Federal Register / Vol. 75, No. 180 / Friday, September 17, 2010 / Proposed Rules 56935 

• 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. 

Dated: September 9, 2010. 

Carol Rushin, 

Acting Regional Administrator, Region 8. 

[FR Doc. 2010–23292 Filed 9–16–10; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R08–OAR–2007–1035; FRL–9202–7] 

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 Act section 110(a)(2)(D)(i)(I)— 

Interstate Transport Regarding the 1997 

8-Hour Ozone Standard’’ addressing the 

‘‘interference with maintenance’’ 

requirement of section 110(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 110(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 110(a)(2)(D)(i)(I) 

requirement prohibiting a state’s 

emissions from interfering with 

maintenance of the 1997 8-hour ozone 

National Ambient Air Quality Standards 

(NAAQS) by any other state. This action 

is being taken under section 110 of the 

CAA. 

DATES: Comments must be received on 

or before October 18, 2010. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R08– 

OAR–2007–1035, by one of the 

following methods: 

• http://www.regulations.gov. Follow 

the on-line instructions for submitting 

comments. 

• E-mail: 

mastrangelo.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 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–OAR–2007– 

1035. 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 I. 

General Information of the 

SUPPLEMENTARY INFORMATION section of 

this 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 a.m. to 4 

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.domenico@epa.gov. 

SUPPLEMENTARY INFORMATION: 

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 

III. What action is EPA proposing? 

IV. What is the State process to submit these 

materials to EPA? 


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56936 Federal Register / Vol. 75, No. 180 / Friday, September 17, 2010 / Proposed Rules 

V. EPA’s Review and Technical Information 

A. EPA’s Evaluation of Interference 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. Submitting CBI. Do not submit CBI 

to EPA through http:// 

www.regulations.gov or e-mail. Clearly 

mark the part or all of the information 

that you claim to be CBI. For CBI 

information in a disk or CD ROM that 

you mail to EPA, mark the outside of the 

disk or CD ROM as CBI and then 

identify electronically within the disk or 

CD ROM the specific information that is 

claimed as CBI. In addition to one 

complete version of the comment that 

includes information claimed as CBI, a 

copy of the comment that does not 

contain the information claimed as CBI 

must be submitted for inclusion in the 

public docket. Information so marked 

will not be disclosed except in 

accordance with procedures set forth in 

40 CFR part 2. 

2. Tips for Preparing Your Comments. 

When submitting comments, remember 

to: 

Identify the rulemaking by docket 

number and other identifying 

information (subject heading, Federal 

Register date and page number). 

Follow directions—The agency may 

ask you to respond to specific questions 

or organize comments by referencing a 

Code of Federal Regulations (CFR) part 

or section number. 

Explain why you agree or disagree; 

suggest alternatives and substitute 

language for your requested changes. 

Describe any assumptions and 

provide any technical information and/ 

or data that you used. 

If you estimate potential costs or 

burdens, explain how you arrived at 

your estimate in sufficient detail to 

allow for it to be reproduced. 

Provide specific examples to illustrate 

your concerns, and suggest alternatives. 

Explain your views as clearly as 

possible, avoiding the use of profanity 

or personal threats. 

Make sure to submit your comments 

by the comment period deadline 

identified. 

II. Background 

On July 18, 1997, EPA promulgated 

new NAAQS for ozone and for fine 

particulate matter (PM2.5). 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 110(a)(1) 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 110(a)(2) lists the 

elements that such new SIPs must 

address, as applicable, including section 

110(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 

110(a)(2)(D)(i) for the 8-Hour Ozone and 

PM2.5 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 110(a)(2)(D)(i) for the 1997 8- 

hour ozone standards and the 1997 

PM2.5 standards. 

As identified in the 2006 Guidance, 

the ‘‘good neighbor’’ provisions in 

section 110(a)(2)(D)(i) require each state 

to submit a SIP that prohibits emissions 

that adversely affect another state in the 

ways contemplated in the statute. 

Section 110(a)(2)(D)(i) contains four 

distinct requirements related to the 

impacts of interstate transport. The SIP 

must prevent sources in the state from 

emitting pollutants in amounts which 

will: (1) Contribute significantly to 

nonattainment of the NAAQS in other 

states; (2) interfere with maintenance of 

the NAAQS in other states; (3) interfere 

with provisions to prevent significant 

deterioration of air quality in other 

states; or (4) interfere with efforts to 

protect visibility in other states. 

On June 18, 2009, EPA received a SIP 

revision from the State of Colorado 

intended to address the requirements of 

section 110(a)(2)(D)(i)(I) for the 1997 8- 

hour ozone standards. In 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. In its 

submission, the State of Colorado 

indicated that its current SIP is adequate 

to prevent such interference. With this 

submission, the state intended to meet 

the recommendations of the 2006 

Guidance for SIP submissions to meet 

the second element of section 

110(a)(2)(D)(i) for the 1997 8-hour ozone 

standard. 

III. What action is EPA proposing? 

EPA is proposing approval of a 

portion of the Colorado Interstate 

Transport of Air Pollution SIP 

addressing the requirements of CAA 

section 110(a)(2)(D)(i)(I) for the 1997 8- 

hour ozone NAAQS. On December 30, 

2008, the Colorado Air Quality Control 

Commission (AQCC) adopted the ‘‘State 

of Colorado Implementation Plan to 

Meet the Requirements of the Clean Air 

Act Section 110(a)(2)(d)(i)(I)—Interstate 

Transport Regarding the 1997 8-Hour 

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 

element (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 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 in early 

December 2008 a public hearing for the 

Colorado Interstate Transport SIP 

revision, adopted it 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 of Colorado and has 

determined that the State met the 

requirements for reasonable notice and 

public hearing under section 110(a)(2) 

of the CAA. 

V. EPA’s Review and Technical 

Information 

A. EPA’s Evaluation of Interference 

With Maintenance 

The second element of section 

110(a)(2)(D)(i) requires that a state’s SIP 

must prohibit any source or other type 

of emissions activity in the state from 


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1See, 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 663 (D.C. Cir. 2000), 

cert denied, 532 U.S. 904 (2001). However, EPA’s 

approach to interference with maintenance in the 

NOX SIP Call was not explicitly reviewed by the 

court. See, North Carolina v. EPA, 531 F.3d 896, 

907–09 (D.C. Cir. 2008). Continued 

2See, 70 FR 25162 (May 12, 2005). 

3Memorandum from William T. Harnett entitled, 

‘‘Guidance for State Implementation Plan (SIP) 

Submissions to Meet Current Outstanding 

Obligations Under Section 110(a)(2)(D)(i) for the 8- 

hour Ozone and PM2.5 National Ambient Air 

Quality Standards,’’ Aug. 15, 2006, p. 5. (‘‘2006 

Guidance’’). Available for review in EPA’s 

September 15, 2010 docket document entitled: 

‘‘Relevant Guidance and Supporting Documentation 

for the Proposed Rulemaking Federal Register 

Action Docket ID # EPA–R08–OAR–2007–1035.’’ 

4See, North Carolina v. EPA, 531 F.3d 896 (D.C. 

Cir. 2008). 

5 Id. at 909. 

6 Id. 

7See ‘‘Federal Implementation Plans to Reduce 

Interstate Transport of Fine Particulate Matter and 

Ozone,’’ 75 FR 45210 (August 2, 2010). 

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 

NOX SIP Call, in which EPA took action 

to eliminate emissions of NOX that 

significantly contributed to 

nonattainment, or interfered with 

maintenance of, the then applicable 

ozone NAAQS through interstate 

transport of NOX and the resulting 

ozone.1 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 PM2.5

NAAQS, EPA again recognized that 

regional transport was a serious concern 

throughout the eastern U.S. and 

therefore developed the 2005 Clean Air 

Interstate Rule (CAIR) to address 

emissions of SO2 and NOX that 

exacerbate ambient ozone and PM2.5

levels in many downwind areas through 

interstate transport.2 Within CAIR, EPA 

likewise interpreted the term ‘‘interfere 

with maintenance’’ as part of the 

evaluation of whether or not the 

emissions of sources in certain states 

had such impacts on areas that EPA 

determined would either be in violation 

of the NAAQS, or would be in jeopardy 

of violating the NAAQS, in a modeled 

future year unless action were taken by 

upwind states to reduce SO2 and NOX

emissions. Through CAIR, EPA again 

required states that had such interstate 

impacts to adopt substantive SIP 

revisions to eliminate the SO2 and NOX

emissions, whether through 

participation in a regional cap and trade 

program or by other means. 

EPA’s 2006 Guidance addressed 

section 110(a)(2)(D) requirements for the 

1997 8-hour ozone NAAQS and 1997 

PM2.5 NAAQS. For those states subject 

to CAIR, EPA indicated that compliance 

with CAIR would meet the two 

requirements of section 110(a)(2)(D)(i)(I) 

for these NAAQS. 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. 

After recommending various types of 

information that could be relevant for 

the technical analysis 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.’’ 3 EPA did not make specific 

recommendations for how states should 

assess ‘‘interfere with maintenance’’ 

separately, and discussed the first two 

elements of section 110(a)(2)(D) together 

without explicitly differentiating 

between them. 

In 2008, however, the U.S. Court of 

Appeals for the DC Circuit found that 

CAIR and the related CAIR federal 

implementation plans were unlawful.4

Among other issues, the court held that 

EPA had not correctly addressed the 

second element of section 

110(a)(2)(D)(i)(I) in CAIR. The court 

noted that ‘‘EPA gave no independent 

significance to the ‘interfere with 

maintenance’ prong of section 

110(a)(2)(D)(i)(I) to separately identify 

upwind sources interfering with 

downwind maintenance.’’ 5 EPA’s 

approach, the court reasoned, would 

leave areas that are ‘‘barely meeting 

attainment’’ with ‘‘no recourse’’ to 

address upwind emissions sources.6

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 

110(a)(2)(D) 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 element of section 

110(a)(2)(D)(i)(I) because the agency’s 

guidance suggested that states use an 

approach comparable to that used by 

EPA in CAIR. States such as Colorado 

developed and adopted their Interstate 

Transport SIPs not long after 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 element. Without 

recommendations from EPA, Colorado’s 

SIP may not have sufficiently 

differentiated between the significant 

contribution to nonattainment and 

interference with maintenance elements 

of the statute, and relied in a general 

way on the difference between 

monitored concentrations and the 1997 

8-hour ozone NAAQS to evaluate the 

impacts of State emissions on 

maintenance of the NAAQS in 

neighboring states. EPA believes that it 

is necessary to evaluate these state 

submissions for section 110(a)(2)(D)(i)(I) 

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, EPA believes it is 

necessary to use 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 interfere with 

maintenance element of section 

110(a)(2)(D)(i). 

EPA has recently proposed a new rule 

to address interstate transport pursuant 

to section 110(a)(2)(D)(i), the ‘‘Federal 

Implementation Plans to Reduce 

Interstate Transport of Fine Particulate 

Matter and Ozone’’ (Transport Rule 

Proposal), in order to address the 

judicial remand of CAIR.7 As part of the 

Transport Rule Proposal, EPA 

specifically reexamined the section 

110(a)(2)(D)(i) requirement that 

emissions from sources in a state must 

not ‘‘interfere with maintenance’’ of the 

1997 8-hour ozone NAAQS and 1997 

PM2.5 NAAQS by other states. In the 

proposal, EPA developed an approach 

to identify areas that it predicts to be 

close to the level of the 1997 8-hour 

ozone NAAQS and 1997 PM2.5 NAAQS 

in the future, and therefore at risk to 

become or continue to be nonattainment 

for these NAAQS unless emissions from 

sources in other states are appropriately 

controlled. This approach starts by 

identifying those specific geographic 


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8To begin this analysis, EPA first identifies all 

monitors projected to be in nonattainment or, based 

on historic variability in air quality, projected to 

have maintenance problems in 2012. These 

maintenance receptors are close to the level of the 

1997 ozone and PM2.5 NAAQS such that minor 

variations in weather or emissions could result in 

violations of the NAAQS in 2012. 

9 2006 Guidance at 4. 

10 Id. at 5. 

11See, Transport Rule Proposal, 75 FR 45210, 

45277. 

12Colorado Interstate Transport SIP, December 

12, 2009, Figure 5 at 15. Note that the modeling 

analysis domain for the DMA/NFR attainment plan 

was limited to the State’s territory, and that the 70 

mile distance represents the approximate distance 

from Denver to the western border of Morgan 

County, Colorado. 

13 Id. at 17. 

areas for which further evaluation is 

appropriate, and differentiates between 

areas where the concern is with 

interference with maintenance, rather 

than with significant contribution 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 2005–2007), as well as 

air quality modeling data, in order to 

determine which areas are predicted to 

be violating the 1997 8-hour ozone and 

PM2.5 NAAQS in 2012, and which areas 

are predicted potentially to have 

difficulty with maintaining attainment 

as of that date. In essence, if an area’s 

projected data for 2012 indicates that it 

would be violating the NAAQS based on 

the average of these three overlapping 

periods, then this monitor location is 

appropriate for comparison for purposes 

of the significant contribution to 

nonattainment element of section 

110(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, but 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 believes that this new 

approach for identifying those areas that 

are predicted to have maintenance 

problems is appropriate to evaluate the 

section 110(a)(2)(D)(i) SIP submission of 

a state for the interfere with 

maintenance element.8 EPA’s 2006 

Guidance did not provide this specific 

recommendation to states, but in light of 

the 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 

110(a)(2)(D)(i) SIP submissions 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 SIP submission required 

by section 110(a)(2)(D)(i) may vary 

depending upon the facts and 

circumstances related to the specific 

NAAQS. In particular, the data and 

analytical tools available at the time the 

State develops and submits a SIP for a 

new or revised NAAQS necessarily 

affects the contents of the required 

submission.’’ 9 EPA also indicated in the 

2006 Guidance 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.10 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 PM2.5

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.11 In the Transport Rule 

Proposal, EPA did not calculate 

interstate ozone or PM2.5 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 for 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 from 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 of the 

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 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 

110(a)(2)(D)(i)(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 

110(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)(I). 

On June 3, 2010, EPA approved the 

Colorado Interstate Transport SIP 

provision that require that emissions 

from a state’s sources do not 

significantly contribute to 

nonattainment of the 1997 8-hour ozone 

NAAQS in any other state. To 

demonstrate that emissions from 

Colorado do not interfere 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 DMA/ 

NFR 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 DMA/NFR area, the 

projected design values decrease to 63 

ppb or less for all downwind Colorado 

counties east of an imaginary northsouth line approximately 70 miles east 

from Denver.12 EPA does not agree with 

the State of Colorado Interstate 

Transport SIP’s assessment that these 

results demonstrate that ‘‘the magnitude 

of ozone transport from Colorado to 

other states is too low to * * * interfere 

with maintenance by any other state 

with respect to the 0.08 ppm NAAQS’’ 

as the sole basis for evaluating the 

state’s interference.13 The limited 

contribution of local emissions to 

nonattainment 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 


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14Similar evidence is provided by the substantial 

gap between the 1997 8-hour ozone standard and 

the design values at monitors in adjacent 

downwind states such as Kansas, New Mexico, 

Utah, and Wyoming. Id. at 7–8. 

15Transport Rule Proposal, 75 FR 45210, 45254. 

16The remaining eight maintenance-only sites are 

in a handful of East Coast states: Connecticut, 

Georgia, New York and Pennsylvania. See Table IV 

C–12, Transport Rule Proposal, at 45252–253. 

17The 500 mile estimate represents the 

approximate distance between Lamar, in the 

southeastern corner of Colorado, and Dallas, Texas. 

The monitors’ Site ID Numbers are: Hinton, 48– 

113–0069; Executive Airport, 48–113–0087; and 

Keller, 48–439–2003. See id. For monitors’ site 

names, see online TCQE web page at http:// 

www.tceq.state.tx.us/cgi-bin/compliance/monops/ 

site_info.pl. 

18This distance underestimates the average 

distance covered by emissions 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 represents the 

distance along a straight pathway from Lamar to 

Dallas, Texas, as compared to the pathways full of 

twists and turns that often characterize the long 

range transport of air parcels. 

19 ‘‘Dallas-Fort Worth Eight-Hour Ozone 

Nonattainment Area: Attainment Demonstration,’’ 

TCEQ, May 23, 2007, p. i. 

20USEPA Region 8 mapped back trajectories 

using software and data files maintained by the 

National Oceanic and Atmospheric Administration 

(NOAA) Air Resource Laboratory (ARL). 

21 Draxler, R.R. and Rolph, G.D., HYSPLIT 

(HYbrid Single-Particle Lagrangian Integrated 

Trajectory) Model (2010), available via NOAA ARL 

READY Web site, http://ready.arl.noaa.gov/ 

HYSPLIT.php. NOAA Air Resources Laboratory, 

Silver Spring, MD. See also Rolph, G.D., Real-time 

Environmental Applications and Display sYstem 

(READY) Web site (2010), http://ready.arl.noaa.gov. 

NOAA Air Resources Laboratory, Silver Spring, 

MD. 

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

EPA is evaluating the Colorado 

Interstate Transport SIP taking into 

account the methodologies 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 8-hour ozone 

NAAQS and the 1997 PM2.5 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 evaluate ambient impacts from 

upwind states to maintenance receptors, 

the Transport Rule Proposal evaluates, 

through air quality modeling of each 

state’s emissions, the contribution 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 0.8 ppb and higher 

are considered above the threshold, 

while ozone contribution less than 0.8 

ppb are below the threshold. 

In the Transport 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 difficulty 

maintaining compliance with the 

NAAQS in 2012. To determine the 

states that may cause interference 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 relies on a weight of 

evidence approach that considers 

relevant information (such as 

identification of maintenance receptors 

and estimates of ozone contributions) 

from the 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 of these 

factors together provides a reliable 

qualitative conclusion that emissions 

from Colorado are not likely to interfere 

with maintenance of the 1997 8-hour 

ozone NAAQS at monitors in other 

states. 

Our analysis begins by assessing 

Colorado’s contribution to the closest 

maintenance receptors for the 1997 8- 

hour ozone standard. The Transport 

Rule Proposal identifies within its 

modeling domain (consisting of 37 

states east of the Rocky Mountains, and 

the District of Columbia) 16 

maintenance receptors, among which 

the eight closest to Colorado are eight 

receptors in the Dallas Fort Worth 

(DFW) and Houston-Galveston-Brazoria 

(HGB) 8-hour ozone nonattainment 

areas.16

Two of the three DFW area 

maintenance receptors are in Dallas 

County (Hinton Street and Dallas 

Executive Airport sites), and the third is 

in Tarrant County (Keller site).17 These 

monitors are at least 500 miles from 

Colorado.18 Distance by itself 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 effect of winds or 

chemical sink processes. As a result, 

one may conclude that the 

approximately 500 miles from Colorado 

sources of X emissions to the DFW area 

maintenance receptors reduces, but does 

not exclude, the possibility that the 

Colorado emissions interfere with 

maintenance of the NAAQS 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 

that includes the maintenance receptors 

identified above. The State of Texas’ 

2007 attainment demonstration for the 

DFW area points out, without 

quantifying contributions, how heavily 

the area’s ozone concentrations are 

affected by substantial transport from 

other areas. Average ozone background 

levels for DFW (reflecting 

concentrations contributed to the area 

by emissions from sources within Texas 

but outside the nonattainment area, and 

from sources outside Texas) are 

estimated to range between 44 and 61 

ppb, with peak averages between 64 and 

68 ppb on days when 8-hour ozone 

concentrations exceed the 1997 

standard.19

To evaluate the impact of wind 

direction on ozone transport from 

Colorado to the DFW maintenance 

receptors, we rely on the results of two 

back trajectory studies, including a set 

of trajectories with end points at the 

maintenance receptors in the DFW 

area.20 EPA generated these trajectories 

using the HYSPLIT 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 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 


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22See back trajectory maps in Appendix A of the 

EPA’s TSD supporting documentation in Docket ID 

No. EPA–R08–OAR–2007–1035. 

23EPA’s TSD is available for review as part of the 

supporting documentation for Docket ID N. EPA– 

R08–OAR–2007–1035. 

24 Dallas-Fort Worth Attainment Demonstration, 

May 23, 2007, at 3–1 to 3–2. 

25 ‘‘New Mexico State Interstate Transport SIP,’’ 

submitted to EPA July 30, 2007: Appendix D, 

Exhibit 9 Modeling Data and Report for New 

Mexico,’’ at 2. 

26For details on the model and on the analysis 

see: id. 

27The 700-mile estimate represents the 

approximate distance between Lamar, in the 

southeastern corner of Colorado, and Houston, 

Texas. The five monitoring sites’ names (ID No.) 

are: Aldine (48–201–0024), Northwest Harris (48– 

201–0029), Lynchburg Ferry (48–201–1015), 

Clinton (48–201–1035), and Seabrook Friendship 

Park (48–201–1050). The approximate 850-mile 

distance between Denver and Houston is intended 

to represent the distance to be covered by the 

emissions from Colorado to the five maintenance 

monitors. It is to be noted that the measured 

distance represents that of the straight (and 

shortest) path, which does not reflect the more 

circuitous paths followed by air parcels. 

28See note 24 above. 

29See Table 1, EPA’s ‘‘Back Trajectories Analysis 

Documentation,’’ Table 1. 

30The trajectory’s path that ended at the 

Northwest Harris receptor on August 31, 2006, is 

almost the same as the one that on June 15, 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 

HGB areas). 

31 Dave Sullivan, ‘‘Effects of Meteorology on 

Pollutant Trends,’’ March 16, 2009, at 27–34. This 

report is available as one of the documents in EPA’s 

TSD documentation, and may also be reviewed 

online at http://www.tceq.state.tx.us/assets/public/ 

implementation/air/am/contracts/reports/da/ 

5820586245FY0801-20090316-utmet_effects_on_pollutant_trends.pdf. 

Coordinated Universal Time (UTC), 

equivalent to 4 p.m. 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 back 

trajectories, ‘‘spider web’’ maps were 

generated for all three monitors 

combined and for each monitor (Figure 

1.1 and Figures 1.1.a 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 exceedance days at maintenance 

receptors in 2005–2006, did the air mass 

pathway go through Colorado, and even 

in this one instance air parcels crossed 

the State along a short pathway through 

its northeast corner, before continuing 

on their southeastward course.23

Back trajectory analysis results 

included in the May 23, 2007 DFW area 

Attainment Demonstration corroborate 

these conclusions. The analysis, also 

based on the HYSPLIT model, includes 

all days during the years 2001–2003, 

with trajectories of 48 hours (2 days) 

duration, heights of 100, 500 and 1300 

meters, and start times of 20, 21 and 22 

UTC (2, 3, and 4 p.m. 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 Colorado 

infrequently end in or pass through the 

DFW area.24

Because back trajectory analysis 

results map pathways of air parcels that 

may or may not transport pollutants, 

they cannot be considered 

determinative 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 are 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 PM2.5 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 (CENRAP) 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.26 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 maintenance-only receptors 

in Texas are located in Harris County, 

which lies within the HGB 

nonattainment area. This area is at least 

700 miles from Colorado.27 General 

considerations on the effect of distance 

on ozone transport from Colorado to the 

DFW area, discussed above, also apply 

to the potential for transport from 

Colorado to the maintenance receptors 

in the HGB area. The greater distance 

(by about one third) between Colorado 

and the HGB area increases the chance 

for dispersion of any Colorado ozone 

during its transport to HGB 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 HGB maintenance 

receptors. 

A similar conclusion is suggested by 

the EPA back trajectories mapped for 

the HGB maintenance receptors. Using 

the same online HYSPLIT 4.9 online 

computer application as for the DFW 

trajectories,28 EPA ran back trajectories 

from the HGB area maintenance 

receptors for all 2005–2006 ozone 

exceedances 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 EPA’s supporting 

documentation. At each monitor, 

trajectories started at 22 Coordinated 

Universal Time (UTC), equivalent to 4 

p.m. CST, and ran backwards in time for 

72 hours (three days), at 1500 meters 

above ground level.29 Results show that 

air parcel pathways passing 1500 meters 

above the HGB maintenance receptors at 

4 p.m. 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 course.30

Back trajectory analysis results from a 

2009 report, ‘‘Effects of Meteorology on 

Pollutant Trends’’ report, corroborate 

these conclusions. The analysis uses 

HYSPLIT with EDAS meteorological 

datasets to plot 72-hour back trajectories 

centered in Houston, at 300 meters 

height and for various times of the day. 

Trajectories are plotted for all days with 

available data between May 1 and 

October 31, 2000–2007. A clustering 

algorithm built into HYSPLIT is used to 

group individual back trajectories into 

several classes based on shape and 

direction.31 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 


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32New Mexico State Interstate Transport SIP, 

2007, Appendix D, at 52. 

33Table IV C–12, Transport Rule, at 196–197. 

34 In addition to North Dakota, South Dakota and 

Nebraska, the 13 states include: Kansas, Oklahoma, 

Minnesota, Iowa, Missouri, Arizona, Wisconsin, 

Michigan, Illinois, and Louisiana. Table IV–C–21, 

Transport Rule Proposal, at 45269–70. 

35A memorandum in the docket for this action 

provides the information EPA used in order to 

identify monitors that are receptors for evaluation 

of interference with maintenance for certain states 

in the western United States. See, Memorandum 

from Brian Timin of EPA’s Office of Air Quality 

Planning and Standards, Air Quality Modeling 

Group entitled ‘‘Documentation of Future Year 

Ozone and Annual PM2.5 Design Values for Western 

States’’ 

‘‘Memorandum to Docket EPA–R08–OAR–2007– 

1035,’’ EPA, August 23, 2010. 

36 Id. at 5. 

37We are excluding the California monitors from 

this portion of our 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, central and southern sections of the state. 

The factors we considered—distance, topography, 

and wind orientation—apply equally to the unmodeled monitors and make it plausible to 

conclude that the same demonstration is true for 

Colorado emissions’ impact on California nonmodeled monitors. 

trajectory analysis referenced above, but 

still show similar results concerning 

trajectories from Colorado. Air parcels 

from Colorado to the Houston area are 

rare, as shown by the few trajectories 

from 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 identified 

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 

of air parcels that may or may not 

transport pollutants, and they cannot be 

considered determinative as to the 

transport of ozone and its precursors. 

However, 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 HGB 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 HGB maintenance 

receptors.32

As noted previously, eight of the 16 

maintenance receptors identified within 

the modeling by the Transport Rule 

Proposal analysis are in a handful of 

East Coast states: Connecticut, Georgia, 

New York and Pennsylvania.33 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.34 In 

addition, among the 13 non-contributing 

states closer than Colorado to the 

maintenance receptors in the east, there 

are states such as Illinois, Wisconsin, 

Iowa, Missouri, Arkansas, and Louisiana 

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 east, 

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 of the 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, EPA 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.35 The analysis 

presented in the memo, ‘‘Documentation 

of Future Year Ozone and Annual PM2.5

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 does not 

necessarily yield less reliable results.36

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 of significant 

northwesterly regional transport winds, 

mountain ranges between Denver and 

the California maintenance receptors, 

such as the Rocky Mountains, the 

Wasatch 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 fact 

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 

south-westerly, westerly, or northwesterly directions, as indicated by the 

typical movement of weather systems. 

To further evaluate the direction of 

regional transport winds affecting the 

California maintenance receptors, we 

have plotted back trajectories starting at 

each maintenance receptor on high 

ozone days. High ozone days include 

the top one-third of the exceedance days 

(for the 1997 8-hour ozone NAAQS) 

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 are no 

pathways from the east/northeast 

directions reaching even as far as the 

eastern Nevada border, let alone 

Colorado. 

For a large number of receptors 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 EPA’s 

modeling guidance. However, the 

observed maximum design values at 

these sites in the 2003–2007 period 

were generally well below the 1997 

ozone NAAQS. The highest (nonCalifornia 37) site had a maximum 

design value of 77 ppb. Additionally, 

the 2012 modeling results at western 

monitors (where a future year design 

value could be estimated, shows a 


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downward trend in ozone. There are no 

areas in the West where ozone is 

predicted to be higher in 2012 (without 

CAIR) compared to 2005. On these bases 

it is plausible to conclude that it is 

highly unlikely, but not impossible, for 

these monitors to be at risk for 

maintenance of the 1997 8-hour ozone 

NAAQS. 

In conclusion, the variety of data and 

the weight of evidence analysis 

presented in this section support the 

position 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 

interfere with maintenance of the 1997 

8-hour ozone NAAQS by any other 

state, consistent with the requirements 

of element (2) of CAA section 

110(a)(2)(D)(i). 

VI. Proposed Action 

EPA is proposing partial approval of 

the Colorado SIP to meet the 

requirements of Section 110(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 element (2): 

Prohibition of interference with 

maintenance of the 1997 8-hour ozone 

NAAQS by any other state. EPA 

approved in a June 3, 2010 final action 

the language and demonstration 

addressing element (1): Prohibition 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 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 

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 (Pub. L. 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) of the National 

Technology Transfer and Advancement 

Act of 1995 (15 U.S.C. 272 note) because 

application of those requirements would 

be inconsistent with the Clean Air Act; 

and 

• Does not provide EPA with the 

discretionary authority to address, as 

appropriate, disproportionate human 

health or environmental effects, using 

practicable and legally permissible 

methods, under Executive Order 12898 

(59 FR 7629, February 16, 1994). 

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. 

Dated: September 9, 2010. 

Carol Rushin, 

Acting Regional Administrator, Region 8. 

[FR Doc. 2010–23294 Filed 9–16–10; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R09–OAR–2010–0569; FRL–9200–7] 

Revisions to the California State 

Implementation Plan, San Diego 

County Air Pollution Control District 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: EPA is proposing to approve 

revisions to the San Diego Air Pollution 

Control District (SDCAPCD) portion of 

the California State Implementation 

Plan (SIP). This revision concerns the 

definition of volatile organic 

compounds (VOC). We are proposing to 

approve a local rule to regulate these 

emission sources under the Clean Air 

Act as amended in 1990 (CAA or the 

Act). 

DATES: Any comments on this proposal 

must arrive by October 18, 2010. 

ADDRESSES: Submit comments, 

identified by docket number [EPA–R09– 

OAR–2010–0569], by one of the 

following methods: 

1. Federal eRulemaking Portal: 

www.regulations.gov. Follow the on-line 

instructions. 

2. E-mail: steckel.andrew@epa.gov. 

3. Mail or deliver: Andrew Steckel 

(Air-4), U.S. Environmental Protection 

Agency Region IX, 75 Hawthorne Street, 

San Francisco, CA 94105–3901. 

Instructions: All comments 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 

Confidential Business Information (CBI) 

or other information whose disclosure is 

restricted by statute. Information that 

you consider CBI or otherwise protected 

should be clearly identified as such and 

should not be submitted through 

http://www.regulations.gov or e-mail. 

http://www.regulations.gov is an 

‘‘anonymous access’’ system, and EPA 

will not know your identity or contact 

information unless you provide it in the 

body of your comment. If you send email directly to EPA, your e-mail 

address will be automatically captured 

and included as part of the public 

comment. 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. 


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