ENVIRONMENTAL PROTECTION AGENCY
 

40 CFR Part 52
 

EPA-R08-0AR-2007-1032; FRL-


Approval and Promulgation of State Implementation Plans; State of Colorado; Interstate
 

Transport of Pollution Revisions for the 1997 8-hour Ozone NAAQS:
 

"Significant Contribution to Nonattainment" Requirement 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Proposed Rule. 

SUMMARY: The Environmental Protection Agency (EPA) is proposing partial approval of the 

State Implementation Plan (SIP) revisions "State of Colorado Implementation Plan to Meet the 

Requirements of Clean Air Act Section 11 0(a)(2)(D)(i)(I) - Interstate Transport Regarding the 

1997 8-Hour Ozone Standard" submitted by the State of Colorado on June 18, 2009. The 

Colorado Interstate Transport SIP revisions submitted June 18, 2009 address the requirements of 

Clean Air Act section 11 0(a)(2)(D)(i)(I) for the 1997 8-hour ozone National Ambient Air 

Quality Standards (NAAQS). In this Federal Register action EPA proposes approval of the 

Colorado SIP sections that address the requirement of section 11 0(a)(2)(D)(i)(I) prohibiting a 

state's emissions from contributing significantly to any other state's nonattainment of the 

NAAQS. EPA will act at a later date on the Colorado Interstate Transport SIP sections that 

address the requirement prohibiting a state's emissions from interfering with any other state's 

maintenance of the NAAQS. This action is being taken under section 110 of the Clean Air Act. 

DATES: Comments must be received on or before [Insert date 30 days after publication in the 

Federal Register]. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-0AR-2007­
1032. by one of the following methods: 

•	 http://www.regulations.gov. Follow the 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 FOR FURTHER 

INFORMATION CONTACT if you 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 of boxed information. 

Instructions: Direct your comments to Docket ID No. EPA-R08-0AR-2007-1032. 

EPA's policy is that all comments received will be included in the public docket without change 

and may be made available online at http://www.regulations.gov, including any personal 

information provided, unless the comment includes information claimed to be Confidential 

Business Information (CBI) or other information whose disclosure is restricted by statute. Do 

not submit information that you consider to be CBI or otherwise protected through 

http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site is an 

"anonymous access" system, which means EPA will not know your identity or contact 

information unless you provide it in the body of your comment. If you send an e-mail comment 
directly to EPA, without going through http://www.regulations.gov, your e-mail address will be 

automatically captured and included as part of the comment that is placed in the public docket 

and made available on the Internet. If you submit an electronic comment, EPA recommends that 

you include your name and other contact information in the body of your comment and with any 

disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties 

and cannot contact you for clarification, EPA may not be able to consider your comment. 

Electronic files should avoid the use of special characters, any form of encryption, and be free of 

any defects or viruses. For additional 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 in the index, some information is not publicly available, e.g., CBI or other 

information whose disclosure is restricted by statute. Certain other material, such as copyrighted 

material, will be publicly available only in hard copy. Publicly-available docket materials are 

available either electronically in http://www.regulations.gov or in hard copy at the Air Program, 

Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop, Denver, 

Colorado 80202-1129. EPA requests that if at all possible, you contact the individual listed in 

the FOR FURTHER INFORMATION CONTACT section to view the hard copy of the 

docket. You may view the hard copy of the docket Monday through Friday, 8:00 a.m. to 4:00 

p.m., excluding Federal holidays.. 

FOR FURTHER 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. 

SUPPLEMENTARY INFORMATION: 

3
 
Definitions 

For the purpose of this document, we are giving meaning to certain words or initials as follows: 

(i) The words or initials Act or CAA mean or refer to the Clean Air Act, unless the context 

indicates otherwise. 

(ii) The words EPA, we, us or our mean or refer to the United States Environmental Protection 

Agency. 

(iii) The initials SIP mean or refer to State Implementation Plan. 

(iv) The words Colorado and State mean the State of Colorado. 

Table of Contents 

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 Order Reviews 

I. General Information 

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

1. Submitting eEl. Do not submit CBl to EPA through http://www.regulations.gov or email. Clearly mark the part or all of the information that you claim to be CBl. For CBl 

information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD 

ROM as CBl and then identify electronically within the disk or CD ROM the specific 

4
 
information that is claimed as CBI. In addition to one complete version of the comment that 

includes information claimed as CBI, a copy of the comment that does not contain the 

information claimed as CBI must be submitted for inclusion in the public docket. Information so 

marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 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.	 Follow directions - The agency may ask you to respond to specific questions or 

organize comments by referencing a Code of Federal Regulations (CFR) part or 

section number. 

c.	 Explain why you agree or disagree; sugg~st alternatives and substitute language 

for your requested changes. 

d.	 Describe any assumptions and provide any technical information and/or data that 

you used. 

e.	 If you estimate potential costs or burdens, explain how you arrived at your 

estimate in sufficient detail to allow for it to be reproduced. 

f.	 Provide specific examples to illustrate your concerns, and suggest alternatives. 

g.	 Explain your views as clearly as possible, avoiding the use of profanity or 

personal threats. 

h.	 Make sure to submit your comments by the comment period deadline identified. 

II. Background Information 

Section 11 0(a)(2)(D)(i) of the CAA requires that a state's SIP must contain adequate 

provisions prohibiting any source or other type of emissions activity within the state from 

5
 
emitting any air pollutant in amounts which will: (1) contribute significantly to nonattainment of 

the NAAQS in any other state; (2) interfere with maintenance of the NAAQS by any other state; 

(3) interfere with any other state's required measures to prevent significant deterioration of air 

quality; or (4) interfere with any other state's required measures to protect visibility. On June 11, 

2008, the State of Colorado submitted to EPA an Interstate Transport SIP addressing the 

interstate transport requirenlents of CAA 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 of elements (1) and (2) of section 11 0(a)(2)(D)(i) for the 1997 8-hour ozone 

NAAQS. The State of Colorado is planning to submit in June 2010 further revisions addressing 

the requirements of elements (3) and (4) for the 1997 8-hour ozone NAAQS and the 

requirements of elements (1) through (4) for the 1997 PM2.5 NAAQS. 

.111. What Action Is EPA Proposing? 

EPA is proposing partial approval of the Colorado Interstate Transport of Air Pollution 

SIP addressing the requirements of CAA section 11 0(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 of Colorado Implementation Plan to Meet the Requirements of the Clean Air 

Act Section 11 0(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) of section 11 0(a)(2)(D)(i): prohibition of significant contribution to 

nonattainment of the 1997 8-hour ozone NAAQS in any other state. 

IV. What Is the State Process to Submit These Materials to EPA? 

6
 
Section 11 O(k) of the 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) of the CAA requires that each SIP revision be 

adopted after reasonable notice and public hearing. This must occur prior to the revision being 

submitted by a state to EPA. 

The Colorado AQCC held a public hearing in December 2008 for the interstate transport 

SIP revision: "State of Colorado Implementation Plan to Meet the Requirements of Clean Air 

Act Section 11 0(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 of the 

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's color 

duplicate, available for review as part of the Docket, makes it easier to understand modeling 

results reported in several graphs that are part of the SIP technical demonstration. 

EPA has reviewed the submittal from the State ofColorado and has detennined that the 

State met the requirements for reasonable notice and public hearing under section 11 0(a)(2) of 

the CAA. 

v. EPA's Review and Technical Information 

The interstate transport provisions at CAA section 11 0(a)(2)(D)(i), also referred to as the 

"good neighbor" provisions, require that each state's SIP contain adequate provisions prohibiting 

emissions that adversely affect any other state's air quality through interstate transport of air 

pollutants. As discussed in the Background Information section of this notice, a state's SIP must 

7
 
contain provisions that satisfy the four elements of section 11 0(a)(2)(D)(i). On August 15, 2006, 

EPA issued guidance for SIP submissions addressing the requirements of section 11 0(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) of section 11 0(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 of the 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 of the 

attainment demonstration SIP for the Denver Metropolitan AreaINorth Front Range (DMAlNFR) 

nonattainment area for the 1997 8-hour ozone 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 of ozone concentration levels reflecting AQS 

monitoring data. 

Section 11 0(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 of the NAAQS in another state. EPA's 

August 15, 2006, guidance to states concerning section 11 O(a)(2)(D)(i) recommended various 

methods by which states might evaluate whether or not its emissions significantly contribute to 

violations of the 1997 ozone standards in another state. Among other methods, EPA 

Memorandum from William T. Harnett entitled Guidance for State Implementation Plan (SIP) Submissions to 

Meet Current Outstanding Obligations Under Section 11 0(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 I 0 docket document entitled: "Relevant Guidance and Supporting Documentation for the Proposed Rulemaking 

Federal Register Action Docket ID # EPA-R08-0AR-2007-1 032. 

8 

I 
recommended consideration of available EPA modeling conducted in conjunction with CAIR,2 

or in the absence of such EPA modeling, consideration of other information such as the amount 

of emissions, the geographic location of violating areas, meteorological data, or various other 

forms of information that would be relevant to assessing the likelihood of significant 

contribution to violations of the NAAQS in another state. The assessment of significant 

contribution to nonattainment is not restricted to impacts upon areas that are formally designated 

nonattainment. Consistent with EPA's approach in CAIR, this impact must be evaluated with 

respect to any monitors showing a violation of the NAAQS (70 FR 25172, May 12,2005, and 63 

FR 57371, October 27, 1998). Furthermore, although relevant information other than modeling 

may be considered in assessing the likelihood of significant contribution to violations ofthe 1997 

8-hour ozone standard in another state, EPA notes that no single piece of information in the 

following discussion is by itself dispositive ofthe issue. Instead, the total weight of all the 

evidence taken together supports the conclusion that emissions from Colorado sources are 

unlikely to contribute significantly to violations of the 1997 8-hour ozone standard in any other 

state. 

The Colorado Interstate Transport SIP uses results from Colorado's 2009 "8-Hour Ozone 

Attainment Plan" for the DMAINFR nonattainment 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 of highest ozone 

concentrations (reflecting a design value of 84.9 ppb) in the DMAlNFR area, the projected 

design values decrease to 63 ppb or less for all downwind Colorado counties east of an 

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 Transport of Fine Particulate Matter and Ozone (Clean Air lnterstate Rule); 

9
 
imaginary north-south Iine approximately 70 miles east from Denver.3 EPA does not accept the 

State of Colorado Interstate Transport SIP assessment that these results demonstrate that "the 

magnitude of ozone transport from Colorado to other states is too low to significantly contribute 

to nonattainment in ... any other state with respect to the 0.08 ppb NAAQS.,,4 Similarly, EPA 

does not accept the claim in Colorado's SIP that the absence of violations of the 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 of local 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 of emission levels, the relatively (to 

the 1997 8-hour ozone NAAQS) moderate ozone concentrations in eastern Colorado and in 

adjacent downwind states somewhat reduces the probability of significant ozone contribution 

from Colorado emission sources to considerably farther downwind nonattainment areas such as 

St. Louis, Missouri, and Chicago, Illinois. 

In addition, significant contribution should be measured not just against nonattainment 

areas, but also against areas with monitors showIng violations of the NAAQS. That said, 

nonattainment areas are a convenient starting point for EPA's analysis. For the 1997 8-hour 

Revisions to Acid Rain Program; Revisions to NOx SIP Call; Final Rule" (70 FR 25162).
 

:I See Figure 5, page 15 of the 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 of Morgan County.
 

4 "State of Colorado Plan to Meet the Requirements of Clean Air Act Section 11 0(a)(2)(D)(i)(I)-Interstate Transport
 

Regarding the 1997 8-hour Ozone Standard," p. 17, December 12,2009.
 

5 Ibid., pp. 8-9.
 

10 
ozone NAAQS, the St. Louis area and the Illinois and Wisconsin Counties along the 

southwestern shore of I..ake Michigan (Illinois/Wisconsin area) are the designated downwind 

nonattainment areas closest to Colorado. 6 EPA's evaluation of whether emissions from 

Colorado contribute significantly to ozone nonattainment in these areas relies on an examination 

of a variety of data 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 of Colorado'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 of the relevant factors. While conclusions reached for each 

of the factors considered in the following analysis are not in and by themselves detenninative, 

consideration of all of these 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 precursor that was the object of the CAIR transport study, may 

be transported for long distances, contributing significantly to high ozone concentrations in other 

states. However, with increasing distance there are greater opportunities for ozone or NOx 

dispersion and/or removal from the atmosphere due to the effect of winds or chemical sink 

6 The Wisconsin nonattainment areas 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). 

11
 
processes. As a result, one may conclude that the 900 mile distance from Colorado sources of 

NOx emissions and the IllinoislWisconsin area reduces, but does 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 of ozone dispersion during the summer months (June to August) of the 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 of Colorado (Kansas, Nebraska, South Dakota, Iowa, 

Minnesota, and North Dakota) had a southerly direction. On high regional ozone days, during 

the same period, regional transport winds in the same states were southwesterly, but with a 

westerly component so weak that a greater portion of NOx emissions from Colorado would 

likely remain significantly west of the Illinois/Wisconsin nonattainment area.

7 To the extent that 

these results are representative of general ozone transport patterns not limited to the 1991-1995 

period, the weak western component of long range transport winds during high ozone days in the 

states east and north of Colorado provides evidence that NOx emissions from Colorado are 

unlikely to contribute significantly to violations of the 1997 ozone NAAQS in the 

Illinois/Wisconsin counties along the southwestern shores of Lake Michigan. 

Additional circumstantial evidence supporting this conclusion is found in technical 

documentation developed in recent years by the states of Kansas and Wisconsin. To support its 

Interstate Transport SIP, the State of Kansas submitted to EPA Region 7 technical 

documentation that includes back trajectory analyses gauging the pathway of air masses 

impacting the Illinois/Wisconsin nonattainment area on the four days with highest ozone 

7 Ozone Transport Assessment Group (OTAG), Air Quality Analysis Workgroup: "3.3 Climatology of Ozone 

Synoptic scale Transport in the Eastern US," Figures I(a) and Sea), pp. 3, 6, January 11, 1998. High ozone days 

12
 
concentrations during each of the years 2005-2007. The back trajectory analyses in Appendix G 

of the technical support section show that, for the four days with the highest ozone readings, 

none of the pathways followed by air masses moving into the Chicago Metropolitan Statistical 

Area (MSA) or into several of the Wisconsin nonattainment counties came from Colorado. 

Since these back trajectories refer to the pathways of air masses and not specifically to ozone 

transport, the results of this analysis cannot be considered detenninative as to the significant 

contribution of ozone or NOx from Colorado emissions to the nonattainment counties along the 

southwestern shores of Lake Michigan. However, the lack of any back trajectories from 

Colorado indicates that it is unlikely that NOx emissions from the State contribute significantly 

to the nonattainment of the Illinois/Wisconsin area. 

Further support is given by a recent attainment demonstration by the Wisconsin 

Department of Natural Resources (WDNR) for the nonattainment counties along the 

southwestern shores of Lake 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 of Lake Michigan. 

Between 40 and 60 percent of the 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 of this arc (Denver is approximately 260 degrees southwest of Chicago) 

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 of Kenosha,
 

Racine, Milwaukee, Waukesha, Ozaukee, Washington, Sheboygan, Manitowoc and Door," September 2009.
 

13 
to nonattainment in the Illinois/Wisconsin area.

9 Given the southerly orientation of regional 

transport winds in states east and north of Colorado, it is likely that Colorado ozone or NOx 

emissions would be heavily dispersed in a northward direction west of this nonattainment area. 

Finally, by 2008, the 8-hour ozone design values for the Illinois and Wisconsin 

nonattainment counties along the shores of Lake Michigan fell below the level of the NAAQS, a 

reduction attributed to the implementation of State and Federal control measures since the 

designation of these counties as nonattainment in 2004. In other words, were there emissions 

from Colorado sources reaching the Illinois and Wisconsin counties along the western rim of 

Lake Michigan, they would no longer be significantly contributing to violations of the NAAQS 

in that area. 10 

The other nonattainment area, St. Louis and adjacent counties, is approximately 800 

miles straight east from the Colorado DMAINFR area. This substantial distance does not, in and 

by itself, exclude the possibility of significant contribution from Colorado's NOx emissions to 

nonattainment in the St. Louis area. However, it is also sufficient to provide many opportunities 

for ozone dispersion and removal from the atmosphere due to the effect of winds and chemical 

sink processes, and thus reduce the likelihood of significant contribution from Colorado to 

nonattainment in this area. 

The impact of wind direction on ozone transport from Colorado to the St. Louis area is 

gauged through the results of several findings. Kansas, immediately east of Colorado and west 

of Missouri, is characterized by strong southerly surface winds that match prevailing regional 

transport winds, which have a southerly orientation during days of elevated ozone concentration. 

') Ibid., p. 51. 

10 Ibid. 

14 
Throughout 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 of general ozone transport patterns not limited to 

the 1991-95 period~ they indicate that ozonefNOx emissions 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 contribution to 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) on days with winds from the south or the east than on days with winds 

from the west (the general direction from Colorado) or southwest. 12 More recent back trajectory 

analyses gauging the pathway of air masses impacting St. Louis on days of high ozone allow 

similar conclusions. The State of Kansas' technical documentation supporting its Interstate 

Transport SIP (approved by EPA in March 2007) include back trajectory analyses independent 

of their source regions (i.e., Colorado or Kansas.) The results show that for each of the 2005­

2007 years, on the four days with the highest ozone readings the frequency of trajectory 

·'contribution" from Colorado to St. Louis was negligible. There is only one instance of a 500 

meter trajectory from Colorado, while there were none for transport at 1500 meter of altitude. 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 of Kansas submittal to EPA ofInterstate Transport SIP revisions, Document ID#
 

EPA-R07-0AR-2007-0 141-0003, pp.6-7.
 

12 OTAG, "Ozone as Function of Local Wind Speed and Direction: Evidence of Local and Regional Transport," p.
 

33, July 26, 1997.
 

13 Document ID# EPA-R07-0AR-2007-014 1-0003, Appendix G.
 

15 
significantly to the nonattainment of the St. Louis area. 

As mentioned above, EPA must consider not only significant contribution to 

nonattainment areas, but also to areas with monitors showing violations of the NAAQS. A 

review of the AQS monitoring data for adjacent downwind states shows that it is highly unlikely 

that emissions from Colorado contribute significantly to downwind areas that have monitors 

showing violations of the 1997 8-hour ozone NAAQS. Between 1999 and 2008 there were no 

violations of the 1997 8-hour ozone NAAQS at any of the monitors in adjacent downwind states, 

such as Kansas, Nebraska and Wyoming. 

Design values for the years 2005-200i 4 show that in adjacent downwind states such as 

Kansas, Nebraska, and Wyoming, there were no violations of the 1997 8-hour ozone NAAQS, 

and that in most counties ozone levels remained substantially below the NAAQS. In Kansas, the 

2007 design value for Trego County, the county with a monitoring station closest to Colorado, 

was 71 ppb, or 16 percent below the ozone NAAQS. The counties that had the highest design 

values are at or near the 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 data reviewed 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, of the Colorado Interstate Transport SIP. 

16 
constant in most of the monitored areas, where ozone monitoring only began between 2003 and 

2005. Kansas design values show a clear trend of declining ozone levels from the late 1990s to 

the most recent years. In Linn, Sedgwick, and Sumner Counties, 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 weight of evidence analysis presented above support the conclusion of the 

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, consistently with the 

requirements of element (1) of CAA section 11 0(a)(2)(D)(i). 

VI. Proposed Action 

EPA is proposing partial approval of the Colorado SIP to meet the requirements of 

Section 11 O(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 of element (1): prohibition of significant contribution to nonattainment of the 1997 

8-hour ozone NAAQS in any other state. At a later date, EPA will act on the language and 

demonstration addressing element (2): prohibition of interference with maintenance of the 1997 

8-hour ozone NAAQS in any other state. 

VII. Statutory and Executive Order Review 

Under the Clean Air Act, the Administrator is required to approve a SIP submission that 

complies with the provisions of the Act and applicable Federal regulations. 42 U.S.C. 7410(k); 

40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, 

provided that they meet the criteria of the Clean Air Act. Accordingly, this action merely 

17 
approves state law as meeting Federal requirements and does not impose additional requirements 

beyond those imposed by state law. For that reason, this action: 

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

and Budget under Executive Order 12866 (58 FR 51735, October 4,1993); 

•	 Does not impose an information collection burden under the provisions of the Paperwork 

Reduction Act (44 U.S.C. 3501 et seq.); 

•	 Is certified as not having a significant economic impact on a substantial number of small 

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

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

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

104-4); 

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

43255, August 10, 1999); 

•	 Is not an economically significant regulatory action based on health or safety risks 

subject to Executive Order 13045 (62 FR 19885, April 23, 1997); 

•	 Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, 

May 22, 2001); 

•	 Is not subject to requirements of Section 12(d) 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 OF DOCUMENT: Approval and Promulgation of State 

Implementation Plans; State of Colorado; Interstate Transport of Pollution Revisions for 

the 1997 8-hour Ozone NAAQS: "Significant Contribution to Nonattainment" 

Requirement. Proposed Rule. (EPA-R08-0AR-2007-1032) Page 19 of 19 

•	 Does not provide EPA with the discretionary authority to address, as appropriate, 

disproportionate human health or environmental effects, using practicable and legally 

permissible methods, under Executive Order 12898 (59 FR 7629, February 16, 1994). 

In addition, this rule does not have tribal implications as specified by Executive Order 13175 (65 

FR 67249, November 9, 2000), because the SIP is not approved to apply in Indian country 

located in the state, and EPA notes that it will not impose substantial direct costs on tribal 

governments or preempt tribal law. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air pollution control, 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. 

c, 0 ,/1 .... /?

((iCh~ c/: Cc.~ .... J{'-C/t . --CCarol L. Campbell ) 

Acting Deputy Regional Administrator 

Region 8 

19