[Federal Register Volume 89, Number 70 (Wednesday, April 10, 2024)]
[Proposed Rules]
[Pages 25216-25223]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-07584]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2023-0441; FRL-11837-01-R8]


Air Plan Approval; Colorado; 2017 Base Year Inventory and 
Emission Statement Rule Marginal Nonattainment Requirements, Revisions 
to Regulation 3

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve state implementation plan (SIP) revisions submitted by the 
State of Colorado to meet certain Clean Air Act (CAA) requirements 
related to the Denver Metro/North Front Range (DMNFR) area's 
classification as Marginal nonattainment for the 2015 8-hour ozone 
national ambient air quality standards (NAAQS). The revisions contain a 
base year emissions inventory for the nonattainment area and certify 
that the State's existing Air Pollutant Emissions Notice (APEN) program 
fulfills the CAA's emission statement rule requirement. The revisions 
also include a new requirement for annual certification of APEN 
reported emissions. Unrelated to Colorado's Marginal ozone 
nonattainment obligations, EPA is also proposing to approve the State's 
revisions to Regulation 3 concerning an update to the date of 
incorporation by reference of global warming potentials used in the 
computation of the carbon dioxide equivalent for comparing emissions 
from various greenhouse gases (GHGs). EPA is taking this action 
pursuant to the CAA.

DATES: Written comments must be received on or before May 10, 2024.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2023-0441, 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

[[Page 25217]]

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: Matthew Lang, Air and Radiation 
Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, 
Colorado 80202-1129, (303) 312-6709, [email protected].

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

Table of Contents

I. Background
II. The EPA's Evaluation of Colorado's SIP Submittals
    A. Base Year Emissions Inventory
    1. Point Source Emissions
    2. Nonpoint Source Emissions
    3. On-Road Mobile Source Emissions
    4. Nonroad Mobile Source Emissions
    5. Oil and Gas Emissions
    6. Biogenic Emissions
    7. EPA's Evaluation of the Base Year Emissions Inventory
    B. Certification of Existing Emission Statement Rule and 
Addition of Annual Certification Requirement
    C. Other Revisions to Regulation 3, Part A
    1. Regulation 3, Part A, Sections I.B.10 and 1.B.44.b.(i)--Date 
of Incorporation by Reference of Global Warming Potentials
    2. Regulation 3, Part A, Section I.B.44.(b).(i)--Computation of 
Mass of Carbon Dioxide Equivalent
III. Proposed Action
IV. Incorporation by Reference
V. Statutory and Executive Order Reviews

I. Background

    EPA determined decades ago that ground-level ozone endangers public 
health and welfare. Ground-level ozone forms when nitrogen oxides 
(NOX) and volatile organic compounds (VOC) react in the 
presence of sunlight. Referred to as ozone precursors, these two 
pollutants are emitted by many types of pollution sources, including 
motor vehicles, power plants, industrial facilities, and nonpoint \1\ 
sources. Scientific evidence indicates that adverse human health 
effects occur following exposure to ozone. These effects are more 
pronounced in children and adults with lung disease. Breathing air 
containing ozone can reduce lung function and inflame airways, which 
can increase respiratory symptoms and aggravate asthma or other lung 
diseases. In 1979, in response to this scientific evidence, EPA 
promulgated the first ozone NAAQS, the 0.12 parts per million (ppm) 1-
hour ozone NAAQS.\2\
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    \1\ Nonpoint sources are also sometimes referred to as area 
sources.
    \2\ 44 FR 8202 (Feb. 8, 1979).
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    EPA has strengthened the ozone NAAQS over the years. In 1997, EPA 
promulgated a revised ozone NAAQS of 0.08 ppm, averaged over eight 
hours, which it determined was more protective of public health than 
the 1979 standard.\3\ In 2008, EPA revised the 8-hour ozone NAAQS from 
0.08 to 0.075 ppm.\4\ In 2015, the Agency further strengthened the 8-
hour ozone NAAQS to 0.070 ppm.\5\
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    \3\ 62 FR 38856 (July 18, 1997).
    \4\ 73 FR 16436 (Mar. 27, 2008).
    \5\ 80 FR 65292 (Oct. 26, 2015).
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    The DMNFR area is in nonattainment status for both the 2008 and the 
2015 ozone NAAQS. It is currently classified as a Severe nonattainment 
area under the 2008 standard,\6\ which is not at issue in this 
rulemaking. Effective August 3, 2018, EPA designated the DMNFR area as 
Marginal nonattainment for the more stringent 2015 ozone NAAQS (2015 
DMNFR Nonattainment Area).\7\ The 2015 DMNFR Nonattainment Area 
includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, 
Jefferson, and Weld counties as well as a portion of Larimer County.\8\ 
While EPA has since reclassified the 2015 DMNFR Nonattainment Area as 
Moderate for failing to attain the 2015 ozone NAAQS by the area's 
Marginal attainment date,\9\ Colorado must still meet the CAA 
requirements applicable to Marginal ozone nonattainment areas.
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    \6\ 40 CFR 81.306; 87 FR 60926, 60933 (Oct. 7, 2022).
    \7\ 83 FR 25776, 25792 (June 4, 2018).
    \8\ As detailed in this proposed rule, EPA initially excluded 
part of Weld County from the 2015 DMNFR Nonattainment Area, but, in 
response to a court decision, subsequently expanded its air quality 
designation to include all of Weld County.
    \9\ 40 CFR 81.306; 87 FR 60897, 60916 (Oct. 7, 2022).
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    This proposed rule addresses only the base year inventory and 
emission statement rule requirements related to the Marginal 
nonattainment classification, as described further below, including SIP 
revisions to address EPA's revised designation incorporating all of 
Weld County into the nonattainment area.\10\ Requirements stemming from 
the DMNFR Nonattainment Area's Moderate nonattainment classification 
for the 2015 ozone NAAQS and the Severe classification for the 2008 
ozone NAAQS will be addressed in separate EPA rulemakings.
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    \10\ See 86 FR 67864, 67869 (Nov. 30, 2021) (noting that states 
affected by the revised air quality designations would ``work with 
their respective EPA Regional office to submit any necessary 
supplements or revisions to fulfill the Marginal area SIP revision 
requirements associated with the nonattainment boundaries in this 
final action as expeditiously as practicable'').
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    The CAA and its implementing regulations--in particular, the 2015 
ozone NAAQS SIP Requirements Rule,\11\ codified at 40 CFR part 51, 
subpart CC--establish several requirements for ozone nonattainment 
areas. Section 172(c)(3) of the CAA, which applies generally to states 
with areas classified as nonattainment for any NAAQS, requires 
submission of comprehensive, accurate, and current inventories of 
actual emissions from all sources of relevant pollutants in Marginal 
nonattainment areas.\12\ Specific to areas classified as Marginal ozone 
nonattainment, section 182(a)(1) requires states to submit a base year 
inventory of ozone precursors (NOX and VOC) within two years 
of the nonattainment designation.\13\ Section 182(a)(3)(B) directs 
states to implement an emission statement rule requiring certain 
stationary sources to report their emissions of NOX and 
VOC.\14\
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    \11\ 83 FR 62998 (Dec. 6, 2018). The SIP Requirements Rule 
established implementation requirements for the 2015 ozone NAAQS, 
including requirements for base year emissions inventories.
    \12\ 42 U.S.C. 7502(c)(3).
    \13\ 42 U.S.C. 7511a(a)(1); 40 CFR 51.1315(a); 40 CFR 51.1300(p) 
(defining ``base year inventory'').
    \14\ 42 U.S.C. 7511a(a)(3)(B).

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    Emissions inventories and emission statements provide data that 
inform a variety of air quality planning tasks. States use emissions 
inventories to establish baseline emissions levels, calculate emissions 
reduction targets needed to attain the NAAQS, determine emissions 
inputs for ozone air quality modeling analyses, and track emissions 
over time to determine progress toward achieving air quality and 
emissions reduction goals. EPA has issued guidance to assist states in 
developing their emission inventories; states retain the discretion to 
adopt approaches on a case-by-case basis that differ from that guidance 
where appropriate.\15\ Emission statements provide important 
information that states may use to develop emissions inventories for 
air quality planning, to support permitting efforts, and to assist in 
demonstrating source compliance.\16\
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    \15\ U.S. EPA, ``Emissions Inventory Guidance for Implementation 
of Ozone and Particulate Matter National Ambient Air Quality 
Standards (NAAQS) and Regional Haze Regulations,'' EPA-454/B-17-002 
(May 2017), 1 (2017 Emissions Inventory Guidance).
    \16\ U.S. EPA, ``Draft Guidance on the Implementation of an 
Emission Statement Program'' (July 1992), 1.
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    On July 27, 2020, through the Colorado Department of Public Health 
and Environment (CDPHE), Colorado submitted a SIP revision titled 
``2015 Ozone National Ambient Air Quality Standard (NAAQS)--Denver 
Metro/North Front Range Marginal Nonattainment Area Requirements'' 
(2020 SIP Submittal) to satisfy, in part, the emissions inventory 
requirements under CAA sections 172(c)(3) and 182(a)(1) and the 
emission statement requirement of CAA section 182(a)(3)(B).\17\ 
Colorado met the CAA's reasonable notice and public hearing 
requirements \18\ for the 2020 SIP Submittal through notice in the 
Denver Legal Post on May 23, 2020, and a public hearing on June 18, 
2020.\19\ However, before EPA proposed action on the 2020 SIP 
Submittal, the 2015 DMNFR Nonattainment Area boundary, and specifically 
the partial nonattainment designation of Weld County, was remanded 
without vacatur in Clean Wisconsin v. EPA, 964 F.3d 1145 (D.C. Cir. 
2020). EPA then issued a revised designation to include the whole of 
Weld County in the nonattainment area and noted that states should work 
with their respective EPA regional office to submit any necessary 
supplements or revisions to fulfill Marginal area SIP requirements.\20\
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    \17\ 2020 SIP Submittal, ``01-Submittal Letter to EPA.'' The 
letter is dated July 6, 2020, but the SIP was submitted to EPA on 
July 27, 2020. The 2020 SIP Submittal was deemed complete by 
operation of law six months after submission.
    \18\ 42 U.S.C. 7410(a)(1), (l); 40 CFR 51.102.
    \19\ 2020 SIP Submittal, ``03-Denver Post Legal Ad'' and ``04-
Meeting Agenda.''
    \20\ 86 FR 67864, 67869. The revised designation was affirmed in 
Board of County Commissioners of Weld County, Colorado v. EPA, 72 
F.4th 284, 289-92 (D.C. Cir. 2023).
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    In response, on June 26, 2023, CDPHE submitted a SIP revision 
titled ``Ozone State Implementation Plan (SIP) and Associated 
Regulations: Regulation Number 3, Regulation Number 7, Regulation 
Number 21, Common Provisions, and Air Quality Standards, Designations, 
and Emissions Budgets'' (2023 SIP Submittal).\21\ Among other 
components,\22\ the 2023 SIP Submittal includes rule revisions to 
address the outstanding Marginal area SIP requirements for the 2015 
DMNFR Nonattainment Area, including an updated base year inventory 
reflecting EPA's revised boundary designation of the 2015 DMNFR 
Nonattainment Area. Colorado met the CAA's reasonable notice and public 
hearing requirements through notice in the Denver Legal Post on 
September 17, 2022, and a public hearing on December 13-16, 2022.\23\
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    \21\ 2023 SIP Submittal, Document Set 1 of 7, ``00_Submittal 
Letter to EPA_Ozone SIP.'' The letter is dated June 22, 2023, but 
the SIP was submitted to EPA on June 26, 2023. EPA determined the 
2023 SIP Submittal to be complete on September 7, 2023.
    \22\ The 2023 SIP Submittal includes elements of Colorado's 2008 
Severe Ozone SIP and its 2015 Moderate Ozone SIP. EPA will take 
action on those SIP components in a separate rulemaking.
    \23\ 2023 SIP Submittal, Document Set 1 of 7, ``05_Denver Post 
Legal Ad'' and ``06_Meeting Agenda.''
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    Finally, for purposes of administrative efficiency, EPA is 
proposing to act on Colorado SIP revisions unrelated to the State's 
Marginal ozone nonattainment obligations. On March 22, 2021, CDPHE 
submitted a SIP revision (``2021 SIP Submittal'') that included 
revisions to Regulation 3, Part A to update the date of incorporation 
by reference of global warming potentials (GWPs) as defined in 40 CFR 
part 98, subpart A, table A-1.\24\ Colorado met the CAA's reasonable 
notice and public hearing requirements through notice in the Denver 
Legal Post on September 26, 2020, and a public hearing on December 16-
18, 2020.\25\ Although EPA approved other elements of the 2021 SIP 
Submittal in a March 27, 2023 final rule, we did not finalize action on 
the revisions updating the date of incorporation by reference of GWPs 
for the reasons discussed in that final rule \26\ and below. In 
addition, Colorado's 2023 SIP Submittal included revisions to 
Regulation 3 related to the incorporation by reference of GWPs that 
build upon the aforementioned 2021 SIP Submittal revisions. We now 
propose to act concurrently on the Regulation 3 GWP revisions from both 
the 2021 SIP Submittal and subsequent 2023 SIP Submittal.
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    \24\ 2021 SIP Submittal, Document Set 1 of 6, ``01_Submittal 
Letter to EPA--121820_Ozone SIP, Reg 3, Reg 7, Air Quality 
Stds_signed''; ``03_Hearing Notice & Proposed Language_R3.'' The 
2021 SIP Submittal was deemed complete by operation of law six 
months after submission.
    \25\ 2021 SIP Submittal, Document Set 1 of 6, ``05_Denver Post 
Legal Ad'' and ``06_Meeting Agenda.''
    \26\ 88 FR 18054, 18054 (Mar. 27, 2023).
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II. The EPA's Evaluation of Colorado's SIP Submittals

A. Base Year Emissions Inventory

    Under CAA sections 172(c)(3) and 182(a)(1), Colorado must submit a 
comprehensive, accurate, and current accounting of actual emissions of 
ozone precursors from all sources (point, nonpoint, nonroad mobile, and 
on-road mobile sources) in the 2015 DMNFR Nonattainment Area. EPA's SIP 
Requirements Rule specifies that the inventory year shall be selected 
consistent with the baseline year for the Reasonable Further Progress 
(RFP) plan under 40 CFR 51.1310(b),\27\ which EPA identified as 
2017.\28\ The rule also requires states to report ``ozone season day 
emissions'' in the base year inventory,\29\ as described in other EPA 
regulations:
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    \27\ 40 CFR 51.1315(a).
    \28\ 83 FR 62998, 63005.
    \29\ 40 CFR 51.1315(c).

    Ozone season day emissions means an average day's emissions for 
a typical ozone season work weekday. The state shall select, subject 
to EPA approval, the particular month(s) in the ozone season and the 
day(s) in the work week to be represented, considering the 
conditions assumed in the development of RFP plans and/or emissions 
budgets for transportation conformity.\30\
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    \30\ 40 CFR 51.1300(q).

    Based on EPA's 2017 Emissions Inventory Guidance for Implementation 
of Ozone and Particulate Matter National Ambient Air Quality Standards 
(NAAQS) and Regional Haze Regulations (2017 Emissions Inventory 
Guidance), the selected ozone season day should be representative of 
the conditions leading to nonattainment.\31\
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    \31\ 2017 Emissions Inventory Guidance, 75.
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    To satisfy these requirements, Colorado included a 2017 base year 
inventory in its 2020 SIP Submittal.\32\ Following EPA's revised 
designation of the 2015 DMNFR Nonattainment Area, Colorado then 
submitted a revised base year inventory in its 2023 SIP Submittal as a 
superseding supplement to its 2020 SIP Submittal to account for 
emissions from the revised nonattainment area, including the whole of 
Weld County.\33\

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Consistent with the SIP Requirements Rule, the revised inventory uses 
2017 as the base year for SIP planning purposes.\34\ It was developed 
for a typical July day in 2017 to estimate NOX and VOC 
emissions during the peak summer ozone season, which is representative 
of the conditions leading to nonattainment in the 2015 DMNFR 
Nonattainment Area.\35\ Consistent with the 2017 Emissions Inventory 
Guidance, the inventory estimates emissions from all major source 
categories including point sources, nonpoint sources, on-road and 
nonroad mobile sources, and biogenic sources.\36\ Additional 
information describing Colorado's general methodology for compiling its 
emissions inventory may be found in the State's inventory technical 
support document included in the 2023 SIP Submittal.\37\
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    \32\ 2020 SIP Submittal, ``08-Denver 2017 Ozone NAA Inventory.''
    \33\ 2023 SIP Submittal, Document Set 6 of 7, ``2017 Baseline 
Inventory Update TSD FINAL,'' 1-2 (``2017 Baseline Inventory Update 
TSD''); 2023 SIP Submittal, Document Set 6 of 7, ``APCD_FINAL_SIP-
2015,'' ch. 3 (``Revised Milestone Emission Inventory'').
    \34\ 83 FR 62998, 63005, 63011 n.29.
    \35\ 2017 Baseline Inventory Update TSD, 2.
    \36\ Id.; Revised Milestone Emission Inventory, ch. 3; 2017 
Emissions Inventory Guidance, 19, 81.
    \37\ 2017 Baseline Inventory Update TSD, 1-14.
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    Tables 1 and 2 of this proposed rule show 2017 ozone season day 
emissions for the 2015 DMNFR Nonattainment Area in units of tons per 
day (tpd). Table 1 summarizes anthropogenic VOC and NOX 
emissions by source sector. Table 2 summarizes biogenic VOC and 
NOX emissions, including those from fire and other naturally 
occuring emissions not included as anthropogenic emissions in Table 1. 
The anthropogenic portion of the base year inventory for a 
nonattainment area may serve as the Rate of Progress (ROP)/RFP baseline 
inventory for Moderate and higher nonattainment classifications.\38\ 
The following sections II.A.1-II.A.6 describe the State's inventory of 
emissions from the various source sectors in more detail.
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    \38\ 2017 Emissions Inventory Guidance, 41.

 Table 1--Denver Metro/North Front Range Nonattainment Area 2017 VOC and
             NOX Base Year Anthropogenic Emissions Inventory
                             [Tons/Day] \39\
------------------------------------------------------------------------
                      Source type                         NOX      VOC
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Point.................................................     24.2     21.9
Nonpoint..............................................      0.1     80.1
On-road Mobile........................................     57.4     48.1
Nonroad Mobile........................................     42.9     44.5
Oil & Gas.............................................     78.2    211.1
                                                       -----------------
    Total.............................................    202.9    405.7
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 Table 2--Denver Metro/North Front Range Nonattainment Area 2017 VOC and
                    NOX Base Year Biogenic Emissions
                             [Tons/Day] \40\
------------------------------------------------------------------------
                      Source type                         NOX      VOC
------------------------------------------------------------------------
Biogenic..............................................     26.5    419.0
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1. Point Source Emissions
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    \39\ Revised Milestone Emission Inventory, 3.2.2.1, tbl. 7.
    \40\ Id. at 3.2.2.7, tbl. 15.
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    Point sources are large, stationary, identifiable sources of 
emissions that release pollutants into the atmosphere. In its 2017 base 
year inventory, the State included point source emissions from source 
categories including power plants/electric generating units, external 
combustion boilers, industrial processes, internal combustion sources, 
petroleum/solvent evaporation not associated with the oil and gas 
industry, and waste disposal.\41\ The SIP Requirements Rule provides 
that emissions from point sources shall be reported according to the 
thresholds of EPA's Air Emissions Reporting Requirements (AERR).\42\ 
The 2017 Emissions Inventory Guidance directs those preparing point 
source inventories to volume 2 of the Emissions Inventory Improvement 
Program technical report series for information on point source 
inventory methodology.\43\ This resource describes the three principal 
methods for estimating point source emissions as source testing, mass 
balance calculations, and emission factors, with a fourth method 
utilizing engineering calculations if the principal methods are not 
possible.\44\
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    \41\ Colorado's methodology and results for the point source 
category are described in section 3.2.2.3 of the Revised Milestone 
Emission Inventory.
    \42\ 40 CFR 51.1315(d).
    \43\ 2017 Emissions Inventory Guidance, 81-82.
    \44\ U.S. EPA, EIIP Technical Report Series Vol. II, Ch. 1: 
``Introduction to Stationary Point Source Emission Inventory 
Development'' (May 2001), 1.4-1--1.4-3.
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    Colorado obtained its point source data from the APEN database, the 
State's emissions reporting system for stationary sources.\45\ Colorado 
requires an APEN to be filed for emission points in a nonattainment 
area with uncontrolled actual emissions of one ton per year or more of 
any criteria pollutant that the area is designated nonattainment 
for.\46\ In order of preferred methodology, APEN emission estimates are 
based on actual test data or, in the absence of such data, on mass 
balance calculations, published emission factors, or engineering 
calculations.\47\ Since Colorado's base year inventory is consistent 
with the reporting thresholds in the AERR and uses methods for 
estimating emissions recommended by EPA guidance, the base year 
inventory adequately addresses emissions from the point source 
category.
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    \45\ Revised Milestone Emission Inventory, 3.2.2.3.
    \46\ 5 CCR 1001-5:3A.II.B.3.a.
    \47\ 5 CCR 1001-5:3A.II.B.1.
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2. Nonpoint Source Emissions
    Nonpoint sources are sources of pollution that are small and 
numerous and that have not been inventoried as specific point sources 
or mobile sources. They include a wide range of categories such as 
coatings, household and personal care products, pesticides, automotive 
aftermarket products, and sealants. Inventorying nonpoint sources 
involves grouping them by category and estimating their emissions 
collectively using one methodology.
    The State developed the nonpoint source emissions inventory \48\ 
from the 2016v2 EPA modeling platform,\49\ which includes emission 
inventories for 2016 and 2023. To establish emissions for 2017 from the 
2016v2 platform, the State used a linear interpolation from 2016 to 
2023. Because a portion of Larimer County is not part of the 2015 DMNFR 
Nonattainment Area, the State scaled the whole-county emissions by the 
ratio of the county population residing within the nonattainment area 
boundary based on 2020 census block data--0.9776--to determine an 
accurate emissions contribution for the relevant part of Larimer 
County. The nonpoint source portion of Colorado's emissions inventory 
includes source categories addressed in the nonpoint portion of the 
inventories developed for EPA's 2016v2 platform. Colorado used EPA 
estimates for the nonpoint source category and apportioned partial 
county emissions using methods consistent with the 2017 Emissions 
Inventory Guidance.\50\

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Therefore, the base year inventory adequately addresses emissions from 
the nonpoint source category.
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    \48\ Colorado's methodology and results for the nonpoint source 
category are described in section 3.2.2.4 of the Revised Milestone 
Emission Inventory.
    \49\ The 2016v2 modeling platform includes a set of emissions 
inventories, data files, software tools, and scripts used for air 
quality modeling. Files and technical support documents are 
available at: https://www.epa.gov/air-emissions-modeling/2016v2-platform. The 2016v2 modeling platform draws on data from the 2017 
National Emissions Inventory and includes point sources, nonpoint 
sources, commercial marine vessels, on-road and nonroad mobile 
sources, and fires for the U.S., Canada, and Mexico. U.S. EPA, 
``Technical Support Document (TSD): Preparation of Emissions 
Inventories for the 2016v2 North American Emissions Modeling 
Platform,'' EPA-454/B-22-001 (Feb. 2022), 1-2.
    \50\ 2017 Emissions Inventory Guidance, 72-73, 131-32.
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3. On-Road Mobile Source Emissions
    For on-road mobile sources (vehicles operated on public roadways), 
Colorado's 2017 base year inventory includes emissions from passenger 
cars, motorcycles, light trucks, refuse/single-unit trucks, short/long-
haul trucks, and buses.\51\ The State estimated these emissions using 
EPA's Motor Vehicle Emissions Simulator model version 3 (MOVES3 \52\) 
along with link-level (roadway) vehicle miles traveled (VMT) provided 
by the two metropolitan planning organizations that serve the 2015 
DMNFR Nonattainment Area, the Denver Regional Council of Governments 
and the North Front Range Metropolitan Planning Organization. The State 
based VMT on travel demand model output data from those two 
organizations and apportioned it to the nonattainment area at the 
roadway level using Geographic Information Systems. Additional MOVES3 
model inputs include vehicle population and age distribution, roadway 
activity data (speed and time of day), roadway classifications (urban, 
rural, restricted, unrestricted), fuel properties, inspection and 
maintenance program characteristics, and hourly meteorology. These 
model inputs are described in greater detail in EPA's MOVES3 technical 
guidance.\53\ Specific MOVES3 on-road inputs used by the State are 
identified in Appendix A to the 2017 Baseline Inventory Update 
Technical Support Document. The State based model inputs on conditions 
on an average July weekday and used the MOVES3 default fuel 
formulation. It calculated NOX and VOC emission factors from 
MOVES3 for each vehicle type and then multiplied these emission factors 
by the roadway-level VMT to establish on-road mobile source emissions.
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    \51\ Colorado's methodology and results for the on-road mobile 
source category are described in section 3.2.2.6 of the Revised 
Milestone Emission Inventory and in section 3.1.1 and Appendix A of 
the 2017 Baseline Inventory Update TSD.
    \52\ MOVES3 files and technical support documents are available 
at: https://www.epa.gov/moves/moves-versions-limited-current-use.
    \53\ U.S. EPA, ``MOVES3 Technical Guidance: Using MOVES to 
Prepare Emission Inventories for State Implementation Plans and 
Transportation Conformity,'' EPA-420-B-20-052 (Nov. 2020), 26-58.
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    Colorado's on-road mobile source emissions inventory methodology 
follows the SIP Requirements Rule, which states that ``the latest 
approved version of the [MOVES] model should be used to estimate 
emissions from on-road and certain nonroad transportation sources.'' 
\54\ MOVES3 was the latest approved version of the model available at 
the time that the State developed its 2017 base year inventory. 
Colorado used local data on vehicle/roadway activity, meteorological 
conditions, fuel use, and other information characterizing the DMNFR 
area in 2017, as called for by EPA's 2017 Emissions Inventory 
Guidance.\55\ Therefore, the base year inventory adequately addresses 
emissions from the on-road mobile source category.
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    \54\ 83 FR 62998, 63022.
    \55\ 2017 Emissions Inventory Guidance, 89-90.
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4. Nonroad Mobile Source Emissions
    Nonroad mobile sources are mobile sources other than on-road 
vehicles, including engines used in lawn and garden equipment, 
commercial and industrial equipment, construction and mining equipment, 
aircraft, and locomotives. Colorado's 2017 base year inventory used 
EPA's MOVES-Nonroad model to estimate emissions from nonroad mobile 
sources in the 2015 DMNFR Nonattainment Area, except for emissions from 
aviation, locomotives, and rail yards.\56\ MOVES-Nonroad exists as a 
separate module from the on-road modeling capabilities within MOVES3. 
The specific MOVES3 nonroad inputs used by the State are identified in 
Appendix A to the 2017 Baseline Inventory Technical Support Document.
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    \56\ Colorado's methodology and results for the nonroad mobile 
source category are described in section 3.2.2.5 of the Revised 
Milestone Emission Inventory and in section 3.1.2 and Appendix A of 
the 2017 Baseline Inventory Update TSD.
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    The State estimated aviation emissions based on data provided by 
Denver International Airport (DIA) on fleet composition and activity 
level, including estimates of emissions from aircraft and ground 
support equipment such as auxiliary power units. It estimated 2017 
aviation emissions from other airports within the nonattainment area 
using a linear interpolation between the 2016 and 2023 point source 
emissions from the 2016v2 EPA modeling platform, with DIA emissions 
excluded. The State also used the 2016v2 modeling platform to estimate 
emissions from railroad locomotives and rail yard switcher locomotives. 
It apportioned line-haul locomotive activity levels by track mileage in 
the nonattainment area. As with the aviation and nonpoint source 
sectors, Colorado determined 2017 locomotive emissions from a linear 
trend between 2016 and 2023 estimates from the 2016v2 platform.
    As directed in the SIP Requirements Rule,\57\ Colorado used the 
most recently available version of EPA's MOVES-Nonroad model to 
estimate emissions from certain nonroad sources. Furthermore, Colorado 
used EPA's own 2016v2 platform to account for emissions from aviation, 
locomotives, and rail yards not covered by the MOVES-Nonroad model. 
Finally, for emissions specifically from DIA, the major international 
airport in the DMNFR nonattainment area, the State relied on data 
provided from the airport that provides valuable detail regarding DIA 
emissions. Therefore, the base year inventory adequately addresses 
emissions from the non-road mobile source category.
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    \57\ 83 FR 62998, 63022.
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5. Oil and Gas Emissions
    To inventory oil and gas emissions for its 2023 SIP Submittal, 
Colorado relied on extensive industry outreach it had conducted between 
2015-2018 to develop emission inventories for its 2008 8-hour Ozone 
DMNFR Nonattainment Area Moderate and Serious SIPs.\58\ The State based 
its approach to the oil and gas emissions component of its inventory on 
actual and survey data from operators in the specific geological basin.
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    \58\ Colorado's methodology and results for the oil and gas 
source category are described in section 3.2.2.2 of the Revised 
Milestone Emission Inventory and in sections 3.2 and 3.3 of the 2017 
Baseline Inventory Update TSD.
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    Colorado's 2017 base year emissions inventory categorizes emissions 
from the oil and gas sector into point sources, condensate/oil tanks, 
and nonpoint sources. The State used APEN reported data to determine 
emissions from point sources, including external combustion boilers, 
industrial processes, internal combustion sources, petroleum/solvent 
evaporation, and waste disposal. As described previously, Colorado's 
APEN reporting program meets the point source thresholds in EPA's AERR 
and uses methods for estimating emissions consistent with that 
recommended by EPA guidance. Therefore, the base year inventory 
adequately addresses the point source component of oil and gas 
emissions.
    Colorado based condensate tank emissions (the largest single source 
of VOC emissions in the 2017 base year inventory) on APEN reported 
data, data collected by the Colorado Energy and Carbon Management 
Commission, and data reported directly by the industry. The State 
developed site-specific uncontrolled tank emission factors and 
multiplied them by facilities' production in barrels per year. It then

[[Page 25221]]

adjusted the resulting emissions to account for several factors 
relevant to condensate tanks: a control device's destruction and 
removal efficiency (DRE) of emissions; the capture efficiency of a 
control device (a fractional factor intended to discount a control 
device's DRE to account for actual operating conditions and potential 
process/device upsets); and the rule effectiveness of regulations (a 
discount factor that scales a control device's DRE downward to account 
for a degree of noncompliance with applicable regulations). Since 
Colorado estimated condensate tank emissions using APEN reported data 
as well as additional industry-specific data and site-specific emission 
factors, the base year inventory adequately addresses emissions from 
the condensate tank portion of the oil and gas component.
    Oil and gas nonpoint sources in Colorado's inventory include 
emissions from certain production equipment and operations (e.g., 
emissions from well pad engines, truck loading, pneumatic devices, 
fugitives, blowdowns, process heaters, separator control, and water 
tank losses). Nonpoint source emissions also result from pre-production 
operations, including from drill rig engines, hydraulic fracturing 
engines, drilling mud degassing, and venting during completion 
operations. The State estimated some of these emissions based on 
facility/equipment level data reported by 11 producers as part of the 
stakeholder group it convened in 2018, with emissions scaled to account 
for the entirety of the 2015 DMNFR Nonattainment Area including the 
whole of Weld County. Colorado used 2017 NEI data to supplement pre-
production emissions for categories not included in producer-submitted 
data. The State determined drilling mud degassing emissions that were 
not captured in producer-submitted information, or the 2017 NEI, from 
EPA's 2016v2 modeling platform by interpolating emissions to 2017 from 
2016 and 2023 emissions. Since Colorado relied on basin-specific 
producer submitted information in developing its oil and gas nonpoint 
source inventory, in addition to emissions from EPA's own 2017 NEI and 
2016v2 platform, the base year inventory adequately addresses emissions 
from the oil and gas nonpoint source component.
6. Biogenic Emissions
    Biogenic emissions come from natural sources. Colorado included a 
2017 inventory of biogenic emissions separate from the anthropogenic 
portion of the inventory.\59\ The State used EPA's Biogenic Emissions 
Inventory System (BEIS), version 3, which EPA developed specifically 
for estimating biogenic emissions for inventories.\60\ Since Colorado 
used the BEIS model to estimate emissions, as recommended by EPA 
guidance, the base year inventory adequately addresses emission from 
the biogenic source category.
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    \59\ Colorado's methodology and results for the biogenic source 
category are described in section 3.2.2.7 of the Revised Milestone 
Emission Inventory.
    \60\ 2017 Emissions Inventory Guidance, 101-102.
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7. EPA's Evaluation of the Base Year Emissions Inventory
    Based on EPA's review and evaluation of the methodologies, 
procedures, and results in Colorado's 2017 base year emissions 
inventory, we propose to find that the inventory meets the requirements 
of CAA sections 172(c)(3) and 182(a)(1) and the SIP Requirements Rule. 
The base year inventory is based on the most current and accurate 
information that was available to the State at the time the inventory 
was developed. Additionally, the 2017 inventory comprehensively 
addresses all source categories in the 2015 DMNFR Nonattainment Area 
including the whole of Weld County and was developed consistent with 
the relevant EPA emissions inventory regulations, guidance, and models.

B. Certification of Existing Emission Statement Rule and Addition of 
Annual Certification Requirement

    Under CAA section 182(a)(3)(B), Colorado must implement an emission 
statement rule requiring certain stationary sources that emit VOC or 
NOX in the nonattainment area to report on their emissions 
at least annually.\61\ Section 182(a)(3)(B)(ii) specifies that a state 
may waive this requirement for sources that emit less than 25 tpy of 
VOC or NOX if the state includes emissions from such sources 
in its base year or periodic inventories.\62\ If a state already has an 
EPA-approved emissions reporting regulation in place and determines 
that it is adequate to meet the requirements of section 182(a)(3)(B), 
EPA may accept a SIP revision with the state's written certification of 
that determination in lieu of the state submitting new revised 
regulations.\63\ In its 2020 SIP Submittal, Colorado certified that its 
existing SIP-approved APEN program meets the source reporting 
requirements for an emission statement rule under CAA section 
182(a)(3)(B).\64\
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    \61\ 42 U.S.C. 7511a(a)(3)(B)(i).
    \62\ 42 U.S.C. 7511a(a)(3)(B)(ii).
    \63\ 83 FR 62998, 63001-02.
    \64\ Collectively, the information contained in ``01-Submittal 
Letter to EPA,'' ``06-Issue Statement,'' and ``07-CAA Elements 
Table'' in the 2020 SIP Submittal satisfies the certification 
requirements outlined in the SIP Requirements Rule, 83 FR 62998, 
63001-02.
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    Colorado's APEN program requires stationary sources with 
uncontrolled actual emissions of one tpy or more of any individual 
criteria pollutant for which the area is in nonattainment to file an 
APEN with the Colorado Air Pollution Control Division (APCD).\65\ 
Emission estimates reported on the APEN must be based on actual test 
data or, in the absence of such data, on an alternative estimation 
acceptable to the APCD.\66\ Each APEN must include the location of the 
source; the operator's name and address; the nature of the facility, 
process or activity; an estimate of the quantity and composition of 
emissions; and other specified information that varies based on the 
type of source.\67\ An APEN is valid for five years \68\ but must be 
revised (1) annually whenever a significant change in annual actual 
emissions occurs or (2) upon the occurrence of a triggering event, such 
as a change in the owner/operator, the installation of new control 
equipment, or the modification of a permit limitation.\69\ To ensure 
the accuracy of APEN reported emissions between triggering events, 
Colorado's 2023 SIP Submittal includes revisions to add section II.A.3 
to Regulation 3, Part A.\70\ The new section II.A.3 requires stationary 
sources in the ozone nonattainment area with the potential to emit 25 
tpy or more of NOX or VOC to annually certify through an 
APCD-approved format that annual actual emissions are as reported on 
the source's APEN.
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    \65\ 5 CCR 1001-5:3A.II.A.1, II.B.3.a.
    \66\ 5 CCR 1001-5:3A.II.B.1.
    \67\ 5 CCR 1001-5:3A.II.A.1.
    \68\ 5 CCR 1001-5:3A.II.B.2.
    \69\ 5 CCR 1001-5:3A.II.C.
    \70\ 2023 SIP Submittal, Document Set 5 of 7, ``17_Reg Lang & 
SBAP Adopted_R3.''
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    EPA is proposing to concurrently approve Colorado's certification 
of its APEN program in its 2020 SIP Submittal, as well as the State's 
associated addition of the annual certification provision in section 
II.A.3 to Regulation 3, Part A in its 2023 SIP Submittal, as meeting 
the requirements for an emission statement rule under CAA section 
182(a)(3)(B). As recommended by EPA guidance, the APEN program requires 
certification of data accuracy and submission of source identification 
information, operating schedule, emissions information, control 
equipment information, and

[[Page 25222]]

process data.\71\ Since Colorado's 2017 base year inventory, as 
described previously in this proposed rule, includes emissions from 
sources below 25 tpy and is based on acceptable methodologies, 
Colorado's APEN reporting program satisfies the criteria for the waiver 
in CAA section 182(a)(3)(B)(ii). Therefore, EPA proposes to approve the 
State's APEN reporting program under CAA section 182(a)(3)(B).
---------------------------------------------------------------------------

    \71\ U.S. EPA, ``Draft Guidance on the Implementation of an 
Emission Statement Program'' (July 1992), 3.
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C. Other Revisions to Regulation 3, Part A

    EPA is also proposing action on certain other revisions to 
Regulation 3 unrelated to the State's Marginal ozone nonattainment 
obligations. Colorado's 2021 and 2023 SIP Submittals included several 
revisions to Regulation 3, Parts A, B, and D. In this rulemaking, we 
are proposing action on the State's revisions to Regulation 3, Part A 
related to the date of incorporation by reference of global warming 
potentials (GWPs) and the computation of the mass of carbon dioxide 
equivalent.\72\ The revisions in the 2021 and 2023 SIP Submittals that 
are described below have State effective dates of February 14, 2021, 
and February 14, 2023, respectively. The revisions do not interfere 
with attainment or maintenance of any of the NAAQS and would not 
interfere with any other applicable requirement of the CAA, and are 
therefore approvable under CAA section 110(l). EPA will propose action 
on the remaining revisions to Regulation 3, Parts A, B, and D in a 
separate rulemaking.
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    \72\ References to specific sections of Regulation 3 in sections 
II.C.1 and II.C.2 of this proposed rule are to the versions of 
Regulation 3 the State included in the 2021 and 2023 SIP Submittals, 
namely: 2021 SIP Submittal, Document Set 4 of 6, ``16_Reg Lang & 
SBAP Adopted_R3''; 2021 SIP Submittal, Document Set 6 of 6, ``22_5 
CCR 1001-5''; 2023 SIP Submittal, Document Set 5 of 7, ``17_Reg Lang 
& SBAP Adopted_R3''; and 2023 SIP Submittal, Document Set 7 of 7, 
``23_5 CCR 1001-5.''
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1. Regulation 3, Part A, Sections I.B.10 and 1.B.44.b.(i)--Date of 
Incorporation by Reference of Global Warming Potentials
    Colorado's Regulation 3, Part A, Section I.B.10 defines ``carbon 
dioxide equivalent'' as a metric used to compare emissions of various 
greenhouse gases. The metric is based in part on each gas's GWP as 
codified in 40 CFR part 98, subpart A, table A-1, which Regulation 3 
incorporates by reference. Regulation 3, Part A, Section I.B.44.b.(i), 
which provides conditions under which GHGs are ``subject to 
regulation,'' makes the same incorporation by reference. In its 2021 
SIP Submittal, the State replaced the outdated November 20, 2013 
incorporation by reference date with December 11, 2014 in both Sections 
1.B.10 and 1.B.44.b.(i).\73\ However, while the November 20, 2013 date 
was removed from Section 1.B.10 in the Code of Colorado Regulations, 
the revised date was inadvertently omitted, leaving the incorporation 
by reference without a corresponding date.\74\ Colorado's 2023 SIP 
Submittal corrects that omission.\75\ Since December 11, 2014, is the 
most recent date of revision to the GWPs in 40 CFR part 98, Subpart A, 
Table A-1, EPA is proposing to approve the revisions from the 2021 and 
2023 SIP Submittals that update the date of incorporation by reference 
in Regulation 3, Part A, sections I.B.10 and 1.B.44.b.(i).
---------------------------------------------------------------------------

    \73\ 2021 SIP Submittal, Document Set 4 of 6, ``16_Reg Lang & 
SBAP Adopted_R3.''
    \74\ 2021 SIP Submittal, Document Set 6 of 6, ``22_5 CCR 1001-
5,'' 4.
    \75\ 2023 SIP Submittal, Document Set 5 of 7, ``17_Reg Lang & 
SBAP Adopted_R3.''
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2. Regulation 3, Part A, Section I.B.44.(b).(i)--Computation of Mass of 
Carbon Dioxide Equivalent
    EPA is proposing to approve an additional revision in Colorado's 
2023 SIP Submittal to Regulation 3, Part A, Section I.B.44.b.(i).\76\ 
The revision removes language stating that, prior to July 21, 2014, the 
mass of carbon dioxide shall not include emissions resulting from the 
combustion or decomposition of non-fossilized and biodegradable organic 
material. The removed language is consistent with the definition of 
``subject to regulation'' at 40 CFR 70.2, which instructed how to 
compute the mass of carbon dioxide equivalent before July 21, 2014. 
This language was meant to defer the application of Prevention of 
Significant Deterioration and Title V programs to certain sources of 
biogenic carbon dioxide for three years.\77\ Because the deferral 
period has since expired, continued inclusion of this language in the 
SIP is unnecessary.
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    \76\ Id.
    \77\ 76 FR 43490, 43490 (July 20, 2011).
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III. Proposed Action

    We are proposing to approve elements of Colorado's July 27, 2020, 
March 22, 2021, and June 26, 2023 SIP Submittals. Specifically, we are 
proposing to approve Colorado's 2017 base year inventory under CAA 
sections 172(c)(3) and 182(a)(1). We are proposing to approve 
Colorado's certification of its APEN reporting program (July 27, 2020 
SIP Submittal) and the addition of the annual certification requirement 
in Section II.A.3 to Regulation 3, Part A (June 26, 2023 SIP Submittal) 
as meeting the emission statement rule requirements of CAA section 
182(a)(3)(B). We are also proposing to approve certain revisions to 
Regulation 3, Part A, specifically to the date of incorporation by 
reference of GWPs in Sections 1.B.10 and 1.B.44.b.(i) (March 22, 2021 
and June 26, 2023 SIP Submittals) and to the computation of the mass of 
carbon dioxide equivalent in Section 1.B.44.b.(i) (June 26, 2023 SIP 
Submittal).

IV. Incorporation by Reference

    In this document, the EPA is proposing to include regulatory text 
in an EPA final rule that includes incorporation by reference. In 
accordance with requirements of 1 CFR 51.5, the EPA is proposing to 
incorporate by reference the APCD revisions regarding annual APEN 
certification, updated incorporation by reference dates of CFR global 
warming potentials, and revisions related to the computation of carbon 
dioxide equivalent, as described in sections II.B and II.C of this 
proposed rule. The EPA has made, and will continue to make, these 
materials generally available through www.regulations.gov and at the 
EPA Region 8 Office. Please contact the person identified in the FOR 
FURTHER INFORMATION CONTACT section of this preamble for more 
information.

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);
     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

[[Page 25223]]

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
    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).
    Executive Order 12898 (Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations, 59 FR 7629, 
Feb. 16, 1994) directs Federal agencies to identify and address 
``disproportionately high and adverse human health or environmental 
effects'' of their actions on minority populations and low-income 
populations to the greatest extent practicable and permitted by law. 
EPA defines environmental justice (EJ) as ``the fair treatment and 
meaningful involvement of all people regardless of race, color, 
national origin, or income with respect to the development, 
implementation, and enforcement of environmental laws, regulations, and 
policies.'' EPA further defines the term fair treatment to mean that 
``no group of people should bear a disproportionate burden of 
environmental harms and risks, including those resulting from the 
negative environmental consequences of industrial, governmental, and 
commercial operations or programs and policies.''
    Colorado did not evaluate environmental justice considerations as 
part of its SIP submittal; the CAA and applicable implementing 
regulations neither prohibit nor require such an evaluation. EPA did 
not perform an EJ analysis and did not consider EJ in this action. 
Consideration of EJ is not required as part of this action, and there 
is no information in the record inconsistent with the stated goal of 
Executive Order 12898 of achieving environmental justice for people of 
color, low-income populations, and Indigenous peoples.

List of Subjects in 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.

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

    Dated: April 2, 2024.
KC Becker,
Regional Administrator, Region 8.
[FR Doc. 2024-07584 Filed 4-9-24; 8:45 am]
BILLING CODE 6560-50-P