Proposed Rule2025-11326
Air Plan Approval; Guam; Clean Data Determination for the Piti-Cabras Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard
Primary source
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Published
June 20, 2025
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing a clean data determination (CDD) for the Piti-Cabras, Guam sulfur dioxide (SO<INF>2</INF>) nonattainment area ("Piti-Cabras area") based on our determination that the area has attained the 2010 1-hour SO<INF>2</INF> National Ambient Air Quality Standard (NAAQS, "standard," or "2010 SO<INF>2</INF> NAAQS"). In designated nonattainment areas where air quality data demonstrate that a NAAQS has been attained, the EPA interprets certain requirements of the Clean Air Act (CAA) as no longer applicable for so long as air quality continues to meet the standard. Under this Clean Data Policy, the EPA may issue a determination of attainment, known as a CDD, that a nonattainment area is attaining the relevant NAAQS. If finalized, this proposed CDD would suspend the obligation to submit certain attainment planning requirements for the Piti-Cabras area for as long as the area continues to attain the 2010 SO<INF>2</INF> NAAQS or until the area is formally redesignated.
Full Text
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<title>Federal Register, Volume 90 Issue 117 (Friday, June 20, 2025)</title>
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[Federal Register Volume 90, Number 117 (Friday, June 20, 2025)]
[Proposed Rules]
[Pages 26235-26240]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-11326]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R09-OAR-2025-0137; FRL-12752-01-R9]
Air Plan Approval; Guam; Clean Data Determination for the Piti-
Cabras Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National
Ambient Air Quality Standard
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing a clean
data determination (CDD) for the Piti-Cabras, Guam sulfur dioxide
(SO<INF>2</INF>) nonattainment area (``Piti-Cabras area'') based on our
determination that the area has attained the 2010 1-hour SO<INF>2</INF>
National Ambient Air Quality Standard (NAAQS, ``standard,'' or ``2010
SO<INF>2</INF> NAAQS''). In designated nonattainment areas where air
quality data demonstrate that a NAAQS has been attained, the EPA
interprets certain requirements of the Clean Air Act (CAA) as no longer
applicable for so long as air quality continues to meet the standard.
Under this Clean Data Policy, the EPA may issue a determination of
attainment, known as a CDD, that a nonattainment area is attaining the
relevant NAAQS. If finalized, this proposed CDD would suspend the
obligation to submit certain attainment planning requirements for the
Piti-Cabras area for as long as the area continues to attain the 2010
SO<INF>2</INF> NAAQS or until the area is formally redesignated.
DATES: Written comments must arrive on or before July 21, 2025.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2025-0137 at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. For comments submitted at
<a href="http://Regulations.gov">Regulations.gov</a>, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
<a href="http://Regulations.gov">Regulations.gov</a>. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>. If you need assistance in a
language other than English or if you are a person with disabilities
who needs a reasonable accommodation at no cost to you, please contact
the person identified in the FOR FURTHER INFORMATION CONTACT section.
FOR FURTHER INFORMATION CONTACT: Karina Oconnor, Manager, Planning
Section, Planning & Analysis Branch, Air & Radiation Division, EPA
Region IX, 75 Hawthorne Street, San Francisco, CA 94105, (415) 972-
3498, or by email at <a href="/cdn-cgi/l/email-protection#8ec1cde1e0e0e1fca0c5effce7e0efceebfeefa0e9e1f8"><span class="__cf_email__" data-cfemail="68272b070606071a4623091a010609280d1809460f071e">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us'' and
``our'' refer to the EPA.
Table of Contents
I. Background
II. EPA Clean Data Policy and Clean Data Determinations
III. The EPA's Analysis Supporting a Clean Data Determination for
the Piti-Cabras Area
A. Overview of the EPA's Modeling Analysis for the Piti-Cabras
Area
B. Results of the EPA's Air Quality Modeling Analysis
IV. Proposed Action
V. Statutory and Executive Order Reviews
I. Background
On June 22, 2010 (75 FR 35520), the EPA published in the Federal
Register a strengthened, primary 1-hour SO<INF>2</INF> NAAQS,
establishing a new standard at a level of 75 parts per billion (ppb),
based on the 3-year average of the annual 99th percentile of daily
maximum 1-hour average concentrations of SO<INF>2.</INF>\1\ Following
promulgation of a new or revised NAAQS, the EPA is required to
[[Page 26236]]
designate all areas of the country as either ``attainment,''
``nonattainment,'' or ``unclassifiable.'' \2\ On December 21, 2017, the
EPA designated six areas in three States and two territories as
nonattainment in the third round of SO<INF>2</INF> designations,
effective April 9, 2018.\3\ With that action, the EPA designated as
nonattainment the portion of Guam within a 6.074-km radius centered on
UTM Easting 249,601.60 m, and UTM Northing 1,489,602.00 m (UTM Zone
55N).\4\
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\1\ On June 2, 2010, the EPA signed the final rule titled,
``Primary National Ambient Air Quality Standard for Sulfur
Dioxide,'' 75 FR 35520 (June 22, 2010), codified at 40 CFR part 50.
\2\ CAA section 107(d)(1).
\3\ 83 FR 1098 (January 9, 2018).
\4\ For designations technical discussions, see the Technical
Support Document, Chapter 11: Intended Round 3 Area Designations for
the 2010 1-Hour SO<INF>2</INF> Primary National Ambient Air Quality
Standard for Guam. EPA Office of Air and Radiation, December 2017,
Section 3, 6-26, available in the docket for this action.
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The Piti-Cabras area is located on the western side of the island
of Guam, centered on the Piti and Cabras power plants, which are both
owned by Guam Power Authority (GPA). The Piti facility (also referred
to as Marianas Energy Company (MEC)) consists of two baseload electric
generating units (8 and 9). Piti 8 and 9 are two 45.2 megawatt (MW)
diesel engines. The Cabras facility consists of two baseload electric
generating units (1 and 2) that are 66 MW units. These facilities are
the primary emitters of SO<INF>2</INF> in the area. Nearby, the Taiwan
Electrical and Mechanical Engineering Services (TEMES) power plant
(also referred to as ``Piti 7''),\5\ and commercial and United States
Navy (``Navy'') marine vessel ports are also significant emitters of
SO<INF>2</INF>. No other sources on or beyond the island were
determined to have the potential to cause concentration gradient
impacts within the area of analysis. The Modeling Technical Support
Document (TSD) included in the docket for this rulemaking contains more
information on the facilities and emissions.
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\5\ TEMES, or Piti 7, is a 40 MW combustion turbine and is also
owned by GPA.
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The CAA directs states containing an area designated nonattainment
for the 2010 SO<INF>2</INF> NAAQS to develop and submit a nonattainment
area SIP revision to the EPA within 18 months of the effective date of
an area's designation as nonattainment. The nonattainment area SIP
revision (also referred to as an attainment plan) must meet the
requirements of subparts l and 5 of part D, of Title 1 of the CAA, 42
U.S.C. 7401 et seq., and provide for attainment of the NAAQS by the
applicable statutory attainment date.\6\ To be approved by the EPA,
under section 192(a), these nonattainment area SIP revisions must
provide for attainment of the NAAQS as expeditiously as practicable,
but no later than five years from the effective date of designation.
The Guam Environmental Protection Agency (Guam EPA) was required to
prepare and submit to the EPA a nonattainment area SIP revision by
October 9, 2019, to bring the area into attainment by the attainment
date of April 9, 2023. However, Guam EPA failed to submit a complete
attainment plan for the area by the October 9, 2019 deadline. On
November 3, 2020, the EPA issued a finding that the Territory, among
other areas, had failed to submit the required attainment plan.\7\
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\6\ See sections 172 and 191-192 of the CAA.
\7\ 85 FR 69504 (November 3, 2020).
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Pursuant to section 179 of the CAA and 40 CFR 52.31, the November
3, 2020 ``finding of failure to submit'' (FFS) triggered sanctions
clocks. More specifically, under 40 CFR 52.31, the offset sanction in
CAA section 179(b)(2) would be imposed 18 months after November 3,
2020, and the highway funding sanction in CAA section 179(b)(1) would
be imposed six months after the offset sanction was imposed, unless the
EPA determined that a subsequent SIP submission corrected the
identified deficiencies before the applicable deadlines.\8\
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\8\ See 40 CFR 52.31(d)(5).
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The FFS action also started a two-year clock by which the EPA is
required under CAA section 110(c) to promulgate a Federal
Implementation Plan (FIP) for the area, unless Guam submits, and the
EPA approves, an attainment plan for the area before December 3, 2022.
Guam EPA has not submitted an attainment plan for the Piti-Cabras area,
and both offset and highway sanctions are currently in effect in the
area.
Because there are no available ambient SO<INF>2</INF> monitoring
data and there are only limited data available regarding recent actual
emissions, the EPA proposes to determine, based on an evaluation of
updated emissions data for the major SO<INF>2</INF> sources in the
Piti-Cabras area and based on more recently available supporting air
quality modeling data, that the Piti-Cabras area is attaining the 2010
SO<INF>2</INF> NAAQS and qualifies for a CDD under the EPA's Clean Data
Policy.
II. EPA Clean Data Policy and Clean Data Determinations
Following enactment of the CAA Amendments of 1990, the EPA
discussed its interpretation of the requirements for implementing the
NAAQS in the ``General Preamble for the Implementation of title I of
the CAA Amendments of 1990'' (``General Preamble'').\9\ In 1995, based
on the interpretation of CAA sections 171, 172, and 182 in the General
Preamble, the EPA set forth what has become known as its ``Clean Data
Policy'' for the 1-hour ozone NAAQS.\10\ Under the Clean Data Policy,
for a nonattainment area that is attaining the NAAQS, the EPA
interprets the requirements of the CAA that are specifically designed
to help an area achieve attainment to be suspended for so long as air
quality continues to meet the standard.\11\ These requirements include
attainment demonstrations, implementation of reasonably available
control measures (RACM), including reasonably available control
technology (RACT), reasonable further progress (RFP) demonstrations,
emissions limitations and control measures as necessary to provide for
attainment, and contingency measures.\12\ The EPA's ``Guidance for 1-
Hour SO<INF>2</INF> Nonattainment Area SIP Submissions,'' provides
guidance and the EPA's rationale for the application of the existing
Clean Data Policy to the 2010 1-hour primary SO<INF>2</INF> NAAQS.\13\
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\9\ 57 FR 13498, 13564 (April 16, 1992).
\10\ Memorandum dated May 10, 1995, from John S. Seitz,
Director, Office of Air Quality Planning and Standards, to Regional
Office Air Division Directors, Regions 1-10, Subject: ``Reasonable
Further Progress, Attainment Demonstration, and Related Requirements
for Ozone Nonattainment areas Meeting the Ozone National Ambient Air
Quality Standard The EPA's statutory interpretation of the Clean
Data Policy is further described in the ``Final Rule to Implement
the 8-hour Ozone National Ambient Air Quality Standard--Phase 2
(referred to as the Phase 2 Final Rule)'', 70 FR 71612 (November 29,
2005). The Tenth, Seventh, and Ninth Circuit Courts have upheld EPA
rulemakings applying the Clean Data Policy. See Sierra Club v. EPA,
99 F. 3d 1551 (10th Cir. 1996); Sierra Club v. EPA, 375 F. 3d 537
(7th Cir. 2004); Our Children's Earth Foundation v. EPA, No. 04-
73032 (9th Cir., June 28, 2005) memorandum opinion.
\11\ Id.
\12\ See 57 FR 13498, 13564; Memorandum dated September 4, 1992
from John Calcagni, Director, Air Quality Management Division, to
Air Directors, Subject: ``Procedures for Processing Requests to
Redesignate Areas to Attainment'' p. 6.
\13\ Memorandum dated April 23, 2014, from Stephen D. Page,
Director, EPA Air Quality Management Division, to Regional Office
Air Division Directors, Regions 1-10, Subject: ``Guidance for 1-Hour
SO<INF>2</INF> Nonattainment Area SIP Submissions.''
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The EPA may issue a CDD under our Clean Data Policy when a
nonattainment area is attaining the 2010 SO<INF>2</INF> NAAQS based on
the most recent available data. The EPA will determine whether the area
has attained the 2010 SO<INF>2</INF> NAAQS based on available
information, including air quality monitoring data and air quality
dispersion modeling information for the affected area.
A determination of attainment under the Clean Data Policy does not
serve to
[[Page 26237]]
alter the area's nonattainment designation. CDDs are not redesignations
to attainment. For the EPA to redesignate an area to attainment the
state must submit, and the EPA must approve, a redesignation request
for the area that meets the requirements of CAA section 107(d)(3).
III. The EPA's Analysis Supporting a Clean Data Determination for the
Piti-Cabras Area
The EPA may issue a CDD for an SO<INF>2</INF> nonattainment area if
the most recent three years of air quality monitoring data from a
monitor sited in the area of peak ambient SO<INF>2</INF> concentrations
show attainment of the NAAQS and any other relevant information, such
as dispersion modeling, show the area is meeting the NAAQS, or based on
modeling of actual emissions or permitted allowable emissions. Initial
designations for the 2010 SO<INF>2</INF> NAAQS were based on the EPA's
technical assessment of, and conclusions regarding the weight of
evidence for, each area, including but not limited to available air
quality monitoring data (for the three most recent calendar years) and/
or air quality modeling. In the case of the Piti-Cabras area, there are
no available monitoring data.
For a CDD, in the absence of available monitoring data, air quality
dispersion modeling based upon the most recent three years of actual
emissions or permitted allowable emissions should show attainment of
the 2010 SO<INF>2</INF> NAAQS. In this case, the EPA's modeling
analysis was based upon permitted allowable emissions.
A. Overview of the EPA's Modeling Analysis for the Piti-Cabras Area
The EPA's SO<INF>2</INF> Modeling Technical Assistant Document
(``Modeling TAD'') outlines modeling approaches for SO<INF>2</INF>
NAAQS attainment designations to assist State, local, and Tribal air
agencies in the characterization of ambient air quality in areas with
significant SO<INF>2</INF> emission sources.\14\ The EPA's
SO<INF>2</INF> Modeling TAD and the Guidance for 1-Hour SO<INF>2</INF>
Nonattainment Area SIP Submissions outline recommended modeling
approaches and provide recommendations on several aspects of dispersion
modeling in this context, including the use of permitted allowable
emissions, source characterization, meteorological data, model
selection, and background concentrations. Consistent with the approach
set forth in the SO<INF>2</INF> Modeling TAD and the Guidance for 1-
Hour SO<INF>2</INF> Nonattainment Area SIP Submissions, the EPA
conducted a dispersion modeling analysis for the Piti-Cabras area to
show the impact on air quality of all large SO<INF>2</INF> emissions
sources.\15\
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\14\ EPA, Office of Air Quality Planning and Standards,
``SO<INF>2</INF> NAAQS Designations Modeling Technical Assistance
Document,'' August 2016.
\15\ We note that Guam EPA provided processed meteorological and
surface datafiles for input to AERMOD and AERMOD files to assist in
the modeled demonstration. Subsequently, we refined AERMOD input
files for purposes of conducting the modeling work discussed here.
See Docket items A-1 to A-3 for relevant email exchanges between
Guam EPA, Guam Power Authority, TRC Corporation, and EPA Region 9.
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For this area, the primary sources of SO<INF>2</INF> emissions
include the Piti facility, which consists of Units 8 and 9, and the
Cabras facility which consists of Units 1 and 2. Nearby, the TEMES
power plant and commercial and Navy marine vessel ports are also
significant emitters of SO<INF>2</INF>. No other sources on or beyond
the island were determined to have the potential to cause concentration
gradient impacts within the area of analysis. We chose to model these
facilities using the federally enforceable emissions limits for
SO<INF>2</INF>. Pursuant to a consent decree with the United States,
GPA was required by July 31, 2022, and continuing thereafter, to use
only ultra-low sulfur diesel (ULSD) to power Piti Units 8 and 9, and by
December 31, 2022, to use fuel oil with no greater than 0.2 percent
sulfur by weight to power Cabras Units 1 and 2.\16\ We also note that,
since an explosion and fire in August 2015, Cabras units 3 and 4 have
not been operational, which was memorialized in a 2020 consent decree.
The consent decree also required the permanent retirement of Cabras
units 3 and 4 by May 20, 2020. The TEMES (Piti 7) facility is limited
to use of 0.5 percent sulfur under the terms of its current permit.\17\
Accordingly, emissions rates corresponding to these fuel sulfur levels
were used in the modeling.
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\16\ D. Guam, Case 1:20-cv-00007, Document 5, Filed 04/20/20; D.
Guam, Case 1:20-cv-00007, Document 7, Filed 01/14/22. See also Guam
Power Authority, Semi-Annual Report dated January 31, 2024, included
in the docket for this action, for compliance verification from GPA.
\17\ GEPA Title V Operating Permit, Taiwan Electrical &
Mechanical Services, Inc. (TEMES Guam), Permit Number:02-
MAJFOPP0329.12, issued March 29, 2007, section II.C.5.
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The modeling TSD prepared by the EPA for this rulemaking contains a
summary of the facilities in the modeling analysis and their associated
potential to emit (PTE) rates.\18\
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\18\ The Modeling TSD is included in the docket for this
rulemaking.
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Based on the source-specific annual SO<INF>2</INF> emissions in the
Modeling TSD, permitted allowable emissions from the Piti facility have
been reduced by 99.9 percent between original designation and CDD
modeling periods, emissions from the Cabras facility have been reduced
by 90 percent between designation and CDD modeling periods, and marine
vessel emissions have been reduced by 75 percent between designation
and CDD modeling periods.
The EPA modeled the emissions impacts from the Cabras, Piti, TEMES,
and marine vessel facilities and sources described in this document in
the Piti-Cabras area. The EPA used permitted allowable emissions for
the Cabras, Piti, TEMES, facilities, and marine vessel emissions. The
EPA's analysis uses the American Meteorological Society/Environmental
Protection Agency Regulatory Model (AERMOD), with pre-processing input
data from the EPA's Regulatory Model Terrain Pre-processor (AERMAP) and
the EPA's AERMOD Meteorological Preprocessor (AERMET) models. AERMOD is
a steady-state plume model that incorporates air dispersion based on
planetary boundary layer (PBL) turbulence structure and scaling
concepts, including treatment of both surface and elevated sources, and
both simple and complex terrain. AERMAP is a stand-alone terrain pre-
processor, which is used to both characterize terrain and generate
receptor grids for use in AERMOD. AERMET is a stand-alone program which
provides AERMOD with the information it needs to characterize the state
of the surface and mixed layer, and the vertical structure of the PBL.
The EPA's modeling comports with the EPA's SO<INF>2</INF> Modeling TAD
and the Guidance for 1-Hour SO<INF>2</INF> Nonattainment Area SIP
Submissions, with additional guidance provided by EPA's AERMOD
Implementation Guide along with appropriate sections of 40 CFR part 51,
appendix W and AERMOD, AERMAP, and AERMET user guides.
The EPA developed the receptor grid consistent with the
SO<INF>2</INF> Modeling TAD. For the area of analysis, the EPA placed
receptors at a spacing of 25 meters along the ambient air boundary
around GPA sources, a spacing of 50 meters out to a distance of 1
kilometer from each major source,\19\ a spacing of 100 meters from that
point out to a distance of 2 kilometers from a major source, a spacing
of 250 meters from that point out to a distance of 10 kilometers from a
major source, and a spacing of 500 meters from that point out to the
furthest coast of the island. Additional receptors were placed to
locate the area of maximum modeled concentration. The receptor network
covered the island
[[Page 26238]]
of Guam. Consistent with the Modeling TAD, the EPA placed receptors in
locations that would be considered ambient air relative to each modeled
facility, including other facilities' property. The EPA's selected
modeling domain for the CDD analysis captures the maximum modeled
concentration from the primary emissions sources in the Piti-Cabras
area, per the appendix W modeling guidance. For further information on
the receptor grid utilized for the EPA's modeling analysis, refer to
the AERMAP/Model Receptor Development section of EPA's Modeling TSD
prepared in support of this rulemaking.
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\19\ In this case, we are referring to a major source of
SO<INF>2</INF> in the Piti-Cabras area, defined in section III.A of
this proposed rulemaking.
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In accordance with the EPA's SO<INF>2</INF> Modeling TAD, the EPA
selected the surface meteorology from an onsite meteorological tower
located at the Cabras Plant and coincident upper air observations from
the Guam Airport (GUM) as best representative of meteorological
conditions within the area of analysis. The modeling analysis used
surface data in Integrated Surface Hourly Data (ISHD) format and upper
air data in Forecast Systems Laboratory (FSL) format for GUM from 2011
through 2015 for analysis.\20\ The onsite meteorological data of wind
speed and direction from the 60-meter tower level located at the Cabras
Plant were used as the primary source of surface wind data for the
analysis. Onsite data collected from 2011 to 2013 were used, as this
was the most recent data collection available.
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\20\ Review of the data indicated that observations of cloud
cover and other stability-type data necessary to run AERMOD were
missing for a significant portion of the year 2014 and this year did
not meet minimum data collection requirements. Thus, the three- year
consecutive data period of 2011 through 2013 was used in this
analysis.
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To estimate surface characteristics of the area of analysis, Guam
EPA did not use AERSURFACE because the National Land Cover Dataset is
not available for Guam. Instead, Guam EPA used Coastal Change Analysis
Program data for Guam for 2005 to determine surface micro-
meteorological characteristics at the primary on-site meteorological
station. The Territory estimated values for albedo and the Bowen ratio
\21\ using a ten-by-ten-kilometer area. The Territory estimated values
for eight spatial sectors out to 1 kilometer centered around the onsite
meteorological station at an annual temporal resolution for wet and
average conditions for calculating the surface roughness. These data
were then provided to the EPA by Guam EPA for use in these modeling
analyses.
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\21\ The Bowen ratio is a method generally used to calculate
heat lost or heat gained in a substance.
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Meteorological data from the above surface and upper air National
Weather Service (NWS) stations were used in generating AERMOD-ready
files with the AERMET processor. The output meteorological data created
by the AERMET processor is used with AERMOD input files for AERMOD
modeling runs. The Territory followed the methodology and settings
presented in the SO<INF>2</INF> NAAQS Designations Modeling Protocol
for the Island of Guam, dated June 22, 2016, in the processing of the
raw meteorological data into an AERMOD-ready format.\22\
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\22\ For designations technical discussions, see the EPA's
Technical Support Document, Chapter 11, Section 3, 6-26, available
in the docket for this rulemaking.
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Hourly surface meteorological data records are read by AERMET and
include all the necessary elements for data processing. However, wind
data taken at hourly intervals may not always portray wind conditions
for the entire hour, which can be variable in nature. Hourly wind data
may also be overly prone to indicate calm conditions, which are not
modeled by AERMOD. In order to better represent actual wind conditions
at the meteorological tower, Automated Surface Observing System (ASOS)
wind data of 1-minute duration was provided by the GUM NWS station.
These ASOS data were subsequently integrated into the AERMET processing
to produce final hourly wind records of AERMOD-ready meteorological
data that better estimate hourly average conditions and that are less
prone to over-report calm wind conditions. This allows AERMOD to apply
more hours of meteorology to modeled inputs, consequently producing a
more complete set of modeled concentrations. To prevent the computation
of unreasonably and excessively high concentrations that could be
produced by AERMOD in calm winds, Guam EPA set a minimum wind speed
threshold of 0.5 meters per second in processing meteorological data
for use in AERMOD, as suggested in the User's Guide for the AERMOD
Meteorological Preprocessor (AERMET).\23\ In setting this threshold, no
wind speeds lower than this value were used for determining
concentrations. This threshold was specifically applied to the 1-minute
wind data.
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\23\ User's Guide for the AERMOD Meteorological Preprocessor
(AERMET), EPA, November 2024.
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In accordance with the EPA's SO<INF>2</INF> Modeling TAD, the
background concentration was calculated using data from the monitoring
site at Nimitz Hill, which operated from 1999 to 2000, but is no longer
in operation. Data collected when the monitor was within a 90-degree
downwind sector from the modeled sources were excluded in the
background concentration calculation to avoid including facility
impacts in the background concentration, as they are explicitly
modeled. These data were the most representative of the area due to its
location, being both closer to the GPA sources than one other option
and downwind of the sources during westerly winds, unlike another
option. Furthermore, the Nimitz Hill monitor is located inland in
mountainous terrain, similar to where the highest concentrations were
expected based on designations modeling. Although other monitoring
sites were considered as well, their 99th percentile concentrations
without excluding the 90-degree sector were lower, suggesting that the
Nimitz Hill monitor was representative, but conservative. The
subsequent background concentration for this area of analysis was
determined by the Territory to be 29 micrograms per cubic meter ([mu]g/
m\3\), or 11 ppb,\24\ which was incorporated into the final AERMOD
results.
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\24\ The SO<INF>2</INF> NAAQS level is expressed in ppb but
AERMOD gives results in [mu]g/m\3\. The conversion factor for
SO<INF>2</INF> (at the standard conditions applied in the ambient
SO<INF>2</INF> reference method) is 1 ppb = approximately 2.619
[mu]g/m\3\.
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To capture the CDD model impacts, the physical stack parameters and
hourly, actual SO<INF>2</INF> emissions rates must be properly
constructed. The CDD modeling analysis utilized stack and building
information and is described in detail in the Source Characterization
section of the Modeling TSD prepared by the EPA in support of this
rulemaking.
B. Results of the EPA's Air Quality Modeling Analysis
The EPA's modeling analysis utilized meteorological data, permitted
allowable hourly SO<INF>2</INF> emissions, and corresponding hourly
stack velocities and stack temperatures to simulate SO<INF>2</INF>
concentrations over the Piti-Cabras nonattainment area. This modeling
analysis shows that in 2023, the Piti-Cabras area did not violate the
2010 1-hour SO<INF>2</INF> NAAQS based on allowable SO<INF>2</INF>
emissions from sources within or near the area.\25\
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\25\ We note that since the EPA is modeling allowable emissions,
the results are the same for 2024 and 2025, as allowable emissions
have remained the same each year.
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The EPA's main modeling analysis based on 2023 allowable emissions
showed a peak design value (i.e., the 3-year average of the annual 99th
percentile of daily maximum 1-hour average concentrations, or the 99th
percentile concentrations) of 178 [mu]g/m\3\.
[[Page 26239]]
This modeled value is approximately 91 percent of the level of the 75
ppb (196.4 [mu]g/m\3\) 2010 SO<INF>2</INF> NAAQS. For added
conservatism in the modeled demonstration, the EPA conducted additional
AERMOD runs which included numerous small generators and boilers
located in the nonattainment area that were not expected to cause
violations of the NAAQS based on modeling performed during the
designations process. Additional details of these runs can be found in
appendix A of the Modeling TSD. In summary, the inclusion of emissions
from these small sources into the modeling analysis also do not result
in violations of the NAAQS.
This analysis demonstrates that the Piti-Cabras area is attaining
the 2010 1-hour SO<INF>2</INF> NAAQS, based on allowable emissions
beginning in 2023. As a result, the Piti-Cabras area for the 2010
SO<INF>2</INF> NAAQS meets the EPA criteria for the area to qualify for
a CDD.
IV. Proposed Action
The EPA is proposing to issue a CDD for the Piti-Cabras area.
Finalizing this CDD would suspend the requirements for the Piti-Cabras
area to submit an attainment demonstration and certain other associated
nonattainment planning requirements for so long as the Piti-Cabras area
continues to attain the 2010 SO<INF>2</INF> NAAQS.\26\ A final CDD
would also suspend the EPA's obligation to promulgate a FIP and the
sanctions clocks associated with the FFS issued on November 3,
2020,\27\ with regard to the attainment demonstration, RACM/RACT, RFP,
emissions limitations and control measures as necessary to provide for
attainment, and contingency measures. If this CDD is finalized, those
elements of the EPA's obligation as to this nonattainment area under
the consent decree in Center for Biological Diversity et al. v. Regan,
No. 4:24-cv-01900 (N.D. Cal.), doc. 28, paragraphs 1.c-d, 2, will be
met. Guam EPA would still be required to submit an emissions inventory
required by CAA section 172(c)(3) and a nonattainment new source review
(NNSR) program required by CAA section 172(c)(5).\28\ This proposed
rulemaking is consistent with the EPA's long-held interpretation of CAA
requirements.
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\26\ On December 19, 2024, the EPA issued a finding that the
Piti-Cabras nonattainment area failed to attain the 2010
SO<INF>2</INF> NAAQS by the statutory attainment date of April 9,
2023. 89 FR 103819. This finding triggered a requirement for Guam
EPA to submit a plan demonstrating attainment of the 2010
SO<INF>2</INF> NAAQS as expeditiously as practicable, but no later
than December 19, 2030. Id. at 103822. A final CDD would suspend the
attainment-related requirements triggered by the finding of failure
to attain, as well as the attainment-related requirements stemming
from the original designation of the area as nonattainment.
\27\ 85 FR 69504, November 3, 2020.
\28\ Guam EPA submitted a SIP revision addressing NNSR on March
13, 2025. The EPA is currently evaluating this submittal for
completeness.
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Finalizing this rulemaking would not constitute a redesignation of
the Piti-Cabras area to attainment for the 2010 SO<INF>2</INF> NAAQS
under section 107(d)(3) of the CAA. The Piti-Cabras area will remain
designated nonattainment for the 2010 SO<INF>2</INF> NAAQS until such
time as the EPA determines that the area meets the CAA requirements for
redesignation to attainment and takes action to redesignate the area.
V. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be found at <a href="https://www.epa.gov/laws-regulations/laws-and-executive-orders">https://www.epa.gov/laws-regulations/laws-and-executive-orders</a>.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is not a significant regulatory action and was
therefore not submitted to the Office of Management and Budget (OMB)
for review. This action proposes to issue a Clean Data Determination
for the Piti-Cabras area in Guam.
B. Executive Order 14192: Unleashing Prosperity Through Deregulation
Executive Order 14192 does not apply because it is not a
significant regulatory action and is therefore exempted from review
under Executive Order 12866.
C. Paperwork Reduction Act (PRA)
This action does not impose an information collection burden under
the PRA. This action proposes to determine that the Piti-Cabras area is
attaining the 2010 SO<INF>2</INF> NAAQS. Thus, this proposed action
does not impose additional requirements beyond those imposed by
territorial law.
D. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities beyond those
imposed by state law. The proposed CDD does not create any new
requirements and does not directly regulate any entities.
E. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. This action does not impose additional requirements
beyond those imposed by state law. Accordingly, no additional costs to
state, local, or tribal governments, or to the private sector will
result from this action.
F. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government. This
action proposes a CDD for the Piti-Cabras nonattainment area under the
CAA.
G. Executive Order 13175: Coordination With Indian Tribal Governments
This action does not have Tribal implications, as specified in
Executive Order 13175, because 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, and it will not
impose substantial direct costs on tribal governments or preempt tribal
law. Thus, Executive Order 13175 does not apply to this action.
H. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
The EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that the EPA has reason to believe may disproportionately affect
children, per the definition of ``covered regulatory action'' in
section 2-202 of the Executive Order. Therefore, this action is not
subject to Executive Order 13045 because it merely proposes a CDD.
Furthermore, the EPA's Policy on Children's Health does not apply to
this action.
I. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use
This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.
[[Page 26240]]
J. National Technology Transfer and Advancement Act (NTTAA)
Section 12(d) of the NTTAA directs the EPA to use voluntary
consensus standards in its regulatory activities unless to do so would
be inconsistent with applicable law or otherwise impractical. The EPA
believes that this action is not subject to the requirements of section
12(d) of the NTTAA because application of those requirements would be
inconsistent with the CAA.
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Sulfur oxides, Reporting and
recordkeeping requirements.
Authority: 42 U.S.C. 7401 et seq.
Dated: June 2, 2025.
Joshua F.W. Cook,
Regional Administrator, Region IX.
[FR Doc. 2025-11326 Filed 6-18-25; 8:45 am]
BILLING CODE 6560-50-P
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This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.