Approval and Promulgation of Air Quality Implementation Plans; Colorado; Attainment Demonstration for the 1997 8-Hour Ozone Standard, and Approval of Related Revisions, 42346-42361 [2010-17810]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 75, Number 139 (Wednesday, July 21, 2010)]
[Proposed Rules]
[Pages 42346-42361]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-17810]


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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:
     https://www.regulations.gov. Follow the on-line 
instructions for submitting comments.
     E-mail: kenney.james@epa.gov.
     Fax: (303) 312-6064 (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 https://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 https://www.regulations.gov or e-mail. The https://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 https://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 https://www.epa.gov/epahome/dockets.htm.
    Docket: All documents in the docket are listed in the https://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 https://

[[Page 42347]]

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 (303) 312-6176, e-mail kenney.james@epa.gov.

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 https://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 https://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

[[Page 42348]]

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

[[Page 42349]]

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

[[Page 42350]]

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 7.2.1.2, 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.

[[Page 42351]]



                          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

[[Page 42352]]

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

[[Page 42353]]

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

[[Page 42354]]

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..............