ENVIRONMENTAL PROTECTION AGENCY 

40 CFR part 52 

[EPA-R08-0AR-2010-0285; FRLApproval 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. 

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 AreaJNorth Front Range nonattainment area by 20 10. 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 confonnity. 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 
2 


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 [insert date 30 days from date of publication]. 


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: 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, 8:00 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-R08-0AR2010-0285. 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 
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http://www.regulations.gov or e-mail. The hrtp:llwww.reguiations.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. Ifyou send an e-mail comment 

directly to EPA, without going throughhttp://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 

tiles 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 ifat all 

possible, you contact the individual listed in the FOR FURTHER INFORMATION 

CONTACT section to view the hard copy of the docket. You may view the hard copy of the 

docket Monday through Friday, 8:00 a.m. to 4:00 p.m., excluding Federal holidays. 
4 


FOR FURTHER INFORMATION CONTACT: James C. Kenney, Air Program, EPA Region 

8, Mai1code 8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-1129, phone (303) 312-6176, 

e-mail kenneyjames@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 
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E. Modeled Attainment Demonstration 

F. Weight of Evidence 

G. Specific OAP Language 

H. SIP Control Measures 

I. Transportation Conformity 

V. Consideration of Section 110(1) 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 eBl: Do not submit CBI to EPA through http://www.regulations.gov or email. 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. 
6 


2. 	 Tips/or 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 ofthe 1997 ozone National Ambient Air Quality Standards (NAAQS) in the 

Denver Metro AreaINorth Front Range (DMAlNFR) nonattainment area. The DMAlNFR 
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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 ~AP. 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-l 

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 ~AP. 
B 


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 11.0. 

• 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 B1.300(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 
9 


support document (TSD). The TSD is available on-line at http://www.regulations.gov, Docket 

No. EPA-R08-0AR-2010-028S. 

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 19970.08 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 DMAlNFR 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 DMAlNFR area violated 
- -------------------

10 


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 §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 DMAlNFR 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 11O(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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B. Monitoring 

The monitoring section ofthe 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 qualit.y 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 Federallyapproved 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. 

I State revisions to the SIP do not become federally effective unless and until they are approved by EPA. 40 CFR 
12 


C. Emissions Inventories 

In the OAP, Colorado presents three different emissions inventories for the DMAINFR 

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. 

51.105. 
13 

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-I 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-I 0 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 systemwide 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 
14 


sources. On-road mobile source emissions data were estimated using EPA models (MOBILE6) 

and Vehicle Miles Traveled eVMT) 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. 

rI 2006 Base i 2010 Base 2010 Control 

• Source Category (tons/ avg. episode day) 	I NOx VOC I NOx VOC NOx VOC 

Point Sources 

Electric Generation Units 55.6 0.7 58.5 1.6. 58.5 i 1.6 

I External Combustion Boilers 9.5 0.4 10.0 0.5 10.0 : 0.5 

I 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 I 3.6 2.0 3.6 2.0 

I I 

I 	 Point Sources Subtotal 81.0 32.1 I 86.4 • 37.0 86.4 37.0 • 

I 

i 

Oil and Gas Point & Area Sources I I 

Condensate Tanks 	 126.5 I 129.6 105.61 

Other O&G Point Sources 	 22.6 6.8 23.6 I 8.6 23.6 8.6 

Pneumatic Devices (Area Source) 24.8 31.1 12.0 

I Unpermitted Fugitives (Area Sources) 16.2 20.4 20.4 I 

I Other Area Sources 17.1 10.8 22.5 i 13.7 i 22.5 13.7 I 

i O&G Point & Area Sources Subtotal 39.7 185.2 46.2 ! 203.3\ 46.2 160.1 

I 	 I I I 	Area Sources j 

Personal Care Products 7.1 7.0 7.0 I 

Household Products 21.4 17.9 17.9 

Automotive Aftermarket Products 11.9 13.0 13.0 

Architectural Coatings 20.1 I 16.8 I 16.8 

Aircraft 	 1.5 . 7.4 1.3 8.2 8.2 1.5 I 

! I Railroad 	 12.8 0.5 13.8 0.6 13.8 0.6 i

Other Coatings/Pesticides/Cooking/Misc. 3.9 4.1 4.1 . 
15 

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 I 0.71 


Airport Equipment 0.7 0.1 0.6 0.1 0.6 0.1 


I Commercial Equipment 5.3 6.2 5.1 7.0 5.1 I 7.0 i 

I Construction and Mining Equipment 35.7 5.5 31.2 4.5 31.2 4.5 

I Industrial Equipment 10.5 2.4 6.9 1.4 6.9 1.4 I 

I Lawn and Garden Equip. (Commercial) 9.4 35.9 8.9 28.1 8.9 28.1 I 

Lawn and Garden Equip. (Residential) 1.2 7.5 1.2 11.8 1.2 11.8 I 

Boats/Recreational Equip/Misc. 0.7 6.9 0.8 7.8 0.8 7.8 I 

Non-Road Mobile Source Subtotal 70.5 65.3 . 61.0 61.3 61.0 61.3 • 

i 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 

Biogenic Subtotal 

Total 429.8 

53.0 

1172.6 

694.0 

391.5 

53.0 

1165.8 

694.0 

I 387.6 

53.0 

1119.41 

~ 

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 
16 


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 ~n 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 -4541B-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 36112/4 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 
17 


goals. Model perfonnance testing is used to detennine 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 detennine model perfonnance. 

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 perfonnance evaluation included such graphical 

and diagnostic evaluation techniques. In addition, EPA modeling guidance includes three 

numerical perfonnance goals that are useful in evaluating ozone models as part of the attainment 

demonstration. These include: unpaired accuracy of the peak 5t20%; nonnalized mean bias 

5t15%; and nonnalized 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" perfonnance goal of:s±20% for 58 of the 60 simulation days ofthe 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, 
18 


no statistics could be calculated for those two days. Of the 58 days, 50 days (or 86%) achieved 

EPA's :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 VOCINOx 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 DMAlNFR 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 19970.08 ppm 8-hour ozone NAAQS. Jfthe 

predicted future concentrations of ozone are lower than 0.08 ppm at all monitors, attainment is 
19 


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, 20 I 0 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 IItC 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, 
20 


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 -4541B-07-002, 

April 2007.) The last set ofDVFs (columns 6 and 7) are displayed to the nearest .0001 ofa ppm. 

Although not relevant to detennining attainment of the NAAQS, Colorado included these last 

columns as part of its evaluation of model perfonnance, 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 perfonned. 

Table 2. Projected 2010 8-hour ozone DVFs for the 2010 Base Case and Final 2010 Control 

Measure Case. 

Monitor County DVC 2010 DVF 2010 DVF I I Name (2005- (EP A Guidance) i (nearest 0.0001 i

2007) i (ppm) I ppm) I 
21 


I (ppm) Base Final Base Final 

Case Control Case Control 

Measure Measure 

Case 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 

I 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 EI Paso 0.074 0.073 0.073 0.0737 I 0.0737 

Arvada Jefferson 0.079 0.079 0.079 0.0792 . 0.0791 i 

Welch Jefferson 0.075 0.075 0.075 0.0750 0.0750 I 

Rocky Flats North Jefferson 0.085 0.084 0.084 0.0849 0.0849 I 

NREL Jefferson 0.082 0.082 0.082 0.0823 0.0822 

Fort Collins West Larimer 0.086 0.084 0.084 0.0849 0.0848 

Note: DVC based on two-years I 

: of measured data. I 

: Fort Collins Larimer 0.074 0.073 0.073 • 0.0730 0.0730 

f_~reeley Weld Tower Weld 0.078 0.077 . 0.077 I 0.0777 0.0775 

. Gunnison Gunnison 0.068 0.067 0.067 J 0.0678 0.0678 : 

I Larimer I Larimer 0.076 0.075 0.075\ 0.0752 0.0752 : 

F or 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 ofthe monitoring sites having identical DVFs for the 2010 base case and final 2010 
22 


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 DMAlNFR 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 SIPapproved 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. 
23 


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-4541B-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 ofthe 19970.08 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 ofthe efficacy ofColorado'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 DMAINFR area will attain the NAAQS. First, 

although individual concentrations have been highly variable, the aggregate trend in weathercorrected 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 DMAlNFR 

and that the modeling conclusions are reasonable. Second, the WOE analysis of the weekend­
24 


weekday effecr 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. 

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. 

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. 
25 


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 ofthis 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 ofthe 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 
26 


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) ~o 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 
27 


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 pennitting. The premise behind all 

the minor source construction pennitting 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 pennit 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 ofoil 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 infonnation regarding emissions related to oil and 

gas operations. This would also subject the specified source categories to the condensate storage 
28 


tank VOC control requirements of Regulation Number 7, Section XII, which uses the APENfiling 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 SIPapproved 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.I.a, as contained in the EPA-approved SIP at 

https:llyosemite.epa.govIRS/R8Sips.nsf/e5eS50cc767bc8b3872573a9004cad73175c2d810353a70 

6a87256b7b0066624d?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 
29 


the numbering of the submitted revisions and the EPA-approved SIP. Colorado added new 

Sections II.D.I.k, I, 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 IILD.l of Part B lists the types of emissions points that are 

exempt from minor source construction permitting requirements.) These emissions points are 

listed in Sections IILD.l.a through j. For purposes of this action, we are interpreting Colorado's 

proposed revisions to Part B, in the form of Sections ILD.l.k through n, as being an addition to 

Section III.D.l, and following immediately after Section III.D.l.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. 

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 EPAapproved 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 

3 Colorado previously submitted revisions to Part B that contain changes to the numbering of Part B provisions; we 
30 


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. 

will be acting on those revisions separately. 
31 


Colorado made substantive revisions to certain limited parts of Regulation Number 7, 

particularly Section XII, and also made non-substantive revisions to numerous parts ofthe 

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 LA.I.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 ofRegulation Number 7 Changes by Section 

Section I: 

Section I contains applicability provisions, definitions of new and existing sources, and 
32 


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. 

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 

I1.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 

4 When we describe changes as clerical in this proposed action, we are referring to changes like section 
33 


rulemaking. 

We are proposing to approve the changes to Sections II.A, B, and C as minor, nonsubstantive revisions. Because section n.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 ofILE and F to conform the 

SIP to the numbering ofColo-rado's regulation. 

In addition to the changes noted above, the submitted revision to Section II reflects 

Colorado's repeal of Section ILD.5 The SIP-approved version of Section ILD 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 n.D in September 1989 to address specific EPA concerns 

that Colorado's RACT rule would allow changes to control requirements or test methods without 

EP A approval. 

We are proposing to disapprove the repeal of Section II.D for the following reasons: (1) a 

renumbering, alphabetizing of definitions, minor grammatical and editorial revisions, and changes in capitalization 

5 In March of 1996, Colorado adopted changes to Section n.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 11.0. 

Based on EPA's indication that it intended to disapprove Colorado's 1996 changes to Section 11.0, Colorado 

repealed Section ILD entirely in November 2003. Colorado did net re-adopt the pre-I 996 version of Section 1I.D, 

and the version of Regulation Number 7 that we are considering in this action indicates that Section Il.D has been 

repealed. 
34 


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 11 O(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 ltD as 

specifying necessary procedures for gaining approval of alternative control requirements and test 

methods (See, e.g., Section IX.AS.c of Regulation Number 7), and, therefore, removing Section 

lID would introduce ambiguity into the Regulation 

Our proposed disapproval of the repeal of Section ILD 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 ltD, 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 ltD will remain in the SIP after disapproval ofColorado's proposed repeal, and it 

will be incumbent on sources and the State to comply with Section ILD'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. 
35 


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: 

Colorado Revised Corresponding Subject 

Section XII EP A-Approved 

Section Number Section XII 

Section Number i 

XII.A XII.A Applicability i 

XII.AI XII.A.l Applicability : 

XII.Al.a through c XII.AI.a through c Applicability I 

XII.Al.d None Applicability 

. XII.A2 XII.DA Exception to applicability for oil refineries 

XII.A3 None Applicability for natural gas processing 

plants and certain natural gas compressor 

i 

stations. Indicates they are subject to 

• Section XILG. 

XII.A4 None Applicability for certain glycol natural gas 

dehydrators, natural gas compressor . stations, drip stations, or gas processing 

plants. Indicates they are only subject to 

XILB and XILH. 

XILA5 XII.A8 Exception to applicability based on 

uncontrolled actual VOC emissions 

I threshold of 30 tons per year. I 
XII.B.l, 2, 3, 9, 12, 


and 14. 


XII.B.4, 5, 6, 7, 8, 


10, 11, and 13. 


XII.C.l.a 

I 

, XILC.l.b 

XILC.l.c 

XII.C.I.d 

! XII.C.l.e and f 

XII.C.2 and 

XILC.2.a 

XII.C.2.b 

XII.D 

i 

f XII.D.I 

XII.E.I 

XILE.2. 


XII.E.3., XII.E.3.a 


and b. 


XILEA. 


XII.EA.a- d. 


XII.E.5. 

XII.D.l; XII.D.5 

through 9. 

None 

XII.D.2.a 

XII.D.2.b 

XII.A.7 and 

XII.A.4.h 

XII.D.2.c 


None 


XII.D.3 

! 

None 

XII.A.2 

None 

i XII.A.2.a through 

h. 

XII.A.9 

XII.A.3 


None 


None 

XILA.3.a and b. 

XII.A.4.·. 

XII.A.3.c - f. 


None 


36 

Definitions of various tenus. I 

Definitions of various tenus. XII.B.13 

contains a State-only definition. 

General requirements for 

operation/maintenance of control 

equipment. 

General requirement to minimize leakage 

VOCs. 

Air pollution control equipment control 

efficiency. Failure to operate and maintain 

control equipment at indicated locations is a 

violation. 

Requirements for combustion devices. 

' State-only requirements related to 

combustion devices. i 

Emission factors for emission estimates. 

State-only. Emission factors for emission 

estimates in areas other than the 8-hour 

ozone control area (DMAlNFR 

nonattainment area). 

Emission control requirements for 

condensate tanks. 

. Control requirement for new and modified 

condensate tanks. 

I System-wide control requirements for 

• condensate stora e tanks. 

i Alternative emission control e ui ment. 

: Monitorin 

Requirements for control equipment other 

than a combustion device. 

State only requirement related to new and 

modified tanks controlled by a combustion 

device. 

, Checks for combustion devices. 

Documentation ofins ections. 

Re uirements for the weeki check. 
I 

XII.F. 

. XII.F.l and 2. 

XII.F.3 

XILF.3.a(i) 

XII.F.3.a(ii) and 

(iii) 


XILF.3 .a(iv) 


XII.F.3.a(v}(vii) 

• XII.F.3.a(viii) 

XII.F.3.a(ix)- (x) 

XII.F.3.b d. 

I

IXII.F.3.e 

I 

I XII.F.3.f 

I 

• XILF.4 

XII.F.4.a 

I XII.F.4.h-c 

, XILFA.d , 

i 

!XII.FA.e , 

XILF.4.f 

XILF.4.g. 

XILF.4.h. 

XII.FA.i. 

XILA.4 and 

i XII.A.S. 

i 	XII.A.lO and 11 

XILA.4. 

XII.AA.a. 

XII.AA.b and c 

XII.A.4.d.i 

XII.A.4.d.ii - iv. 

XII.A.4.e. 


XII.AA.f - g 


XILA.4.h - j. 


None 

None 

XII.A.S 

XII.A.S.a 


XII.A.S.h-c 


XILA.S.d 

XII.A.S.e 

XII.A.S.f 

XILA.S.g. 

XILA.S.h 

XII.A.S.i. 

37 

systems. 


Recordkeeping and reporting requirements. 


Marking of AIRS numbers on tanks. I 


Introductory langua~e for recordkeeping. 
 I 

List of tanks and production volumes. 


Listing of emission factors and location and 


control efficiencies. 


List weekly and monthly production values. 


Describes how to determine the averages. 


List weekly and monthly uncontrolled actual 


and controlled actual emissions by tank and 


system-wide. List percent reductions 


weekly and monthly . 


Note any downtime and account for it. 


Maintaining and mailin~ ofspreadsheet. 


Failure to have control equipment as 


indicated on spread sheet is violation. 


Retain spread sheets for five years. 


Maintain records of inspections. 


State only. Maintain records of required 


i 	surveillance system. 

State only. Keep records for new and 

modified , tanks - when installed, etc. 

' Reportin~ for ~stem-wide r~uirements. 

List , tanks andproduction volumes. 


List emission factor and location and control 


efficiency. 


What different reports must show based on 


i time of year. Emissions individual tanks. 

-,\ 

What different reports must show based on 

time of year. Emissions ~stem-wide. 

What different reports must show based on 

time of year. Percent reduction systemwide. 

Note shutdown of control equipment and 

account for same in totals. 

State whether required reductions were 

achieved. I 

Include any information requested by the 

Division. J 
38 


I 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.
 IXII.F~- n None. 	 I State-only additional requirements for ! 

certifications. 

XlI.F.5 XILA.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.l XII.B.l 	 Part 60 leak detection applies. .. i XII.G.2 I XII.B.2 Apphcablhty of control eqUIpment. 

i XII G 3 XII B 3 Compllance r dt a e fI or eXlS'1'109 plan It s.

IXII.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 gasfired stationary or portable engine is subject 

to Section XII.H and/or XVI. 

XILH 	 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. 
 I 	 i 

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 
39 


uncontrolled actual condensate tank VOC emissions in the DMAlNFR 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% systemwide 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 XILA. 

Section XII.A defines the applicability of Section XII requirements and is consistent with 
40 


the current EPA-approved applicability provisions in Section XII. 

Section XII.B. 

Section XII.B contains definitions specific to Section XII. The substance ofthe 

definitions contained in Sections XII.B.I, 2, 3,9,12, and 14 is unchanged from the definitions 

contained in SIP-approved Sections XII.D.I and XII.D.S 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.l. 

Section XII.C.I contains general requirements for air pollution control equipment and 

prevention of leakage. Colorado did not change the substance of the corresponding EP Aapproved 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 EPAapproved SIP (Sections XII.D.3.b and 3.b.i), the emission factors to be used are specified for 
41 


condensate storage tanks at natural gas compressor stations, natural gas drip stations, and gascondensate-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 detennined under Section XII.C.2 will not be 

needed to detennine 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 fonns 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.l for new and 

modified condensate tanks applies to every tank, this misstatement would not undennine the 

enforceability of the requirements in Section XII.D.l. However, Colorado should correct this 

statement. 

Section XII.D.l. 

Section XII.D.l 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 
42 


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 XILD.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 in201 O. As noted above, the revised section significantly 

increases the summer ozone season weekly VOC reduction requirements from the current EPAapproved 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 

6 

summer ozone season. 

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 
43 


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 XILD.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 

ofthis provision, but simply renumbered it from Section XII.A.9 to now be section XILD.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 EPA6 We note that the system-wide weekly reduction requirement of78% that commences in May 2012 in the current 
44 


approved Sections XII.A.3 and XILA.4.j. Colonuo 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 XILE.l 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 XIl.EA (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.EA.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 

EPA-approved version of Section XlI contains no tennination date. 
45 


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 ofthe provisions are identical to those in the current EPA-approved SIP. 

Sections XII.F.l through 4. 

In Sections XII.F.l 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 
46 


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 XILF.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.AA.i. 

Revised Section XII.F.3.d requires owners/operators to maintain records ofinspections 

required by Section XII.E but does not specify a period for maintenance ofthe 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. 
47 


Revised Section XILF.3 does not contain adequate recordkeeping for the control 

requirement that applies to new and modified condensate tanks under Section XII.D.l. 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.FJ.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 fiveyear 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 
48 


with the requirements of Section XII.D.l within a reasonable time frame. The deficiencies in 

recordkeeping and reporting requirements pertaining to the control requirements of revised 

Section XII.D.I form part of the basis for our proposed disapproval ofrevised 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 fColorado 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 EPAapproved 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. 
49 


Revised Section XII.F.4.1 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 XlI'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 ofthis 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 II 0(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 ofrevised Section XII. 
so 


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 ofNGCSs 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.S also contains 

typographical errors. In the first line, the reference to "Sections XII" should be to "Section XII." 

In XII.F.S.a, the reference to "this Section XII.A" should be to "Section XII.D." 

Section XII.G. 

Section XII.G specities the control requirements applicable to gas-processing plants and 

corresponds to current EPA-approved Section XII.S. EPA-approved Section XII.B requires gasprocessing plants to meet the requirements in Section XII.B specifically applicable to such plants 

as well as the requirements in current EPA-approved Section XILC, 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.I.a and XII.C.I.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. 
51 


Section XII.G.l. 

Section XII.G.l specifies that NSPS leak detection and repair requirements apply 

regardless ofthe date of construction of the facility. Colorado made no substantive changes to 

this provision. 

Section Xn.G.2. 

Section XILG.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 XILB.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 tot:ls 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 ifthe 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 ofthe basis for our 

proposed disapproval ofrevised Section XII. 
52 


Section XILG.3. 

Section XII.G.3 specifies the compliance date for existing natural gas processing plants. 

Colorado did not change the substance ofthis provision. 

Section XII.GA. 

Revised Section XII.GA, 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 XILG." 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. 
53 


This deficiency forms part of the basis for our proposed disapproval of revised Section XII. 

Section XILG.6. 

Section XILO.6 is new. It specifies that a NOCS or NODS subject to Section XILO 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.O. We view this as a clarifYing change that is consistent with CAA 

requirements. 

Section XII.H. 

Section XILH specifies control requirements for still vents and vents from gascondensate-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 XILH, Colorado attempted to clarifY current EPA-approved Section 

XILC's applicability threshold for control requirements. The relevant language in revised 

Section XILH reads as follows: 

"This Section XILC 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 
54 


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 

XILH. 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 n.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 l5-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. 
55 


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 

ofthe 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 
56 


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 
57 


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 ofthe 

total allowable emissions defined in the SIP for a certain date, for the purpose ofmeeting 

reasonable further progress milestones or demonstrating attainment or maintenance ofthe 

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 of2010 NOx and VOC MVEBs , Area of Applicability I 

I Northern Subarea 

Southern Subarea 

Total Nonattainment Area 

2010 NOx Emissions 


(tons per d'!Y) 


20.5 


102.4 

122.9 

2010 VOC Emissions 

(tons~er day) 

19.5 

89.7 

109.2 I 
58 


Once Colorado submitted the OAP to us, we determined the adequacy ofthe 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 website 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 website: 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 ofthat date, the Denver Regional 

Council ofGovernments (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 
59 


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 ofthe Boulder County northern boundary and extended through 

southern Weld County to the Morgan County line. This area includes the nonattainment portion 

of DR COG's regional planning area and the southern Weld County portion ofthe Upper Front 

Range TPR. We note that both subareas are further identified in Figure 2: "8-hour Ozone 

Emission Budget Subareas" at page VJ-6 in the ~AP. 

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 
60 


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(1) ofthe CAA 

Section 110(1) 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 ofthe 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 ltD ofRegulation 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 ofthe 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
61 


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 ofthe 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 11.0. 

• 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 11.0. 

• Revisions to Section XII. 
62 


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 Sl.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. 

EP A 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. 741O(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: 
63 


• 	 is not a "significant regulatory action" subject to review by the Office of Management aOO 

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 smaH 

entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.); 

• 	 does not contain any unfunded mandate or significantly or uniquely affect small 

governments, as described in the Unfunded Mandates Reform Act of 1995 (Public Law 

104-4); 

• 	 does not have Federalism implications as specified in Executive Order 13132 (64 FR 

43255, August to, 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). 
64 

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. 
65 


Approval and Promulgation of Air Quality Implementation Plans; Colorado; Attainment 

Demonstration for the 1997 8-Hour Ozone Standard, and Approval of Related Revisions 

List of Subjects 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: 	 Carol Rushin 

Acting Regional Administrator 

Region 8