ENVIRONMENTAL PROTECTION AGENCY 40 CFRpart 52 [EPA-R08-0AR-2010-0285; FRLApproval and Promulgation ofAir Quality Implementation Plans; Colorado; Attainment Demonstration for the 1997 8-Hour Ozone Standard, and Approval ofRelated Revisions AGENCY: Environmental ProtectionAgency (EPA). ACTION: Proposed rule. SUMMARY: EPA is proposing to act onproposedrevisions to Colorado's State· Implementation Plan (SIP). OnJune 18,2009, Colorado submitted proposed SIP revisions intended to ensure attainment ofthe 1997 ozone National Ambient AirQuality Standards (NAAQS) in the DenverMetro AreaJNorth Front Range nonattainment area by 2010. The June 18, 2009 submittal consists ofan ozone attainment plan, which includes emission inventories, a modeled attainment demonstration using photochemical grid modeling, a weight ofevidence analysis, and 2010 motorvehicle emissions budgets for transportation confonnity. The submittal also includes revisions to Colorado Regulation Numbers 3 and 7 and to Colorado'sAmbient Air Quality Standards Regulation. EPA is proposing to approve the attainment demonstration, the rest ofthe ozone attainment plan, with limited exceptions, and the revisions to Colorado Regulation Number 3, Parts A and B. EPA is proposing to approve portions ofthe revisions to Colorado Regulation Number 7 and to disapprove otherportions. EPA is proposing to disapprove Colorado Regulation Number 3, Part C, and Colorado's AmbientAir Quality Standards Regulation. EPA is proposing to disapprove limited portions ofthe ozone attainment2 plan. EPA is proposing these actions pursuant to section 110 and part D ofthe Clean AirAct (CAA) and EPA's regulations. 

### DATES: Comments mustbe received onorbefore [insert date 30 days from date ofpublication]. 

### ADDRESSES: Submit yourcomments, identified by DocketID Regulation Number

### EPA-R08­ OAR-2010-0285, by one ofthe following methods:
• http://www.regulations.gov
. Followthe on-line instructions for submitting comments.
• E-mail: kenney.james@epa.gov
• Fax: (303) 312-6064 (please alertthe individual listed in the 

### FOR FURTHER INFORMATION CONTACTifyou are faxing comments).
• Mail: James Kenney, AirProgram, 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. Suchdeliveries 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 ofboxed information. Instructions: Directyourcomments 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 commentincludes information claimedto be Confidential Business Information (CBI) orotherinformation whose disclosure is restricted by statute. Do not submit information that you considerto be CBI orotherwise protected through3 http://www.regulations.gov ore-mail. The hrtp:llwww.reguiations.gov web site is an "anonymous access" system, which means EPA will not know your identity orcontact information unless you provide 

### it in the body ofyour 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 ofthe commentthat is placed in the public docket and made available on the Internet. Ifyou submit an electronic comment, EPA recommends that you includeyourname and other contact information in the body ofyourcomment and with any disk orCD-ROM you submit. IfEPA cannot read yourcomment due to technical difficulties and cannot contactyou for clarification, EPA may not be able to consideryour comment. Electronic tiles should avoid the use ofspecial characters, any form ofencryption, and be free ofany defects
orviruses. Foradditional information about EPA'spublic 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 othermaterial, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available eitherelectronically inhttp://www.regulations.gov orin hard copy at the AirProgram, 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 sectionto view the hard copy ofthe docket. You may viewthe hard copy ofthe 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 ofthis document, we are giving meaning to certain words or initials as follows:
• The words or initials Act or CAA mean orrefer 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 orrefer to State Implementation Plan.
• The words Colorado and State mean the State ofColorado. TableofContents I. General Information II. What Action is EPA Proposing? III. What is the Background ofThis Action? IV. What is EPA's Evaluation ofthe SIP Revision? A. Procedural Requirements B. Monitoring C. Emission Inventories D. Photochemical Grid Modeling5 E. Modeled Attainment Demonstration F. Weight ofEvidence G. Specific OAP Language H. SIP Control Measures I. Transportation Conformity V. Consideration ofSection 110(1) ofthe CAA VI. ProposedAction VII. Statutory and Executive OrderReviews



### I. GeneralInformation What should I consideras Iprepare my comments for EPA? 1. Submitting eBl: Do not submit CBI to EPA throughhttp://www.regulations.gov oremail. Clearly mark the part orall ofthe information that you claim to be CBI. For CBI information in a disk orCD ROM that you mail to EPA, mark the outside ofthe disk orCD ROM as CBI and then identifY electronically within the disk orCD ROM the specific information that is claimed as CBI. In addition to one complete version ofthe commentthat includes information claimed as CBI, a copy ofthe commentthat does not containthe 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 CFRpart 2.

### 6 2. Tips/or Preparing Your Comments: When submitting comments, rememberto:
• IdentifY the rulemaking by docket number and otheridentifYing information (subject heading, Federal Registerdate and page number).
• Follow directions

- The agency may ask you to respond to specific questions or organize comments by referencing a CFRpart or section number.
• Explain why you agree or disagree; suggest alternatives and substitute language for yourrequested changes.
• Describe any assumptions and provide any technical information and/ordatathatyou used.
• Ifyouestimate potentialcosts orburdens, explain howyou arrived at your estimate in sufficientdetail to allow for it to be reproduced.
• Provide specific examples to illustrate your concerns, and suggest alternatives.
• Explainyourviews as clearly as possible, avoiding the use ofprofanity orpersonal threats.
• Make sure to submit your comments by the commentperiod 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 submittedto EPA on June 18,2009,to
ensure attainment ofthe 1997 ozoneNational Ambient Air Quality Standards (NAAQS) in the DenverMetro AreaINorth Front Range (DMAlNFR) nonattainment area. The DMAlNFR

### 7 nonattainment area includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, and Jefferson Counties, and portions ofLarimer and Weld Counties (40 CFR §81.306).

Colorado's proposed SIP revisions consist ofthe following parts:
• 8-Hour Ozone Attainment Plan (OAP), which includes monitoring information, emission inventories, a modeled attainment demonstration using photochemical grid modeling, a weight ofevidence 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 hourozone NAAQS. We are proposing to approve the motorvehicle emissionsbudgets contained in the**~AP.** We are proposing to approve all other aspects ofthe OAP, with the following limited exceptions: we are proposingto disapprove the last paragraph on page IV-l 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 ofthe OAP, and we are proposing to disapprove the reference to Attachment A in the OAP's Table ofContents and on page IV-3 ofthe**~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 RegulationNumber 3, Part C.

We are proposing to approve the following portions ofthe revisionsto Colorado Regulation Number 7:
• Revisions to Sections I through XI, except for Colorado's repeal ofSection 11.0.
• Revisions to SectionsXIII throughXVI.

We are proposing to disapprove the following portions ofthe revisions to Colorado Regulation Number 7:
• Colorado's proposed repeal ofSection II.D.
• Revisions to Section XII.

We are proposing to disapprove the revisions to Colorado'sAmbient Air Quality Standards Regulation.

The provisions we are proposing to approve meet the requirements ofthe 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 ourregulations. The specific bases for
ourproposed actions and ouranalyses and findings are discussed in this proposedrulemaking. Technical informationthat we rely upon in this proposal is contained in the State'stechnical

### 9 support document (TSD). The TSD is available on-line athttp://www.regulations.gov, Docket No. EPA-R08-0AR-2010-028S.

III. What is the Background ofThisAction? On July 18, 1997, EPA promulgated a revised 8-hourozone standard of0.08 parts per million (ppm) (62 FR38855). Ozone is formed from the photochemical reaction ofnitrogen oxides (NOx) with volatile organic compounds (VOCs). Under EPA regulations (40 CFRpart 50, Appendix I), the 19970.08ppm 8-hour ozone NAAQS is attained when the 3-year average of the annual fourth highest daily maximum 8-houraverage ambient ozone concentrations is less than orequal to 0.08 ppm. Forty CFRpart 50, Appendix I, section 2.3, directs that the third decimal place ofthe computed 3-year average be rounded, with values equal to or greaterthan 0.005 rounding up. Thus, under ourregulations, a computed 3-year average ozone concentration of0.085 ppm is the smallest value that is considered to be greaterthan 0.08 ppm and a violation ofthe standard.

On April 30, 2004, we designated areas as attaining ornot attaining the 1997 8-hour
ozone NAAQS. As part ofthat rule, we deferred the effective date ofa designation as nonattainment for multiple areas ofthe country, including the DMAlNFRarea. These areas, which were called Early Action Compact (EACs) areas, agreed to follow a program to achieve early reduction ofemissions necessary to attain the 1997 8-hour standard in orderto attainthat standard no later than December 31,2007 (69 FR23857). Becausethe DMAlNFR area violated

# -------------------

-



### 10 the 1997 8-hour standard during the summer of2007, the nonattainment designation for the area became effective onNovember 20,2007.

Ourregulations 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 areaon June 18,2009.

IV. What is EPA's Evaluation ofthe 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) ofthe CAA requires that states adopt SIP revisions afterreasonable 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 onJanuary 30, 2009. 1 Colorado met the CAA's procedural requirements for reasonable notice and public hearing.11 

### B. Monitoring The monitoring section ofthe OAP provides information with respectto the location of
ozone monitors in Colorado (from southern Metropolitan Denverto northern Fort Collins, including Rocky MountainNational Park); the State's ambient air qualit.y data assurance program; a description and commitmentfor continued operation ofthe ozone monitoring network; and relevant 8-houraverage ozone monitoring data and recovery rates from 2000 through September2008.

Ozone monitoring data was collected following 40 CFRpart 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 FR49435).

Datafor 2005-2007 and 2006-2008 reflect violations ofthe 8-hour ozone NAAQS atthe Rocky Flats North monitor (values of0.085 and 0.086 ppm, respectively). Monitoring data are used as a basis for photochemical grid modeling inthe attainment demonstration, a process described below. In the OAP, Colorado indicatesthat it will continue to operate an appropriate air quality monitoring network in accordance with 40 CFRpart 58.

I State revisions to the SIPdo not become federally effective unless and until they are approved by EPA. 40 CFR12 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 catalogNOx 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 ofthe NAAQS. A base year emissions inventory serves as the starting point for attainment-demonstration airquality modeling and for determining the need for additional SIPcontrol measures.
Using 2006 as the base yearemissions inventory ensures that the inventory reflects one of the years used for calculatingthe design value thatresulted in the area's nonattainment designation. The design value is the 3-year average ofthe 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 periodof2005-2007, 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 ofthe OAP. As described in greaterdetail 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 beyondthe measures assumed for the 2010 base case. These additional control measures are described at page V-I0 ofthe OAP (2008 State-onlyrevisions to Regulation Number 11 that tightened tailpipe standards, 2008 State-only revisions to Regulation Number 7that required low-bleed devices for pneumatic controllers, an increase in the systemwide reduction ofcondensate tank VOC emissions from 75%to 81% in 2010, and 7.8 psi RVP gasoline in the NFRarea). 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 ofozone.

. The three emissions inventories discussed above (i.e., 2006 base case emissions inventory, 2010 base case emissions inventory, andthe 2010 control case emissions inventory)
were developed using EPA-approved guidelines for stationary, mobile, and area/off-road emission sources. Point source emissions datawere self-reported to the State by individual14
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 ofeconomic growth modeling and analysis. Table 1shows the emissionsby 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 SolventEvaporation 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 I Condensate Tanks 126.5 129.6 105.61 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 IArea 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 1.5
. Aircraft 7.4 1.3 8.2 8.2 1.5 I ! i 

### I Railroad 12.8 0.5 13.8 0.6 13.8 0.6

OtherCoatings/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 ILawn 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-RoadMobile 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 53.0 694.0 53.0 694.0 53.0

# ~ Total 429.8 1172.6 391.5 1165.8 

### I 387.6 1119.41
Colorado employedEPA guidelines for rule effectiveness when preparingthese emission inventories. Rule effectiveness, expressed as a percentage, represents the ability ofa 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 forrule effectiveness. A rule effectiveness of83 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 of83 percent is reasonable for rule effectiveness for oil and gas control measures. Forfurther detail regarding Colorado's analysis, the readershould referto Colorado's TSD.

For oil and gas point and area sources, the 2010 control case inventory reflects a 43.2 tpd16 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 conductedphotochemical grid modeling (hereafterreferred to as "modeling")to demonstrate that the emissions control strategy leads to attainmentofthe NAAQS by 2010. The modeling followed EPA's photochemical modeling guidance (Guidance on the Use ofModels and Other Analyses for Demonstrating Attainment ofAir 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 setup using a nested 36112/4 kilometer (km) domain structure. The 36 km domain covering most ofNorth America was used to generate boundaryconditions (BCs) for the 12 km modeling domain. CAMx was then used to simulate ozone formation within the 12/4km 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 performancebe tested againstcertainperformance17 goals. Model perfonnance testing is used to detennine the model'sreliability in projecting future yearozone concentrations. Using meteorological and emissions datafrom a historical base period, ozone concentrations predicted by the model are compared to monitored ozone concentrations to detennine model perfonnance.

EPA'smodeling guidance emphasizes the use ofgraphical 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 thatthe model is getting the right
answer for the right reason). Colorado's model perfonnanceevaluation 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 ofthe attainment demonstration. These include: unpaired accuracy ofthe peak 5t20%; nonnalized mean bias 5t15%; and nonnalized mean gross error ::;35%.
Using a June 1through July 30, 2006 episode period, Colorado calculatedthe mean normalized bias and gross error statistical measures using all the predicted and observed hourly
ozonepairs, matched by time and location, for which the observedozone was equal to orgreater than 0.060 ppm. The evaluation showed that the modeling achieved the "Unpaired Accuracy of the Peak" perfonnance goal of:s±20%for 58 ofthe 60 simulation days ofthe episode (i.e., 97% ofthe modeled days). There were 58 daysrather than 60 with bias and error comparisons during the episode period because two days had no observed ozone values greaterthan 0.060 ppm; thus,18
no statistics could be calculated for those two days. Ofthe 58 days, 50 days (or 86%) achieved EPA's 

### :s±15% performance for mean normalized bias and all ofthem 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 ofobserved 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 attainmentdemonstration for ozone is one in which model estimates are used in a relative senseratherthan absolute sense. That is, we take the ratio ofthe model's future (2010) to current (2006) predictions at ozone monitors in the DMAlNFRarea. We call these ratios "Relative Response Factors" (RRFs). Future ozone concentrations are estimated at existing monitoring sites by multiplying a modeled RRF at locationsnear each monitorby the observation-based, monitor-specific, baseline design value. The resulting predicted future concentrations are then compared with the 19970.08ppm 8-hourozoneNAAQS. Jfthe predicted future concentrations ofozone are lowerthan 0.08 ppm at all monitors, attainment is19 demonstrated. The test for ozone is based on the calculation ofa 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, 20I 0 base case, and final 2010 control measure case modeling. The final 2010 control measure case is notthe same as the 2010 control case discussed in section IItC ofthis 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 of81% - and additional control requirements. Colorado used the final adopted version ofRegulation Number7 to create a final 2010 control
measure case inventory and then modeled that inventory. Forfurther details, see page V-7 ofthe OAP and Appendix IofColorado'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-hourozone concentration DVFs. Per EPA guidance, the first set ofDVFs 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 CFRpart 51, Appendix W, section 7.2.1.2, 40 CFRpart 50, Appendix I,20 section 2.1.1, and Guidance on the Use ofModels and Other Analyses for Demonstrating Attainment ofAir 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 ofappm. Although not relevant to detennining attainment ofthe NAAQS, Colorado included these last columns as part ofits evaluation ofmodel perfonnance, to attempt to distinguish any differences in the ozone projections betweenthe 2010 base case and final 2010 control measure modeling and as part ofits weight ofevidence analysis.

The maximum projected 8-hourozone 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 below0.085 ppm, the 2010 base case and final 2010 control measure case bothpass the modeled ozone attainment demonstration test. However, because there are four monitoring sites withprojected 2010 DVFs of0.082 ppm orhigher (0.084 ppm at Rocky FlatsNorth and Fort Collins West, 0.083 ppm at Chatfield, and 0.082 ppm atNREL), EPA's modeling guidance indicates a "weight ofevidence' (WOE) analysis should be perfonned.

Table 2. Projected 2010 8-hourozone DVFs for the 2010 Base Case and Final 2010 Control Measure Case. Monitor County DVC 2010 DVF 2010 DVF 

# I I

i i Name (2005- (EPA Guidance) (nearest 0.0001 2007) (ppm) 

# I ppm) i I21 

# 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. BoulderCreek 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 FlatsNorth 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 : ofmeasured 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 :
For values that Colorado reported to the nearest 0.0001 ofa ppm, the maximum projected DVF for the 2010 Base Case is 0.0849 ppm at both the Rocky FlatsNorthand FortCollins 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 FlatsNorthmonitoring 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 atone site, withthe remainder ofthe monitoring sites having identical DVFs for the 2010base case and final 201022 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 Towermonitoring site (Greeley), which is expected given the proximity ofthe monitorto the oil and gas developments in Weld County. Weld County is where the largest VOC emissionreductions would occurdue to Colorado's final 2010 control measures for condensate storage tanks. These results are consistent with Colorado's 2010 sensitivity modeling, which found thatproposed 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 ofColorado'smodeled attainment demonstration. Both the 2010 base case modeling and the final 2010 control measure case modeling showthat the DMAlNFRarea will attain the 8-hourozoneNAAQS by 2010. However, because we are proposing to disapprove Colorado's revisions to Regulation Number7, Section XII, which Coloradorelied on in its final 2010 control measure modeling, ourproposed approval ofColorado'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 ofthe CAA. Additional control measures would not advance the attainment date.23 F. Weight ofEvidence As noted above, since four monitors (Rocky Flats North, Fort Collins West, Chatfield, and NREL) modeled concentrations that fall into the range of0.082 to 0.087 ppm, a weight of evidence (WOE) analysis is recommended by EPA (see "Guidance onthe Use ofModels and OtherAnalyses for Demonstrating AttainmentofAir Quality Goals for Ozone, PM2.5, and Regional Haze," EPA-4541B-07-002, April 2007). A WOE analysis involves one ormore supplemental analyses to enhance the assessment ofwhether the planned emissions reductions will result in attainment ofthe 19970.08 ppm 8-hourozone NAAQS. The WOE analysis includes: monitoring and emission inventory trend analysis; reviewofthe conceptual model for
ozone formation along the North Front Range; additional modeling metrics; alternative attainmenttest methods; and assessment ofthe efficacy ofColorado's SIP-approved regulations, state-onlyregulations, and voluntary control measures. The WOE analysis is then used to determine ifthe four monitors that modeled ozone concentrations in the range of0.082 to 0.087 ppm are expected to demonstrate attainment ofthe NAAQS.

Ourreview ofthe WOE analysis identified a number ofkey pointsthat provide further evidence that the modeling is reliable and thatthe DMAINFR areawill attain the NAAQS. First, although individual concentrationshave been highly variable, the aggregate trend in weathercorrected 4th maximumtime 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 ofthe weekend­24 weekday effecrrelated to potential disbenefits from NOxreductions shows a strongereffect 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 ofthe WOE analysis supports the validity ofthe modeling. Third, within the DMA, potential increases in ozoneconcentrations due to NOx emissions reductions from the federal motorvehicle control program do not appear significant and should notthreaten the NAAQS. Atmonitoring locations outsidethe DMA, the WOE analysis suggests thatreductions in NOx emissions will reduce ozone, possibly with greaterefficiency than VOC reductions. Fourth, the WOE analysis includes othermodeled metrics that indicate reductions by 2010 in total ozone, grid cells over0.080 and 0.085 ppm 8-hourozone, and grid cell-hours over 0.080 and 0.085 ppm ozone based on the various control scenarios. Forexample, these metrics indicate a reduction in total ozone and grid cells greaterthan 0.085 ppm betweenthe 2006 and 2010 base cases of21% and 14%, respectively. This suggests thatthechanges in emissions between the 2006 and 2010 base cases will reduce orhave reduced ozone concentrations.

EPA finds the WOE analysisprovides further support to the photochemical grid modeling, and the modeling and WOE support a determination thatthe area will attain the 1997 0.08 ppm 8-hourozone 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 ofemissions. Undercertain 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 ofthe OAP because these paragraphs indicate that the OAP revises Section XII of Regulation Number 7 as part ofthe SIP. We are proposing to disapprove revised Section XII of Regulation Number 7, and approval ofthis language in the OAP would potentially conflict with
ourproposed disapproval ofrevised Section XII. We are proposing to disapprove the words "federally enforceable" in the second to last paragraph onpage V-6 ofthe OAP for the same
reason. The language in question reads, "AQCC action on December 12,2008 adopted a federally enforceable SIP control measurerevising Regulation No.7
..." Only our approval can make the revisions federally enforceable.
Elsewhere, the OAP discusses "adopted SIP control measures" orprovisions that will be part ofthe SIP. We interpret these various references as reflecting the AQCC'sintent to submit the referenced regulations to us for approval and not as an indication that they are already part of the federally approved SIP orthat ourapproval ofthe OAP alone will make the referenced regulationspart ofthe federally approved SIP. We are acting on the referenced regulations as separate elements.

We are also proposingto disapprove the reference to Attachment A in the OAP'sTable of Contents and on page IV-3 ofthe OAP because Attachment A was not submitted to us with the OAP and because the revisions referenced as being included in thatAttachment 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 submittedrevisions to Regulation Number 3, Parts A, B, and C, along with the OAP. Among other things, Part A requires stationary sources to submitAir Pollutant Emission Notices (APENs)**~o** Colorado beforeemitting pollutants. A source's APEN must include information about location and nature ofthe source and expected emissions. Part A also contains various exemptions from APEN filing. Colorado'sproposedrevisions to PartA would remove several ofthese exemptions from the regulation. This would subject the specified source categories to APEN filing and potential regulation underRegulation Number 7, which uses the APEN-filing threshold in Regulation Number 3, Part A, as the trigger for applicabilityofvarious requirements.
Regulation Number 3, Part B, contains construction permit requirements for stationary
sources. Part B also contains various exemptions from minor source constructionpermit requirements. Part B contains a generic exemption for sources that are not required to file an APEN. Colorado recognized that its proposed removal ofthe APEN-filing exemption for certain
sources under Part A would also have the effect ofsubjecting those sources to minor source27 construction permit requirements under Part B. For four types ofsources, Colorado determined that this would not be appropriate and adopted a revision to Part B that would continue to exempt these four types ofsources from minor source construction pennitting. Thepremisebehind all the minor source construction pennitting exemptions in Part B is thatthe emissions from the specified sources are deemed to have a negligible impact on air quality.
Regulation Number 3, Part C, contains Colorado's operating pennitrequirements. 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, eliminateprovisions that exempt the following specific types ofoil and gas-related.emissionpoints from the APEN requirements: petroleum industry flares with emissions ofless than 5 tons peryear, 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 storagetanks where production through the tank amounts to less than 730 barrels per year. The elimination ofthese exemptions means that the facility will need to file APENs withthe State, which should allow Colorado to collect more accurate inventory infonnationregarding emissions related to oil and gas operations. This would also subject the specified source categories to the condensate storage28 tank VOC control requirements ofRegulation Number 7, SectionXII, which uses the APENfiling threshold in RegulationNumber 3, PartA, as an applicability threshold.

The proposed revisions to Regulation Number 3, Part B maintain an existing exemption from minor source constructionpermitting requirements for certain emissionpoints. The emissionpoints consist ofcertainpetroleum industry flares with emissions less than 5tons per year, crude oil truck loading equipmentand condensate truck loading equipment, oil and gas production wastewater, and crude oil storage tanks. As noted above, under the current SIPapproved version ofRegulation Number 3, Part B, any emissionpoints exempt from filing APENs are also exempt from minor source constructionpermit 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 ofColorado's proposed revisions to Part Bwould not change the status quo with regard to constructionpermitting requirements for these emission points.

The revisions to Parts A and B make the SIP more stringentby subjecting additional emission sources to reporting requirements. We are proposing to approve these revisions because they strengthen the SIP.
Regarding Part B ofRegulation Number 3, we note thatthere is a discrepancy between29 the numbering ofthe submitted revisions and the EPA-approved SIP. Colorado added new Sections II.D.I.k, I, m, and nto Part B to specify thefour types ofemissions points that will continue to be exemptfrom minor source constructionpermittingrequirements. However, in the current EPA-approved SIP, Section IILD.l ofPart B lists the types ofemissions points that are exempt from minor source constructionpermittingrequirements.) These emissionspoints are listed in Sections IILD.l.athroughj. Forpurposes ofthis action, we are interpreting Colorado's proposed revisions to Part B, in the form ofSections ILD.l.kthrough n, as being an addition to Section III.D.l, and following immediatelyafter Section III.D.l.j ofPart B ofthe EPA-approved SIP. As part ofour 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, RegulationNumber 3, Part C, contains Colorado's operatingpermit regulations, which we do not approve into the SIP. Instead, we approve operatingpermit regulations under ouroperatingpermit regulations at40 CFRpart 70. Thus, we intend to consider approval ofColorado's proposed Part C revisions pursuant to ourpart 70 regulations at such time as Colorado submits an appropriate requestunder40 CFR70.4(i). The revisions are meaningless absent theirregulatory context, and that regulatory context is notpart ofthe EPAapproved SIP and is not incorporated by reference into 40 CFRpart 52. Instead, the approval status ofColorado's part 70 program is reflected in 40 CFRpart 70, Appendix A. Thus, because

3 Colorado previously submitted revisions to Part Bthat contain changes to the numbering ofPart B provisions; we30
we are obligated to act on the State's SIP submission, we plan to disapprove these revisions as a revision to the SIP. Ifthe 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, ifrequested by the State,
we will separately consider these revisions as a revisionto 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 ofspecific emission limits applicable to various industries and generic Reasonably Available Control Technology (RACT) requirements. EPA approvedthe repeal and re·promulgation ofRegulationNumber7 in 1981 (46 FR 16687, March 13, 1981) and has approved various revisions to parts ofRegulationNumber7 overthe 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 proposedrevisions to RegulationNumber7 along with the OAP. On November 18, 2009, Colorado corrected the version ofRegulation Number7 it had submittedto reposition the words "State Only"in various sections ofRegulation Number 7.

will be acting on those revisions separately.31 Colorado made substantive revisions to certain limited parts ofRegulation Number 7, particularly Section XII, and also made non-substantive revisions to numerous parts ofthe regulation. Forease ofconsideration, Colorado submittedthe full text ofRegulation Number 7
as a SIP revision for our approval (with the exception ofprovisions 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 viewthis rulemaking as re-opening
ourpast approval ofthe portions ofthe regulation that were not substantively modified by the State as part ofthis submission.

As noted above, Colorado designated various parts ofRegulation Number7 "State Only" and in Section LA.I.c indicated that sections designated "State Only" are not federally enforceable. Ourinterpretation is that provisions designated "State Only"have not been submitted to us for approval since one ofthe key purposes ofa 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 notproposing to act on the portions of Regulation Number 7 designated "State Only" and do not discuss them further unless they impact the portions ofthe regulation that Colorado intended to be federally enforceable.
Analysis ofRegulation Number7 Changes by Section Section I: Section Icontains applicability provisions, definitions ofnew and existing sources, and32 related provisions. Except for minorclerical 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.Acontains 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 oforganic compounds having negligible photochemical reactivity. The State made minor clerical changes to Section II.C, which contains generic RACT requirements.

Section II as submittedreflects Colorado's repeal ofSections 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 ofa source-specific SIP revision. However, subsequent to submitting Section II.E to us, Coloradorepealed 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 partofits December 12, 2008

4 When we describe changes as clerical in this proposed action, we are referring tochanges like section33 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 partofthe SIP, the Staterepeal ofthose provisions has no meaning for this action. However, we are proposing to approve the language ofRegulation Number7 that reflects the repeal ofILE and F to conform the SIP to the numbering ofColo-rado's regulation.

In additionto the changes noted above, the submitted revision to Section II reflects Colorado's repeal ofSection ILD.5 The SIP-approved version ofSection ILD requires sourcesto seek a revision to the SIP to gain approval ofalternative control plans and testmethods and indicates that no alternative is effective until the alternative is approved as a revisionto the SIP. Colorado originally adopted Section n.D in September 1989 to address specific EPA concerns that Colorado's RACTrule would allow changes to control requirements ortest methods without EPA approval.

We are proposing to disapprove the repeal ofSection II.D for the following reasons: (1)a
renumbering, alphabetizingofdefinitions, minorgrammatical and editorial revisions, and changes in capitalization 5 In March of 1996, Colorado adopted changes to Section 

### n.D as a matter ofState law and submitted the revisions to us for approval. The revisions were part ofan effort by Colorado at thattime to establish a de minimis exemption from Regulation Number 7's RACTrequirements. 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 November2003. Colorado did net re-adoptthe pre-I996 version ofSection 1I.D, and the version ofRegulation Number 7 thatwe are considering in this action indicates that Section Il.D has been repealed.

### 34 court might interpretthe repeal to allowthe State to approve alternative control requirements and test methods without EPA approval, and without public involvement, which could undermine the enforceability ofRegulation Number 7's RACT requirements and would be inconsistent with the CAA, particularly section 11O(i); (2) the State has offered no explanation orjustificationfor the repeal; and (3) other sections ofRegulationNumber 7 still cross-reference Section ltD as specifying necessary procedures for gaining approval ofalternative control requirements and test methods (See, e.g., Section IX.AS.c ofRegulation Number 7), and, therefore, removing Section lIDwould introduce ambiguity into the Regulation

Ourproposed disapproval oftherepeal ofSection ILD does not undermine the validity of the attainment demonstration. Rather, it strengthens it by ensuring that EPA and public review will berequired 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 ofthe program as relied on for purposes ofdemonstrating attainment. Although we are proposing to disapprove the repeal ofSection ltD,ourdisapproval would nottrigger sanctions ora FIP obligation. This is because the repeal ofSection II.D is not required by the CAA (see CAA section 179), and our disapproval ofthe repeal ofSection II.D would not leave a deficiency in the SIP. Section ltDwill 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'srequirements. 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 affectthe substance ofthe requirements. Therefore, we are proposingto approve the changes.

Section XII: SectionXII contains the emission control requirements for condensate storage tanks. The Statereorganized Section XII and included additional control requirements for condensate tanks. The following table outlines the reorganization/renumbering contained in Colorado'sproposed revisions to Section XII: Colorado Revised Corresponding Subject Section XII EPA-Approved Section Number Section XII Section Number i XII.A XII.A Applicability i XII.AI XII.A.l Applicability 

### : XII.Al.athrough c XII.AI.athrough 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 subjectto •Section XILG. XII.A4 None Applicability for certain glycol natural gas dehydrators, natural gas compressor

. stations, drip stations, orgas processing plants. Indicates they are only subjectto XILB and XILH. XILA5 XII.A8 Exception to applicability based on uncontrolled actual VOC emissions 

# I threshold of30 tons peryear. IXII.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.athrough



### 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 ofvarious tenus. 

## I Definitions ofvarious tenus. XII.B.13 contains a State-only definition. General requirements for operation/maintenance ofcontrol equipment. General requirementto minimize leakage VOCs. Airpollution control equipmentcontrol 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 emissionestimates. State-only. Emission factors for emission estimates in areas otherthanthe 8-hour ozone control area (DMAlNFR nonattainment area). Emission control requirements for condensate tanks.

. Control requirement for newand 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 requirementrelated to newand 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 

# I XII.F.3.e I 

### IXII.F.3.f I •XILF.4

XII.F.4.a 

### IXII.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 ofAIRS numbers on tanks. I Introductory**langua~e** for recordkeeping. I List oftanks and production volumes. Listing ofemission factors and location and control efficiencies. Listweekly and monthly production values. Describes howto determine the averages. Listweekly and monthly uncontrolled actual and controlled actual emissions by tank and system-wide. Listpercent 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 ofinspections. State only. Maintain records ofrequired i surveillance system.

State only. Keep records for new and

, modified tanks

- when installed, etc. '**Reportin~** for**~stem-wide r~uirements.** 

,

Listtanks andproductionvolumes. List emission factor and location and control efficiency. What different reports must showbased on i time ofyear. Emissions individual tanks. 

### -, \ What different reports must showbased on time ofyear. Emissions**~stem-wide.** Whatdifferent reports must showbased on time ofyear. Percentreduction systemwide. Note shutdown ofcontrol equipment and account for same in totals. Statewhether 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. 

# I**XII.F~-** n None. 

## IState-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 operatepursuant to a construction oroperatingpermit.

. XII.G
. XII.B. Requirements for gas processingplants
. Introductory statement. XII.G.l XII.B.l Part 60 leak detection applies.



## .. i XII.G.2 

### IXII.B.2 Apphcablhty ofcontrol eqUIpment. 

### i XII G 3 XII B 3 Compllance dt oreXlS '1' 109 plan s. 

## r a e fI It 

# IXII.G.4 XII.B.4 Compliance date for newplants.

XII.G.5 None Newexemption for natural gas compressor stations and drip stations ifcertain

. 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/ornatural gasfired stationary orportable engine is subject to SectionXII.H and/orXVI. XILH XII.C Requirements that apply to vents from gas- condensate-glycol separators on glycol natural gas dehydrators at an oil and gas explorationand production operation, natural gas compressor station, drip station orgas-processingplant. I i The main feature ofSection XII remains the requirement for system-widereductions in condensate storage tank VOC emissions. The current EPA-approved Section XII requires that39 uncontrolled actual condensate tank VOC emissions in the DMAlNFRarea be reduced on a weekly basis duringthe summer ozone season by 75% system-wide beginningMay 1,2007, and 78% beginning May 1,2012. Revised Section XII (Section XII.D.2) requiresan 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 ofthe 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 approverevised Section XII. Below, wedescribe in detail Colorado's proposed revisions to SectionXII and the basis for
ourproposed disapproval ofsuch revisions.

As noted above, Colorado was ableto demonstrate attainment using the 2010 base case inventory. This inventory assumed the continuation ofSection XII requirements as contained in the current EPA-approved SIP, and no new SIP control measures. Thus, disapproval of Colorado'sproposed Section XII revisions would not invalidate the attainment demonstration and, thus, would not trigger sanctions ora FIP obligation.
Analysis ofSpecific Section XII Revisions

Section XILA. Section XII.A defines the applicability ofSection 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 ofauto-igniter and existing are onlypertinent 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 airpollution control equipment and prevention ofleakage. Colorado did not change the substance ofthe corresponding EPAapproved 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. Coloradomade one change to the substance ofthe 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 ordetennined under Section XII.C.2 will notbe needed to detennine compliancewith SectionXII.H. We believe anemission factor will be needed to ensure that the reductionrequirement in SectionXII.H can be enforced. Thus, this is a deficiency in revised SectionXII that fonns part ofthe basis for ourproposed disapproval of

SectionXII.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]missionreductions 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 misstatementwould notundennine the enforceability ofthe requirements in Section XII.D.l. However, Colorado should correctthis statement.

Section XII.D.l. Section XII.D.l requires owners oroperators ofany new ormodified condensate tank at exploration and production sites to route emissions to air pollution control equipmentthat has a42 control efficiency ofat least 95% for VOCs. This requirement applies for the first 90 days after the date offirst production orafter 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 providedthe sourcecan demonstrate compliance with the system-wide provisions specified in other subsections ofsection XII. This newrequirementwould strengthen the SIP.

Section XII.D.2.a. Section XILD.2.acontains the system-wide control requirements for condensate storage tanks. The current SIP provides for a weekly 75% system-wide VOC reduction during the
summerozone season beginning in201

### O. As noted above, the revised section significantly increases the summerozone 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 afterthe 2012 6 summer ozone season.

As noted previously, Colorado was able to demonstrate attainmentbased on a 75% system-wide weekly VOC reduction from condensate storage tanks beginning in 2010. While revised Section XII wouldprovide more stringentreductions in the short term, including the attainment year, itcontains no weekly emission reduction requirement after the 2012 summer43
ozone season. Thus, although it is more stringent in the short term, itis less stringent over the longterm, and the State has not demonstrated how this weakening ofthe SIP will not interfere with maintenance ofthe NAAQS. This deficiency forms part ofthe basis for ourproposed disapproval ofrevised Section XII.

Section XII.D.2.b. Section XILD.2.bis a re-numbered version ofcurrent EPA-approved Section XII.A.9. This section contains aprocess for approval ofalternative emissions control equipment and pollutionprevention devices and processes. Among otherthings, the section specifies requirements for public participation and EPA approval. Colorado did not change the substance ofthisprovision, but simply renumbered itfrom 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 ofSection 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.4and 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 commencesin May 2012 in the current44 approved Sections XII.A.3 and XILA.4.j. Colonuoretained the basic requirement for weekly inspections ormonitoring.

Colorado improved certainprovisions. Forexample, underrevised Section XII.E, an
owner oroperatormust ensure that the control equipment is not only operating, butthat it is operatingproperly. Revised Section XILE.l adds a requirement that owners oroperators of control equipment otherthan a combustiondevice follow manufacturer's recommended maintenance and inspectthe equipment to ensure propermaintenance and operation. Revised Section XIl.EA (current XII.A.4.j) adds arequirementthatthe owner oroperatordocument any corrective actions taken and the name ofthe individual performing the corrective actions resulting from a weekly inspection. Revised Sections XII.EA.athrough d add the requirement that the owneror operatornot only perform certain checks, but that the owneroroperator document those checks.

Revised Section XII.E.3 isdeficient. Itspecifies certain inspection and/or monitoring requirements for combustiondevices. Itintroduces two possible means to monitor/inspect the combustion device, but one ofthem

- use ofa 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 ofState law. Discussions with the State have revealed that use ofa surveillance system was not intended as an alternative to the monitoring method contained in Section EPA-approved version ofSection 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 SectionXII.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 ofthe basis for our proposed disapproval ofrevised SectionXII.

SectionXII.F. Section XII.F containsrecordkeeping and reporting requirements that are currently specified in EPA-approved SectionsXII.A.4 and XII.A.5. The recordkeeping requirements specify information that mustbe listed on a spreadsheet that owners/operators must maintain. Many oftheprovisions 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 operatorto track VOC reductions on a calendar weekly andcalendar monthly basis to demonstrate compliance with system-wide VOC reductionrequirements. Colorado also specified that owners/operators would need to use the Division-approved spreadsheetto track VOC emissions and reductions, notjustany spreadsheet. These changes are reasonable and consistentwith CAArequirements.

In revised Section XII.F.3.a(i), which requires thespreadsheetto list the condensate46 storage tanks subject to Section XII and the production volumes for eachtank, Colorado specified that the spreadsheet must list monthly production volumes. Itis unclear why Colorado added the word "monthly" becausethe following sentence, which Colorado did not change, requires the owner/operatorto list the most recent measurement ofsuch production and the time period covered by the measurement. Also, revised SectionXII.F.3.a(iv) requires the owner/operatorto 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 overthe weekly ormonthly period. Given the specificity ofSection XII.F.3.a(iv),
we are not concerned that the addition ofthe word "monthly"in revised Section XII.F.3.a(i) would undermine the enforceability ofthe regulation. However, Colorado shouldremove the word "monthly"in revised Section XII.F.3.a(i).

Revised Section XILF.3.c requires owners/operators to retain a copy ofeach weekly and monthly spreadsheet for five years instead ofthe three years required by current EPA-approved Section XII.AA.i.

Revised Section XII.F.3.d requires owners/operators to maintainrecords ofinspections required by Section XII.E but does not specify aperiod for maintenance oftherecords. This is consistent with EPA-approved Section XII.A.4.j. However, we consider this something that Colorado should address. Typically, EPA recommends thatsuch records be kept for a minimum offive years.

### 47

Revised SectionXILF.3 does not contain adequate recordkeeping for the control requirement that appliesto 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 equipmentwith a control efficiency ofat least 95% for the first 90 days. However, the regulation only specifies State-only recordkeeping requirements relevantto this requirement

- in SectionXII.FJ.f

- and includes no reporting requirements thatwould be federally enforceable. To meet CAArequirements, the regulation, at a minimum, should specify that owners/operators provide notification and maintain certainrecords. We believerelevant records would include, but may not be limited to: the date a new atmospheric condensate storage tank was installed, orthe date a well was newly drilled, re-completed, re-fractured or otherwise stimulated; the date the control equipment was installed and, ifapplicable, 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 ofthe control equipment orotheroperational problems and corrective action taken. Theregulation should also specify arecord retention period for such records. Theregulation specifies a fiveyearretention period for otherrecords, and it would be appropriate to specify the sameretention period for these records. The regulation should also specify that owners/operators need to report within a reasonable period oftime afterthe date the new atmospheric condensate storage tank
was installed orthe date the well was newly drilled, re-completed, re-fractured orotherwise stimulated. The regulation should also require the owner/operatorto report any non-compliance48 with the requirements ofSection XII.D.l within a reasonable time frame. The deficiencies in recordkeeping and reporting requirements pertaining to the control requirements ofrevised Section XII.D.I form part ofthe basis for ourproposed disapproval ofrevised SectionXII.

In revised Section XII.F.4, Colorado made minor changes to currentEPA-approved reporting requirements. Revised Section XII.F.4.arequires the semi-annual reports to list all condensate storage tanks subject to orused to comply with the system-wide reduction requirements, notjustthose subjectto 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 mustinclude 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/operatornote in the report "the date the source believes the shutdown [ofcontrol 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 ofthe date the shutdown occurred, and, thus, the information is not likely to be meaningful in an enforcement context. In revised SectionXII.F.4.h, Colorado clarified monthly
versus weekly reporting requirements. In revised SectionXII.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 SectionXII.F.4.1 contains a reference to "this SectionXII.D.2." The word "this" should be deleted. This typographical error is not significant enoughto undermine the enforceability oftheregulation, but Colorado should correct it.

Section XII.F.5. Section XII.F.5 contains an exemption from Section XlI'srecord-keeping and reporting requirements for owners/operators ofnatural gas compressor stations (NGCSs) or natural gas drip stations (NGDSs) authorized to operate pursuant to a construction permit orTitle V operating permit ifcertain conditions are met. Coloradoremoved one ofthe conditions for this exemption contained in current EPA-approved SectionXII.A.6. The removed condition provided thattotal emissions from condensate storage tanks associated with suchNGCSs and NGDSs could not exceed 30tons peryear. Ifwe approve the deletion ofthis condition, the recordkeeping and reporting requirements for the relevant sources with emissions exceeding the 30 tons peryearthreshold would need to be established through construction orTitle V operating permits. Our interpretation ofthe CAA is that provisions such as monitoring, recordkeeping, and reporting requirements that are needed to ensurethe enforceability ofthe applicable control requirements contained in a SIP must also becontained in the SIP and cannot be left to development in a permit. See. e.g., CAA sections II0(a)(2)(A) and (F), 40 CFRpart 51, Subpart K, and 40 CFRpart 51, Appendix V. This deficiency forms part ofthe basis for ourproposed disapproval ofrevised Section XII.

# so

We approved the prior version ofthe exemption because Section XII's system-wide VOC reduction requirements were limited to systems with emissions over 30 tons peryear. 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, ifemissions from their units were under 30 tons peryear. Revised Section XII.F.S also contains typographical errors. In the first line, the reference to "Sections XII" shouldbe to "SectionXII." 

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

SectionXII.G. Section XII.G specitiesthe control requirements applicable to gas-processing plants and corresponds to current EPA-approved SectionXII.S. EPA-approved Section XII.B requires gasprocessing plants to meet the requirements in SectionXII.B specifically applicable to such plants
as well asthe 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 SectionXII.G requiresgas-processing plants to additionally comply with the requirements ofrevised Section XII.B, the definitions section, and revised Sections XII.C.I.aand XII.C.I.b, which specify maintenance and design requirements for control equipment and the obligation to minimize leakage ofVOCsto the atmosphere. Itappears thatthis 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 ofconstruction ofthe facility. Colorado made no substantive changes to this provision.

Section Xn.G.2. Section XILG.2 specifies the applicability threshold for installation ofcontrol equipment at gas-processing plants and the efficiency requirement forthe control equipment. In current EPA-approved Section XILB.2, installation ofcontrol equipmentis triggered ifcondensate storage tankthroughput exceeds "APEN de minimis levels." In revised Section XII.G.2, installation is triggered ifuncontrolled emissions from a tank ortankbattery are greaterthan or equal to two tot:ls peryear. We cannotdetermine whetherthis change would strengthen the regulation, weaken it, orleave it the same because we cannotdetermine whetherthe same tanks
ortank 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 ordetermining whether the 95% control has been achieved on arolling 12-month basis, and ifthe goal is to have owners/operators install and operate flares with a control efficiency ofat least 95%, specifying an averaging period is not particularly meaningful. These issues form part ofthe basis for our proposed disapproval ofrevised SectionXII.

### 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 SectionXILG." The reference to Section XII.C should be to SectionXII.H.

Section XII.G.5. Section XII.G.5 is entirely new. Itadds an exemption from the otherwise applicable requirements ofSection XII for an owneroroperatorofany NGCS orNGDS, but only ifthe
owneror operator applies control equipment designedto achieve a VOC control efficiency ofat least 95% to each condensate storage tank ortank battery with uncontrolled VOC emissions greaterthan or equal to two tons peryear 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 ortank battery overthe threshold rather than a maximum of90% control system-wide,

. Section XII does not specify recordkeeping and reporting requirements to supportthe provisions

ofrevised Section XII.G.5. Adequate recordkeeping and reporting requirements in the SIP are necessary to ensure the enforceability ofthe control requirement and to meet CAArequirements.

### 53 This deficiency forms part ofthe basis for ourproposed disapproval ofrevised Section XII.

Section XILG.6. Section XILO.6 is new. Itspecifies that a NOCS orNODS subjectto Section XILO at which a glycol natural gas dehydrator or natural gas-fired stationary orportable engine is operated shall be subjectto Section XII.H and/orXVI. We interpretthisto mean that the provisions ofSections XII.H and XVI, as applicable, would apply to such facilities in additionto the provisions ofSection 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 onglycol natural gas dehydrators located at oil and gas exploration and production operations, natural gas compressor stations, drip stations, or gas-processing plants. In revised SectionXILH, Colorado attempted to clarifY currentEPA-approved Section XILC's applicability threshold for control requirements. The relevant language in revised Section XILH reads as follows: "This Section XILC shall not applyto 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 ofvolatile organic compounds ofless than 15 tons per year. To determine ifa54 grouping ofdehydrators exceeds the 15 tons per yearthreshold 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 peryear. Thecontrol 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.Dthat is part ofa grouping ofdehydrators, but the emissions from such dehydrator shall be included in the calculation."

As written, this passage lacks clarity and contains redundant languagethat EPA cannot approve. While we think we understand the intent

- that emissions from all dehydrators are counted in determining whetherthe l5-ton-per-yearthreshold is exceeded, butthe control requirement only applies to dehydrators with actual uncontrolledemissions above one ton per year - the redundant language and lack ofpunctuation or missing words in the third sentence of revised Section XII.H create uncertainty. The same is true ofstating the threshold for control in two different ways: controls apply where emissions exceed one ton peryear versus controls don't apply where emissions are below the APEN reporting thresholds. This deficiency forms part ofthe basis for ourproposed disapproval ofrevised 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 onthe deficiencies noted above, we are proposing to disapprove the Section XII revisions. While several ofthe 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 ourinterpretation ofthe CAA, it is not appropriate to replace a fully approved Section XII in the SIP with arevised 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 ofany relevant subsections that we could approve would not match the numbering ofthe current EPA-approved subsections; the resulting SIP rule would be unintelligible. Thus, we find that our only available course ofaction is to propose to disapprove all ofrevised Section XII.

Sections XIII through XVI. Sections XIII throughXVI changes are clerical in nature and do not affect the substance oftherequirements. Therefore, we are proposingto approve the changes in Sections XIII through XVI.

Ambient Air Quality Standards Regulation We are proposingto disapprove Colorado's proposed revisions to its ambient air quality56 standards regulation. Colorado's ambient air quality standards regulation duplicates information contained in other parts ofthe SIP and in ourregulations. For example, the ambient air quality standards regulation restates the motorvehicle emissions budgets for various areas. However, under ourregulations, 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 ofvarious areas in Colorado. However, EPA defines the designations and boundaries ofareas in its own regulations. Approval ofthe ambient air quality standards regulation could lead to confusion in the event ofconflict between the ambient airquality standards regulation and our regulations or otherparts ofthe 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. Ifthe State requests to withdrawthe 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) ofthe CAA, transportation plans, transportation improvement programs, and new transportation projects, such as the construction ofnewhighways, must "conform" to (i.e., be consistent with) applicable SIPs. Conformity to a SIP means that57 transportation activities will notproduce new air quality violations, worsen existing violations, or delay timely attainment ofthe NAAQS. EPA's conformity rule provisions in 40 CFRpart 93 establishthe criteria and procedures for determining whether or not these plans, programs, and projects conform to the SIP. In particular, ourregulations require a demonstration thatemissions 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 thatportion ofthe total allowable emissions defined in the SIP for acertain 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'srequirements on MVEBs are found in40 CFR 93.118 and 93.124, and MVEBs are further explained in the preamble to the November 24, 1993, transportation conformityrule (58 FR 62193 62196). Coloradoderivedthe MVEBs for NOx and VOCs from its 2010 base case attainment demonstration and defined the MVEBs in Chapter VI ofthe OAP. We listthe MVEBs in Table 3, below.

Table 3' Identification of2010NOx and VOC MVEBs 

## , Area ofApplicability 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 I58

Once Colorado submitted the OAP to us, we determined the adequacy ofthe MVEBsper the procedures and criteriacontained in40 CFR 93.118. On October 15, 2009, we announced the availability ofthe attainment demonstration and the MVEBs on EPA'stransportation conformity adequacy website and solicited public comment. The public commentperiod closed
on November 16,2009; we received no comments. All ofthis information is available at EPA's conformity website: http://www.epa.gov/otaq/stateresources/transconf/currsips.htm#denver-me.

In aJanuary 21, 2010 letterto the Colorado Department ofPublic Health and Environment, we found that the 2010 NOx and VOC MVEBs in the OAP were adequate. We announced ouradequacy finding in the Federal Registeron 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 RangeTransportation and Air Quality Planning Council (NFRT), the Colorado Department ofTransportation, and the U.S. Department ofTransportation were required to use these MVEBs for transportation conformity determinations. However, we note that we are not boundbyourprior adequacy determinationin this action.

Our analysis indicates that the MVEBs are consistent with and clearly related to the emissions inventory and the control measures inthe SIP, and thatthe MVEBs, when considered59 together with all otheremissions sources, are consistent with attainment ofthe 1997 8-hour
ozone NAAQS in 2010. (See 40 CFR93.118(e)(4).) Therefore we are proposing approval ofthe MVEBs as reflected in Table 3 above.

We note that ourproposed approval applies to the Northern Subarea and Southern SubareaMVEBs as well as the Total Nonattainment Area MVEBs. The Northern Subareais defined in the OAP as the area denoted by the ozone nonattainment area north ofthe Boulder County northern boundary and extended through southern Weld County to the Morgan County line. This area includes NFRT'sregional planning area as well as part ofthe 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 ofDRCOG'sregional planning area and the southern Weld County portion ofthe UpperFront 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 ofthe MVEBs, we are also proposing to approve the process described in the OAP for use ofthe Total Nonattainment Area MVEBs and the subarea MVEBs. Perthe OAP, the initial conformity determination mustuse the Total Nonattainment60 AreaMVEBs 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 determiningconformity. To switch to use ofthe subareaMVEBs (orto subsequently switch back to use ofthe Total Nonattainment AreaMVEBs,) DRCOG and the NFRT must use the process described in the OAP at pages VI-4 and VI-5.

V. Consideration ofSection 110(1) ofthe CAA Section 110(1) ofthe CAA states that a SIP revision cannotbe approved ifthe revision would interfere with any applicable requirement concerning attainment andreasonable further progress towards attainment ofa NAAQS orany other applicable requirement ofthe CAA The parts ofthe OAP and the regulationrevisions we are proposing to approve will not interfere with attainment, reasonable further progress, or any otherapplicable requirement ofthe CAA. The OAP contains a valid modeled attainment demonstration showing the areawill attain by 2010. As described elsewhere in this action, we are proposing to disapprove Colorado's proposed repeal ofSection ltDofRegulation Number

### 7, Colorado's revisions to Section 

### XII ofRegulation Number

### 7, Colorado's revisions to Part C ofRegulation Number

### 3, Colorado'srevisions to its Ambient Air Quality Standardsregulation, and specific limited portions ofthe OAP because those provisions do not meet all applicable requirements ofthe CAA.

VI. Proposed Action We are proposing to approve Colorado's 2010 attainment demonstration for the 1997 8­61 hour ozone NAAQS. We areproposing to approve the motorvehicle emissions budgets contained in the OAP. We are proposing to approve all otheraspects ofthe OAP, with the following limited exceptions: we are proposingto disapprove the last paragraph onpage 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 ofthe OAP, and we are proposing to disapprove the reference to Attachment A in the OAP'sTable ofContents and on page IV-3 ofthe OAP.

We are proposing to approve the revisions to Colorado RegulationNumber 3, Parts A and B. We are proposing to disapprove the revisions to Colorado RegulationNumber 3, Part C.

We are proposing to approve the following portions ofthe revisions to Colorado RegulationNumber7:
• Revisions to Sections Ithrough XI, except for Colorado'srepeal ofSection 11.0.
• Revisions to SectionsXIII through XVI.

We are proposing to disapprove the following portions ofthe revisions to Colorado RegulationNumber 7:
• Colorado'sproposed repeal ofSection 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 ofthe CAA and our regulations, including 40 CFRSl.300(e)(3)(ii)(D). The provisions we are proposing to disapprove are inconsistentwith CAArequirements and ourregulations. Our specific analyses and findings are discussed above in the body ofthisproposed rulemaking.

EPA is soliciting public comments on its proposed rulemaking as discussed in this document. EPA will consider these comments before taking final action. Interested parties may participate in the Federal rulemaking process by submitting written commentsto EPA as discussed in this action.

VII. Statutory and Executive OrderReviews Under the CAA, the Administrator is required to approve a SIP submissionthat complies with the provisions ofthe Actand applicable Federal regulations (42 U.S.c. 741O(k), 40 CFR 52.02(a». Thus, in reviewing SIP submissions, EPA'srole is to approve state choices, provided that they meet the criteriaofthe CAA. Accordingly, this proposed action merely approves some state law as meeting Federal requirements and disapproves other state law because itdoes not meetFederal requirements; this proposed action does not impose additional requirements beyond those imposed by state law. Forthat reason, this proposed action:63
• is not a "significantregulatory action" subjectto review by the Office ofManagement 

### aOO Budget under Executive Order 12866 (58 FR51735, October4, 1993);
• does not impose an information collection burden underthe provisions ofthe Paperwork Reduction Act (44 U.S.c. 3501 etseq.);
• is certified as not having a significant economic impact on a substantial numberofsmaH entities under the Regulatory Flexibility Act (5 U.S.C. 601 etseq.);
• does not contain any unfunded mandate or significantly oruniquely 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 significantregulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• is not a significantregulatory action subject to Executive Order 13211 (66 FR28355, May 22, 2001);
• is not subjectto requirements ofSection 12(d) ofthe National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application ofthose requirements would be inconsistent with the CAA; and
• does not provide EPA with the discretionary authorityto address, as appropriate, disproportionate humanhealth orenvironmental effects, using practicable and legally permissible methods, under Executive Order 12898 (59 FR7629, 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 Indiancountry located inthe state, and EPA notes that 

### itwill not impose substantial direct costs ontribal governments orpreempttribal law.65 Approval and Promulgation ofAir Quality Implementation Plans; Colorado; Attainment Demonstration for the 1997 8-HourOzone Standard, and Approval ofRelated Revisions
ListofSubjects 40 CFRpart 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