[Federal Register: July 21, 2010 (Volume 75, Number 139)]
[Proposed Rules]
[Page 42346-42361]
[DOCID:fr21jy10-19]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2010-0285; FRL-9177-2]

Approval and Promulgation of Air Quality Implementation Plans;
Colorado; Attainment Demonstration for the 1997 8-Hour Ozone Standard,
and Approval of Related Revisions

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to act on proposed revisions to Colorado's
State Implementation Plan (SIP). On June 18, 2009, Colorado submitted
proposed SIP revisions intended to ensure attainment of the 1997 ozone
National Ambient Air Quality Standards (NAAQS) in the Denver Metro
Area/North Front Range nonattainment area by 2010. The June 18, 2009
submittal consists of an ozone attainment plan, which includes emission
inventories, a modeled attainment demonstration using photochemical
grid modeling, a weight of evidence analysis, and 2010 motor vehicle
emissions budgets for transportation conformity. The submittal also
includes revisions to Colorado Regulation Numbers 3 and 7 and to
Colorado's Ambient Air Quality Standards Regulation. EPA is proposing
to approve the attainment demonstration, the rest of the ozone
attainment plan, with limited exceptions, and the revisions to Colorado
Regulation Number 3, Parts A and B. EPA is proposing to approve
portions of the revisions to Colorado Regulation Number 7 and to
disapprove other portions. EPA is proposing to disapprove Colorado
Regulation Number 3, Part C, and Colorado's Ambient Air Quality
Standards Regulation. EPA is proposing to disapprove limited portions
of the ozone attainment plan. EPA is proposing these actions pursuant
to section 110 and part D of the Clean Air Act (CAA) and EPA's
regulations.

DATES: Comments must be received on or before August 20, 2010.

ADDRESSES: Submit your comments, identified by Docket ID Regulation
Number EPA-R08-OAR-2010-0285, by one of the following methods:
     http://www.regulations.gov. Follow the on-line
instructions for submitting comments.
     E-mail<EMAIL_ADDRESS>     Fax:<PHONE_NUMBER> (please alert the individual listed in
the FOR FURTHER INFORMATION CONTACT if you are faxing comments).
     Mail: James Kenney, Air Program, EPA Region 8, Mailcode
8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-1129.
     Hand Delivery: James Kenney, Air Program, EPA, Region 8,
Mailcode 8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-1129. Such
deliveries are only accepted Monday through Friday, 8 a.m. to 4:30
p.m., excluding Federal holidays. Special arrangements should be made
for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID Regulation Number
EPA-R08-OAR-2010-0285. EPA's policy is that all comments received will
be included in the public docket without change and may be made
available online at http://www.regulations.gov, including any personal
information provided, unless the comment includes information claimed
to be Confidential Business Information (CBI) or other information
whose disclosure is restricted by statute. Do not submit information
that you consider to be CBI or otherwise protected through http://
www.regulations.gov or e-mail. The http://www.regulations.gov web site
is an ``anonymous access'' system, which means EPA will not know your
identity or contact information unless you provide it in the body of
your comment. If you send an e-mail comment directly to EPA, without
going through http://www.regulations.gov, your e-mail address will be
automatically captured and included as part of the comment that is
placed in the public docket and made available on the Internet. If you
submit an electronic comment, EPA recommends that you include your name
and other contact information in the body of your comment and with any
disk or CD-ROM you submit. If EPA cannot read your comment due to
technical difficulties and cannot contact you for clarification, EPA
may not be able to consider your comment. Electronic files should avoid
the use of special characters, any form of encryption, and be free of
any defects or viruses. For additional information about EPA's public
docket, visit the EPA Docket Center homepage at http://www.epa.gov/
epahome/dockets.htm.
    Docket: All documents in the docket are listed in the http://
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 http://

www.regulations.gov or in hard copy at the Air Program, EPA Region 8,
1595 Wynkoop Street, Denver, Colorado 80202-1129. 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 a.m. to 4
p.m., excluding Federal holidays.

FOR FURTHER INFORMATION CONTACT: James C. Kenney, Air Program, EPA
Region 8, Mailcode 8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-
1129, phone<PHONE_NUMBER>, e-mail<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Definitions

    For the purpose of this document, we are giving meaning to certain
words or initials as follows:
     The words or initials Act or CAA mean or refer to the
Clean Air Act, unless the context indicates otherwise.
     The words EPA, we, us or our mean or refer to the United
States Environmental Protection Agency.
     The initials SIP mean or refer to State Implementation
Plan.
     The words Colorado and State mean the State of Colorado.

Table of Contents

I. General Information
II. What action is EPA proposing?
III. What is the background of this action?
IV. What is EPA's evaluation of the SIP revision?
    A. Procedural Requirements
    B. Monitoring
    C. Emission Inventories
    D. Photochemical Grid Modeling
    E. Modeled Attainment Demonstration
    F. Weight of Evidence
    G. Specific OAP Language
    H. SIP Control Measures
    I. Transportation Conformity
V. Consideration of Section 110(l) of the CAA
VI. Proposed Action
VII. Statutory and Executive Order Reviews

I. General Information

What should I consider as I prepare my comments for EPA?

    1. Submitting CBI: Do not submit CBI to EPA through http://
www.regulations.gov or e-mail. Clearly mark the part or all of the
information that you claim to be CBI. For CBI information in a disk or
CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as
CBI and then identify electronically within the disk or CD ROM the
specific information that is claimed as CBI. In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket.
Information so marked will not be disclosed except in accordance with
procedures set forth in the Code of Federal Regulations (CFR) pursuant
to 40 CFR part 2.
    2. Tips for Preparing Your Comments: When submitting comments,
remember to:
     Identify the rulemaking by docket number and other
identifying information (subject heading, Federal Register date and
page number).
     Follow directions--The agency may ask you to respond to
specific questions or organize comments by referencing a CFR part or
section number.
     Explain why you agree or disagree; suggest alternatives
and substitute language for your requested changes.
     Describe any assumptions and provide any technical
information and/or data that you used.
     If you estimate potential costs or burdens, explain how
you arrived at your estimate in sufficient detail to allow for it to be
reproduced.
     Provide specific examples to illustrate your concerns, and
suggest alternatives.
     Explain your views as clearly as possible, avoiding the
use of profanity or personal threats.
     Make sure to submit your comments by the comment period
deadline identified.

II. What action is EPA proposing?

    As enumerated below, EPA is proposing various actions on Colorado's
proposed revisions to its State Implementation Plan (SIP) that it
submitted to EPA on June 18, 2009, to ensure attainment of the 1997
ozone National Ambient Air Quality Standards (NAAQS) in the Denver
Metro Area/North Front Range (DMA/NFR) nonattainment area. The DMA/NFR
nonattainment area includes Adams, Arapahoe, Boulder, Broomfield,
Denver, Douglas, and Jefferson Counties, and portions of Larimer and
Weld Counties (40 CFR 81.306).
    Colorado's proposed SIP revisions consist of the following parts:
     8-Hour Ozone Attainment Plan (OAP), which includes
monitoring information, emission inventories, a modeled attainment
demonstration using photochemical grid modeling, a weight of evidence
analysis, and 2010 motor vehicle emissions budgets (MVEBs) for
transportation conformity.
     Revisions to Regulation Number 3, Parts A, B, and C.
     Revisions to Regulation Number 7.
     Revisions to Colorado's Ambient Air Quality Standards
Regulation.
    We are proposing to approve Colorado's 2010 attainment
demonstration for the 1997 8-hour ozone NAAQS. We are proposing to
approve the motor vehicle emissions budgets contained in the OAP. We
are proposing to approve all other aspects of the OAP, with the
following limited exceptions: we are proposing to disapprove the last
paragraph on page IV-1 and the first paragraph on page IV-2 of the OAP,
we are proposing to disapprove the words ``federally enforceable'' in
the second to last paragraph on page V-6 of the OAP, and we are
proposing to disapprove the reference to Attachment A in the OAP's
Table of Contents and on page IV-3 of the OAP.
    We are proposing to approve the revisions to Colorado Regulation
Number 3, Parts A and B. We are proposing to disapprove the revisions
to Colorado Regulation Number 3, Part C.
    We are proposing to approve the following portions of the revisions
to Colorado Regulation Number 7:
     Revisions to Sections I through XI, except for Colorado's
repeal of Section II.D.
     Revisions to Sections XIII through XVI.
    We are proposing to disapprove the following portions of the
revisions to Colorado Regulation Number 7:
     Colorado's proposed repeal of Section II.D.
     Revisions to Section XII.
    We are proposing to disapprove the revisions to Colorado's Ambient
Air Quality Standards Regulation.
    The provisions we are proposing to approve meet the requirements of
the CAA and our regulations, including 40 CFR 81.300(e)(3)(ii)(D). The
provisions we are proposing to disapprove are inconsistent with CAA
requirements and our regulations. The specific bases for our proposed
actions and our analyses and findings are discussed in this proposed
rulemaking. Technical information that we rely upon in this proposal is
contained in the State's technical support document (TSD). The TSD is
available on-line at http://www.regulations.gov, Docket No. EPA-R08-
OAR-2010-0285.

III. What is the background of this action?

    On July 18, 1997, EPA promulgated a revised 8-hour ozone standard
of 0.08 parts per million (ppm) (62 FR 38855). Ozone is formed from the
photochemical reaction of nitrogen oxides (NOX) with
volatile organic compounds (VOCs). Under EPA regulations (40 CFR part
50, Appendix I), the 1997 0.08 ppm 8-hour ozone

NAAQS is attained when the 3-year average of the annual fourth highest
daily maximum 8-hour average ambient ozone concentrations is less than
or equal to 0.08 ppm. Forty CFR part 50, Appendix I, section 2.3,
directs that the third decimal place of the computed 3-year average be
rounded, with values equal to or greater than 0.005 rounding up. Thus,
under our regulations, a computed 3-year average ozone concentration of
0.085 ppm is the smallest value that is considered to be greater than
0.08 ppm and a violation of the standard.
    On April 30, 2004, we designated areas as attaining or not
attaining the 1997 8-hour ozone NAAQS. As part of that rule, we
deferred the effective date of a designation as nonattainment for
multiple areas of the country, including the DMA/NFR area. These areas,
which were called Early Action Compact (EACs) areas, agreed to follow a
program to achieve early reduction of emissions necessary to attain the
1997 8-hour standard in order to attain that standard no later than
December 31, 2007 (69 FR 23857). Because the DMA/NFR area violated the
1997 8-hour standard during the summer of 2007, the nonattainment
designation for the area became effective on November 20, 2007.
    Our regulations addressing EAC areas that failed to attain the 1997
8-hour ozone standard by December 31, 2007 (40 CFR Sec.
81.300(e)(3)(ii)(D)) required that Colorado submit an attainment
demonstration SIP for the 1997 8-hour standard. Colorado submitted its
revised attainment demonstration SIP for the DMA/NFR area on June 18,
2009.

IV. What is EPA's evaluation of the SIP revision?

A. Procedural Requirements

    The CAA requires that states meet certain procedural requirements
before submitting SIP revisions to EPA. Specifically, section 110(a)(2)
of the CAA requires that states adopt SIP revisions after reasonable
notice and public hearing.
    The Colorado Air Quality Control Commission (AQCC) provided notice
in the Colorado Register on October 10, 2008 and held a public hearing
on the SIP revision on December 11 and 12, 2008. The Colorado AQCC
adopted the SIP revision on December 12, 2008. The SIP revision became
State effective on January 30, 2009.\1\ Colorado met the CAA's
procedural requirements for reasonable notice and public hearing.
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    \1\ State revisions to the SIP do not become federally effective
unless and until they are approved by EPA. 40 CFR 51.105.
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B. Monitoring

    The monitoring section of the OAP provides information with respect
to the location of ozone monitors in Colorado (from southern
Metropolitan Denver to northern Fort Collins, including Rocky Mountain
National Park); the State's ambient air quality data assurance program;
a description and commitment for continued operation of the ozone
monitoring network; and relevant 8-hour average ozone monitoring data
and recovery rates from 2000 through September 2008.
    Ozone monitoring data was collected following 40 CFR part 58; EPA's
``Quality Assurance Handbook for Air Pollution Measurement Systems,
Vol. II--Ambient Air Quality Monitoring Program''; the Colorado Air
Pollution Control Division's (APCD) Quality Management Plan and Quality
Assurance Project Plan documents; and Colorado's Federally-approved
monitoring SIP (September, 23, 1993, 58 FR 49435).
    Data for 2005-2007 and 2006-2008 reflect violations of the 8-hour
ozone NAAQS at the Rocky Flats North monitor (values of 0.085 and 0.086
ppm, respectively). Monitoring data are used as a basis for
photochemical grid modeling in the attainment demonstration, a process
described below. In the OAP, Colorado indicates that it will continue
to operate an appropriate air quality monitoring network in accordance
with 40 CFR part 58.

C. Emissions Inventories

    In the OAP, Colorado presents three different emissions inventories
for the DMA/NFR nonattainment area: 2006 base case, 2010 base case, and
2010 control case. The inventories, in tons per summer day, represent
emissions estimates for all source categories during a typical summer
day when ozone formation is pronounced. The emissions inventories
catalog NOX and VOC emissions because these pollutants are
precursors to ozone formation.
    The 2006 base case inventory is the ``base year'' inventory for the
attainment demonstration. Base year inventories are developed to help
determine the emissions reductions needed to demonstrate attainment of
the NAAQS. A base year emissions inventory serves as the starting point
for attainment-demonstration air quality modeling and for determining
the need for additional SIP control measures.
    Using 2006 as the base year emissions inventory ensures that the
inventory reflects one of the years used for calculating the design
value that resulted in the area's nonattainment designation. The design
value is the 3-year average of the annual fourth highest daily maximum
8-hour average ozone concentration (see 40 CFR part 50, Appendix D). In
Colorado's case, the Denver area was violating the ozone standard
during the period of 2005-2007, and, therefore, the nonattainment
designation became effective.
    The 2010 base case emissions inventory assumes the same federally
enforceable control measures that were in place in 2006 and all
federally enforceable control measures that became effective after
2006. These control measures are described at pages III-1 through III-3
of the OAP. As described in greater detail below, Colorado was able to
demonstrate attainment in 2010 based on the 2010 base case emissions
inventory.
    The 2010 control case emissions inventory assumes the adoption and
implementation of additional control measures beyond the measures
assumed for the 2010 base case. These additional control measures are
described at page V-10 of the OAP (2008 State-only revisions to
Regulation Number 11 that tightened tailpipe standards, 2008 State-only
revisions to Regulation Number 7 that required low-bleed devices for
pneumatic controllers, an increase in the system-wide reduction of
condensate tank VOC emissions from 75% to 81% in 2010, and 7.8 psi RVP
gasoline in the NFR area). While Colorado was able to demonstrate
attainment without these additional control measures, Colorado modeled
the 2010 control case emissions inventory to determine whether
additional reductions in ozone precursors (NOX and VOCs)
beyond the 2010 base case would result in further reductions of ozone.
    The three emissions inventories discussed above (i.e., 2006 base
case emissions inventory, 2010 base case emissions inventory, and the
2010 control case emissions inventory) were developed using EPA-
approved guidelines for stationary, mobile, and area/off-road emission
sources. Point source emissions data were self-reported to the State by
individual sources. On-road mobile source emissions data were estimated
using EPA models (MOBILE6) and Vehicle Miles Traveled (VMT) data. Area/
off-road vehicle emissions were

developed using demographic information. Future emissions were
projected through the use of economic growth modeling and analysis.
Table 1 shows the emissions by source category, in tons per day (tpd),
from the three emission inventories.

                        Table 1--Emissions Inventory Data for Specific Source Categories
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                                                                2006 Base         2010 Base       2010 Control
          Source Category (tons/avg. episode day)          -----------------------------------------------------
                                                              NOX      VOC      NOX      VOC      NOX      VOC
----------------------------------------------------------------------------------------------------------------
Point Sources:
    Electric Generation Units.............................     55.6      0.7     58.5      1.6     58.5      1.6
    External Combustion Boilers...........................      9.5      0.4     10.0      0.5     10.0      0.5
    Industrial Processes..................................     12.5     10.2     14.0     11.0     14.0     11.0
    Petroleum and Solvent Evaporation.....................      0.3     19.0      0.3     22.0      0.3     22.0
    Other.................................................      3.1      1.8      3.6      2.0      3.6      2.0
                                                           -----------------------------------------------------
        Point Sources Subtotal............................     81.0     32.1     86.4     37.0     86.4     37.0
----------------------------------------------------------------------------------------------------------------
Oil and Gas Point & Area Sources:
    Condensate Tanks......................................  .......    126.5  .......    129.6  .......    105.6
    Other O&G Point Sources...............................     22.6      6.8     23.6      8.6     23.6      8.6
    Pneumatic Devices (Area Source).......................  .......     24.8  .......     31.1  .......     12.0
    Unpermitted Fugitives (Area Sources)..................  .......     16.2  .......     20.4  .......     20.4
    Other Area Sources....................................     17.1     10.8     22.5     13.7     22.5     13.7
                                                           -----------------------------------------------------
        O&G Point & Area Sources Subtotal.................     39.7    185.2     46.2    203.3     46.2    160.1
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Area Sources
    Personal Care Products................................  .......      7.1  .......      7.0  .......      7.0
    Household Products....................................  .......     21.4  .......     17.9  .......     17.9
    Automotive Aftermarket Products.......................  .......     11.9  .......     13.0  .......     13.0
    Architectural Coatings................................  .......     20.1  .......     16.8  .......     16.8
    Aircraft..............................................      7.4      1.3      8.2      1.5      8.2      1.5
    Railroad..............................................     12.8      0.5     13.8      0.6     13.8      0.6
    Other Coatings/Pesticides/Cooking/Misc................  .......      3.9  .......      4.1  .......      4.1
                                                           -----------------------------------------------------
        Area Source Subtotal..............................     20.2     66.3     22.1     61.0     22.1     61.0
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Non-Road Mobile Sources:
    Agricultural Equipment................................      7.0      0.9      6.3      0.7      6.3      0.7
    Airport Equipment.....................................      0.7      0.1      0.6      0.1      0.6      0.1
    Commercial Equipment..................................      5.3      6.2      5.1      7.0      5.1      7.0
    Construction and Mining Equipment.....................     35.7      5.5     31.2      4.5     31.2      4.5
    Industrial Equipment..................................     10.5      2.4      6.9      1.4      6.9      1.4
    Lawn and Garden Equip. (Commercial)...................      9.4     35.9      8.9     28.1      8.9     28.1
    Lawn and Garden Equip. (Residential)..................      1.2      7.5      1.2     11.8      1.2     11.8
    Boats/Recreational Equip/Misc.........................      0.7      6.9      0.8      7.8      0.8      7.8
                                                           -----------------------------------------------------
        Non-Road Mobile Source Subtotal...................     70.5     65.3     61.0     61.3     61.0     61.3
                                                           -----------------------------------------------------
        On-Road Mobile Sources Subtotal...................    165.5    129.7    122.9    109.2    118.9    106.0
                                                           -----------------------------------------------------
        Anthropogenic Subtotal............................    376.8    478.6    338.5    471.8    334.6    425.4
                                                           -----------------------------------------------------
        Biogenic Subtotal.................................     53.0    694.0     53.0    694.0     53.0    694.0
                                                           -----------------------------------------------------
            Total.........................................    429.8   1172.6    391.5   1165.8    387.6   1119.4
----------------------------------------------------------------------------------------------------------------

    Colorado employed EPA guidelines for rule effectiveness when
preparing these emission inventories. Rule effectiveness, expressed as
a percentage, represents the ability of a regulatory program to control
point sources to achieve emissions reductions. Based on control
strategies for the oil and gas source category, Colorado used 83
percent for rule effectiveness. A rule effectiveness of 83 percent
discounts the emissions reductions from the control measures by 17
percent. Based on Colorado's analysis, which considered compliance
rates with existing control measures, EPA finds that a value of 83
percent is reasonable for rule effectiveness for oil and gas control
measures. For further detail regarding Colorado's analysis, the reader
should refer to Colorado's TSD.
    For oil and gas point and area sources, the 2010 control case
inventory reflects a 43.2 tpd reduction in VOC emissions as compared to
the 2010 base case inventory. For on-road mobile sources, the 2010
control case inventory reflects a 3.2 tpd reduction in VOC emissions as
compared to the 2010 base case inventory.

D. Photochemical Grid Modeling

    Colorado conducted photochemical grid modeling (hereafter referred
to as ``modeling'') to demonstrate that the emissions control strategy
leads to attainment of the NAAQS by 2010. The modeling followed EPA's
photochemical modeling guidance (Guidance on the Use of Models and
Other Analyses for Demonstrating Attainment of Air Quality Goals for

Ozone, PM2.5, and Regional Haze, EPA-454/B-07-002, April 2007).
    The attainment demonstration modeling utilized the Comprehensive
Air-quality Model with extensions (CAMx), Sparse Matrix Operating
Kernel Emissions (SMOKE) system, and Mesoscale Model 5 (MM5). Colorado
applied these models to data from June 2006 and July 2006. These models
were set up using a nested 36/12/4 kilometer (km) domain structure. The
36 km domain covering most of North America was used to generate
boundary conditions (BCs) for the 12 km modeling domain. CAMx was then
used to simulate ozone formation within the 12/4 km modeling domain.
The CAMx simulation, sensitivity, and control strategy evaluations runs
were made on the 12/4 km modeling domain.
    EPA guidance recommends that model performance be tested against
certain performance goals. Model performance testing is used to
determine the model's reliability in projecting future year ozone
concentrations. Using meteorological and emissions data from a
historical base period, ozone concentrations predicted by the model are
compared to monitored ozone concentrations to determine model
performance.
    EPA's modeling guidance emphasizes the use of graphical and
diagnostic evaluation techniques to assure that the modeling captures
the correct chemical regimes and emission sources that result in high
ozone concentrations (i.e., assuring that the model is getting the
right answer for the right reason). Colorado's model performance
evaluation included such graphical and diagnostic evaluation
techniques. In addition, EPA modeling guidance includes three numerical
performance goals that are useful in evaluating ozone models as part of
the attainment demonstration. These include: unpaired accuracy of the
peak <=20%; normalized mean bias <=15%; and
normalized mean gross error <=35%.
    Using a June 1 through July 30, 2006 episode period, Colorado
calculated the mean normalized bias and gross error statistical
measures using all the predicted and observed hourly ozone pairs,
matched by time and location, for which the observed ozone was equal to
or greater than 0.060 ppm. The evaluation showed that the modeling
achieved the ``Unpaired Accuracy of the Peak'' performance goal of
<=20% for 58 of the 60 simulation days of the episode
(i.e., 97% of the modeled days). There were 58 days rather than 60 with
bias and error comparisons during the episode period because two days
had no observed ozone values greater than 0.060 ppm; thus, no
statistics could be calculated for those two days. Of the 58 days, 50
days (or 86%) achieved EPA's <=15% performance for mean
normalized bias and all of them achieved EPA's performance goal for
mean normalized gross error.
    The CAMx model also exhibited very good agreement for VOC/
NOX ratios on most days, indicating that the model was
simulating the correct chemical regimes. The performance of the CAMx
model in predicting ozone concentrations, and precursor concentrations,
met EPA's guidelines for model performance. The model outputs were
consistent with the day-to-day patterns of observed data, with low bias
and error. EPA concurs with Colorado's assessment that the model was
properly set up, met EPA performance requirements, and was
appropriately used in its application.

E. Modeled Attainment Demonstration

    The modeled attainment demonstration for ozone is one in which
model estimates are used in a relative sense rather than absolute
sense. That is, we take the ratio of the model's future (2010) to
current (2006) predictions at ozone monitors in the DMA/NFR area. We
call these ratios ``Relative Response Factors'' (RRFs). Future ozone
concentrations are estimated at existing monitoring sites by
multiplying a modeled RRF at locations near each monitor by the
observation-based, monitor-specific, baseline design value. The
resulting predicted future concentrations are then compared with the
1997 0.08 ppm 8-hour ozone NAAQS. If the predicted future
concentrations of ozone are lower than 0.08 ppm at all monitors,
attainment is demonstrated. The test for ozone is based on the
calculation of a single mean ozone RRF for each monitor.
    Table 2, below, summarizes the estimated concentrations within the
Colorado 4 km grid domain for Colorado's 2006 base case, 2010 base
case, and final 2010 control measure case modeling. The final 2010
control measure case is not the same as the 2010 control case discussed
in section III.C of this action, above. Unlike the 2010 control case,
the final 2010 control measure case does not include emission
reductions from State-only measures. Also, at the time Colorado
prepared the 2010 control case inventory, the AQCC had not yet adopted
final changes to Regulation Number 7. The final changes included
greater system-wide condensate tank VOC reductions in 2010--85% instead
of 81%--and additional control requirements. Colorado used the final
adopted version of Regulation Number 7 to create a final 2010 control
measure case inventory and then modeled that inventory. For further
details, see page V-7 of the OAP and Appendix I of Colorado's TSD.
    Table 2, below, displays three scenarios: (1) 2005-2007 8-hour
ozone concentration Current Design Values (DVC); (2) projected 2010
base case 8-hour ozone concentration Future Design Values (DVF); and
(3) final 2010 control measure case 8-hour ozone concentration DVFs.
Per EPA guidance, the first set of DVFs in Table 2 (columns 4 and 5)
are shown in ppm to the third decimal place, with additional digits to
the right truncated, for comparison with the NAAQS. (See 40 CFR part
51, Appendix W, section <IP_ADDRESS>, 40 CFR part 50, Appendix I, section
2.1.1, and Guidance on the Use of Models and Other Analyses for
Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and
Regional Haze, EPA-454/B-07-002, April 2007.) The last set of DVFs
(columns 6 and 7) are displayed to the nearest .0001 of a ppm. Although
not relevant to determining attainment of the NAAQS, Colorado included
these last columns as part of its evaluation of model performance, to
attempt to distinguish any differences in the ozone projections between
the 2010 base case and final 2010 control measure modeling and as part
of its weight of evidence analysis.
    The maximum projected 8-hour ozone design value for the 2010 base
case and final 2010 control measure case is 0.084 ppm at the Rocky
Flats North and Fort Collins West monitoring sites. Because all
projected 2010 8-hour ozone design values are below 0.085 ppm, the 2010
base case and final 2010 control measure case both pass the modeled
ozone attainment demonstration test. However, because there are four
monitoring sites with projected 2010 DVFs of 0.082 ppm or higher (0.084
ppm at Rocky Flats North and Fort Collins West, 0.083 ppm at Chatfield,
and 0.082 ppm at NREL), EPA's modeling guidance indicates a ``weight of
evidence'' (WOE) analysis should be performed.

                          Table 2--Projected 2010 8-Hour Ozone DVFs for the 2010 Base Case and Final 2010 Control Measure Case
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                2010 DVF (EPA Guidance) (ppm)   2010 DVF (nearest 0.0001 ppm)
                                                                            DVC (2005-   ---------------------------------------------------------------
               Monitor name                            County               2007) (ppm)                    Final control                   Final control
                                                                                Base case     measure case      Base case     measure case
--------------------------------------------------------------------------------------------------------------------------------------------------------
Welby....................................  Adams........................           0.070           0.070           0.070          0.0702          0.0702
Highland.................................  Arapahoe.....................           0.078           0.077           0.077          0.0773          0.0773
S. Boulder Creek.........................  Boulder......................           0.081           0.080           0.080          0.0808          0.0807
Denver-CAMP..............................  Denver.......................           0.056           0.056           0.056          0.0560          0.0560
Carriage.................................  Denver.......................           0.074           0.074           0.074          0.0741          0.0741
Chatfield State Park.....................  Douglas......................           0.084           0.083           0.083          0.0834          0.0834
USAF Academy.............................  El Paso......................           0.073           0.072           0.072          0.0720          0.0720
Manitou Springs..........................  El Paso......................           0.074           0.073           0.073          0.0737          0.0737
Arvada...................................  Jefferson....................           0.079           0.079           0.079          0.0792          0.0791
Welch....................................  Jefferson....................           0.075           0.075           0.075          0.0750          0.0750
Rocky Flats North........................  Jefferson....................           0.085           0.084           0.084          0.0849          0.0849
NREL.....................................  Jefferson....................           0.082           0.082           0.082          0.0823          0.0822
Fort Collins West--Note: DVC based on two  Larimer......................           0.086           0.084           0.084          0.0849          0.0848
 years of measured data.
Fort Collins.............................  Larimer......................           0.074           0.073           0.073          0.0730          0.0730
Greeley Weld Tower.......................  Weld.........................           0.078           0.077           0.077          0.0777          0.0775
Gunnison.................................  Gunnison.....................           0.068           0.067           0.067          0.0678          0.0678
Larimer..................................  Larimer......................           0.076           0.075           0.075          0.0752          0.0752
--------------------------------------------------------------------------------------------------------------------------------------------------------

    For values that Colorado reported to the nearest 0.0001 of a ppm,
the maximum projected DVF for the 2010 Base Case is 0.0849 ppm at both
the Rocky Flats North and Fort Collins West monitoring sites (see Table
2). According to Colorado's modeling, Colorado's final 2010 control
measures would reduce the DVF at the Fort Collins West monitoring site
by 0.0001 ppm (to 0.0848 ppm) and would have no effect at the Rocky
Flats North monitoring site (0.0849 ppm). Overall, Colorado's modeling
projected that Colorado's final 2010 control measures would reduce the
2010 DVF by 0.0001 ppm at four sites and by 0.0002 ppm at one site,
with the remainder of the monitoring sites having identical DVFs for
the 2010 base case and final 2010 control measure case. The largest
ozone reduction due to Colorado's final 2010 control measures (0.0002
ppm) was projected to occur at the Weld County Tower monitoring site
(Greeley), which is expected given the proximity of the monitor to the
oil and gas developments in Weld County. Weld County is where the
largest VOC emission reductions would occur due to Colorado's final
2010 control measures for condensate storage tanks. These results are
consistent with Colorado's 2010 sensitivity modeling, which found that
proposed oil and gas emission controls would have a bigger impact on
ozone concentrations at Fort Collins West than Rocky Flats North.
    Based on our analysis, we are proposing approval of Colorado's
modeled attainment demonstration. Both the 2010 base case modeling and
the final 2010 control measure case modeling show that the DMA/NFR area
will attain the 8-hour ozone NAAQS by 2010. However, because we are
proposing to disapprove Colorado's revisions to Regulation Number 7,
Section XII, which Colorado relied on in its final 2010 control measure
modeling, our proposed approval of Colorado's attainment demonstration
is based on the 2010 base case modeling.
    Because Colorado's modeling demonstrates attainment in 2010 based
on existing SIP-approved measures, and it is now 2010, such SIP-
approved measures represent all measures necessary to demonstrate
attainment as expeditiously as practicable as per section 172 of the
CAA. Additional control measures would not advance the attainment date.

F. Weight of Evidence

    As noted above, since four monitors (Rocky Flats North, Fort
Collins West, Chatfield, and NREL) modeled concentrations that fall
into the range of 0.082 to 0.087 ppm, a weight of evidence (WOE)
analysis is recommended by EPA (see ``Guidance on the Use of Models and
Other Analyses for Demonstrating Attainment of Air Quality Goals for
Ozone, PM2.5, and Regional Haze,'' EPA-454/B-07-002, April 2007). A WOE
analysis involves one or more supplemental analyses to enhance the
assessment of whether the planned emissions reductions will result in
attainment of the 1997 0.08 ppm 8-hour ozone NAAQS. The WOE analysis
includes: Monitoring and emission inventory trend analysis; review of
the conceptual model for ozone formation along the North Front Range;
additional modeling metrics; alternative attainment test methods; and
assessment of the efficacy of Colorado's SIP-approved regulations,
state-only regulations, and voluntary control measures. The WOE
analysis is then used to determine if the four monitors that modeled
ozone concentrations in the range of 0.082 to 0.087 ppm are expected to
demonstrate attainment of the NAAQS.
    Our review of the WOE analysis identified a number of key points
that provide further evidence that the modeling is reliable and that
the DMA/NFR area will attain the NAAQS. First, although individual
concentrations have been highly variable, the aggregate trend in
weather-corrected 4th maximum time series suggests ozone levels have
been flat from 2004 through 2008. The WOE analysis suggests that ozone
levels are not trending upward in the DMA/NFR and that the modeling
conclusions are reasonable. Second, the WOE analysis of the weekend-
weekday effect \2\ related to potential disbenefits from NOX
reductions shows a stronger effect in the DMA and a weaker effect in
outlying areas. This spatial pattern is consistent with the localized
NOX disbenefit predicted by the photochemical grid modeling;
thus, this aspect of the WOE

analysis supports the validity of the modeling. Third, within the DMA,
potential increases in ozone concentrations due to NOX
emissions reductions from the federal motor vehicle control program do
not appear significant and should not threaten the NAAQS. At monitoring
locations outside the DMA, the WOE analysis suggests that reductions in
NOX emissions will reduce ozone, possibly with greater
efficiency than VOC reductions. Fourth, the WOE analysis includes other
modeled metrics that indicate reductions by 2010 in total ozone, grid
cells over 0.080 and 0.085 ppm 8-hour ozone, and grid cell-hours over
0.080 and 0.085 ppm ozone based on the various control scenarios. For
example, these metrics indicate a reduction in total ozone and grid
cells greater than 0.085 ppm between the 2006 and 2010 base cases of
21% and 14%, respectively. This suggests that the changes in emissions
between the 2006 and 2010 base cases will reduce or have reduced ozone
concentrations.
---------------------------------------------------------------------------

    \2\ Some urban areas show higher ozone levels on weekends. Some
studies indicate that this increase in ozone concentrations may
result from decreased weekend NOX emissions due to fewer
trucks on the road and differences in the distribution of emissions.
Under certain conditions, NOX acts to reduce ozone
concentrations.
---------------------------------------------------------------------------

    EPA finds the WOE analysis provides further support to the
photochemical grid modeling, and the modeling and WOE support a
determination that the area will attain the 1997 0.08 ppm 8-hour ozone
NAAQS by 2010.

G. Specific OAP Language

    We are proposing to disapprove the last paragraph on page IV-1 and
the first paragraph on page IV-2 of the OAP because these paragraphs
indicate that the OAP revises Section XII of Regulation Number 7 as
part of the SIP. We are proposing to disapprove revised Section XII of
Regulation Number 7, and approval of this language in the OAP would
potentially conflict with our proposed disapproval of revised Section
XII. We are proposing to disapprove the words ``federally enforceable''
in the second to last paragraph on page V-6 of the OAP for the same
reason. The language in question reads, ``AQCC action on December 12,
2008 adopted a federally enforceable SIP control measure revising
Regulation No. 7 * * * '' Only our approval can make the revisions
federally enforceable.
    Elsewhere, the OAP discusses ``adopted SIP control measures'' or
provisions that will be part of the SIP. We interpret these various
references as reflecting the AQCC's intent to submit the referenced
regulations to us for approval and not as an indication that they are
already part of the federally approved SIP or that our approval of the
OAP alone will make the referenced regulations part of the federally
approved SIP. We are acting on the referenced regulations as separate
elements.
    We are also proposing to disapprove the reference to Attachment A
in the OAP's Table of Contents and on page IV-3 of the OAP because
Attachment A was not submitted to us with the OAP and because the
revisions referenced as being included in that Attachment A (revisions
to Regulation Number 7, Regulation Number 3, and the Ambient Standards
Regulation) were submitted to us separately for our action. As noted,
we are acting on the revisions to those regulations as separate
elements in this action.

H. SIP Control Measures

Colorado Regulation Number 3
    Colorado submitted revisions to Regulation Number 3, Parts A, B,
and C, along with the OAP. Among other things, Part A requires
stationary sources to submit Air Pollutant Emission Notices (APENs) to
Colorado before emitting pollutants. A source's APEN must include
information about location and nature of the source and expected
emissions. Part A also contains various exemptions from APEN filing.
Colorado's proposed revisions to Part A would remove several of these
exemptions from the regulation. This would subject the specified source
categories to APEN filing and potential regulation under Regulation
Number 7, which uses the APEN-filing threshold in Regulation Number 3,
Part A, as the trigger for applicability of various requirements.
    Regulation Number 3, Part B, contains construction permit
requirements for stationary sources. Part B also contains various
exemptions from minor source construction permit requirements. Part B
contains a generic exemption for sources that are not required to file
an APEN. Colorado recognized that its proposed removal of the APEN-
filing exemption for certain sources under Part A would also have the
effect of subjecting those sources to minor source construction permit
requirements under Part B. For four types of sources, Colorado
determined that this would not be appropriate and adopted a revision to
Part B that would continue to exempt these four types of sources from
minor source construction permitting. The premise behind all the minor
source construction permitting exemptions in Part B is that the
emissions from the specified sources are deemed to have a negligible
impact on air quality.
    Regulation Number 3, Part C, contains Colorado's operating permit
requirements. Colorado submitted proposed revisions to Part C that
remove certain oil and gas activities from Part C's insignificant
activity exemption.
    For the reasons discussed below, we are proposing to approve Parts
A and B.
    The proposed revisions to Regulation Number 3, Part A, eliminate
provisions that exempt the following specific types of oil and gas-
related emission points from the APEN requirements: Petroleum industry
flares with emissions of less than 5 tons per year, specified crude oil
truck loading equipment, oil and gas production wastewater, crude oil
storage tanks, surface water storage impoundments for certain oil
production wastewater, and condensate storage tanks where production
through the tank amounts to less than 730 barrels per year. The
elimination of these exemptions means that the facility will need to
file APENs with the State, which should allow Colorado to collect more
accurate inventory information regarding emissions related to oil and
gas operations. This would also subject the specified source categories
to the condensate storage tank VOC control requirements of Regulation
Number 7, Section XII, which uses the APEN-filing threshold in
Regulation Number 3, Part A, as an applicability threshold.
    The proposed revisions to Regulation Number 3, Part B maintain an
existing exemption from minor source construction permitting
requirements for certain emission points. The emission points consist
of certain petroleum industry flares with emissions less than 5 tons
per year, crude oil truck loading equipment and condensate truck
loading equipment, oil and gas production wastewater, and crude oil
storage tanks. As noted above, under the current SIP-approved version
of Regulation Number 3, Part B, any emission points exempt from filing
APENs are also exempt from minor source construction permit
requirements. See Regulation Number 3, Part B, Section III.D.1.a, as
contained in the EPA-approved SIP at https://yosemite.epa.gov/R8/
R8Sips.nsf/e5e850cc767bc8b3872573a9004cad73/
75c2d810353a706a87256b7b0066624d?OpenDocument. Thus, approval of
Colorado's proposed revisions to Part B would not change the status quo
with regard to construction permitting requirements for these emission
points.
    The revisions to Parts A and B make the SIP more stringent by
subjecting additional emission sources to reporting requirements. We
are proposing to approve these revisions because they strengthen the
SIP.
    Regarding Part B of Regulation Number 3, we note that there is a
discrepancy between the numbering of

the submitted revisions and the EPA-approved SIP. Colorado added new
Sections II.D.1.k, l, m, and n to Part B to specify the four types of
emissions points that will continue to be exempt from minor source
construction permitting requirements. However, in the current EPA-
approved SIP, Section III.D.1 of Part B lists the types of emissions
points that are exempt from minor source construction permitting
requirements.\3\ These emissions points are listed in Sections
III.D.1.a through j. For purposes of this action, we are interpreting
Colorado's proposed revisions to Part B, in the form of Sections
II.D.1.k through n, as being an addition to Section III.D.1, and
following immediately after Section III.D.1.j of Part B of the EPA-
approved SIP. As part of our final rulemaking action, we will craft
appropriate regulatory language to effectuate our interpretation.
---------------------------------------------------------------------------

    \3\ Colorado previously submitted revisions to Part B that
contain changes to the numbering of Part B provisions; we will be
acting on those revisions separately.
---------------------------------------------------------------------------

    EPA is proposing to disapprove Colorado's proposed revisions to
Regulation Number 3, Part C. As noted above, Regulation Number 3, Part
C, contains Colorado's operating permit regulations, which we do not
approve into the SIP. Instead, we approve operating permit regulations
under our operating permit regulations at 40 CFR part 70. Thus, we
intend to consider approval of Colorado's proposed Part C revisions
pursuant to our part 70 regulations at such time as Colorado submits an
appropriate request under 40 CFR 70.4(i). The revisions are meaningless
absent their regulatory context, and that regulatory context is not
part of the EPA-approved SIP and is not incorporated by reference into
40 CFR part 52. Instead, the approval status of Colorado's part 70
program is reflected in 40 CFR part 70, Appendix A. Thus, because we
are obligated to act on the State's SIP submission, we plan to
disapprove these revisions as a revision to the SIP. If the State
requests to withdraw Part C from the SIP revision prior to the time we
take final action, we would not be obligated to take final action
because Part C would no longer be pending before the Agency as a SIP
revision. Additionally, if requested by the State, we will separately
consider these revisions as a revision to the approved operating permit
program for the State.
Colorado Regulation Number 7
    Regulation Number 7 contains various requirements intended to
reduce emissions of ozone precursors. These are in the form of specific
emission limits applicable to various industries and generic Reasonably
Available Control Technology (RACT) requirements. EPA approved the
repeal and re-promulgation of Regulation Number 7 in 1981 (46 FR 16687,
March 13, 1981) and has approved various revisions to parts of
Regulation Number 7 over the years. Most recently, in 2008 EPA approved
revisions to the control requirements for condensate storage tanks in
Section XII (73 FR 8194, February 13, 2008).
    Colorado submitted proposed revisions to Regulation Number 7 along
with the OAP. On November 18, 2009, Colorado corrected the version of
Regulation Number 7 it had submitted to reposition the words ``State
Only'' in various sections of Regulation Number 7.
    Colorado made substantive revisions to certain limited parts of
Regulation Number 7, particularly Section XII, and also made non-
substantive revisions to numerous parts of the regulation. For ease of
consideration, Colorado submitted the full text of Regulation Number 7
as a SIP revision for our approval (with the exception of provisions
designated ``State Only''). We are only seeking comment on Colorado's
proposed changes to the SIP-approved version of Regulation Number 7,
which are described below; we do not view this rulemaking as re-opening
our past approval of the portions of the regulation that were not
substantively modified by the State as part of this submission.
    As noted above, Colorado designated various parts of Regulation
Number 7 ``State Only'' and in Section I.A.1.c indicated that sections
designated ``State Only'' are not federally enforceable. Our
interpretation is that provisions designated ``State Only'' have not
been submitted to us for approval since one of the key purposes of a
SIP approval is to make the submitted regulations federally
enforceable. Instead, we interpret these provisions to have been
submitted for informational purposes. Hence, we are not proposing to
act on the portions of Regulation Number 7 designated ``State Only''
and do not discuss them further unless they impact the portions of the
regulation that Colorado intended to be federally enforceable.
Analysis of Regulation Number 7 Changes by Section
    Section I:
    Section I contains applicability provisions, definitions of new and
existing sources, and related provisions. Except for minor clerical
changes,\4\ this section remains unchanged from the current SIP-
approved version. Thus, we are proposing to approve the changes to
conform the SIP to Colorado's regulation.
---------------------------------------------------------------------------

    \4\ When we describe changes as clerical in this proposed
action, we are referring to changes like section renumbering,
alphabetizing of definitions, minor grammatical and editorial
revisions, and changes in capitalization.
---------------------------------------------------------------------------

    Section II:
    Section II contains general provisions. Section II.A contains
definitions. The State alphabetized the definitions Otherwise, the
definitions are unchanged. The State made minor clerical changes to
Section II.B, which contains an exemption for emissions of organic
compounds having negligible photochemical reactivity. The State made
minor clerical changes to Section II.C, which contains generic RACT
requirements.
    Section II as submitted reflects Colorado's repeal of Sections II.E
and F. Colorado had previously submitted Sections II.E and F to us for
approval, but we never acted on them. Section II.E would have allowed
Colorado to approve alternative emission control plans, compliance
methods, test methods, and test procedures without EPA approval of a
source-specific SIP revision. However, subsequent to submitting Section
II.E to us, Colorado repealed it (in November 2003). Section II.F would
have allowed Gates Rubber Company to satisfy VOC RACT requirements in
Regulation Number 7 related to surface coating operations by obtaining
emission reduction credits from Coors Brewing Company. Gates Rubber
Company stopped operating a few years ago, and Colorado repealed
Section II.F as part of its December 12, 2008 rulemaking.
    We are proposing to approve the changes to Sections II.A, B, and C
as minor, non-substantive revisions. Because section II.E and F were
never approved as part of the SIP, the State repeal of those provisions
has no meaning for this action. However, we are proposing to approve
the language of Regulation Number 7 that reflects the repeal of II.E
and F to conform the SIP to the numbering of Colorado's regulation.
    In addition to the changes noted above, the submitted revision to
Section II reflects Colorado's repeal of Section II.D.\5\ The SIP-
approved version of

Section II.D requires sources to seek a revision to the SIP to gain
approval of alternative control plans and test methods and indicates
that no alternative is effective until the alternative is approved as a
revision to the SIP. Colorado originally adopted Section II.D in
September 1989 to address specific EPA concerns that Colorado's RACT
rule would allow changes to control requirements or test methods
without EPA approval.
---------------------------------------------------------------------------

    \5\ In March of 1996, Colorado adopted changes to Section II.D
as a matter of State law and submitted the revisions to us for
approval. The revisions were part of an effort by Colorado at that
time to establish a de minimis exemption from Regulation Number 7's
RACT requirements. EPA never approved Colorado's 1996 changes to
Section II.D. Based on EPA's indication that it intended to
disapprove Colorado's 1996 changes to Section II.D, Colorado
repealed Section II.D entirely in November 2003. Colorado did not
re-adopt the pre-1996 version of Section II.D, and the version of
Regulation Number 7 that we are considering in this action indicates
that Section II.D has been repealed.
---------------------------------------------------------------------------

    We are proposing to disapprove the repeal of Section II.D for the
following reasons: (1) A court might interpret the repeal to allow the
State to approve alternative control requirements and test methods
without EPA approval, and without public involvement, which could
undermine the enforceability of Regulation Number 7's RACT requirements
and would be inconsistent with the CAA, particularly section 110(i);
(2) the State has offered no explanation or justification for the
repeal; and (3) other sections of Regulation Number 7 still cross-
reference Section II.D as specifying necessary procedures for gaining
approval of alternative control requirements and test methods (See,
e.g., Section IX.A.5.c of Regulation Number 7), and, therefore,
removing Section II.D would introduce ambiguity into the Regulation.
    Our proposed disapproval of the repeal of Section II.D does not
undermine the validity of the attainment demonstration. Rather, it
strengthens it by ensuring that EPA and public review will be required
before a source may use an alternative control requirement or test
method. Such review will help ensure that any such alternative would
not interfere with the effectiveness of the program as relied on for
purposes of demonstrating attainment. Although we are proposing to
disapprove the repeal of Section II.D, our disapproval would not
trigger sanctions or a FIP obligation. This is because the repeal of
Section II.D is not required by the CAA (see CAA section 179), and our
disapproval of the repeal of Section II.D would not leave a deficiency
in the SIP. Section II.D will remain in the SIP after disapproval of
Colorado's proposed repeal, and it will be incumbent on sources and the
State to comply with Section II.D's requirements. Thus, there would be
nothing for the State to correct through a SIP revision and nothing for
us to correct through a FIP.
    Sections III through XI:
    The changes are clerical in nature and do not affect the substance
of the requirements. Therefore, we are proposing to approve the
changes.
    Section XII:
    Section XII contains the emission control requirements for
condensate storage tanks. The State reorganized Section XII and
included additional control requirements for condensate tanks. The
following table outlines the reorganization/renumbering contained in
Colorado's proposed revisions to Section XII:

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                            Corresponding EPA-
 Colorado revised section XII section      approved section XII                                           Subject
                number                        section number
--------------------------------------------------------------------------------------------------------------------------------------------------------
XII.A.................................  XII.A....................  Applicability.
XII.A.1...............................  XII.A.1..................  Applicability.
XII.A.1.a through c...................  XII.A.1.a through c......  Applicability.
XII.A.1.d.............................  None.....................  Applicability.
XII.A.2...............................  XII.D.4..................  Exception to applicability for oil refineries.
XII.A.3...............................  None.....................  Applicability for natural gas processing plants and certain natural gas compressor
                                                                    stations. Indicates they are subject to Section XII.G.
XII.A.4...............................  None.....................  Applicability for certain glycol natural gas dehydrators, natural gas compressor
                                                                    stations, drip stations, or gas processing plants. Indicates they are only subject
                                                                    to XII.B and XII.H.
XII.A.5...............................  XII.A.8..................  Exception to applicability based on uncontrolled actual VOC emissions threshold of 30
                                                                    tons per year.
XII.B.1, 2, 3, 9, 12, and 14..........  XII.D.1; XII.D.5 through   Definitions of various terms.
                                         9.
XII.B.4, 5, 6, 7, 8, 10, 11, and 13...  None.....................  Definitions of various terms. XII.B.13 contains a State-only definition.
XII.C.1.a.............................  XII.D.2.a................  General requirements for operation/maintenance of control equipment.
XII.C.1.b.............................  XII.D.2.b................  General requirement to minimize leakage VOCs.
XII.C.1.c.............................  XII.A.7 and XII.A.4.h....  Air pollution control equipment control efficiency. Failure to operate and maintain
                                                                    control equipment at indicated locations is a violation.
XII.C.1.d.............................  XII.D.2.c................  Requirements for combustion devices.
XII.C.1.e and f.......................  None.....................  State-only requirements related to combustion devices.
XII.C.2 and XII.C.2.a.................  XII.D.3..................  Emission factors for emission estimates.
XII.C.2.b.............................  None.....................  State-only. Emission factors for emission estimates in areas other than the 8-hour
                                                                    ozone control area (DMA/NFR nonattainment area).
XII.D.................................  XII.A.2..................  Emission control requirements for condensate tanks.
XII.D.1...............................  None.....................  Control requirement for new and modified condensate tanks.
XII.D.2.a(i) through (x)..............  XII.A.2.a through h......  System-wide control requirements for condensate storage tanks.
XII.D.2.b.............................  XII.A.9..................  Alternative emission control equipment.
XII.E.................................  XII.A.3..................  Monitoring.
XII.E.1...............................  None.....................  Requirements for control equipment other than a combustion device.
XII.E.2...............................  None.....................  State only requirement related to new and modified tanks controlled by a combustion
                                                                    device.

XII.E.3., XII.E.3.a and b.............  XII.A.3.a and b..........  Checks for combustion devices.
XII.E.4...............................  XII.A.4.j................  Documentation of inspections.
XII.E.4.a-d...........................  XII.A.3.c-f..............  Requirements for the weekly check.
XII.E.5...............................  None.....................  State-only requirements for surveillance systems.
XII.F.................................  XII.A.4 and XII.A.5......  Recordkeeping and reporting requirements.
XII.F.1 and 2.........................  XII.A.10 and 11..........  Marking of AIRS numbers on tanks.
XII.F.3...............................  XII.A.4..................  Introductory language for recordkeeping.
XII.F.3.a(i)..........................  XII.A.4.a................  List of tanks and production volumes.
XII.F.3.a(ii) and (iii)...............  XII.A.4.b and c..........  Listing of emission factors and location and control efficiencies.
XII.F.3.a(iv).........................  XII.A.4.d.i..............  List weekly and monthly production values. Describes how to determine the averages.
XII.F.3.a(v)-(vii)....................  XII.A.4.d.ii-iv..........  List weekly and monthly uncontrolled actual and controlled actual emissions by tank
                                                                    and system-wide. List percent reductions weekly and monthly.
XII.F.3.a(viii).......................  XII.A.4.e................  Note any downtime and account for it.
XII.F.3.a(ix)-(x).....................  XII.A.4.f-g..............  Maintaining and mailing of spreadsheet.
XII.F.3.b-d...........................  XII.A.4.h-j..............  Failure to have control equipment as indicated on spread sheet is violation. Retain
                                                                    spread sheets for five years. Maintain records of inspections.
XII.F.3.e.............................  None.....................  State only. Maintain records of required surveillance system.
XII.F.3.f.............................  None.....................  State only. Keep records for new and modified tanks--when installed, etc.
XII.F.4...............................  XII.A.5..................  Reporting for system-wide requirements.
XII.F.4.a.............................  XII.A.5.a................  List tanks and production volumes.
XII.F.4.b-c...........................  XII.A.5.b-c..............  List emission factor and location and control efficiency.
XII.F.4.d.............................  XII.A.5.d................  What different reports must show based on time of year. Emissions individual tanks.
XII.F.4.e.............................  XII.A.5.e................  What different reports must show based on time of year. Emissions system-wide.
XII.F.4.f.............................  XII.A.5.f................  What different reports must show based on time of year. Percent reduction system-
                                                                    wide.
XII.F.4.g.............................  XII.A.5.g................  Note shutdown of control equipment and account for same in totals.
XII.F.4.h.............................  XII.A.5.h................  State whether required reductions were achieved.
XII.F.4.i.............................  XII.A.5.i................  Include any information requested by the Division.
XII.F.4.j.............................  XII.A.5.j................  Retention period.
XII.F.4.k.............................  XII.A.5.k................  Additional reporting, monthly reporting of problems and corrective actions.
XII.F.4.l.............................  XII.A.5.l................  Identify before ozone season tanks being controlled to meet system-wide control
                                                                    requirements.
XII.F.4.m-n...........................  None.....................  State-only additional requirements for certifications.
XII.F.5...............................  XII.A.6..................  Exemption from record-keeping and reporting requirements for natural gas compressor
                                                                    stations and drip stations authorized to operate pursuant to a construction or
                                                                    operating permit.
XII.G.................................  XII.B....................  Requirements for gas processing plants. Introductory statement.
XII.G.1...............................  XII.B.1..................  Part 60 leak detection applies.
XII.G.2...............................  XII.B.2..................  Applicability of control equipment.
XII.G.3...............................  XII.B.3..................  Compliance date for existing plants.
XII.G.4...............................  XII.B.4..................  Compliance date for new plants.
XII.G.5...............................  None.....................  New exemption for natural gas compressor stations and drip stations if certain
                                                                    conditions are met.
XII.G.6...............................  None.....................  Says that natural gas compressor station or natural gas drip station that has a
                                                                    glycol natural gas dehydrator and/or natural gas-fired stationary or portable engine
                                                                    is subject to Section XII.H and/or XVI.
XII.H.................................  XII.C....................  Requirements that apply to vents from gas-condensate-glycol separators on glycol
                                                                    natural gas dehydrators at an oil and gas exploration and production operation,
                                                                    natural gas compressor station, drip station or gas-processing plant.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The main feature of Section XII remains the requirement for system-
wide reductions in condensate storage tank VOC emissions. The current
EPA-approved Section XII requires that uncontrolled actual condensate
tank VOC emissions in the DMA/NFR area be reduced on a weekly basis
during the summer ozone season by 75% system-wide beginning May 1,
2007, and 78% beginning May 1, 2012. Revised Section XII (Section
XII.D.2) requires an 81% system-wide reduction in uncontrolled actual
weekly condensate tank VOC emissions during the summer ozone season
beginning May 1, 2009, an 85% reduction beginning May 1, 2010, and a
90% reduction beginning May 1, 2011. Also, most of the definitions and
monitoring, recordkeeping, and reporting requirements in Section XII
are unchanged. However, because of deficiencies in Colorado's proposed
revisions to Section XII, we cannot

approve revised Section XII. Below, we describe in detail Colorado's
proposed revisions to Section XII and the basis for our proposed
disapproval of such revisions.
    As noted above, Colorado was able to demonstrate attainment using
the 2010 base case inventory. This inventory assumed the continuation
of Section XII requirements as contained in the current EPA-approved
SIP, and no new SIP control measures. Thus, disapproval of Colorado's
proposed Section XII revisions would not invalidate the attainment
demonstration and, thus, would not trigger sanctions or a FIP
obligation.
Analysis of Specific Section XII Revisions
Section XII.A.
    Section XII.A defines the applicability of Section XII requirements
and is consistent with the current EPA-approved applicability
provisions in Section XII.
Section XII.B.
    Section XII.B contains definitions specific to Section XII. The
substance of the definitions contained in Sections XII.B.1, 2, 3, 9,
12, and 14 is unchanged from the definitions contained in SIP-approved
Sections XII.D.1 and XII.D.5 through 9. The other definitions in
revised Section XII.B define the following terms that are used in
Section XII: auto-igniter, calendar week, condensate storage tank,
downtime, existing, modified or modification, and new. The definitions
are clear, straightforward, and accurate. The definitions of auto-
igniter and existing are only pertinent to State-only provisions and
thus have no meaning for our SIP action.
Section XII.C.1.
    Section XII.C.1 contains general requirements for air pollution
control equipment and prevention of leakage. Colorado did not change
the substance of the corresponding EPA-approved provisions.
Section XII.C.2.
    Section XII.C.2 describes the emission factors to be used for
estimating emissions and emissions reductions from condensate storage
tanks under Section XII. Colorado made one change to the substance of
the corresponding EPA-approved provisions: In the current EPA-approved
SIP (Sections XII.D.3.b and 3.b.i), the emission factors to be used are
specified for condensate storage tanks at natural gas compressor
stations, natural gas drip stations, and gas-condensate-glycol
separators. In revised Sections XII.C.2.a.(ii) and a.(ii)(A), Colorado
deleted the reference to gas-condensate-glycol separators. Revised
Section XII.H still requires a 90 percent reduction in emissions at
certain gas-condensate-glycol separators, and Colorado has not
explained why an emission factor specified or determined under Section
XII.C.2 will not be needed to determine compliance with Section XII.H.
We believe an emission factor will be needed to ensure that the
reduction requirement in Section XII.H can be enforced. Thus, this is a
deficiency in revised Section XII that forms part of the basis for our
proposed disapproval of
Section XII.D.
    Section XII.D contains an introductory statement regarding the
control requirements for atmospheric condensate storage tanks. The
changes to current SIP-approved Section XII.A.2 are minor. While the
statement that ``[e]mission reductions shall not be required for each
and every unit'' is misleading because the control requirement in
revised Section XII.D.1 for new and modified condensate tanks applies
to every tank, this misstatement would not undermine the enforceability
of the requirements in Section XII.D.1. However, Colorado should
correct this statement.
Section XII.D.1.
    Section XII.D.1 requires owners or operators of any new or modified
condensate tank at exploration and production sites to route emissions
to air pollution control equipment that has a control efficiency of at
least 95% for VOCs. This requirement applies for the first 90 days
after the date of first production or after a well is newly drilled,
re-completed, re-fractured, or otherwise stimulated. After the initial
90 days, the emission controls required by this subsection may be
removed provided the source can demonstrate compliance with the system-
wide provisions specified in other subsections of section XII. This new
requirement would strengthen the SIP.
Section XII.D.2.a.
    Section XII.D.2.a contains the system-wide control requirements for
condensate storage tanks. The current SIP provides for a weekly 75%
system-wide VOC reduction during the summer ozone season beginning in
2010. As noted above, the revised section significantly increases the
summer ozone season weekly VOC reduction requirements from the current
EPA-approved requirements, to 85% beginning in 2010 and 90% beginning
in 2011. However, the revised provisions specify no system-wide weekly
VOC reduction requirement after the 2012 summer ozone season.\6\
---------------------------------------------------------------------------

    \6\ We note that the system-wide weekly reduction requirement of
78% that commences in May 2012 in the current EPA-approved version
of Section XII contains no termination date.
---------------------------------------------------------------------------

    As noted previously, Colorado was able to demonstrate attainment
based on a 75% system-wide weekly VOC reduction from condensate storage
tanks beginning in 2010. While revised Section XII would provide more
stringent reductions in the short term, including the attainment year,
it contains no weekly emission reduction requirement after the 2012
summer ozone season. Thus, although it is more stringent in the short
term, it is less stringent over the long term, and the State has not
demonstrated how this weakening of the SIP will not interfere with
maintenance of the NAAQS. This deficiency forms part of the basis for
our proposed disapproval of revised Section XII.
Section XII.D.2.b.
    Section XII.D.2.b is a re-numbered version of current EPA-approved
Section XII.A.9. This section contains a process for approval of
alternative emissions control equipment and pollution prevention
devices and processes. Among other things, the section specifies
requirements for public participation and EPA approval. Colorado did
not change the substance of this provision, but simply renumbered it
from Section XII.A.9 to now be section XII.D.2.b.
    The revised section contains typographical errors that Colorado
should correct. In Section XII.D.2.b, Colorado should delete the word
``this'' in ``this Section XII.D.2.a'' because Section XII.D.2.a is not
part of Section XII.D.2.b. In Section XII.D.2.b.(i)(E), the reference
to ``the spreadsheet and annual report required by Sections XII.F.4 and
XII.F.5'' should be to ``the spreadsheet and annual report required by
Sections XII.F.3 and XII.F.4.''
Section XII.E.
    Section XII.E contains the monitoring requirements that are
currently specified in EPA-approved Sections XII.A.3 and XII.A.4.j.
Colorado retained the basic requirement for weekly inspections or
monitoring.
    Colorado improved certain provisions. For example, under revised
Section XII.E, an owner or operator must ensure that the control
equipment is not only operating, but that it is operating properly.
Revised Section XII.E.1 adds a requirement that owners

or operators of control equipment other than a combustion device follow
manufacturer's recommended maintenance and inspect the equipment to
ensure proper maintenance and operation. Revised Section XII.E.4
(current XII.A.4.j) adds a requirement that the owner or operator
document any corrective actions taken and the name of the individual
performing the corrective actions resulting from a weekly inspection.
Revised Sections XII.E.4.a through d add the requirement that the owner
or operator not only perform certain checks, but that the owner or
operator document those checks.
    Revised Section XII.E.3 is deficient. It specifies certain
inspection and/or monitoring requirements for combustion devices. It
introduces two possible means to monitor/inspect the combustion device,
but one of them--use of a surveillance system--is designated as a State
Only option. The federally-enforceable SIP cannot provide a compliance
option that is only available as a matter of State law. Discussions
with the State have revealed that use of a surveillance system was not
intended as an alternative to the monitoring method contained in
Section XII.E.3.a, but as a technique that owners/operators could use
on a trial basis in addition to the method contained in Section
XII.E.3.a. Thus, the word ``either'' in Section XII.E.3 and the words
``and/or'' in XII.E.3.a are not appropriate. This deficiency forms part
of the basis for our proposed disapproval of revised Section XII.
Section XII.F.
    Section XII.F contains recordkeeping and reporting requirements
that are currently specified in EPA-approved Sections XII.A.4 and
XII.A.5. The recordkeeping requirements specify information that must
be listed on a spreadsheet that owners/operators must maintain. Many of
the provisions are identical to those in the current EPA-approved SIP.
Sections XII.F.1 through 4.
    In Sections XII.F.1 through 4, Colorado made a few substantive
changes to the existing provisions. In revised Section XII.F.3,
Colorado added a sentence requiring the owner or operator to track VOC
reductions on a calendar weekly and calendar monthly basis to
demonstrate compliance with system-wide VOC reduction requirements.
Colorado also specified that owners/operators would need to use the
Division-approved spreadsheet to track VOC emissions and reductions,
not just any spreadsheet. These changes are reasonable and consistent
with CAA requirements.
    In revised Section XII.F.3.a(i), which requires the spreadsheet to
list the condensate storage tanks subject to Section XII and the
production volumes for each tank, Colorado specified that the
spreadsheet must list monthly production volumes. It is unclear why
Colorado added the word ``monthly'' because the following sentence,
which Colorado did not change, requires the owner/operator to list the
most recent measurement of such production and the time period covered
by the measurement. Also, revised Section XII.F.3.a(iv) requires the
owner/operator to list the production volume for each tank as a weekly
and monthly average based on the most recent measurement available and
specifies the method for pro-rating that measurement over the weekly or
monthly period. Given the specificity of Section XII.F.3.a(iv), we are
not concerned that the addition of the word ``monthly'' in revised
Section XII.F.3.a(i) would undermine the enforceability of the
regulation. However, Colorado should remove the word ``monthly'' in
revised Section XII.F.3.a(i).
    Revised Section XII.F.3.c requires owners/operators to retain a
copy of each weekly and monthly spreadsheet for five years instead of
the three years required by current EPA-approved Section XII.A.4.i.
    Revised Section XII.F.3.d requires owners/operators to maintain
records of inspections required by Section XII.E but does not specify a
period for maintenance of the records. This is consistent with EPA-
approved Section XII.A.4.j. However, we consider this something that
Colorado should address. Typically, EPA recommends that such records be
kept for a minimum of five years.
    Revised Section XII.F.3 does not contain adequate recordkeeping for
the control requirement that applies to new and modified condensate
tanks under Section XII.D.1. As noted above, for new and modified
condensate tanks, owners or operators are required to use air pollution
control equipment with a control efficiency of at least 95% for the
first 90 days. However, the regulation only specifies State-only
recordkeeping requirements relevant to this requirement--in Section
XII.F.3.f--and includes no reporting requirements that would be
federally enforceable. To meet CAA requirements, the regulation, at a
minimum, should specify that owners/operators provide notification and
maintain certain records. We believe relevant records would include,
but may not be limited to: The date a new atmospheric condensate
storage tank was installed, or the date a well was newly drilled, re-
completed, re-fractured or otherwise stimulated; the date the control
equipment was installed and, if applicable, removed; the manufacturer's
design specifications for the control equipment; the manufacturer's
operation and maintenance specifications/instructions for the control
equipment; and any downtime of the control equipment or other
operational problems and corrective action taken. The regulation should
also specify a record retention period for such records. The regulation
specifies a five-year retention period for other records, and it would
be appropriate to specify the same retention period for these records.
The regulation should also specify that owners/operators need to report
within a reasonable period of time after the date the new atmospheric
condensate storage tank was installed or the date the well was newly
drilled, re-completed, re-fractured or otherwise stimulated. The
regulation should also require the owner/operator to report any non-
compliance with the requirements of Section XII.D.1 within a reasonable
time frame. The deficiencies in recordkeeping and reporting
requirements pertaining to the control requirements of revised Section
XII.D.1 form part of the basis for our proposed disapproval of revised
Section XII.
    In revised Section XII.F.4, Colorado made minor changes to current
EPA-approved reporting requirements. Revised Section XII.F.4.a requires
the semi-annual reports to list all condensate storage tanks subject to
or used to comply with the system-wide reduction requirements, not just
those subject to such requirements. This reflects the change to the
regulation that allows owners/operators to control tanks with emissions
below the APEN filing levels to meet the percent reduction requirement
in Section XII.D.2. In revised Sections XII.F.4.d through f Colorado
clarified that the April 30 reports must include the monthly emissions
information and the November 30 reports must include the weekly
emissions information. In revised Section XII.F.4.g, Colorado deleted
the requirement in current EPA-approved Section XII.A.5.g that the
owner/operator note in the report ``the date the source believes the
shutdown [of control equipment] occurred, including the basis for such
belief.'' We believe this deletion is reasonable because the owner/
operator is not likely to be able to make an accurate estimate

of the date the shutdown occurred, and, thus, the information is not
likely to be meaningful in an enforcement context. In revised Section
XII.F.4.h, Colorado clarified monthly versus weekly reporting
requirements. In revised Section XII.F.4.j, Colorado increased the
retention period for reports from three years to five years. These
changes are consistent with CAA requirements.
    Revised Section XII.F.4.l contains a reference to ``this Section
XII.D.2.'' The word ``this'' should be deleted. This typographical
error is not significant enough to undermine the enforceability of the
regulation, but Colorado should correct it.
Section XII.F.5.
    Section XII.F.5 contains an exemption from Section XII's record-
keeping and reporting requirements for owners/operators of natural gas
compressor stations (NGCSs) or natural gas drip stations (NGDSs)
authorized to operate pursuant to a construction permit or Title V
operating permit if certain conditions are met. Colorado removed one of
the conditions for this exemption contained in current EPA-approved
Section XII.A.6. The removed condition provided that total emissions
from condensate storage tanks associated with such NGCSs and NGDSs
could not exceed 30 tons per year. If we approve the deletion of this
condition, the recordkeeping and reporting requirements for the
relevant sources with emissions exceeding the 30 tons per year
threshold would need to be established through construction or Title V
operating permits. Our interpretation of the CAA is that provisions
such as monitoring, recordkeeping, and reporting requirements that are
needed to ensure the enforceability of the applicable control
requirements contained in a SIP must also be contained in the SIP and
cannot be left to development in a permit. See. e.g., CAA sections
110(a)(2)(A) and (F), 40 CFR part 51, Subpart K, and 40 CFR part 51,
Appendix V. This deficiency forms part of the basis for our proposed
disapproval of revised Section XII.
    We approved the prior version of the exemption because Section
XII's system-wide VOC reduction requirements were limited to systems
with emissions over 30 tons per year. In other words, all owners/
operators, including owners/operators of NGCSs and NGDSs, were exempt
from Section XII's main requirements, including the recordkeeping and
reporting requirements, if emissions from their units were under 30
tons per year. Revised Section XII.F.5 also contains typographical
errors. In the first line, the reference to ``Sections XII'' should be
to ``Section XII.'' In XII.F.5.a, the reference to ``this Section
XII.A'' should be to ``Section XII.D.''
Section XII.G.
    Section XII.G specifies the control requirements applicable to gas-
processing plants and corresponds to current EPA-approved Section
XII.B. EPA-approved Section XII.B requires gas-processing plants to
meet the requirements in Section XII.B specifically applicable to such
plants as well as the requirements in current EPA-approved Section
XII.C, pertaining to certain still vents and vents from gas-condensate-
glycol separators, and Section XVI, pertaining to emissions from
stationary and portable engines. Revised Section XII.G requires gas-
processing plants to additionally comply with the requirements of
revised Section XII.B, the definitions section, and revised Sections
XII.C.1.a and XII.C.1.b, which specify maintenance and design
requirements for control equipment and the obligation to minimize
leakage of VOCs to the atmosphere. It appears that this change would
strengthen the requirements applicable to gas-processing plants.
Section XII.G.1.
    Section XII.G.1 specifies that NSPS leak detection and repair
requirements apply regardless of the date of construction of the
facility. Colorado made no substantive changes to this provision.
Section XII.G.2.
    Section XII.G.2 specifies the applicability threshold for
installation of control equipment at gas-processing plants and the
efficiency requirement for the control equipment. In current EPA-
approved Section XII.B.2, installation of control equipment is
triggered if condensate storage tank throughput exceeds ``APEN de
minimis levels.'' In revised Section XII.G.2, installation is triggered
if uncontrolled emissions from a tank or tank battery are greater than
or equal to two tons per year. We cannot determine whether this change
would strengthen the regulation, weaken it, or leave it the same
because we cannot determine whether the same tanks or tank batteries
would have to install control equipment or not. Colorado also revised
the control efficiency requirement from 95%, with no averaging period
specified, to 95% with a rolling 12-month averaging period. We are not
convinced this change is consistent with CAA requirements. The revised
regulation contains no provisions for testing or determining whether
the 95% control has been achieved on a rolling 12-month basis, and if
the goal is to have owners/operators install and operate flares with a
control efficiency of at least 95%, specifying an averaging period is
not particularly meaningful. These issues form part of the basis for
our proposed disapproval of revised Section XII.
Section XII.G.3.
    Section XII.G.3 specifies the compliance date for existing natural
gas processing plants. Colorado did not change the substance of this
provision.
Section XII.G.4.
    Revised Section XII.G.4, which specifies the compliance date for
new gas processing plants, contains typographical errors. The reference
to ``this Section XII.B'' should be to ``this Section XII.G.'' The
reference to Section XII.C should be to Section XII.H.
Section XII.G.5.
    Section XII.G.5 is entirely new. It adds an exemption from the
otherwise applicable requirements of Section XII for an owner or
operator of any NGCS or NGDS, but only if the owner or operator applies
control equipment designed to achieve a VOC control efficiency of at
least 95% to each condensate storage tank or tank battery with
uncontrolled VOC emissions greater than or equal to two tons per year
and meets certain other requirements. While this is a more stringent
requirement than the system-wide requirement because it requires 95%
control at each tank or tank battery over the threshold rather than a
maximum of 90% control system-wide, Section XII does not specify
recordkeeping and reporting requirements to support the provisions of
revised Section XII.G.5. Adequate recordkeeping and reporting
requirements in the SIP are necessary to ensure the enforceability of
the control requirement and to meet CAA requirements. This deficiency
forms part of the basis for our proposed disapproval of revised Section
XII.
Section XII.G.6.
    Section XII.G.6 is new. It specifies that a NGCS or NGDS subject to
Section XII.G at which a glycol natural gas dehydrator or natural gas-
fired stationary or portable engine is operated shall be subject to
Section XII.H and/or XVI. We interpret this to mean that the provisions
of Sections XII.H and XVI, as applicable, would apply to such
facilities in addition to the provisions of Section XII.G. We view this
as a

clarifying change that is consistent with CAA requirements.
Section XII.H.
    Section XII.H specifies control requirements for still vents and
vents from gas-condensate-glycol separators on glycol natural gas
dehydrators located at oil and gas exploration and production
operations, natural gas compressor stations, drip stations, or gas-
processing plants. In revised Section XII.H, Colorado attempted to
clarify current EPA-approved Section XII.C's applicability threshold
for control requirements. The relevant language in revised Section
XII.H reads as follows:

    This Section XII.C shall not apply to any single natural gas
dehydrator, or grouping of dehydrators at an oil and gas exploration
and production operation, natural gas compressor station, drip
station or gas-processing plant, with uncontrolled actual emissions
of volatile organic compounds of less than 15 tons per year. To
determine if a grouping of dehydrators exceeds the 15 tons per year
threshold aggregate emissions from all dehydrators on site
(contiguous and adjacent). The control requirement in this Section
XII.H. shall apply to each natural gas dehydrator within a grouping
that has actual uncontrolled emissions above one ton per year. The
control requirement in this Section XII.H. shall not apply to a
natural gas dehydrator with emissions below the APEN reporting
thresholds in Regulation Number 3, Part A, Section II.D that is part
of a grouping of dehydrators, but the emissions from such dehydrator
shall be included in the calculation.

    As written, this passage lacks clarity and contains redundant
language that EPA cannot approve. While we think we understand the
intent--that emissions from all dehydrators are counted in determining
whether the 15-ton-per-year threshold is exceeded, but the control
requirement only applies to dehydrators with actual uncontrolled
emissions above one ton per year--the redundant language and lack of
punctuation or missing words in the third sentence of revised Section
XII.H create uncertainty. The same is true of stating the threshold for
control in two different ways: Controls apply where emissions exceed
one ton per year versus controls don't apply where emissions are below
the APEN reporting thresholds. This deficiency forms part of the basis
for our proposed disapproval of revised Section XII.
    We also note that in the quoted passage above, the reference to
``This section XII.C'' should be to ``This section XII.H'' and that
Colorado should correct this typographical error.
Proposed Action on Section XII Revisions
    Based on the deficiencies noted above, we are proposing to
disapprove the Section XII revisions. While several of the changes
contained in revised Section XII would strengthen the SIP, we are
unable to use our authority for partial or limited approval. First,
under the circumstances involved here and based on our interpretation
of the CAA, it is not appropriate to replace a fully approved Section
XII in the SIP with a revised Section XII that contains deficiencies.
Second, we have no means to approve only those provisions that
strengthen the SIP and reject the rest because Colorado completely
reorganized and renumbered Section XII's provisions. The numbering of
any relevant subsections that we could approve would not match the
numbering of the current EPA-approved subsections; the resulting SIP
rule would be unintelligible. Thus, we find that our only available
course of action is to propose to disapprove all of revised Section
XII.
Sections XIII through XVI
    Sections XIII through XVI changes are clerical in nature and do not
affect the substance of the requirements. Therefore, we are proposing
to approve the changes in Sections XIII through XVI.

Ambient Air Quality Standards Regulation

    We are proposing to disapprove Colorado's proposed revisions to its
ambient air quality standards regulation. Colorado's ambient air
quality standards regulation duplicates information contained in other
parts of the SIP and in our regulations. For example, the ambient air
quality standards regulation restates the motor vehicle emissions
budgets for various areas. However, under our regulations, the budgets
are determined by the applicable control strategy SIP or maintenance
plan, not by Colorado's ambient air quality standards regulation.
Similarly, the ambient air quality standards regulation defines the
boundaries and designations of various areas in Colorado. However, EPA
defines the designations and boundaries of areas in its own
regulations. Approval of the ambient air quality standards regulation
could lead to confusion in the event of conflict between the ambient
air quality standards regulation and our regulations or other parts of
the SIP.
    Because we are obligated to act on the State's SIP submission, we
plan to disapprove these revisions to the ambient air quality standards
regulation as a revision to the SIP. If the State requests to withdraw
the regulation from the SIP revision prior to the time we take final
action, we would not be obligated to take final action because the
revisions to the ambient air quality standards regulation would no
longer be pending before the Agency as a SIP revision.

I. Transportation Conformity

    Under section 176(c) of the CAA, transportation plans,
transportation improvement programs, and new transportation projects,
such as the construction of new highways, must ``conform'' to (i.e., be
consistent with) applicable SIPs. Conformity to a SIP means that
transportation activities will not produce new air quality violations,
worsen existing violations, or delay timely attainment of the NAAQS.
EPA's conformity rule provisions in 40 CFR part 93 establish the
criteria and procedures for determining whether or not these plans,
programs, and projects conform to the SIP. In particular, our
regulations require a demonstration that emissions from these plans,
programs, and projects will be consistent with the motor vehicle
emissions budgets (MVEBs) in the SIP (40 CFR 93.118). The MVEBs are
defined as that portion of the total allowable emissions defined in the
SIP for a certain date, for the purpose of meeting reasonable further
progress milestones or demonstrating attainment or maintenance of the
NAAQS, allocated to highway and transit vehicle use and emissions.
    EPA's requirements on MVEBs are found in 40 CFR 93.118 and 93.124,
and MVEBs are further explained in the preamble to the November 24,
1993, transportation conformity rule (58 FR 62193-62196). Colorado
derived the MVEBs for NOX and VOCs from its 2010 base case
attainment demonstration and defined the MVEBs in Chapter VI of the
OAP. We list the MVEBs in Table 3, below.

            Table 3--Identification of 2010 NOX and VOC MVEBs
------------------------------------------------------------------------
                                          2010 NOX          2010 VOC
        Area of applicability          Emissions (tons   Emissions (tons
                                          per day)          per day)
------------------------------------------------------------------------
Northern Subarea....................              20.5              19.5
Southern Subarea....................             102.4              89.7
                                     -----------------------------------
    Total Nonattainment Area........             122.9             109.2
------------------------------------------------------------------------

    Once Colorado submitted the OAP to us, we determined the adequacy
of the MVEBs per the procedures and criteria contained in 40 CFR
93.118. On October 15, 2009, we announced the availability of the
attainment demonstration and the MVEBs on EPA's transportation
conformity adequacy Web site and solicited public comment. The public
comment period closed on November 16, 2009; we received no comments.
All of this information is available at EPA's conformity Web site:
http://www.epa.gov/otaq/stateresources/transconf/currsips.htm#denver-
me.
    In a January 21, 2010 letter to the Colorado Department of Public
Health and Environment, we found that the 2010 NOX and VOC
MVEBs in the OAP were adequate. We announced our adequacy finding in
the Federal Register on March 4, 2010, and the OAP's MVEBs became
effective on March 19, 2010. As a result, as of that date, the Denver
Regional Council of Governments (DRCOG), the North Front Range
Transportation and Air Quality Planning Council (NFRT), the Colorado
Department of Transportation, and the U.S. Department of Transportation
were required to use these MVEBs for transportation conformity
determinations. However, we note that we are not bound by our prior
adequacy determination in this action.
    Our analysis indicates that the MVEBs are consistent with and
clearly related to the emissions inventory and the control measures in
the SIP, and that the MVEBs, when considered together with all other
emissions sources, are consistent with attainment of the 1997 8-hour
ozone NAAQS in 2010. (See 40 CFR 93.118(e)(4).) Therefore we are
proposing approval of the MVEBs as reflected in Table 3 above.
    We note that our proposed approval applies to the Northern Subarea
and Southern Subarea MVEBs as well as the Total Nonattainment Area
MVEBs. The Northern Subarea is defined in the OAP as the area denoted
by the ozone nonattainment area north of the Boulder County northern
boundary and extended through southern Weld County to the Morgan County
line. This area includes NFRT's regional planning area as well as part
of the Upper Front Range Transportation Planning Region (TPR) in
Larimer and Weld counties.
    The Southern Subarea is defined in the OAP as the area denoted by
the ozone nonattainment area south of the Boulder County northern
boundary and extended through southern Weld County to the Morgan County
line. This area includes the nonattainment portion of DRCOG's regional
planning area and the southern Weld County portion of the Upper Front
Range TPR. We note that both subareas are further identified in Figure
2: ``8-hour Ozone Emission Budget Subareas'' at page VI-6 in the OAP.
    In addition to proposing approval of the MVEBs, we are also
proposing to approve the process described in the OAP for use of the
Total Nonattainment Area MVEBs and the subarea MVEBs. Per the OAP, the
initial conformity determination must use the Total Nonattainment Area
MVEBs for NOX and VOCs. After the initial conformity
determination, DRCOG and NFRT may switch from using the Total
Nonattainment Area MVEBs to using the subarea MVEBs for determining
conformity. To switch to use of the subarea MVEBs (or to subsequently
switch back to use of the Total Nonattainment Area MVEBs,) DRCOG and
the NFRT must use the process described in the OAP at pages VI-4 and
VI-5.

V. Consideration of Section 110(l) of the CAA

    Section 110(l) of the CAA states that a SIP revision cannot be
approved if the revision would interfere with any applicable
requirement concerning attainment and reasonable further progress
towards attainment of a NAAQS or any other applicable requirement of
the CAA. The parts of the OAP and the regulation revisions we are
proposing to approve will not interfere with attainment, reasonable
further progress, or any other applicable requirement of the CAA. The
OAP contains a valid modeled attainment demonstration showing the area
will attain by 2010. As described elsewhere in this action, we are
proposing to disapprove Colorado's proposed repeal of Section II.D of
Regulation Number 7, Colorado's revisions to Section XII of Regulation
Number 7, Colorado's revisions to Part C of Regulation Number 3,
Colorado's revisions to its Ambient Air Quality Standards regulation,
and specific limited portions of the OAP because those provisions do
not meet all applicable requirements of the CAA.

VI. Proposed Action

    We are proposing to approve Colorado's 2010 attainment
demonstration for the 1997 8-hour ozone NAAQS. We are proposing to
approve the motor vehicle emissions budgets contained in the OAP. We
are proposing to approve all other aspects of the OAP, with the
following limited exceptions: we are proposing to disapprove the last
paragraph on page IV-1 and the first paragraph on page IV-2 of the OAP,
we are proposing to disapprove the words ``federally enforceable'' in
the second to last paragraph on page V-6 of the OAP, and we are
proposing to disapprove the reference to Attachment A in the OAP's
Table of Contents and on page IV-3 of the OAP.
    We are proposing to approve the revisions to Colorado Regulation
Number 3, Parts A and B. We are proposing to disapprove the revisions
to Colorado Regulation Number 3, Part C.
    We are proposing to approve the following portions of the revisions
to Colorado Regulation Number 7:
     Revisions to Sections I through XI, except for Colorado's
repeal of Section II.D.
     Revisions to Sections XIII through XVI.
    We are proposing to disapprove the following portions of the
revisions to Colorado Regulation Number 7:
     Colorado's proposed repeal of Section II.D.
     Revisions to Section XII.
    We are proposing to disapprove the revisions to Colorado's Ambient
Air Quality Standards Regulation.
    The provisions we are proposing to approve meet the requirements of
the CAA and our regulations, including 40 CFR 81.300(e)(3)(ii)(D). The
provisions

we are proposing to disapprove are inconsistent with CAA requirements
and our regulations. Our specific analyses and findings are discussed
above in the body of this proposed rulemaking.
    EPA is soliciting public comments on its proposed rulemaking as
discussed in this document. EPA will consider these comments before
taking final action. Interested parties may participate in the Federal
rulemaking process by submitting written comments to EPA as discussed
in this 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, EPA's role is to approve state choices,
provided that they meet the criteria of the CAA. Accordingly, this
proposed action merely approves some State law as meeting Federal
requirements and disapproves other State law because it does not meet
Federal requirements; this proposed action 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 Order
12866 (58 FR 51735, October 4, 1993);
     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 CAA; and
     Does not provide 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, this rule does not have tribal implications as
specified by Executive Order 13175 (65 FR 67249, November 9, 2000),
because the SIP is not approved to apply in Indian country located in
the State, and EPA notes that it will not impose substantial direct
costs on tribal governments or preempt tribal law.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Intergovernmental
relations, Nitrogen dioxide, Ozone, Reporting and recordkeeping
requirements, Volatile organic compounds.

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

    Dated: July 12, 2010.
Carol Rushin,
Acting Regional Administrator, Region 8.
[FR Doc. 2010-17810 Filed 7-20-10; 8:45 am]
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