[Federal Register Volume 83, Number 242 (Tuesday, December 18, 2018)]
[Proposed Rules]
[Pages 64774-64795]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-27257]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2017-0728; FRL-9988-01-Region 9]


Approval and Promulgation of Air Quality State Implementation 
Plans; California; Plumas County; Moderate Area Plan for the 2012 PM2.5 
NAAQS

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve most elements of the state implementation plan (SIP) revisions 
submitted by California to address Clean Air Act (CAA or ``Act'') 
requirements for the 2012 annual fine particulate matter 
(PM2.5) national ambient air quality standards (NAAQS or 
``standards'') in the Plumas County Moderate PM2.5 
nonattainment area (``Portola nonattainment area''). The SIP revisions 
are the ``Portola Fine Particulate Matter (PM2.5) Attainment 
Plan'' submitted on February 28, 2017, and the 2019 and 2022 
transportation conformity motor vehicle emission budgets (``budgets'') 
submitted on December 20, 2017. We refer to these submittals 
collectively as the ``Portola PM2.5 Plan'' or ``Plan.'' The 
EPA is proposing to approve the following elements of the Portola 
PM2.5 Plan: The 2013 base year emissions inventories, the 
reasonably available control measure/reasonably available control 
technology (RACM/RACT) demonstration, the attainment demonstration, the 
reasonable further progress (RFP) demonstration, the quantitative 
milestones, and the budgets for 2019 and 2021. The EPA is not proposing 
any action at this time on the contingency measures in the Portola 
PM2.5 Plan.

DATES: Any comments must arrive by January 17, 2019.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2017-0728 at https://www.regulations.gov, or via email to John 
Ungvarsky, at [email protected]. For comments submitted at 
Regulations.gov, follow the online instructions for submitting 
comments. Once submitted, comments cannot be removed or edited from 
Regulations.gov. For either manner of submission, 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, please contact 
the person identified in the FOR FURTHER INFORMATION CONTACT section. 
For 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.

FOR FURTHER INFORMATION CONTACT: John Ungvarsky, EPA Region IX, (415) 
972-3963, [email protected].

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

Table of Contents

I. Background for Proposed Action
II. Clean Air Act Requirements for Moderate PM2.5 
Nonattainment Area Plans
III. Completeness Review of the Portola PM2.5 Attainment 
Plan
IV. Review of the Portola PM2.5 Plan
V. Summary of Proposed Actions and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background for Proposed Action

    Under section 109 of the CAA, the EPA has established NAAQS for 
certain pervasive air pollutants (referred to as ``criteria 
pollutants'') and conducts periodic reviews of the NAAQS to determine 
whether they should be revised or whether new NAAQS should be 
established. The EPA sets the NAAQS for criteria pollutants at levels 
required to protect public health and welfare.\1\ Particulate matter is 
one of the criteria pollutants for which the EPA has established 
health-based standards. The CAA requires states to submit regulations 
that control particulate matter emissions.
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    \1\ For a given air pollutant, ``primary'' national ambient air 
quality standards are those determined by the EPA as requisite to 
protect the public health. ``Secondary'' standards are those 
determined by the EPA as requisite to protect the public welfare 
from any known or anticipated adverse effects associated with the 
presence of such air pollutant in the ambient air. CAA section 
109(b).
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    Particulate matter includes particles with diameters that are 
generally 2.5 microns or smaller (PM2.5) and particles with 
diameters that are generally 10 microns or smaller (PM10). 
It contributes to effects that are harmful to human health and the 
environment, including premature mortality, aggravation of respiratory 
and cardiovascular disease, decreased lung function, visibility 
impairment, and damage to vegetation and ecosystems. Individuals 
particularly sensitive to PM2.5 exposure include older 
adults, people with heart and lung disease, and children.\2\ 
PM2.5 can be emitted by sources directly into the atmosphere 
as a solid or liquid particle (``primary PM2.5'' or ``direct 
PM2.5'') or can be formed in the atmosphere (``secondary 
PM2.5'') as a result of various chemical reactions among 
precursor pollutants from sources such as nitrogen oxides 
(NOX), sulfur dioxide (SO2), volatile organic 
compounds (VOC), and ammonia.\3\
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    \2\ 78 FR 3086, 3088 (January 15, 2013).
    \3\ EPA, Air Quality Criteria for Particulate Matter, No. EPA/
600/P-99/002aF and EPA/600/P-99/002bF, October 2004.
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    On July 18, 1997, the EPA revised the NAAQS for particulate matter 
to add new standards for PM2.5.\4\ The EPA established 
primary and secondary annual and 24-hour standards for 
PM2.5. The annual standard was set at 15.0 micrograms per 
cubic meter ([micro]g/m\3\)

[[Page 64775]]

based on a 3-year average of annual mean PM2.5 
concentrations, and the 24-hour (daily) standard was set at 65 
[micro]g/m\3\ based on the 3-year average of the annual 98th percentile 
values of 24-hour PM2.5 concentrations at each population-
oriented monitor within an area.\5\
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    \4\ 62 FR 38652.
    \5\ The primary and secondary standards were set at the same 
level for both the 24-hour and the annual PM2.5 
standards.
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    On October 17, 2006, the EPA retained the annual average NAAQS at 
15 [micro]g/m\3\ but revised the level of the 24-hour PM2.5 
NAAQS to 35 [micro]g/m\3\ based on a 3-year average of the annual 98th 
percentile values of 24-hour concentrations.6 7
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    \6\ Under EPA regulations at 40 CFR part 50, the primary and 
secondary 2006 24-hour PM2.5 NAAQS are attained when the 
annual arithmetic mean concentration, as determined in accordance 
with 40 CFR part 50, Appendix N, is less than or equal to 35 
[micro]g/m\3\ at all relevant monitoring sites in the subject area, 
averaged over a 3-year period.
    \7\ 71 FR 61144.
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    On January 15, 2013, the EPA finalized the 2012 PM2.5 
NAAQS, including a revision of the annual standard to 12.0 [micro]g/
m\3\ based on a 3-year average of annual mean PM2.5 
concentrations, and retaining the current 24-hour standard of 35 
[micro]g/m\3\ based on a 3-year average of the 98th percentile of 24-
hour concentrations.\8\
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    \8\ 78 FR 3086.
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    Following promulgation of a new or revised NAAQS, the EPA is 
required by CAA section 107(d) to designate areas throughout the nation 
as attaining or not attaining the NAAQS. The EPA designated and 
classified the Portola area as ``Moderate'' nonattainment for the 2012 
annual PM2.5 standards based on ambient monitoring data that 
showed the area was above 12.0 [micro]g/m\3\ for the 2011-2013 
monitoring period.\9\ For the 2011-2013 period, the annual 
PM2.5 design value for the Portola area was 12.8 [micro]g/
m\3\ based on monitored readings at the 161 Nevada Street and 420 
Gulling Street monitors.\10\
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    \9\ 80 FR 2206 (January 15, 2015).
    \10\ From 2000 through early 2013, the Portola PM2.5 
monitoring site was located at 161 Nevada Street. In 2013, the site 
was relocated to 420 Gulling Street.
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    The Portola PM2.5 nonattainment area includes the City 
of Portola (``Portola''), which has a population of approximately 2,100 
and is located at an elevation of 4,890 feet in an intermountain basin 
isolated by rugged mountains. Portola averages 20 inches of 
precipitation annually. From October through March the nonattainment 
area has very cold temperatures with the average daily low temperature 
of approximately 22 degrees Fahrenheit. The combination of mountains, 
cold temperatures, and elevation can cause inversions and impair 
PM2.5 dispersion, especially during the winter. For a 
precise description of the geographic boundaries of the Portola 
PM2.5 nonattainment area, see 40 CFR 81.305.
    The local air district with primary responsibility for developing a 
plan to attain the 2012 annual PM2.5 NAAQS in this area is 
the Northern Sierra Air Quality Management District (NSAQMD or 
``District''). The District worked cooperatively with the California 
Air Resources Board (CARB) in preparing the Portola PM2.5 
Plan. Under state law, authority for regulating sources under state 
jurisdiction in the Portola nonattainment area is split between the 
District, which has responsibility for regulating stationary and most 
area sources, and CARB, which has responsibility for regulating most 
mobile sources.

II. Clean Air Act Requirements for Moderate PM2.5 Nonattainment Area 
Plans

    With respect to the statutory requirements for attainment plans for 
the 2012 annual PM2.5 NAAQS, the general CAA part D 
nonattainment area planning requirements are found in subpart 1, and 
the Moderate area planning requirements specifically for particulate 
matter are found in subpart 4.
    The EPA has a longstanding general guidance document that 
interprets the 1990 amendments to the CAA, commonly referred to as the 
General Preamble for the Implementation of Title I of the Clean Air Act 
Amendments of 1990 (``General Preamble'').\11\ The General Preamble 
addresses the relationship between the subpart 1 and the subpart 4 
requirements and provides recommendations to states for meeting certain 
statutory requirements for particulate matter attainment plans. As 
explained in the General Preamble, specific requirements applicable to 
Moderate area attainment plan SIP submissions for the particulate 
matter NAAQS are set forth in subpart 4 of part D, title I of the Act, 
but such SIP submissions must also meet the general attainment planning 
provisions in subpart 1 of part D, title I of the Act, to the extent 
these provisions ``are not otherwise subsumed by, or integrally related 
to,'' the more specific subpart 4 requirements.\12\
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    \11\ General Preamble, 57 FR 13498 (April 16, 1992).
    \12\ 57 FR 13538.
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    To implement the PM2.5 NAAQS, the EPA has also 
promulgated the ``Fine Particle Matter National Ambient Air Quality 
Standard: State Implementation Plan Requirements; Final Rule'' 
(hereinafter, the ``PM2.5 SIP Requirements Rule'').\13\ The 
PM2.5 SIP Requirements Rule provides additional regulatory 
requirements and guidance applicable to attainment plan submissions for 
the PM2.5 NAAQS, including the 2012 annual PM2.5 
NAAQS at issue in this action.
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    \13\ 81 FR 58010, August 24, 2016.
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    The subpart 1 statutory requirements for attainment plans include: 
(i) The section 172(c)(1) requirements for RACM/RACT and attainment 
demonstrations; (ii) the section 172(c)(2) requirement to demonstrate 
RFP; (iii) the section 172(c)(3) requirement for emissions inventories; 
(iv) the section 172(c)(5) requirements for a nonattainment new source 
review (NNSR) permitting program; and (v) the section 172(c)(9) 
requirement for contingency measures.
    The more specific subpart 4 statutory requirements for Moderate 
PM2.5 nonattainment areas include: (i) The section 
189(a)(1)(A) and 189(e) NNSR permit program requirements; (ii) the 
section 189(a)(1)(B) requirements for attainment demonstrations; (iii) 
the section 189(a)(1)(C) requirements for RACM; and (iv) the section 
189(c) requirements for RFP and quantitative milestones. Under subpart 
4, states with Moderate PM2.5 nonattainment areas must 
provide for attainment in the area as expeditiously as practicable but 
no later than December 31, 2021, for the 2012 PM2.5 annual 
NAAQS. In addition, under subpart 4, direct PM2.5 and all 
precursors to the formation of PM2.5 are subject to control 
unless the EPA approves a demonstration from the State establishing 
that a given precursor does not contribute significantly to 
PM2.5 levels that exceed the PM2.5 NAAQS in the 
area.\14\
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    \14\ 40 CFR 51.1006 and 51.1009.
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III. Completeness Review of the Portola PM2.5 Attainment Plan

    CAA sections 110(a)(1) and (2) and 110(l) require each state to 
provide reasonable public notice and opportunity for public hearing 
prior to the adoption and submission of a SIP or SIP revision to the 
EPA. To meet this requirement, every SIP submission should include 
evidence that adequate public notice was given and an opportunity for a 
public hearing was provided consistent with the EPA's implementing 
regulations in 40 CFR 51.102.
    Both the District and CARB satisfied applicable statutory and 
regulatory requirements for reasonable public

[[Page 64776]]

notice and hearing prior to adoption and submission of the Portola 
PM2.5 Plan. The District provided a 30-day public comment 
period prior to its January 23, 2017 public hearing to adopt the main 
SIP submission.\15\ CARB provided the required public notice and 
opportunity for public comment prior to its February 16, 2017 public 
hearing and adoption of the main SIP submission.\16\ CARB then adopted 
its supplemental SIP submission pertaining to 2019 and 2022 
transportation conformity motor vehicle emission budgets at its October 
26, 2017 Board meeting after reasonable public notice.\17\ Each 
submission includes proof of publication of notices for the respective 
public hearings. We find, therefore, that the Portola PM2.5 
Plan meets the requirements for reasonable notice and public hearings 
in CAA sections 110(a) and 110(l).
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    \15\ The District public notice posted on its website for 
January 23, 2017 public hearing (undated); February 14, 2017 proof 
of publication from Plumas County News of public notice for January 
23, 2017 public hearing; December 14, 2016 proof of publication from 
Feather Publishing Co., Inc. of public notice that public notice for 
January 23, 2017 public hearing published in the Feather River 
Bulletin, Indian Valley Record, and Portola Reporter during the week 
beginning December 14, 2016; and NSAQMD Governing Board Resolution 
2017-01, ``In the Matter of Adopting the Portola Fine Particulate 
Matter (PM2.5) Attainment Plan (Portola Plan) as required 
by the Federal Clean Air Act,'' January 13, 2017.
    \16\ CARB, Notice of evidence of listserve publication, 
``arbcombo--Notice of Public Meeting for February 16, 2017,'' and 
``Notice of Public Meeting to Consider the Approval of the Portola 
PM2.5 State Implementation Plan,'' both dated January 13, 
2017; CARB Board Resolution 17-2, ``Portola PM2.5 State 
Implementation Plan,'' February 16, 2017.
    \17\ CARB Board Resolution 17-28, ``Supplemental Transportation 
Conformity Emissions Budgets for the Portola Fine Particulate Matter 
(PM2.5) Attainment Plan,'' October 26, 2017.
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    CAA section 110(k)(1)(B) requires the EPA to determine whether a 
SIP submission is complete within 60 days of receipt. This section also 
provides that any plan that the EPA has not affirmatively determined to 
be complete or incomplete will become complete by operation of law six 
months after the date of submission. The EPA's SIP completeness 
criteria are found in 40 CFR part 51, appendix V. The February 28, 2017 
and December 20, 2017 SIP submissions became complete by operation of 
law on August 28, 2017 and June 20, 2018, respectively.

IV. Review of the Portola PM2.5 Plan

A. Emissions Inventory

1. Requirements for Emissions Inventories
    CAA section 172(c)(3) requires that each SIP include a 
``comprehensive, accurate, current inventory of actual emissions from 
all sources of the relevant pollutant or pollutants in [the] area . . . 
.'' By requiring an accounting of actual emissions from all sources of 
the relevant pollutants in the area, this section provides for the base 
year inventory to include all emissions that contribute to the 
formation of a particular NAAQS pollutant. For the 2012 
PM2.5 NAAQS, this includes emissions of direct 
PM2.5 as well as the main chemical precursors to the 
formation of secondary PM2.5: NOX, 
SO2, VOC, and ammonia. Primary PM2.5 includes 
condensable and filterable particulate matter.
    A state must include in its SIP submission documentation explaining 
how the emissions data were calculated. In estimating mobile source 
emissions, a state should use the latest emissions models and planning 
assumptions available at the time it develops the SIP submission. 
States are also required to use the EPA's ``Compilation of Air 
Pollutant Emission Factors'' (AP-42) \18\ road dust method for 
calculating re-entrained road dust emissions from paved roads.\19\ The 
latest EPA-approved version of California's mobile source emission 
factor model is EMFAC2014.\20\
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    \18\ The EPA released an update to AP-42 in January 2011 that 
revised the equation for estimating paved road dust emissions based 
on an updated data regression that included new emission tests 
results.
    \19\ 76 FR 6328 (February 4, 2011).
    \20\ The EMFAC model (short for EMission FACtor) is a computer 
model developed by CARB. The EPA approved EMFAC2014 for use in SIP 
revisions and transportation conformity at 80 FR 77337 (December 14, 
2015).
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    In addition to the base year inventory submitted to meet the 
requirements of CAA section 172(c)(3), the State must also submit 
future ``baseline inventories'' for the projected attainment year and 
each RFP milestone year, and any other year of significance for meeting 
applicable CAA requirements.\21\ By ``baseline inventories'' (also 
referred to as ``projected baseline inventories''), we mean projected 
emissions inventories for future years that account for, among other 
things, the ongoing effects of economic growth and adopted emissions 
control requirements. The SIP submission should include documentation 
to explain how the state calculated the emissions projections.
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    \21\ 40 CFR 51.1007(a), 51.1008(b), and 51.1009(f); see also 
U.S. EPA, ``Emissions Inventory Guidance for Implementation of Ozone 
[and Particulate Matter] National Ambient Air Quality Standards 
(NAAQS) and Regional Haze Regulations,'' available at http://www.epa.gov/sites/production/files/2014-10/documents/2014revisedeiguidance_0.pdf.
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2. Emissions Inventory in the Portola PM2.5 Plan
    The Portola PM2.5 nonattainment area emissions inventory 
is typical of a small, high elevation mountain community. There are no 
major stationary sources or large industrial sources (existing or 
anticipated) and residential wood burning is a significant source of 
direct PM2.5. A summary of the planning emissions 
inventories for direct PM2.5 and all PM2.5 
precursors (NOX, SOX, VOC, and ammonia) \22\ for 
the Portola PM2.5 nonattainment area is found in section 
III. Detailed inventories for the Portola PM2.5 
nonattainment area together with documentation for the inventories are 
found in Appendix B of the Plan. CARB and District staff worked jointly 
to develop the emissions inventory for the Portola PM2.5 
nonattainment area. The District worked with operators of the three 
stationary facilities in the nonattainment area to develop the 
stationary source emissions estimates.\23\ CARB staff developed the 
emissions inventory for mobile sources, both on-road and off-road.\24\ 
The District and CARB shared responsibility for developing estimates 
for the area sources such as residential wood burning and paved road 
dust.
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    \22\ The Portola PM2.5 Plan generally uses ``sulfur 
oxides'' or ``SOX'' in reference to SO2 as a 
precursor to the formation of PM2.5. We use 
SOX and SO2 interchangeably throughout this 
notice.
    \23\ CARB's facility search engine website shows for 2016 in the 
Portola PM2.5 nonattainment area there are no major 
stationary sources and only three non-major stationary sources. Two 
of the non-major sources reported zero particulate matter (PM) 
emissions in 2016, and the third non-major source (i.e., White Cap 
Ready Mix #1) reported 1.9 tons per year of PM emissions. For more 
information see https://www.arb.ca.gov/app/emsinv/facinfo/facinfo.php.
    \24\ The EPA regulations refer to ``nonroad'' vehicles and 
engines whereas California Air Resources Board (CARB) regulations 
refer to ``off-road'' vehicles and engines. These terms refer to the 
same types of vehicles and engines, and for the purposes of this 
action, we will be using CARB's chosen term, ``off-road,'' to refer 
to such vehicles and engines.
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    The Plan includes annual average emissions inventories for the 2013 
base year and estimated emissions for the 2019, 2021, and 2022 future 
baseline years. Future baseline inventories are a projection of the 
base year inventory taking into account expected growth trends for each 
source category and emission reductions from control measures adopted 
prior to January 1, 2013. CARB develops emissions projections by 
applying growth and control profiles to the base year inventory.\25\
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    \25\ Portola PM2.5 Plan, Appendix B.
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    Each inventory includes emissions from stationary, area, on-road, 
and non-

[[Page 64777]]

road sources. The inventories use EMFAC2014 for estimating on-road 
motor vehicle emissions.\26\ Re-entrained paved road dust emissions 
were calculated using the EPA's AP-42 road dust methodology.\27\
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    \26\ Portola PM2.5 Plan, Appendix B.
    \27\ Id.
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    Table 1 provides a summary of the annual average inventories in 
tons per day (tpd) of direct PM2.5 and PM2.5 
precursors for the base year of 2013. These inventories provide the 
basis for the control measure analysis and the RFP and attainment 
demonstrations in the Portola PM2.5 Plan. For a detailed 
breakdown of the inventories, see Appendix B, Tables 6-10 in the 
Portola PM2.5 Plan.

Table 1--Portola Annual Average Emissions Inventory for Direct PM2.5 and PM2.5 Precursors for the 2013 Base Year
                                                      (tpd)
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                                   Direct PM2.5
            Category                                    NOX             SOX             VOC           Ammonia
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Stationary Sources..............           0.007           0.002           0.000           0.016           0.018
Area Sources....................           0.468           0.048           0.015           0.661           0.142
On-Road Mobile Sources..........           0.005           0.181          0.0003           0.101           0.005
Off-Road Mobile Sources.........           0.011           0.273          0.0001           0.162          0.0001
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    Totals......................           0.490           0.504           0.016           0.940           0.149
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Source: Portola PM2.5 Plan, Section III, Table 3 (p. 24) and Appendix B, Tables 6-10.

3. The EPA's Evaluation and Proposed Action
    The inventories in the Portola PM2.5 Plan are based on 
the most current and accurate information available to the State and 
District at the time the Plan and its inventories were being developed 
in 2015 and 2016, including the latest version of California's mobile 
source emissions model, EMFAC2014. The inventories comprehensively 
address all source categories in the Portola PM2.5 
nonattainment area and were developed consistent with the EPA's 
inventory guidance. For these reasons, we are proposing to approve the 
2013 base year emissions inventory in the Portola PM2.5 Plan 
as meeting the requirements of CAA section 172(c)(3). We are also 
proposing to find that the projected baseline inventories in the Plan 
provide an adequate basis for the RACM, RFP, and attainment 
demonstrations in the Portola PM2.5 Plan.

B. PM2.5 Precursors

1. Precursor Requirements
    The provisions of subpart 4 of part D, title I of the CAA do not 
define the term ``precursor'' for purposes of PM2.5, nor do 
they explicitly require the control of any specifically identified PM 
precursor. The statutory definition of ``air pollutant'' in CAA section 
302(g), however, provides that the term ``includes any precursors to 
the formation of any air pollutant, to the extent the Administrator has 
identified such precursor or precursors for the particular purpose for 
which the term `air pollutant' is used.'' The EPA has identified 
SO2, NOX, VOC, and ammonia as precursors to the 
formation of PM2.5. Accordingly, the attainment plan 
requirements of subpart 4 apply to emissions of all four precursor 
pollutants and direct PM2.5 from all types of stationary, 
area, and mobile sources, except as otherwise provided in the Act 
(e.g., in CAA section 189(e)).
    Section 189(e) of the Act requires that the control requirements 
for major stationary sources of direct PM10 (which includes 
PM2.5) also apply to major stationary sources of 
PM10 precursors, except where the Administrator determines 
that such sources do not contribute significantly to PM10 
levels that exceed the standard in the area. Section 189(e) contains 
the only expressed exception to the control requirements under subpart 
4 for sources of PM2.5 precursor emissions. Although section 
189(e) explicitly addresses only major stationary sources, the EPA 
interprets the Act as authorizing it also to determine, under 
appropriate circumstances, that regulation of specific PM2.5 
precursors from other sources in a given nonattainment area is not 
necessary.
    Under the PM2.5 SIP Requirements Rule, a state may elect 
to submit to the EPA a ``comprehensive precursor demonstration'' for a 
specific nonattainment area to show that emissions of a particular 
precursor from all existing sources located in the nonattainment area 
do not contribute significantly to PM2.5 levels that exceed 
the standard in the area.\28\ Such a comprehensive precursor 
demonstration must include a concentration-based contribution analysis 
(i.e., evaluation of the contribution of a particular precursor to 
PM2.5 levels in the area) and may also include a 
sensitivity-based contribution analysis (i.e., evaluation of the 
sensitivity of PM2.5 levels in the area to a decrease in 
emissions of the precursor). If the EPA determines that the 
contribution of the precursor to PM2.5 levels in the area is 
not significant and approves the demonstration, the state is not 
required to control emissions of the relevant precursor from existing 
sources in the current attainment plan.\29\
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    \28\ 40 CFR 51.1006(a)(1).
    \29\ Id.
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    The EPA issued the draft PM2.5 Precursor Demonstration 
Guidance (``Draft Guidance'') to provide recommendations to states for 
appropriate precursor demonstrations in nonattainment plan SIP 
submissions.\30\ For the annual PM2.5 NAAQS, section 2.2 of 
the Draft Guidance recommends use of 0.2 [micro]g/m\3\ as a threshold 
below which ambient air quality impacts could be considered 
``insignificant,'' i.e., impacts that do not ``contribute'' to 
PM2.5 concentrations that exceed the NAAQS. When considering 
whether a precursor contributes significantly to PM2.5 
levels which exceed the NAAQS in the area, a state may also consider 
additional factors based on the facts and circumstances of the area. As 
to air quality impacts that exceed the 0.2 [micro]g/m\3\ contribution 
threshold, states may provide additional support for a conclusion that 
a particular precursor does not contribute significantly to ambient 
PM2.5 levels that exceed the NAAQS. States may consider 
information such as the amount by which the impacts exceed the 
recommended contribution threshold, the severity of nonattainment at 
relevant monitors and/or grid cell locations in the area, anticipated 
growth or loss of sources, analyses of speciation data and

[[Page 64778]]

precursor emission inventories, and air quality trends.\31\
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    \30\ EPA Office of Air Quality Planning and Standards, 
``PM2.5 Precursor Demonstration Guidance,'' EPA-454/P-16-
001, November 17, 2016 draft, available at https://www.epa.gov/pm-pollution/draft-pm25-precursor-demonstration-guidance.
    \31\ Id. at 17.
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2. Precursor Demonstration in the Plan
    Section V.C. of the Plan contains the State's demonstration that 
emissions of SOX, NOX, ammonia, and VOC from all 
existing sources in the nonattainment area do not contribute 
significantly to PM2.5 levels that exceed the NAAQS. The 
demonstration includes a concentration-based portion, a sensitivity-
based portion, and additional relevant information. The concentration-
based portion is summarized in Table 8 of the Plan, based on 2013-2014 
species composition data, and used to represent the base year design 
value used as the starting point in the rollback attainment 
demonstration as described in section IV.E.\32\ All four precursors 
together account for 6.3% of the 2013 PM2.5 design value. 
Organic matter and elemental carbon, mainly from wood burning, are the 
dominant contributors and account for 89% of the 2013 design value.
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    \32\ Portola PM2.5 Plan, 51.
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    For VOC emissions, the corresponding ambient PM2.5 
component is anthropogenic Secondary Organic Aerosol (SOA). Based on 
comparison to ambient SOA concentrations per ton of total VOC emissions 
at other California locations, the State estimated Portola SOA 
concentrations of 0.02-0.05 [micro]g/m\3\. The State also noted that 
seasonal organic carbon (OC) measurements at Portola are 
indistinguishable from background levels during the summer. Because SOA 
is a subset of OC, and summer is when SOA is highest due to the warmer 
temperatures, the State found that Portola's SOA is comparable to the 
0.06 [micro]g/m\3\ observed at nearby background interagency monitoring 
of protected visual environments (IMPROVE) sites \33\ and well below 
the 0.2 [micro]g/m\3\ contribution threshold.
---------------------------------------------------------------------------

    \33\ IMPROVE is a monitoring program managed by the EPA and 
other federal and state agencies to assess visibility and aerosol 
conditions including PM2.5 species in Class I areas such 
as national parks. For more information, go to http://vista.cira.colostate.edu/Improve/reconstructed-fine-mass/.
---------------------------------------------------------------------------

    The ambient species concentrations corresponding to SOX, 
NOX, and ammonia were 0.41, 0.46, and 0.48 [micro]g/m\3\, 
respectively. Because these are all above the recommended contribution 
threshold of 0.2 [micro]g/m\3\, the State conducted a follow-up 
sensitivity-based analysis. The sensitivity-based portion of the 
precursor demonstration used a variant of the rollback attainment 
demonstration based on Positive Matrix Factorization (PMF) as described 
in section IV.B.2 of this notice.\34\ The rollback model scales 
PM2.5 component concentrations (excluding background) 
according to changes in emissions. Ammonium nitrate was scaled 
proportional to NOX emissions; ammonium sulfate was scaled 
proportional to SOX emissions; and ammonium was scaled 
proportional to ammonia emissions. These were all on a conservative 
one-to-one basis; that is, a 1% emission change leads to a 1% 
concentration change. The sensitivity emission reductions modeled were 
10%, 25%, 30%, 50%, and 70%.
---------------------------------------------------------------------------

    \34\ PMF is a multivariate source apportionment method that 
attributes PM2.5 observed concentrations to sources 
through statistical and meteorological interpretation of data. PMF 
is one of several EPA recommended receptor modeling methods for 
understanding of source impacts on ambient PM2.5 levels.
---------------------------------------------------------------------------

    As in the attainment demonstration, the precursor demonstration 
used the estimated 2021 design value. The PM2.5 effect of 
both the sensitivity reductions and the yearly reductions were combined 
to estimate the effect on the design value. Table 9 of the Plan lists 
the PM2.5 design values resulting from a 10 to 70% reduction 
in emissions of each pollutant.\35\ For SOX and ammonia, the 
reductions have a negligible impact on the attainment year design 
value. The design values listed for the 70% emission reduction show 
PM2.5 responses of 0.09 and 0.11 [micro]g/m\3\ for 
SOX and ammonia respectively, both well below the 
recommended contribution threshold.
---------------------------------------------------------------------------

    \35\ Portola PM2.5 Plan, 53.
---------------------------------------------------------------------------

    For NOX sensitivity, the Plan includes a discussion of 
the ambient response to a 30% reduction, 0.16 [micro]g/m\3\, which is 
below the 0.2 [micro]g/m\3\ contribution threshold. However, the given 
design values for 50% and 70% reductions show responses of 0.26 
[micro]g/m\3\ and 0.39 [micro]g/m\3\ respectively, which are above the 
recommended contribution threshold.
    Beyond the concentration-based and sensitivity-based analyses, the 
Plan provides several pieces of additional information to help assess 
the significance of NOX as a PM2.5 precursor. 
Table 7 of the Plan shows that NOX emissions in the Portola 
nonattainment area, estimated at 0.5 tpd, are far smaller than the 
NOX emissions in several other California counties, which 
range from 46.5 to 104.0 tpd.\36\ The Plan also shows that 90% of the 
NOX emissions in Portola are from mobile sources, which 
already are stringently controlled; PM2.5 concentrations 
would be not be sensitive to realistic additional control on these 
sources.
---------------------------------------------------------------------------

    \36\ Id. at 47.
---------------------------------------------------------------------------

    Supporting supplemental data from CARB shows trends in emissions 
and species concentrations during 2002-2016.\37\ The data are for the 
Mountain Counties Air Basin, which comprises Plumas County and eight 
other similar counties that are also largely rural, wooded areas 
spanning the foothills to the crest of the Sierra Nevada mountains. 
Ammonia emissions during this period were essentially constant, but 
NOX and SOX emissions decreased by 46% and 67%, 
respectively. During the same time span, nitrate and sulfate 
concentrations decreased by 23% and 16%, respectively. Since nitrate 
and sulfate were responding to NOX and SOX 
emissions reductions, this suggests that ammonium nitrate formation is 
NOX-limited and ammonium sulfate is SOX-limited, 
rather than either being ammonia-limited. These observations support a 
finding that ammonia is an insignificant PM2.5 precursor, 
for which controls would be of little benefit.
---------------------------------------------------------------------------

    \37\ Email with attachment (i.e., Species Trends.xlsx) dated 
February 13, 2018, from Kasia Turkiewicz, CARB, to Scott Bohning and 
John Ungvarsky, EPA.
---------------------------------------------------------------------------

    Based on its evaluations, the State concluded that additional 
controls on PM2.5 precursors would have an insignificant 
effect on PM2.5 concentrations, and that precursors need not 
be included in the controls analysis.
3. The EPA's Evaluation and Proposed Action
    The comprehensive precursor demonstration provided in the Plan 
meets the requirements of 40 CFR 51.1006(a)(1) and is consistent with 
the EPA's recommendations in the Draft Guidance. The demonstration 
contains a concentration-based contribution analysis for VOC and 
sensitivity-based contribution analyses for NOX, 
SOX, and ammonia, together with additional information about 
the Portola area, as recommended in the Draft Guidance (e.g., emission 
inventory and ambient PM2.5 composition data).
    For the SO2 concentration-based analysis, the Plan 
states that background sulfate concentrations are 97% of the 0.41 
[micro]g/m\3\ measured at Portola. The remaining 3% of the sulfate, or 
0.012 [micro]g/m\3\, is attributable to Portola sources. This 3% 
contribution from Portola sources to PM2.5 levels above the 
NAAQS is well below the EPA's 0.2 [micro]g/m\3\ contribution threshold.
    For the VOC concentration analysis, the Plan provides several 
estimates of SOA at Portola. The estimates, which

[[Page 64779]]

can be considered ``data analysis techniques'' as described in the 
Draft Guidance, are appropriate for refining SOA estimates from 
available measurements and provide a convincing case that VOCs do not 
contribute significantly to PM2.5 levels that exceed the 
NAAQS in the area.
    For NOX, the Plan's estimate for the nitrate 
contribution and the corresponding sensitivity to NOX 
reductions may be unrealistically high. The PMF modeling results 
estimated the secondary nitrate contribution to be 5.1% of the total 
PM2.5, whereas the raw chemical composition data estimated 
only 3.3%.\38\ In addition, the concentration-based analysis may have 
overestimated nitrate concentrations because it does not apply the 
sulfate, adjusted nitrate, derived water, inferred carbonaceous balance 
approach (SANDWICH) \39\ for reconciling the mass from speciation 
measurements with that from the Federal Reference Method (FRM) used for 
design values. Because the SANDWICH adjustment generally reduces 
nitrate, due to nitrate losses from FRM monitors, the precursor 
demonstration in the Plan may be overestimating the amount of nitrate 
and the nitrate response to NOX emission reductions. Thus, 
the approach used in the Plan results in a more conservative precursor 
demonstration.
---------------------------------------------------------------------------

    \38\ Plan, Figure 9, 20, and Table 8, 51.
    \39\ Draft Guidance, 23.
---------------------------------------------------------------------------

    The sensitivity-based precursor analysis relies on the same 
methodology as the attainment demonstration, including the very 
conservative assumption that the ambient response to NOX 
reductions is in a 1:1 ratio to the emission change (on a percent 
basis). The responses to SO2 and ammonia reductions were 
below the recommended 0.2 [micro]g/m\3\ contribution threshold, but the 
response to NOX was above the threshold at 50% and 70% 
reductions.
    The Plan includes additional information supporting a conclusion 
that NOX emissions do not contribute significantly to 
PM2.5 levels that exceed the NAAQS in the area. The 
information includes the small size of the NOX emission 
inventory relative to other areas and recognition that mobile sources 
are already highly controlled. These are indications that ambient 
PM2.5 levels would not be sensitive to additional 
NOX controls.
    The EPA also considered two other implications of the data provided 
with the Plan or as a supplement. The supplemental 2002-2016 emissions 
and speciation trends can be used to derive a response factor, the 
percent change in nitrate concentration for each percent change in 
NOX emissions. Because ammonia emissions are constant, they 
provide a reasonable factor to use as the response to reductions of 
NOX in the sensitivity analysis. Using 2002-2016 data 
results in a NOX response factor of 0.378. Using this in a 
variant of the Plan's NOX sensitivity analysis in place of 
the 1:1 assumption, the EPA found that the ambient PM2.5 
response to a 50% NOX reduction is 0.105 [micro]g/m\3\, and 
the response to a 70% reduction is 0.147 [micro]g/m\3\. Both of these 
are below the EPA's recommended contribution threshold of 0.2 [micro]g/
m\3\. (The original responses were 0.277 and 0.388 [micro]g/m\3\.) 
Since the years 2013-2016 were somewhat anomalous, with some nitrate 
increases, the EPA carried out the same exercise using just 2002-2011 
data, which resulted in a NOX response factor of 0.625. In 
turn, this results in a 50% response of 0.173 [micro]g/m\3\ and a 70% 
response of 0.243 [micro]g/m\3\. The 70% response is above but 
considerably closer to the recommended 0.2 [micro]g/m\3\ contribution 
threshold. When considered in light of the additional information 
discussed above, the 70% response supports a conclusion that 
NOX emissions do not contribute significantly to 
PM2.5 levels that exceed the NAAQS in the area.
    A second implication of the data from the Plan concerns the effect 
of a 70% NOX reduction on the year that the Portola area can 
attain the NAAQS. Under the PM2.5 SIP Requirements Rule at 
40 CFR 51.1009(a)(4)(i), if a Moderate PM2.5 nonattainment 
area, such as the Portola area, can show that reducing emission of a 
precursor is not necessary for expeditious attainment of the NAAQS and 
cannot advance attainment by a year,\40\ then that precursor need not 
be controlled for attainment purposes. Even assuming a NOX 
reduction of 70%, which is very large in comparison with the historical 
reductions of about 6% per year, and assuming an unrealistically 
conservative 1:1 nitrate response ratio, the resulting response is 
0.388 [micro]g/m\3\, which is less than the average 0.41 [micro]g/m\3\ 
per year PM2.5 decrease seen during 2019-2021 in the 
attainment demonstration. This observation supports a conclusion that 
controlling NOX is not necessary for expeditious attainment 
of the NAAQS because it would not advance the attainment date by a year 
in the Portola nonattainment area.
---------------------------------------------------------------------------

    \40\ 81 FR 58010, 58020 (August 24, 2016).
---------------------------------------------------------------------------

    The EPA is proposing to approve the State's demonstration that 
emissions of PM2.5 precursors (i.e., SOX, 
NOX, ammonia, and VOC) from all existing sources located in 
the nonattainment area do not contribute significantly to 
PM2.5 levels that exceed the standards in the area. If the 
EPA finalizes this proposal, the State and District would not be 
required to control emissions of these precursors from existing sources 
in the Portola PM2.5 Plan for purposes of the 2012 annual 
PM2.5 NAAQS. The State, District, and the EPA will reexamine 
this issue if the Portola area fails to attain the NAAQS and EPA 
reclassifies the area to Serious for the 2012 annual PM2.5 
NAAQS.

C. Reasonably Available Control Measures/Reasonably Available Control 
Technology

1. Requirements for RACM/RACT
    The general subpart 1 attainment plan requirement for RACM and RACT 
is described in CAA section 172(c)(1), which requires that attainment 
plan submissions ``provide for the implementation of all reasonably 
available control measures as expeditiously as practicable (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)'' and provide for attainment of the NAAQS.
    The attainment planning requirements specific to PM2.5 
under subpart 4 likewise impose upon states with nonattainment areas 
classified as Moderate an obligation to develop attainment plans that 
require RACM/RACT on sources of direct PM2.5 and all 
PM2.5 plan precursors. CAA section 189(a)(1)(C) requires 
that Moderate area PM2.5 SIPs contain provisions to assure 
that RACM/RACT are implemented no later than 4 years after designation 
of the area. The EPA reads CAA sections 172(c)(1) and 189(a)(1)(C) 
together to require that attainment plans for Moderate nonattainment 
areas provide for the implementation of RACM and RACT for existing 
sources of PM2.5 and those PM2.5 precursors 
subject to control in the nonattainment area as expeditiously as 
practicable but no later than 4 years after designation.\41\
---------------------------------------------------------------------------

    \41\ This interpretation is consistent with guidance provided in 
the General Preamble at 13540.
---------------------------------------------------------------------------

    The PM2.5 SIP Requirements Rule defines RACM as ``any 
technologically and economically feasible measure that can be 
implemented in whole or in part within 4 years after the effective date 
of designation of a PM2.5 nonattainment area and that 
achieves permanent and enforceable reductions in direct 
PM2.5 emissions and/or PM2.5 plan precursor

[[Page 64780]]

emissions from sources in the area.\42\ RACM includes reasonably 
available control technology (RACT).'' The EPA has historically defined 
RACT as the lowest emission limitation that a particular stationary 
source is capable of meeting by the application of control technology 
(e.g., devices, systems, process modifications, or other apparatus or 
techniques that reduce air pollution) that is reasonably available 
considering technological and economic feasibility.\43\
---------------------------------------------------------------------------

    \42\ 40 CFR 51.1000. ``PM2.5 plan precursors'' are 
defined as ``those PM2.5 precursors required to be 
regulated in the applicable attainment plan and/or NNSR program'' 
and ``PM2.5 precursors'' are SO2, 
NOX, VOC, and ammonia.
    \43\ General Preamble at 13541 and 57 FR 18070, 18073-74 (April 
28, 1992).
---------------------------------------------------------------------------

    Under the PM2.5 SIP Requirements Rule, those control 
measures that otherwise meet the definition of RACM but ``can only be 
implemented in whole or in part during the period beginning 4 years 
after the effective date of designation of a nonattainment area and no 
later than the end of the sixth calendar year following the effective 
date of designation of the area'' must be adopted and implemented by 
the state as ``additional reasonable measures.'' \44\
---------------------------------------------------------------------------

    \44\ 40 CFR 51.1000, 51.1009(a)(i)(B), and 51.1009(a)(ii)(B).
---------------------------------------------------------------------------

    States must provide written justification in a SIP submission for 
eliminating potential control options from further review on the basis 
of technological or economic infeasibility.\45\ An evaluation of 
technological feasibility may include consideration of factors such as 
a source's process and operating conditions, raw materials, physical 
plant layout, and non-air quality and energy impacts (e.g., increased 
water pollution, waste disposal, and energy requirements).\46\ An 
evaluation of economic feasibility may include consideration of factors 
such as cost per ton of pollution reduced (cost-effectiveness), capital 
costs, and operating and maintenance costs.\47\ Absent other 
indications, the EPA presumes that it is reasonable for similar sources 
to bear similar costs of emissions reductions. Economic feasibility of 
RACM and RACT is thus largely informed by evidence that other sources 
in a source category have in fact applied the control technology, 
process change, or measure in question in similar circumstances.\48\
---------------------------------------------------------------------------

    \45\ 40 CFR 51.1009(a)(3).
    \46\ 40 CFR 51.1009(a)(3); see also 57 FR 18070, 18073-74.
    \47\ Id.
    \48\ 57 FR 18070, 18074.
---------------------------------------------------------------------------

    Consistent with these requirements, NSAQMD must implement RACM, 
including RACT, for direct PM2.5 emission sources no later 
than April 15, 2019, and must implement additional reasonable measures 
for these sources no later than December 31, 2021.
    The CAA explicitly provides for the use of economic incentive 
programs (EIPs), such as the Portola voluntary wood stove change-out 
program, as one tool for states to use to achieve attainment of the 
NAAQS.\49\ EIPs use market-based strategies to encourage the reduction 
of emissions from stationary, area, and mobile sources in an efficient 
manner. The EPA has promulgated regulations for statutory EIPs required 
under section 182(g) of the Act and has issued guidance for 
discretionary EIPs.\50\ Where a state relies on a discretionary EIP in 
a SIP submission, the EPA evaluates the programmatic elements of the 
EIP to determine whether the resulting emission reductions are 
quantifiable, surplus, enforceable and permanent.\51\ These four 
fundamental ``integrity elements,'' which apply to all EIPs and other 
incentive/voluntary measures relied on for SIP purposes, are designed 
to ensure that such programs and measures satisfy the applicable 
requirements of the Act.
---------------------------------------------------------------------------

    \49\ See, e.g., CAA sections 110(a)(2)(A), 172(c)(6), and 
183(e)(4).
    \50\ A ``discretionary economic incentive program'' is ``any EIP 
submitted to the EPA as an implementation plan revision for purposes 
other than to comply with the statutory requirements of sections 
182(g)(3), 182(g)(5), 187(d)(3), or 187(g) of the Act.'' 40 CFR 
51.491; see also 59 FR 16690 (April 7, 1994) (codified at 40 CFR 
part 51, subpart U) and ``Improving Air Quality with Economic 
Incentive Programs,'' EPA, January 2001 (``2001 EIP Guidance'').
    \51\ 2001 EIP Guidance, section 4.1.
---------------------------------------------------------------------------

2. RACM/RACT Analysis in the Portola PM2.5 Plan
    The State's RACM and RACT analysis is in section VI.D of the 
Portola PM2.5 Plan. The emissions inventory analysis, 
conducted as part of the RACT analysis, confirmed that no major 
stationary sources of direct PM2.5 or any PM2.5 
precursor are located in the Portola PM2.5 nonattainment 
area. As discussed above in section IV.C, the State provided a 
demonstration that PM2.5 precursor emissions do not 
contribute significantly to ambient PM2.5 levels that exceed 
the standards in the area. Therefore, the Portola PM2.5 Plan 
contains a RACM demonstration addressing only sources of direct 
PM2.5.
3. Primary Sources of PM2.5 in the Nonattainment Area
    PM2.5 concentrations in the Portola PM2.5 
nonattainment area are dominated by direct PM2.5 emissions 
from residential wood burning. Chapter II of the Plan documents the 
State and District's bases for concluding that wood burning is the 
dominant source of PM2.5 throughout the nonattainment area. 
The documentation includes seasonal and diurnal patterns in 
PM2.5 concentrations, chemical composition data, PMF 
modeling, and statistical correlations between PM2.5 mass 
and levoglucosan (a wood burning tracer). The PMF model estimated that 
76% of ambient PM2.5 on an annual basis is from wood 
burning. Burning of garbage in stoves, fireplaces, and in open burn 
piles contributes another 2.5% of annual PM2.5 levels.
4. RACM Measures
    Table 2 lists the RACM measures in the Portola PM2.5 
Plan. We discuss each of these measures in detail further below.

                          Table 2--Summary of RACM in Portola PM2.5 Nonattainment Area
----------------------------------------------------------------------------------------------------------------
                                        Direct PM2.5 emission
               Measure                     reductions (tpd)         Scheduled action       Implementation year
 
----------------------------------------------------------------------------------------------------------------
Voluntary Wood Stove Change-out        0.062 \a\..............  2016...................  2016-2020.
 Program with Enforceable Commitment.
City of Portola Wood Stove and         Not estimated \b\......  2016...................  2021.
 Fireplace Ordinance Mandatory Wood
 Burning Curtailment.
Other Provisions in City of Portola    Not estimated \d\......  2016...................  2016.
 Wood Stove and Fireplace Ordinance
 \c\.
Open Burning Requirements (NSAQMD      Not estimated \e\......  2019...................  2019.
 Rules 300-317).
CARB Mobile Source Programs..........  0.006..................  Ongoing................  Ongoing.
Opacity Rule (NSAQMD Rule 202).......  Not estimated..........  Ongoing................  Ongoing.

[[Page 64781]]

 
Educational Campaign.................  Not estimated \f\......  Ongoing................  Ongoing.
Voluntary Wood Burning Curtailment     Not estimated \f\......  2016...................  2017.
 Program (``Clear the Air; Check
 Before You Light'').
----------------------------------------------------------------------------------------------------------------
\a\ The reductions from the wood stove change-out program are based on the average of the cumulative annual
  emission reductions from 2019-2021 (i.e., 0.045 tpd in 2019, 0.065 tpd in 2020, and 0.077 tpd in 2021).
\b\ Additional reductions not calculated because a variety of factors affect the amount of any potential
  reductions still available after implementation of change-out program (e.g., number of remaining uncertified
  wood stoves within City of Portola; whether the 30 [mu]g/m\3\ air quality threshold is triggered to implement
  the curtailment; and enforcement of the curtailment).
\c\ Additional reductions from the other provisions in the Ordinance and the distribution of 20 moisture meters
  per year are uncertain (e.g., reductions from prohibition on burning unseasoned wood) and/or overlap with
  reductions from the change-out program. To avoid double counting of reductions from the Ordinance and the
  change-out programs, no additional reductions from the Ordinance are relied on for attainment.
\d\ Other provisions that apply in the Ordinance include, for example, prohibiting: Installation of an
  uncertified wood burning device, unqualified fireplace, or uncertified fireplace in new construction or
  remodel; more than one certified wood burning heater per dwelling unit in new construction; a wood burning
  device as the sole source of heat in new construction; installation of an outdoor wood-burning boiler or
  hydronic heater; uncertified wood burning heater remaining in any property upon change of ownership; burning
  of garbage or unpermitted fuels, including unseasoned wood (less than 20% moisture content) in a wood burning
  devices.
\e\ Additional reductions from strengthening requirements applicable to non-agricultural open burning (e.g.,
  backyard and barrel burning) to be determined at time of anticipated rulemaking in 2019, but because the non-
  agricultural open burning inventory is small, the additional reductions will not advance attainment.
\f\ For RACM, attainment, and RFP, the District is not relying on any reductions from the educational programs
  or the voluntary wood burning curtailment program.
Source: Portola PM2.5 Plan, 37 (Table 4).

a. Voluntary Wood Stove Change-Out Program
    Because ambient PM2.5 in the Portola area is primarily 
caused by residential wood burning, CARB and the NSAQMD have chosen to 
implement a voluntary wood stove change-out program as the primary RACM 
control strategy for the entire Portola PM2.5 nonattainment 
area. Appendix L of the Plan details the voluntary wood stove change-
out program. Its implementation began in 2016 and will continue through 
2020. See Table 3 below for the phased schedule of changeouts.

                 Table 3--Wood Stove Change-Out Schedule
------------------------------------------------------------------------
                                                 Stove changeouts
                  Year                   -------------------------------
                                             Per year       Cumulative
------------------------------------------------------------------------
2016....................................             100             100
2017....................................             100             200
2018....................................             150             350
2019....................................             150             500
2020....................................             100             600
2021....................................               0             600
2022....................................               0             600
------------------------------------------------------------------------

    The woodstove change-out program is primarily funded by the EPA and 
the District. The District has approximately $3 million to fund the 
replacement of 600 of the estimated 664 uncertified wood stoves \52\ in 
use in the nonattainment area. The District is utilizing $2.48 million 
through the EPA's 2015 Targeted Air Shed Grant program \53\ and 
$400,000 from H&S Performance (H&S) pursuant to a December 17, 2015 
Consent Agreement and Final Order between H&S and the EPA.\54\ 
Additionally, the District is contributing up to $60,000 from the 
Plumas County portion of the District's Assembly Bill 2766 Motor 
Vehicle Registration fee surcharge.
---------------------------------------------------------------------------

    \52\ Throughout this notice, we use the term ``uncertified wood 
stove'' to refer to a wood heater that is not certified under the 
applicable Phase II requirements of the EPA's new source performance 
standards (NSPS) promulgated in 1988 for new residential wood 
heaters at 40 CFR part 60, subpart AAA, as effective February 26, 
1988 (53 FR 5860). In 2015, the EPA revised subpart AAA, Standards 
of Performance for New Residential Wood Heaters (``2015 NSPS'') with 
an effective date of May 15, 2015, and a sell-through date of 
December 31, 2015. See 53 FR 5860 (March 15, 2015). Because the 
Voluntary Wood Stove Change-out Program began after December 31, 
2015, all new certified wood heaters sold in the Portola 
PM2.5 nonattainment area must meet the applicable 
requirements in the 2015 NSPS.
    \53\ The Targeted Air Shed grant program is intended to improve 
air quality in areas of the US with the highest levels of pollution. 
For more information, see https://www.epa.gov/grants/air-grants-and-funding.
    \54\ In the Matter of H&S Performance, LLC, Consent Agreement 
and Final Order (docket no. CAA-HQ-2015-8248), entered December 17, 
2015. Under this agreement, H&S Performance, LLC agreed to provide 
$400,000 to the NSAQMD to replace, retrofit, or upgrade at least 400 
inefficient wood-burning appliances.
---------------------------------------------------------------------------

    The change-out program includes specific requirements designed to 
achieve quantifiable, surplus, enforceable, and permanent 
PM2.5 emission reductions in the entire Portola 
PM2.5 nonattainment area. The program requirements ensure, 
among other things, that older, dirtier wood stoves currently in 
operation in the Portola PM2.5 nonattainment area will be 
replaced with EPA-certified wood stoves or other less-polluting 
devices. Residents of the City of Portola and low-income residents 
living outside the city but within the nonattainment area qualify for 
up to $3,500 to replace an uncertified wood burning device with an EPA-
certified wood burning device. The $3,500 covers all or most of the 
change-out costs. In an effort to replace the uncertified devices with 
the cleanest technology available, the District offers an additional 
$1,000 to city residents or low-income residents within the 
nonattainment area for every uncertified wood stove replaced with a 
pellet, propane, or kerosene device. For all other residents living 
outside the City of Portola but within the nonattainment area, the 
District offers $1,500 to replace an uncertified wood burning device 
with an EPA-certified wood burning device and $3,000 to replace an 
uncertified wood burning device with a pellet, propane or kerosene 
heating device. An incentive is available within the entire 
nonattainment area, but the two-tier funding approach increases the 
likelihood of the greatest number of changeouts occurring in the city, 
the area with the greatest concentration of people and low-income 
residents in the nonattainment area. As of September 30, 2018, 
approximately 260 changeouts were completed, and an additional 49 
applications were approved for possible future changeouts.\55\
---------------------------------------------------------------------------

    \55\ Portola Monthly Air Quality Update from NSAQMD, September 
2018.
---------------------------------------------------------------------------

    The change-out program also includes requirements for participating

[[Page 64782]]

contractors/retailers to sign a contract with NSAQMD. Contractors/
retailers must meet licensing, permitting, and certification 
requirements. The contract includes specific requirements for the 
collection and retention of documents, such as:
    [ssquf] Program tracking form,
    [ssquf] Copy of change-out cost estimate with District approval 
signature,
    [ssquf] Photo of uncertified woodstove installed and operational in 
home (prior to replacement by certified device),\56\
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    \56\ The District also developed a memorandum of understanding 
with the City of Portola to destroy the replaced stoves. The City 
matches the stove with the program tracking number, cuts the stove 
in half with a plasma torch, and stores the stove in a locked yard. 
The City fills out and signs a verification of destruction form and 
submits it to the District. The form contains the tracking number 
and photo of the destroyed stove. See Portola PM2.5 Plan, 
32.
---------------------------------------------------------------------------

    [ssquf] Photo of certified device installed,
    [ssquf] Copy of building permit,
    [ssquf] Acknowledgement of training form (homeowner/renter), and
    [ssquf] Final invoice.
    The retailer/contractor must also meet the following requirements 
for retention of records and providing training to homeowners:
    [ssquf] Accounting records relating to the change-out program must 
be retained for five years and made available for possible review by 
federal, State and District agencies,
    [ssquf] Encourage homeowners to consider replacing wood appliances 
with alternative fuel devices, such as propane, pellet or kerosene, and
    [ssquf] Train homeowners on proper appliance operation and 
acceptable fuels to maximize the emission reductions, including a form 
signed by homeowners stating that they were trained to properly operate 
their new heating device.
    To provide assurance that the voluntary change-out program will 
achieve the intended emissions reductions, the District adopted an 
enforceable commitment to replace 600 uncertified stoves with cleaner 
burning devices by December 31, 2020. The EPA approved this enforceable 
commitment into the SIP at 83 FR 13871 (April 2, 2018). The enforceable 
commitment obligates the NSAQMD to achieve specific amounts of 
PM2.5 emission reductions through implementation of the 
woodstove change-out program by specific years, to submit annual 
reports to the EPA detailing its implementation of the program and the 
projected emission reductions, and to adopt and submit substitute 
measures by specific dates if the EPA determines that the woodstove 
change-out program will not achieve the necessary emission reductions. 
The EPA's Technical Support Document for its April 2, 2018 final action 
has more information about the enforceable commitment.
b. City of Portola Wood Stove and Fireplace Ordinance
    On June 22, 2016, the City of Portola adopted Ordinance No. 344, 
``An Ordinance of the City of Portola, County of Plumas Amending 
Chapter 15.10 of the City of Portola Municipal Code Providing for 
Regulation of Wood Stoves and Fireplaces'' (``City Ordinance''). The 
City Ordinance is in Appendix M of the Plan. The EPA approved the City 
Ordinance into the SIP at 83 FR 9213 (March 5, 2018).
    The City Ordinance includes a mandatory burning curtailment 
provision effective January 1, 2021. The mandatory curtailment will 
restrict wood burning under specific conditions. If the District 
determines that adverse meteorological conditions are expected to 
persist and PM2.5 may exceed 30 [mu]g/m\3\ on a given day in 
January, February, November, or December, the District will call a ``No 
Burn Day.'' When a No Burn Day is called, no person may operate a wood 
burning heater, wood burning fireplace, wood-fired fire pit or wood-
fired cookstove within the city limits unless it is an approved and 
currently registered EPA-certified wood burning heater.\57\ The 
curtailment provision encourages owners of uncertified stoves to 
upgrade to certified stoves or risk not being able to use their 
uncertified wood burning device on No Burn Days called after January 1, 
2021. The curtailment provision does not take effect until January 1, 
2021, giving homeowners and renters time to change their stoves to EPA-
certified devices during the five-year implementation of the voluntary 
change-out program.
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    \57\ See section 15.10.060 of the City Ordinance. In section 
15.10.020 of the City Ordinance, ``wood burning heater'' is defined 
as an enclosed wood-burning device capable of and intended for space 
heating such as a wood stove, pellet-fueled wood heater, or wood-
burning fireplace insert, and ``EPA-certified'' is defined as any 
wood burning heater with a Phase II certification or a more 
stringent certification as currently enforced in the NSPS.
---------------------------------------------------------------------------

    The City Ordinance and the District's wood stove change-out program 
collectively establish most of the recommended program elements 
outlined in the EPA's guidance document entitled ``Strategies for 
Reducing Residential Wood Smoke,'' \58\ including:
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    \58\ EPA, ``Strategies for Reducing Residential Wood Smoke,'' 
Publication No. EPA-456/B-13-001, revised March 2013.
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    [ssquf] A wood burning curtailment program (section 15.10.060),
    [ssquf] Requirements to remove uncertified wood burning stoves upon 
home resale (section 15.10.040.A),
    [ssquf] Restrictions on wood burning devices in new construction 
(section 15.10.030.B),
    [ssquf] Restrictions on the installation of wood burning fireplaces 
(sections 15.10.030.A and 15.10.040.B),
    [ssquf] A requirement that all wood burning stoves sold or 
transferred within the District meet the EPA's current new source 
performance standard certification (section 15.10.030.A),
    [ssquf] A prohibition on the installation of wood fired boilers or 
hydronic heaters (sections 15.10.030.15, 15.10.030.A and 15.10.070),
    [ssquf] Requirements regarding wood moisture content (section 
15.10.050.A),
    [ssquf] Restrictions on types of materials that may be burned 
(seasoned wood, uncolored paper, pellets, and manufactured logs) 
(section 15.10.050),
    [ssquf] A wood burning stove change-out program (described above), 
and
    [ssquf] Education and outreach programs, including a requirement 
for wood stove retailers to distribute educational materials provided 
by the District (section 15.10.080).
    Although natural gas is not available in the area, the City 
Ordinance does not include any exemption for a residence where an 
uncertified wood stove is the sole source of heat. The City Ordinance 
is thus more stringent than curtailment provisions implemented by other 
air districts, most of which exempt households using wood stoves as a 
sole source of heat from curtailment requirements.\59\
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    \59\ See e.g., South Coast Air Quality Management District Rule 
445 (amended May 3, 2013), paragraph (f)(7)(A), and Sacramento 
Metropolitan Air Quality Management District Rule 421 (amended 
September 24, 2009), paragraph 112.
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    The District considered expanding the requirements of the City 
Ordinance to the entire nonattainment area but determined that this was 
not feasible because the District did not have sufficient funding to 
offer incentives to cover the full cost of changeouts outside of the 
City of Portola. Some residents living outside of the city limits may 
not have sufficient resources to changeout their stoves. For these 
residents, the wood burning prohibition in the City Ordinance could 
cause unintended health risks if their sole source of heat is an 
uncertified wood stove, and they were prohibited from using it. In the 
future, expanding application of the City Ordinance beyond city limits 
will be contingent upon availability of more generous incentive funds 
for people residing outside the city limits. The

[[Page 64783]]

Plan states that if additional funding becomes available in the future, 
the District will offer more generous incentives to residents living 
outside city limits and consider expanding mandatory burning 
curtailment to the entire nonattainment area.\60\
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    \60\ Portola PM2.5 Plan, Table 4, 84-85.
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c. Open Burning (NSAQMD Rules 300-317)
    The District enforces open burning requirements in NSAQMD Rules 
300--317 that apply to a variety of area sources such as agricultural 
burning, forest burning, range improvement, and residences. The 
District's smoke management program ensures that open burning occurs on 
days with good dispersion to minimize the impact from PM2.5 
concentrations. The EPA approved these rules into the SIP at 62 FR 
48480 (September 16, 1997) and 64 FR 45170 (August 19, 1999).
    Within the Portola nonattainment area, wood smoke can originate 
from open burning or from home heating devices. Residents of this area 
occasionally burn yard debris in open piles. Land managers (e.g., U.S. 
Forest Service) perform prescribed burns of timber harvest waste to 
promote fire safety and maintain forest health. Both residents and land 
managers must request a burn permit prior to starting a fire. The 
District, in coordination with CARB, makes a declaration of either a 
permissive Burn Day or a No Burn Day in the context of open burning 
only. It does not apply to wood burning devices and is distinct from 
the more stringent No Burn Day program previously described in the City 
Ordinance. The District and CARB consider a number of factors in making 
no-burn declarations to ensure that smoke from open burning will not 
unduly contribute to the ambient PM2.5 mass.\61\
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    \61\ Id. at 22.
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    To further reduce PM2.5 emissions during winter, the 
Portola PM2.5 Plan contains a commitment by the District to 
strengthen its open burning rule in 2019. The District is assessing the 
feasibility of green waste collection in the nonattainment area and 
will consider whether to adopt open burning requirements similar to 
District Rule 318 (``American Valley Burning Restrictions''), which 
prohibits the open burning of yard waste and debris or other rubbish 
from November 15 to March 15 in a portion of the American Valley 
containing Quincy and East Quincy.\62\
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    \62\ Id. at 36.
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d. Mobile Source Measures
    Mobile sources account for approximately 3% of the overall direct 
PM2.5 emissions inventory in the Portola PM2.5 
nonattainment area. The Plan projects that CARB's continued 
implementation of adopted mobile source control measures \63\ will 
decrease direct PM2.5 emissions by 2021 and provide 7% of 
the total reductions needed to attain the 2012 PM2.5 NAAQS. 
As part of the State's RACM analysis for the mobile source control 
program, described on pages 86-90 of the Portola PM2.5 Plan, 
CARB concludes that in light of the comprehensiveness and stringency of 
its mobile source program, all RACM under CARB's jurisdiction are 
already being implemented.
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    \63\ CARB has unique authority under CAA section 209 (subject to 
a waiver or authorization by the EPA) to adopt and implement new 
emissions standards for many categories of vehicles and engines. 
CARB has adopted standards and other requirements related to the 
control of emissions from numerous types of new and in-use on-road 
and off-road vehicles and engines, such as trucks, buses, 
motorcycles, passenger cars, off-road engines (gasoline and diesel-
powered), off-road diesel fueled fleets, portable equipment, and 
marine engines. Generally, these regulations have been submitted and 
approved as revisions to the California SIP. See, e.g., 77 FR 20308 
(April 4, 2012), 81 FR 39424 (June 16, 2016), 82 FR 14446 (March 21, 
2017), and 83 FR 23232 (May 18, 2018).
---------------------------------------------------------------------------

e. Visible Emissions (NSAQMD Rule 202)
    Rule 202 limits visible emissions (e.g., particulates) and is 
enforced by NSAQMD. The EPA approved this rule into the SIP at 62 FR 
48480 (September 16, 1997). Enforcement of Rule 202 will help identify 
households with highly visible emissions that may still be using 
uncertified wood stoves and possibly eligible for the change-out 
program. Rule 202 prohibits any person from discharging into the 
atmosphere any air contaminant for more than 3 minutes in any hour that 
is as dark as, or darker in shade than, that designated as No. 1 on the 
Ringelmann Chart or ``of such opacity as to obscure an observer's view 
to a degree equal to or greater than does smoke.'' \64\
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    \64\ NSAQMD Rule 202, ``Visible Emissions'' (adopted September 
11, 1991).
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f. Educational Campaign
    The District is developing other voluntary measures to reduce the 
impact of wood smoke on PM2.5. The District is conducting an 
aggressive outreach and educational campaign to help residents 
understand the benefits of changing from an old wood stove to a cleaner 
home heating device and the importance of clean burning. The District 
worked closely with the City of Portola and enlisted outreach partners 
such as the local hardware and grocery store, post office, library, 
senior community center, and schools to assist in the distribution of 
educational materials and advertise the change-out program. In 
addition, the Ordinance includes a requirement that retailers and 
contractors provide educational materials with the sale of a wood-
burning device.\65\
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    \65\ Portola PM2.5 Plan, 34-35.
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g. Voluntary Wood Burning Curtailment Program
    On November 1, 2017, the District began implementing ``Clear the 
Air; Check Before You Light,'' a voluntary wood burning curtailment 
program that runs during the peak wood-burning period (i.e., November 1 
through February 28) in the Portola nonattainment area. When conditions 
exist for potentially poor air quality, the District will issue an air 
quality advisory to notify the public. When an advisory is triggered 
the District will recommend avoiding the use of any wood burning device 
(including wood stoves, fireplaces, fire pits and cook stoves) to help 
reduce potential health impacts and possibly prevent an exceedance of 
federal/state air pollution standards. Use of alternative sources of 
heat such as electricity, propane or kerosene, are encouraged when an 
advisory is announced.\66\
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    \66\ NSAQMD Press Release dated October 25, 2017, Greater 
Portola Area Wintertime Advisory Program in Effect.
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5. The EPA's Evaluation and Proposed Action
    As part of the EPA's March 5, 2018, final action approving the City 
Ordinance into the SIP, the EPA considered whether the City Ordinance 
includes all technologically and economically feasible measures for 
wood burning devices. We compared the provisions in the City Ordinance 
with other wood burning rules and with the recommendations in the EPA's 
guidance document entitled ``Strategies for Reducing Residential Wood 
Smoke.'' \67\ Based on this evaluation, we concluded that the City 
Ordinance and the District's wood stove change-out program collectively 
implement RACM and additional reasonable measures for residential wood 
burning devices in the Portola nonattainment area.\68\
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    \67\ EPA, ``Strategies for Reducing Residential Wood Smoke,'' 
Publication No. EPA-456/B-13-001, revised March 2013, and EPA, 
``Residential Wood Combustion Summary of Measures--DRAFT,'' January 
2016.
    \68\ 83 FR 9213 (November 3, 2017) and EPA, Region IX Air 
Division, ``Technical Support Document for the EPA's Rulemaking for 
the California State Implementation Plan, Northern Sierra Air 
Quality Management District, City of Portola Ordinance 344, Wood 
Stove and Fireplace Ordinance,'' July 2017.

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[[Page 64784]]

    We note that the curtailment provisions of the City Ordinance do 
not take effect until 2021. Given that uncertified wood stoves are 
currently the primary source of heat for many residents in Portola, we 
do not believe it is reasonable to require implementation of a 
mandatory curtailment program prior to implementation of the District's 
five-year wood stove change-out program, which provides funding for the 
replacement of 600 uncertified wood stoves between 2016 and 2020. After 
these incentive funds are disbursed, however, implementation of a 
mandatory curtailment program in the Portola nonattainment area is 
feasible. We propose to find that the District's enforceable 
commitments concerning implementation of the wood stove change-out 
program and related monitoring and reporting commitments implement RACM 
for the control of PM2.5 emissions from residential wood 
burning in the Portola area. Because the curtailment provision in the 
City Ordinance otherwise meets the definition of RACM but is 
implemented during the period beginning 4 years after the area's 
designation as nonattainment and before the attainment date, we 
consider it an additional reasonable measure for purposes of attaining 
the 2012 PM2.5 NAAQS.
    Under the CAA, the EPA is charged with establishing national 
emissions limits for mobile sources. States are generally preempted 
from establishing such limits except for California, which can 
establish these limits subject to EPA waiver or authorization under CAA 
section 209 (referred to herein as ``waiver measures''). Over the 
years, the EPA has issued waivers (for on-road vehicles and engines 
measures) or authorizations (for non-road vehicle and engine measures) 
for many mobile source regulations adopted by CARB.
    In the past, the EPA allowed California to take into account 
emissions reductions from waiver measures, notwithstanding the fact 
that these regulations had not been approved as part of the California 
SIP. However, in response to the decision by the United States Court of 
Appeals for the Ninth Circuit in Committee for a Better Arvin v. 
EPA,\69\ the EPA approved waiver measures as revisions to the 
California SIP.\70\ CARB's mobile source program extends beyond 
regulations that are subject to the waiver or authorization process set 
forth in CAA section 209 to include standards and other requirements to 
control emissions from in-use heavy duty trucks and buses, gasoline and 
diesel fuel specifications, and many other types of mobile sources. 
Generally, these regulations have been submitted and approved as 
revisions to the California SIP.\71\ The Portola PM2.5 Plan 
relies to a very small extent on emissions reductions from 
implementation of the waiver measures through the use of emissions 
models such as EMFAC2014.
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    \69\ Committee for a Better Arvin v. EPA, 786 F.3d 1169 (9th 
Cir. 2015) (``Arvin''). In Arvin, the Ninth Circuit concluded that 
CAA section 110(a)(2)(A) requires that all state and local control 
measures on which SIPs rely to attain the NAAQS, including 
California waiver measures, be included in the SIP and thereby 
subject to enforcement by the EPA and the general public. This 
decision struck down the EPA's longstanding practice of approving 
California plans that rely on emissions reductions from waiver 
measures notwithstanding their lack of approval as part of the SIP.
    \70\ See, e.g., 81 FR 39424 (June 16, 2016), 82 FR 14447 (March 
21, 2017), and 83 FR 23232 (May 18, 2018).
    \71\ See, e.g., the EPA's approval of standards and other 
requirements to control emissions from in-use heavy-duty diesel-
powered trucks, at 77 FR 20308 (April 4, 2012), revisions to the 
California on-road reformulated gasoline and diesel fuel regulations 
at 75 FR 26653 (May 12, 2010), and revisions to the California motor 
vehicle I/M program at 75 FR 38023 (July 1, 2010).
---------------------------------------------------------------------------

    The EPA is proposing to find that the District's enforceable 
commitment to implement the voluntary wood stove change-out program, 
the City Ordinance, CARB's mobile source program, the District's 
commitment to strengthen its open burning measure, and other controls 
on sources in the nonattainment area together implement all RACM and 
RACT for the control of direct PM2.5 in the Portola 
nonattainment area. This collective set of PM2.5 control 
requirements, particularly with respect to homes where wood-burning is 
the sole source of heat, is at least as stringent as analogous measures 
implemented in other Moderate PM2.5 nonattainment areas with 
similar geography and demographics. Accordingly, the EPA is proposing 
to approve the PM2.5 RACM demonstration in the Portola 
PM2.5 Plan as meeting the requirements of CAA sections 
172(c)(1) and 189(a)(1)(C) and 40 CFR 51.1009.

D. Major Stationary Source Control Requirements Under CAA Section 
189(e)

    Section 189(e) of the Act specifically requires that the control 
requirements applicable to major stationary sources of direct 
PM2.5 also apply to major stationary sources of 
PM2.5 precursors, except where the Administrator determines 
that such sources do not contribute significantly to PM2.5 
levels that exceed the standards in the area.\72\ The control 
requirements applicable to major stationary sources of direct 
PM2.5 in a Moderate PM2.5 nonattainment area 
include, at minimum, the requirements of a NNSR permit program meeting 
the requirements of CAA sections 172(c)(5) and 189(a)(1)(A). In the 
PM2.5 SIP Requirements Rule, we established a deadline for 
states to submit NNSR plan revisions to implement the PM2.5 
NAAQS 18 months after an area is initially designated and classified as 
a Moderate nonattainment area.\73\ On September 6, 2016, California 
submitted the required NNSR SIP revisions. We are not proposing any 
action on the NNSR submittal at this time and will address these 
requirements in a separate rulemaking.
---------------------------------------------------------------------------

    \72\ General Preamble, 13539 and 13541-42. There are no major 
stationary sources (existing or anticipated) of direct 
PM2.5 or PM2.5 precursors in the Portola 
PM2.5 nonattainment area.
    \73\ 81 FR 58528 at 58010 (August 24, 2016).
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E. Air Quality Modeling

1. Requirements for Air Quality Modeling
    Section 189(a)(1)(B) of the CAA requires that a plan for a Moderate 
PM2.5 nonattainment area include a demonstration (including 
air quality modeling) that the plan will provide for attainment by the 
applicable attainment date, or a demonstration that attainment by such 
date is impracticable. An attainment demonstration must show that the 
control measures in the plan are sufficient for attainment of the NAAQS 
by the attainment date. The attainment demonstration predicts future 
ambient concentrations for comparison to the NAAQS, making use of 
available information on ambient concentrations, meteorology, and 
current and projected emissions inventories, including the effect of 
control measures in the plan. This information is typically used in 
conjunction with a computer model of the atmosphere.
    The EPA has provided additional modeling requirements and guidance 
for modeling analyses in the ``Guideline on Air Quality Models'' 
(``Guideline'').\74\ For areas where emissions are dominated by primary 
PM10 or PM2.5 emitted by many small dispersed 
sources, such as fugitive dust or residential wood burning, states have 
historically used a ``rollback model'' to evaluate the impacts of 
emissions on ambient air quality. EPA recently

[[Page 64785]]

approved rollback-based attainment demonstrations in the wood smoke-
dominated Klamath Falls and Oakridge-Westfir PM2.5 
nonattainment areas in Oregon.\75\ In a simple rollback model, the 
monitored ambient concentration (excluding any unchanging background 
concentration) is assumed to be proportional to emissions; when 
emissions are reduced by a given percentage, the concentration is 
assumed to scale or ``roll back'' by the same percentage. A variant is 
``proportional rollback,'' in which rollback is applied to each 
emission source category individually, then summed in proportion to 
their ambient contributions. The proportions, or source apportionment, 
can be estimated using chemically speciated PM2.5 
measurements. This can be done with a receptor model such as the 
Chemical Mass Balance model or the PMF model, which compute the source 
category contributions that are the best statistical fit to the 
measured chemical species concentrations, given measured or estimated 
source species profiles.
---------------------------------------------------------------------------

    \74\ 40 CFR part 51 Appendix W, ``Guideline on Air Quality 
Models,'' 82 FR 5182, January 17, 2017; available at https://www.epa.gov/scram/clean-air-act-permit-modeling-guidance.
    \75\ 81 FR 36176 (June 6, 2016), docket EPA-R10-OAR-2013-0005 
for Klamath Falls; and 83 FR 5537 (February 8, 2018), docket EPA-
R10-OAR-2017-0051 for Oakridge-Westfir.
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2. Modeling in the Portola PM2.5 Plan
    The attainment demonstration, described in section V of the Plan, 
is based on proportional rollback, with source category proportions 
(source apportionment) determined using the PMF receptor model. Section 
V of the Plan describe the concentration starting point for the 
rollback, background concentrations, the mapping of ambient 
PM2.5 components to PM2.5 emission categories, 
and the rollback calculation procedure. In addition to a ``Traditional 
Rollback,'' the Plan also provides an ``Alternative Rollback,'' which 
is based on a more precise accounting of the impacts of various wood 
stove types.
    The concentration starting point for rollback is typically a base 
year design value concentration that corresponds to the base year 
emissions. Instead of using the 2013 design value for the base year, 
the Plan used 13.9 [micro]g/m\3\, the average of the design values from 
2013, 2014, and 2015. Because a single design value is a three-year 
average, the Plan's procedure gives a five-year weighted average 
centered on 2013, using concentrations from 2011-2015. This was done to 
reduce the effect of year-to-year variability, and to avoid basing the 
attainment demonstration solely on the unusually warm, dry years of 
2011-2013.
    In rollback, the area's emissions are used to scale only the 
portion of the concentration due to sources in the nonattainment area, 
excluding background concentrations. CARB chose speciated 
PM2.5 concentrations from Bliss State Park next to Lake 
Tahoe in the Plan as background concentrations that would occur in the 
airshed in the absence of local anthropogenic emissions.
    The State determined the contributions of emission source 
categories to ambient PM2.5 using the PMF receptor model, 
described in Plan Appendix A. PMF was applied to 2011-2014 speciated 
PM2.5 data for 15 chemical species. PMF determines source 
species profiles and source contribution levels that best fit the full 
set of data. The result was a source apportionment with estimates for 
the ambient contributions of six source categories: Wood burning, 
refuse burning, mobile, airborne soil, secondary nitrate, secondary 
sulfate.
    The contributions of these source categories to the rollback base 
year PM2.5 concentration are shown in the Figure 9 pie chart 
in the Plan, ``2011-2015 Annual Average PM2.5 Source 
Contribution.'' Wood burning contributed by far the largest amount, 
76.1%; mobile sources contributed 7.6%; airborne soil 3.9%; and refuse 
burning 2.5%. Secondary PM2.5 in the form of ammonium 
nitrate and ammonium sulfate contributed 5.1% and 4.8%, respectively, 
of ambient PM2.5 concentrations. Figure 11 in the Plan shows 
the strong correlation between concentrations of PM2.5 and 
of levoglucosan, a marker for wood combustion.\76\ This correlation 
corroborates the significant contribution of wood burning to Portola's 
ambient PM2.5 levels.
---------------------------------------------------------------------------

    \76\ Levoglucosan is an organic compound formed from the 
pyrolysis of carbohydrates, such as starch and cellulose, the key 
component of wood. As a result, levoglucosan is often used as a 
chemical tracer for biomass burning in atmospheric chemistry 
studies, particularly with respect to airborne particulate matter. 
Jordan, T., Seen, A., Jacobsen, G., 2006, ``Levoglucosan as an 
atmospheric tracer for woodsmoke,'' Atmospheric Environment, 40 
(27): 5316-5321.
---------------------------------------------------------------------------

    Table 12 in the Portola PM2.5 Plan shows the State's 
rollback calculation, in which the percent changes in the 2013 
emissions of the inventory source categories are applied to their 
respective 2013 base year ambient contributions (excluding background). 
The main emissions change between base year and future emissions is for 
wood burning, reflecting the effect of the wood stove change-out 
program. For this source category, the State calculated emission 
reductions due to the wood stove change-out program during that period 
for each of the years from 2017 to 2021 using the EPA's Burn Wise 
Emission Calculator.\77\ CARB applied reductions in tpd to the baseline 
emission inventory projections for annual average direct 
PM2.5 emissions from residential wood burning in Table 8 of 
Appendix B in the Plan.
---------------------------------------------------------------------------

    \77\ Portola PM2.5 Plan Appendix E, Figure 1 and 
Table 2. The Burn Wise Emission Calculator is available at https://www.epa.gov/burnwise/burn-wise-additional-resources.
---------------------------------------------------------------------------

    The Plan includes future year contributions from 2017 to 2021 for 
each source category and a total concentration for each year. Only the 
wood burning emissions differed for each of these years; emissions from 
other categories reflected their 2021 values. CARB then averaged the 
predicted concentrations for the 2019-2021 period to arrive at a 2021 
predicted design value. The State's procedure of averaging projected 
concentrations for the three individual years 2019, 2020, and 2021 is 
similar to the procedure used for computing the 2021 monitored design 
value. The result of the rollback was a predicted 2021 PM2.5 
annual design value of 12.03 [micro]g/m\3\; with the rounding to one 
digit prescribed by 40 CFR 50 App. N, section 4.3, this meets the 12.0 
[micro]g/m\3\ NAAQS.
    Section V.F. of the Plan provided an ``Alternative Rollback'' model 
that more precisely quantified the effect of the stove change-out 
program on wood burning emissions. For this rollback model, all other 
source category emissions and their ambient contributions were assumed 
to remain at their base year 2013 levels. CARB calculated wood stove 
emissions and contributions separately for new certified stoves and 
uncertified stoves. This approach used the individual heating 
efficiency and emissions factors for these sources from the EPA's Burn 
Wise Emission Calculator and accounted for the number of each type of 
stove and the number of stove changeouts expected to occur in 2019, 
2020, and 2021. CARB applied the fractional changes in emissions for 
these years to the wood burning portion of the 5-year weighted 13.9 
[micro]g/m\3\ design value, and the three years' results averaged to 
arrive at a 2021 design value of 11.1 [micro]g/m\3\, which meets the 
12.0 [micro]g/m\3\ NAAQS.
3. The EPA's Evaluation and Proposed Action
    The EPA evaluated the State's choice of model for the attainment 
demonstration, as well as how the State applied the model, in terms of

[[Page 64786]]

concentration starting point, background concentrations, mapping of 
emissions to concentrations, and the calculations used. The choice of 
an appropriate model for the District's attainment demonstration was 
informed by particular circumstances in the Portola PM2.5 
nonattainment area, most notably the dominance of primary 
PM2.5 in ambient concentrations, the dispersed nature of the 
many small area sources responsible for it, and the relatively small 
fraction that is composed of secondary particulate matter. As discussed 
in the Plan, wood burning emissions of organic carbon and elemental 
carbon contribute 76% and 8%, respectively, of annual PM2.5 
concentrations in the Portola area.\78\ Based on examination of 
meteorology, PM2.5 emissions data and ambient 
PM2.5 data, the Plan provides a well-supported demonstration 
that residential wood burning is the dominant contributor to the 
PM2.5 air quality problem in the Portola area. The key 
assumption in a rollback analysis, i.e., that ambient concentrations 
are proportional to emissions, is true for these primary 
PM2.5 emissions. The EPA modeling guidance cited above does 
not mention rollback for attainment demonstrations but also does not 
fully address situations like that in the Portola area, where the 
dominant contributor to ambient PM2.5 is primary 
PM2.5 from many small area sources. Given that the key 
contributor to the air quality problem in the Portola area is already 
understood, neither photochemical grid models nor dispersion models 
would provide much information that is not already available from the 
rollback model. The EPA agrees that the use of rollback analysis under 
these facts and circumstances is consistent with EPA guidance and is 
appropriate for the Portola attainment demonstration and meets the 
Clean Air Act requirement for air quality modeling.
---------------------------------------------------------------------------

    \78\ Portola PM2.5 Plan, 20 (Figure 9, 2011-2015 
Annual Average PM2.5 Source Contribution).
---------------------------------------------------------------------------

    In addition, the EPA agrees that the Plan identifies an appropriate 
starting point concentration for the rollback model. The use of a five-
year weighted average for the design value is not standard for 
rollback, but is consistent with the EPA's recommendation for the 
starting point of photochemical modeling attainment demonstrations. The 
Plan contains a reasonable justification for using a longer period to 
determine the starting point for the design value, based on the 
variable meteorology of the 2011-2015 period; the chosen procedure thus 
yields a more representative concentration that is appropriate for the 
rollback attainment demonstration. It makes for a more robust 
attainment demonstration that is not overly dependent on meteorological 
conditions in any one particular year.
    The Plan contains convincing arguments for the State's selection of 
Bliss State Park as the source of background concentrations. The EPA 
agrees that the Plan's estimates for background concentrations are 
appropriate. The source attribution using PMF carried out for the Plan 
provides a good basis for the rollback model. The States also used 
several conservative assumptions, such as keeping certain ambient 
components constant instead of declining with emissions, so that the 
final concentration result is likely higher than would be expected with 
a more precise accounting.
    As noted above, the Plan used the average of projections for the 
individual years 2019, 2020, and 2021 for the future year projection. 
In comparison with projecting just the single attainment year emissions 
and concentration, the approach used by the State is conservatively 
high, because the 2019 and 2020 projections do not account for all of 
the emission reductions from stove changeouts that will occur by the 
2021 attainment year.\79\
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    \79\ The attainment demonstration need only show that emissions 
in the attainment year and the resulting projected concentration are 
consistent with attainment of the NAAQS; it does not need to show 
that the projected three-year design value meets the NAAQS. Future 
emissions need only be projected to the attainment year itself. See 
EPA, Office of Air Quality Planning and Standards, ``Modeling 
Guidance for Demonstrating Attainment of Air Quality Goals for 
Ozone, PM2.5, and Regional Haze,'' December 2014 Draft, 
17 (section 2.3.2, Future Year Selection); available at https://www.epa.gov/scram/state-implementation-plan-sip-attainment-demonstration-guidance.
---------------------------------------------------------------------------

    The Plan also provides a second rollback model, termed 
``Alternative Rollback.'' A key difference between the two rollback 
approaches is that the ``Alternative'' rollback relies more completely 
on the emission methodology for the residential wood burning category 
in the Burn Wise Emission Calculator. For both rollback approaches, the 
wood stove change-out program was by far the greatest source of 
emission and concentration reductions. The approaches relied on PMF 
source apportionment for the ambient effect of reductions, and they 
accounted for both the PM2.5 reductions per amount of wood 
burned in certified stoves and for the lower amount of wood burned from 
their increased burn efficiency. The ``Alternative'' rollback 
corroborated the results of the ``Traditional'' rollback model and 
provides additional confidence in the attainment demonstration.
    The EPA finds that the State correctly implemented the rollback 
model in a reasonable way, used an appropriate mapping of ambient 
PM2.5 components to emission inventory categories, and 
incorporated an appropriate degree of conservatism. For these reasons, 
the EPA finds that the rollback modeling in the Plan is adequate for 
purposes of supporting the Portola attainment demonstration for the 
2012 annual PM2.5 NAAQS.

F. Attainment Demonstration

1. Requirements for Attainment Demonstrations
    CAA section 189(a)(1)(B) requires that each state in which all or 
part of a Moderate PM2.5 nonattainment area is located 
submit an attainment plan that includes, among other things, either a 
demonstration (including air quality modeling) that the plan will 
provide for attainment by the applicable attainment date or a 
demonstration that attainment by such date is impracticable. In 
addition, CAA section 172(c)(1) generally requires, for each 
nonattainment area, a plan that provides for the implementation of all 
RACM and RACT as expeditiously as practicable and provides for 
attainment of the NAAQS. The EPA interprets these two provisions 
together to require that an attainment demonstration for a Moderate 
PM2.5 nonattainment area meet the following criteria:
    (1) The attainment demonstration must show the projected attainment 
date for the Moderate nonattainment area that is as expeditious as 
practicable;
    (2) The attainment demonstration must meet the requirements of 40 
CFR part 51, appendix W and must include inventory data, modeling 
results, and emission reduction analyses on which the state has based 
its projected attainment date;
    (3) The base year for the emissions inventory required for the 
attainment demonstration must be one of the 3 years used for 
designations or another technically appropriate inventory year if 
justified by the state in the plan submission; and
    (4) The control strategies modeled as part of the attainment 
demonstration must be consistent with the control strategy requirements 
under 40 CFR 51.1009(a), including the requirements for RACM/RACT and 
additional reasonable measures.\80\
---------------------------------------------------------------------------

    \80\ 40 CFR 51.1011(a).

---------------------------------------------------------------------------

[[Page 64787]]

    In addition, the attainment demonstration must provide for the 
implementation of all control measures needed for attainment as 
expeditiously as practicable and no later than the beginning of the 
year containing the applicable attainment date.\81\
---------------------------------------------------------------------------

    \81\ Id.
---------------------------------------------------------------------------

    Under longstanding guidance, the EPA has recommended presumptive 
limits on the amounts of emission reductions from voluntary and other 
nontraditional measures that may be credited in an attainment plan. 
Specifically, for voluntary stationary and area source measures, the 
EPA has identified a presumptive limit of 6% of the total amount of 
emission reductions required for RFP, attainment, or maintenance 
demonstration purposes.\82\ The EPA may, however, approve measures for 
SIP credit in amounts exceeding the presumptive limits ``where a clear 
and convincing justification is made by the State as to why a higher 
limit should apply in [its] case.'' \83\
---------------------------------------------------------------------------

    \82\ See, e.g., EPA, Office of Air Quality Planning and 
Standards, ``Incorporating Emerging and Voluntary Measure in a State 
Implementation Plan (SIP),'' October 4, 2004 (``2004 Emerging and 
Voluntary Measures Guidance''), 9; EPA, Office of Air Quality 
Planning and Standards and Office of Transportation and Air Quality, 
``Guidance on Incorporating Bundled Measures in a State 
Implementation Plan,'' August 16, 2005 (``2005 Bundled Measures 
Guidance''), 8; and EPA, Office of Air Quality Planning and 
Standards, ``Guidance for Quantifying and Using Emission Reductions 
from Voluntary Woodstove Changeout Programs in State Implementation 
Plans,'' EPA-456/B-06-001, January 2006 (``2006 Woodstove 
Guidance''), 4.
    \83\ See, e.g., 2004 Emerging and Voluntary Measures Guidance, 
9; 2005 Bundled Measures Guidance, 8, n. 6, and 2006 Woodstove 
Guidance, 4.
---------------------------------------------------------------------------

    We discuss each of these requirements and recommendations for 
attainment demonstrations below.

2. Attainment Demonstration in the Portola PM2.5 Plan

    Table 4 shows the relationship between the 2013 base year inventory 
and the 2021 attainment year inventory before and after the wood stove 
change-out program. The changes to the inventory reflect a 17% 
reduction in the direct PM2.5 emissions inventory is needed 
to demonstrate attainment by December 31, 2021.

              Table 4--Summary of Attainment Demonstration
------------------------------------------------------------------------
                                                           Direct PM2.5
                        Category                               (tpd)
 
------------------------------------------------------------------------
a. 2013 Baseline Emissions..............................           0.490
b. Projected 2021 Emissions without Change-out Program             0.486
 \a\....................................................
c. Reductions from Wood Stove Change-out Program \b\....           0.062
d. Attainment Year Emission Inventory = Projected 2021             0.424
 Emissions (b) minus Reductions from Wood Stove Change-
 out Program (c)........................................
------------------------------------------------------------------------
\a\ Mobile source reductions of 0.006 tpd from previously adopted
  measures credited in projected 2021 emission inventory. See Table 8 in
  Appendix B of Portola PM2.5 Plan.
\b\ The average reduction for the 2019-2021 time frame is 0.062 tpd.
  Source: Portola PM2.5 Plan, Table 4, 37.

    Traditional rollback analysis as described in section IV.B. of this 
proposed rule indicates that direct PM2.5 reductions from 
the woodstove change-out program (i.e., 0.062 tpd average for 2019-2021 
as used in the rollback) and CARB's mobile source program (i.e., 0.006 
tpd) result in a predicted 2021 design value of 12.03 [micro]g/m\3\ and 
is adequate for the State to demonstrate that the Portola area will 
attain the 2012 annual PM2.5 standards by the outermost 
statutory attainment date as a Moderate nonattainment area of December 
31, 2021.\84\ Table 5 below shows the projected cumulative impact of 
the change-out program on emission reductions and design values. The 
cumulative reductions and design value calculations are offset by one 
year to allow for full deployment of stove changeouts in a prior year. 
Because the bulk of the changeouts presumably occur during the late 
spring, summer, and early fall, the October-December period of a given 
year would likely see the greatest air quality benefits from that 
year's changeouts, but the January-March period would not. The State's 
calculations result in a conservative estimate of the benefits of the 
wood stove change-out program because the State is only taking credit 
for changeouts that have been in effect for a full year. Thus, the 
projected benefit of changing out 600 stoves will not be fully 
reflected in the design value until the 2023 design value, which will 
include 2021, 2022, and 2023, the first period of three consecutive 
years with the 600 new certified devices in operation. The Portola 
PM2.5 Plan also includes an alternative rollback modeling 
demonstration that results in a 2021 DV of 11.1 [mu]g/m\3\. The 
alternative rollback is described in section IV.B. of this proposed 
rule and in section V.F. of the Plan.

 Table 5--Relationship Between Cumulative Stove Changeouts, Reductions, and Design Values From Rollback Analysis
----------------------------------------------------------------------------------------------------------------
                                                                                Cumulative
                                                                                direct PM
                                                         Cumulative  stove    reductions in
                                         Stove  change-      changeouts          rollback       Annual  average
                  Year                        outs       credited  towards       analysis       DV  ([mu]g/m\3\)
                                                             attainment     credited  towards
                                                                                attainment
                                                                                  (tpd)
----------------------------------------------------------------------------------------------------------------
2016...................................             100                  0                  0    Not calculated.
2017...................................             100                100               .013             13.22.
2018...................................             150                200               .026             12.91.
2019...................................             150                350               .045             12.45.

[[Page 64788]]

 
2020...................................             100                500               .065             11.97.
2021...................................               0                600               .077             11.68.
Projected 2021 DV (average of 2019-      ..............  .................  .................             12.03.
 2021).................................
----------------------------------------------------------------------------------------------------------------
Source: Portola PM2.5 Plan, 56-57 (tables 10 and 11).

    The Portola PM2.5 Plan relies on the wood stove change-
out program to achieve 0.077 tpd of PM2.5 emission 
reductions in 2021, approximately 93% of the PM2.5 
reductions relied upon in the Plan to demonstrate attainment by the 
December 31, 2021 attainment date. The remaining 7% of necessary 
emission reductions will be achieved through ongoing implementation of 
federal emission reduction programs and CARB's mobile source control 
program. To justify this extensive reliance on the voluntary wood stove 
change-out program for attainment purposes, the Plan: (1) Provides a 
detailed description of the clear need for PM2.5 emission 
reductions from wood stove changeouts in the Portola area, (2) 
describes features of the wood stove program that provide a greater 
level of certainty in the quantification of emission reductions than 
that normally associated with voluntary programs, and (3) includes a 
detailed, enforceable commitment by the District to monitor and report 
on program implementation and to submit substitute measures by specific 
dates if necessary to remedy any shortfall in required emission 
reductions.\85\
---------------------------------------------------------------------------

    \85\ EPA, Region IX Air Division, ``Technical Support Document 
for EPA's Notice of Proposed Rulemaking for the California State 
Implementation Plan, Evaluation of incentive-based emission 
reductions relied upon in the Portola Fine Particulate Matter 
(PM2.5) Attainment Plan,'' December 2017.
---------------------------------------------------------------------------

    The PM2.5 problem in the Portola nonattainment area is 
overwhelmingly caused by residential wood smoke. The District estimates 
that between 2011 and 2015, residential wood smoke emissions 
contributed 76% of annual average PM2.5 concentrations and 
86% of daily PM2.5 concentrations on days exceeding 35 
[micro]g/m\3\ at the PM2.5 monitor located in the City of 
Portola. Other sources contributing to annual average PM2.5 
concentrations include refuse burning (2.5%), mobile sources (7.6%), 
secondary sulfates (4.8%), secondary nitrates (5.1%), and airborne soil 
(3.9%).\86\
---------------------------------------------------------------------------

    \86\ Portola PM2.5 Plan, 20.
---------------------------------------------------------------------------

    The average daily low temperature from October to March in the 
Portola nonattainment area is 21.8 degrees Fahrenheit with an average 
of 218 frost days per year, necessitating ample home heating.\87\ CARB 
estimates that of 2,458 households in the nonattainment area, 1,401 use 
wood burning devices as a primary or secondary heating source. Of those 
wood burning devices, 664 are uncertified woodstoves.\88\ The 2011-2015 
median household income in the Portola area was 54% that of the state 
median and home values were 40% of the state median.\89\ The 
unemployment rate for the City of Portola averaged 10.6% during the 
2014-2016 time frame.\90\ According to the District, most residents 
cannot afford to replace their uncertified wood burning devices without 
significant financial assistance.\91\ Natural gas is not an option for 
residential heating because it is not available in the Portola 
nonattainment area.\92\ While propane and electric options are 
available, the abundance of wood in the area (at no or low cost) and 
high cost of these alternative forms of residential heat limit their 
feasibility as primary heat sources.\93\
---------------------------------------------------------------------------

    \87\ Id. at 8-9.
    \88\ Email dated November 29, 2017, from Katarzyna Turkiewicz, 
CARB, to Rynda Kay, EPA, RE: questions about the number of wood 
stoves in the Portola nonattainment area.
    \89\ U.S. Census, 2011-2015 American Community Survey 5-year 
estimate for City of Portola, CA and State of California.
    \90\ Additional information on unemployment rates in Portola is 
available at http://www.homefacts.com/unemployment/California/Plumas-County/Portola/96122.html.
    \91\ Portola PM2.5 Plan, 20.
    \92\ Id. at 29.
    \93\ The average residential electricity rate in the City of 
Portola is 17.87[cent]/kWh, which is approximately 50% greater than 
the national average rate. See Electricity Local at http://www.electricitylocal.com/states/california/portola/.
---------------------------------------------------------------------------

    The bowl-shaped topography, cold stagnant winters, and extensive 
use of residential wood stoves in the Portola nonattainment area have 
caused evening and morning PM2.5 concentrations to peak 
during the winter. According to the District, the diurnal and seasonal 
pattern of PM2.5 concentrations peaking in the winter 
evening and overnight hours further suggests that residential wood 
burning is the primary cause of elevated PM2.5 
concentrations in the Portola area rather than open burning of 
agricultural wastes, forest management, and other burning 
activities.\94\ Although the District has implemented many other 
control measures for other sources of direct PM2.5 emissions 
in the area,\95\ these measures alone are not sufficient to provide for 
attainment in the Portola area given the small percentage of the 
PM2.5 emissions inventory attributed to these emission 
sources.
---------------------------------------------------------------------------

    \94\ Portola PM2.5 Plan, 21.
    \95\ See Portola PM2.5 Plan, 81-82, and our 
discussion of RACM/RACT and additional reasonable measures in 
section IV.D of this proposed rule.
---------------------------------------------------------------------------

    The Plan describes a number of features of the wood stove program 
that provide a greater level of certainty in the quantification of 
emission reductions than that normally associated with voluntary 
programs. First, full funding is already secured to entirely fund the 
replacement of 600 wood stoves, which the State projects to be 
sufficient to provide for attainment of the 2012 annual 
PM2.5 NAAQS by the applicable attainment date. Second, the 
emission reduction projections are conservative and relatively well 
understood compared to other voluntary programs. This is because wood 
stove technologies are generally well understood; wood stoves usually 
remain in the residence in which they are installed and have a long 
useful life; usage is generally predictable due to the fixed size of 
the home and heating needs; emission control technology is unlikely to 
be

[[Page 64789]]

tampered with; education campaigns and training requirements help 
ensure proper operation and fuel selection; and conservative emission 
factors are used in emission projections. Third, the program 
infrastructure is well-established. The State and District's 2017 
annual report on the wood stove program shows that as of December 31, 
2017, the program had successfully funded the replacement of 196 
stoves.\96\ The State and District estimated that replacement of these 
196 uncertified stoves achieved 0.031 tpd of PM2.5 emission 
reductions, 19% higher than the projected emissions reductions 
accounted for in the attainment demonstration, due to the fact that new 
stoves were cleaner than assumed in the attainment demonstration.\97\
---------------------------------------------------------------------------

    \96\ CARB, ``Portola Wood Stove Change-Out, 2017 Progress 
Report, Covering Change-outs Completed Through 12/31/2017'' (``2017 
Annual Report''), 3.
    \97\ Id. at 6 and 13-18.
---------------------------------------------------------------------------

    Finally, the Plan includes detailed, enforceable commitments by the 
District to monitor and report on program implementation in advance of 
the attainment date and to submit substitute measures, if necessary, to 
remedy any shortfall in required emission reductions. Specifically, the 
District has committed to: Implement the necessary number of woodstove 
changeouts in accordance with specific program criteria provided in the 
SIP submission; to achieve, by identified dates, specific amounts of 
PM2.5 emission reductions from projected baseline levels 
identified in the Portola PM2.5 Plan; to submit annual 
reports to the EPA that identify the calculator used to quantify 
emission reductions and describe, among other things, the projects 
implemented, actions taken by the State to confirm project compliance, 
and any changes to program implementation forms; and to adopt and 
submit to the EPA, by specific dates, any substitute measures necessary 
to address a shortfall in required emission reductions. These 
commitments became federally enforceable under the CAA upon the EPA's 
approval of the commitments into the SIP.\98\
---------------------------------------------------------------------------

    \98\ 83 FR 13871 (April 2, 2018).
---------------------------------------------------------------------------

3. The EPA's Evaluation and Proposed Action
    The EPA has reviewed the emissions inventories, RACM/RACT 
demonstration, air quality modeling, and control strategy fully 
described in the Portola PM2.5 Plan.
    In summary and as described in section IV.B of this action, the 
State used two modeling techniques to demonstrate attainment of the 
2012 annual PM2.5 NAAQS in the Portola nonattainment area. 
First, the State used a traditional rollback model to demonstrate 
attainment of the 2012 annual PM2.5 NAAQS. Second, the State 
corroborated the results of the traditional rollback model by using an 
alternative rollback model to also demonstrate attainment. The results 
using the alternative rollback model provide additional confidence in 
the attainment demonstration. The EPA accepts these modeling approaches 
for the attainment demonstration in the Portola PM2.5 Plan.
    Consistent with the requirements of 40 CFR 51.1011(a), the 
attainment demonstration shows the projected attainment date that is as 
expeditious as practicable in the Portola area, meets the requirements 
of 40 CFR part 51, appendix W, and includes inventory data, modeling 
results, and emission reduction analyses on which the State has based 
its projected attainment date. In addition, the base year for the 
emissions inventory used in the attainment demonstration, 2013, is one 
of the three years used for designation of the Portola area as a 
nonattainment area \99\ and the control strategies modeled as part of 
the attainment demonstration are consistent with the control strategy 
requirements under 40 CFR 51.1009(a), including the requirements for 
RACM/RACT and additional reasonable measures.
---------------------------------------------------------------------------

    \99\ 80 FR 2206 (January 15, 2015).
---------------------------------------------------------------------------

    With respect to the wood stove change-out program, the EPA believes 
that the Portola PM2.5 Plan provides a clear and convincing 
justification for more extensive reliance on a voluntary incentive 
program to achieve emission reductions necessary for attainment than 
the EPA normally recommends. First, the District has shown a clear need 
for additional reductions from the wood stove program, as additional 
regulatory measures for other PM2.5 emission sources in the 
area are not sufficient to provide for attainment, and a mandatory 
curtailment on use of wood stoves on high-PM2.5 winter days 
is not economically feasible for implementation at this time in the 
Portola area. Second, the State and District have identified a number 
of program features that provide adequate assurance that the wood stove 
changeout program will achieve, at minimum, the emission reductions 
attributed to it in the attainment demonstration. Third, the District's 
SIP-approved enforceable commitment ensures that the EPA and citizens 
can hold the District responsible for achieving the emission reductions 
attributed to the wood stove change-out program in the attainment 
demonstration.
    Finally, the City Ordinance includes a mandatory curtailment of 
uncertified stoves on days when the 24-hour average PM2.5 
concentration is forecasted to exceed 30 [mu]g/m\3\ that begins January 
1, 2021. This clear prohibition on the operation of uncertified wood 
stoves on days with higher PM2.5 levels after January 1, 
2021, provides additional assurance that projected emission reductions 
will occur in time to provide for attainment of the 2012 
PM2.5 NAAQS by the December 31, 2021 attainment date.
    For all of these reasons, we propose to approve the attainment 
demonstration in the Portola PM2.5 Plan as satisfying the 
requirements of sections 189(a)(1)(B) and 172(c)(1) of the CAA and 40 
CFR 51.1011(a).

G. Reasonable Further Progress and Quantitative Milestones

1. Requirements for Reasonable Further Progress and Quantitative 
Milestones
    CAA section 172(c)(2) states that all nonattainment area plans 
shall require reasonable further progress (RFP). In addition, CAA 
section 189(c) requires that all PM2.5 nonattainment area 
SIPs include quantitative milestones to be achieved every three years 
until the area is redesignated to attainment and which demonstrate RFP, 
as defined in CAA section 171(1). Section 171(1) defines RFP as ``such 
annual incremental reductions in emissions of the relevant air 
pollutant as are required by [Part D] or may reasonably be required by 
the Administrator for the purpose of ensuring attainment of the 
applicable [NAAQS] by the applicable date.'' Neither subpart 1 nor 
subpart 4 of part D, title I of the Act requires that a set percentage 
of emissions reductions be achieved in any given year for purposes of 
satisfying the RFP requirement.
    For purposes of the PM2.5 NAAQS, EPA has interpreted the 
RFP requirement to require that nonattainment area plans show annual 
incremental emission reductions sufficient to maintain generally linear 
progress toward attainment by the applicable deadline.\100\ As 
discussed in EPA guidance in the Addendum to the General Preamble 
(``Addendum''),\101\ requiring linear progress in reductions of direct 
PM2.5 and any individual precursor in a PM2.5 
plan may be appropriate in situations where:
---------------------------------------------------------------------------

    \100\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), 42015.
    \101\ Id.

---------------------------------------------------------------------------

[[Page 64790]]

     The pollutant is emitted by a large number and range of 
sources,
     The relationship between any individual source or source 
category and overall air quality is not well known,
     A chemical transformation is involved (e.g., secondary 
particulate significantly contributes to PM2.5 levels over 
the standard), and/or
     The emission reductions necessary to attain the 
PM2.5 standard are inventory-wide.\102\
---------------------------------------------------------------------------

    \102\ Id.
---------------------------------------------------------------------------

    The Addendum indicates that requiring linear progress may be less 
appropriate in other situations, such as:
     Where there are a limited number of sources of direct 
PM2.5 or a precursor,
     Where the relationships between individual sources and air 
quality are relatively well defined, and/or
     Where the emission control systems utilized (e.g., at 
major point sources) will result in swift and dramatic emission 
reductions.
    In nonattainment areas characterized by any of these latter 
conditions, RFP may be better represented as step-wise progress as 
controls are implemented and achieve significant reductions soon 
thereafter. For example, if an area's nonattainment problem can be 
attributed to a few major sources, EPA guidance indicates that ``RFP 
should be met by `adherence to an ambitious compliance schedule' which 
is likely to periodically yield significant emission reductions of 
direct PM2.5 or a PM2.5 precursor.'' \103\
---------------------------------------------------------------------------

    \103\ Id. at 42015.
---------------------------------------------------------------------------

    Attainment plans for PM2.5 nonattainment areas should 
include detailed schedules for compliance with emission regulations in 
the area and provide corresponding annual emission reductions to be 
realized from each milestone in the schedule.\104\ In reviewing an 
attainment plan under subpart 4, the EPA considers whether the annual 
incremental emission reductions to be achieved are reasonable in light 
of the statutory objective of timely attainment. Although early 
implementation of the most cost-effective control measures is often 
appropriate, states should consider both cost-effectiveness and 
pollution reduction effectiveness when developing implementation 
schedules for its control measures and may implement measures that are 
more effective at reducing PM2.5 earlier to provide greater 
public health benefits.\105\
---------------------------------------------------------------------------

    \104\ Id. at 42016.
    \105\ Id.
---------------------------------------------------------------------------

    The PM2.5 SIP Requirements Rule establishes specific 
regulatory requirements for purposes of satisfying the Act's RFP 
requirements and provides related guidance in the preamble to the rule. 
Specifically, under the PM2.5 SIP Requirements Rule, each 
PM2.5 attainment plan must contain an RFP analysis that 
includes, at minimum, the following four components: (1) An 
implementation schedule for control measures; (2) RFP projected 
emissions for direct PM2.5 and all PM2.5 plan 
precursors for each applicable milestone year, based on the anticipated 
control measure implementation schedule; (3) a demonstration that the 
control strategy and implementation schedule will achieve reasonable 
progress toward attainment between the base year and the attainment 
year; and (4) a demonstration that by the end of the calendar year for 
each milestone date for the area, pollutant emissions will be at levels 
that reflect either generally linear progress or stepwise progress in 
reducing emissions on an annual basis between the base year and the 
attainment year.\106\ States should estimate the RFP projected 
emissions for each quantitative milestone year by sector on a 
pollutant-by-pollutant basis.\107\
---------------------------------------------------------------------------

    \106\ 40 CFR 51.1012(a).
    \107\ 81 FR 58010, 58056 (August 24, 2016).
---------------------------------------------------------------------------

    Section 189(c) requires that attainment plans include quantitative 
milestones that demonstrate RFP. The purpose of the quantitative 
milestones is to allow for periodic evaluation of the area's progress 
towards attainment of the NAAQS consistent with RFP requirements. 
Because RFP is an annual emission reduction requirement and the 
quantitative milestones are to be achieved every three years, when a 
state demonstrates compliance with the quantitative milestone 
requirement, it will demonstrate that RFP has been achieved during each 
of the relevant three years. Quantitative milestones should provide an 
objective means to evaluate progress toward attainment meaningfully, 
e.g., through imposition of emission controls in the attainment plan 
and the requirement to quantify those required emission reductions. The 
CAA also requires states to submit milestone reports (due 90 days after 
each milestone), and these reports should include calculations and any 
assumptions made by the state concerning how RFP has been met, e.g., 
through quantification of emission reductions to date.\108\
---------------------------------------------------------------------------

    \108\ Id. at 42016, 42017.
---------------------------------------------------------------------------

    The CAA does not specify the starting point for counting the three-
year periods for quantitative milestones under CAA section 189(c). In 
the General Preamble and Addendum, the EPA interpreted the CAA to 
require that the starting point for the first three-year period be the 
due date for the Moderate area plan submission.\109\ Consistent with 
this longstanding interpretation of the Act, the PM2.5 SIP 
Requirements Rule requires that each plan for a Moderate 
PM2.5 nonattainment area contain quantitative milestones to 
be achieved no later than milestone dates 4.5 years and 7.5 years from 
the date of designation of the area.\110\ Because the EPA designated 
the Portola area nonattainment for the 2012 annual PM2.5 
NAAQS effective April 15, 2015,\111\ the applicable quantitative 
milestone dates for purposes of the Portola PM2.5 Plan are 
October 15, 2019 and October 15, 2022.
---------------------------------------------------------------------------

    \109\ General Preamble, 13539 and Addendum, 42016.
    \110\ 40 CFR 51.1013(a)(1).
    \111\ 80 FR 2206 (January 15, 2015).
---------------------------------------------------------------------------

2. RFP Demonstration and Quantitative Milestones in the Portola 
PM2.5 Plan
    The RFP demonstration and quantitative milestones are in section 
VI.A of the Portola PM2.5 Plan. The Plan estimates that 
emissions of direct PM2.5 will decline steadily from 2016 to 
2021 and that emissions of direct PM2.5 will generally 
remain below the levels needed to show step-wise progress toward 
attainment. According to the State and District, step-wise progress 
toward attainment is justified here because before the Portola area was 
designated as a PM2.5 nonattainment area in 2015, the area 
was designated attainment for all NAAQS and was not required to 
implement any air quality control program. The development of the wood 
stove change-out program involved an intensive effort to secure 
funding, establish requirements for contractors/retailers, identify and 
educate potential applicants, review and process completed 
applications, coordinate the installation of new stoves along with the 
removal and destruction of the old stoves, and track the progress of 
the program at every step. Given the time necessary to develop this 
program, direct PM2.5 emissions remained flat between 2013, 
the base year of the Plan, and 2016, the year that the District began 
to implement the wood stove change-out program. By 2016, however, the 
District had secured the necessary funding and developed the program 
infrastructure, enabling it to begin full implementation of its five-
year voluntary wood stove change-out program to provide for attainment 
by December 2021, the earliest practicable attainment date for the 2012 
annual

[[Page 64791]]

PM2.5 NAAQS in this area. The District estimates that the 
change-out program will achieve PM2.5 emission reductions 
representing generally linear progress toward attainment between 2016 
and 2022. Because the majority of the changeouts will be completed 
during the summer months when homeowners are not heating their homes, 
the District expects that direct PM2.5 concentrations during 
the second half of the year will be lower than during the first half of 
the year. For RFP purposes, only the changeouts accomplished during the 
prior year are accounted for in the projected emission reductions 
(i.e., only reductions from changeouts in effect for a full year are 
credited toward RFP).\112\
---------------------------------------------------------------------------

    \112\ Portola PM2.5 Plan, 66-72.
---------------------------------------------------------------------------

    The Plan's emissions inventory shows that direct PM2.5 
is emitted predominantly by residential wood combustion.\113\ The Plan 
specifically describes the District's procedures for calculating the 
2019 and 2022 RFP targets for direct PM2.5 and documents the 
District's conclusion that projected PM2.5 emission levels, 
based on the adopted control strategy for the area, would meet the RFP 
targets in both milestone years, as shown in Table 6 below.\114\
---------------------------------------------------------------------------

    \113\ Id. at Appendix B.
    \114\ Id. at 66-70.

                                Table 6--RFP Demonstration for Direct PM2.5 (tpd)
----------------------------------------------------------------------------------------------------------------
                           Description                                 2013            2019            2022
----------------------------------------------------------------------------------------------------------------
Baseline inventory \a\..........................................           0.490           0.487           0.487
Reductions from RACM control strategy \a\.......................           0.000           0.045           0.077
Inventory after RACM control strategy implemented \b\...........            0.49            0.44            0.41
RFP target \b\..................................................  ..............            0.44            0.41
RFP target achieved?............................................  ..............             Yes             Yes
----------------------------------------------------------------------------------------------------------------
\a\ Reductions from CARB's mobile source measures are already included in the projected 2019 and 2022 baseline
  inventories.
\b\ Rounding to two decimal places (hundredths of a ton).

    With respect to quantitative milestones, the Portola 
PM2.5 Plan identifies RFP emissions levels for direct 
PM2.5 in 2019 and 2022 that show, beginning in 2016, 
stepwise progress towards attaining the annual PM2.5 NAAQS 
in 2021. The quantitative milestones are the differences in emissions 
between the future baseline inventories and the future controlled 
inventories for 2019 and 2022, i.e., the projected emission reductions 
in each of these years, as shown in Table 7.\115\
---------------------------------------------------------------------------

    \115\ Id. at 71-72.

  Table 7--RFP Projected Emission Reductions for Quantitative Milestone
                               Years (tpd)
------------------------------------------------------------------------
                 Sector                        2019            2022
------------------------------------------------------------------------
Wood Stove Changeouts...................           0.045           0.077
                                         -------------------------------
    Total...............................           0.045           0.077
------------------------------------------------------------------------
Source: Portola PM2.5 Plan, 71-72.

    The Portola PM2.5 Plan also contains an enforceable 
commitment by the District to implement specific numbers of wood stove 
change-out projects and to achieve specific amounts of PM2.5 
emission reductions through implementation of these projects by the 
2019 RFP year and the 2021 attainment year.\116\
---------------------------------------------------------------------------

    \116\ Id. at Appendix E, 10. The EPA approved this commitment 
into the SIP at 83 FR 13871 (April 2, 2018).
---------------------------------------------------------------------------

    Finally, the Portola PM2.5 Plan states the District's 
commitment to track, quantify, and report to the EPA on its 
implementation of the adopted control strategy and on the area's 
progress toward attainment. The Plan also states that the District will 
submit to the EPA a quantitative milestone report no later than 90 days 
after a given milestone date (i.e., by January 15, 2020 and January 15, 
2023, respectively), each of which will include the following 
information:
    [ssquf] Certification that the SIP strategy is being implemented 
consistent with RFP;
    [ssquf] Technical support, including calculations to document 
completion statistics for each quantitative milestone; and
    [ssquf] Discussion of whether the PM2.5 NAAQS will be 
attained by the projected attainment date.\117\
---------------------------------------------------------------------------

    \117\ Id. at 71.
---------------------------------------------------------------------------

3. The EPA's Evaluation and Proposed Action
a. Reasonable Further Progress Demonstration
    As discussed in section IV.C. of this proposed rule, we are 
proposing to determine that PM2.5 precursors do not 
contribute significantly to ambient PM2.5 levels that exceed 
the 2012 annual PM2.5 NAAQS in the Portola PM2.5 
nonattainment area and, accordingly, that no RFP demonstrations for 
PM2.5 precursors are necessary for purposes of the 2012 
annual PM2.5 NAAQS in this area.
    With respect to direct PM2.5, we agree that step-wise 
progress is an appropriate measure of RFP for the 2012 PM2.5 
NAAQS in the Portola area. It is justified because direct 
PM2.5 is emitted primarily from hundreds of individual 
residential wood combustion sources, and the District needed adequate 
time to secure funding and develop the infrastructure necessary to 
implement a wood stove change-out program. Accordingly, the emission 
reductions that result from this program did not begin until 2016, but 
will continue throughout the duration of the Plan.
    The Portola PM2.5 Plan documents the State's conclusion 
that it is implementing all RACM and RACT and additional reasonable 
measures for direct PM2.5 as expeditiously as practicable 
and identifies projected levels of direct PM2.5 emissions in 
2019 and 2022 that reflect full implementation of the State's and

[[Page 64792]]

District's attainment control strategy for direct 
PM2.5.\118\ The wood stove change-out program provides 
incremental reductions of direct PM2.5 emission from 2016 to 
2021. CARB's mobile source measures also provide incremental reductions 
of direct PM2.5 emissions from 2013 to 2022, and the City 
Ordinance is projected to achieve emission reductions beginning in 
2021, to the extent those reductions have not already occurred through 
implementation of the wood stove change-out program. All of these 
measures achieve PM2.5 reductions each year and the State 
and District will be reporting on RFP in the 2019 and 2022 RFP 
milestone years and through the 2021 attainment year.\119\
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    \118\ Portola PM2.5 Plan, Chapter VI, section D.3.
    \119\ Portola PM2.5 Plan, Chapter VI, section A.
---------------------------------------------------------------------------

    Thus, the Portola PM2.5 Plan demonstrates that emissions 
of direct PM2.5 will be reduced at rates representing 
stepwise progress toward attainment. The Plan also demonstrates that 
all RACM, RACT, and additional reasonable measures that provide the 
bases for the direct PM2.5 emissions projections in the RFP 
analysis in the Plan are being implemented as expeditiously as 
practicable. Accordingly, we propose to determine that the Plan 
requires the annual incremental reductions in emissions of direct 
PM2.5 that are necessary for the purpose of ensuring 
reasonable further progress towards attainment of the 2012 annual 
PM2.5 NAAQS by 2021, in accordance with the requirements of 
CAA sections 171(1) and 172(c)(2).
b. Quantitative Milestones
    The Plan adequately documents the District's methodology for 
identifying and calculating appropriate RFP targets for the 2019 and 
2022 milestone years and contains, as part of the RACM control strategy 
for the area, an enforceable commitment by the District to implement 
specific numbers of wood stove change-out projects and thereby achieve 
specific amounts of PM2.5 emission reductions by the 2019 
RFP year and the 2021 attainment year.\120\ These quantitative 
milestones provide an objective means for evaluating the area's 
progress toward attainment of the PM2.5 NAAQS. We propose to 
approve these quantitative milestones in the Portola PM2.5 
Plan as meeting the requirements of CAA section 189(c) and 40 CFR 
51.1013(a)(1). We note that, consistent with the requirements of CAA 
section 189(c)(2) as interpreted in longstanding EPA policy, each of 
the upcoming milestone reports should include technical support 
sufficient to document completion statistics for appropriate 
milestones, e.g., calculations and any assumptions made concerning 
emission reductions to date.\121\
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    \120\ Id. at Appendix E, 10.
    \121\ Addendum, 42017.
---------------------------------------------------------------------------

H. Contingency Measures

1. Requirements for Contingency Measures
    Under CAA section 172(c)(9), each SIP for a nonattainment area must 
include contingency measures to be implemented if an area fails to meet 
RFP (``RFP contingency measures'') or fails to attain the NAAQS by the 
applicable attainment date (``attainment contingency measures''). Under 
the PM2.5 SIP Requirements Rule, PM2.5 attainment 
plans must include contingency measures to be implemented following a 
determination by the EPA that the state has failed: (1) To meet any RFP 
requirement in the approved SIP; (2) to meet any quantitative milestone 
in the approved SIP; (3) to submit a required quantitative milestone 
report; or (4) to attain the applicable PM2.5 NAAQS by the 
applicable attainment date.\122\ Contingency measures must be fully 
adopted rules or control measures that are ready to be implemented 
quickly upon failure to meet RFP or failure of the area to meet the 
relevant NAAQS by the applicable attainment date.\123\
---------------------------------------------------------------------------

    \122\ See 40 CFR 51.1014(a).
    \123\ See 81 FR 58010, 58066; see also Addendum, 42015.
---------------------------------------------------------------------------

    The purpose of contingency measures is to continue progress in 
reducing emissions while a state revises its SIP to meet the missed RFP 
requirement or to correct ongoing nonattainment. Neither the CAA nor 
the EPA's implementing regulations establish a specific level of 
emissions reductions that implementation of contingency measures must 
achieve, but the EPA recommends that contingency measures should 
provide for emissions reductions equivalent to approximately one year 
of reductions needed for RFP, calculated as the overall level of 
reductions needed to demonstrate attainment divided by the number of 
years from the base year to the attainment year. In general, we expect 
all actions needed to effect full implementation of the measures to 
occur within 60 days after the EPA notifies the State of a failure to 
meet RFP or to attain.\124\
---------------------------------------------------------------------------

    \124\ See 81 FR 58010, 58066; see also General Preamble, 13512, 
13543-44 and Addendum, 42014-42015.
---------------------------------------------------------------------------

    To satisfy the requirements of 40 CFR 51.1014, the contingency 
measures adopted as part of a PM2.5 attainment plan must 
consist of control measures for the area that are not otherwise 
required to meet other nonattainment plan requirements or that achieve 
emissions reductions not otherwise relied upon in the control strategy 
for the area (e.g., to meet RACM/RACT requirements) and must specify 
the timeframe within which their requirements become effective 
following any of the EPA determinations specified in 40 CFR 51.1014(a).
    The Ninth Circuit Court of Appeals recently rejected the EPA's 
interpretation of CAA section 172(c)(9) to allow approval of already 
implemented control measures as contingency measures, in a decision 
called Bahr v. EPA (``Bahr'').\125\ In Bahr, the Ninth Circuit 
concluded that contingency measures must be measures that are triggered 
only after the EPA determines that an area fails to meet RFP 
requirements or to attain by the applicable attainment date, not 
before. Thus, within the geographic jurisdiction of the Ninth Circuit, 
states cannot rely on already implemented measures to comply with the 
contingency measure requirements under CAA section 172(c)(9).
---------------------------------------------------------------------------

    \125\ Bahr v. EPA, 836 F.3d 1218, 1235-1237 (9th Cir. 2016).
---------------------------------------------------------------------------

2. Contingency Measures in the 2016 PM2.5 Plan
    The District's contingency measures are described in section VI.B 
of the Portola PM2.5 Plan.
3. The EPA's Evaluation and Proposed Action
    We are not proposing any action at this time on the contingency 
measures in the Portola PM2.5 Plan. We intend to work with 
the State and District to assist them with the development and 
submission of contingency measures consistent with the Bahr decision 
and to act on the revised contingency measures, as appropriate, through 
a subsequent rulemaking.

I. Motor Vehicle Emission Budgets

1. Requirements for Motor Vehicle Emissions Budgets
    Section 176(c) of the CAA requires federal actions in nonattainment 
and maintenance areas to conform to the SIP's goals of eliminating or 
reducing the severity and number of violations of the NAAQS and 
achieving expeditious attainment of the standards. Conformity to the 
SIP's goals means that such actions will not: (1) Cause or contribute 
to violations of a NAAQS, (2) worsen the severity of an existing 
violation, or

[[Page 64793]]

(3) delay timely attainment of any NAAQS or any interim milestone.
    Actions involving Federal Highway Administration (FHWA) or Federal 
Transit Administration (FTA) funding or approval are subject to the 
EPA's transportation conformity rule, codified at 40 CFR part 93, 
subpart A. Under this rule, metropolitan planning organizations (MPOs) 
in nonattainment and maintenance areas coordinate with state and local 
air quality and transportation agencies, EPA, FHWA, and FTA to 
demonstrate that an area's regional transportation plans and 
transportation improvement programs conform to the applicable SIP.\126\ 
This demonstration is typically done by showing that estimated 
emissions from existing and planned highway and transit systems are 
less than or equal to the motor vehicle emissions budgets (``budgets'') 
contained in all control strategy SIPs. An attainment, maintenance, or 
RFP SIP should include budgets for the attainment year, each required 
RFP milestone year, and the last year of the maintenance plan, as 
appropriate. Budgets are generally established for specific years and 
specific pollutants or precursors and must reflect all of the motor 
vehicle control measures contained in the attainment and RFP 
demonstrations or maintenance plan, as applicable.\127\
---------------------------------------------------------------------------

    \126\ The Portola nonattainment area does not lie within, or 
share a border with any MPO, nor does any MPO model any projects 
within the Portola nonattainment area. Therefore, the Portola 
nonattainment area meets the definition in the transportation 
conformity rule for an isolated rural nonattainment area. The 
California Department of Transportation performs many of the 
functions in isolated rural nonattainment areas that the conformity 
rule requires of MPOs. Isolated rural nonattainment areas have no 
federally required metropolitan transportation plan or program. A 
regional emissions analysis is required only when a non-exempt 
regionally significant project is proposed in the isolated rural 
area. For further details on isolated rural nonattainment areas and 
the transportation conformity requirements in those areas, see 40 
CFR 93.101 and 93.109(g).
    \127\ 40 CFR 93.118(e)(4)(v).
---------------------------------------------------------------------------

    All direct PM2.5 SIP budgets should include direct 
PM2.5 motor vehicle emissions from tailpipes, brake wear, 
and tire wear. With respect to PM2.5 from re-entrained road 
dust and emissions of VOC, SO2.and/or ammonia, the 
transportation conformity provisions of 40 CFR part 93, subpart A, 
apply only if the EPA Regional Administrator or the director of the 
state air agency has made a finding that emissions of these pollutants 
within the area are a significant contributor to the PM2.5 
nonattainment problem and has so notified the MPO and Department of 
Transportation (DOT), or if the applicable implementation plan (or 
implementation plan submission) includes any of these pollutants in the 
approved (or adequate) budget as part of the RFP, attainment or 
maintenance strategy.\128\
---------------------------------------------------------------------------

    \128\ 40 CFR 93.102(b)(3), 93.102(b)(2)(v), and 93.122(f); see 
also conformity rule preamble at 69 FR 40004, 40031-40036 (July 1, 
2004).
---------------------------------------------------------------------------

    By contrast, transportation conformity requirements apply with 
respect to emissions of NOX unless both the EPA Regional 
Administrator and the director of the state air agency have made a 
finding that transportation-related emissions of NOX within 
the nonattainment area are not a significant contributor to the 
PM2.5 nonattainment problem and have so notified the MPO and 
DOT, or the applicable implementation plan (or implementation plan 
submission) does not establish an approved (or adequate) budget for 
such emissions as part of the reasonable further progress, attainment 
or maintenance strategy.\129\ The criteria for insignificance 
determinations can be found in 40 CFR 93.109(f). In order for a 
pollutant or precursor to be considered an insignificant contributor, 
the control strategy SIP must demonstrate that it would be unreasonable 
to expect that such an area would experience enough motor vehicle 
emissions growth in that pollutant/precursor for a NAAQS violation to 
occur. Insignificance determinations are based on factors such as air 
quality, SIP motor vehicle control measures, trends and projections of 
motor vehicle emissions, and the percentage of the total SIP inventory 
that is comprised of motor vehicle emissions. The EPA's rationale for 
the providing for insignificance determinations is described in the 
July 1, 2004 revision to the Transportation Conformity Rule at 69 FR 
40004.
---------------------------------------------------------------------------

    \129\ 40 CFR 93.102(b)(2)(iv).
---------------------------------------------------------------------------

    For motor vehicle emissions budgets to be approvable, they must 
meet, at a minimum, the EPA's adequacy criteria (40 CFR 93.118(e)(4)).
    Under the PM2.5 SIP Requirements Rule, each attainment 
plan submittal for a Moderate PM2.5 nonattainment area must 
contain quantitative milestones to be achieved no later than 4.5 years 
and 7.5 years after the date the area was designated 
nonattainment.\130\ The second of these milestone dates, October 15, 
2022,\131\ falls after the attainment date for the Portola area, which 
is December 31, 2021. As the EPA explained in the preamble to the 
PM2.5 SIP Requirements Rule, it is important to include a 
post-attainment year quantitative milestone to ensure that, if the area 
fails to attain by the attainment date, the EPA can continue to monitor 
the area's progress toward attainment while the state develops a new 
attainment plan.\132\ Although the post-attainment year quantitative 
milestone is a required element of a Moderate area plan, it is not 
necessary to demonstrate transportation conformity for 2022 or to use 
the 2022 budgets in transportation conformity determinations until such 
time as the area fails to attain the 2012 PM2.5 NAAQS.
---------------------------------------------------------------------------

    \130\ 40 CFR 51.1013(a)(1).
    \131\ Because the Portola area was designated nonattainment 
effective April 15, 2015, the first milestone date is October 15, 
2019 and the second milestone date is October 15, 2022. 80 FR 2206 
(January 15, 2015).
    \132\ 81 FR 58010, 58058 and 58063-64 (August 24, 2016).
---------------------------------------------------------------------------

    2. Motor Vehicle Emissions Budgets in the Portola PM2.5 
Plan
    The Portola PM2.5 Plan includes budgets for direct 
PM2.5 for 2019 and 2022 (RFP milestone years) and 2021 
(projected attainment year for the 2012 annual NAAQS).\133\ The direct 
PM2.5 budgets include tailpipe, brake wear, and tire wear 
emissions.\134\
---------------------------------------------------------------------------

    \133\ Portola PM2.5 Plan, section VI.C (for 2021 
budgets) and ``Transportation Conformity Budgets for the Portola 
PM2.5 SIP Plan Supplement'' (for 2019 and 2022 budgets) 
dated December 20, 2017, and adopted by CARB Board on October 26, 
2017.
    \134\ Plan at Chapter VI, section C.4, 77.
---------------------------------------------------------------------------

    The PM2.5 budgets were calculated using EMFAC2014, 
CARB's latest approved version of the EMFAC model for estimating 
emissions from on-road vehicles operating in California,\135\ and 
reflect annual daily average emissions consistent with the 2019 and 
2022 RFP milestone years and the 2021 attainment demonstration for the 
annual PM2.5 NAAQS. The 2019 and 2021 conformity budgets for 
direct PM2.5, expressed in annual average tons per day, are 
provided in Table 8. As explained further below, we are not acting on 
the 2022 budgets at this time.
---------------------------------------------------------------------------

    \135\ See footnote 20.

       Table 8--Annual Average Conformity Budgets for PM2.5 (tpd)
------------------------------------------------------------------------
                   Category                         2019         2021
------------------------------------------------------------------------
Direct exhaust, tire, and brake wear from on         0.0026       0.0026
 road vehicles \a\............................
                                               -------------------------
  Total.......................................       0.0026       0.0026
------------------------------------------------------------------------
Conformity Budget \b\.........................        0.003        0.003
------------------------------------------------------------------------
\a\ Calculated from default EMFAC2014 v.1.07 output for Plumas County
  adjusted to reflect only the emissions from the Portola nonattainment
  area.
\b\ Budgets are rounded up to the nearest 0.001 ton.

    Appendix P of the Portola PM2.5 Plan contains the 
State's evaluation of PM2.5 precursors and the bases for its 
conclusion that emissions of VOC, SO2,

[[Page 64794]]

NOX, and ammonia from on-road motor vehicles are not 
significant contributors to the PM2.5 nonattainment problem 
in the Portola area. The State focused its analysis on the contribution 
of on-road emissions of each precursor to the PM2.5 design 
value in the Portola area, the changes in emission levels from 2013 to 
2021, and motor vehicle emission control measures included in the Plan. 
Table 1 in Appendix P of the Portola PM2.5 Plan shows that 
the on-road emission totals for direct PM2.5 and all 
precursors decrease from 2013 to the 2021 attainment year. According to 
the State, on-road emissions of direct PM2.5 and all 
precursors contribute less than 10% and on-road NOX 
emissions contribute less than 2% to the PM2.5 design value 
in the Portola area, compared to wood burning, which accounts for over 
76% of the PM2.5 design value.\136\ On-road NOX 
emissions account for approximately 36% of the total 2013 base year 
inventory but decline to 29% and 26% of the 2019 and 2021 inventories, 
respectively. The on-road NOX emissions decrease from the 
2013 base year is 0.07 tpd (or 37%) in 2019 and 0.09 tpd (or 47%) in 
2021.\137\ The State also evaluated on-road construction dust and paved 
and unpaved road dust and concluded that emissions of these pollutants 
are not significant contributors to the PM2.5 nonattainment 
problem in the Portola area. Therefore, the Plan does not include 
budgets for VOC, SO2, NOX, ammonia, or 
PM2.5 from re-entrained road dust or dust from road 
construction.
---------------------------------------------------------------------------

    \136\ Portola PM2.5 Plan, Appendix P.
    \137\ Portola PM2.5 Plan, Appendix B, Table 7.
---------------------------------------------------------------------------

3. The EPA's Evaluation and Proposed Actions
    With respect to PM2.5 from re-entrained road dust, VOC, 
SO2, and ammonia, neither the EPA nor the State has made a 
finding that on-road emissions of any of these pollutants or precursors 
are a significant contributor to the PM2.5 nonattainment 
problem in the Portola area, and neither the approved California SIP 
for Portola nor the submitted Portola PM2.5 Plan establish 
adequate budgets for such emissions as part of an RFP, attainment or 
maintenance strategy for the PM2.5 NAAQS. Accordingly, the 
transportation conformity provisions of 40 CFR part 93, subpart A, do 
not apply with respect to PM2.5 from re-entrained road dust 
or to emissions of VOC, SO2 or ammonia for purposes of the 
2012 PM2.5 NAAQS in the Portola area.
    With respect to NOX emissions, we find that the State's 
evaluation of emission trends, projections of motor vehicle emissions, 
and the percentage of the total SIP inventory that is comprised of 
motor vehicle emissions is sufficient to demonstrate, consistent with 
40 CFR 93.109(f), that it would be unreasonable to expect that this 
area would experience such growth in NOX emissions from 
motor vehicles as to result in a violation of the PM2.5 
NAAQS. Accordingly, the EPA is proposing to determine that 
transportation-related emissions of NOX are insignificant 
contributors to the PM2.5 nonattainment problem in the 
Portola area.
    We have evaluated the submitted direct PM2.5 budgets for 
2019 and 2021 in the Plan against our adequacy criteria in 40 CFR 
93.118(e)(4) and (5) as part of our review of the budgets' 
approvability and will complete the adequacy review concurrent with our 
final action on the Portola PM2.5 Plan.\138\ On January 5, 
2018, the EPA announced the availability of the budgets in the Portola 
PM2.5 Plan and provided a 30-day public comment period. This 
announcement was posted on the EPA's Adequacy website at: https://www.epa.gov/state-and-local-transportation/state-implementation-plans-sip-submissions-currently-under-epa#portola2018. The comment period for 
this notification ended on February 5, 2018, and we did not receive any 
comments.
---------------------------------------------------------------------------

    \138\ Under the Transportation Conformity regulations, the EPA 
may review the adequacy of submitted motor vehicle emission budgets 
simultaneously with the EPA's approval or disapproval of the 
submitted implementation plan. 40 CFR 93.118(f)(2).
---------------------------------------------------------------------------

    The EPA has not yet reviewed and is not taking any action at this 
time on the submitted budget for 2022 for the Portola PM2.5 
nonattainment area. Therefore, the submitted budget for 2022 for the 
Portola nonattainment area will not be used in transportation 
conformity determinations at this time. The EPA will begin reviewing 
the 2022 budget for adequacy and approval only if the area fails to 
attain the PM2.5 NAAQS by December 31, 2021, the applicable 
Moderate area attainment date.
    If the EPA were to either find adequate or approve the post-
attainment milestone year motor vehicle emissions budgets now, those 
budgets would have to be used in transportation conformity 
determinations that are made after the effective date of the adequacy 
finding or approval even if the Portola PM2.5 nonattainment 
area ultimately attains the PM2.5 NAAQS by the Moderate area 
attainment deadline. As a result, the California Department of 
Transportation, which performs many of the MPO functions in the Portola 
PM2.5 nonattainment area, would be required to demonstrate 
conformity for the post-attainment date milestone year and all later 
years addressed in the conformity determination to the post-attainment 
date RFP motor vehicle emissions budgets rather than the budgets 
associated with the attainment year for the area (i.e., the motor 
vehicle emissions budgets for 2021). The EPA does not believe that it 
is necessary to demonstrate conformity using these post-attainment year 
budgets in areas that either the EPA anticipates will attain by the 
attainment date or in areas that, in fact, attain by the attainment 
date.
    If the EPA determines that the Portola area has failed to attain 
the PM NAAQS by the applicable attainment date, the EPA will begin the 
budget adequacy and approval processes for the post-attainment year 
(2022) budget. If the EPA finds the 2022 budget adequate or approves 
it, that budget will have to be used in subsequent transportation 
conformity determinations. The EPA believes that initiating these 
processes following a determination that the area has failed to attain 
by the attainment date ensures that transportation activities will not 
cause or contribute to new violations, increase the frequency or 
severity of any existing violations, or delay timely attainment or any 
required interim emission reductions or milestones in the Portola area, 
consistent with the requirements of CAA section 176(c)(1)(B).
    For the reasons discussed in sections V.E.v and V.F of this 
proposed rule, we are proposing to approve the RFP and attainment 
demonstrations in the Portola PM2.5 Plan. The budgets, as 
given in Table 9 of this proposed rule, are consistent with these 
demonstrations, are clearly identified and precisely quantified, and 
meet all other applicable statutory and regulatory requirements 
including the adequacy criteria in 40 CFR 93.118(e)(4) and (5). For 
these reasons, the EPA proposes to approve the budgets listed in Table 
8 above.
    The transportation conformity rule allows us to limit the approval 
of budgets,\139\ and CARB requested that we limit the duration of our 
approval of the budgets in the Plan to the period before the effective 
date of the EPA's adequacy finding for any subsequently submitted 
budgets.\140\ However, we will consider

[[Page 64795]]

the State's request to limit an approval of its budgets only if the 
request includes the following elements: \141\
---------------------------------------------------------------------------

    \139\ 40 CFR 93.118(e)(1).
    \140\ Letter dated December 20, 2017, from Richard W. Corey, 
Executive Officer, California Air Resources Board, to Alexis 
Strauss, Acting Regional Administrator, EPA Region 9.
    \141\ 67 FR 69141 (November 15, 2002), limiting our prior 
approval of budgets in certain California SIPs.
---------------------------------------------------------------------------

     An acknowledgement and explanation as to why the budgets 
under consideration have become outdated or deficient;
     A commitment to update the budgets as part of a 
comprehensive SIP update; and
     A request that the EPA limit the duration of its approval 
to the time when new budgets have been found to be adequate for 
transportation conformity purposes.
    Because CARB's request does not include all of these elements, we 
cannot at this time propose to limit the duration of our approval of 
the submitted budgets. In order to limit the approval, we would need 
the information described above in order to determine whether such 
limitation is reasonable and appropriate in this case. Once CARB has 
provided the necessary information, we intend to review it and take 
appropriate action. If we propose to limit the duration of our approval 
of the budgets in the Portola PM2.5 Plan, we will provide 
the public an opportunity to comment. The duration of the approval of 
the budgets, however, would not be limited until we complete such a 
rulemaking.

V. Summary of Proposed Actions and Request for Public Comment

    Under CAA sections 110(k)(3), the EPA is proposing to approve SIP 
revisions submitted by California to address the Act's Moderate area 
planning requirements for the 2012 PM2.5 NAAQS in the 
Portola nonattainment area. Specifically, the EPA is proposing to 
approve the following elements of the Portola PM2.5 Plan:
    1. The 2013 base year emissions inventories as meeting the 
requirements of CAA section 172(c)(3);
    2. The reasonably available control measure/reasonably available 
control technology demonstration as meeting the requirements of CAA 
sections 172(c)(1) and 189(a)(1)(C);
    3. The attainment demonstration as meeting the requirements of CAA 
sections 172(c)(1) and 189(a)(1)(B);
    4. The reasonable further progress demonstration as meeting the 
requirements of CAA section 172(c)(2);
    5. The quantitative milestones as meeting the requirements of CAA 
section 189(c); and
    6. The motor vehicle emissions budgets for 2019 and 2021, because 
they are derived from approvable attainment and RFP demonstrations and 
meet the requirements of CAA section 176(c) and 40 CFR part 93, subpart 
A.
    The EPA is not proposing any action at this time on the contingency 
measures or the post-attainment year (2022) budget in the Portola 
PM2.5 Plan.
    We will accept comments from the public on these proposals for the 
next 30 days. The deadline and instructions for submission of comments 
are provided in the DATES and ADDRESSES sections at the beginning of 
this preamble.

VI. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Act and 
applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, the EPA's role is to approve state 
choices, provided that they meet the criteria of the Clean Air Act. 
Accordingly, this proposed 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 
proposed 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 Clean Air Act; and
     Does not provide the EPA with the discretionary authority 
to address disproportionate human health or environmental effects with 
practical, appropriate, 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 the EPA or an Indian tribe 
has demonstrated that a tribe has jurisdiction. In those areas of 
Indian country, the rule does not have tribal implications and will not 
impose substantial direct costs on tribal governments or preempt tribal 
law as specified by Executive Order 13175 (65 FR 67249, November 9, 
2000).

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Particulate matter, Reporting 
and recordkeeping requirements.

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

    Dated: December 4, 2018.
Deborah Jordan,
Acting Regional Administrator, Region IX.
[FR Doc. 2018-27257 Filed 12-17-18; 8:45 am]
 BILLING CODE 6560-50-P