[Federal Register Volume 84, Number 29 (Tuesday, February 12, 2019)]
[Proposed Rules]
[Pages 3389-3395]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-01908]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2018-0723; FRL-9988-63--Region 8]


Approval and Promulgation of Air Quality Implementation Plans; 
Wyoming; Interstate Transport for the 2008 Ozone National Ambient Air 
Quality Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing action 
on a submission from the State of Wyoming that is intended to 
demonstrate that the Wyoming State Implementation Plan (SIP) meets 
certain interstate transport requirements of the Clean Air Act (Act or 
CAA) for the 2008 ozone National Ambient Air Quality Standards (NAAQS). 
This submission addresses interstate transport ``prong 2,'' which 
requires each state's SIP to prohibit emissions which will interfere 
with maintenance of the NAAQS in other states. The EPA is proposing to 
approve this submittal as meeting the requirement that Wyoming's SIP 
contain adequate provisions to prohibit emissions in amounts which will 
interfere with maintenance of the 2008 ozone NAAQS in any other state.

DATES: Written comments must be received on or before March 14, 2019.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2018-0723, to the Federal Rulemaking Portal: https://www.regulations.gov. Follow the online instructions for submitting 
comments. Once submitted, comments cannot be edited or removed from 
www.regulations.gov. The EPA may publish any comment received to its 
public docket. Do not submit electronically any information you 
consider to be Confidential Business Information (CBI) or other 
information whose disclosure is restricted by statute. Multimedia 
submissions (audio, video, etc.) must be accompanied by a written 
comment. The written comment is considered the official comment and 
should include discussion of all points you wish to make. The EPA will 
generally not consider comments or comment contents located outside of 
the primary submission (i.e., on the web, cloud, or other file sharing 
system). For additional submission methods, the full EPA public comment 
policy, information about CBI or multimedia submissions, and general 
guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
    Docket: All documents in the docket are listed in the 
www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in www.regulations.gov or in hard copy at the Air Program, 
Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop Street, 
Denver, Colorado 80202-1129. The EPA requests that if at all possible, 
you contact the individual listed in the FOR FURTHER INFORMATION 
CONTACT section to view the hard copy of the docket. You may view the 
hard copy of the docket Monday through Friday, 8:00 a.m. to 4:00 p.m., 
excluding federal holidays.

FOR FURTHER INFORMATION CONTACT: Adam Clark, Air Program, EPA, Region 
8, Mailcode 8P-AR, 1595 Wynkoop Street, Denver, Colorado 80202-1129, 
(303) 312-7104, [email protected].

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

I. Background

    On March 12, 2008, the EPA revised the levels of the primary and 
secondary 8-hour ozone NAAQS to 0.075 parts per million (ppm). 73 FR 
16436 (Mar. 27, 2008). The 2008 ozone NAAQS are met at an ambient air 
quality monitoring site when the 3-year average of the annual fourth-
highest daily maximum 8-hour average ozone concentration is less than 
or equal to the NAAQS, as determined in accordance with Appendix P to 
40 CFR part 50. Under Appendix P, digits to the right of the third 
decimal place are truncated.
    Section 110(a)(1) of the CAA requires states to submit, within 3 
years after promulgation of a new or revised NAAQS, SIPs meeting the 
applicable ``infrastructure'' elements of sections 110(a)(1) and (2). 
One of these applicable infrastructure elements, CAA section 
110(a)(2)(D)(i), requires SIPs to address the ``good neighbor'' 
provision which requires states to prohibit certain adverse air quality 
effects on other states due to interstate transport of pollution.

A. The EPA's Interpretation and Implementation of the Good Neighbor 
Provision

    Specifically, section 110(a)(2)(D)(i)(I) requires SIPs to contain 
adequate provisions prohibiting any source or other type of emissions 
activity in one state from emitting any air pollutant in amounts that 
will contribute significantly to nonattainment, or interfere with 
maintenance, of the NAAQS in any other state. The two provisions of 
this section are referred to as prong 1 (significant contribution to 
nonattainment) and prong 2 (interfere with maintenance). Section 
110(a)(2)(D)(i)(II) requires SIPs to contain adequate provisions to 
prohibit emissions that will interfere with measures required to be 
included in the applicable implementation plan for any other state 
under part C to prevent significant deterioration of air quality (prong 
3) or to protect visibility (prong 4).
    The EPA has established a four-step interstate transport framework 
to address the prong 1 and 2 requirements for ozone and fine 
particulate matter (PM2.5) NAAQS through the development and 
implementation of several previous rulemakings.\1\ The four steps of 
this framework are as follows: (1) Identify downwind air quality 
problems; (2) identify upwind states that impact those downwind air 
quality problems enough to warrant further review and analysis; (3) 
identify the emissions reductions, if any, necessary to prevent an 
identified upwind state

[[Page 3390]]

from contributing significantly or interfering with maintenance with 
respect to those downwind air quality problems; and (4) adopt permanent 
and enforceable measures needed to achieve those emissions reductions. 
The EPA has applied this framework in various actions addressing prongs 
1 and 2 for the PM2.5 and ozone NAAQS.\2\
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    \1\ See, e.g., Finding of Significant Contribution and 
Rulemaking for Certain States in the Ozone Transport Assessment 
Group Region for Purposes of Reducing Regional Transport of Ozone 
(also known as the NOx SIP Call). 63 FR 57356 (October 27, 1998); 
Clean Air Interstate Rule (CAIR) Final Rule. 70 FR 25162 (May 12, 
2005); Cross-State Air Pollution Rule (CSAPR) Final Rule. 76 FR 
48208 (August 8, 2011); CSAPR Update. 81 FR 74504 (October 26, 
2016).
    \2\ See, e.g., ``Interstate Transport Prongs 1 and 2 for the 
2012 Fine Particulate Matter (PM2.5) Standard for 
Colorado, Montana, North Dakota, South Dakota and Wyoming,'' 83 FR 
21227 (May 9, 2018); ``Approval and Promulgation of Air Quality 
State Implementation Plans; California; Interstate Transport 
Requirements for Ozone, Fine Particulate Matter, and Sulfur 
Dioxide,'' 83 FR 5375 (February 7, 2018).
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    On August 4, 2015, the EPA issued a Notice of Data Availability 
(NODA) containing air quality modeling to assist states with meeting 
section 110(a)(2)(D)(i)(I) requirements for the 2008 ozone NAAQS within 
the context of the four-step framework.\3\ Specifically, the air 
quality modeling helped states address steps 1 and 2 of the framework 
by (1) identifying locations in the United States where the EPA 
anticipated nonattainment or maintenance issues in 2017 for the 2008 
ozone NAAQS, and (2) quantifying the projected contributions from 
emissions from upwind states to downwind ozone concentrations at the 
receptors in 2017. The EPA also used this modeling to support the 
Cross-State Air Pollution Rule Update for the 2008 Ozone NAAQS (``CSAPR 
Update'') proposed rule (80 FR 75706, December 3, 2015); we updated the 
modeling in 2016 to support the CSAPR Update final rule (81 FR 74504, 
October 26, 2016). The projections in this updated version of the 
modeling (hereon referred to as the ``CSAPR Update modeling'') were 
part of the technical record for the EPA's February 3, 2017 final 
action on the prongs 1 and 2 portions of the Wyoming 2008 Ozone 
Infrastructure SIP, which is discussed in more detail later in this 
notice. 82 FR 9153.
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    \3\ See Notice of Availability of the Environmental Protection 
Agency's Updated Ozone Transport Modeling Data for the 2008 Ozone 
National Ambient Air Quality Standard (NAAQS), 80 FR 46271 (August 
4, 2015); see also ``Updated Air Quality Modeling Technical Support 
Document for the 2008 Ozone NAAQS Transport Assessment,'' August 
2015 (included in the docket to the NODA).
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    In the CSAPR Update, the EPA used the CSAPR Update modeling to 
identify downwind nonattainment and maintenance receptors at step 1 of 
the four-step framework (see 81 FR 74530-74532, October 26, 2016). 
Specifically, the EPA identified nonattainment receptors as those 
monitoring sites with current measured design values exceeding the 
NAAQS that also have projected (i.e., in 2023) average design values 
exceeding the NAAQS. The EPA identified maintenance receptors as those 
monitoring sites with projected maximum design values exceeding the 
NAAQS. The EPA considered all nonattainment receptors to also be 
maintenance receptors because a monitoring site with a projected 
average design value above the standard necessarily also has a 
projected maximum design value above the standard. Monitoring sites 
with projected maximum design values that exceed the standard and which 
are not also nonattainment receptors are thus referred to as 
maintenance-only receptors.
    To address step 2 of the framework for the CSAPR Update, the EPA 
used the CSAPR Update modeling to determine whether an eastern state's 
impact on each projected downwind air quality problem would be at or 
above a specific threshold. The EPA's modeling projected ozone 
concentrations and contributions in 2017, which would be the last ozone 
season before the then-upcoming July 2018 attainment date for 
nonattainment areas classified as Moderate for the 2008 ozone NAAQS. 
Consistent with the original CSAPR rulemaking (76 FR 48208, August 8, 
2011), the EPA applied a threshold of one percent of the 2008 ozone 
NAAQS of 75 ppb (0.75 ppb) to identify linkages between upwind states 
and downwind nonattainment and maintenance receptors in the CSAPR 
Update. 81 FR 74518 (October 26, 2016). If a state's impact on 
identified downwind nonattainment and maintenance receptors did not 
exceed 0.75 ppb, the state was not considered ``linked'' to those 
receptors and was therefore not considered to significantly contribute 
to nonattainment or interfere with maintenance of the standard in those 
downwind areas. If a state's impact exceeded the 0.75 ppb threshold, 
that state was considered ``linked'' to the downwind nonattainment or 
maintenance receptor(s) and the state's emissions were evaluated 
further, taking into account both air quality and cost considerations, 
to determine what, if any, emissions reductions might be necessary to 
address the state's obligation pursuant to CAA section 
110(a)(2)(D)(i)(I).

B. Wyoming's Submittals To Address the Good Neighbor Provisions

    On February 6, 2014, the Wyoming Department of Environmental 
Quality (WDEQ) submitted a certification that the approved Wyoming SIP 
adequately addressed the ``good neighbor'' provision for the 2008 ozone 
NAAQS. See 81 FR 71712, 71713 (Nov. 18, 2016). On November 18, 2016, 
the EPA proposed to approve Wyoming's submission for prong 1 and 
disapprove Wyoming's submission for prong 2 of the good neighbor 
provision (81 FR 81712), and on February 3, 2017, the EPA finalized the 
proposed approval and disapproval. 82 FR 9153. This disapproval 
established a 2-year deadline, under CAA section 110(c), for the EPA to 
promulgate a federal implementation plan (FIP) or approve a SIP that 
meets the requirements of prong 2 of the good neighbor provision for 
the 2008 ozone NAAQS for Wyoming. The EPA acted on the portions of the 
submission addressing prongs 1, 3 and 4 of the good neighbor provision 
for the 2008 ozone NAAQS.\4\
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    \4\ See 81 FR 70362 (Oct. 12, 2016) for prong 3 final action, 
and 82 FR 9142 (February 3, 2017) for prongs 1 and 4 final action.
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    The EPA based its February 3, 2017 disapproval for prong 2 in the 
first instance on a determination that the February 6, 2014 submission 
lacked an analysis to support the conclusion that the Wyoming SIP 
contained adequate provisions prohibiting emissions that will interfere 
with maintenance of the 2008 ozone NAAQS in any other state. 81 FR 
81714 (proposal); 82 FR 9147 (final). As explained in the notices for 
the proposed and final action, in accordance with the decision of the 
United States Court of Appeals for the District of Columbia Circuit 
(D.C. Circuit) in North Carolina v. EPA, 531 F.3d 896, 910-11 (2008), 
states and the EPA are required to give ``independent significance'' to 
prong 2 by considering the potential impacts of emissions on areas that 
may have issues maintaining the standards. 82 FR 9145.
    However, if the EPA's supplemental analysis supports the state's 
conclusion that the SIP is adequate to address the statutory 
requirements, we may approve the state's submittal. 82 FR 9149. In this 
case, the EPA evaluated the CSAPR Update modeling, described above. 
That modeling showed that emissions from Wyoming were not linked to any 
nonattainment receptors for the 2008 ozone NAAQS in the 2017 analytic 
year. However, the modeling also showed that emissions from Wyoming 
were projected to contribute above the 1% threshold to one maintenance 
receptor at the Chatfield Reservoir in Douglas County, Colorado 
(monitor I.D. # 80350004).\5\ The CSAPR Update

[[Page 3391]]

modeling identified two other maintenance receptors in the Denver 
Metro/North Front Range (DMNFR) 2008 Ozone Moderate nonattainment area, 
but emissions from Wyoming were projected to impact those receptors 
below the 0.75 ppb threshold. For the purpose of our action on the 
Wyoming SIP submission, we determined that a 1% screening threshold was 
appropriate to use for the Douglas County maintenance receptor because 
the air quality problem in that area resulted in part from the 
relatively small individual contributions of upwind states that 
collectively contribute a large portion of the ozone concentrations 
(9.7%), comparable to some eastern receptors addressed in the CSAPR 
Update. 82 FR 9149-50. The CSAPR Update modeling projected that Wyoming 
emissions would contribute 1.18 ppb, or approximately 1.57% of the 2008 
ozone NAAQS, at the Douglas County maintenance receptor in 2017.\6\ As 
this contribution was above the screening threshold, we could not 
conclude on the basis of the CSAPR Update modeling that Wyoming's SIP 
contained sufficient provisions to prohibit emissions that will 
interfere with maintenance of the 2008 ozone NAAQS at the Douglas 
County maintenance receptor. As a result, the EPA disapproved the 
February 6, 2014 submittal for prong 2.
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    \5\ The Douglas County maintenance receptor is located in the 
2008 ozone Denver Metro/North Front Range (DMNFR) Moderate 
nonattainment area. See https://www3.epa.gov/airquality/greenbook/hnp.html#Ozone_8-hr.2008.Denver. However, the EPA has routinely 
interpreted the section 110(a)(2)(D)(i)(I) requirements to be 
independent of formal designations because any area may be in 
nonattainment or struggle to maintain the NAAQS, regardless of 
formal area designation.
    \6\ The updated modeling data (published on EPA's website at 
https://www.epa.gov/airmarkets/final-cross-state-air-pollution-rule-update on September 7, 2016) are available in the docket for this 
action.
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II. State Submittal

    WDEQ submitted a new interstate transport SIP on October 17, 2018, 
providing additional information to demonstrate that the State meets 
the prong 2 requirement for the 2008 ozone NAAQS. In this submittal, 
WDEQ addressed the prong 2 requirements of section 110(a)(2)(D)(i)(I) 
using a weight of evidence analysis and concluded that emissions from 
Wyoming will not interfere with maintenance of the 2008 ozone NAAQS in 
any other state. The submittal states that weight of evidence analyses 
are a valid approach to assessing ozone transport in western states and 
have been used by the EPA and in submittals by other western states, 
specifically California. Consistent with the CSAPR Update modeling, 
which only found one potential linkage with the Douglas County 
maintenance receptor, WDEQ focused its analysis on the potential 
impacts of Wyoming emissions on that receptor. WDEQ's analysis included 
information about recent and forthcoming emission reductions at sources 
in Wyoming; ozone modeling for the 2023 analytic year from the EPA's 
October 27, 2017 memorandum ``Supplemental Information on the 
Interstate Transport State Implementation Plan Submissions for the 2008 
Ozone National Ambient Air Quality Standards under Clean Air Act 
Section 110(a)(2)(D)(i)(I)'' (hereon ``October 2017 Memo''); and the 
EPA's proposed approval (since finalized) of the ``Colorado Attainment 
Demonstration for the 2008 8-Hour Ozone Standard for the DMNFR Moderate 
nonattainment area'' (hereon ``DMNFR attainment demonstration''). 83 FR 
14807 (April 6, 2018).
    WDEQ indicated that the Douglas County monitor was projected to be 
a maintenance receptor for the year 2017 in the CSAPR Update modeling. 
However, WDEQ stated that it is unclear whether it should still 
consider the Douglas County monitor to be maintenance for this NAAQS, 
given its review of information available subsequent to the CSAPR 
Update modeling. Specifically, WDEQ cited the EPA's October 2017 Memo 
and the State of Colorado's attainment demonstration for the 2008 8-
Hour Ozone Standard for the DMNFR nonattainment area to argue that the 
Douglas County receptor should not be considered a maintenance receptor 
for the 2008 ozone NAAQS.
    First, WDEQ referenced the EPA's October 2017 Memo. As described in 
further detail in Section III of this notice, the EPA performed air 
quality modeling, released in the October 2017 Memo, to project 2008 
ozone nonattainment and maintenance receptors for the analytic year 
2023 to assist the states in addressing remaining prong 1 or prong 2 
obligations for the 2008 ozone NAAQS. This modeling projected a maximum 
design value of 73.2 ppb (below the 75 ppb NAAQS) for the Douglas 
County receptor in the 2023 analytic year. October 2017 Memo at A-7. 
WDEQ also cited language from the October 2017 Memo which states that 
``no areas in the United States, outside of California, are expected to 
have problems attaining and maintaining the 2008 ozone NAAQS in 2023.'' 
Id. at 4.
    WDEQ then referenced modeling performed by the State of Colorado as 
part of its DMNFR attainment demonstration.\7\ Specifically, WDEQ 
referenced modeling from Colorado's weight of evidence attainment 
demonstration in which Colorado removed monitoring data for certain 
days during 2010-2013 from the calculation of the 2011 baseline ozone 
design value because these data were likely influenced by atypical 
events such as stratospheric intrusions or wildfires. Colorado's 
modeling, which will be discussed in further detail in Section III of 
this notice, projected the Douglas County monitor would have a maximum 
modeled design value below the 2008 NAAQS in 2017 when the adjusted 
2011 baseline was used. 83 FR 14813 (April 6, 2018). As noted by WDEQ, 
in the EPA's proposed approval of Colorado's DMNFR attainment 
demonstration, we concurred with Colorado's assessment that this 
modeling was properly configured, met EPA performance requirements, and 
was appropriately used in its application. Id. The EPA has since 
finalized our proposed approval of Colorado's DMNFR attainment 
demonstration. 83 FR 31068 (July 3, 2018).
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    \7\ The Colorado 2008 Ozone Moderate Nonattainment Area SIP 
Submission is available on regulations.gov as document ID # EPA-R08-
OAR-2017-0567-0004.
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    In its October 17, 2018 submission, WDEQ asserted that the modeling 
from both the EPA's October 2017 Memo and Colorado's DMNFR attainment 
demonstration indicate that all future design values for the Douglas 
County receptor are below the 2008 ozone NAAQS. Therefore, WDEQ asserts 
that this receptor should no longer be considered a maintenance 
receptor, as it was identified in the CSAPR Update modeling, but should 
instead be considered to be attainment.
    WDEQ also included information about recent and forthcoming 
emission reductions at sources in Wyoming in its weight-of-evidence 
analysis. Specifically, WDEQ provided information about nitrogen oxide 
(NOX) and volatile organic compounds (VOC) emissions 
reductions that occurred between 2011 and 2017, and NOX 
reductions that will occur before 2023. WDEQ focused on these 
pollutants as both are precursors to ozone. WDEQ calculated that 
permitting actions, including Title V permit rescissions for sources 
that have reduced their emissions from major to minor source levels, 
accounted for a statewide reduction of 12,392.5 tons per year (tpy) of 
NOX and 905.6 tpy of VOC between 2011 and 2017. WDEQ noted 
that regulations covering nonpoint sources and reductions from leak 
detection and repair or fugitive emissions monitoring programs had led 
to additional VOC reductions, though WDEQ had not quantified the 
reductions from these regulations. WDEQ also calculated a 21,525 tpy 
NOX reduction between 2017

[[Page 3392]]

and 2023, concluding NOX emissions would decrease by nearly 
18% from those reported in the 2011 Emission Inventory (the inventory 
used in the CSAPR Update modeling and October 2017 Memo modeling) by 
2023 through permitting actions alone. WDEQ also asserted that the 
emissions reductions listed in its submission do not appear to have 
been accounted for in the CSAPR Update modeling.
    WDEQ concludes that all elements of its weight-of-evidence analysis 
combined demonstrate that emissions from the State of Wyoming will not 
interfere with maintenance of the 2008 8-hour ozone NAAQS in any other 
state, including at the Douglas County, Colorado receptor.

III. EPA's Evaluation

    The EPA has reviewed all elements of WDEQ's weight-of-evidence 
analysis and additional relevant technical information to determine 
whether the SIP has adequate provisions to ensure emissions from the 
state will not interfere with maintenance of the 2008 ozone NAAQS in 
any other state. The EPA conducted this review within the four-step 
interstate transport framework. Therefore, the EPA's first step in 
reviewing WDEQ's submission is to identify downwind air quality 
problems.

A. Identification of Downwind Air Quality Problems

    The EPA first reviewed WDEQ's information about modeling conducted 
by the State of Colorado that projected attainment of the 2008 ozone 
NAAQS at the Douglas County receptor and all other ozone monitors in 
the DMNFR Moderate ozone nonattainment area in 2017. Based on 
Colorado's DMNFR attainment demonstration modeling results, WDEQ 
asserts that the Douglas County receptor should not be considered a 
maintenance receptor at step 1 of the four-step interstate transport 
framework. As noted, the Douglas County receptor was the only 
maintenance receptor to which emissions from Wyoming contributed above 
1% of the 2008 ozone NAAQS in the EPA's 2016 CSAPR Update modeling.
    The EPA's review of Colorado's DMNFR attainment demonstration 
modeling, provided below, begins with an overview of the modeling 
analysis in the attainment planning context for which it was originally 
generated. Then, we expand on Wyoming's analysis by considering 
Colorado's modeling in the context of interstate transport. 
Specifically, we consider how Colorado's removal of atypical event-
influenced monitor data in 2010, 2011 and 2012 from the 2011 baseline 
ozone design value would impact the CSAPR Update modeling results with 
regard to the Colorado receptor to which Wyoming was linked.
    In Colorado's primary modeling for the DMNFR attainment 
demonstration, the State calculated relative response factors (RRFs) 
using the maximum modeled ozone in a 3x3 matrix of grid cells around 
each ozone receptor to model a 2017 projected concentration of 76.2 ppb 
at the Douglas County receptor. See 83 FR 14811 (April 6, 2018). 
Because this projection was close to the 75 ppb NAAQS, Colorado 
developed its DMNFR attainment demonstration using a weight-of-evidence 
analysis, as recommended by EPA guidance. Id. at 14812. Colorado's 
weight-of-evidence analysis included two modeling analyses in addition 
to the primary (3x3 matrix) analysis. The first was performed using a 
7x7 matrix of grid cells around each receptor. Colorado contended that 
this model performed better than the 3x3 matrix in simulating the 2011 
period when monitored concentrations were compared to model results in 
the 7x7 matrix, potentially as a result of challenges in accurately 
simulating meteorological data in Colorado's complex terrain combined 
with the use of a high resolution 4-km grid in the Colorado modeling 
platform. In this modeling analysis, Colorado modeled the Douglas 
County receptor as attaining the NAAQS in 2017 with a projected 
concentration of 75 ppb. Id. All other receptors in the Denver ozone 
moderate nonattainment area were also projected as attainment in the 
modeling analysis using the 7x7 matrix.
    In the second modeling analysis, Colorado evaluated high ozone days 
from 2009 to 2013 that were likely influenced by atypical, extreme, or 
unrepresentative events (collectively, ``atypical events'') such as 
wildfire or stratospheric intrusion, but were included in the 
calculation of the 2011 baseline ozone design value.\8\ Colorado did 
not submit formal demonstrations under the Exceptional Events Rule (40 
CFR 50.14) for these days because they do not affect the DMNFR's 
attainment status and thus do not have regulatory significance under 
the Exceptional Events Rule. However, these days do affect the baseline 
design value and thus affect the model projected future design value 
for 2017. After removing the data that were likely influenced by 
atypical events, Colorado modeled attainment in 2017 at the Douglas 
County receptor using both the 3x3 (74 ppb) and 7x7 (73 ppb) matrices 
for calculating the model RRF. Id. at 14813. All other receptors in the 
DMNFR ozone Moderate nonattainment area were also projected as 
attainment in 2017 when atypical event-influenced data were removed 
from the baseline calculation, with the highest projection at any 
receptor in the area at 74 ppb. As noted in Section II, the EPA 
concurred with Colorado's assessment that this modeling was appropriate 
for Colorado's weight of evidence attainment demonstration, and 
subsequently finalized our approval of Colorado's attainment 
demonstration. 83 FR 31068 (July 3, 2018).
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    \8\ See Colorado's November 17, 2016 TSD ``Analyses in Support 
of Exceptional Event Flagging and Exclusion for the Weight of 
Evidence Analysis,'' in the docket for this action.
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    While Wyoming listed the DMNFR attainment demonstration modeling 
results as evidence that the Douglas County receptor should not be 
considered a maintenance receptor as of 2017, the EPA did not reach the 
same conclusion based on these results alone. This is because the 
Colorado modeling results, while appropriate in an attainment planning 
context, were calculated from a baseline design value that is the 
weighted average of three 3-year design values. In an interstate 
transport modeling context, EPA evaluates the transport contribution 
for both the weighted average design value and individually for each of 
the three 3-year average design values. As noted in Section I of this 
proposed action, in the CSAPR Update the EPA identified as 
``nonattainment receptors'' monitoring sites with a current measured 
value exceeding the NAAQS that also have a projected average design 
value exceeding the NAAQS and identified maintenance receptors as those 
monitoring sites with a projected maximum design value exceeding the 
NAAQS. Colorado's DMNFR attainment demonstration modeling results 
calculated the 2011 baseline by averaging the three relevant design 
values (2009-2011, 2010-2012, and 2011-2013). Therefore, the 2017 
modeled projections presented in the DMNFR attainment demonstration 
(and referenced by Wyoming) would only have some relevance with regard 
to whether the Douglas County receptor should be identified as a 
nonattainment receptor in an interstate transport context. However, the 
determination of whether the Douglas County receptor should continue to 
be identified as a maintenance receptor, as it was in the CSAPR Update 
modeling, is based on the 2017 projection of the maximum of

[[Page 3393]]

the three base year design values (in this case, 2011-2013).
    Nonetheless, the information regarding atypical event-influenced 
data in the DMNFR attainment demonstration is relevant to the 
determination of whether the Douglas County monitor should continue to 
be identified as a maintenance receptor in the EPA's 2017 modeling for 
the 2008 ozone NAAQS. Because the CSAPR Update modeling was conducted 
in 2016, the EPA did not consider Colorado's ``Analyses in Support of 
Exceptional Event Flagging and Exclusion for the Weight of Evidence 
Analysis'' in the CSAPR Update modeling.\9\ After reviewing this 
document, the EPA finds it appropriate to consider the impact of 
removing atypical event-influenced data from the CSAPR Update modeling 
baseline as part of our review of Wyoming's prong 2 weight-of-evidence 
analysis. After removal of the atypical event-influenced data from the 
2009-2013 baseline, listed in Table 1 below, the baseline maximum 
design value at the Douglas County receptor (2011-2013) decreases from 
83 ppb to 81 ppb, as shown in Table 2.
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    \9\ As noted, this document is available in the docket for this 
proposed action.

               Table 1--Douglas County Ozone Monitoring Data Flagged as Atypical Event and Excluded From Baseline Design Value Calculation
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                        Date                            April 13, 2010       June 7, 2011        July 4, 2012       August 9, 2012      August 21, 2012
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8-hour Ozone Concentration (ppb)....................                 79                  84                  96                  98                  80
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       Table 2--Douglas County Ozone Monitoring With Data Flagged as Atypical Event Included and Excluded
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                                                                                                   2011-2013 DV
                            Year                                2011        2012        2013       (truncated)
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4th Max Monitored Value with Atypical Event Data Included           82          86          83               83
 (ppb).....................................................
4th Max Monitored Value with Atypical Event Data Excluded           81          79          83               81
 (ppb).....................................................
----------------------------------------------------------------------------------------------------------------

    We then applied the RRF from the CSAPR Update Modeling to this 
adjusted design value, and the results are shown in Table 3 below.\10\
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    \10\ The EPA notes that the RRFs are based on the ``3x3'' 
approach as recommended in EPA's Draft Modeling Guidance for 
Demonstrating Attainment of the Air Quality Goals for Ozone, 
PM2.5, and Regional Haze, December 2014.

                               Table 3--Revised CSAPR Update Modeling Maximum Design Value for the Douglas County Receptor
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                                             2009-2013 Max DV with                                                            CSAPR Update Modeling 2017
            2009-2013 Max DV                  atypical event data     CSAPR Update Modeling 2017  CSAPR Update Modeling 2017  Max DV with atypical event
                                                   excluded                       RRF                       Max DV                   data excluded
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83......................................                         81                       .9358                        77.6                        75.8
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    The projected maximum design value of 75.8 shown in Table 3 (which 
excludes monitoring data determined by Colorado to be influenced by 
atypical events from the baseline period) indicates attainment of the 
2008 ozone NAAQS at the Douglas County receptor in 2017. On this basis, 
the EPA is proposing to concur with Wyoming's assertion that the 
Douglas County receptor should not be considered a maintenance receptor 
at step 1 of the four-step interstate transport framework.
    In its weight of evidence analysis, WDEQ also asserted that the 
modeling from the EPA's October 2017 Memo indicates no areas in the 
United States are expected to have problems attaining and maintaining 
the 2008 ozone NAAQS in 2023 outside of California. This includes a 
projection of attainment for each receptor in the DMNFR Moderate 
nonattainment area, most notably the Douglas County receptor. The EPA 
finds that the modeling from the EPA's October 2017 Memo supports the 
analysis above regarding whether emissions from Wyoming will interfere 
with maintenance of the 2008 ozone NAAQS. Details about this modeling 
analysis are provided in the October 2017 Memo, which is available in 
the docket for this action.
    As with the CSAPR Update, the EPA used the results of the October 
2017 Memo modeling to identify as nonattainment receptors those 
monitors that both measure nonattainment based on measured 2014-2016 
design values and have a projected average design value exceeding the 
2008 ozone NAAQS in 2023 and identify receptors that have a projected 
maximum design value exceeding the NAAQS in 2023 as maintenance 
receptors.
    The October 2017 Memo modeling results indicate that Wyoming 
emissions will not interfere with maintenance at the Douglas County 
receptor or elsewhere in the DMNFR Moderate nonattainment area in 2023, 
because each receptor in the area is projected to attain and maintain 
the NAAQS in that year. Table 4, below, shows the projected 2023 
maximum design values for the three receptors in Colorado that had been 
projected as maintenance (there were no projected nonattainment 
receptors in the state) for the year 2017 in the CSAPR Update modeling. 
Table 4 also shows the projected maximum design values for these 
receptors when the 2010-2012 DMNFR monitor values that were likely 
influenced by atypical events were removed from the 2011 baseline, as 
this baseline was also used for the October 2017 Memo modeling.

[[Page 3394]]



      Table 4--Modeled 2023 Maximum Design Values for Colorado Receptors Previously Modeled as Maintenance
----------------------------------------------------------------------------------------------------------------
                                                                      Modeled 2023     Modeled 2023 Max Design
                                                                       Max Design     Value with Atypical Event
           Monitor I.D.                         County                    Value        Data Excluded from 2011
                                                                        (ppb)\11\              baseline
----------------------------------------------------------------------------------------------------------------
80350004.........................  Douglas, CO.....................            73.2                         71.5
80590006.........................  Jefferson, CO...................            73.7                         71.1
80590011.........................  Jefferson, CO...................            73.9                         72.1
----------------------------------------------------------------------------------------------------------------

    The modeled 73.9 ppb projection at one of the Jefferson County, 
Colorado receptors is the highest maximum design value for any receptor 
in the DMNFR Moderate nonattainment area (and the state overall). This 
decreases to a 72.1 maximum design value when the atypical event-
influenced data in the DMNFR are removed from the model's 2011 
baseline. As noted by WDEQ in its October 17, 2018 submission, the only 
2008 ozone maintenance receptors projected in 2023 are located in the 
state of California. Wyoming's highest modeled contribution to any 
projected 2023 maintenance receptor is 0.02 ppb (less than 0.03% of the 
NAAQS) in Kern County, California (monitor I.D. 60295002).\12\ 
Therefore, the EPA proposes to find that emissions from Wyoming will 
not interfere with maintenance at any area [or monitor] outside of 
California in 2023, because there are no projected maintenance 
receptors outside of California in that year. Moreover, the EPA 
proposes to find emissions from Wyoming will not interfere with any 
projected maintenance receptors in California in 2023 because their 
modeled contribution at each such receptor is well below 1% of the 2008 
ozone NAAQS at step 2 of the four-step framework.
---------------------------------------------------------------------------

    \11\See October 2017 Memo at page A-7.
    \12\ See the EPA's March 27, 2018 Memo ``Information on the 
Interstate Transport State Implementation Plan Submissions for the 
2015 Ozone National Ambient Air Quality Standards under Clean Air 
Act Section 110(a)(2)(D)(i)(I),'' at page C-6.
---------------------------------------------------------------------------

    In referencing the modeling from both the EPA's October 2017 Memo 
and Colorado's DMNFR attainment demonstration, WDEQ asserted that the 
Douglas County receptor is projected to attain and maintain the NAAQS 
in both 2017 and 2023. On this basis, there would be no requirement for 
any state to address upwind ozone contributions to the Douglas County 
receptor in advance of 2023, because Colorado's DMNFR attainment 
demonstration modeling projects the 2008 ozone NAAQS is currently being 
met.\13\ As just discussed, the EPA finds that the relevance of the 
DMNFR attainment demonstration modeling to Wyoming's weight-of-evidence 
analysis is not the projection of attainment Wyoming references, 
because that modeling does not project a maximum design value as is 
done in interstate transport modeling. Rather, the relevance of the 
DMNFR attainment demonstration is the showing that monitor values from 
the 2011 baseline were likely influenced by atypical events, which 
supports the EPA's exclusion of the same values from the CSAPR Update 
modeling and shows that the Douglas County monitor should not be 
identified as a maintenance receptor in 2017. Based on the EPA's review 
of the two modeling analyses referenced in WDEQ's submission, and our 
additional analysis as described, the EPA is proposing to conclude that 
there are no downwind air quality (specifically maintenance) problems 
in 2017 to which Wyoming contributes, and that this conclusion is 
further bolstered by the October 2017 Memo modeling that shows these 
areas will continue to maintain the standard in 2023. Therefore, the 
EPA proposes to find that emissions from Wyoming sources will not 
interfere with maintenance of the 2008 ozone NAAQS in downwind states.
---------------------------------------------------------------------------

    \13\ The EPA is not proposing to make any determinations 
regarding the DMNFR Moderate nonattainment area, most notably the 
CAA section 181(b)(2) requirement that the EPA determine whether the 
area attained the NAAQS by its applicable attainment date. 
Colorado's attainment demonstration modeling cited by WDEQ was found 
by the EPA to meet the requirements for a modeled demonstration that 
the area will meet the standard in the attainment year. 83 FR 31069.
---------------------------------------------------------------------------

    As discussed in Section II, WDEQ also provided information about 
recent and forthcoming ozone precursor emissions reductions in Wyoming. 
The EPA agrees with WDEQ that these reductions have been and/or will be 
beneficial in reducing ozone transport from Wyoming to downwind states. 
However, we did not quantitatively analyze these reductions because of 
our proposed finding above that there are no relevant downwind air 
quality issues. However, we invite comment on these reductions and 
their relevance to our proposed action. Regarding WDEQ's assertion that 
the emissions reductions listed in its submission that occurred between 
2011 and 2017 do not appear to have been accounted for in the EPA's 
2016 CSAPR Update modeling, the CSAPR Update modeling includes all 
implemented or scheduled federally enforceable emissions reductions 
measures that were known at the time the EPA conducted this modeling, 
and therefore, we are not relying on WDEQ's assertion.

B. EPA's Proposed Conclusion

    Based on our review of WDEQ's October 17, 2018 submission and other 
relevant information, the EPA proposes to concur with WDEQ's conclusion 
that Wyoming will not interfere with maintenance of the 2008 ozone 
NAAQS in the DMNFR Moderate nonattainment area, specifically the 
Douglas County receptor, or in any other downwind state. The EPA is 
therefore proposing to approve Wyoming's October 17, 2018 submittal, 
which states that Wyoming's SIP includes adequate provisions to 
prohibit sources or other emission activities within the State from 
emitting ozone precursors in amounts that will interfere with 
maintenance by any other state with respect to the 2008 ozone NAAQS.

IV. Proposed Action

    The EPA is proposing to fully approve Wyoming's October 17, 2018 
submittal addressing CAA section 110(a)(2)(D)(i)(I), prong 2, for the 
2008 ozone NAAQS. Should we finalize this proposed approval, the EPA 
will no longer have an obligation under CAA section 110(c)(1) to 
promulgate a FIP addressing the previous disapproval. The EPA is 
soliciting public comments on this proposed action and will consider 
public comments received during the comment period.

V. Statutory and Executive Order Reviews

    Under the CAA, the Administrator is required to approve a SIP 
submission that complies with the provisions of the Act and applicable 
federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in 
reviewing SIP submissions, the

[[Page 3395]]

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

In addition, the SIP is not approved to apply on any Indian reservation 
land or in any other area where the EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the proposed rule does not have tribal implications and will 
not impose substantial direct costs on tribal governments or preempt 
tribal law as specified by Executive Order 13175 (65 FR 67249, November 
9, 2000).

List of Subjects in 40 CFR Part 52

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

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

    Dated: February 6, 2019.
Douglas Benevento,
Regional Administrator, EPA Region 8.
[FR Doc. 2019-01908 Filed 2-11-19; 8:45 am]
 BILLING CODE 6560-50-P