Document ID: EPA-R08-OAR-2020-0741-0001
Agency: epa
Document Type: Proposed Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: Montana; Butte PM10 Nonattainment Area Limited Maintenance Plan and Redesignation Request
Posted Date: 2021-04-19T04:00Z

[Federal Register Volume 86, Number 73 (Monday, April 19, 2021)]
[Proposed Rules]
[Pages 20353-20359]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-07793]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R08-OAR-2020-0741; FRL-10022-27-Region 8]

Approval and Promulgation of Implementation Plans; Montana; Butte 
PM10 Nonattainment Area Limited Maintenance Plan and Redesignation 
Request

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
fully approve the Limited Maintenance Plan (LMP) submitted by the State 
of Montana to EPA on March 23, 2020, for the Butte Moderate 
nonattainment area (NAA) for particulate matter with an aerodynamic 
diameter less than or equal to a nominal 10 micrometers 
(PM10) and concurrently redesignate the NAA to attainment 
for the 24-hour PM10 National Ambient Air Quality Standard 
(NAAQS). In order to approve the LMP and redesignation, EPA is 
proposing to determine that the Butte, MT NAA has attained the 1987 24-
hour PM10 NAAQS of 150 [micro]g/m\3\. This determination is 
based upon monitored air quality data for the PM10 NAAQS 
during the years 2014-2018. EPA is taking this action pursuant to the 
Clean Air Act (CAA).

DATES: Written comments must be received on or before May 19, 2021.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2020-0741 to the Federal Rulemaking Portal: https://www.regulations.gov. Follow the online instructions for submitting 
comments. Once submitted, comments cannot be edited or removed from 
www.regulations.gov. The EPA may publish any comment received to its 
public docket. Do not submit electronically any information you 
consider to be Confidential Business Information (CBI) or other 
information whose disclosure is restricted by statute. Multimedia 
submissions (audio, video, etc.) must be accompanied by a written 
comment. The written comment is considered the official comment and 
should include discussion of all points you wish to make. The EPA will 
generally not consider comments or comment contents located outside of 
the primary submission (i.e., on the web, cloud, or other file sharing 
system). For additional submission methods, the full EPA public comment 
policy, information about CBI or multimedia submissions, and general 
guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
    Docket: All documents in the docket are listed in the 
www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available electronically in 
www.regulations.gov. To reduce the risk of COVID-19 transmission, for 
this action we do not plan to offer hard copy review of the docket. 
Please email or call the person listed in the FOR FURTHER INFORMATION 
CONTACT section if you need to make alternative arrangements for access 
to the docket.

FOR FURTHER INFORMATION CONTACT: Kate Gregory, Air and Radiation 
Division, U.S. Environmental Protection Agency (EPA), Region 8, Mail 
Code 8P-ARD-QP, 1595 Wynkoop Street, Denver, Colorado 80202-1129, (303) 
312-6175, gregory.kate@epa.gov.

SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,'' 
``us,'' or ``our'' is used, we mean the EPA.

I. Background

Description of the Butte NAA

    The Butte NAA is the only NAA in Silver Bow County, is irregularly 
shaped, and generally encompasses the populated areas surrounding the 
city of Butte, except for the town of Walkerville. Butte was originally 
designated as a Group I area on August 7, 1987, meaning it was likely 
to violate the PM10 NAAQS, and was subsequently classified 
as a Moderate NAA for the 1987 24-hour PM10 NAAQS on March 
15, 1991. See 56 FR 11101. States containing initial Moderate 
PM10 NAAs were required to submit, by November 15, 1991, a 
Moderate NAA State Implementation Plan (SIP) that, among other 
requirements, implemented Reasonably Available Control Measures (RACM) 
by December 10, 1993, and demonstrated whether it was practicable to 
attain the PM10 NAAQS by December 31, 1994. See generally 57 
FR 13498 (April 16, 1992); see also 57 FR 18070 (April 28, 1992).
    The State of Montana submitted an initial PM10 SIP to 
EPA on July 9, 1992, and a subsequent submission on January 13, 1993. 
EPA approved the Butte initial control plan on March 11, 1994 (59 FR 
11550). Revisions to emissions limits, associated attainment and 
maintenance demonstrations and contingency measures were submitted to 
EPA on August 26, 1994. The State of Montana's SIP for the Butte 
Moderate NAA included, among other things: A comprehensive emissions 
inventory; RACM; A demonstration that attainment of the PM10 
NAAQS would be achieved in Butte by December 31, 1994; Reasonable 
Further Progress (RFP) requirements; and control measures that satisfy 
the contingency measures requirement of section 172(c)(9) of the CAA. 
The EPA fully approved the Butte NAA PM10 attainment plan on 
March 22, 1995 (60 FR 15056).

II. Requirements for Redesignation

A. CAA Requirements for Redesignation of NAAs

    NAAs can be redesignated to attainment after the area has measured 
air quality data showing it has attained the NAAQS and when certain 
planning requirements are met. Section 107(d)(3)(E) of the CAA, and the 
General Preamble to Title I provide the criteria for redesignation. See 
57 FR 13498 (April 16, 1992). These criteria are further clarified in a 
policy and guidance memorandum from John Calcagni, Director, Air 
Quality Management Division, EPA Office of Air Quality Planning and 
Standards dated September 4, 1992, ``Procedures for Processing Requests 
to Redesignate Areas to Attainment.\1\ '' The criteria for 
redesignation are:
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    \1\ The ``Procedures for Processing Requests to Redesignate 
Areas to Attainment'' (Calcagni memo) outlines the criteria for 
redesignation (see docket for memo).
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    (1) The Administrator has determined that the area has attained the 
applicable NAAQS;
    (2) The Administrator has fully approved the applicable SIP for the 
area under section 110(k) of the CAA;
    (3) The state containing the area has met all requirements 
applicable to the area under section 110 and part D of the CAA;
    (4) The Administrator has determined that the improvement in air 
quality is due to permanent and enforceable reductions in emissions; 
and
    (5) The Administrator has fully approved a maintenance plan for the 
area as meeting the requirements of section 175A of the CAA.

[[Page 20354]]

B. The LMP Option for PM10 NAAs

    On August 9, 2001, the EPA issued guidance on streamlined 
maintenance plan provisions for certain moderate PM10 NAAs 
seeking redesignation to attainment (Memo from Lydia Wegman, Director, 
Air Quality Standards and Strategies Division, entitled ``Limited 
Maintenance Plan Option for Moderate PM10 Nonattainment 
Areas,'' (hereafter the LMP Option memo)).\2\ The LMP Option memo 
contains a statistical demonstration to show that areas meeting certain 
air quality criteria will, with a high degree of probability, maintain 
the standard 10 years into the future. Thus, the EPA has already 
provided the maintenance demonstration for areas meeting the criteria 
outlined in the LMP Option memo. It follows that future year emission 
inventories for these areas, and some of the standard analyses to 
determine transportation conformity with the SIP are no longer 
necessary.
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    \2\ The ``Limited Maintenance Plan Option for Moderate 
PM10 Nonattainment Areas'' outlines the criteria for 
development of a PM10 limited maintenance plan (see 
docket for memo).
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    To qualify for the LMP Option, the area should have attained the 
1987 24-hour PM10 NAAQS, based upon the most recent 5 years 
of air quality data at all monitors in the area, and the 24-hour design 
value should be at or below the Critical Design Value (CDV). The CDV is 
a calculated design value that indicates that the area has a low 
probability (1 in 10) of exceeding the NAAQS in the future. For the 
purposes of qualifying for the LMP option, a presumptive CDV of 98 
[micro]g/m\3\ is most often employed, but an area may elect to use a 
site-specific CDV should the average design value be above 98 [micro]g/
m\3\, while demonstrating that the area has a low probability of 
exceeding the NAAQS in the future. The annual PM10 standard 
was effectively revoked on December 18, 2006 (71 FR 61143), and as such 
will not be discussed as a requirement for qualifying for the LMP 
option. In addition, the area should expect only limited growth in on-
road motor vehicle PM10 emissions (including fugitive dust) 
and should have passed a motor vehicle regional emissions analysis 
test. The LMP Option memo also identifies core provisions that must be 
included in the LMP. These provisions include an attainment year 
emissions inventory, assurance of continued operation of an EPA-
approved air quality monitoring network, and contingency provisions.

C. Conformity Under the LMP Option

    The transportation conformity rule (40 CFR parts 51 and 93) and the 
general conformity rule (40 CFR parts 51 and 93) apply to NAAs and 
maintenance areas covered by an approved maintenance plan. Under either 
conformity rule, an acceptable method of demonstrating that a federal 
action conforms to the applicable SIP is to demonstrate that expected 
emissions from the planned action are consistent with the emissions 
budget for the area.
    While the EPA's LMP Option does not exempt an area from the need to 
affirm conformity, it explains that the area may demonstrate conformity 
without submitting an emissions budget. Under the LMP Option, emissions 
budgets are treated as essentially not constraining for the length of 
the maintenance period because it is unreasonable to expect that the 
qualifying areas would experience so much growth in that period that a 
violation of the PM10 NAAQS would result. For transportation 
conformity purposes, the EPA would conclude that emissions in these 
areas need not be capped for the maintenance period; and therefore, a 
regional emissions analysis would not be required. Similarly, federal 
actions subject to the general conformity rule could be considered to 
satisfy the ``budget test'' specified in 40 CFR 93.158(a)(5)(i)(A) for 
the same reasons that the budgets are essentially considered not 
limited.

III. Review of Montana's Submittal Addressing the Requirements for 
Redesignation and Limited Maintenance Plan

A. Has the Butte NAA attained the applicable NAAQS?

    States must demonstrate that an area has attained the 24-hour 
PM10 NAAQS through analysis of ambient air quality data from 
an ambient air monitoring network representing peak PM10 
concentrations. The data should be stored in the EPA Air Quality System 
(AQS) database. Today, EPA is proposing to determine that the Butte NAA 
has attained the PM10 NAAQS based on monitoring data from 
calendar years 2014-2018. The 24-hour standard is attained when the 
expected number of days with levels above 150 [micro]g/m\3\ (averaged 
over a 3-year period) is less than or equal to one. See 40 CFR 50.6(a). 
Three consecutive years of air quality data are generally necessary to 
show attainment of the 24-hour and annual standards for 
PM10. See 40 CFR part 50, appendix K. A complete year of air 
quality data, as referred to in 40 CFR part 50, appendix K, is 
comprised of all four calendar quarters with each quarter containing 
data from at least 75% of the scheduled sampling days.
    The Butte NAA has one State and Local Air Monitoring Station 
(SLAMS) monitor operated by the Montana Department of Environmental 
Quality (MDEQ). Table 1 summarizes the PM10 data collected 
from 2014-2019 for the Butte NAA.\3\ The EPA deems the data collected 
from these monitors valid, and the data have been submitted by the MDEQ 
to be included in AQS.
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    \3\ While the submission from the State for this action includes 
2014-2018 monitoring data, the EPA supplied 2019 monitoring data in 
this action in order to provide an analysis of PM10 
concentrations in the Butte, MT area using the most current 
monitoring data available.

           Table 1--Summary of Maximum 24-Hour PM10 Concentrations ([micro]g/m\3\) for Butte 2014-2019
                [Based on data from Greeley School site, AQS identification number (30-093-0005)]
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                                    Maximum          2nd Maximum         Number of
             Year                concentration      concentration       exceedances         Monitoring  site
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2014.........................                 60                 57                  0  Greeley School.
2015.........................                118                115                  0  Greeley School.
2016.........................                 52                 51                  0  Greeley School.
2017.........................                144                111                  0  Greeley School.
2018.........................                 72                 66                  0  Greeley School.
2019.........................                 69                 56                  0  Greeley School.
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    The PM10 concentrations reported at the Butte monitoring 
site showed no measured exceedances of the 24-hour PM10 
NAAQS from 2014-2018, and as such, the EPA proposes to determine that 
the Butte NAA has attained the

[[Page 20355]]

standard for the 24-hour PM10 NAAQS. Additionally, EPA 
analysis of PM10 concentrations reported at the Butte 
monitoring site in the year 2019 show no measured exceedances.

B. Does the Butte NAA have a fully approved SIP under CAA section 
110(k)?

    In order to qualify for redesignation, the SIP for the area must be 
fully approved under CAA section 110(k) and must satisfy all 
requirements that apply to the area. Section 189 of the CAA contains 
requirements and milestones for all initial Moderate NAA SIPs 
including: (1) Provisions to assure that RACM (including such 
reductions in emissions from existing sources in the area as may be 
obtained through the adoption, at a minimum, of Reasonably Available 
Control Technology (RACT) shall be implemented no later than December 
10, 1993; (2) A demonstration (including air quality modeling) that the 
plan will provide for attainment as expeditiously as practicable by no 
later than December 31, 1994, or, where the state is seeking an 
extension of the attainment date under section 188(e), a demonstration 
that attainment by December 31, 1994, is impracticable and that the 
plan provides for attainment by the most expeditious alternative date 
practicable (CAA sections 189(a)(1)(A)); (3) Quantitative milestones 
which are to be achieved every 3 years and which demonstrate RFP toward 
attainment by December 31, 1994, (CAA sections 172(c)(2) and 189(c)); 
and (4) Contingency measures to be implemented if the area fails to 
make RFP or attain by its attainment deadline. These contingency 
measures are to take effect without further action by the state or the 
EPA. (CAA section 172(c)(9)).
    The EPA approved the Butte Moderate area plan on May 22, 1995 (60 
FR 15056). The Butte plan included RACM, an attainment demonstration, 
emissions inventory, quantitative milestones, and control and 
contingency measure requirements. As such, the area has a fully 
approved NAA SIPs under section 110(k) of the CAA.

C. Has the State met all applicable requirements under section 110 and 
Part D of the CAA?

    Section 107(d)(3)(E) of the CAA requires that a state containing a 
NAA must meet all applicable requirements under section 110 and Part D 
of the CAA for an area to be redesignated to attainment. The EPA 
interprets this to mean that the state must meet all requirements that 
applied to the area prior to, and at the time of, the submission of a 
complete redesignation request. The following is a summary of how 
Montana meets these requirements.
1. CAA Section 110 Requirements
    Section 110(a)(2) of the CAA contains general requirements for 
SIPs. These requirements include, but are not limited to, submittal of 
a SIP that has been adopted by the state after reasonable notice and 
public hearing; provisions for establishment and operation of 
appropriate apparatus, methods, systems and procedures necessary to 
monitor ambient air quality; implementation of a permit program; 
provisions for Part C--Prevention of Significant Deterioration (PSD) 
and Part D--New Source Review (NSR) permit programs; criteria for 
stationary source emission control measures, monitoring and reporting, 
provisions for modeling; and provisions for public and local agency 
participation. See the General Preamble for further explanation of 
these requirements. See 57 FR 13498 (April 16, 1992).
    For purposes of redesignation, the EPA's review of the Montana SIP 
shows that the State has satisfied all requirements under section 
110(a)(2) of the CAA. Further, in 40 CFR 52.1372, the EPA has approved 
Montana's plan for the attainment and maintenance of the national 
standards under section 110.
2. Part D Requirements
    Part D contains general requirements applicable to all areas 
designated nonattainment. The general requirements are followed by a 
series of subparts specific to each pollutant. All PM10 NAAs 
must meet the general provisions of Subpart 1 and the specific 
PM10 provisions in Subpart 4, ``Additional Provisions for 
Particulate Matter Nonattainment Areas.'' The following paragraphs 
discuss these requirements as they apply to the Butte NAA.
3. Subpart 1, Section 172(c)
    Subpart 1, section 172(c) contains general requirements for NAA 
plans. A thorough discussion of these requirements may be found in the 
General Preamble. See 57 FR 13538 (April 16, 1992). CAA section 
172(c)(2) requires nonattainment plans to provide for RFP. Section 
171(1) of the CAA defines RFP as ``such annual incremental reductions 
in emissions of the relevant air pollutant as are required by this part 
(part D of title I) or may reasonably be required by the Administrator 
for the purpose of ensuring attainment of the applicable national 
ambient air quality standard by the applicable date.'' Since EPA is 
proposing to determine that the Butte NAA is in attainment of the 
PM10 NAAQS, we believe that no further showing of RFP or 
quantitative milestones is necessary.
4. Section 172(c)(3)--Emissions Inventory Section
    Section 172(c)(3) of the CAA requires a comprehensive, accurate, 
current inventory of actual emissions from all sources in the Butte 
PM10 NAA. Montana included an emissions inventory for the 
calendar year 2014 with the March 23, 2020 submittal of the LMP for the 
NAA. The LMP Option memo states that an attainment inventory should 
represent emissions during the same 5-year period associated with the 
air quality data used to determine that the area meets the 
applicability requirements of the LMP option. The Butte LMP includes an 
emission inventory from 2014, representative of the 2013-2017 5-year 
period which served as the 5-year period relied upon in the LMPs as 
meeting the air quality data requirements of the LMP option memo.\4\
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    \4\ The emissions inventory included in the Butte MT submission 
is the 2014 National Emissions Inventory (NEI). The NEI is a 
composite of data from many different sources, with PM data coming 
primarily from EPA models as well as from state, tribal, and local 
air quality management agencies. Different data sources use 
different data collection methods, and many of the emissions data 
are based on estimates rather than actual measurements. The EPA 
considers the 2014 NEI representative of the period from 2014-2018 
because MT provided comparable vehicle miles traveled (VMT) data in 
their submission. See Butte, MT Submission, Appendix C, Montana 
Department of Transportation Future VMT Projections, p.C-1 in 
docket.
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5. Section 172(c)(5)--NSR
    The 1990 CAA Amendments contained revisions to the NSR program 
requirements for the construction and operation of new and modified 
major stationary sources located in NAAs. The CAA requires states to 
amend their SIPs to reflect these revisions but does not require 
submittal of this element along with the other SIP elements. The CAA 
established June 30, 1992, as the submittal date for the revised NSR 
programs (section 189 of the CAA).
    Montana has a fully approved nonattainment NSR program, approved on 
August 30, 1995 (60 FR 45051). Montana also has a fully approved PSD 
program, approved on August 30, 1995 (60 FR 45051). Upon the effective 
date of redesignation of an area from nonattainment to attainment, the 
requirements of the Part D NSR program will be replaced by the PSD 
program and the maintenance area NSR program.

[[Page 20356]]

6. Section 172(c)(7)--Compliance With CAA Section 110(a)(2): Air 
Quality Monitoring Requirements
    Once an area is redesignated, the state must continue to operate an 
appropriate air monitoring network in accordance with 40 CFR part 58 to 
verify attainment status of the area. The State of Montana operates one 
PM10 SLAMS in each of the NAAs. The Butte monitoring site 
meets EPA SLAMS network design and siting requirements set forth at 40 
CFR part 58, appendices D and E. In section 3.5 of the LMP that we are 
proposing to approve, the State commits to continued operation of the 
monitoring network.
7. Section 172(c)(9)--Contingency Measures
    The CAA requires that contingency measures take effect if the area 
fails to meet RFP requirements or fails to attain the NAAQS by the 
applicable attainment date. Since the Butte NAA has attained the 1987 
24-hour PM10 NAAQS, contingency measures are no longer 
required under section 172(c)(9) of the CAA. However, contingency 
provisions are required for maintenance plans under section 175(a)(d). 
We describe the contingency provisions Montana provided in the LMP 
section below.
8. Part D Subpart 4
    Part D subpart 4, section 189(a), (c) and (e) requirements apply to 
any Moderate NAA before the area can be redesignated to attainment. The 
requirements which were applicable prior to the submission of the 
request to redesignate the area must be fully approved into the SIP 
before redesignating the area to attainment. These requirements 
include: (a) Provisions to assure that RACM was implemented by December 
10, 1993; (b) Either a demonstration that the plan provided for 
attainment as expeditiously as practicable but not later than December 
31, 1994, or a demonstration that attainment by that date was 
impracticable; (c) Quantitative milestones which were achieved every 3 
years and which demonstrate RFP toward attainment by December 31, 1994; 
and (d) Provisions to assure that the control requirements applicable 
to major stationary sources of PM10 also apply to major 
stationary sources of PM10 precursors except where the 
Administrator determined that such sources do not contribute 
significantly to PM10 levels which exceed the NAAQS in the 
area. These provisions were fully approved into the SIP upon the EPA's 
approval of the PM10 Moderate area plan for the Butte NAA on 
March 22, 1995 (60 FR 15056).

D. Has the State demonstrated that the air quality improvement is due 
to permanent and enforceable reductions?

    The state must be able to reasonably attribute the improvement in 
air quality to permanent and enforceable emission reductions. In making 
this showing, the state must demonstrate that air quality improvements 
are the result of actual enforceable emission reductions. This showing 
should consider emission rates, production capacities, and other 
related information. The analysis should assume that sources are 
operating at permitted levels (or historic peak levels) unless evidence 
is presented that such an assumption is unrealistic. Permanent and 
enforceable control measures in the Butte NAA SIP includes RACM. 
Emission sources in the NAA has been implementing RACM for at least 10 
years.
    Areas that qualify for the LMP will meet the NAAQS, even under 
worst case meteorological conditions. Under the LMP option, the 
maintenance demonstration is presumed to be satisfied if an area meets 
the qualifying criteria. Thus, by qualifying for the LMP, Montana has 
demonstrated that the air quality improvements in the Butte NAA is the 
result of permanent emission reductions and not a result of either 
economic trends or meteorology. A description of the LMP qualifying 
criteria and how the Butte area meets these criteria is provided in the 
following section.
    Permanent and enforceable emission reductions in the Butte NAA have 
reduced emissions 76% since 1990. The primary controls incorporated 
into the SIP included rules specifying wood combustion control, rules 
specifying open burning controls, rules specifying fugitive road dust 
control, permit condition revisions at the Montana Resources mine, 
crusher, and concentrator and at Rh[ocirc]ne-Poulenc industrial 
sources, and federal tailpipe standards. Based on the 2014 national 
emissions inventory, PM10 emissions in all source areas are 
below the levels approved in the original control plan.\5\
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    \5\ See Butte, MT submission in docket, Table 2.4--Butte, MT--
PM10 Emission Summary, p. 18.
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E. Does the area have a fully approved maintenance plan pursuant to 
section 175A of the CAA?

    In this action, we are proposing to approve the LMP for the Butte 
NAA in accordance with the principles outlined in the LMP Option.

F. Has the State demonstrated that the Butte NAA qualifies for the LMP 
Option?

    The LMP Option memo outlines the requirements for an area to 
qualify for the LMP Option. First, the area should be attaining the 
NAAQS. As stated above in Section III. A., the EPA has determined that 
the Butte NAA is attaining the PM10 NAAQS.
    Second, the average design value (ADV) for the past 5 years of 
monitoring data (2014-2018) must be at or below the CDV. As noted in 
Section II.B., the CDV is a margin of safety value and is the value at 
which an area has been determined to have a 1 in 10 probability of 
exceeding the NAAQS. The LMP Option memo provides two methods for 
review of monitoring data for the purpose of qualifying for the LMP 
option. The first method is a comparison of a site's ADV with the CDV 
of 98 [micro]g/m\3\ for the 24-hour PM10 NAAQS. A second 
method that applies to the 24-hour PM10 NAAQS is the 
calculation of a site-specific CDV and a comparison of the site-
specific CDV with the ADV for the past 5 years of monitoring data. 
Table 2 outlines the design values for the years 2014-2018, and 
presents the ADC.
    Table 3 summarizes the wildfire related events that were excluded 
from the calculated design values in Table 2. Table 3 include all 
regionally concurred exceptional events, as well as values between 98 
[micro]g/m\3\ and 155 [micro]g/m\3\, which were treated in a manner 
analogous to exceedance data under the Exceptional Events Rule (EER) 
for the purpose of determining the LMP option eligibility. The values 
between 98 [micro]g/m\3\ and 155 [micro]g/m\3\ will remain in the Air 
Quality System (AQS) database for use in calculating DV's for every 
purpose besides determining LMP eligibility.\6\ The EER can be found in 
40 CFR 50.14 and 40 CFR 51.930, and outlines the requirements for the 
treatment of monitored air quality data that has been heavily 
influenced by an exceptional event. 40 CFR 50.1(j) defines an 
exceptional event as an event which affects air quality, is not 
reasonably controllable or preventable, is an event caused by human 
activity that is unlikely to recur at a particular location or a 
natural event and is determined by the Administrator in accordance with 
40 CFR 50.14 to be an exceptional event. Exceptional events do not 
include stagnation of air masses or meteorological inversions,

[[Page 20357]]

meteorological events involving high temperatures or lack of 
precipitation, or air pollution relating to source noncompliance. 40 
CFR 50.14(b) states that the EPA shall exclude data from use in 
determinations of exceedances and NAAQS violations where a state 
demonstrates to the EPA's satisfaction that an exceptional event caused 
a specific air pollution concentration in excess of one or more NAAQS 
at a particular air quality monitoring location and otherwise satisfies 
the requirements of section 50.14. Table 3 below includes some 
exceptional events not formally concurred on by EPA. These exceptional 
events were excluded by EPA in accordance with the LMP guidance.\7\ We 
have concurred that these values can be excluded for the sole purpose 
of determining PM10 LMP eligibility and supporting 
documentation of EPA's concurrence with the wildfire related events can 
be found in the docket.\8\
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    \6\ Update on Application of the Exceptional Events Rule to the 
PM10 Limited Maintenance Plan Option, U.S. EPA, William 
T. Harnett, Director, Air Quality Policy Division, OAQPS, May 7, 
2009.
    \7\ See Update on Application of the Exceptional Events Rule to 
the PM10 Limited Maintenance Plan Option, U.S. EPA, 
William T. Harnett, Director, Air Quality Policy Division, OAQPS, 
May 7, 2009 and Additional Methods, Determinations, and Analyses to 
Modify Air Quality Data Beyond Exceptional Events, U.S. EPA, Richard 
Wayland, Director, Air Quality Assessment Division and Anna Marie 
Wood, Director, Air Quality Policy Division, April 4, 2019 memos in 
docket.
    \8\ February 8, 2019 letter to MDEQ, Re: Exceptional Events 
Requests Regarding Exceedances of the 24-hour PM10 NAAQS 
and the LMP Eligibility Threshold at Montana Monitoring Sites with 
PM10 Nonattainment Areas; and November 1, 2018 letter to 
MDEQ, Re: Request for EPA concurrence on exceptional event claims 
for fine (PM2.5) and coarse (PM10) particulate 
matter data impacted by wildfires in 2015 and 2016. See Butte, MT 
submission in docket.

            Table 2-Summary of 24-Hour PM10 Design Concentrations ([micro]g/m\3\) for Butte 2014-2018
                [Based on data from Greeley School site, AQS identification number (30-029-0049)]
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                                                Design concentration
          Design concentration years               ([micro]g/m\3\)                  Monitoring site
----------------------------------------------------------------------------------------------------------------
2014-2016.....................................                    60  Greeley School.
2015-2017.....................................                    85  Greeley School.
2016-2018.....................................                    80  Greeley School.
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Average Design Concentration (Of Most Recent 3 Design                 75 [micro]g/m\3\
 Concentrations)
----------------------------------------------------------------------------------------------------------------

      Table 3-Butte 24-Hour PM10 Events Excluded From the 2014-2019 Data for the Purpose of Determining LMP
                                                   Eligibility
----------------------------------------------------------------------------------------------------------------
                                                    24-Hour value
                     Date                          ([micro]g/m\3\)                  Monitoring site
----------------------------------------------------------------------------------------------------------------
8/15/2015.....................................                   100  Greeley School.
8/20/2015.....................................                   103  Greeley School.
8/28/2015.....................................                   115  Greeley School.
8/29/2015.....................................                   118  Greeley School.
9/2/2017......................................                   111  Greeley School.
9/3/2017......................................                   144  Greeley School.
----------------------------------------------------------------------------------------------------------------
These values were excluded by EPA solely for the purpose of determining limited maintenance plan (LMP)
  eligibility in accordance with LMP guidance. The values remain in AQS and are still used for all other
  purposes (including calculating the estimated exceedances and official design concentrations).

    The ADV for the 24-hour PM10 NAAQS for Butte, based on 
data from the SLAMS monitor for the years 2014-2018 is 75 [micro]g/
m\3\. This value falls below the presumptive 24-hour CDV of 98 
[micro]g/m\3\ and would all meet the first threshold for LMP 
eligibility.
    In addition to having an ADV that is lower than either the 
presumptive or area specific CDV, and in order to qualify for the LMP, 
the area must meet the motor vehicle regional emissions analysis test 
in attachment B of the LMP Option memo. Using the methodology outlined 
in the memo, based on monitoring data for the period 2014-2018, the EPA 
has determined that the Butte NAA passes the motor vehicle regional 
emissions analysis test, with a projected design value of 74.3 
[micro]g/m\3\ after 10 years, respectively, attributable to motor 
vehicle emission growth. For the calculations used to determine how the 
Butte NAA passed the motor vehicle regional analysis test, see the 
supporting documents in the docket.\9\
---------------------------------------------------------------------------

    \9\ See memo to file in docket dated February 16, 2021 titled 
``Memo to File--Butte, MT Motor Vehicle Regional Emissions 
Analysis''.
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    The monitoring data for the period 2014-2018 shows that Butte has 
attained the 24-hour NAAQS for PM10, and the 24-hour ADV for 
the area is less than the 24-hour PM10 presumptive and area-
specific CDV. Finally, the area has met the regional vehicle emissions 
analysis test. Thus, the Butte NAA qualifies for the LMP Option 
described in the LMP Option memo. The LMP Option memo also indicates 
that once a state selects the LMP Option and it is in effect, the state 
will be expected to determine, on an annual basis, that the LMP 
criteria are still being met. If the state determines that the LMP 
criteria are not being met, it should take action to reduce 
PM10 concentrations enough to requalify for the LMP. One 
possible approach the state could take is to implement contingency 
measures. Please see section 3.6 of the Butte LMP for a description of 
contingency provisions submitted as part of the State's submittal.

G. Does the State have an approved attainment emissions inventory which 
can be used to demonstrate attainment of the NAAQS?

    The state's approved attainment plan should include an emissions 
inventory (attainment inventory) which can be used to demonstrate 
attainment of the NAAQS. The inventory should represent emissions 
during the same 5-year period associated with air quality data used to 
determine whether the area meets the applicability requirements of the 
LMP Option. The state should review its inventory every 3 years to 
ensure emissions growth is incorporated in the attainment inventory if 
necessary.

[[Page 20358]]

In this instance, Montana completed an attainment year inventory for 
the attainment year 2014 for the Butte NAA. The EPA has reviewed the 
2014 emissions inventories and determined that they are current, 
accurate and complete. In addition, the emissions inventory submitted 
with the LMP for the calendar year 2014 is representative of the level 
of emissions during the time period used to calculate the ADV since 
2014 is included in the 5-year period used to calculate the design 
values (2014-2018).

H. Does the LMP include an assurance of continued operation of an 
appropriate epa-approved air quality monitoring network, in accordance 
with 40 CFR part 58?

    The PM10 monitoring network for the Butte NAA has been 
developed and maintained in accordance with federal siting and design 
criteria in 40 CFR part 58, appendices D and E and in consultation with 
the EPA Region 8. In Section 3.5 of the Butte LMP, Montana states that 
it will continue to operate its monitoring network to meet EPA 
requirements.

I. Does the plan meet the CAA requirements for contingency provisions 
for maintenance plans?

    Section 175A of the CAA states that a maintenance plan must include 
contingency provisions, as necessary, to promptly correct any violation 
of the NAAQS which may occur after redesignation of the area to 
attainment. As explained in the LMP Option memo, these contingency 
measures do not have to be fully adopted at the time of redesignation. 
As noted above, CAA section 175A requirements are distinct from CAA 
section 172(c)(9) contingency measures. Section 3.6 of the Butte LMP 
describes a process and timeline to identify and evaluate appropriate 
contingency measures in the event of a quality assured violation of the 
PM10 NAAQS. Upon notification of a PM10 
exceedance in any of the three areas, the MDEQ and the appropriate 
local government will develop contingency measures designed to prevent 
or correct a violation of the PM10 standard. This process 
will be completed within twelve months of the exceedance notification. 
Upon violating the PM10 standard, the MDEQ and local 
government will determine if the local contingency measures will be 
adequate to prevent further exceedances or violations. If the agencies 
determine that local measures will be inadequate, the MDEQ and local 
government will adopt state-enforceable measures.
    The current and proposed contingency provisions in the Butte LMP 
meet the requirements for contingency provisions as outlined in the LMP 
Option memo.

J. Has the State met transportation and general conformity 
requirements?

1. Transportation Conformity
    Transportation conformity is required by section 176(c) of the CAA. 
Conformity to a SIP means that transportation activities will not 
produce new air quality violations, worsen existing violations, or 
delay timely attainment of the NAAQS (CAA section 176(c)(1)(B)). The 
EPA's conformity rule at 40 CFR part 93, subpart A requires that 
transportation plans, programs and projects conform to SIPs and 
establishes the criteria and procedures for determining whether or not 
they conform. To effectuate its purpose, the conformity rule typically 
requires a demonstration that emissions from the applicable Regional 
Transportation Plan and the Transportation Improvement Program are 
consistent with the motor vehicle emission budget (MVEB) contained in 
the control strategy SIP revision or maintenance plan (40 CFR 93.101, 
93.118, and 93.124). The EPA notes that a MVEB is usually defined as 
the level of mobile source emissions of a pollutant relied upon in the 
attainment or maintenance demonstration to attain or maintain 
compliance with the NAAQS in the nonattainment or maintenance areas. 
MVEBs are, however, treated differently with respect to LMP areas.\10\
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    \10\ Further information concerning the EPA's interpretations 
regarding MVEBs can be found in the preamble to the EPA's November 
24, 1993, transportation conformity rule (see 58 FR 62193-62196).
---------------------------------------------------------------------------

    Our LMP Option memorandum does not require that MVEBs be identified 
in the maintenance plan. While the EPA's LMP Option memorandum does not 
exempt an area from the need to affirm conformity, it explains that the 
area may demonstrate transportation conformity without identifying and 
submitting a MVEB. The basis for this provision is that it is 
unreasonable to expect that an LMP area will experience so much growth 
during the maintenance period that a violation of the PM10 
NAAQS would result. Therefore, for transportation conformity purposes, 
the EPA has concluded that mobile source emissions in LMP areas need 
not be capped, with respect to a MVEB, for the maintenance period and a 
regional emissions analysis (40 CFR 93.118), for transportation 
conformity purposes, is also not required.
    However, since LMP areas are still maintenance areas, certain 
aspects will continue to be required for transportation projects 
located within the Butte PM10 maintenance area. 
Specifically, for conformity determinations, projects will have to 
demonstrate that they are fiscally constrained (40 CFR 93.108) and meet 
the criteria for consultation (40 CFR 93.105 and 40 CFR 93.112) and 
timely implementation (as applicable) of Transportation Control 
Measures (40 CFR 93.113). In addition, projects located within the 
Butte PM10 LMP area will be required to be evaluated for 
potential PM10 hot-spot issues in order to satisfy the 
``project level'' conformity determination requirements. As 
appropriate, a project may then need to address the applicable criteria 
for a PM10 hot-spot analysis as provided in 40 CFR 93.116 
and 40 CFR 93.123.
    Finally, our proposed approval of the Butte PM10 LMP may 
affect future PM10 project-level transportation conformity 
determinations prepared by the Montana Department of Transportation in 
conjunction with the Federal Highway Administration and the Federal 
Transit Administration. See 40 CFR 93.100. As such, the EPA is 
proposing to approve the Butte LMP as meeting the appropriate 
transportation conformity requirements found in 40 CFR part 93, subpart 
A.
2. General Conformity
    Federal actions, other than transportation conformity, that meet 
specific criteria need to be evaluated with respect to the requirements 
of 40 CFR part 93, subpart B. The EPA's general conformity rule 
requirements are designed to ensure that emissions from a federal 
action will not cause or contribute to new violations of the NAAQS, 
exacerbate current violations, or delay timely attainment. However, as 
noted in our LMP Option memorandum and similar to the above discussed 
transportation conformity provisions, federal actions subject to our 
general conformity requirements would be considered to satisfy the 
``budget test,'' as specified in 40 CFR 93.158(a)(5)(i)(A). As 
discussed above, the basis for this provision in the LMP Option 
memorandum is that it is unreasonable to expect that an LMP area will 
experience so much growth during the maintenance period that a 
violation of the PM10 NAAQS would result. Therefore, for 
purposes of general conformity, a general conformity PM10 
emissions budget does not need to be identified in the maintenance 
plan, nor

[[Page 20359]]

submitted, and the emissions from federal agency actions are 
essentially considered to not be limited.

IV. The EPA's Proposed Action

    For the reasons explained in Section III, we are proposing to 
approve the LMP for the Butte NAA and the State's request to 
redesignate the Butte NAA from nonattainment to attainment for the 1987 
24-hour PM10 NAAQS. Additionally, the EPA is proposing to 
determine that the Butte NAA has attained the NAAQS for 
PM10. This determination is based upon monitored air quality 
data for the PM10 NAAQS during the years 2014-2018. The EPA 
is proposing to approve the Butte LMP as meeting the appropriate 
transportation conformity requirements found in 40 CFR part 93, subpart 
A.

V. Statutory and Executive Order Reviews

    Under the CAA, 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 CAA. Accordingly, this 
action merely proposes to approve 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, as 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 proposed rule does not have tribal implications and will 
not impose substantial direct costs on tribal governments or preempt 
tribal law as specified by Executive Order 13175 (65 FR 67249, November 
9, 2000).

List of Subjects

40 CFR Part 52

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

40 CFR Part 81

    Environmental protection, Air pollution control, National parks, 
and Wilderness areas.

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

    Dated: April 8, 2021.
Debra H. Thomas,
Acting Regional Administrator, Region 8.
[FR Doc. 2021-07793 Filed 4-16-21; 8:45 am]
BILLING CODE 6560-50-P