Air Act. 
Accordingly, this action merely approves state law as meeting Federal 
requirements and does not impose additional requirements beyond those 
imposed by state law. For that reason, this action:
     Is not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Is not an Executive Order 13771 (82 FR 9339, February 2, 
2017) regulatory action because SIP approvals are exempted under 
Executive Order 12866;
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, described in the Unfunded Mandates 
Reform Act of 1995 (Pub. L. 104-4);
     Does not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the CAA; and
     Does not provide EPA with the discretionary authority to 
address, as appropriate, disproportionate human health or environmental 
effects, using practicable and legally permissible methods, under 
Executive Order 12898 (59 FR 7629, February 16, 1994).

In addition, the SIP is not approved to apply on any Indian reservation 
land or in any other area where EPA or an Indian tribe has demonstrated 
that a tribe has jurisdiction. In those areas of Indian country, the 
rule does not have tribal implications and will not impose substantial 
direct costs on tribal

[[Page 30570]]

governments or preempt tribal law as specified by Executive Order 13175 
(65 FR 67249, November 9, 2000).
    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. EPA will submit a report containing this action and 
other required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal Register. A major rule cannot 
take effect until 60 days after it is published in the Federal 
Register. This action is not a ``major rule'' as defined by 5 U.S.C. 
804(2).
    Under section 307(b)(1) of the Clean Air Act, petitions for 
judicial review of this action must be filed in the United States Court 
of Appeals for the appropriate circuit by August 28, 2018. Filing a 
petition for reconsideration by the Administrator of this final rule 
does not affect the finality of this action for the purposes of 
judicial review nor does it extend the time within which a petition for 
judicial review may be filed, and shall not postpone the effectiveness 
of such rule or action. This action may not be challenged later in 
proceedings to enforce its requirements. (See section 307(b)(2).)

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting 
and recordkeeping requirements, Sulfur oxides, Volatile organic 
compounds.

    Dated: June 20, 2018.
Anne Idsal,
Regional Administrator, Region 6.

    40 CFR part 52 is amended as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

    Authority:  42 U.S.C. 7401 et seq.

Subpart E--Arkansas

0
2. In Sec.  52.170(c), the table titled ``EPA-Approved Regulations in 
the Arkansas SIP'' is amended by:
0
a. Revising entries for Reg. 19.401 and Reg. 19.407; and
0
b. Adding an entry for Reg. 19.417 immediately following the entry for 
Reg. 19.413.
    The amendments read as follows:

Sec.  52.170  Identification of plan.

* * * * *
    (c) * * *

                                  EPA-Approved Regulations in the Arkansas SIP
----------------------------------------------------------------------------------------------------------------
                                                             State
                                                           submittal/
    State citation                Title/subject            effective    EPA approval date        Explanation
                                                              date
----------------------------------------------------------------------------------------------------------------
         Regulation No. 19: Regulations of the Arkansas Plan of Implementation for Air Pollution Control
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                         Chapter 4: Minor Source Review
----------------------------------------------------------------------------------------------------------------
Reg. 19.401...........  General Applicability...........     03/24/17  6/29/2018, [Insert   Includes
                                                                        Federal Register     supplemental
                                                                        citation].           information
                                                                                             provided on 11/30/
                                                                                             2015, 05/26/2016,
                                                                                             07/05/2017, and
                                                                                            03/16/2018.
 
                                                  * * * * * * *
Reg. 19.407...........  Permit Amendments...............     03/24/17  6/29/2018, [Insert   Includes
                                                                        Federal Register     supplemental
                                                                        citation].           information
                                                                                             provided on 11/30/
                                                                                             2015, 05/26/2016,
                                                                                             07/05/2017, 07/27/
                                                                                             2017, and 03/16/
                                                                                             2018.
 
                                                  * * * * * * *
Reg. 19.417...........  Registration....................     07/26/10  6/29/2018, [Insert   Includes
                                                                        Federal Register     supplemental
                                                                        citation].           information
                                                                                             provided on 11/30/
                                                                                             2015, 05/26/2016,
                                                                                             07/05/2017, and
                                                                                            03/16/2018.
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------

* * * * *
[FR Doc. 2018-13942 Filed 6-28-18; 8:45 am]
 BILLING CODE 6560-50-P