ENVIRONMENTAL PROTECTION AGENCY
 

40 CFR Part 52
 

EPA-R08-0AR-2007-1035; FRL-


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

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

"Interference with Maintenance" Requirement 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Proposed Rule. 

SUMMARY: EPA is proposing to approve the "State of Colorado Implementation Plan to Meet 

the Requirements of Clean Air Aet Section 110(a)(2)(D)(i)(I) - Interstate Transport Regarding 

the 1997 8-Hour Ozone Standard" addressing the "interference with maintenance" requirement 

01' section 11 0(a)(2)(D)(i)(I). On June 18,2009 the State of Colorado submitted an interstate 

transport State Implementation Plan (SIP) addressing the interstate transport requirements under 

section 11 0(a)(2)(D)(i) of the Clean Air Act (CAA). In this action, EPA is proposing to approve 

the Colorado Interstate Transport SIP provisions that address the section 11O(a)(2 )(D)(i)(I) 

requirement prohibiting a state's emissions from interfering with maintenance of the 1997 8-hoUi' 

ozone National Ambient Air Quality Standards (NAAQS) by any other state. This action is 

being taken under section 110 of the CAA. 

--Federal __._._·· Reoisterj, .0_·· .-- _...-. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-0AR-2007­

1035, by one of the following methods: 

ht1n)/wwW.. regulations.go.\::. Follow the on-line instructions for submitting 

comments, 
Page 2 orJO 

E-mail: mastmp~J~LQ9.menico{(I)epa.\LOV 

Fax: (303) 312-6064 (please alcl1 the individual listed in the FOR FURTHER 

I~FORVIATIONCONTACT ir you arc 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 accept(2d Monday through Friday, 8:00 

a.m. to 4:30 p.m., excluding federal holidays. Special arrangements should be 

made !()r deliveries of boxed information. 

Instructions: Direct your comments to Docket ID No. EPA-R08-0AR-2007-1 035. 

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

and may be made available online at httnJlwww.regulatiQmggy, including any personal 

inl()rmation provided. unless the comment includes inl()rmation claimed to be Confidential 

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

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

http://www.regulati_QDs.gov or e-mail. The http://www.regu[ations.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 h.llilj/\y'y.rw.r~g),l9tions.u.ov,your e-mail address will be 

automatically captured and included as part or the comment that is placed in the public docket 
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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 suhmit. If EPA cannot read your comment due to technical difficulties 

and cannot contact you for clarification, EPA may not be ahle 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 ol'the SUPPLEMENTARY INFORMIATION section of this document. 

f)ocket· All documents in the docket are listed in the b!!.p:l/www.rygulations.!.!.ov index. 

Although listed in the index, some information is not publicly available, e.g., CBI or other 

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

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

availahle either electronically in http://v.::ww.regulations.!.!.ov or in hard copy at the Air Program, 

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

Colorado 80202-1129. EPA requests that if at all possihle, 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, Olastr~ngelo.~iol11enj~Q(fiJ,epa.goV',

SUPPLEMENTARY I~FORMATION:

Definitions 
Page 4 of 30 

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

(i) The words or initials Act or ~J\f1 mean or refer to the Clean Air Act, unless the context 

indicates otherwise. 

(ii) The words I~EA_,\:Y~(?, us or 91!.I: mean or refer to the United States Environmcntal Protection 

Agency. 

(iii) Thc initials SIP mean or refcr to State Implementation Plan. 

(iv) The words Co19L~<J..Q. 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 

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 

A. EPA 's l~valuation ofInterfcrence with Maintenance 

B. Colorado Transport SIP 

VI. Proposed Action 

VII. Statutory and Executive Order Reviews 

I. General Information 

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

1. ,\'uhll7i/ling ('8/ Do not suhmit CBI to EPA through J)JJ11.H~~:yv,rel!qI<I.1i_t)ns:lli.l_Yor email. Clearly mark the part or all of the information that you claim to be CHI. For CHI 
Page 5 of 30 

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

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

information that is claimed as em. In addition to one complete version orthe comment that 

includes information claimed as em, a copy of the comment that docs not contain the 

inror111ation 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. Tipsj(Jr PreparinR Your ('omrnents. When submitting comments, remember to: 

a.	 Identiry 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; suggest altematives 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 sufJicient detail to allow for it to be reproduced. 

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

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

personal threats. 

h. Make sure to submit your comments by the comment period deadline identified. 
Page 6 or 30 

II. Background 

On July 18, I c)C)7, EPA promulgated new NAAQS for ozone and for tine particulate 

matter (PM25 ). This action is being taken in response to the promulgation of the 1997 8-hour 

ozone NAAQS. This action does not address the requirements for the 1997 or 2006 PM2 5, or the 

2008 8-hour ozone NAAQS; those standards will be addressed in later actions. 

Section 11 O(a)( I) of the CAA requires states to submit SIPs to address a new or revised 

NAAQS within 3 years after promulgation of such standards, or within such shorter period as 

EPA may prescribe. Section 11 0(a)(2) lists the clements that such new SIPs must addrcss, as 

applicable, induding scction I I0(a)(2)(D)(i), which pertains to interstate transport of certain 

emissions. On August 15,2006, EPA issued its "Guidance for State Implementation Plan (SIP) 

Submissions to Meet Current Outstanding Obligations Under Section 11 O(a)(2)(D)(i) for the 8­

I-IOLlr Ozone and PM25 National Ambient Air Quality Standards" (2006 Guidance). EPA 

developed the 2006 Guidance to make recommendations to states for making submissions to 

meet the requirements of section II 0(a)(2)(D)(i) for the 1997 8-hour ozone standards and the 

19')7 PM25 standards. 

As identified in the 2006 Guidance, the "good neighbor" provisions in section 

11 O(a)(2)(D)(i) require each state to submit a SIP that prohibits emissions that adverscly affect 

another state in the ways contemplated in the statute. Section 11 0(a)(2)(D)(i) contains four 

distinct requirements related to the impacts of interstate transport. The SIP mLlst prevent sources 

in the state from emitting pollutants in amounts which will: (1) contribute significantly to 

nonattainment of the i\iAAQS in olhcr slates; (2) interfere with maintenance of the NAAQS in 

other states; (3) interfere with provisions to prevent significant deterioration of air quality in 
Page 7 of 30 

other states; or (4) interfCre with efhnts to protect visibility in other states. 

On June IiL 2009. EPA received a SIP revision from the State of CoJarado intended to 

address the requirements of section 11 O(a)(2)(D)(i)(I) for the 1097 8-hour ozone standards. ln 

this rulemaking, EPA is addressing only the requirements that pertain to preventing sources in 

Colorado from emitting pollutants that will interfere with maintenance of the 1997 8-hour ozone 

NAAQS by other states. 1n its submission, the State ofCo[orado indicated that its current SIP is 

adequate to prevent such interference. With this submission, the state intended to meet the 

recornmendations of the 2006 Guidance for SIP submissions to meet the second clement of 

section J 1O(a)(2)(D)(i) for the 1997 8-hour ozone standard. 

Ill. What Action Is EllA Proposing? 

EPA is proposing approval of a portion of the Colorado Interstate Transport of Air 

Pollution SIP addressing the requirements of CAA section 11 O(a)(2)(D)(i)(l) 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)(l) - Interstate Transport Regarding the 1997 8-1 lour Ozone 

Standard" (Colorado Interstate Transport SIP). Colorado submitted this SIP revision to EPA on 

June 18,2009. In this Federal Register action EPA is proposing to approve only the language 

and demonstration that, in this SIP revision, address the requirements of clement (2), i.e., the 

prohibition of interference with maintenance of the 1997 8-hour ozone NAAQS by any other 

state. 

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

Section 110(k) of the CAA addresses EPA's rulcmaking action on SIP submissions by 
Page 8 of 30 

states. The CAA requires states to observe certain procedural requirements in developing SI P 

revisions t(lr submittal to EPi\. Section 11 0(a)(2) of the CAA requires that each SIP revision be 

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

submitted by a state to EPA. 

The Colorado AC)CC held in early December 2008 a public hearing f()r the Colorado 

Interstate Transport SIP revision, adopted it on December ]0, 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 AQeC on December 30, 2008 and included in the June 18, 2009 submittal to 

EPA. In the original submittaL AQee 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 of Colorado and has determined that the 

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

the ('Ai\. 

V. EPA's Review and Technical Information 

A. EPA's Evaluation oflnterference with :vIaintenance 

The second element of section II O(a)(2 )(D)(i) requires that a state's SIP must prohi bit 

any source or other type of emissions activity in the state from emitting pollutants that would 

'"interfere with maintenance" of the applicable NAAQS by any other state. This term is not 

defined in the statute. Therefore, EPA has interpreted this term in past regulatory actions, such 

as the 1998 \()x SIP CalL in which EPA took action to eliminate emissions of NOx that 
Page 9 01'30 

signdicantly contributed to nonattainment, or interfered with maintenance of, the then applicable 

ozone NAAQS through interstate transport of NOx and the resulting ozone. I The NOx SIP Call 

was the mechanism through which EPA evaluated whether or not the NOx emissions from 

sources in certain states had such prohibited interstate impacts, and if they had such impacts, 

required the states to adopt substantive SIP revisions to eliminate the NOx emissions, whether 

through participation in a regional cap and trade program or by other means. 

After promulgation of the 1997 8-hour ozone NAAQS and the 1997 PM25 NAAQS, EPA 

again recognized that regional transport was a serious concern throughout the eastern C).S. and 

therefore developed the 2005 Clean Air Interstate Rule (CAJR) to address emissions of S02 and 

NOx that exacerbate ambient ozone and PM25 levels in many downwind areas through interstate 

transport. 2 Within CAIR, EPA likewise interpreted the term "interfere with maintenance" as part 

of the evaluation ot' whether or not the emissions of sources in certain states had such impacts on 

areas that EPA determined would either be in violation ofthe NAAQS, or would be in jeopardy 

of violating the NAAQS, in a modeled future year unless action were taken by upwind states to 

reduce S02 and NOx emissions. Through CAIR, EPA again required states that had such 

interstate impacts to adopt substantive SIP revisions to eliminate the S02 and NOx emissions, 

whether through participation in a regional cap and trade program or by other means. 

EPA's 2006 Guidance addressed section 11 O(a)(2)(D) requirements for the 1997 8-hour 

ozone NAAQS and 1997 PM25NAAQS. For those states subject to CAIR, EPA indicated that 

--_.._. __ ..-..--.. _.--_.._._. --'---

Sec, 63 FR 57356 (October 27, 1998). EPA's general approach to section 110(a)(2)(D) was upheld in Michigan v. 

EPA, 213 F.3d M3 (D.C. Cir. 20(0), cert denied, 532 U.S. 904 (2001) However, EPA's approach to interference 

with maintellance in the NOx SIP Call was not explicitly reviewed by the coul1. Sec, North Carolina v. EPA, 531 

F.3d 896, 907·-09 (DC. Cir. 20(8). 

) Sec, 70 FR 25162 (May 12,2005) 

I 
Page 10 of 30 

compliance with ('AIR would meet the two requirements of section llO(a)(2)(D)(i)(I) for these 

~AAQS. For states not within the CAIR region, EPA recommended that states evaluate 

whether or not emissions from their sources would "interfere with maintenance" in other states. 

following the conceptual approach adopted by EPA in CAIR. A11er recommending various types 

of information that could be relevant for the technical analy5is to support the SIP submission, 

such as the amount of emissions and meteorological conditions in the state, EPA further 

indicated that it would be appropriate for the state to assess impacts of its emissions on other 

states using considerations comparable to those used by EPA "in evaluating significant 

contribution to nonattainment in the CAIR."" EPA did not r1ake specific recommendations for 

how states should assess "interfere with maintenance" separately, and discussed the first two 

elements of section] 1O(a)(2)( D) together without explicitly differentiating between them. 

In 2008, however, the U.S. Court of Appeals for the D.C. Circuit found that CAIR and 

the related CArR federal implementation plans were unlawful.·1 Among other issues. the court 

held that EPA had not correctly addressed the second clement ofseetion 110(a)(2)(D)(i)(I) in 

CAIR. The court noted that "EPA gave no independent significance to the' interfere with 

maintenance' prong or section 11 0(a)(2)(D)(i)(I) to separately identify upwind sources 

interfering with downwind maintenanee."s EPA's approach, the court reasoned, would leave 

areas that arc "barely meeting attainment" with "no recourse" to address upwind emissions 

3 Memorandum hom William T. Ilarllett entitled, "Guidance for State Implementation Plan (SIP) Submissions to 

Meet Current Outstanding Obligations Under- Section 110(a)(2)(D)(i) 1'0:' the 8-hour O/.one and PM25 N8tional 

Ambient Air (,)u,lIity Standards." Aug. 15,2006, p. 5. ("2006 Guidance"). Available for review in [~PA 's 

September 15.20 10 doc"et document entitled: "Relevant Guidance and Supporting Documentation for the Proposed 

Rulcmaking b:del'~II_RcgistCl" Action Docket rD /f EPA-R08-0AR-2007--1 035" 

: Scc, :\onh Carolilia v. !':I'/\, 531 1,3d 896 (DC. Cir. :2(08) 

; Id,at()09, 
Page] ] of 30 

sources. l

) The court therefore concluded that a plain language reading of the statute requires EPA 

to give independent meaning to the interfere with maintenance requirement of section 

] 1O(a)(2)(])) and that the approach used by EPA in CAIR failed to do so. 

In addition to affecting CAIR directly, the court's decision in the North Carolina case 

indirectly affects EPA's recommendations to states in the 2006 Guidance with respect to the 

interfere with maintenance clement of section 110(a)(2)(D)(i)(I) because the agency's guidance 

suggested that states use an approach comparable to that Llscd hy EPA in CAIR. States such as 

Colorado developed and adopted their Interstate Transport SIPs not long alter the Court's July 

2008 decision, but well before EPA, in the Transport Rule Proposal (see below), was able to 

propose a new approach for the interference with maintenance clement. Without 

recommendations from EPA, Colorado's SIP may not have sufficiently differentiated between 

the signilicant contribution to nonattainment and interference with maintenance clements of the 

statute, and relied in a general way on the difference between monitored concentrations and the 

1097 is-hour ozone .\/\AQS to evaluate the impacts or State emissions on maintenance of the 

NAAQS in neighboring states. EPA believes that it is necessary to evaluate these state 

submissions for section 11 O(a)(2)(D)(i)(1) in such a way as to assure that the interfere with 

maintenance element of the statute is given independent meaning and is appropriately evaluated 

using the types of information that EPA recommended in the 2006 Guidance. To accomplish 

this, U>A believes it is necessary to usc an updated approach to this issue and to supplement the 

technical analysis provided by the state in order to evaluate the submissions with respect to the 

(, Id. 
Page 12 of 30 

inter1Cre with maintenance element of section 11 0(a)(2)(D)(I). 

EPA has recently proposed a new rule to address interstate transport pursuant to section 

II O(a)(2)(D)(i), the "'Federal Implementation Plans to Reduce Interstate Transpol1 of Fine 

Particulate Matter and Ozone" Crransport Rule Proposal), in order to address the judicial remand 

orCAIR. 7 As part of the Transport Rule ProposaL EPA specifically reexamined the section 

11 0(a)(2)(D)(i) requirernent that emissions from sources in ,I state must not "interfere with 

maintenance" of the 1997 8-hour ozone NAAQS and 1997 PM25 NAAQS hy other states In the 

proposal, EPA developed an approach to identify areas that it predicts to he close to the level of 

the 1997 8-hour ozone NAAQS and 1997 PM25 NAAQS in the future, and therefore at risk to 

hecome or continue to he nonattainment for these NAAQS c:nlcss emissions from sources in 

other states are appropriately controlled. This approach star~~s hy identifyi:1g those specific 

geographic areas jClr which further evaluation is appropriate. and difTerentiates hetween areas 

where the concern is with interference with maintenance, rather than with significant 

contrihution to nonattainment. 

As described in more detail below, EPA's analysis evaluates data from existing monitors 

over three overlapping three year periods (i.e., 2003-2005, 2004-2006, and 2005-2(07). as well 

as air quality modeling data. in order to determine which areas arc prcdict(~d to be violating the 

1997 8-hour ozone and PM2 .'i NAAQS in 2012. and which areas arc predicted potentially to have 

difficulty with maintaining attainment as arthat date. In essence, if' an area's projected data f'or 

2012 indicates that it would be violating the NAAQS based ~)J1 the average of these three 

- _---.----_.__.. _----­

7 See "Federal Implementation Plans to Reduce Interstate Transport of Fine Particulate Matter and Ozone," 75 FR 

45210 (August 2, 20 I0). 
Page 13 ono 

overlapping periods, then this monitor location is appropriate for comparison for purposes of the 

significant contribution to nonattainment element of section 1IO(a)(2)(D)(i). If~ however, an 

area's projected data indicate that it would be violating the NAAQS based on the highest single 

period, hut not over the average of the three periods, then this monitor location is appropriate for 

comparison for purposes of the interfere with maintenance element of the statute. 

By this method, EPA has identified those areas with monitors that are appropriate 

"maintenance sites" or maintenance "receptors" for evaluating whether the emissions from 

sources in another state could interfere with maintenance in that particular area.. EPA then uses 

other analytical tools to examine the potential impacts of emissions from upwind states on these 

maintenance receptors in downwind states. EPA helieves that this new approach for identifying 

those areas that arc predicted to have maintenance problems is appropriate to evaluate the section 

110(a)(2)(D)(i) SIP submission ofa state for the interfere with maintenance element. x EPA's 

2006 Guidance did not provide this specific recommendation to states, but in light ofthe court's 

decision on CAIR, EPA will itself follow this approach in acting upon the Colorado submission. 

As explained in the 2006 Guidance, EPA does not believe that section 11 0(a)(2)(D)(i) 

SIP suhmissions from all states necessarily need to follow precisely the same analytical approach 

as CAIR. In the 2006 Guidance, EPA stated that: "EPA believes that the contents of the SIr 

submission required by section II 0(a)(2)(D)(i) may vary depending upon the facts and 

circumstances related to the specific NAAQS. In particular, the data and analytical tools 

--_._.-.._--_.... ­

" To begin tllis Cln<1lysis, U'A !irst identifies alllllonitors projected to be in nonattainment or, based on historic 

variability in air quality, projected to have maintenance problems in 2012, These maintenance receptors arc close to 

the level of the )l)97 ozone and PM.>, l\iAAQS such that minor variations in weather or emissions could result in 

violations of the NAAQS in 2012. 
Page 1401'30 

available at the time the State develops and submits a SIP for a new or revised NAAQS 

necessarily alTccts the contents of the required submission. ,,') EPA also indicated in the 2006 

Cluidance that it did not anticipate that sources in states outside the geographic area covered by 

CAIR were significantly contributing to nonattainment, or interfering with maintenance, in other 

states. IO As noted in the Transport Rule ProposaL EPA continues to believe that the more 

widespread and serious transport problems in the eastern United States are analytically distinct. 

For the 1997 8-hour ozone NAAQS and the 1997 PM: 5 NAAQS, EPA believes that 

nonattainment and maintenance problems in the western United States are relatively local in 

nature with only limited impacts from interstate transport. I I In the Transport Rule Proposal, 

EPA did not calculate interstate ozone or PM2 , contributions to or from western states. 

Accordingly, EPA believes that section 110(a)(2)(D)(i) SIP submissions for states not 

evaluated in the Transport Rule Proposal may be evaluated using a "weight of the evidence" 

approach that takes into account available relevant information, such as that recommended by 

EPA in the 2006 Guidance lor states outside the area affected by CAIR. Such information may 

include, but is not limited to, the amount of emissions in the state relevant to the NAAQS in 

question, the meteorological conditions in the area, the distance hom the state to the nearest 

monitors in other states that are appropriate receptors, or such other information as may be 

probative to consider whether sources in the state may interfere with maintenance ofthe 1997 8­

hour ozone NAAQS in other states. These submissions can rely on modeling when acceptable 

modeling technical analyses are available, but EPA does not believe that modeling is necessarily 

'J 200() (iuidancc at 4. 

I() Id. at 5. 
Page 15 of 30 

required if other available information is sufficient to evaluate the presence or degree of 

interstate transport in a given situation. 

B. Colorado Transport SIP 

To meet the requirements of section 11 O(a)(2)(D)(i)( [) for the 1997 8-hour ozone 

standard, the State of Colorado developed and submitted to EPA on June 18, 2009 an Interstate 

Transport SIP that focused primarily on the "significant contribution to nonattainment" 

requirement of section 11 O(a)(2)(D)(i) and, as noted earlier, addressed only in a limited way the 

interference with maintenance requirement of section 110(a)(2)(D)(i)(l). On June 3, 2010, EPA 

approved the Colorado Interstate Transport SIP provision that require that emissions from a 

state's sourccs do not significantly contribute to nonattainmcnt of the 1997 8-hour ozone 

NAAQS in any other state. To demonstrate that emissions from Colorado do not inter1ere with 

maintenance of the 1997 8-hour ozone NAAQS in neighboring states, the Colorado Interstate 

Transport SIP uses results from Colorado's 2009 "8-Hour Ozone Attainment Plan" for the 

D!'v1A/NFR. nonattainmcnt 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 day~; of highest ozone concentrations 

(reflecting a design value of 84.9 ppb) in the DMA/NFR area. the projected design values 

decrease to 63 ppb or less for all downwind Colorado counties cast of an imaginary north-south 

line approximately 70 miles cast from Denver. 12 EPA does not agree the State of Colorado 

._- .- - _._..-.- --------,.._---

Ii See, Trans[Jol"t Rule Proposal, 75 FR 45210, 45277. 

I! COlora(lo Interstutc Transpol1 SII), December 12,2009, Figure 5 at 15. Note that the modeling analysis domain 

,"or the DMA/NFR attainment plan was limitcd to the Statc's tCITitory, and that the 70 mile distance ['cpresents the 

approximate distancc t1'O!1l Denver to the westem border of Morgan County, Colorado. 
Page 1601'30 

Interstate Transport SIP' s assessment that these results demonstrate that "'the magnitudc 0 I' o/.one 

transport rrom Colorado to other states is too low to .. , interlere with maintenance by any other 

state with respect to the O.Og ppm NAAQS" as thc sole basis for evaluating the state's 

interference. 13 The limited contribution of local emissions to nonattainmcnt in the DMA/NFR 

and the quick drop in ozone levels in the easternmost Colorado counties, in and by themselves do 

not exclude a potential for interference with maintenance of the 8-hour ozone NAAQS from 

Colorado emissions to downwind maintenance areas. Rather, as a reflection of emission levels, 

the relatively (to the 1997 8-hour ozone NAAQS) moderate ozone concentrations in eastern 

Colorado and in neighboring states somewhat reduce the probability that State emissions 

interfere with maintenance of the NAAQS by these states. 14 

I~PI\ is evaluating the Colorado Interstate Transport SIP taking into account thc 

mcthodologies and analysis results developed in the Transport Rule Proposal in response to the 

judicial remand of CAIR. As noted previously. the Transport Rule Proposal includes a new 

approach to determine whether emissions from a state interfere with maintenance of the 1997 ghour ozone NAAQS and the 1997 PMn NAAQS by other states. In this action, EPA is using a 

comparable approach to that of the Transport Rule Proposal in order to determine if emissions 

from Colorado sources interfere with maintenance of the 1997 8-hour ozone NAAQS by other 

states. 

To eval uate ambient impacts from upwind states to maintenance receptors, the Transport 

Rule Proposal evaluates. through air quality modeling of each state's emissions, the contribution 

,; lei at 17. 
Page 170f30 

from individual states to downwind maintenance receptors. States that contribute pollutant 

concentrations below the significance threshold for interference with maintenance, proposed at 

one percent of the NAAQS. are excluded from further analysis. 15 For the 1997 8-hour ozone 

standard state contributions of (J.8 ppb and higher are considered above the threshold. while 

()/onc contribution less than 0.8 ppb are below the threshold. 

[n the Transp0l1 Rule Proposal, EPA projected future concentrations of ozone at monitors 

to identify areas that are expected to be out of attainment with NAAQS or to have diflicu[ty 

maintaining compliance with the NAAQS in 20]2. To determine the states that may cause 

interlcrcnce at the maintenance receptors, the Transport Rule Proposal models the states' ozone 

contribution to these maintenance receptors. Because the Transport Rule Proposal does not 

model the contribution of emissions from Colorado (and other western states not fully inside the 

Transport Rule Proposal's modeling domain) to 8-hour ozone maintenance receptors in other 

states, our assessment relics on a weight of evidence approach that considers relevant 

information (such as identi fication of maintenance receptors and estimates of ozone 

contriolltions) lJ"Oln th(;' Transport Rule Proposal pertaining to states within its modeling domain, 

and additional material such as geographical and meteorological factors. modeling analysis 

results from other studies, back trajectory analyses, and AQS monitoring data. While 

conclusions reached for each of the factors considered in the following analysis are not in and by 

themselves determinative, consideration ofthese factors together provides a reliable qualitative 

conclusion that emissions from Colorado arc not likely to interfere with maintenance of the 1997 

------...__.-_._._-----.__.._-------- ------'­

II Similar cvidt:nl.:l: is provided by the substantial gap between the 1997 R-hour ozone standard and the dt:sign values 

at monitors in adjal.:l.:nt downwind states sUl.:h ilS Kansas, 1\ew Mexico, l;tah, and WY0Inmg Id. at 7-8. 
Page 18 ofJO 

8-hour ozone l\;\AQS at monitors in other states. 

Our analysis begins by assessing Colorado's contribution to the closest maintenance 

receptors Itl!' the 1997 8-hour ozone standard. The Transport Rule Proposal identifies within its 

modeling domain (consisting of J 7 states cast of the Rocky Mountains, and the District or 

Columbia) 16 maintenance receptors, among which the eight closest to Colorado are eight 

receptors in the Dallas Fort Worth (DFW) and llouston-Galveston-Brazoria (HUB) 8-hour ozone 

. I~ nonatta1l1ment areas. 

Two of the three D1"W area maintenancc receptors arc in Dallas County (I-linton Street 

and Dallas Executive Airport sites), and the third is in Tarrant County (Keller site).17 These 

monitors arc at least 500 miles from Colorado. I g Distance by itscIf is not an obstacle to long 

range transport of ozone and/or its precursors. NOx, the primary ozone precursor that is the 

object of the Transport Rule ProposaL may be transported for long distances, and contribute 

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 ciTect of winds or chemical sink processes. As a result, one may conclude that the 

approximately 500 miles from Colorado sources of NOx emissions to the DFW area 

maintenance receptors reduces, but does not exclude, the possibility that the Colorado emissions 

I) Transport Rule Proposal, 75 FR 45210.45254. 

1(, Thl: rl:maining eight maintenance-only sites are in a handfu! of East Coast states: Connecticut, (jeorgia. New York 

and Pennsylvania See Table IV C-11. Transpol't Rule Proposal, at 452S2-253 

[7 The 500 mile estimate represents the approximate distance between Lamar, in the southeastern corner or 

Colorado, and Dallas, Texas. The monitors' Site [[) Numbers are: Hinton, 48-113-0069; Executive Airport, 48-11]­

0087; and Keller, 48-439-2003. See id. For monitor~' site names, ~ee online TCQC web page at 

11ll~2:f/!\,_\y~,-t&~,state. tx. ~ls/cgi.:.QinLs;,9m121 iance.LmoIJSWii!.'? ite in foJ2l 

IX Thi~ distance underestimates the average distance covered by emis~ions from Colorado sources for at least two 

reasons: a) most Colorado sources are further north and/or west from the DFW area than Lamar; b) 500 miles 
Page 19 of 30 

interlere with mainknance of the 0JAAQS at these receptors. 

Because pollutant transport is linked to wind direction, we examine how frequently air 

masses from Colorado pass through or end in the DFW area lhat includes the maintenance 

receptors identified above. The State of 'I'exas' 2007 attainment demonstration for the DFW area 

points out, without quantifying contributions, how heavily the area's ozone concentrations are 

aftected by substantial transport from other areas. Average ozone background levels for DfW 

(re!lecting concentrations contributed to the area by emissions from sources within Texas but 

olltside the nonattainment area, and from sources outside Texas) arc estimated to range between 

44 and () I ppb, with peak averages between 64 and 68 ppb on days when 8-hour ozone 

concentrations exceed the 1997 standard. IY 

To eval uate the impact of wind direction on ozone transport from Colorado to the DFW 

maintenance receptors, we rely on the results of two back tra;jectory studies, including a set of 

traj ectories wi tl1 end points at the maintenance receptors in the DFW area. 

20 EPA generated 

these trajectories using the IIYSPLIT 4.9 online computer application, selecting the archived Eta 

Data Assimilation System (EDAS) meteorological data sets with the highest degree of resolution 

(40 km).21 Back trajectories were run for the days of the 2005-2006 years in which ozone 

concentrations at these receptors exceeded the 1997 8-hour NAAQS-i.e., monitored ozone 

-----------------_._-- ---------_._-------­

rerresents the distance along a straight pathway from Lamar to Dallas, Texas, as compared to the rathways full of 

twists and turns that often characterize the long range transpon of air parcels. 

I') "Dallas-!'"ort Wonh Eight-Hour Ozone Nonattainll1ent Area: Attainme:lt Demonstration," TCEQ, May 23, 2007, 

p. I 

'II USL~I'A Region 8 marped o,teK traJectories using software and data files maintained by the National Oceanic and 

i\tll1osrheric Administration (:'';OA;\) Air Resource Laboratory (ARL). 

21 [)rax ieI', R R. and Rolph, (j D.. II YS 1)1,11' (I IYbrid Single-Partie Ie Lagrangian Integrated Trajectory) Model 

(20 10), available via NOAA ARL READY Website, http://rcady.arlnoaa.gov/IIYSPLlT.php. NOAA Air R.esources 

l,aboratory, Silver Spring, MD. See also Rolph, G.D., R.eal-time Environmental Applications and Display sYstem 
Page 20 of 30 

concentrations were 85 ppb or above. Exceedance days were identified using the Air Quality 

System (AQS), EPA's repository of monitored ambient air quality data. At each monitor, 

trajectories were started at 22:00 Coordinated Universal Time (UTC), equivalent to 4:00 pm 

CST, and were run backwards in time for 72 hours (three days.) The trajectory height at the 

starting point is 1500 meters above ground level. From the individual bal:k trajectories, "spider 

web" maps were generated for all three monitors combined and for each monitor (Figure 1.1 and 

Figures 1.1.21 through 1.1.c in Appendix A of EPA's TSD).22 These maps indicate that air parcel 

pathways from Colorado and ending at maintenance receptors in Dallas and Tarrant Counties are 

rare during the three days preceding ozone exceedances at these receptors. On only one day, of 

the 35 exeeedance-days at maintenance receptors in 2005-2006, did the air mass pathway go 

through Colorado, and even in this one instance air parl:cls crossed the State along a short 

pathway through its northeast corner, before continuing on their southeastward l:ourse. 23 

Back trajectory analysis results included in the May 23, 2007 DFW area Attainment 

Demonstration corroborate' these conclusions. The analysis, also based on the IIYSPLIT model, 

includes all Jays during the years 2001-2003, with trajectories 01'48 hours (2 days) duration, 

heights of 100, 500 and 1300 meters, and start times of 20, 21 and 22 UTe (2 :00, 3:00, and 4:00 

pm CST.) The resulting density plots in Figure 3-1 of the DFW attainment demonstration clearly 

show that during most of the ozone season, on high and low ozone days, air parcels from 

---_. ---.-.. _.._---_..._......._..... _ ...._._. -_._---._-- ---_ _ _-_.__.
 

(READY) Website (20 I0). hltp:l/n:ady.arl.noaa.gov. ~()AA Air Resources Laboratory. Silver Spring. MD.
 

~'See back trajectory maps in Appendix A oCthe EPA's TSD supporting documentation in Docket ID No. r'YA­


R08-0A R-2007-! 035
 

"EPA's TSD is available for review as part oCthe supporting documentation for Docket ID N. EPA-ROR-OAR­


2007-1035.
 
Page 21 01'30 

Colorado infrequently end in or pass through the DFW area. 

24 

Because back trajectory analysis results map pathways of air parc<:\s that mayor may not 

transport pollutants, they cannot be considered deterrninativ(~as to the transport of ozone and its 

precursors, or of the absence of such transport, from Colorado emissions. However, the rarity of 

air parcel trajectories from Colorado to the DFW area and to its maintenance receptors strongly 

support the conclusion that emissions of ozone and its precursors from Colorado arc not likely to 

interfere with maintenance of the 1997 ozone NAAQS at these receptors. 

A final piece of evidence of a different type is found in a modeling analysis developed 

by EPA to assist the State of New Mexico in its assessment of ozone and PM25 transport from 

New Mexico to other states. This modeling analysis, part of the New Mexico Interstate 

Transport SIP submission of July 30, 2007, relies on data developed by the Central Regional Air 

Planning Association (CI:NRAP) that includes a 2002 third quarter CENRAP modeling 

dataset. 25 It is based on a 36 km national grid that includes Colorado, and uses the ozone source 

apportionment tool (OSAT) to determine potential linkages between state emissions and 

downwind states. 2() Modeling results indicate that at the height of the 2002 ozone season, the 

highest ozone contribution from Colorado emissions to the DFW monitors (including its 

maintenance receptors) averaged 0.4 ppb or less. That is well below the contribution threshold 

of 0.8 ppb, used in the proposed Transport Rule. 

The other five Texas monitors identified by the Transport Rule Proposal as maintenancconly receptors in Texas arc located in lIarris County, which lies within the HGB nonattainment 

.!I Dallas-r:ort Worth Attainment Demonstration, May 23, 2007, at 3-1 to 3-2.
 

2) "\.;ew Mexico State Interstate Tl'ansport SIP," submitted to [PA July 30, 2007: Appendix D, Exhibit 9 Modeling
 
Page 22 of 30 

area. This area is at least 700 miles from Colorado?? General considerations on the effect of 

distance on ozone transport from Colorado to the DFW area, discussed above, also apply to the 

potential ror transport rrom Colorado to the maintenance receptors in the HGB area. The greater 

distance (hy ahuut onc third) hetwecn Colorado and the 11GB area increases the chance !()r 

dispersion of any Colorado ozone during its transport to IIG f3 maintenance receptors. and 

increases the odds for air masses from Colorado to pick up greater quantities of ozone and/or 

precursors during their longer travel through emissions rich Texas. Again, these considerations 

reduce, but do not exclude, the possibility of emissions from Colorado interfering with 

maintenance of the 8-hour ozone NAAQS at the 11GB maintenance receptors. 

A similar conclusion is suggested by the EPA hack trajectories mapped for the 11GB 

maintenance receptors. Using the same online HYSPUT 4.9 online computer application as for 

the ])FW trajectories,28 EPA ran back trajectories from the HGB area maintenance receptors for 

all 2005-2006 ozone excecdances days. The pathways of air parcels ending at, or passing 

through, these monitors when ozone concentrations reached levels of 85 ppb or higher are shown 

in Figure 2.1 of Appendix A in FPA's supporting documentation. At each monitor, trajectories 

started at 22:00 Coordinated Universal Time (UTC), equivalent to 4:00 pIll CST. and ran 

Data and Rep0l1 for New Mexico," at 2. 

26 For details on the model and on the analysis see: id . 

.27 The 700 mile estimate represents the approximate .distance between Lamar. in the southeastern corner of' 

Colorado. and Houston, Texas. The jive monitoring sites' names (ID No.) are: Aldine (48-201-0024), NOl1hwest 

l!aITis (48-201-0029), Lynchburg Ferry (48-201-101S), Clinton (48-201-1tnS), and Seabrook [;riendship Park 

(48-20 I-I (50). The approximate 850 mile distance between Denver and Houston is intended to represent the 

distance to be covered by the emi.'isions from Colorado to the five maintenance monitors. It is to be noted that the 

measured distance represents that of the straight (and shOltest) path, which docs not reflect the more circuitous paths 

I"ollowed by air parcels. 

'x Sec note 24 'Ibovl'. 
Page 23 or 30 

backwards in time for 72 hours (three days), at 1500 mcters above ground level. 2 

'i Results show 

that air parcel pathways passing 1500 meters above the HGB maintenance receptors at 4:00 pm 

on exceedance days rarely came from Colorado. Figure 3 of the back trajectories report shows 

that only in one out of 53 exceedance days at the maintenance receptors did the air parcel's 

pathway go through Colorado. Even in this one instance, the pathway crossed Colorado for a 

very short distance through the State's northeast corner, before continuing on its southeastward 

\Ii 

course. 

Back trajectory analysis results from a 2009 report, "Effects of Meteorology on Pollutant 

Trends" report, corroborate these conclusions. The analysis uses 1IYSPUT with EDAS 

meteorological datasets to plot 72 hour back trajectories centered in fIouston, at 300 meters 

height and for various times ofthe day. Trajectories are plotted for all days with available data 

between May 1 and October 31, 2000-2007. A clustering algorithm built into I[YSPUT is used 

to group individual back trajectories into several classes based on shape ancl direction. 3l Due to 

the greater number of days plotted, the six clusters of trajectories shown in Figures 6-17 to 6-22 

include a much larger number of air parcel pathways than EPA's back trajectory analysis 

referenced above, but still show similar results concerning trajectories from Colorado. Air 

parcels from Colorado to the I[ouston area are rare, as shown by the few trajectories from 

"J Sec Tabk I, !:IlA's "B,IC~ Trajectories Analysis f)ocumeillatiun," Table [. 

't, The trajectory's path that ended at the :\onhwest HaiTi, !'eceptor on August 31, :2006, is almost the same as the 

one that on June IS, 2005 ended at the Keller receptor in Tarrant. This IS likely to be a coincidence, or an Indication 

about the pathways of air masses that go through eastern Colorado before ending in eastern Texas (DFW and 11GB 

areas). 

31 f),lve Sullivan, "Effects oPv1eteoroiogy on Pollutant Trends," March 16,2009, at 27-34. This repon is available 

as one of the documents in EPA's TSD documentation, and may also be reviewed 0111 ine at 

http://www.t~.lUiJ~.tx.us!~sscts!pll.QllcjjmnJ~nJ.mill1iS)ll!air!.i!.IJJ!G_()Il\ract"Lrepol"\~LQ.<tl5&2Q5QP24 5FY080 I 

200903 16-LJt.:-IJ1£L£JJ~ts ...Q!l....J2QlliLtlJ!lUlfI19S.pdf. 
Page 24 of 30 

Colorado in cluster 3 (Figure 6-19) as compared with the total sample of 1416 trajectories 

included in the six clusters. Figure 6-15 summarizes effectively the overall scarcity of wind 

pathways from Colorado, and from the west/lower northwest sector in generaL to the HGB area. 

It shows the mean centerlines for the six identitied clusters, and at their closest point to 

Colorado's borders the mean centerline (number 3) is still at an estimated distance of 

approximately 200 miles. 

Again, back trajectories map pathways or air parcels that mayor may not transport 

pollutants, and they cannot be considered determinative as to the transport of ozone and its 

precursors. llowever, the infrequency of air parcels trajectories from Colorado to the HGB area 

in generaL and to its maintenance receptors in particular, strongly support the conclusion that 

ozone precursors' emissions and ozone from Colorado are not likely to interfere with 

maintenance of the 1997 ozone NAAQS at these receptors. 

The EPA modeling analysis referenced earlier (concerning contribution from Colorado 

sources to the DFW area) includes information on the contribution of the State emissions to the 

11GB area as well. The 2002 modeled contribution from Colorado ozone emissions to the HGB 

area is estimated at 0.3 ppb or less. This fraction of the significant contribution threshold of 0.8 

ppb, set in EPA's Transport Rule Proposal of August 2,2010, strengthens our assessment that 

Colorado emissions are unlikely to interfere with maintenance of the 1997 ozone NAAQS at the 

11GB maintenance receptors.}2 

As noted previously, eight of the 16 maintenance receptors identified within the modeling 

" l'\ew Vlexieo Stille Interstate Trallsport SIP, 2007. Appendix D, at 52. 
Page 25 of30 

by the Transport Rule Proposal analysis are in a handful of East Coast states: Connecticut, 

Cicorgia, New York and Pennsylvania.]] The westernmost states "linked" by the Transport Rule 

Proposal to the eight maintenance receptors in these states include Indiana, Kentucky, 

Tennessee, and Alabama. None of the 13 states west of these contributing states and east of 

Colorado (such as North and South Dakota and Nebraska) was found to contribute significantly 

to the maintenance receptors in the east.]l In addition, among the 13 non-contributing states 

closer than Colorado to the maintenance receptors in the easL there arc states such as Illinois, 

Wisconsin, Iowa, Missouri, Arkansas, and I,ouisiana that in 2005 had NOx emissions up to twice 

as high as Colorado's. Because the analysis for the Transport Rule Proposal found that these 

states with substantially larger NOx emissions than Colorado, and closer than Colorado to the 

maintenance receptors in the cast, do not to contribute significantly to maintenance receptors in 

Connecticut, Georgia, New York and Pennsylvania, it is logical to conclude that it is quite 

unlikely for Colorado emissions to interfere with maintenance ofthe 1997 8-hour ozone NAAQS 

at these same receptors. 

To assist in the evaluation of whether states' emissions interfere with maintenance of the 

NAAQS in western states, t;;PA has developed, independent of the Transport Rule Proposal, a 

modeling analysis identifying monitors at risk for maintenance of the NAAQS within a modeling 

domain that includes the western states.';'; The analysis presented in the memo, "Documentation 

;) Table IV C-12, Transport Rule, at 196-197.
 

;·1 [n addition to North Dakota, South Dakota and Nebraska, the 13 state~; include: Kansas, Oklahoma, Minnesota,
 

Iowa, Missouri, Arizona. Wisconsin, Michigan. Illinois, and [,ouisiana. Table IV-C-21, Transport Rule Proposal, at
 

45269-70.
 

l'; !\ memorandum in the docket for tillS action provides the inlonnation EPA used in order to identify monitors that
 

'In: !'ccep(ors for l'vahldtion of interference with maintenance for cCl1ain staks in the western Unitcd States. See.
 
Page 26 of 30 

of Future Year Ozone and Annual PM2 :i Design Values for Western States" (Western States 

Design Values), uses model results from the Transport Rule modeling Continental U.S. 36 km 

grid, which is coarser than the 12 km grid used in the Transport Rule, but docs not necessarily 

yield less reliable results. 3

!> 

EPA's modeling analysis of western states to determine the monitors that are at risk for 

maintenance of the 1997 8-hour ozone NAAQS identifies only four such maintenance receptors, 

and all four are in California, in Mercer, Placer, Riverside, and Sacramento Counties. Distance 

and topography are not favorable to ozone transport from Denver, which is approximately 750 

miles east of the monitors in Placer and Sacramento Counties. and 850 miles northeast to a 

Riverside County monitor. In the absence o( significant norlhwesterly regional transport winds. 

mountain ranges between Denver and the California maintenance receptors, such as the Rocky 

Mountains, theWasatch and the Sierra Nevada, present large obstacles to ozone transport from 

Colorado to California. Thus, geography and topography reduce the likelihood of transport from 

Colorado to California's maintenance receptors. 

Prevailing wind orientation in t~lct strongly supports the conclusion that Colorado's 

emissions are unlikely to interfere with maintenance of the 1997 8-hour ozone standard in 

California. West of the Continental Divide the prevailing winds generally move from southwesterly, westerly, or north-westerly directions, as indicated by the typical movement of weather 

systems. To further evaluate the direction ofregional transport winds affecting the Calif()rnia 

maintenance receptors, we have plotted back trajectories sterting at each maintenance receptor 

\!kll1orandull1 rrOIl1 Bnan Tirn in or leI'A's Ortice or J\ ir Qual ity Plann il;g and Standal'd~. Ait' Qual it)' Mode ling 

Ciroup entitled "Docull1entation of Future Year Ozone and Annual PM::! 5 Design Value, ror Western Stales" 
Page 27 of 30 

on high ozone days. I ligh ozone days include the top one trlird of the exceedance days (for the 

1997 8-hour ol:one :,\AAQS) registered at each monitor in 2005 and 2006. As shown by the 

trajectories mapped for all four maintenance receptors in Figure 3.1, Appendix A of EPA's 

supporting documentation, on high ozone days air parcels converge on the Mercer, Placer, 

Sacramento and Riverside monitors from the northwest, south and southeast, but there arc no 

pathways from the cast/northeast directions reaching even as far as the eastern Nevada border, let 

alone Colorado 

For a large number ofreceptors in western states, EPA's modeling analysis could not 

calculate 2012 projected design values because these receptors did not have at least 5 days with 

base year concentrations equal to or greater than 70 ppb, as required by ~PA's modeling 

guidance. However, the observed maximum design values at these sites in the 2003-2007 period 

were generally well below the 1997 ozone N/\AQS. The highest (non-Calit()rnial?) site had a 

maximum design value 01'77 ppb. Additionally, the 2012 modeling results at western monitors 

(where a future year design value could be estimated, shows a downward trend in ol:one. There 

are no areas in the West where ozone is predicted to be higher in 2012 (without CArR) compared 

to 2005. On these bascs it is plausible to conclude that it is highly unlikely, but not impossible, 

!()r these monitors to be at risk for maintenance of the 1997 8-hour ozone NAAQS. 

In conclusion. the variety or data and the weight of evidence analysis prcsenkd in this 

----------------- -------~--------------.. ---._-- - .-- ._-- ----­

"Memorandum to Docket EPA-RO~-OAR-2()07-1035,,. EPA, August 23, 2010. 

ii, Id. at 5.
 

37 We are excluding the California monitors from this portion afoul' analysis because above we have already
 

demonstrated that Colorado's emissions are unlikely to interfere with maintenance at the mOdeled California
 

maintenance monitors in the northern, centra] and southern sections of the state. The factors we considered-·­


distance, topography, and wind orientation·apply equally to the un-modeled monitors and make it plausible to
 

cOJl(.:lude th,1t the same demol1stratiol1 is true for Colorado emissions' impact on California non-modeled monitors.
 
Page 28 of 30 

scction support the position or the Colorado Interstatc Transport SIP (adopted into the State SIP 

on Dccembcr 3D, 2008 and submitted to EPA June 18,2009) that emissions from Colorado do 

not intertCre with maintenancc of thc 1997 8-hour ozone NAAQS by any othcr state, consistent 

with the rcquiremcnts of elcment (2) of CAA section II O(a)(2)(D)(i). 

VI.	 Proposed Action 

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

Section II O(a)(2)(D)(i)(I) regarding the 1997 8-hour ozone standard. Specifically, in this action 

EPA is proposing to approve only the language and demonstration that address the requirements 

of clement (2): prohibition of interference with maintenance of the 1997 8-hour ozone NAAQS 

by any other state. EPA approved in a JLIne 3, 2010 final action the language and demonstration 

addressing clement (1): prohi bition of significant contribution to nonattainment 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 

complics 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 

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

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

•	 Is not a "significant regulatory action" subject to review by thc Office of Managemcnt 

and Budget under l~xecLltive Order 128G6 (58 FR 51735. October 4, 1993); 
Page 29 of:;O 

•	 J)oes not impose an information collection burden under the provisions of the Paperwork 

Reduction Act (44 Us.c. 3501 el 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 speci1ied in Execlltive Order 13132 (64 FR 

43255, August J0, 1(99); 

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

subject to Executive Order 13045 (62 FR 19885, April 23, 19(7); 

•	 Is not a significant regulatory action subject to Executivc Order 132 J 1 (66 FR 28355, 

May 22, 2001); 

•	 Is not subject to requircments of Section 12(d) ofthi~ National Technology Transfer and 

Advancement Act of 1995 (15 U.S.c. 272 note) because application of those 

requirements would be inconsistent with the Clean Air Act; and 

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

disproportionate human health or environmental efkcts, using practicable and legally 

permissible methods, under Executive Order 12i{98 (59 FR 7629, February 1(), 19(4). 

In addition, this rule c10es not have tribal implications as specified by Executive Order J3 J75 (65 

FE 67249, November 9,2000), because the SIP is not approved to apply in Indian country 
Page 30 of30 

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: "Interference with Maintenance" Requirement. Proposed 

Rule. (EPA-R08-0AR-2007-1035) Page 30 of30 

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 rccordkeeping 

requirements, Volatile Organic Compounds. 

Authority: 42 U.S.c. 7401 et seq. 

__

Dated: 

rL9~ Carol 

~~~ Rushin 

Acting Regional Administrator 

Region 8