### ENVIRONMENTAL PROTECTION AGENCY 40 CFRPart52 EPA-R08-0AR-2007-1032; FRL- Approval and Promulgation ofStateImplementation Plans; State ofColorado; Interstate TransportofPollution Revisions for the 1997 8-hourOzone NAAQS: "SignificantContributionto Nonattainment" Requirement AGENCY: Environmental Protection Agency (EPA). 

### ACTION: Proposed Rule. 

### SUMMARY: The Environmental Protection Agency (EPA) is proposing partial approval ofthe State Implementation Plan (SIP)revisions "State ofColorado Implementation Plan to Meet the Requirements ofClean Air Act Section 110(a)(2)(D)(i)(I)

- Interstate Transport Regarding the 1997 8-Hour Ozone Standard" submitted by the State ofColorado on June 18, 2009. The Colorado Interstate Transport SIP revisions submittedJune 18, 2009 address the requirements of Clean Air Act section 110(a)(2)(D)(i)(I) for the 1997 8-hourozoneNational Ambient Air Quality Standards (NAAQS). In this Federal Register action EPA proposes approval ofthe Colorado SIP sections that address the requirement ofsection 110(a)(2)(D)(i)(I) prohibiting a state's emissions from contributing significantlyto any other state's nonattainment ofthe NAAQS. EPA will act at a later date on the Colorado Interstate Transport SIP sections that address the requirement prohibiting a state'semissions from interfering with any other state's maintenance ofthe NAAQS. This action is being taken under section 110 ofthe Clean Air Act. 

### DATES: Comments must be received on orbefore [Insertdate 30 days afterpublication in the Federal Register]. 

### ADDRESSES: Submityour comments, identifiedby Docket ID No. EPA-R08-0AR-2007­1032. by one ofthe following methods:
• http://www.regulations.gov. Followthe on-line instructions for submitting comments.
• E-mail: videtich.callie@epa.gov and n1astrangelo.domenico@epa.gov
• Fax: (303) 312-6064 (please alert the individual listed in the FORFURTHER INFORMATION CONTACT ifyou are faxing comments).
• Mail: Callie Videtich, Director, Air Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop Street, Denver, Colorado 80202-1129.
• Hand Delivery: Callie Videtich, Director, Air Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop, Denver, Colorado 80202-1129. Such deliveries are only accepted Monday through Friday, 8:00
a.m. to 4:30 p.m., excluding Federal holidays. Special arrangements should be made for deliveries ofboxed information. 

### Instructions: Direct yourcomments to Docket ID No. EPA-R08-0AR-2007-1032. EPA's policy is that all comments received will be included in the public docketwithout change and may be made available online at http://www.regulations.gov, including any personal informationprovided, unlessthe comment includes information claimedto be Confidential Business Information (CBI) orotherinformation whose disclosure isrestricted by statute. Do not submit information that you considerto be CBI or otherwise protectedthrough http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site is an "anonymous access" system, which means EPA will not know your identity or contact information unless you provide it in the body ofyour comment. Ifyou send an e-mail commentdirectly 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 onthe Internet. Ifyou submit an electronic comment, EPA recommends that you include your name and other contact information inthe body ofyour comment and with any disk or CD-ROM you submit. IfEPAcannotread your comment due to technical difficulties and cannot contact you for clarification, EPAmay not be able to consider your comment. Electronic files should avoid the use ofspecial characters, any form ofencryption, and be free of any defects or viruses. For additional instructions on submitting comments, go to Section 1. General Information ofthe SUPPLEMENTARY INFORMATION section ofthis document. Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed inthe index, some information is not publicly available, e.g., CBI or other informationwhose 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 either electronically in http://www.regulations.gov or in hard copy at the Air Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop, Denver, Colorado 80202-1129. EPA requests that ifat all possible, you contactthe individual listed in the FOR FURTHER INFORMATION CONTACT section to viewthe hard copy ofthe docket. You may view the hard copy ofthe docket Monday through Friday, 8:00 a.m. to 4:00 p.m., excluding Federal holidays
.. FORFURTHER INFORMATION CONTACT: Domenico Mastrangelo, Air Program, U.S. Environmental Protection Agency, Region 8, Mailcode 8P-AR, 1595 Wynkoop, Denver, Colorado 80202-1129, (303) 312-6436, mastrangelo.don1enico@epa.gov. SUPPLEMENTARYINFORMATION: 3Definitions Forthe purpose ofthis document, we are giving meaning to certain words orinitials as follows: (i) The words or initials Act or CAA mean or referto the Clean Air Act, unless the context indicates otherwise. (ii) The words EPA, we, us orourmean orreferto the United States Environmental Protection Agency. (iii) The initials SIP mean orreferto State Implementation Plan. (iv) The words Colorado and State meanthe State ofColorado. Table ofContents I. General Information What Should I Consider as I Prepare My Comments for EPA? II. Background Information III. What Action Is EPA proposing? IV. What Is the State Process to Submit These Materials to EPA? V. EPA's Review and Technical Information VI. Proposed Action VII. Statutory and Executive OrderReviews I. General Information What should Iconsider as Iprepare my comments for EPA? 1. Submitting eEl. Do not submit CBl to EPA through http://www.regulations.gov oremail. Clearly mark the part orall ofthe information that you claim to be CBl. For CBl information in a disk or CD ROM that you mail to EPA, mark the outside ofthe disk or CD ROM as CBl and then identify electronically within the disk or CD ROMthe specific 

### 4information that is claimed as CBI. In addition to one complete version ofthe comment that includes information claimed as CBI, a copy ofthe commentthat does not contain the information claimed as CBI mustbe submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFRpart 2. 2. Tips/or Preparing Your Comments. When submitting comments, remember to:
a. Identify the rulemaking by docket number and other identifying information (subject heading, Federal Register date and page number). b. Followdirections

- The agency may ask you to respond to specific questions or organize comments by referencing a Code ofFederal Regulations (CFR) part or section number.
c. Explain why you agree ordisagree;**sugg~st** alternatives and substitute language for your requested changes. d. Describe any assumptions and provide any technical information and/or datathat you used.
e. Ifyou estimate potential costs or burdens, explain howyou arrived at your estimate in sufficient detail to allow for it to be reproduced. f. Provide specific examplesto illustrate your concerns, and suggest alternatives. g. Explain your views as clearly as possible, avoiding the use ofprofanity or personal threats. h. Make sure to submit your comments by the commentperiod deadline identified. II. Background Information Section 110(a)(2)(D)(i) ofthe CAArequires that a state's SIP must contain adequate provisions prohibiting any source or othertype ofemissions activity within the state from 

### 5emitting any airpollutant in amounts which will: (1) contribute significantly to nonattainment of the NAAQS in any other state; (2) interfere with maintenance oftheNAAQS by any other state; (3) interfere with any other state'srequired measures to prevent significant deterioration ofair quality; or (4) interfere with any other state'srequired measures to protect visibility. On June 11, 2008, the State ofColorado submitted to EPA an Interstate Transport SIP addressing the interstate transport requirenlents ofCAA section 11 0(a)(2)(D)(i) for the 1997 PM2.5 and 8-hour
ozone NAAQS. In response to EPA's concerns with the June 11, 2008 submittal, on December 30, 2008 the State adopted and on June 18, 2009 submitted a revised SIP addressing the requirements ofelements (1) and (2) ofsection 110(a)(2)(D)(i) for the 1997 8-hourozone NAAQS. The State ofColorado is planning to submit in June 2010 further revisions addressing the requirements ofelements (3) and (4) for the 1997 8-hour ozone NAAQS and the requirements ofelements (1) through (4) for the 1997 PM2.5 NAAQS
.



### .111. WhatAction IsEPA Proposing? EPA is proposingpartial approval ofthe Colorado Interstate Transport ofAir Pollution SIP addressing the requirements ofCAA section 110(a)(2)(D)(i)(I) for the 1997 8-hour ozone NAAQS. On December 30, 2008, the Colorado Air Quality Control Commission (AQCC) adopted the "State ofColorado Implementation Plan to Meet the Requirements ofthe Clean Air Act Section 110(a)(2)(d)(i)(I)

- Interstate Transport Regarding the 1997 8-Hour Ozone Standard." Colorado submitted the December 30,2008 SIP revision to EPA on June 18, 2009. In this Federal Register action EPA is proposing to approve only the language and demonstration that addresses element (1) ofsection 110(a)(2)(D)(i): prohibition ofsignificant contribution to nonattainment ofthe 1997 8-hour ozone NAAQS in any other state. 

### IV. WhatIsthe StateProcess to SubmitTheseMaterials to EPA? 6Section 11O(k) ofthe CAA addresses EPA's rulemaking action on SIP submissions by states. The CAA requires states to observe certain procedural requirements in developing SIP revisions for submittal to EPA. Section 110(a)(2) ofthe CAA requires that each SIP revision be adopted after reasonable notice and public hearing. This must occurpriorto the revision being submittedby a state to EPA. The Colorado AQCC held a public hearing in December 2008 for the interstate transport SIP revision: "State ofColorado Implementation Plan to Meetthe Requirements ofClean Air Act Section 110(a)(2)(D)(i)(I)

- Interstate Transport Regarding the 1997 8-Hour Ozone Standard." The AQCC adopted this revision on December 30, 2008, and the State submitted it to EPA on June 18, 2009. On November 18, 2009, the AQCC provided EPA with an exact color duplicate ofthe SIP adopted by the AQCC on December 30, 2008 and included in the June 18, 2009 submittal to EPA. In the original submittal, AQCC provided a black and white copy. The SIP'scolor duplicate, available for review as part ofthe Docket, makes it easierto understand modeling results reported in several graphs that are part ofthe SIP technical demonstration. EPA has reviewedthe submittal from the State ofColorado and has detennined thatthe State met the requirements for reasonable notice and public hearing under section 110(a)(2) of the CAA. 

## v. EPA's Review and Technical Information The interstate transport provisions at CAA section 110(a)(2)(D)(i), also referred to as the "good neighbor" provisions, require that each state's SIP contain adequate provisionsprohibiting emissions that adversely affect any other state's air quality through interstate transport ofair pollutants. As discussed in the Background Information section ofthis notice, a state's SIP must 7contain provisions that satisfy the four elements ofsection 110(a)(2)(D)(i). On August 15, 2006, EPA issued guidance for SIP submissions addressing the requirements ofsection 110(a)(2)(D)(i) for the 1997 PM2.5 and 8-hour ozone NAAQS.l The portions ofthe Colorado Interstate Transport SIP revision that address element (l) ofsection 110(a)(2)(D)(i) for the 1997 8-hour
ozone NAAQS are consistent with EPA's 2006 guidance. To demonstrate that emissions from Colorado do not contribute significantly to nonattainment ofthe 1997 8-hour ozone NAAQS in any other state, the Colorado Interstate Transport SIP relies on a combination of: (a) modeling analysis done by the State as part ofthe attainment demonstration SIP for the DenverMetropolitan AreaINorth Front Range (DMAlNFR) nonattainment areafor the 1997 8-hourozone standard; (b) monitoring data gathered by states and reported to EPA in the Air Quality System (AQS) database; and (c) considerations of geographical and meteorological factors. In this action, EPA expands on the analysis of geographical and meteorological factors, and ofozone concentration levels reflecting AQS monitoring data. Section 110(a)(2)(D)(i) provides that EPA cannot approve a state's SIP for a new or revised NAAQS unless it contains adequate measures to prohibit emissions from sources within the state from contributing significantly to nonattainment ofthe NAAQS in another state. EPA's August 15, 2006, guidance to states concerning section 11O(a)(2)(D)(i) recommended various methods by which states mightevaluate whether ornot its emissions significantly contribute to violations ofthe 1997 ozone standards in another state. Among othermethods, EPA

Memorandum from William T. Harnett entitled Guidancefor State Implementation Plan (SIP) Submissions to Meet Current Outstanding Obligations Under Section 110(a)(2)(D)(i) for the 8-hour Ozone and PM2.5 National Ambient Air Quality Standards (Aug. 15,2006) ("2006 Guidance"). Available for review in EPA's January 14, 20 I0 docket document entitled: "Relevant Guidance and Supporting Documentation for the Proposed Rulemaking Federal Register Action Docket ID # EPA-R08-0AR-2007-1032. 8 Irecommended consideration ofavailable EPA modeling conducted in conjunction with CAIR,2
orin the absence ofsuch EPA modeling, consideration ofother information such as the amount ofemissions, the geographic location ofviolating areas, meteorological data, orvarious other forms ofinformation that would be relevantto assessing the likelihood ofsignificant contribution to violations ofthe NAAQS in another state. The assessment ofsignificant contribution to nonattainment is not restricted to impacts upon areas that are formally designated nonattainment. Consistent with EPA's approach in CAIR, this impact mustbe evaluated with respect to any monitors showing a violation ofthe NAAQS (70 FR25172, May 12,2005, and 63 FR 57371, October27, 1998). Furthermore, although relevant information otherthan modeling may be considered in assessing the likelihood ofsignificant contribution to violations ofthe 1997 8-hour ozonestandard in another state, EPA notes that no single piece ofinformation in the following discussion is by itselfdispositive ofthe issue. Instead, the total weight ofall the evidence taken together supports the conclusion that emissions from Colorado sources are unlikely to contribute significantly to violations ofthe 1997 8-hour ozone standard in any other state. The Colorado Interstate Transport SIP uses results from Colorado's 2009 "8-HourOzone Attainment Plan" for the DMAINFRnonattainment area, and a report from the Western States Air Resource (WESTAR) Council to underscore that: (a) local anthropogenic ozone contribution to high ozone concentrations in Denver is only about 25%; and (b) on days ofhighest ozone concentrations (reflecting a design value of84.9 ppb) in the DMAlNFR area, the projected design values decrease to 63 ppb or less for all downwind Colorado counties east ofan

2 In this action the expression "CAIR" refers to the final rule published in the May 12, 2005 Federal Register and entitled "Rule to Reduce Interstate TransportofFine Particulate Matter and Ozone (Clean Air lnterstate Rule); 9imaginary north-south Iine approximately 70 miles east from Denver.3 EPA does not accept the State ofColorado Interstate Transport SIP assessmentthat these results demonstrate that "the magnitude ofozone transport from Colorado to other states is too low to significantly contribute to nonattainment in
...any other state withrespectto the 0.08 ppb NAAQS.,,4 Similarly, EPA does not acceptthe claim in Colorado's SIPthat the absence ofviolations ofthe 8-hour ozone NAAQS in adjacent downwind states such as Kansas, Nebraska and Wyoming suffices to show that emissions from Colorado sources do not significantly affect farther downwind ozone nonattainment areas such as St. Louis.

### s The relatively limited contribution oflocal emissions to nonattainment in the DMAINFR, the quick drop in ozone levels in the easternmost Colorado counties, and even the substantial gap between the 1997 NAAQS and design values in adjacent downwind states do not exclude a potential significant contribution from Colorado emissions to downwind nonattainment areas. However, as a reflection ofemission levels, the relatively (to the 1997 8-hour ozone NAAQS) moderate ozone concentrations in eastern Colorado and in adjacent downwind states somewhatreduces the probability ofsignificant ozone contribution from Colorado emission sources to considerably farther downwindnonattainment areas such as St. Louis, Missouri, and Chicago, Illinois. In addition, significant contribution should be measured notjustagainst nonattainment areas, but also against areas with monitors showIng violations ofthe NAAQS. That said, nonattainment areas are a convenient starting point for EPA's analysis. Forthe 1997 8-hour

Revisions to Acid Rain Program; Revisions to NOx SIP Call; Final Rule" (70 FR 25162). :I See Figure 5, page 15 ofthe Interstate Transport SIP submitted June 18,2009. It must be noted that the modeling analysis domain for the DMAINFR attainment plan was limited to the State territory, and that the 70 mile distance represents the approximate distance from Denver to the western border ofMorgan County. 4 "State ofColorado Plan to Meet the Requirements ofClean Air Act Section 110(a)(2)(D)(i)(I)-Interstate Transport Regarding the 1997 8-hour Ozone Standard," p. 17, December 12,2009. 5Ibid., pp. 8-9. 10ozone NAAQS, the St. Louis area and the Illinois and Wisconsin Counties along the southwestern shore ofI
..ake Michigan (Illinois/Wisconsin area) are the designated downwind nonattainment areas closestto Colorado. 6 EPA's evaluation ofwhether emissions from Colorado contribute significantly to ozone nonattainment in these areas relies on an examination ofa variety ofdata and analysis that provide insight on ozone transport from Colorado to these two areas. Because EPA does not have detailed modeling for Colorado and nearby downwind states, our approach does not rely on a quantitative determination ofColorado's contribution, as EPA did for other states in its CAIR rulemaking, but on a weight-of-evidence analysis based on qualitative assessments and estimates ofthe relevant factors. While conclusions reached for each ofthe factors considered in the following analysis are not in and by themselves detenninative, consideration ofall ofthese factors provides a reliable qualitative conclusion on whether Colorado's emissions are likely to contribute significantly to nonattainment in the S1. Louis and the Illinois/Wisconsin areas. The Illinois/Wisconsin nonattainment area is approximately 900 miles east/northeast from the Colorado DMA/NFR area. Distance per se is not an obstacle to long range transport of
ozone and/or its precursors, as discussed in the January 30, 2004 notice proposing CAIR (69 FR 4599). NOx, the primary ozone precursorthat was the object ofthe CAIRtransport study, may betransported for long distances, contributing significantlyto high ozone concentrations in other states. However, with increasing distance there are greater opportunities for ozone orNOx dispersion and/orremoval from the atmosphere due to the effect ofwinds orchemical sink

6 The Wisconsin nonattainmentareas for the 1997 8-hour ozone standard include: Door, Kewaunee, Manitowoc, Sheboygan, Ozaukee, Washington, Milwaukee, Waukesha, Racine and Kenosha counties; the Chicago nonattainment area includes Cook County and several adjacent Illinois and Indiana counties (69 FR 23858, April 30, 2004). 11processes. As a result, one may conclude that the 900 mile distance from Colorado sources of NOx emissions and the IllinoislWisconsin areareduces, butdoes not exclude, the possibility of significant contribution to this area's nonattainment. Another transport factor is wind direction. For long range transport winds, a modeling analysis ofozone dispersion during the summermonths (June to August) ofthe five year period 1991-1995 shows that on high local ozone days the prevailing long range transport winds in states immediately to the east and north ofColorado (Kansas, Nebraska, SouthDakota, Iowa, Minnesota, and North Dakota) had a southerly direction. Onhigh regional ozone days, during the sameperiod, regional transport winds in the same states were southwesterly, but with a westerly component so weakthat a greaterportion ofNOx emissions from Colorado would likely remain significantly west ofthe Illinois/Wisconsin nonattainment area. 7 To the extent that these results are representative ofgeneral ozone transport patterns not limited to the 1991-1995 period, the weak western component oflong range transport winds during high ozone days in the states east and north ofColorado provides evidence thatNOx emissions from Colorado are unlikely to contribute significantly to violations ofthe 1997 ozoneNAAQS in the Illinois/Wisconsin counties along the southwestern shores ofLake Michigan. Additional circumstantial evidence supporting this conclusion is found in technical documentation developed in recent years by the states ofKansas and Wisconsin. To support its Interstate Transport SIP, the State ofKansas submitted to EPA Region 7 technical documentationthat includes back trajectory analyses gauging the pathway ofair masses impactingthe Illinois/Wisconsin nonattainment area onthe four days with highest ozone

7 Ozone Transport Assessment Group (OTAG), Air Quality Analysis Workgroup: "3.3 Climatology ofOzone Synoptic scale Transport in the Eastern US," Figures I(a) and Sea), pp. 3, 6, January 11, 1998. High ozone days 12concentrations during each ofthe years 2005-2007. The back trajectory analyses in Appendix G ofthe technical support section showthat, for the four days with the highest ozone readings,
none ofthe pathways followed by air masses moving into the Chicago Metropolitan Statistical Area (MSA) or into several ofthe Wisconsin nonattainment counties came from Colorado. Since these back trajectories referto the pathways ofair masses and not specifically to ozone transport, the results ofthis analysis cannotbe considered detenninative as to the significant contribution ofozone orNOx from Colorado emissions to the nonattainment counties alongthe southwestern shores ofLake Michigan. However, the lack ofany backtrajectories from Colorado indicates that it is unlikely that NOx emissions from the State contribute significantly to the nonattainment ofthe Illinois/Wisconsin area. Further support is given by a recent attainment demonstration by the Wisconsin Department ofNatural Resources (WDNR) for the nonattainment counties along the southwestern shores ofLake Michigan.s The WDNR analysis identifies heavy industrial activity and dense urbanization as the major local contributors to the high ozone concentrations in the Indiana, Illinois and Wisconsin Counties along the southwestern shores ofLake Michigan. Between 40 and 60 percent ofthe maximum ozone concentrations in the Lake Michigan airshed is attributed to regional transport, occurring from emission sources located within a southsouthwesterly arc spanning from 160 to 270 degrees (compass direction). Colorado's location at the western margins ofthis arc (Denver is approximately 260 degrees southwest ofChicago) substantially reduces the likelihood for NOx emissions from the State to contribute significantly

were days with ozone concentrations in the 90th percentile. S Wisconsin Department ofNatural Resources, "Attainment Demonstration-The Wisconsin Counties ofKenosha, Racine, Milwaukee, Waukesha, Ozaukee, Washington, Sheboygan, Manitowoc and Door," September 2009. 13to nonattainment in the Illinois/Wisconsin area. 9 Given the southerly orientation ofregional transport winds in states east and north ofColorado, it is likely that Colorado ozone orNOx emissions would be heavily dispersed in a northward direction west ofthis nonattainment area. Finally, by 2008, the 8-hour ozone design values for the Illinois and Wisconsin nonattainmentcounties along the shores ofLake Michigan fell belowthe level ofthe NAAQS, a reduction attributed to the implementation ofState and Federal control measures since the designation ofthese counties as nonattainment in 2004. In other words, were there emissions from Colorado sources reaching the Illinois and Wisconsincounties along the western rim of Lake Michigan, they would no longer be significantly contributing to violations ofthe NAAQS in that area. 10 The other nonattainment area, St. Louis and adjacentcounties, is approximately 800 miles straight east from the Colorado DMAINFR area. This substantial distance does not, in and by itself, exclude the possibility ofsignificant contribution from Colorado'sNOx emissions to nonattainment in the St. Louis area. However, it is also sufficientto provide many opportunities for ozone dispersion and removal from the atmosphere due to the effect ofwinds and chemical sink processes, and thus reduce the likelihood ofsignificant contribution from Colorado to nonattainment in this area. The impact ofwind direction on ozone transport from Colorado to the St. Louis area is gauged through the results ofseveral findings. Kansas, immediately eastofColorado and west ofMissouri, is characterized by strong southerly surface winds that match prevailingregional transport winds, which have a southerly orientation during days ofelevated ozone concentration.
') Ibid., p. 51. 10 Ibid. 14Throughout 2005 its winds averaged daily speeds slightly over 9 mph. I I The OTAG modeling analysis referred to earlier shows that, during the five years from 1991 to 1995, on high ozone days regional transport winds in Kansas and Missouri have a prevailing southerly orientation. To the extent that these results are representative ofgeneral ozone transport patterns not limited to the 1991-95**period~** they indicatethat ozonefNOxemissions from Colorado reaching Kansas or Missouri were very likely to be redirected northward and away from the St. Louis area, thus lessening the likelihood for a significant ozone contributionto nonattainment from Colorado.' Results from other studies are consistent with these tentative conclusions. In a study published by OTAG in 1997, the St. Louis area showed higher ozone concentrations (70 as compared with 55 ppb) ondays with winds from the south or the eastthan on days with winds from the west (the general direction from Colorado) or southwest. 12 More recent back trajectory analyses gauging the pathwayofair masses impacting St. Louis on days ofhigh ozone allow similar conclusions. The State ofKansas' technical documentation supporting its Interstate Transport SIP (approved by EPA in March 2007) include back trajectory analyses independent oftheir source regions (i.e., Colorado orKansas.) The results showthat for each ofthe 2005­ 2007 years, on the four days with the highest ozone readings the frequency oftrajectory ·'contribution" from Colorado to St. Louis was negligible. There is only one instance ofa 500 metertrajectory from Colorado, while there were none for transport at 1500 meter ofaltitude. 13 These findings, in combination with the other circumstantial evidence examined above, strengthen the conclusion that it is unlikely that emissions from Colorado sources contribute

11 See the January 4,2007 State ofKansas submittal to EPA ofInterstateTransport SIP revisions, Document ID# EPA-R07-0AR-2007-0141-0003, pp.6-7. 12 OTAG, "Ozone as Function ofLocal Wind Speed and Direction: Evidence ofLocal and Regional Transport," p. 33, July 26, 1997. 13 Document ID# EPA-R07-0AR-2007-0141-0003, Appendix G. 15significantly to the nonattainment ofthe St. Louis area. As mentioned above, EPA must consider not only significant contribution to nonattainment areas, but also to areas with monitors showing violations ofthe NAAQS. A review ofthe AQS monitoring datafor adjacent downwind states shows that it is highly unlikely that emissions from Colorado contribute significantly to downwind areas that have monitors showing violations ofthe 1997 8-hour ozone NAAQS. Between 1999 and 2008 there were no violations ofthe 1997 8-hour ozone NAAQS at any ofthe monitors in adjacent downwind states, such as Kansas, Nebraska and Wyoming. Design values for the years 

### 2005-200i4 show that in adjacent downwind states such as Kansas, Nebraska, and Wyoming, there were no violations ofthe 1997 8-hour ozone NAAQS, and that in most counties ozone levels remained substantiallybelowthe NAAQS. In Kansas, the 2007 design value for Trego County, the county with a monitoring station closest to Colorado,
was 71 ppb, or 16 percentbelowthe ozoneNAAQS. The counties that had the highest design values are at or nearthe eastern edge ofthe state, about 400 miles from Colorado's eastern border, and their design values ranged from 76 ppb for Johnson and Sumner Counties to 77 ppb for Leavenworth and Wyandotte Counties. In Nebraska and Wyoming, the highest ozone design values did not exceed 69 ppb in Douglas County, Nebraska and 72 ppb in Sublette County, Wyoming. The historical trend over the period 1998-2008 for the 1997 8-hour ozone design values in these states places the 2005-2007 datareviewed above in context. In Nebraska, ozone design values were consistently low throughout the period. In Wyoming, design values were also

14 See Table 4, pages 7 and 8, ofthe Colorado Interstate Transport SIP. 16constant in most ofthe monitored areas, where ozone monitoring only began between 2003 and 2005. Kansas design values showa clear trend ofdeclining ozone levels from the late 1990s to the most recent years. In Linn, Sedgwick, and SumnerCounties, design values decreased from highs ranging between 77 and 82 ppb during 2000-2003 to levels ranging between 66 and 75 ppb in 2006-2008. The data and weightofevidence analysis presented above support the conclusion ofthe Colorado Interstate Transport SIP (adopted into the State SIP on December 30, 2008 and submitted to EPA June 18, 2009) that emissions from Colorado do not contribute significantly to nonattainment in any other state for the 1997 8-hour ozone NAAQS, consistentlywith the requirements ofelement (1) ofCAA section 110(a)(2)(D)(i). VI. Proposed Action EPA is proposing partial approval ofthe Colorado SIP to meetthe requirements of Section 11O(a)(2)(D)(i)(I) regarding the 1997 ozone standard. Specifically, in this action EPA is proposing to approve only the language and demonstration that, in this SIP revision, address the requirements ofelement (1): prohibition ofsignificant contribution to nonattainment ofthe 1997 8-hourozone NAAQS in any other state. At a later date, EPA will act on the language and demonstration addressing element (2): prohibition ofinterference with maintenance ofthe 1997 8-hour ozone NAAQS in any other state. VII. Statutory and Executive OrderReview Under the Clean Air Act, the Administrator is required to approve a SIP submission that complies with the provisions ofthe Act and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA'srole is to approve state choices, provided that they meet the criteria ofthe Clean AirAct. Accordingly, this action merely 17approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. Forthat reason, this action:
• Is not a "significant regulatory action" subjectto review by the Office ofManagement and Budget under Executive Order 12866 (58 FR 51735, October4,1993);
• Does not impose an information collection burden underthe provisions ofthe Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• Is certified as not having a significant economic impact on a substantial number ofsmall entities under the Regulatory Flexibility Act (5 U.S.C. 601 etseq.);
• Does not contain anyunfunded mandate or significantly oruniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Public Law 104-4);
• Does nothave Federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Is not an economically significant regulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• Is not a significant regulatory action subjectto Executive Order 13211 (66 FR 28355, May 22, 2001);
• Is not subject to 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 Clean Air Act; and

18

### IDENTIFICATION OFDOCUMENT: Approval and Promulgation ofState ImplementationPlans; State ofColorado; InterstateTransportofPollution Revisions for the 1997 8-hourOzone NAAQS: "SignificantContributionto Nonattainment" Requirement. Proposed Rule. (EPA-R08-0AR-2007-1032) Page 19 of 19
• Does notprovide EPA with the discretionary authority to address, as appropriate, disproportionate human health or environmental effects, using practicable and legally permissible methods, under Executive Order 12898 (59 FR 7629, February 16, 1994). In addition, this rule does not have tribal implications as specified by Executive Order 13175 (65 FR 67249, November 9, 2000), because the SIP is not approved to apply in Indian country located in the state, and EPA notes that it will not impose substantial direct costs on tribal governments orpreempt tribal law. 

### ListofSubjectsin 40 CFRPart52 Environmental protection, Airpollution control, Incorporation by reference, Intergovernmental relations, Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeeping requirements, Volatile Organic Compounds. 

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

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## -CCarol L. Campbell ) Acting Deputy Regional Administrator Region 8

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