Document ID: EPA-R09-OAR-2018-0181-0001
Agency: epa
Document Type: Proposed Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: California; Chico Redesignation Request and Maintenance Plan for the 2006 24-hour PM2.5 Standard
Posted Date: 2018-05-09T04:00Z

[Federal Register Volume 83, Number 90 (Wednesday, May 9, 2018)]
[Proposed Rules]
[Pages 21238-21254]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-09792]

[[Page 21238]]

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

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R09-OAR-2018-0181; FRL-9977-77-Region 9]

Approval and Promulgation of Air Quality State Implementation 
Plans; California; Chico Redesignation Request and Maintenance Plan for 
the 2006 24-hour PM2.5 Standard

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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

SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve, as a revision of the California state implementation plan 
(SIP), the State's request to redesignate the Chico nonattainment area 
to attainment for the 2006 24-hour fine particulate matter 
(PM2.5) national ambient air quality standard. The EPA is 
also proposing to approve the PM2.5 maintenance plan and the 
determination that contributions from motor vehicle emissions to the 
PM2.5 pollution in the Chico nonattainment area are 
insignificant. The EPA is proposing this action because the SIP 
revision meets the requirements of the Clean Air Act and EPA guidance 
for such plans. We are taking comments on this proposal and plan to 
follow with a final action.

DATES: Any comments on this proposal must arrive by June 8, 2018.

ADDRESSES: Submit comments, identified by docket number EPA-R09-OAR-
2018-0181, at https://www.regulations.gov, or via email to 
[email protected]. For comments submitted at Regulations.gov, 
follow the online instructions for submitting comments. Once submitted, 
comments cannot be edited or removed 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 
EPA's full 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: Ginger Vagenas, EPA Region IX, 415-
972-3964, [email protected].

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

Table of Contents

I. Summary of Today's Proposed Action
II. Background
    A. The PM2.5 NAAQS
    B. Designation of PM2.5 Nonattainment Areas
    C. PM2.5 Planning Requirements
III. Procedural Requirements for Adoption and Submittal of SIP 
Revisions
IV. Substantive Requirements for Redesignation
V. Evaluation of the State's Redesignation Request for the Chico 
PM2.5 Nonattainment Area
    A. Determination That the Area Has Attained the PM2.5 
NAAQS
    B. The Area Must Have a Fully Approved SIP Meeting the 
Requirements Applicable for Purposes of Redesignation Under Section 
110 and Part D
    C. The Area Must Show the Improvement in Air Quality Is Due to 
Permanent and Enforceable Emission Reductions
    D. The Area Must Have a Fully Approved Maintenance Plan Under 
Section 175A
VI. Proposed Action and Request for Public Comment
VII. Statutory and Executive Order Reviews

I. Summary of Today's Proposed Action

    Under Clean Air Act (CAA or ``the Act'') section 107(d)(3)(D), the 
EPA is proposing to approve California's request to redesignate the 
Chico nonattainment area to attainment for the 2006 24-hour fine 
particulate matter (PM2.5) national ambient air quality 
standards (NAAQS or ``standards''). We are doing so based on our 
conclusion that the area has met the five criteria for redesignation 
under CAA section 107(d)(3)(E). Specifically, we have concluded that: 
(1) The area has attained the 24-hour PM2.5 NAAQS in the 
2014-2016 time period and continues to attain the PM2.5 
standard since that time; (2) the relevant portions of the California 
SIP are fully approved; (3) the improvement in air quality is due to 
permanent and enforceable reductions in emissions; (4) California has 
met all requirements applicable to the Chico PM2.5 
nonattainment area with respect to section 110 and part D of the CAA; 
and (5) the Chico, CA/Butte County PM2.5 Nonattainment Area 
Redesignation Request and Maintenance Plan (``Chico PM2.5 
Plan'' or ``Plan'') meets the requirements of section 175A of the CAA.
    In addition, the EPA is proposing to approve the Chico 
PM2.5 Plan as a revision to the SIP under section 110(k)(3) 
of the CAA because we find that the maintenance demonstration shows how 
the area will continue to attain the 24-hour PM2.5 NAAQS for 
at least 10 years beyond redesignation (through 2030) and that the 
contingency provisions describing the action the Butte County Air 
Quality Management District (BCAQMD or ``District'') will take in the 
event of a future monitored violation meet all applicable requirements 
for maintenance plans and section 175A of the CAA.
    The EPA is proposing these actions because the SIP revision meets 
the requirements of the CAA and EPA guidance for such plans.

II. Background

A. The PM2.5 NAAQS

    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 (78 FR 3086 at 
3088, January 15, 2013). PM2.5 can be emitted 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 such as nitrogen oxides 
(NOX), sulfur oxides (SOx), volatile organic 
compounds (VOC), and ammonia (NH3).\1\
---------------------------------------------------------------------------

    \1\ EPA, Air Quality Criteria for Particulate Matter, No. EPA/
600/P-99/002aF and EPA/600/P-99/002bF, October 2004.
---------------------------------------------------------------------------

    Under section 109 of the CAA, the EPA has established national 
ambient air quality standards 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

[[Page 21239]]

welfare.\2\ PM2.5 is one of the ambient pollutants for which 
the EPA has established health-based standards. Section 110(a) of the 
CAA requires states to submit regulations that control PM2.5 
emissions.
---------------------------------------------------------------------------

    \2\ 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).
---------------------------------------------------------------------------

    On July 18, 1997, the EPA revised the NAAQS for particulate matter 
to add new standards for PM2.5. The EPA established primary 
and secondary annual and 24-hour standards for PM2.5 (62 FR 
38652). The annual standard was set at 15.0 micrograms per meter cubed 
([micro]g/m\3\) 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.\3\
---------------------------------------------------------------------------

    \3\ The primary and secondary standards were set at the same 
level for both the 24-hour and the annual PM2.5 
standards.
---------------------------------------------------------------------------

    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 (71 FR 61144).\4\
---------------------------------------------------------------------------

    \4\ 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.
---------------------------------------------------------------------------

    On December 14, 2012, the EPA promulgated 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 maintaining 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 (78 FR 3086, January 15, 2013).

B. Designation of PM2.5 Nonattainment Areas

    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. On April 25, 2007, the EPA 
promulgated its Clean Air Fine Particle Implementation Rule, codified 
at 40 CFR part 51, subpart Z, in which the Agency provided guidance for 
state and tribal plans to implement the PM2.5 NAAQS (72 FR 
20586). Effective December 14, 2009, the EPA established initial air 
quality designations under subpart 1 of the Act for most areas in the 
United States for the 2006 24-hour PM2.5 NAAQS, including 
the Chico area (74 FR 58688, November 13, 2009).\5\
---------------------------------------------------------------------------

    \5\ All 1997 and 2006 PM2.5 NAAQS areas were 
designated under subpart 1 of the Act. Subpart 1 contains the 
general requirements for nonattainment areas for any pollutant 
governed by a NAAQS and is less prescriptive than the other subparts 
of title I, part D.
---------------------------------------------------------------------------

    The United States Court of Appeals District of Columbia Circuit 
(D.C. Circuit) remanded the Clean Air Fine Particle Implementation Rule 
and the final rule entitled ``Implementation of the New Source Review 
(NSR) Program for Particulate Matter Less than 2.5 Micrometers 
(PM2.5)'' (73 FR 28321, May 16, 2008) (collectively, ``1997 
PM2.5 Implementation Rules'') to the EPA on January 4, 2013, 
in Natural Resources Defense Council v. EPA, 706 F.3d 428 (D.C. Cir. 
2013). The Court found that the EPA erred in implementing the 1997 
PM2.5 NAAQS pursuant to the general implementation 
provisions of subpart 1 rather than the particulate matter-specific 
provisions of Part D of title I (subpart 4). The EPA responded to the 
D.C. Circuit's decision by identifying all PM2.5 
nonattainment areas for the 1997 and 2006 nonattainment areas for the 
1997 and 2006 NAAQS as ``moderate'' nonattainment areas under subpart 4 
and by establishing a new SIP submission date of December 31, 2014, for 
moderate area attainment plans and for any additional attainment-
related or nonattainment new source review plans necessary for areas to 
comply with the requirements applicable under subpart 4 (79 FR 31566, 
June 2, 2014).
    On July 29, 2016, EPA issued a rule entitled, ``Fine Particulate 
Matter National Ambient Air Quality Standards: State Implementation 
Plan Requirements'' (``PM2.5 SIP Requirements Rule'') that 
clarifies how states should meet the statutory SIP requirements that 
apply to areas designated nonattainment for any PM2.5 NAAQS 
under subparts 1 and 4 (81 FR 58010, August 24, 2016). It does so by 
establishing regulatory requirements and by providing guidance that is 
applicable to areas that are currently designated nonattainment for 
existing PM2.5 NAAQS and areas that are designated 
nonattainment for any PM2.5 NAAQS in the future. In 
addition, the rule responds to the D.C. Circuit's remand of the 1997 
PM2.5 Implementation Rules. As a result, the requirements of 
the rule also govern future actions associated with states' ongoing 
implementation efforts for the 1997 and 2006 PM2.5 NAAQS.
    The Chico PM2.5 nonattainment area is located within 
Butte County, California, in the northern Sacramento Valley, which is 
defined by the southern Cascade Mountains and northern Sierra Nevada 
mountains to the east and the Coastal Mountains to the north and west. 
As noted in the Chico PM2.5 Plan, the surrounding mountains 
provide ``a substantial physical barrier to both locally created 
pollution and the pollution that has been transported northward on 
prevailing winds from the metropolitan areas to the south.'' (Plan, p. 
4.) Most of the population lives and works at elevations below 1,000 
feet, where wintertime inversions can result in poor air quality.
    The local air district with primary responsibility for air quality 
planning in this area is the BCAQMD. Authority for regulating sources 
under State jurisdiction in the Chico nonattainment area is split 
between the District, which has responsibility for regulating 
stationary and most area sources, and the California Air Resources 
Board (CARB), which has responsibility for regulating most mobile 
sources. The District worked cooperatively with CARB in preparing the 
Chico PM2.5 redesignation request and maintenance plan.

C. PM2.5 Planning Requirements

    Within three years of the effective date of designations, states 
with areas designated as nonattainment for the 2006 24-hour 
PM2.5 NAAQS are required to submit SIP revisions that, among 
other elements, provide for implementation of reasonably available 
control measures (RACM), reasonable further progress (RFP), attainment 
of the standard as expeditiously as practicable but no later than five 
years from the nonattainment designation (in this instance, no later 
than December 14, 2014), as well as contingency measures.\6\ Prior to 
the due date for these submissions, the State requested that the EPA 
make a determination that, based on quality assured and certified data 
from the 2008-2010 period, the Chico PM2.5 nonattainment 
area had attained the 2006 24-hour PM2.5 NAAQS.\7\ In 
addition to requesting a finding of attainment, the State requested 
that the EPA suspend the attainment-related planning requirements.
---------------------------------------------------------------------------

    \6\ See CAA sections 172(a)(2), 172(c)(1), 172(c)(2), and 
172(c)(9).
    \7\ Letter from James N. Goldstene, Executive Officer, CARB, to 
Jared Blumenfeld, Regional Administrator, EPA Region 9, dated June 
2, 2011.
---------------------------------------------------------------------------

    Effective October 10, 2013, the EPA determined that the Chico 
nonattainment area had attained the

[[Page 21240]]

2006 24-hour PM2.5 standard based on the 2010-2012 
monitoring period (78 FR 55225, September 10, 2013). Based on that 
determination and pursuant to 40 CFR 51.1004(c), the requirements for 
this area to submit an attainment demonstration, together with RACM, an 
RFP plan, and contingency measures for failure to meet RFP and 
attainment deadlines were suspended for so long as the area continued 
to attain the 2006 24-hour PM2.5 NAAQS or until the area is 
redesignated to attainment.\8\ The EPA subsequently issued a 
determination that the Chico area had attained the 2006 24-hour 
PM2.5 NAAQS by the applicable attainment date of December 
31, 2015, based on 2013-2015 data (82 FR 21711, May 10, 2017). On 
December 18, 2017, CARB submitted the Chico PM2.5 Plan and 
requested that the EPA redesignate the Chico PM2.5 
nonattainment area to attainment for the 2006 24-hour PM2.5 
NAAQS.
---------------------------------------------------------------------------

    \8\ For more information on the regulatory basis for determining 
attainment of the NAAQS, see the proposed determination of 
attainment (77 FR 65651, October 30, 2012).
---------------------------------------------------------------------------

III. Procedural Requirements for Adoption and Submittal of SIP 
Revisions

    Section 110(l) of the Act requires states to provide reasonable 
notice and public hearing prior to adoption of SIP revisions. CARB's 
December 18, 2017 submittal of the Chico PM2.5 Plan 
documents the public review process followed by BCAQMD and CARB in 
adopting the Chico PM2.5 Plan prior to submittal to the EPA 
as a revision to the California SIP. The submittal provides evidence 
that reasonable notice of a public hearing was provided to the public 
and that a public hearing was conducted prior to adoption. 
Specifically, a notice of public hearing was published on September 26, 
2017, in the Chico Enterprise-Record, a newspaper of general 
circulation in the City of Chico and Butte County. The notice announced 
the availability of the Chico PM2.5 Plan at the District 
office and on its website, and it opened the comment period 30 days 
prior to the public hearing. The public hearing was held on October 26, 
2017. No comments on the Plan were made during the public hearing and 
no written comments were received during the public comment period. 
Following adoption by BCAQMD's Air Quality Governing Board, the 
District provided the maintenance plan to CARB and requested that it 
submit the redesignation request and maintenance plan to the EPA.\9\
---------------------------------------------------------------------------

    \9\ Letter from W. James Wagoner, Air Pollution Control Officer, 
BCAQMD, to Richard Corey, Executive Officer, CARB, dated October 31, 
2017.
---------------------------------------------------------------------------

    On November 16, 2017, CARB adopted the Chico PM2.5 Plan, 
as certified in Resolution 17-41. No public comments were received 
during the CARB hearing. CARB submitted the Plan to the EPA on December 
18, 2017. On February 15, 2018, CARB provided additional information 
regarding its development of the 2012 winter emission inventory and 
other emissions inventories for the Chico PM2.5 Plan.\10\ 
Based on the documentation provided, we find that submittal of the 
Chico PM2.5 Plan as a revision to the California SIP 
satisfies the procedural requirements of section 110(l) of the Act.
---------------------------------------------------------------------------

    \10\ Letter with enclosures from Sylvia Vanderspeck, Chief, Air 
Quality Planning Branch, CARB, to GwenYoshimura, Manager, Air 
Quality Analysis Section, EPA Region 9.
---------------------------------------------------------------------------

    Section 110(k)(1)(B) of the CAA requires the EPA to determine 
whether a SIP submittal is complete within 60 days of receipt. This 
section also provides that any plan that we have not affirmatively 
determined to be complete or incomplete will become complete by 
operation of law six months after the day of submittal. A completeness 
review allows us to determine if the submittal includes all the 
necessary items and information we need to act on it.
    We make completeness determinations using criteria we have 
established in 40 CFR part 51, Appendix V. These criteria fall into two 
categories: administrative information and technical support 
information. The administrative information provides documentation that 
the state has followed basic administrative procedures during the SIP 
adoption process. The technical support information provides the 
information we need to determine the impact of the proposed revisions 
on attainment and maintenance of the air quality standard.
    We notify a state of our completeness determination by letter 
unless the submittal becomes complete by operation of law. A finding of 
completeness does not approve a submittal as part of the SIP nor does 
it indicate that the SIP is approvable. It does start a 12-month clock 
for the EPA to act on the SIP submittal. On April 5, 2018, we notified 
CARB that we had determined the submittal of the Chico PM2.5 
Plan to be complete.\11\
---------------------------------------------------------------------------

    \11\ Letter from Elizabeth J. Adams, Acting Air Division 
Director, EPA Region 9 to Richard W. Corey, Executive Officer, CARB.
---------------------------------------------------------------------------

IV. Substantive Requirements for Redesignation

    The CAA establishes the requirements for redesignation of a 
nonattainment area to attainment. Specifically, section 107(d)(3)(E) 
allows for redesignation provided that the following criteria are met: 
(1) The EPA determines that the area has attained the applicable NAAQS; 
(2) the EPA has fully approved the applicable implementation plan for 
the area under 110(k); (3) the EPA determines that the improvement in 
air quality is due to permanent and enforceable reductions; (4) the EPA 
has fully approved a maintenance plan for the area as meeting the 
requirements of CAA 175A; and (5) the state containing such area has 
met all requirements applicable to the area under section 110 and part 
D of the CAA. Section 110 identifies a comprehensive list of elements 
that SIPs must include, and part D establishes the SIP requirements for 
nonattainment areas. Part D is divided into six subparts. The 
generally-applicable nonattainment SIP requirements are found in part 
D, subpart 1, and the particulate matter-specific SIP requirements are 
found in part D, subpart 4.
    The EPA provided guidance on redesignations in a document entitled 
``State Implementation Plans; General Preamble for the Implementation 
of Title I of the Clean Air Act Amendments of 1990,'' published in the 
Federal Register on April 16, 1992 (57 FR 13498), and supplemented on 
April 28, 1992 (57 FR 18070) (referred to herein as the ``General 
Preamble''). Additional guidance was issued on September 4, 1992, in a 
memorandum from John Calcagni, Director, Air Quality Management 
Division, EPA Office of Air Quality Planning and Standards, entitled 
``Procedures for Processing Requests to Redesignate Areas to 
Attainment'' (referred to herein as the ``Calcagni memo''). Maintenance 
plan submittals are SIP revisions, and as such, the EPA is obligated 
under CAA section 110(k) to approve them or disapprove them depending 
upon whether they meet the applicable CAA requirements for such plans.
    For reasons set forth in section V. of this document, we propose to 
approve CARB's request for redesignation of the Chico nonattainment 
area to attainment for the 2006 24-hour PM2.5 NAAQS based on 
our conclusion that all the criteria under CAA section 107(d)(3)(E) 
have been satisfied.

[[Page 21241]]

V. Evaluation of the State's Redesignation Request for the Chico 
PM[bdi2].[bdi5] Nonattainment Area

A. Determination That the Area Has Attained the PM2.5 NAAQS

    Section 107(d)(3)(E)(i) of the CAA requires that for an area to be 
redesignated to attainment the EPA must determine that the area has 
attained the relevant NAAQS. In this case, the relevant NAAQS is the 
2006 24-hour PM2.5 NAAQS. In 2013, the EPA determined that 
the Chico nonattainment area had attained the 2006 24-hour 
PM2.5 NAAQS based on the 2010-2012 monitoring period. In 
2017, the EPA determined that the Chico nonattainment area attained the 
2006 24-hour PM2.5 NAAQS by the area's applicable attainment 
date of December 31, 2015, based on data for the years 2013-2015.\12\ 
Today's action updates these determinations based on the most recent 
available PM2.5 monitoring data.
---------------------------------------------------------------------------

    \12\ See Section II.C. of this document.
---------------------------------------------------------------------------

    Generally, the EPA determines whether an area's air quality is 
meeting the 2006 24-hour PM2.5 NAAQS based upon complete, 
quality-assured, and certified data measured at established state and 
local air monitoring stations (SLAMS) in the nonattainment area and 
entered into the EPA Air Quality System (AQS) database. The EPA will 
consider air quality data from air monitoring sites other than SLAMS in 
the nonattainment area provided those stations meet the federal 
monitoring requirements for SLAMS, including the quality assurance and 
quality control criteria in 40 CFR part 58, appendix A.\13\
---------------------------------------------------------------------------

    \13\ See 40 CFR 58.20; 71 FR 61236 at 61242 (October 17, 2006).
---------------------------------------------------------------------------

    Data from air monitoring sites operated by state, local, or tribal 
agencies in compliance with EPA monitoring requirements must be 
submitted to AQS. These monitoring agencies certify annually that these 
data are accurate to the best of their knowledge. Accordingly, the EPA 
relies primarily on data in AQS when determining the attainment status 
of an area.\14\ All valid data are reviewed to determine the area's air 
quality status in accordance with 40 CFR part 50, appendix N.
---------------------------------------------------------------------------

    \14\ See 40 CFR 50.13; 40 CFR part 50, appendix L; 40 CFR part 
53; 40 CFR part 58; and, 40 CFR part 58, appendices A, C, D, and E.
---------------------------------------------------------------------------

    As described previously, the 2006 24-hour PM2.5 NAAQS is 
met when the design value is less than or equal to 35 [micro]g/m\3\. 
The PM2.5 24-hour average is considered valid when 75 
percent of the hourly averages for the 24-hour period are available. 
Data completeness requirements for a given year are met when at least 
75 percent of the scheduled sampling days for each quarter have valid 
data.
    The California Air Resources Board is responsible for monitoring 
ambient air quality within Butte County and operates the 
PM2.5 monitoring network in Butte County. CARB submits 
annual monitoring network plans to the EPA. These network plans 
describe the monitoring network operated by CARB within Butte County 
and discuss the status of the air monitoring network, as required under 
40 CFR 58.10. The EPA regularly reviews these annual plans for 
compliance with the applicable reporting requirements in 40 CFR part 
58. With respect to PM2.5, the EPA has found that the area's 
network plans meet the applicable reporting requirements under 40 CFR 
part 58.\15\ The EPA also concluded from its 2015 Technical Systems 
Audit that CARB's monitoring network currently meets or exceeds the 
requirements for the minimum number of SLAMS for PM2.5 in 
the Chico, CA Metropolitan Statistical Area (MSA), which comprises the 
Chico PM2.5 nonattainment area.\16\ CARB annually certifies 
that the data it submits to AQS are complete and quality-assured.\17\
---------------------------------------------------------------------------

    \15\ For example, see letter from Gwen Yoshimura, Manager, Air 
Quality Analysis Office, EPA Region IX, to Ravi Ramalingam, Chief, 
Consumer Products and Air Quality Assessment Branch, CARB, dated 
December 14, 2017, approving CARB's 2017 Annual Network Plan.
    \16\ EPA Region IX, Technical System Audit Final Report, CARB 
Ambient Air Monitoring Program, April-August 2015. Enclosed with 
letter from Elizabeth Adams, Acting Director, Air Division, EPA 
Region IX, to Richard Corey, Executive Officer, CARB, dated August 
31, 2016.
    \17\ For example, see letter from Ravi Ramalingam, Chief, 
Consumer Products and Air Quality Assessment Branch, CARB, to 
Elizabeth Adams, Acting Director, Air Division, EPA Region IX, 
certifying calendar year 2016 ambient air quality data and quality 
assurance data, dated June 2, 2017.
---------------------------------------------------------------------------

    During the 2014-2016 period, CARB operated one PM2.5 
SLAMS monitoring site, Chico-East Avenue (AQS ID: 06-007-0008), within 
the Chico PM2.5 nonattainment area. SLAMS produce data 
comparable to the NAAQS, and therefore, the monitor must be an approved 
Federal Reference Method (FRM), Federal Equivalent Method, or Approved 
Regional Method. The Chico-East Avenue monitor measures 
PM2.5 concentrations on a daily, year-round basis using a 
method that has been designated an FRM by the EPA. Butte County also 
had two additional monitoring sites operated by CARB during this 
period, Gridley (AQS ID: 06-007-4001) and Paradise-Theater (06-007-
2002), whose data are not comparable to the NAAQS and cannot be used 
for attainment demonstration purposes. CARB continues to meet EPA 
requirements for the minimum number of PM2.5 monitoring 
sites in Butte County within the Chico MSA.
    Consistent with the requirements contained in 40 CFR part 50, the 
EPA has reviewed the quality-assured and certified PM2.5 
ambient air monitoring data collected at the Chico-East Avenue 
monitoring site, as recorded in AQS, for the applicable monitoring 
period. We have determined that the data are of sufficient completeness 
for the purposes of making comparisons with the 2006 24-hour 
PM2.5 NAAQS. The EPA's evaluation of whether the Chico 
PM2.5 nonattainment area has attained the 2006 24-hour 
PM2.5 NAAQS is based on our review of the monitoring data 
and takes into account the adequacy of the PM2.5 monitoring 
network in the nonattainment area and the reliability of the data 
collected by the network as discussed earlier in this section of this 
document.
    Table 1 below shows the 24-hour PM2.5 design value 
monitored at the Chico-East Avenue monitoring site over the most recent 
three-year period (2014-2016). The data show that the 24-hour design 
value for the 2014-2016 period was equal to or less than 35 [micro]g/
m\3\ at the Chico-East Avenue monitor. Therefore, we find that, based 
on complete, quality-assured, and certified data for 2014-2016, the 
Chico PM2.5 nonattainment area has attained the 2006 24-hour 
PM2.5 NAAQS. Preliminary data available in AQS for 2017 
indicate that the area continues to attain the 2006 24-hour 
PM2.5 NAAQS.

[[Page 21242]]

                                                    Table 1--Chico-East Avenue 2014-2016 Design Value
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                           2006 24-hour            98th Percentile ([mu]g/m\3\)            2014-2016 24-
                                                                            PM2.5 NAAQS  ------------------------------------------------   hour design
                     Monitoring Site                          AQS ID       ([mu]g/m\3\)                                                    value ([mu]g/
                                                                                               2014            2015            2016            m\3\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Chico-East Avenue.......................................     06-007-0008              35            26.0            29.5            21.2              26
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: EPA, AQS Design Value Report, March 29, 2018.

B. The Area Must Have a Fully Approved SIP Meeting the Requirements 
Applicable for Purposes of Redesignation Under Section 110 and Part D

    Sections 107(d)(3)(E)(ii) and (v) require the EPA to determine that 
the area has a fully approved applicable SIP under section 110(k) that 
meets all applicable requirements under section 110 and part D for the 
purposes of redesignation.
1. Basic SIP Requirements Under Section 110
    The general SIP elements and requirements set forth in section 
110(a)(2) include, but are not limited to, the following: Submittal of 
a SIP that has been adopted by the state after reasonable public notice 
and hearing; provisions for establishment and operation of appropriate 
procedures needed to monitor ambient air quality; implementation of a 
source permitting program; provision for the implementation of part C 
requirements for prevention of significant deterioration; provisions 
for the implementation of part D requirements for nonattainment new 
source review permit programs; provisions for air pollution modeling; 
and provisions for public and local agency participation in planning 
and emission control rule development.
    We note that SIPs must be fully approved only with respect to 
applicable requirements for purposes of redesignation in accordance 
with section 107(d)(3)(E)(ii). The section 110(a)(2) (and part D) 
requirements that are linked to a particular nonattainment area's 
designation and classification are the relevant measures to evaluate in 
reviewing a redesignation request. Requirements that apply regardless 
of the designation of any particular area of a state are not applicable 
requirements for the purposes of redesignation, and the State will 
remain subject to these requirements after the Chico PM2.5 
nonattainment area is redesignated to attainment.
    For example, CAA section 110(a)(2)(D) requires that SIPs contain 
certain measures to prevent sources in a state from significantly 
contributing to air quality problems in another state: These SIPs are 
often referred to as ``transport SIPs.'' Because the section 
110(a)(2)(D) requirements for transport SIPs are not linked to a 
particular nonattainment area's designation and classification, but 
rather apply regardless of the area's attainment status, these are not 
applicable requirements for the purposes of redesignation under section 
107(d)(3)(E).
    Similarly, the EPA believes that other section 110(a)(2) (and part 
D) requirements that are not linked to nonattainment plan submissions 
or to an area's attainment status are not applicable requirements for 
purposes of redesignation. The EPA believes that the section 110 (and 
part D) requirements that relate to a particular nonattainment area's 
designation and classification are the relevant measures to evaluate in 
reviewing a redesignation request. This view is consistent with the 
EPA's existing policy on applicability of the conformity SIP 
requirement for redesignations.\18\
---------------------------------------------------------------------------

    \18\ See, e.g., 75 FR 36023 at 36026 (June 24, 2010).
---------------------------------------------------------------------------

    On numerous occasions, CARB and BCAQMD have submitted and we have 
approved provisions addressing the basic CAA section 110 provisions. 
The Butte County portion of the California SIP \19\ contains 
enforceable emission limitations; requires monitoring, compiling and 
analyzing of ambient air quality data; requires preconstruction review 
of new or modified stationary sources; provides for adequate funding, 
staff, and associated resources necessary to implement its 
requirements; and provides the necessary assurances that the State 
maintains responsibility for ensuring that the CAA requirements are 
satisfied in the event that Butte County is unable to meet its CAA 
obligations. There are no outstanding or disapproved applicable SIP 
submittals with respect to the Butte County portion of the SIP that 
prevent redesignation of the Chico PM2.5 nonattainment area 
for the 24-hour PM2.5 standard. Therefore, we propose to 
conclude that CARB and BCAQMD have met all general SIP requirements for 
Chico that are applicable for purposes of redesignation under section 
110 of the CAA.
---------------------------------------------------------------------------

    \19\ The Butte County portion of the federally approved SIP can 
be viewed at https://www.epa.gov/sips-ca/epa-approved-butte-county-air-district-regulations-california-sip.
---------------------------------------------------------------------------

2. SIP Requirements Under Part D
    Subparts 1 and 4 of part D, title 1 of the CAA contain air quality 
planning requirements for PM2.5 nonattainment areas. Subpart 
1 contains general requirements for all nonattainment areas of any 
pollutant, including PM2.5, governed by a NAAQS. The subpart 
1 requirements include, among other things, provisions for RACM, RFP, 
emissions inventories, contingency measures, and conformity. Subpart 4 
contains specific planning and scheduling requirements for 
PM2.5 nonattainment areas. Section 189(a), (c), and (e) 
requirements apply specifically to moderate PM2.5 
nonattainment areas and include: An approved permit program for 
construction of new and modified major stationary sources; provisions 
for RACM; an attainment demonstration; quantitative milestones 
demonstrating RFP toward attainment by the applicable attainment date; 
and provisions to ensure that the control requirements applicable to 
major stationary sources of PM2.5 also apply to major 
stationary sources of PM2.5 precursors, except where the 
Administrator has determined that such sources do not contribute 
significantly to PM2.5 levels that exceed the NAAQS in the 
area.
    As noted in Section II.C.of this document, the EPA determined in 
2013 that the Chico PM2.5 nonattainment area attained the 
24-hour PM2.5 NAAQS based on 2010-2012 data. In accordance 
with the EPA's Clean Data Policy, we determined that the following 
requirements do not apply to the Chico PM2.5 nonattainment 
area for so long as the area continues to attain the PM2.5 
standard or until the area is redesignated to attainment: An attainment 
demonstration under section 189(a)(1)(B); RACM provisions under 
sections 172(c) and 189(a)(1)(C); reasonable further progress 
provisions under section 189(c)(1); and contingency measures under 
section 172(c)(9).\20\
---------------------------------------------------------------------------

    \20\ The EPA's Clean Data Policy for PM2.5 
nonattainment areas is set forth in a memorandum entitled ``Clean 
Data Policy for the Fine Particle National Ambient Air Quality 
Standards,'' issued on December 14, 2004, by Stephen D. Page, 
Director, EPA Office of Air Quality Planning and Standards. For 
examples of other rulemaking actions applying the Clean Data Policy 
in PM2.5 nonattainment areas, see 78 FR 41901, July 12, 
2013 (West Central Pinal, Arizona); 80 FR 22666, April 23, 2015 
(Liberty-Clairton, Pennsylvania); and 82 FR 13392, March 13, 2017 
(Imperial County, California). The PM2.5 SIP Requirements 
Rule includes a discussion of EPA's Clean Data Policy (81 FR 58010 
at 58127) and codifies the Clean Data Policy governing the 
implementation of current and future PM2.5 NAAQS at 40 
CFR 51.1015.

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

[[Page 21243]]

    Moreover, in the context of evaluating an area's eligibility for 
redesignation, there is a separate and additional justification for 
finding that requirements associated with attainment are not applicable 
for purposes of redesignation. Prior to and independently of the Clean 
Data Policy,\21\ and specifically in the context of redesignations, the 
EPA interpreted attainment-linked requirements as not applicable for 
purposes of redesignation. In the General Preamble, the EPA explained 
that the section 172(c)(9) requirements are directed at ensuring RFP 
and attainment by the applicable date. We noted that these requirements 
no longer apply when an area has attained the standard and is eligible 
for redesignation. Furthermore, CAA section 175A for maintenance plans 
provides specific requirements for contingency measures that 
effectively supersede the requirements of section 172(c)(9) for these 
areas.
---------------------------------------------------------------------------

    \21\ The Calcagni memo states that the requirements for 
reasonable further progress and other measures needed for attainment 
will not apply for redesignations because they only have meaning for 
areas not attaining the standard (p. 6).
---------------------------------------------------------------------------

    Thus, even if the requirements associated with attainment had not 
previously been suspended, they would not apply for purposes of 
evaluating whether an area that has attained the standard qualifies for 
redesignation. The EPA has enunciated this position since the General 
Preamble was published more than 25 years ago, and it represents the 
Agency's interpretation of what constitutes applicable requirements 
under section 107(d)(3)(E). The courts have recognized the scope of the 
EPA's authority to interpret ``applicable requirements'' in the 
redesignation context.\22\
---------------------------------------------------------------------------

    \22\ See Sierra Club v. EPA, 375 F.3d 537 (7th Cir. 2004).
---------------------------------------------------------------------------

    The remaining applicable Part D requirements for moderate 
PM2.5 areas are: (1) An emission inventory under section 
172(c)(3); (2) a permit program for the construction and operation of 
new and modified major stationary sources of PM2.5 under 
sections 172(c)(5) and 189(a)(1)(A); (3) control requirements for major 
stationary sources of PM2.5 precursors under section 189(e), 
except where the Administrator determines that such sources do not 
contribute significantly to PM2.5 levels that exceed the 
standard in the area; (4) requirements under section 172(c)(7) that 
meet the applicable provisions of section 110(a)(2); and (5) provisions 
to ensure that federally supported or funded projects conform to the 
air quality planning goals in the applicable SIP under section 176(c).
    The Chico redesignation request substantively meets the Part D 
requirements for redesignation purposes. We discuss each of these 
requirements below.
a. Emissions Inventory
    Section 172(c)(3) of the CAA requires states to submit a 
comprehensive, accurate, current inventory of relevant PM2.5 
pollutants for the baseline year from all sources within the 
nonattainment area. The inventory must address direct and secondary 
PM2.5 emissions, and all stationary (generally referring to 
larger stationary source or ``point'' sources), area (generally 
referring to smaller stationary and fugitive sources), and mobile (on-
road, non-road, locomotive and aircraft) sources are to be included in 
the inventory.
    On November 15, 2012, CARB submitted a SIP revision for the Chico 
nonattainment area that provided a 2011 winter-time emissions inventory 
with emissions estimates in tons per day (tpd) for PM2.5 and 
PM2.5 precursors.\23\ After reviewing the CARB submittal of 
the Chico emissions inventory and supporting documentation, the EPA 
determined that the emissions inventory met the requirements of the CAA 
and EPA guidance and approved it consistent with CAA sections 110 and 
172(c)(3) (79 FR 14404, March 14, 2014).
---------------------------------------------------------------------------

    \23\ Monitoring data for the Chico nonattainment area indicate 
that high concentrations of PM2.5 occur primarily during 
the winter months; consequently, the District submitted a winter-
season inventory.
---------------------------------------------------------------------------

b. Permits for New and Modified Major Stationary Sources
    CAA sections 172(c)(5) and 189(a)(1)(A) require that states submit 
SIP revisions that establish certain requirements for new or modified 
stationary sources in nonattainment areas, including provisions to 
ensure that new major sources or major modifications of existing 
sources of nonattainment pollutants incorporate the highest level of 
control, referred to as the lowest achievable emission rate, and that 
increases in emissions from such stationary sources are offset so as to 
provide for reasonable further progress towards attainment in the 
nonattainment area.
    The process for reviewing permit applications and issuing permits 
for new or modified major stationary sources of air pollution is 
referred to as new source review (NSR). With respect to nonattainment 
pollutants in nonattainment areas, this process is referred to as 
nonattainment NSR (NNSR). Areas that are designated as attainment or 
unclassifiable for one or more NAAQS are required to submit SIP 
revisions that ensure that major new stationary sources or major 
modifications of existing stationary sources meet the federal 
requirements for prevention of significant deterioration (PSD), 
including application of best available control technology for each 
applicable pollutant emitted in significant amounts, among other 
requirements.\24\
---------------------------------------------------------------------------

    \24\ PSD requirements control the growth of new source emissions 
in areas designated as attainment for a NAAQS.
---------------------------------------------------------------------------

    The District is responsible for stationary source emissions units, 
and its regulations govern air permits issued for such units. Although 
BCAQMD does not have a fully approved NNSR rule,\25\ it does not affect 
EPA approval of the redesignation request because the maintenance 
demonstration does not rely on implementation of NNSR \26\ and upon 
redesignation the nonattainment permitting program requirements shift 
to the PSD permitting program requirements under 40 CFR 51.166.
---------------------------------------------------------------------------

    \25\ The EPA partially approved and partially disapproved 
BCAQMD's nonattainment NSR rule (Rule 432) because ammonia was not 
listed as a PM2.5 precursor (81 FR 93820, December 22, 
2016). On June 12, 2017, the District submitted a revised rule to 
correct this deficiency. The EPA proposed to approve the revised 
rule on March 23, 2018 (83 FR 12694).
    \26\ Because PSD requirements will apply after redesignation, an 
area being redesignated to attainment need not comply with the 
requirement that a nonattainment NSR program be approved prior to 
redesignation, providing the state demonstrates maintenance of the 
NAAQS in the area without implementation of nonattainment NSR. A 
more detailed rationale for this view is described in a memorandum 
from Mary Nichols, Assistant Administrator for Air and Radiation, 
dated October 14, 1994, titled ``Part D New Source Review 
Requirements for Areas Requesting Redesignation to Attainment.'' See 
also redesignation rulemakings for Detroit, Michigan (60 FR 12459, 
March 7, 1995); Cleveland-Akron-Lorain, Ohio (61 FR 20458, May 7, 
1996); Louisville, Kentucky (66 FR 53665, October 23, 2001); Grand 
Rapids, Michigan (61 FR 31831, June 21, 1996); and Yuba City-
Marysville, California (79 FR 61822, October 15, 2014).
---------------------------------------------------------------------------

    The District has a SIP-approved PSD program (Rule 1107) that will 
apply to PM2.5 and PM2.5 precursor emissions from 
new major sources or major modifications upon redesignation of the

[[Page 21244]]

area to attainment.\27\ Thus, new major sources with significant 
PM2.5 emissions and major modifications of PM2.5 
at major sources as defined under 40 CFR 51.166 will be required to 
obtain a PSD permit or address PM2.5 emissions in their 
existing PSD permit. Further, the maintenance demonstration does not 
rely on implementation of NNSR because the Plan applies standard growth 
factors to stationary source emissions and does not rely on NSR offsets 
to reduce the rate of increase in emissions over time from point 
sources. In addition, the Chico PM2.5 Plan adds emission 
reduction credits (ERCs) for PM10,\28\ NOX, 
SOX, and reactive organic gasses (ROG) \29\ to future 
projected emissions to ensure that the use of ERCs will not be 
inconsistent with the future PM2.5 maintenance goals. 
Therefore, the EPA concludes that a fully-approved nonattainment NSR 
program is not necessary for approval of the State's redesignation 
request for the Chico PM2.5 nonattainment area.
---------------------------------------------------------------------------

    \27\ Rule 1107 was approved on November 12, 2015 (80 FR 69880).
    \28\ BCAQMD issues ERCs for PM10. When creating the 
future year inventories for the maintenance demonstration, the 
District added the amount of PM10 ERCs to the future year 
inventories of PM2.5. Because PM2.5 is a 
fraction of PM10, this approach conservatively estimates 
the maximum pollutant increase if all ERCs were redeemed within the 
BCAQMD during the maintenance period. Plan, p. 18 and Attachment D.
    \29\ California plans sometimes use the term Reactive Organic 
Gases (ROG) for VOC. These terms are essentially synonymous.
---------------------------------------------------------------------------

    We conclude that Butte County's portion of the California SIP 
adequately meets the requirements of section 172(c)(5) and 189(a)(1)(A) 
for purposes of this redesignation.
c. Control Requirements for PM2.5 Precursors
    CAA section 189(e) provides that control requirements for major 
stationary sources of direct PM10 (including 
PM2.5) shall also apply to PM precursors from those sources, 
except where the EPA determines that major stationary sources of such 
precursors do not contribute significantly to PM10 levels 
that exceed the standard in the area. The CAA does not explicitly 
address whether it would be appropriate to include a potential 
exemption from precursor controls for all source categories under 
certain circumstances. In implementing subpart 4 with regard to 
controlling PM10, the EPA permitted states to determine that 
a precursor was ``insignificant'' where the state could show in its 
attainment plan that it would expeditiously attain without adoption of 
emission reduction measures aimed at that precursor. This approach was 
upheld in Association of Irritated Residents v. EPA, 423 F.3d 989 (9th 
Cir. 2005) and extended to PM2.5 implementation in the 
PM2.5 SIP Requirements Rule. A state may develop its 
attainment plan and adopt RACM that target only those precursors that 
are necessary to control for purposes of timely attainment. See 81 FR 
58010 at 58020.
    Therefore, because the requirement of section 189(e) is primarily 
actionable in the context of addressing precursors in an attainment 
plan, a precursor exemption analysis under section 189(e) and the EPA's 
implementing regulations is not an applicable requirement that needs to 
be fully approved in the context of a redesignation under CAA section 
107(d)(3)(E)(ii). As discussed above, for areas that are attaining the 
standard, the EPA does not interpret attainment planning requirements 
of subparts 1 and 4 to be applicable requirements for the purposes of 
redesignating an area to attainment.
    As previously noted, the EPA determined in 2013 that the Chico 
PM2.5 nonattainment area had attained the 2006 24-hour 
PM2.5 NAAQS, and in 2017 affirmed that the area had attained 
the NAAQS by the statutory attainment date. The Chico area has 
expeditiously attained the 2006 24-hour PM2.5 NAAQS, and 
therefore, no additional controls of any pollutant, including any 
PM2.5 precursor, are necessary to bring the area into 
attainment. In Section V.A. of this document, we find that the area 
continues to attain the NAAQS. In section V.C. of this document, the 
EPA is proposing to determine that the Chico PM2.5 
nonattainment area has attained the standard due to permanent and 
enforceable emissions reductions. Further, as set forth in section V.D. 
of this document, we believe that the Plan demonstrates continued 
maintenance of the 2006 24-hour PM2.5 standard through 2030. 
Taken together, these factors support our conclusion that 
PM2.5 precursors are adequately controlled.
d. Compliance With Section 110(a)(2)
    Section 172(c)(7) requires the SIP to meet the applicable 
provisions of section 110(a)(2). As described in section V.B. of this 
document, we conclude the California SIP meets the requirements of 
section 110(a)(2) applicable for purposes of this redesignation.
e. General and Transportation Conformity Requirements
    Under section 176(c) of the CAA, states are required to establish 
criteria and procedures to ensure that federally supported or funded 
projects conform to the air quality planning goals in the applicable 
SIP. Section 176(c) further provides that state conformity provisions 
must be consistent with federal conformity regulations that the CAA 
requires the EPA to promulgate. The EPA's conformity regulations are 
codified at 40 CFR part 93, subparts A (referred to herein as 
``transportation conformity'') and B (referred to herein as ``general 
conformity''). Transportation conformity applies to transportation 
plans, programs, and projects developed, funded, and approved under 
title 23 U.S.C. or the Federal Transit Act, and general conformity 
applies to all other federally-supported or funded projects. SIP 
revisions intended to address the conformity requirements are referred 
to herein as ``conformity SIPs.'' The EPA believes it is reasonable to 
interpret the conformity SIP requirements as not applying for purposes 
of a redesignation request under section 107(d) because state 
conformity rules are still required after redesignation and federal 
conformity rules apply where state rules have not been approved. See 
Wall v. EPA, 265 F.3d 426 (6th Cir. 2001), upholding this 
interpretation.\30\
---------------------------------------------------------------------------

    \30\ See, e.g., 60 FR 62748 (December 7, 1995).
---------------------------------------------------------------------------

C. The Area Must Show the Improvement in Air Quality Is Due to 
Permanent and Enforceable Emission Reductions

    In order to approve a redesignation to attainment, section 
107(d)(3)(E)(iii) of the CAA requires the EPA to determine that the 
improvement in air quality is due to emission reductions that are 
permanent and enforceable, and that the improvement results from the 
implementation of the applicable SIP and applicable federal air 
pollution control regulations and other permanent and enforceable 
regulations. Under this criterion, a state must be able to reasonably 
attribute the improvement in air quality to emissions reductions that 
are permanent and enforceable. Attainment resulting from temporary 
reductions in emission rates (e.g., reduced production or shutdown due 
to temporary adverse economic conditions) or unusually favorable 
meteorology would not qualify as an air quality improvement due to 
permanent and enforceable emission reductions (Calcagni memo, p. 4).
    In its demonstration that improvements in air quality are 
reasonably attributable to emissions reductions that are permanent and 
enforceable, BCAQMD evaluated several factors: The composition of 
PM2.5 in the

[[Page 21245]]

nonattainment area; control measures that have been implemented since 
the area was redesignated to nonattainment; changes to the emissions 
inventory over time; and meteorological and economic trends. Based on 
these factors, the District concluded that permanent and enforceable 
reductions in emissions from residential wood burning and mobile 
sources provided the greatest emissions reductions (Plan, Section 
3.c.).
    Using chemical composition data from speciation samplers located at 
the Chico monitoring site, the District calculated the average 
contribution of different components to the PM2.5 design 
value on the 10 percent of days with highest monitored concentrations 
of PM2.5 for 2014-2016.\31\ Total carbonaceous mass, which 
is linked to smoke from residential wood burning stoves and fireplaces, 
contributed 76 percent (19.84 [mu]g/m\3\) of the 26 [mu]g/m\3\ design 
value. The second largest fraction is ammonium nitrate, formed from 
precursor emissions of NOX and ammonia, which accounted for 
16 percent of the total (4.07 [mu]g/m\3\). Other contributors (i.e., 
ammonium sulfate, formed from precursor emissions of SOX and 
ammonia--4 percent, geological materials--2 percent, and elements--2 
percent) account for a much smaller portion of the ambient 
PM2.5 (Plan, Section 4.a. and Attachment F). As described in 
our analysis of the District's maintenance demonstration,\32\ the Plan 
makes the case that residential wood burning is the primary contributor 
to the air quality problem in the Chico nonattainment area and that 
secondary PM2.5 (ammonium nitrate and ammonium sulfate), 
geological materials, and elements are relatively small contributors.
---------------------------------------------------------------------------

    \31\ This matches the three years used to derive the 2016 design 
value.
    \32\ Section V.D.2., of this document.
---------------------------------------------------------------------------

    The Chico PM2.5 Plan credits control measures adopted 
and implemented by BCAQMD and CARB and approved into the SIP by the EPA 
as reducing emissions to attain the 2006 24-hour PM2.5 
NAAQS. The District has jurisdiction over air quality planning 
requirements for the Chico nonattainment area and is largely 
responsible for the regulation of stationary sources and most area 
sources. Table 2 lists BCAQMD rules adopted and SIP-approved since the 
area's PM2.5 nonattainment designation that contribute 
towards attainment and maintenance of the 2006 24-hour PM2.5 
NAAQS.

  Table 2--BCAQMD SIP-Approved Control Measures and Programs Contributing Towards Attainment and Maintenance of
                                          the 2006 24-Hour PM2.5 NAAQS
----------------------------------------------------------------------------------------------------------------
                                                                 Adoption or amendment
                 Rule                           Title                     date                    Status
----------------------------------------------------------------------------------------------------------------
207..................................  Wood Burning Devices...  Amended December 11,     EPA approved--78 FR
                                                                 2008.                    21540.
300..................................  Open Burning             Amended December 9,      EPA approved--81 FR
                                        Requirements,            2010, February 24,       70018.
                                        Prohibitions, and        2011, and August 27,
                                        Exemptions \a\.          2015.
400..................................  Permit Requirements....  Amended May 26, 2011     EPA approved--81 FR
                                                                 and April 24, 2014.      93820.
401..................................  Permit Exemptions......  Amended May 26, 2011     EPA approved--81 FR
                                                                 and April 24, 2014.      93820.
432..................................  Federal New Source       Adopted May 26, 2011,    81 FR 93820 (limited
                                        Review.                  Amended April 24, 2014   approval/limited
                                                                 and March 23, 2017.      disapproval), 83 FR
                                                                                          12694 (proposed
                                                                                          approval).
433..................................  Rice Straw Emission      Amended April 24, 2014.  EPA approved--83 FR
                                        Reduction Credits.                                17380.
1107.................................  Prevention of            Adopted June 28, 2012..  EPA approved--80 FR
                                        Significant                                       69880.
                                        Deterioration.
----------------------------------------------------------------------------------------------------------------
Source: Plan, Table 3-2.
\a\ BCAQMD participates in the State's Sacramento Valley Air Basin Smoke Management Program (Plan, p. 11). The
  program describes the policies and procedures used with hourly and daily measurements of air quality and
  meteorology to determine how much open biomass burning can be allowed in the Sacramento Valley Air Basin. The
  program ensures that agricultural burning is prohibited on days meteorologically conducive to potentially
  elevated PM10 concentrations. See Title 17 California Code of Regulations, Subchapter 2, Section 80100 et seq.
  The regulations can be viewed at http://www.arb.ca.gov/smp/regs/RevFinRegwTOC.pdf.

    The large contribution of wood smoke on days when the ambient 
concentrations are elevated illustrates the dominance of this source 
category. BCAQMD managed three woodstove replacement programs between 
2005 and 2015. The District calculated that these programs reduced 
PM2.5 emissions by 40.5 tons per year (Plan, Attachment 
C).\33\ These reductions were made federally enforceable by SIP 
approval of Rule 207, which prohibits the installation of non-certified 
wood burning devices in new and existing dwellings. The Plan 
illustrates the correlation in improvement in air quality with the 
decline of carbonaceous aerosols, further emphasizing the role that 
reductions to this category played in attaining the 24-hour 
PM2.5 NAAQS. In addition, the District has adopted or 
strengthened open burning requirements and stationary source rules. 
Together, these rules have provided and will continue to provide 
permanent and enforceable emissions reductions that have contributed to 
the improvement in air quality.
---------------------------------------------------------------------------

    \33\ In addition to the woodstove replacement program, BCAQMD 
has a voluntary wood burning curtailment program. Because reductions 
from this program are not federally enforceable, the District does 
not categorize them as permanent and enforceable (Plan, p. 11).
---------------------------------------------------------------------------

    Source categories for which CARB has primary responsibility for 
reducing emissions in California include most new and existing on- and 
off-road engines and vehicles, motor vehicle fuels, and consumer 
products. In addition, California has unique authority under CAA 
section 209 (subject to a waiver by EPA) to adopt and implement new 
emission standards for many categories of on-road vehicles and engines, 
and new and in-use off-road vehicles and engines.
    California has been a leader in the development of some of the most 
stringent control measures nationwide for on-road and off-road mobile 
sources and the fuels that power them. These standards have reduced new 
car emissions by 99 percent and new truck emissions by 90 percent from 
uncontrolled levels.\34\ In addition, the State has standards for lawn 
and garden

[[Page 21246]]

equipment, recreational vehicles and boats, and other off-road sources 
that require newly manufactured equipment to be 80-98 percent cleaner 
than their uncontrolled counterparts.\35\ Finally, the State has 
adopted many measures that focus on achieving reductions from in-use 
mobile sources that include more stringent inspection and maintenance 
or ``Smog Check'' requirements and truck and bus idling restrictions. 
The State's measures have generally been approved by the EPA into the 
SIP and as such are fully creditable for meeting CAA requirements.\36\ 
While reductions in PM2.5 emissions from residential wood 
burning have been the primary driver for improved air quality in the 
Chico nonattainment area, we note that many of the State measures cited 
above have provided emissions reductions of PM2.5 and its 
precursors since 2006, and thus, some improvement in air quality may 
reasonably be attributed to them.
---------------------------------------------------------------------------

    \34\ See page 37 of the 2007 State Strategy, which was adopted 
by CARB on September 27, 2007 and submitted to the EPA on November 
16, 2007. The 2007 State Strategy and associated documents can be 
viewed at https://www.arb.ca.gov/planning/sip/2007sip/2007sip.htm#state.
    \35\ Id.
    \36\ A list of SIP-approved state measures is available at 
https://www.epa.gov/sips-ca/epa-approved-regulations-california-sip.
---------------------------------------------------------------------------

    Finally, in addition to the local district and State rules 
discussed above, the Chico PM2.5 nonattainment area has also 
benefitted from emission reductions from federal measures. These 
federal measures include the EPA's national emissions standards for 
heavy-duty diesel trucks, certain emissions standards for new 
construction and farm equipment (i.e., Tier 2 and 3 non-road engines 
standards, and Tier 4 diesel non-road engine standards), locomotive 
engine standards and motor vehicle (Tier 3) standards.\37\ These on-
road and off-road vehicle and engine standards, along with State 
measures cited above, have contributed to improved air quality through 
the gradual, continued turnover and replacement of older vehicle models 
with newer models manufactured to meet increasingly stringent emissions 
standards.
---------------------------------------------------------------------------

    \37\ See 66 FR 5001 (January 18, 2001), 63 FR 56968 (October 23, 
1998), 69 FR 38958 (June 29, 2004), 63 FR 18978 (April 16, 1998), 73 
FR 37096 (June 30, 2008), and 79 FR 23414 (April 28, 2014).
---------------------------------------------------------------------------

    Wintertime emissions of the two largest contributors to ambient 
PM2.5 concentrations (i.e., direct PM2.5 and 
NOX in the form of ammonium nitrate) declined significantly 
between 2006 and 2015. In 2006, wintertime PM2.5 emissions 
in the Chico PM2.5 nonattainment area were estimated to be 
approximately 6 tpd. By 2015, total emissions of PM2.5 had 
declined 12 percent to 5.3 tpd. These reductions were largely 
attributable to reductions in emissions from residential fuel 
combustion and mobile sources. Over the same period, NOX 
emissions declined from 22.5 tpd to 13 tpd. This 41 percent reduction 
in NOX emissions came primarily from the mobile source 
category and, to a lesser extent, from stationary sources.\38\
---------------------------------------------------------------------------

    \38\ Plan, Table 3-3 and Attachment D.
---------------------------------------------------------------------------

    The Plan demonstrates that the air quality improvement in the Chico 
PM2.5 nonattainment area between 2006 and 2015 was not the 
result of a local economic downturn or unusual or extreme weather 
patterns. As illustrated by Figure 3-9 of the Plan, the gross domestic 
product of the Chico Metropolitan Statistical Area has increased 
continuously since 2008, while at the same time, ambient levels of 
PM2.5 were improving. The area has continued to attain the 
PM2.5 NAAQS under conditions that were both colder and 
warmer, and both drier and wetter than average, supporting the 
conclusion that attainment of the standard is not the result of unusual 
meteorological conditions (Plan, Figures 3-7 and 3-8).
    We find that the improvement in air quality in the Chico 
PM2.5 nonattainment area is the result of permanent and 
enforceable emissions reductions from a combination of EPA-approved 
local and State control measures and federal control measures. As such, 
we propose to find that the criterion for redesignation set forth at 
CAA section 107(d)(3)(E)(iii) is satisfied.

D. The Area Must Have a Fully Approved Maintenance Plan Under Section 
175A

    Section 175A of the CAA sets forth the required elements of a 
maintenance plan for areas seeking redesignation from nonattainment to 
attainment. Under section 175A, the plan must demonstrate continued 
attainment of the applicable NAAQS for at least 10 years after the 
Administrator approves a redesignation to attainment. Eight years after 
redesignation, the State must submit a revised maintenance plan that 
demonstrates continued attainment for the subsequent ten-year period 
following the initial ten-year maintenance period. To address the 
possibility of future NAAQS violations, the maintenance plan must 
contain such contingency provisions as the EPA deems necessary to 
promptly correct any violation of the NAAQS that occurs after 
redesignation of the area. The Calcagni memo provides further guidance 
on the content of a maintenance plan, explaining that a maintenance 
plan should include an attainment emissions inventory, maintenance 
demonstration, monitoring and verification of continued attainment, and 
a contingency plan. Based on our review and evaluation of the Plan, as 
detailed below, we are proposing to approve the Chico PM2.5 
Plan because we believe that it meets the requirements of CAA section 
175A.
1. Attainment Inventory
    In demonstrating maintenance in accordance with CAA section 175A 
and the Calcagni memo, a state should provide an attainment year 
emissions inventory to identify the level of emissions in the area 
sufficient to attain the NAAQS.\39\ Where a state has made an adequate 
demonstration that air quality has improved as a result of the SIP, the 
attainment inventory will generally be an inventory of actual emissions 
at the time the area attained the standard. The inventory must also be 
comprehensive, including emissions from stationary point sources, area 
sources, and mobile sources.
---------------------------------------------------------------------------

    \39\ A maintenance plan for the 2006 24-hour PM2.5 
NAAQS must include an inventory of emissions of directly emitted 
PM2.5 and its precursors: NOX, SO2, 
VOCs, and NH3. 40 CFR 51.1008. Consistent with CARB's 
usual practice, the Plan provides an inventory of ROG rather than 
VOC. ROG has a slightly broader group of compounds than those 
identified in the EPA's VOC list and is acceptable for use by the 
District.
---------------------------------------------------------------------------

    Section 175A requires a state seeking redesignation to attainment 
to submit a SIP revision to provide for the maintenance of the NAAQS 
for a period of at least ten years following redesignation. This can be 
shown either by demonstrating that future emissions of a pollutant and 
its precursors will not exceed the level of the attainment inventory or 
by conducting modeling that shows the future emissions will not cause a 
violation of the standard. In accordance with EPA guidance, the state 
should project emissions for the 10-year period following 
redesignation, for either purpose (Calcagni memo, p. 9). Projected 
emissions inventories for future years must account for, among other 
things, the ongoing effects of economic growth and adopted emissions 
control requirements, and the inventories are expected to be the best 
available representation of future emissions. The plan submission 
should include documentation explaining how the state calculated the 
emissions data for the base year and projected inventories.
    The specific PM2.5 emissions inventory requirements are 
set forth in the Air Emissions Reporting Rule (40 CFR 51, subpart A) 
and in 40 CFR 51.1008. The EPA has provided additional guidance for 
developing PM2.5 emissions inventories in Emissions 
Inventory Guidance for Implementation of Ozone and

[[Page 21247]]

Particulate Matter National Ambient Air Quality Standards (NAAQS) and 
Regional Haze Regulations (July 2017) (``EPA 2017 EI Guidance'').\40\
---------------------------------------------------------------------------

    \40\ This document is available at https://www.epa.gov/sites/production/files/2017-07/documents/ei_guidance_may_2017_final_rev.pdf.
---------------------------------------------------------------------------

    The emissions inventories are presented in Chapter 4 of the Plan 
and in Attachment D, Emissions Inventory Data. Additional information 
regarding the development of the emissions inventories in the Plan was 
provided by CARB on February 15, 2018.\41\
---------------------------------------------------------------------------

    \41\ Letter with enclosures from Sylvia Vanderspeck, Chief, Air 
Quality Planning Branch, CARB, to GwenYoshimura, Manager, Air 
Quality Analysis Section, EPA Region 9.
---------------------------------------------------------------------------

    The Chico PM2.5 Plan's demonstration that the area has 
attained the standard is based on monitoring data from 2014-2016. The 
District selected 2015 for the base year inventory, which is consistent 
with this time period. Monitoring data for the Chico nonattainment area 
have shown that high PM2.5 concentrations occur primarily 
during the winter months; therefore, the Plan's three emissions 
inventories (the 2015 base year, and the 2025 and 2030 future year 
inventories) are all winter-season inventories. All three inventories 
have been projected from actual 2012 inventories.
a. 2015 Base Year Emissions Inventory
    The 2015 base year inventory provides the foundation for 
demonstrating maintenance for a 10-year period. A summary of the 2015 
winter episode average-season-day emissions inventory for the Chico 
PM2.5 nonattainment area is listed in Table 3 and is shown 
in tons per day (tpd).

 Table 3--Chico PM2.5 Nonattainment Area 2015 Base Year Emissions Inventory (tpd) Winter Episode Average-Season-
                                                       Day
----------------------------------------------------------------------------------------------------------------
                                      PM2.5 a
      Source type/category                              NOX             SO2             ROG             NH3
----------------------------------------------------------------------------------------------------------------
Stationary......................           0.560           1.653           0.096           1.973           0.126
Areawide........................           4.560           1.449           0.145           6.848           3.937
Mobile..........................           0.375          10.121           0.053           4.103           0.165
Benefit of woodstove changeout..          -0.238
                                 -------------------------------------------------------------------------------
    Totals......................           5.257          13.223           0.294          12.924           4.228
----------------------------------------------------------------------------------------------------------------
Source: Plan, Attachment D.
\a\ The EPA's 2017 EI Guidance notes that emissions inventories are required to include direct PM2.5 emissions,
  separately reported as PM2.5 filterable and condensable emissions, as applicable. In order to clarify ``as
  applicable,'' the 2017 EI Guidance provides a list of source types that are expected to include condensable
  particulate matter (2017 EI Guidance, Table 15). Because the Chico area's air quality problem is largely
  driven by wood smoke and because there are currently no data available for condensable PM from wood smoke,
  reporting total direct PM2.5 is acceptable.

    Areawide sources occur over a wide geographic area. Examples of 
these sources are consumer products, paved and unpaved road dust, 
fireplaces, farming operations, and prescribed burning. Emissions for 
these categories are estimated by both CARB and the BCAQMD using 
various models and methodologies.
    The Plan uses the EMFAC (short for EMissions FACtor) model to 
assess emissions from on-road vehicles. Off- road mobile source 
emissions are estimated using various models with the back-up model 
being OFFROAD2007. On-road and off-road models account for the effects 
of various adopted regulations, technology types, and seasonal 
conditions on emissions.
    Emissions from on-road mobile sources, which include passenger 
vehicles, buses, and trucks, were estimated using outputs from CARB's 
EMFAC2014 model.\42\ These emission factors were then applied to 
specific transportation activity data from the 2015 Federal Statewide 
Transportation Improvement Program (FSTIP).
---------------------------------------------------------------------------

    \42\ The EPA approved EMFAC2014 for use in SIP revisions and 
transportation conformity at 80 FR 77337 (December 14, 2015).
---------------------------------------------------------------------------

    Emissions from off-road mobile sources, which include cargo 
handling equipment, pleasure craft, recreational vehicles, and 
locomotives, were grown from the 2012 emissions inventory.
b. Projected Emissions Inventories
    Projected inventories are derived by applying expected growth 
trends for each source category and expected emissions reductions 
resulting from adopted control measures to the base year inventory. In 
this instance, emissions projections for 2025 and 2030 were generated 
by applying growth and control profiles to the 2015 base year 
inventory. Growth profiles for point and areawide sources are derived 
from surrogates (e.g., economic activity, fuel usage, population, 
housing units, etc.) that best reflect the expected growth trends for 
each specific source category. Growth projections were obtained 
primarily from government entities with expertise in developing 
forecasts for specific sectors or econometric models. Control profiles, 
which account for emission reductions resulting from adopted rules and 
regulations, are derived from data provided by the regulatory agencies 
responsible for the affected emission categories. A summary of the 
Chico PM2.5 nonattainment area projected winter episode 
average-season-day emissions inventories for the years 2025 and 2030 is 
provided in Table 4.

         Table 4--2025 and 2030 Projected CA/Butte County PM2.5 Nonattainment Area Winter Episode Average-Season-Day Emissions Inventories (tpd)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       PM2.5[thinsp]                NOX                     SOX                     ROG                     NH3
      Source type/category       -----------------------------------------------------------------------------------------------------------------------
                                     2025        2030        2025        2030        2025        2030        2025        2030        2025        2030
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stationary......................       0.652       0.699       1.621       1.662       0.113       0.122       2.086       2.238       0.141       0.147
Areawide........................       4.597       4.529       1.446       1.450       0.151       0.153       7.374       7.557       4.067       4.113
Mobile..........................       0.255       0.236       4.829       3.809       0.053       0.055       2.379       2.090       0.131       0.130
ERC Bank........................       0.107       0.107       0.164       0.164       0.008       0.008       0.164       0.164
Woodstove Changeout.............      -0.238      -0.238
                                 -----------------------------------------------------------------------------------------------------------------------

[[Page 21248]]

 
    Total.......................       5.373       5.333       8.060       7.085       0.325       0.338      12.003      12.049       4.338       4.390
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: Plan, Attachment F.

    The EPA has reviewed the results, procedures, and methodologies for 
the Chico PM2.5 nonattainment area emissions inventories. We 
have determined that the 2015 base year inventory and the 2025 and 2030 
projected inventories are based on the most current and accurate 
information available to CARB and BCAQMD at the time the Plan and its 
inventories were being developed. The selection of 2015 for the base 
year inventory is also appropriate because it is within the 2014-2016 
period during which the area attained the standard. The inventories 
comprehensively address all source categories in the Chico 
PM2.5 nonattainment area and appropriate procedures were 
used to develop the inventories. In addition, CARB and BCAQMD developed 
the 2025 and the 2030 projected inventories based on the 2015 base year 
inventory and accounted for projected growth and reductions in 
emissions. We are therefore proposing to approve the 2015 base year 
emissions inventory and the 2025 and 2030 projected year inventories 
for the Chico PM2.5 Nonattainment Area as meeting the 
requirements of CAA section 175A of the CAA.
2. PM2.5 Maintenance Demonstration
a. PM2.5 Modeling Requirements
    As noted previously, the requirement that maintenance plans must 
demonstrate attainment of the NAAQS for at least 10 years after the 
redesignation can be met in one of two ways: By showing that future 
emissions will not exceed the level of the attainment inventory or by 
using modeling to show that the future emissions will not cause a 
violation of the NAAQS. Modeling predicts future ambient concentrations 
for comparison to the NAAQS, making use of information such as ambient 
concentrations, meteorology, and current and projected emission 
inventories, including the effect of control measures in the plan.
    The main EPA source of guidance on modeling is the Guideline on Air 
Quality Models (``Guideline'').\43\ Section 4.2.3.5 of the Guideline 
notes that PM2.5 is a mixture of components: Primary 
(directly emitted) and secondary (chemically formed in the atmosphere 
from precursor emissions). In its discussion of modeling for 
PM2.5 New Source Review,\44\ the Guideline refers to the 
general dispersion modeling requirements located in sections 4.2.1 and 
4.2.2 for primary PM2.5, and in Section 5.4 for secondary 
PM2.5. The Guideline's discussion of PM2.5 SIP 
attainment demonstrations \45\ references Section 5.4 and associated 
SIP modeling guidance that mainly pertain to photochemical models to 
handle secondarily formed PM2.5.\46\ These modeling 
recommendations address situations that involve a few major point 
sources emitting primary PM2.5 (Section 4.2) and situations 
with a few large sources or many sources of secondary PM2.5 
(Section 5.4).
---------------------------------------------------------------------------

    \43\ 40 CFR 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.
    \44\ See subsection (b) of the Guideline.
    \45\ See subsection (c) of the Guideline.
    \46\ Modeling Guidance for Demonstrating Attainment of Air 
Quality Goals for Ozone, PM2.5, and Regional Haze, 
December 2014 Draft, EPA OAQPS; available at https://www.epa.gov/scram/state-implementation-plan-sip-attainment-demonstration-guidance.
---------------------------------------------------------------------------

    For areas such as the Chico area that are dominated by primary 
PM10 or PM2.5 emitted by many small dispersed 
sources such as fugitive dust or residential wood burning, the rollback 
model has historically been used. In simple rollback, the monitored 
ambient concentration (net of 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 of this technique is 
``proportional rollback,'' in which rollback is applied to each 
emission source category individually, then summed in proportion to 
each source category's ambient contribution. 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 Positive Matrix 
Factorization model, which finds the source category contributions that 
are the best statistical fit to the measured chemical species 
concentrations, given measured or estimated source species profiles. 
More simply, in ``speciated rollback,'' rollback is applied to each 
species or species group separately, then the individual components are 
summed. Within each species, a source category's contribution is 
proportional to its share of the corresponding species emission 
inventory.
    For any of the rollback approaches, assumptions must be made about 
secondary PM2.5 such as ammonium nitrate and ammonium 
sulfate, since they do not correspond directly to emission inventory 
pollutants and because chemical interactions between precursors are not 
represented in rollback's linear scaling. The secondary components 
could conservatively be assumed to be part of the unchanging background 
concentration, or they might be assumed to scale in proportion to their 
corresponding precursor emissions, e.g., ammonium nitrate in proportion 
to NOX emissions. While these approaches are relatively 
imprecise in comparison to photochemical grid models, if secondary 
particulates are a small portion of ambient PM2.5 in a 
particular area, the uncertainty in the model results will also be 
small.
b. Modeling in the Plan
    Because some precursors increase slightly over the 10-year 
maintenance period, the Chico PM2.5 Plan uses modeling to 
demonstrate ongoing maintenance of the standard. The Plan's maintenance 
demonstration is based on speciated rollback modeling, with 
concentrations for PM2.5 species scaled according to changes 
in corresponding species emission inventory categories.\47\ The Plan 
shows the chemical composition of PM2.5 in tables and pie 
charts, showing concentrations and percentages for five species groups

[[Page 21249]]

(ammonium nitrate, ammonium sulfate, carbonaceous aerosols, geological, 
and elements) for the 10 percent of days with the highest monitored 24-
hour PM2.5 concentrations.48 49 The species 
percentages were derived from averages of speciated Chico 
PM2.5 monitoring data during 2014-2016, which matches the 
three years used to derive the 2016 design value.
---------------------------------------------------------------------------

    \47\ Plan, Section 4.a. The Plan uses the terms ``rollback'' and 
``proportional rollback.'' Here and elsewhere, the terms 
``proportional rollback'' and ``speciated rollback'' are used 
loosely. These and other rollback variants all assume concentrations 
are proportional to emissions but vary in how they map emissions to 
concentrations.
    \48\ Plan, Figure 4.1, p. 20; Attachment E, table in Figure 4.1, 
p.1; and Attachment F, Figure 1, p.1.
    \49\ The ``geological'' group comprises those species typically 
found in soil (such as silicon). The ``elements'' group consists of 
all species not in other groups.
---------------------------------------------------------------------------

    The speciation data show that days with high PM2.5 
concentrations in the Chico nonattainment area are dominated by 
carbonaceous aerosol, which accounted for 76 percent of the total. The 
District's attribution of this principally to organic matter from wood 
burning is corroborated by the close agreement between the 
concentration trends of carbonaceous aerosol and of potassium, a marker 
element for wood burning.\50\ Wood burning emissions are 85 percent of 
the total direct PM2.5 emissions. The Plan states that the 
highest concentrations occur under stagnant conditions in winter, 
typically in the evening and early morning hours. The diurnal pattern 
of concentrations is consistent with this and with increased 
residential wood burning in the evening hours.\51\ The geological and 
elements species groups each contributed 2 percent to high 
PM2.5 levels.
---------------------------------------------------------------------------

    \50\ Plan, p.13.
    \51\ Plan, p.13, including Figure 3-4, and p.15.
---------------------------------------------------------------------------

    Secondarily formed PM2.5 in the form of ammonium nitrate 
and ammonium sulfate respectively comprised 16 percent and 4 percent of 
PM2.5 concentrations. These species are formed from 
precursor emissions of NOX, SOX, and ammonia.
    The instruments and techniques used to measure speciated 
PM2.5 do not measure all species, so some adjustments are 
needed for the total speciated to match the full PM2.5 mass, 
as measured with the FRM for PM2.5.\52\ For the rollback, 
the Plan mainly used the adjustments followed in the IMPROVE 
(Interagency Monitoring of Protected Visual Environments) network for 
each species group.\53\ The exception was carbonaceous aerosol or 
organic matter, which was estimated by mass balance, that is, the total 
PM2.5 mass less the mass of all the other species.\54\ The 
concentrations were then scaled so the total matched the 2016 design 
value of 26 [mu]g/m\3\. This procedure yielded species group 
concentrations representative of the design value as the starting point 
for speciated rollback.
---------------------------------------------------------------------------

    \52\ For example, carbon and various ions are measured but the 
oxygen originally chemically bound to them is not. Also, the 
sampling schedules and averaging procedures differ between the FRM 
and speciated measurements.
    \53\ Plan, Table 4.1, p. 21; IMPROVE (Interagency Monitoring of 
Protected Visual Environments) is a monitoring program managed by 
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. http://vista.cira.colostate.edu/Improve/reconstructed-fine-mass/.
    \54\ Due to large uncertainties in carbonaceous mass 
measurements, mass balance is also used in the EPA-recommended 
SANDWICH approach (Sulfate, Adjusted Nitrate, Derived Water, 
Inferred Carbonaceous material balance approach), described in EPA 
draft Modeling Guidance for Demonstrating Attainment, section 4.4.4.
---------------------------------------------------------------------------

    Ambient concentrations of PM2.5 have both a local 
component and a background component. The local component is generated 
by emissions from sources located with the nonattainment area. The 
background component is not attributed to local sources; it consists of 
PM2.5 (and its precursors) that is transported into the area 
by air flowing in from upwind. Since only the local component can be 
affected by changes in the area's emissions, rollback scales 
concentrations with background concentrations subtracted out (i.e., net 
of background). Speciated concentrations from Bliss State Park next to 
Lake Tahoe were chosen in the Plan as background concentrations that 
would occur in the airshed in the absence of local anthropogenic 
emissions. These concentrations were subtracted from Chico 
concentrations for the corresponding species groups, resulting in local 
concentrations to be scaled according to emissions changes (``available 
for rolling'').
    To perform the rollback analysis, the species groups must be 
matched to emission inventory categories that affect those species' 
concentrations. Since the highest PM2.5 concentrations occur 
during winter months when residential wood burning is greatest, a 
winter season inventory was used. Five groups of ambient species were 
mapped to emission inventory categories. The geological (or fugitive 
dust) component was assumed to be proportional to fugitive dust 
emissions, including farming operations, construction, road dust, and 
fugitive wind-blown dust. The sum of the carbonaceous aerosols 
component and the elements component was assumed to be proportional to 
the total emissions from all other directly-emitted primary 
PM2.5 emissions categories. The ammonium nitrate component 
was assumed to scale with total NOX emissions, and ammonium 
sulfate with total SOX emissions.
    The maintenance demonstration base year was 2015, the center of the 
2014--2016 period upon which the 2016 design value is based. The 
predicted emission changes between base year 2015 and future year 2030 
were used to scale the species components of the 2016 design value. A 
bank of ERCs is maintained by the District for equipment shutdowns and 
voluntary controls at permitted sources; these are emissions that are 
not occurring presently, but potentially could occur in the future if 
the credits were used by new sources to offset their emissions as part 
of the NSR permitting process. The ERCs were added to 2030 emissions 
for each pollutant but not to 2015 emissions. ERCs are not maintained 
for direct PM2.5 emissions, so PM10 ERCs were 
used. Both of these choices make the 2030 emission estimate 
conservatively high. The District had a successful wood burning device 
change out program. As previously noted, between 2005-2015, 739 wood 
stoves were replaced with cleaner-burning devices. The resulting 
emission reductions were included in both the base and future year 
emissions, reflecting baseline emission inventory estimates through the 
maintenance period. No credit was taken for later stove change outs or 
for the District's Check Before You Light voluntary curtailment 
program, both of which are expected to yield additional emission 
reductions through 2030.
    Fugitive dust emissions for the geological component are projected 
to increase by 14 percent, mainly due to increased paved road dust, 
residential building, and road construction,\55\ but this component 
accounts for only 2.3 percent of PM2.5 concentrations. The 
sum of all other directly-emitted primary PM2.5 emissions 
categories is the largest single component of concentrations; it is 
expected to decline by only 0.8 percent by 2030. NOX 
emissions, used to scale ammonium nitrate, are expected to fall by some 
46 percent; this is mainly due to declining mobile source emissions, 
which are 80 percent of the NOX inventory. SOX 
emissions, used to scale ammonium sulfate, are projected to increase by 
about 15 percent, mainly due to an increase in stationary source fuel 
combustion from electricity generation.

[[Page 21250]]

As noted above, ammonium sulfate is only 4 percent of PM2.5 
concentrations.
---------------------------------------------------------------------------

    \55\ California Air Resources Board, CEPAM--California Emissions 
Projection Analysis Model, https://www.arb.ca.gov/app/emsinv/fcemssumcat/fcemssumcat2016.php, retrieved March 4th, 2018.
---------------------------------------------------------------------------

    The last steps in rollback are summing the emissions-scaled 
concentrations for the species groups and then adding the background 
concentrations back in. Considered individually, projected reductions 
in NOX emissions will yield a 1.83 [mu]g/m\3\ reduction to 
the design value. The decrease in non-dust PM2.5 accounts 
for an additional reduction of 0.16 [mu]g/m\3\. Projected increases in 
ammonium sulfate and fugitive dust emissions are predicted to 
contribute a 0.18 [mu]g/m\3\ increase. The final result of the 
maintenance demonstration modeling was a decrease of 1.8 [mu]g/m\3\ 
from the 2016 level, resulting in a 2030 design value of 24.2 [mu]g/
m\3\, well below the 35 [mu]g/m\3\ NAAQS.
c. EPA Evaluation of the Maintenance Demonstration
    The choice of an appropriate model for the District's maintenance 
demonstration was informed by particular circumstances of the Chico 
nonattainment area, most notably the dominance of primary 
PM2.5 in ambient concentrations, the dispersed nature of the 
many sources responsible for it, and the relatively small fraction 
composed of secondary particulate matter. As discussed in the Plan, 
organic carbon from wood burning emissions is 76 percent of 
PM2.5 on the highest concentration days, and the highest 
concentrations occur under stagnant winter conditions. The Plan 
examined meteorology, PM2.5 emissions, ambient 
PM2.5 data, including speciated PM2.5 monitoring 
data over the past decade, and how the diurnal PM2.5 pattern 
changed over time, to make the case that residential wood burning is 
the dominant contributor to the air quality problem in the Chico 
nonattainment area. The key assumption in rollback, i.e., that 
concentrations are proportional to emissions, is true for these primary 
PM2.5 emissions. Current EPA guidance does not mention 
rollback; however, it also does not fully cover the Chico situation of 
dominant primary PM2.5 from many dispersed sources. Instead, 
it mainly discusses photochemical grid models and dispersion models 
that are more appropriate for other situations. It would be 
unreasonable to require the use of a photochemical grid model just to 
handle the minor secondary particulate component in Chico, given the 
time and resources involved, the established nature of the main 
PM2.5 problem in the area (wood smoke), and the monitored 
concentrations that are well below the NAAQS. Nor would a dispersion 
model be appropriate, given the large number and dispersed distribution 
of sources, especially since the highest concentrations occur under 
stagnant conditions, which dispersion models do not handle well. Given 
that the key air quality problem 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 finds that the use of rollback meets available guidance and is 
appropriate for the Chico maintenance demonstration.
    The EPA also finds that the Plan correctly implemented the 
calculations needed for rollback, used an appropriate mapping of 
ambient PM2.5 components to emission inventory categories, 
and incorporated a degree of conservatism.
    The main drawback to rollback for Chico PM2.5 is its 
inherently simple handling of secondary particulates, which, though a 
minor ambient component in this instance, are not negligible. The 
assumption that ammonium nitrate and ammonium sulfate scale linearly 
with NOX and SOX emissions, respectively, is 
simple and is consistent with rollback, but may not be fully correct. 
Even if they do scale in a reasonably linear manner, they might not 
respond on a one-to-one basis, e.g. a 10 percent NOX 
emission reduction might yield only a 7 percent ambient ammonium 
nitrate response. As noted above, the decline in NOX 
emissions accounts for much of the predicted 1.8 [mu]g/m\3\ decrease in 
PM2.5 concentrations between 2015 and 2030. However, ambient 
concentrations in Chico are far enough below the level of the NAAQS 
that, even using highly conservative assumptions for secondary 
particulates, maintenance of the NAAQS is not jeopardized. If ammonium 
nitrate does not respond at all to the 46 percent NOX 
reduction, but instead remains at its 2016 design value level, and 
ammonium sulfate does conservatively respond on a one-to-one basis to 
the 15 percent SOX emission increase of 0.036 tpd, the 
rollback model predicts a 2030 design value of 26.03 [mu]g/m\3\ 
(starting from 26.00 [mu]g/m\3\ in 2015), still well below the NAAQS. 
Despite the greater ammonium nitrate in the highly conservative 
assumption described above as compared to the maintenance demonstration 
in the Plan, the increase in predicted 2030 design value from 24.2 to 
26.0 is relatively small because ammonium nitrate is only 16 percent of 
PM2.5 concentrations. Therefore, even if the reasonable and 
straightforward assumptions in the rollback modeling were not fully 
correct, the maintenance demonstration would still be adequate given 
how clean the air is in Chico. Consequently, we are proposing to 
determine that the Chico PM2.5 Plan adequately demonstrates 
maintenance of the 2006 24-hour PM2.5 NAAQS through 2030.
3. Verification of Continued Attainment
    Under CAA section 175A, a maintenance plan must demonstrate 
continued attainment of the applicable NAAQS for at least ten years 
after EPA approves a redesignation to attainment. Eight years after 
redesignation, the State must submit a revised maintenance plan that 
demonstrates continued attainment for the subsequent ten-year period 
following the initial ten-year maintenance period. To address the 
possibility of future NAAQS violations, the maintenance plan must 
contain such contingency provisions that EPA deems necessary to 
promptly correct any violation of the NAAQS that occurs after 
redesignation of the area. Based on our review and evaluation of the 
plan, as detailed below, we are proposing to approve the Chico 
PM2.5 Plan because we believe that it meets the CAA section 
175A requirements for verification of continued attainment.
    In demonstrating maintenance, continued attainment of the NAAQS can 
be verified through operation of an appropriate air quality monitoring 
network. The Calcagni memo (p. 11) states that the maintenance plan 
should contain provisions for continued operation of air quality 
monitors that will provide such verification. As discussed in section 
V.A. of this document, PM2.5 is currently monitored by CARB 
within the Chico PM2.5 nonattainment area. In Section 4.c. 
of the Chico PM2.5 Plan, the District indicates that CARB 
intends to maintain an appropriate PM2.5 monitoring network 
and review data through the maintenance period and will collaborate 
with the EPA and stakeholders on any potential changes to the network. 
The District commits to using ambient data to track the progress of the 
maintenance plan. We find that the Chico PM2.5 Plan contains 
adequate provisions for continued operation of air quality monitors 
that will provide verification of continued attainment.
    In addition, CARB and BCAQMD must inventory emissions sources and 
report to EPA on a periodic basis under 40 CFR part 51, subpart A 
(``Air Emissions Reporting Requirements''). These emissions inventory 
updates will provide a second way to evaluate emissions trends in the 
area and thereby verify continued attainment of the NAAQS. The District 
commits to monitoring the emissions inventory for unexpected changes 
that could affect

[[Page 21251]]

maintenance of the PM2.5 NAAQS. We are proposing to 
determine that these methods are sufficient for verifying continued 
attainment.
4. Contingency Provisions
    Section 175A(d) of the CAA requires that maintenance plans include 
contingency provisions, as EPA deems necessary, to promptly correct any 
violations of the NAAQS that occur after redesignation of the area. 
Such provisions must include a requirement that the state will 
implement all measures with respect to the control of the air pollutant 
concerned that were contained in the SIP for the area before 
redesignation of the area as an attainment area. These contingency 
provisions are distinguished from those generally required for 
nonattainment areas under CAA section 172(c)(9) in that they are not 
required to be fully-adopted measures that will take effect without 
further action by the state in order for the maintenance plan to be 
approved. However, the contingency plan is considered to be an 
enforceable part of the SIP and should ensure that the contingency 
measures are adopted expeditiously once they are triggered by a 
specified event. The maintenance plan should clearly identify the 
measures to be adopted, a schedule and procedure for adoption and 
implementation, and a specific timeline for action by the State. As a 
necessary part of the plan, the State should also identify the specific 
indicators or triggers that will be used to determine when the 
contingency measures need to be implemented.
    The District has adopted a contingency plan to address possible 
future PM2.5 air quality problems. The contingency 
provisions in the Chico PM2.5 Plan are contained in Section 
4.e. of the Plan. BCAQMD identifies the contingency plan trigger as a 
violation of the 2006 24-hour PM2.5 NAAQS. If that should 
occur, BCAQMD commits to the following steps:
    (1) Within 60 days of the trigger, BCAQMD will commence an analysis 
to determine if the violation was caused by an exceptional event or 
instrument malfunction, and evaluate meteorological conditions and 
emissions inventory.
    (2) BCAQMD will consult with interested parties, community 
organizations, and industry to identify and implement, within nine 
months after the trigger, voluntary and incentive measures to reduce 
directly emitted PM2.5 or precursors.
    (3) If voluntary and incentive based measures do not bring the area 
back into attainment 12 months after the contingency plan is triggered, 
the BCAQMD will propose for adoption and implementation any necessary 
new rules to the BCAQMD Governing Board within 24 months of the trigger 
date. The measures that BCAQMD would consider and analyze include but 
are not limited to those listed in Table 4-6 in the Plan.
    Upon our review of the Plan, as summarized above, we find that the 
contingency provisions of the Chico PM2.5 Plan clearly 
identify specific contingency measures, contain tracking and triggering 
mechanisms to determine when contingency measures are needed, contain a 
description of the process of recommending and implementing contingency 
measures, and contain specific timelines for action. Thus, we conclude 
that the contingency provisions of the Chico PM2.5 Plan are 
adequate to ensure prompt correction of a violation and that they 
comply with section 175A(d) of the CAA. For the reasons set forth 
above, EPA is proposing to find that the Chico PM2.5 Plan is 
consistent with the maintenance plan contingency provision requirements 
of the CAA and EPA guidance.
5. Transportation and 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 (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, the EPA, FHWA, and FTA to 
demonstrate that an area's regional transportation plans and 
transportation improvement programs conform to the applicable SIP. 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.
    Under the CAA, states are required to submit, at various times, 
control strategy SIPs and maintenance plans in nonattainment areas. 
These control strategy SIPs and maintenance plans typically set budgets 
for criteria pollutants and/or their precursors to address pollution 
from cars and trucks. Budgets are generally established for specific 
years and specific pollutants or precursors and must reflect the motor 
vehicle control measures contained in the RFP plan and the attainment 
or maintenance demonstration. Per 40 CFR part 93, budgets must be 
established for the last year of the maintenance plan for direct 
PM2.5 and PM2.5 precursors subject to 
transportation conformity analyses.\56\ 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)).
---------------------------------------------------------------------------

    \56\ Section 93.102(b)(2)(v) of the conformity rule identifies 
VOC, SOX, and ammonia as PM2.5 precursor 
pollutants that that are presumed insignificant unless the SIP makes 
a finding that the precursor is significant. In contrast, 
NOX is presumed to be a significant contributor, unless 
the state and the EPA determine that transportation-related 
emissions of NOX are not a significant contributor 
(93.102(b)(2)(iv)).
---------------------------------------------------------------------------

    The Transportation Conformity Rule allows areas to forgo 
establishment of a budget where it is demonstrated that the regional 
motor vehicle emissions for a particular pollutant or precursor are an 
insignificant contributor to the air quality problem in an area. 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 SIP would have to 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 a 
number of factors, including (1) the current state of air quality as 
determined by monitoring data for that NAAQS; (2) the absence of SIP 
motor vehicle control measures; (3) historical trends and future 
projections of the growth of motor vehicle emissions; and (4) the 
percentage of motor vehicle emissions in context of the total SIP 
inventory. The EPA's rationale for providing for insignificance 
determinations is described in the July 1, 2004, revision to the 
transportation conformity rule (69 FR 40004). Specifically, the 
rationale is explained on p. 40061 under the subsection entitled 
``XXIII. B. Areas With Insignificant Motor Vehicle Emissions.''
    As part of the Chico PM2.5 Plan, the BCAQMD requested 
that the EPA find

[[Page 21252]]

that on-road emissions of direct PM2.5 and NOX 
are insignificant for conformity purposes, and therefore the District 
did not submit any budgets. The EPA is proposing to approve BCAQMD's 
insignificance demonstration for the on-road motor vehicle contribution 
of NOX and PM2.5 emissions to the overall 
PM2.5 emissions in the maintenance plan.
    The information provided by BCAQMD to the EPA as part of the SIP 
revision addresses each of the factors listed in 40 CFR 93.109(f), and 
is summarized below. Design values for the area are trending downward 
from 69 [mu]g/m\3\ in 2008, to 33 [mu]g/m\3\ in 2012, to 28 [mu]g/m\3\ 
in 2014, and to 26 [mu]g/m\3\ in 2016. NOX emissions from 
on-road mobile sources are predicted to decrease by 70 percent from 
2015-2030 and PM2.5 emissions are predicted to decrease by 
24 percent during the same time frame. In addition, the 2030 on-road 
PM2.5 emissions will account for less than three percent of 
the total direct non-dust PM2.5 emissions from all sources 
in the Chico nonattainment area. Because on-road NOX 
emissions account for a larger percentage (28 percent) of the total 
emissions, the plan includes a sensitivity analysis that demonstrates 
that the NOX emissions from on-road mobile sources would 
need to increase by 600 percent from 2015 levels before the area would 
violate the 2006 24-hour PM2.5 standard in the Chico 
nonattainment area. Our detailed evaluation and conclusions are as 
follows.
(1) The Chico Area Is Attaining the PM2.5 NAAQS
    The EPA determined that the Chico nonattainment area attained the 
2006 24-hour PM2.5 standard on September 10, 2013 (78 FR 
55225). This finding was based on ambient air quality data for the 
period of 2010 to 2012. More recently on May 10, 2017, the EPA 
determined that the Chico nonattainment area met the 2006 24-hour 
PM2.5 standard by its attainment date of December 31, 2015 
(82 FR 21711). This finding was based on air quality data for the 
period from 2013 to 2015. Since that period the air quality has 
remained well below the 2006 24-hour PM2.5 standard. Table 5 
summarizes the air quality design values for the 2014-2016 period.

  Table 5--Summary of Design Values for the 24-hour PM2.5 NAAQS in the
                  Chico Nonattainment Area ([mu]g/m\3\)
------------------------------------------------------------------------
          2014                     2015                    2016
------------------------------------------------------------------------
            28                       29                       26
------------------------------------------------------------------------
Source: Plan, Table 3-1.

(2) Motor Vehicle Control Measures Were Not Adopted for the Purpose of 
Bringing the Area Into Attainment
    As discussed in more detail in sections V.C. and V.D.2. of this 
document, the control measures relied upon in the Chico 
PM2.5 plan to bring the area into attainment are primarily 
associated with residential wood burning. While there are statewide 
motor vehicle emission controls (smog check and vehicle standards) that 
apply throughout California, those measures were not adopted 
specifically to bring this area into attainment.
(3) Historical Trends and Future Projections Indicate Motor Vehicle 
PM2.5 Emissions Are Decreasing
    Trends and projections in emissions of PM2.5 and 
precursors are presented in several sections of the Chico 
PM2.5 plan. Table 3.3 of the Chico PM2.5 plan 
shows reductions of total NOX, PM2.5 and 
SOX emissions from 2006-2015. During this period, total 
wintertime emissions of PM2.5 decreased 11.8 percent while 
NOX emissions decreased by 41.3 percent and SOX 
emissions decreased by 45.3 percent. These trends are projected to 
continue as shown in Table 6, below. Emissions of NOX, for 
the period from the attainment year of 2015 to the maintenance year of 
2030, are estimated to decrease 47 percent and total non-dust 
PM2.5 emissions are projected to decrease by 1 percent. On-
road motor vehicle emissions decrease even further. Emissions of on-
road NOX and PM2.5 are projected to decrease 70 
percent and 24 percent, respectively, from 2015 to 2030. These 
reductions are projected to occur even while vehicle miles travelled 
are predicted to increase 40 percent from 2014-2040. These reductions 
are due to federal and California motor vehicle regulations such as 
heavy-duty highway vehicle standards and fuel standards.

                                        Table 6--NOX and PM2.5 Emissions
                                              [tons per winter day]
----------------------------------------------------------------------------------------------------------------
                                                                                                  Percent change
                                                       2015            2025            2030          from 2015
----------------------------------------------------------------------------------------------------------------
Total NOX.......................................            13.2             7.9             6.9             -47
    On-Road NOX.................................             6.3             2.4             1.9             -70
Total Non-Dust PM2.5............................            4.47             4.5            4.43              -1
    Direct PM from On-Road Motor Vehicles                   0.17            0.13            0.13              -4
     (exhaust, tire wear, and brake wear).......
----------------------------------------------------------------------------------------------------------------
Source: Plan, Tables 4-5 and 4-6.

(4) The Percentage of Motor Vehicle Emissions in the Context of the 
Total SIP Inventory Decreases Over Time
    As shown in Table 7, the percentage contribution of motor vehicle 
emissions to total emissions for both NOX and 
PM2.5 generally decreases over time. In the 2015 attainment 
year, emissions of NOX from on-road motor vehicles 
contribute 48 percent of the total Chico NOX emission 
inventory. By 2030, the contribution of on-road NOX is 
reduced to 28 percent. The overall contribution of on-road motor 
vehicles to the PM2.5 inventory is very small. In the 2015 
attainment year, emissions of PM2.5 from on-road motor 
vehicles contributed only 3.9 percent of the Chico total non-dust 
emission inventory. By 2030, the percentage declines to 3.0 percent.

                            Table 7--Percent Contribution of NOX and PM2.5 Emissions
----------------------------------------------------------------------------------------------------------------
                                                                       2015            2025            2030
----------------------------------------------------------------------------------------------------------------
Percent On-Road Contribution to Total NOX Emission..............           47.7%           30.4%           27.5%

[[Page 21253]]

 
Percent On-Road Contribution to Non-Dust Total PM2.5 Emissions..            3.9%            2.8%            3.0%
----------------------------------------------------------------------------------------------------------------
Source: Plan, Tables 4.5 and 4.6.

    Although both the total NOX inventory and the percentage 
contribution to the NOX inventory from mobile sources 
decline over time, on-road NOX will account for over 27 
percent of the total NOX inventory in 2030. As verification 
that this would not affect maintenance of the standard, the Plan 
includes a modified roll-back analysis that was conducted to determine 
how much on-road NOX emissions would need to increase before 
the Chico PM2.5 nonattainment area would experience 
violations of the 2006 PM2.5 NAAQS (Attachment F). The roll-
back analysis demonstrates that on-road NOX emissions would 
have to increase by approximately 600 percent from 2015 NOX 
emission levels before violations of the PM2.5 NAAQS would 
occur in 2030. With NOX emissions for the area trending 
downward, it is highly unlikely that on-road NOX emissions 
could increase 600 percent by 2030.
    After evaluating the information provided by BCAQMD and weighing 
the factors for the insignificance determination outlined in 40 CFR 
93.109(f), the EPA is proposing to approve the determination that the 
PM2.5 and NOX contributions from motor vehicle 
emissions to the PM2.5 pollution for the Chico nonattainment 
area are insignificant.
    If the EPA's insignificance finding is finalized, the Butte County 
Association of Governments would no longer be required to perform 
regional emissions analyses for either directly emitted 
PM2.5 or NOX as part of future PM2.5 
conformity determinations for the 2006 24-hour PM2.5 NAAQS 
for the Chico area (the subject of today's proposed action). The EPA's 
insignificance finding should, however, be noted in the transportation 
conformity documentation that is prepared for this area. Areas with 
insignificant regional motor vehicle emissions for a pollutant or 
precursor are still required to make a conformity determination that 
satisfies other relevant conformity requirements such as financial 
constraint, timely implementation of transportation control measures 
and project level conformity.

VI. Proposed Action and Request for Public Comment

    Pursuant to sections 107(d)(3)(E) and 175A of the CAA and based on 
our review of the Chico PM2.5 Plan submitted by the State, 
air quality monitoring data, and other relevant materials, the EPA is 
proposing to find that the State has addressed all the necessary 
requirements for redesignation of the Chico nonattainment area to 
attainment of the 24-hour PM2.5 NAAQS.
    First, under CAA section 107(d)(3)(D), we are proposing to approve 
CARB's request, which accompanied the submittal of the Chico 
PM2.5 Plan, to redesignate the Chico PM2.5 
nonattainment area to attainment for the 2006 24-hour PM2.5 
NAAQS. We are doing so based on our conclusion that the area has met 
the five criteria for redesignation under CAA section 107(d)(3)(E). Our 
conclusion is based on our proposed determination that the area has 
attained the 2006 24-hour PM2.5 NAAQS; that relevant 
portions of the California SIP are fully approved; that the improvement 
in air quality is due to permanent and enforceable reductions in 
emissions; that California has met all requirements applicable to the 
Chico PM2.5 nonattainment area with respect to section 110 
and part D of the CAA; and is based on our proposed approval of the 
Chico PM2.5 Plan as part of this action.
    Second, in connection with the Chico PM2.5 Plan showing 
maintenance through 2030, the EPA is proposing to find that the 
maintenance demonstration, which documents how the area will continue 
to attain the 2006 24-hour PM2.5 NAAQS for 10 years beyond 
redesignation (i.e., through 2030) and the actions that BCAQMD will 
take if a future monitored violation triggers the contingency plan, 
meets all applicable requirements for maintenance plans and related 
contingency provisions in section 175A of the CAA. The EPA is also 
proposing to approve the determination that the PM2.5 and 
NOX contributions from motor vehicle emissions to the 
PM2.5 pollution for the Chico nonattainment area are 
insignificant.
    We are soliciting comments on these proposed actions. We will 
accept comments from the public on this proposal for 30 days following 
publication of this proposal in the Federal Register and will consider 
these comments before taking final action.

VII. Statutory and Executive Order Reviews

    Under the CAA, the Administrator is required to approve a SIP 
submission that complies with the provisions of the Act and applicable 
federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in 
reviewing SIP submissions, the EPA's role is to approve state choices, 
provided that they meet the criteria of the CAA. Accordingly, this 
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

[[Page 21254]]

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). We have offered to consult with the Enterprise Rancheria of 
Maidu Indians of California, the Berry Creek Rancheria of Maidu Indians 
of California, the Mooretown Rancheria of Maidu Indians of California, 
and the Mechoopda Indian Tribe of Chico Rancheria, which have lands 
within the Chico PM2.5 nonattainment area.

List of Subjects in 40 CFR Part 52

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

List of Subjects in 40 CFR Part 81

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

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

    Dated: May 1, 2018.
Alexis Strauss,
Acting Regional Administrator, Region IX.
[FR Doc. 2018-09792 Filed 5-8-18; 8:45 am]
 BILLING CODE 6560-50-P