ENVIRONMENTAL PROTECTION AGENCY
 

40 CFR Part 52
 

(EPA-R08-0AR-2007-0645); FRL-


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

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

"Significant Contribution to Nonattainment" Requirement
 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Final rule. 

SUMMARY: EPA is partially approving State Implementation Plan (SIP) revisions submitted 

by the State of Colorado on June 18, 2009. These revisions, referred to as the Colorado 

Interstate Transport SIP, address the requirements ofClean Air Act section 11 O(a)(2)(D)(i)(I) for 

the 1997 8-hour ozone National Arnbient Air Quality Standards (NAAQS). In this action EPA is 

approving the Colorado Interstate Transport SIP non-regulatory provisions that address the 

requirement of section 11 O(a)(2)(D)(i)(I) that emissions from the state's sources do not 

"contribute significantly" to nonattainment of the 1997 8-hour ozone NAAQS in any other state. 

EPA will act at a later date on the Colorado Interstate Transport SIP provisions that address the 

requirement of section 11 0(a)(2)(D)(i)(I) that emissions from the state's sources do not "interfere 

with maintenance" of the 1997 8-hour ozone NAAQS in any other state. This action is being 

taken under section 110 of the Clean Air Act. 

EFFECTIVE DATE: This final rule is effective [insert date 30 days after publication in the 

Federal Register]. 

ADDRESSES: EPA has established a docket for this action under Docket ID No. EPA-R08­

OAR-2007-1032. All documents in the docket are listed on the www.regulations.gov Web site. 
Although listed in the index, some information is not publicly available, e.g., Confidential 

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

Certain other material, such as copyrighted material, is not placed on the Internet and will be 

publicly available only in hard copy form. Publicly available docket materials are available 

either electronically through www.regulations.gov, or in hard copy at the Air Program, 

Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop Street, 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 ofthe 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, Mai1code 8P-AR, 1595 Wynkoop Street, Denver, 

Colorado 80202-1129, (303) 312-6416, 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 State or Colorado mean the State of Colorado, unless the context indicates 

otherwise. 

2 
Table of Contents 

I. Background 

II. Response to Comments 

III . Section 110(1) 

IV. Final Action 

V. Statutory and Executive Order Reviews 

I. Background 

Section 110(a)(2)(D)(i) of the CAA requires that a state's SIP must contain adequate 

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

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

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

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

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

31, 2010, EPA published a notice of proposed rulenlaking (NPR) proposing partial approval of 

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

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

the 1997 8-Hour Ozone Standard," submitted by the State on June 18, 2009. As indicated by the 

title, this SIP addresses the first two ofthe four requirements listed above-i.e., (1), "significant 

contribution," and (2), "interference with maintenance." EPA's proposed rule action reviewed 

and proposed approval of the Colorado SIP's section addressing only the "significant 

contribution" requirement. EPA will act at a later date on the Colorado Interstate Transport SIP 

section that addresses the "interference with maintenance" requirement. 

To assess whether emissions from Colorado contribute significantly to downwind 

3
 
nonattainment for the 1997 8-hour ozone NAAQS, EPA's technical analysis relied on EPA's 

2006 Guidance, recommending consideration of available EPA modeling conducted in 

conjunction with CAIR,l or in the absence of such EPA modeling, consideration of other 

information such as the amount of emissions, the geographic location of violating areas, 

meteorological data, or various other forms of information that would be relevant to assessing 

the likelihood of significant contribution to violations of the NAAQS in another state. 

Consistent with the NOx SIP Call and CAIR, our technical analysis assessed the extent of ozone 

transport from Colorado not just to areas designated nonattainment, but also to areas in violation 

of the NAAQS. Because EPA did not have detailed modeling for Colorado and nearby 

downwind states, our approach did not rely on a quantitative determination of Colorado's 

contribution but on a weight-of-evidence approach using quantitative information such as 

Colorado's distance from areas with monitors showing violations of the NAAQS, modeling 

results outlining wind vectors for regional transport of ozone on high ozone days, back trajectory 

analyses for the downwind nonattainment areas closest to the State, and results of modeling 

studies for the nonattainment areas specifying the range of wind directions along which 

contribution of ozone transport occurred. Given that the assessments for each of these pieces of 

evidence are not individually definitive or outcome determinative, EPA concluded in its 

proposed action that the various factual and technical considerations supported a determination 

of no significant contribution from Colorado emissions to the ozone nonattainment areas noted 

above. EPA did not receive comments that persuade the Agency that there is such significant 

contribution, and thus in today's final action EPA is making a final regulatory determination that 

1 In this action the expression "CAIR" refers to the final rule published in the May 12,2005 Federal Register and 

entitled "Rule to Reduce Interstate Transport of Fine Particulate Matter and Ozone (Clean Air Interstate Rule); 

Revisions to Acid Rain Program; Revisions to NOx SIP Ca11; Final Rule" (70 FR 25162). 

4
 
Colorado emissions sources do not contribute significantly to violations of the 1997 8-hour 

ozone NAAQS in any other state. 

II. Response to Comments 

EPA received one letter fron1 WildEarth Guardians (WG) commenting on EPA's federal 

register action proposing approval of the portion ofthe Colorado Interstate Transport SIP that 

addresses the "significant contribution to nonattainmenf' requirement of CAA Section 

110(a)(2)(D)(i)(I) for the 1997 8-hour ozone NAAQS. In this section EPA responds to the 

significant adverse comments made by the commenter. 

Comment No. 1 - The commenter asserted that EPA's proposed approval was based on a 

"flawed legal standard." According to the commenter, EPA erred in the proposal by explaining 

that various factual or technical assessments indicate that it is "unlikely" that emissions from 

Colorado sources significantly contribute to violations of the 8-hour ozone NAAQS in other 

states. The commenter's position was that EPA cannot approve a SIP submission based upon 

"unlikelihood" because CAA Section 110(a)(2)(D)(i)(I) prohibits emissions that contribute 

significantly to nonattainment in other States and does not allow EPA to approve SIPs simply 

because a state's emissions are "unlikely" to contribute significantly to nonattainment. 

EPA Response - EPA disagrees with the commenter's characterization of EPA's analysis 

and the commenter's interpretation of the statutory requirements. First, EPA notes that the 

discussion in the proposal was intended to present the various factual and technical 

considerations available to assess whether there is or is not significant contribution to 

nonattainment in other states as a result of emissions from Colorado sources. Given that these 

assessments are not individually definitive or outcome determinative, EPA believes that it is 

entirely appropriate to present and describe the relative probative value of the various 

5
 
considerations accurately. Second, EPA notes that all such technical evaluations are by their 

nature subject to some degree of uncertainty. Indeed, the modeling that the commenter 

elsewhere contends should be the sole method for evaluating interstate transport is itself but one 

means of evaluating the real world impacts of emissions in light of meteorological conditions, 

wind direction, and other such variables and produces a result that is itself subject to some 

degree of uncertainty. Third, EPA believes that it was also appropriate to describe the various 

factual and technical considerations and whether they indicated a "likelihood" of significant 

contribution to nonattainment in another state because the proposal was seeking comment from 

the public upon whether these considerations together supported a determination of no such 

significant contribution. EPA did not receive comments that persuade the Agency that there is 

such significant contribution, and thus in today's final action EPA is making a final regulatory 

determination that Colorado emissions sources do not significantly contribute to violations of the 

1997 8-hour ozone NAAQS in any other state, for the reasons explained elsewhere in this notice. 

In other words, EPA has concluded that the existing SIP for Colorado already contains adequate 

provisions to prevent emissions from Colorado sources from significantly contributing to 

violations of the 1997 8-hour ozone NAAQS in other states and is therefore approving 

Colorado's submission for this purpose. 

Comment No.2 - The commenter argued that Colorado and EPA did not appropriately 

assess impacts to nonattainment in downwind states. According to the commenter, Colorado 

failed to assess significance of downwind impacts in accordance with EPA guidance and 

precedent. Although this is unclear from the comment, the commenter evidently believes that 

EPA's applicable guidance for this purpose appears only in the 1998 NOx SIP call. The 

commenter asserts that, based on the precedent of the NOx SIP Call, the following issues need to 

6
 
be addressed in determining whether or not an area is significantly contributing to nonattainment 

in downwind States: (a) The overall nature of the ozone problem; (b) the extent of downwind 

nonattainment problems to which upwind State's emissions are linked; (c) the ambient impact of 

the emissions from upwind States' sources on the downwind nonattainment problems; and (d) 

the availability of high cost-effective control measures for upwind emissions. (63 FR 57356­

57376, October 27, 1998). 

EPA Response - EPA disagrees with the commenter on this point. Section 11 O(a)(2)(D) 

does not explicitly specify how states or EPA should evaluate the existence of, or extent of, 

interstate transport and whether that interstate transport is ofsufficient magnitude to constitute 

"significant contribution to nonattainment" as a regulatory matter. The statutory language is 

ambiguous on its face and EPA must reasonably interpret that language when it applies it to 

factual situations before the Agency. 

EPA agrees that the NOx SIP Call is one rulemaking in which EPA evaluated the 

existence of, and extent of, interstate transport. In that action, EPA developed an approach that 

allowed the Agency to evaluate whether there was significant contribution to ozone 

nonattainment across an entire region that was comprised of many states. That approach 

included regional scale modeling and other technical analyses that EPA deemed useful to 

evaluate the issue of interstate transport on that geographic scale and for the facts and 

circumstances at issue in that rulemaking. EPA does not agree, however, that the approach of 

the NOx SIP Call is necessarily the only way that states or EPA may evaluate the existence of, 

and extent of, interstate transport in all situations, and especially in situations where the state and 

EPA are evaluating the question on a state by state basis, and in situations where there is not 

evidence 0 f widespread interstate transport. 

7 
Indeed, EPA issued specific guidance making recommendations to states about how to 

address section 11 0(a)(2)(D) in SIP submissions for the 8-hour ozone NAAQS. EPA issued this 

guidance document, entitled "Guidance for State Implementation Plan (SIP) Submissions to 

Meet Current Outstanding Obligations Under Section 11 0(a)(2)(D)(i) for the 8-Hour Ozone and 

PM2.5 National Ambient Air Quality Standards" on August 15, 2006.2 This guidance document 

postdated the NOx SIP Call, and was developed by EPA specifically to address SIP submissions 

for the 1997 8-hour ozone NAAQS. 

Within that 2006 guidance document, EPA notes that it explicitly stated its view that the 

"precise nature and contents of such a submission [are] not stipulated in the statute" and that the 

contents of the SIP submission "may vary depending upon the facts and circumstances related to 

the specific NAAQS.,,3 Moreover, within that guidance, EPA expressed its view that "the data 

and analytical tools available" at the time of the SIP submission "necessarily affect[] the content 

of the required submission.,,4 To that end, EPA specifically recommended that states located 

within the geographic region covered by the "Clean Air Interstate Rule" (CAIR)5 comply with 

section 11 0(a)(2)(D) for the 1997 8-hour ozone NAAQS by complying with CAIR itself. For 

states outside the CAIR rule region, however, EPA recommended that states develop their SIP 

submissions for section 11 0(a)(2)(D) considering relevant infonnation. 

EPA explicitly recommended that relevant infonnation for section 11 O(a)(2)(D) 

submissions addressing significant contribution to nonattainment "might include, but is not 

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

Meet Current Outstanding Obligations Under Section 11 0(a)(2)(D)(i) for the 8-hour Ozone and PM2.5 National
 

Ambient Air Quality Standards (Aug. 15,2006) ("2006 Guidance"); p. 3. An electronic copy is available for review
 

at the regulations.gov web site as Document ID No. EPA-R08-0AR-2007-1 032.0004.1.
 

3 Id. at 3.
 

4Id.
 

5 In this action the expression "CAIR" refers to the final rule published in the May] 2, 2005 Federal Register and
 
limited to, information concerning emissions in the State, meteorological conditions in the State, 

the distance to the nearest nonattainment area in another State, reliance on modeling conducted 

by EPA in determining that such State should not be included within the ambit of the CAIR, or 

such other infonnation as the State considers probative on the issue of significant contribution.,,6 

In addition, EPA recommended that states might elect to evaluate significant contribution to 

nonattainment using relevant considerations comparable to those used by EPA in CAIR, 

including evaluating impacts as of an appropriate year (such as 2010) and in light of the cost of 

control to mitigate emissions that resulted in interstate transport. 

The commenter did not acknowledge or discuss EPA's actual guidance for section 

110(a)(2)(D) SIP submissions for the 1997 8-hour ozone NAAQS, and thus it is unclear whether 

the commenter was aware of it. In any event, EPA believes that the Colorado submission and 

EPA's evaluation of it was consistent with EPA's guidance for the 1997 8-hour ozone NAAQS. 

For example, as discussed in the proposal notice, the state and EPA considered infonnation such 

as monitoring data in Colorado and downwind states, geographical and meteorological 

infonnation, and technical studies of the nature and sources of nonattainment problems in 

various downwind states. These are among the types of infonnation that EPA recommended and 

that EPA considers relevant. Thus, EPA has concluded that the state's submission, and EPA's 

evaluation of that submission, meet the requirements of section 11 0(a)(2)(D) and are consistent 

with applicable guidance. 

Finally, EPA notes that the considerations the Agency recommended to states in the 2006 

guidance document are consistent with the concepts that the commenter enumerated from the 

entitled "Rule to Reduce Interstate Transport of Fine Particulate Matter and Ozone (Clean Air Interstate Rule);
 

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

6 Id. at 5.
 

9 
NOx SIP Call context: (a) the overall nature of the ozone problem; (b) the extent of downwind 

nonattainment problems to which upwind State's emissions are linked; (c) the ambient impact of 

the emissions from upwind States' sources on the downwind nonattainment problems; and (d) 

the availability of high cost-effective control measures for upwind emissions. The only 

distinction in the case of the Colorado submission at issue here would be that because the 

available evidence indicates that there is very little contribution from emissions from Colorado 

sources to nonattainment in other states, it is not necessary to advance to the final step and 

evaluate whether the cost of controls for those sources is above or below a certain cost of control 

as part of determining whether the contribution constitutes "significant contribution to 

nonattainment" for regulatory purposes, as was necessary in the NOx SIP Call and in CAIR. 

Comment No. 3 - The commenter argued that Colorado based its claim of no significant 

contribution "primarily on attainment plan modeling for the Denver Metropolitan AreaINorth 

Front Range (DMAINFR) nonattainment area" and noted that EPA itself "does not accept" that 

modeling for purposes of assessing impacts on nonattainment in downwind States. 

EPA Response - EPA disagrees with the commenter's characterization of the state's 

submission and of EPA's evaluation of it. This comment reflects an incomplete reading of 

EPA's evaluation of how the results ofColorado's modeling analysis for the DMAINFR relate to 

an assessment of whether emissions from Colorado sources contribute significantly to downwind 

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

It is correct that the State relied upon this information in its submission to EPA. It is 

correct that EPA did not agree with Colorado's view that the modeling analysis results for the 

DMAfNFR attainment plan, in and of themselves, prove that there could be no significant 

contribution from Colorado sources to downwind ozone nonattainment in other states. EPA 

10
 
explicitly disagreed with the state's beliefthat: " ...these results [ofthe DMAlNFR modeling 

analysisl demonstrate that the magnitude of ozone transport from Colorado to other States is too 

low to significantly contribute to nonattainment. ..." 

Nevertheless, EPA did agree that these modeling results were a relevant piece of 

information that could be useful when considered in conjunction with other information. EPA 

stated that these modeling results do support the conclusion that there is not significant transport 

of ozone from Colorado to other states with violations of the NAAQS: " .... [h]owever, as a 

reflection of emission levels, the relatively (to the 1997 8-hour ozone NAAQS) moderate 

concentrations in eastern Colorado ... somewhat reduce the probability of significant contribution 

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

St. Louis, Missouri, and Chicago, Illinois." (See 75 FR 16034-35). The commenter suggests 

that EPA approved the State's submission based wholly upon technical support that EPA itself 

rejected and this is incorrect. 

Comment No.4 - The commenter reiterated its concern that the Colorado section 

110(a)(2)(D) submission was deficient because it did not strictly follow the commenter's 

summary of the structure of the analysis of interstate transport in the NOx SIP Call: (a) the 

overall nature of the ozone problem; (b) the extent of downwind nonattainment problems to 

which upwind State's emissions are linked; (c) the ambient impact of the emissions from upwind 

States' sources on the downwind nonattainment problems; and (d) the availability of high costeffective control measures for upwind emissions. 

EPA Response - EPA disagrees with the commenter's view that any analysis of interstate 

transport must follow a specific formulaic structure to be approvable. As noted above, EPA 

issued specific guidance to states making recommendations for section 110(a)(2)(D) SIP 

11 
submissions for the 1997 8-hour ozone NAAQS. Within that guidance, EPA recommended 

various types of information that states might wish to consider in the process of evaluating 

whether their sources contributed significantly to nonattainment in other states. EPA has 

concluded that the submission from Colorado, augmented by EPA's own analysis, sufficiently 

establishes that Colorado sources do not significantly contribute to violations of the 1997 8-hour 

ozone NAAQS in other states. As noted above, EPA believes that the state's submission, and 

EPA's analysis of it, address the same conceptual considerations that the commenter advocated. 

Comment No.5 - The commenter asserted that Colorado and EPA provided "no analysis" 

of the contribution from Colorado to downwind states and no "actual assessment" of the 

significance of any such contribution. 

EPA Re.\ponse - EPA disagrees with the commenter's position. The commenter again 

assumes that section 11 O(a)(2)(D) explicitly requires the type of modeling analysis that the 

commenter advocates throughout its comments. Because the commenter apparently views the 

NOx SIP Call as the applicable guidance, the commenter contends that any analytical approach 

that is not identical to that approach is impermissible. In addition, the commenter overlooks the 

fact that in other actions based upon section 11 O(a)(2)(D), EPA has also used a variety of 

analytical approaches, short of modeling, to evaluate whether specific states are significantly 

contributing to violations of the NAAQS in another state (e.g., the west coast states that EPA 

concluded should not be part of the geographic region of the CAIR rule based upon qualitative 

factors, and not by the zero out modeling EPA deemed necessary for some other States). 

In the proposed approval, EPA explained that other forms of available information were 

sufficient to make the determination that there is no significant contribution from Colorado 

12
 
sources to downwind nonattainment ofthe 1997 8-hour ozone NAAQS. As stated in the 

proposal: 

~~EPA's evaluation ofwhether emissions from Colorado contribute significantly to ozone 

nonattainment in these areas [St. Louis and Chicago] relies on an examination of a 

variety of data and analysis that provide insight on ozone transport from Colorado to 

these two areas. Because EPA does not have detailed modeling for Colorado and nearby 

downwind states, our approach does not rely on a quantitative determination of 

Colorado's contribution, as EPA did for other states in its CAIR rulemaking, but on a 

weight-of-evidence analysis based on qualitative assessments and estimates of the 

relevant factors. While conclusions reached for each ofthe factors considered in the 

following analysis are not in and by themselves determinative, consideration of all of 

these factors provides a reliable qualitative conclusion on whether Colorado's emissions 

are likely to contribute significantly to nonattainment in the St. Louis and the 

Illinois/Wisconsin areas." 

EPA acknowledged that the various forms ofinformation considered in the proposal 

(such as distance, orientation of surface and regional transport winds, back trajectory analyses, 

monitoring data) were not individually outcome determinative, but concluded that when taken 

together served to establish that Colorado sources do not significantly contribute to downwind 

nonattainment of the 1997 8-hour ozone NAAQS in other states. Thus, contrary to the 

commenter's assertion, EPA did perform an "analysis" and an "assessment" that was a 

reasonable basis for its conclusion that emissions from Colorado do not contribute significantly 

to downwind ozone nonattainment, using a combination of quantitative data and qualitative 

13
 
[analYSes. EPA does not agree that only the type of analysis advocated by the commenter could 

adequately evaluate the issue and support a rational determination in this instance. 

Comment No.6 - The commenter objected to EPA's proposed approval because 

Colorado assessed impacts in downwind states by considering monitoring data in those states as 

a means of evaluating significant contribution to nonattainment. In other words, the commenter 

is concerned that Colorado did not assess impacts in areas that have no monitor. The commenter 

likewise objected to EPA's "endorsement" of this approach. The commenter argued that this 

reliance on monitor data is inconsistent with both section 1IO(a)(2)(D) and with EPA's guidance, 

by which the commenter evidently means the NOx SIP Call. In support of this assertion, the 

commenter quoted from the NOx SIP Call proposal in which EPA addressed the proper 

interpretation of the statutory phrase "contribute significantly to nonattainment:" 

"The EPA proposes to interpret this term to refer to air quality and not to be limited to 

currently-designated nonattainment areas. Section 11 O(a)(2)(D) does not refer to 

'nonattainment areas,' which is a phrase that EPA interprets to refer to areas that are 

designated nonattainment under section 107(section 107(d)(l)(A)(I»" 

According to the commenter, this statement, and similar ones in the context of the final NOx SIP 

Call rulemaking, establish that states and EPA cannot utilize monitoring data to evaluate the 

existence of, and extent of, interstate transport. Furthermore, the commenter interprets the 

reference to "air quality" in these statements to support its contention, amplified in later 

comments, that EPA must evaluate significant contribution in areas in which there is no 

monitored nonattainment. 

EPA response - EPA disagrees with the commenter's arguments. First, the commenter 

misunderstands the point that EPA was making in the quoted statement from the NOx SIP Call 

14 
proposal (and that EPA has subsequently made in the context of CAIR). When EPA stated that it 

would evaluate impacts on air quality in downwind states, independent of the current formal 

'"designation" of such downwind states, it was not referring to air quality in the absence of 

monitor data. EPA's point was that it was inappropriate to wait for either initial designations of 

nonattainment for a new NAAQS under section I07(d)(l), or for a redesignation to 

nonattainment for an existing NAAQS under section I07(d)(3), before EPA could assess whether 

there is significant contribution to nonattainment of a NAAQS in another state. 

For example, in the case of initial designations, section I07(d) contemplates a process 

and timeline for initial designations that could well extend for two or three years following the 

promulgation of a new or revised NAAQS. By contrast, section .11 O(a)(l) requires states to 

make SIP submissions that address section 11 O(a)(2)(D) and interstate transport '"within 3 years 

or such shorter period as the Administrator may prescribe" of EPA's promulgation of a new or 

revised NAAQS. This schedule does not support a reading of section 11 O(a)(2)(D) that is 

dependent upon formal designations having occurred first. This is a key reason why EPA 

determined that it was appropriate to evaluate interstate transport based upon monitor data, not 

designation status, in the CArR rulemaking. 

The commenter's misunderstanding of EPA's statement concerning designation status 

evidently caused the commenter to believe that EPA's assessment of interstate transport in the 

NOx SIP Call was not limited to evaluation of downwind areas with monitors. This is simply 

incorrect. In both the NOx SIP Call and CAIR, EPA evaluated significant contribution to 

nonattainment as measured or predicted at monitors. For example, in the technical analysis for 

the NOx SIP Call, EPA specifically evaluated the impacts of emissions from upwind states on 

monitors located in downwind states. The NOx SIP Call did not evaluate impacts at points 

15 
without monitors, nor did the CAIR rulemaking. EPA believes that this approach to evaluating 

significant contribution is correct under section 11 0(a)(2)(D), and EPA's general approach to this 

threshold determination has not been disturbed by the courts. 7 

Finally, EPA disagrees with the commenter's argument that the assessment of significant 

contribution to downwind nonattainment must include evaluation of impacts on non-monitored 

areas. First, neither section 11 0(a)(2)(D)(i)(I) provisions, nor the EPA guidance issued for the 

1997 8-hour ozone NAAQS on August 15, 2006, support the commenter's position, as neither 

refers to any explicit mandatory or recommended approach to assess air quality in non-monitored 

areas. 8 The same focus on monitored data as a means of assessing interstate transport is found in 

the NOx SIP Call and in CAIR. An initial step in both the NOx SIP Call and CAIR was the 

identification of areas with current monitored violations ofthe ozone and/or PM1.5 NAAQS. 9 

The subsequent modeling analyses for NAAQS violations in future years (2007 for the SIP Call 

and 2010 for CAIR) likewise evaluated future violations at monitors in areas identified in the 

initial step. Thus, the commenter is simply in error that EPA has not previously evaluated the 

presence and extent of interstate transport under section 11 0(a)(2)(D) by focusing on monitoring 

data. Indeed, such monitoring data was at the core of both of these efforts. In neither of these 

rulemakings did EPA evaluate significant contribution to nonattainment in areas in which there 

was no monitor. This is reasonable and appropriate, because data from a properly placed federal 

7 Michigan v. U.S. EPA, 213 F.3d 663, 674-681 (D.C. Cir. 2000); North Carolina v. EPA, 531 F.3d 896, 913-916 

(D.C. Cir. 2008) (upholding EPA approach to determining threshold despite remanding other aspects ofCAIR).
 

8 2006 Guidance, p. 5.
 

9 "Based on this approach, we predicted that in the absence of additional control measures, 47 counties with air
 

quality monitors [emphasis ours] would violate the 8-hour ozone NAAQS in 2010...." From the CAIR proposed
 

rule of January 30, 2004 (69 FR 4566, 4581). The NOx SIP call proposed rule action reads: " ... For current
 

nonattainment areas, EPA used air quality data for the period 1993 through 1995 to determine which counties are
 

violating the I-hour and/or 8-hour NAAQS. These are the most recent 3 years of fully quality assured data which
 

were available in time for this assessment," 62 FR 60336.
 

16 
reference method monitor is the way in which EPA ascertains that there is a violation of the 1997 

8-hour ozone NAAQS in a particular area. Put another way, in order for there to be significant 

contribution to nonattainment for the 1997 8-hour ozone NAAQS, there must be a monitor with 

data showing a violation of that NAAQS. EPA has concluded that by considering data from 

monitored areas, its assessment of whether emissions from Colorado contribute significantly to 

ozone nonattainment in downwind States is consistent with the 2006 Guidance, and with the 

approach used by both the CAIR rule and the NOx SIP Call. 

Comment No. 7 - In support of its comments that EPA should assess significant 

contribution to nonattainment in nonmonitored areas, the commenter argued that existing 

modeling performed by another organization "indicates that large areas of neighboring states will 

be likely to violate the ozone NAAQS." According to the commenter, these likely "'violations" 

of the ozone NAAQS were predicted for the year 2018, as reflected in a slide from a July 30, 

2008 presentation before the Western Regional Air Partnership ("Review of Ozone Performance 

in WRAP Modeling and Relevant to Future Regional Ozone Planning"). The commenter 

asserted that: "Slide 28 ofthis presentation displays projected 4th highest 8-hour ozone reading 

for 2018 and indicates that air quality in areas such as northern New Mexico, western Wyoming, 

southern Utah, and central Arizona will exceed and/or violate the 1997 ozone NAAQS ....".10 In 

short, the commenter argues that modeling performed by the WRAP establishes that there will be 

violations of the 1997 8-hour ozone NAAQS in 2018 in non-monitored areas of states adjacent to 

Colorado. 

EPA Re,sponse - EPA disagrees with this comment on several grounds. First, as 

explained in response to other comments, EPA does not agree that it is appropriate to evaluate 

17
 
significant contribution to nonattainment for the 1997 8-hour ozone NAAQS by modeling 

ambient levels in areas where there is no monitor to provide data to establish a violation of the 

NAAQS in question. Section 11 0(a)(2)(D) does not require such an approach, EPA has not 

taken this approach in the NOx SIP Call or other rulemakings under section 11 0(a)(2)(D), and 

EPA's prior analytical approach has not been disturbed by the courts. 

Second, the commenter's own description of the ozone concentrations predicted for the 

year 2018 as projecting "violations" of the ozone NAAQS is inaccurate. Within the same 

sentence, quoted above, slide 28 is described as displaying the projected 4th max ozone reading 

for the year 2018, and as indicating that" ... air quality ... will exceed or violate [emphasis ours] 

the 1997 ozone NAAQS." By definition, a one year value of the 4th max above the NAAQS only 

constitutes an exceedance of the NAAQS; to constitute a violation of the 1997 8-hour ozone 

NAAQS, the standard must be exceeded for three consecutive years at the same monitor. Thus, 

even if the WRAP presentation submitted by the commenter were technically sound, the 

conclusion drawn from it by the commenter is inaccurate and does not support its claim of 

projected violations of the NAAQS in large areas (monitored or unmonitored) of Colorado's 

neighboring States. 

Finally, EPA has reviewed the WRAP presentation submitted by the commenter, and 

believes that there was a substantial error in the WRAP modeling software that led to 

overestimation of ground level ozone concentrations. A recent study conducted by Environ for 

the Four Corners Air Quality Task Force (FCAQTF; Stoeckenius et aI., 2009) has demonstrated 

that excessive vertical transport in the CMAQ and CAMx models over high terrain was 

responsible for overestimated ground level ozone concentrations due to downward transport of 

10 The presentation is available for review as Document ID # EPA-R08-0AR-2007-1032-0007.8 at Regulations.gov, 

18 
stratospheric ozone. II Environ has developed revised vertical velocity algorithms in a new 

version of CAMx that eliminated the excessive downward transport of ozone from the top layers 

of the model. This revised version of the model is now being used in a number of applications 

throughout high terrain areas in the West. In conclusion, EPA believes that this key inadequacy 

of the WRAP model, noted above, makes it inappropriate support for the commenter's concerns 

about large expanses of 8-hour ozone nonattainment areas projected for 2018 in areas without 

monitors. 

Comment No.8 - As additional support for its assertion that EPA should require 

modeling to assess ambient levels in unmonitored portions of other states, the commenter relied 

on an additional study entitled the "Uinta Basin Air Quality Study (UBAQS)." The commenter 

argued that UBAQS further supports its concern that Colorado and EPA, having limited the 

evaluation of downwind impacts only to areas with monitors, failed to assess ozone 

nonattainment in non-monitored areas. According to the commenter, UBAQS modeling results 

show that: (a) the Wasatch front region is currently exceeding and will exceed in 2012 the 1997 

8-hour ozone NAAQS; and (b) based on 2005 meteorological data, portions of the four counties 

in the southwest comer of Utah are also currently in nonattainment and will be in nonattainment 

in 2012. 12 

EPA Response - As noted above, EPA does not agree that it is appropriate to assess 

significant contribution to nonattainment for the 1997 8-hour ozone NAAQS in the way 

advocated by the commenter. Even taking the UBAQS modeling results at face value, however, 

Docket ID # EPA-R08-0AR-2007-J032. 

II Stoeckenius, T.E" C.A. Emery, T.P. Shah, J.R. Johnson, L.K. Parker, A.K. Pollack, 2009. "Air Quality Modeling 

Study for the Four Comers Region," pp. ES-3, ES-4, 3-4, 3-12, 3-30, 5-1. Prepared for the New Mexico 

Environment Department, Air Quality Bureau, Santa Fe, NM, by ENVIRON International Corporation, Novato, CA. 

12 The southwestern area referred to by the commenter includes portions of Washington, Iron, Kane, and Garfield 

19 
EPA does not agree that the 8-hour ozone nonattainment (current and proj ected) in the Wasatch 

Front Range area supports the commenter's concerns about the need to evaluate the possibility of 

significant contribution to nonattainment in non-monitored areas. EPA sees several problems 

with the commenter's interpretation of the UBAQS analysis results for counties in Utah's 

southwestern comer: "based on 2005 meteorological data, portions of Washington, Iron, Kane, 

and Garfield Counties are also in nonattainment and will be in nonattainment in 2012." 

First, the commenter's interpretation ofthe predicted ozone concentrations shown in 

Figures 4-3a and 4-3b (pages 5 and 6 of the comment letter) is inaccurate. A close review ofthe 

legend in these figures indicates that the highest ozone concentrations predicted by the model for 

portions of the counties noted above are somewhere between 81.00 and 85.99 ppb, but it is not 

specified. If it is actually predicted smaller than or equal to 84.9 ppb then the area is attaining 

the 1997 8-hour ozone NAAQS, ifit is predicted as greater than 84.9 ppb then it is not attaining 

those NAAQS. Thus, the current and predicted design values for the southwestern Utah area 

identified in Figures 4-3a and 4-3b could both be in attainment or both in nonattainment, or one 

ofthem in attainment and the other in nonattainment, for the 1997 8-hour ozone NAAQS. EPA 

does not believe that this evidence adequately establishes that one or both areas definitely violate 

the NAAQS, even if the infonnation were taken at face value. 

Second, even if the design values predicted for these unmonitored areas were at the top of 

the 81.00-85.99 ppb range, their reliability would remain questionable. The UBAQS itself 

identifies and illustrates major shortcomings of its modeling analysis, only to neglect assessing 

the impact of these shortcomings on the modeling results. 13 The study deviates in at least two 

Counties.
 

13 See UBAQS, pp. 4-27 to 4-29.
 

20 
significant ways from EPA's 2007 guidance on SIP modeling. 14 One issue is the UBAQS 

modeling reliance on fewer than the five years of data recommended by EPA to generate a 

current 8-hour ozone design value (DVC). UBAQS relaxed this requirement so that sites with as 

little as 1 year of data were included as DVCs in the analysis. The other issue is the computation 

of the relative responsive factor (RRF), which directly affects the modeling's future design value 

(DVF).15 Again due to unavailability of data satisfying EPA's recommendation that the RRF be 

based on a minimum of five days of ozone concentrations above 85 ppb, UBAQS modeling uses 

RRFs based on one or more days of ozone concentrations above 70 ppb. 16 EPA concludes that 

the modeling analysis results used by the WG are unreliable for projecting non-attainment status 

and therefore do not support its comn1ents. 

Comment No.9 - In support of its arguments that EPA should not assess significant 

contribution to nonattainment through evaluation of impacts at monitors instead of modeling 

impacts where there is no such monitor, the commenter cited a past statement by EPA to the 

effect that the monitor network in the western United States needs to be expanded. The quoted 

statements included EPA's observation that "[v]irtually all States east of the Mississippi River 

have at least two to four non-urban 03 monitors, while many large mid-western and western 

States have one or no non-urban monitors." 74 FR 34,525 (July 16, 2009). From this statement, 

the commenter argues that it is not appropriate for EPA to limit evaluation of significant 

contribution to nonattainment of the ozone NAAQS in other states relying on monitoring data 

instead of modeling ambient levels. 

14 EPA, Guidance on the Use of Models and other Analyses for Demonstrating Attainment of Air Quality Goals for 

Ozone, PM2.5 and Regional Haze. Office of Air Quality Planning and Standards, Air Modeling Group. Research 

Triangle Park, North Carolina (2007), available at http://www.epa.gov/scramOO l/guidance/guide/final-03-pm-rhguidance.pdf. 

15 DYC X RRF = DYF. 

21 
EPA Re.~ponse - EPA does not disagree that there are relatively few monitors in the 

western states, and that relatively few monitors are currently located in non-urban areas of 

western states. However, the commenter failed to note that the quoted statement from EPA 

concerning the adequacy of western monitors came from the Agency's July 16,2009, proposed 

rulemaking entitled "Ambient Ozone Monitoring Regulations: Revisions to Network Design 

Requirements." This statement was thus taken out of context, because EPA was in that proposal 

referring to changes in state monitoring networks that it anticipates will be necessary in order to 

implement not the 1997 8-hour ozone NAAQS that are the subject of this rulemaking, but rather 

the next iteration of the ozone NAAQS for which there are concerns that there will be a need to 

evaluate ambient levels in previously unmonitored areas of the western United States. The fact 

that additional monitors may be necessary in the future for newer ozone NAAQS does not 

automatically mean that the existing ozone monitoring networks are insufficient for the 1997 8­

hour ozone NAAQS, as the commenter implies. Indeed, states submit annual monitor network 

reports to EPA and EPA evaluates these to insure that they meet the applicable requirements. 

For example, Colorado itself submits just such a report on an annual basis, and EPA 

reviews it for adequacy. 17 All other states submit comparable reports. Absent a specific concern 

that another state's current monitor network is inadequate to evaluate ambient levels of the 1997 

8-hour ozone NAAQS, EPA has no reason to believe that the evaluation of possible significant 

contribution from Colorado sources in reliance on those monitors is incorrect. 

Comment No.1 0 - The commenter objected to EPA's proposed approval of the Colorado 

SIP submission because neither Colorado nor EPA performed a specific modeling analysis to 

16 See UBAQS, p. 4-28 

17 See, for example, "Colorado Annual Monitoring Network Plan" dated 2009-2010. Plan is available for review at 

the regulations.gov web site under Docket ID No. EPA-R08-0AR-2007-1032. 

22 
assure that emissions from Colorado sources do not significantly contribute to nonattainment in 

downwind States. According to the commenter, EPA's decision to use a qualitative approach to 

determine whether emissions from Colorado contribute significantly to downwind nonattainment 

is not consistent with its own preparation of a regional model to evaluate such impacts from 

other states as part of CAIR. 

EPA Response - EPA disagrees with the commenter's belief that only J:11odeling can 

establish whether or not there is significant contribution from one state to another. First, as noted 

above, EPA does not believe that section 11 O(a)(2)(D) requires modeling. While modeling can 

be useful, EPA believes that other forms of analysis can be sufficient to evaluate whether or not 

there is significant contribution to nonattainment. For this reason, EPA's 2006 guidance 

recommended other forms of information that states might wish to evaluate as part of their 

section 110(a)(2)(D) submissions for the 1997 8-hour ozone NAAQS. EPA has concluded that 

its qualitative approach to the assessment of significant contribution to downwind ozone 

nonattainment is consistent with EPA's 2006 Guidance. 

Second, EPA notes that the commenter's position also reflects a misunderstanding ofthe 

approach EPA used in the remanded CAIR due to an exclusive focus on those States that were 

selected for the modeling analysis. A wider understanding of the CAIR approach would 

recognize that EPA decided, based on other criteria, that it was not necessary to conduct 

modeling for certain western states: "[i]n analyzing significant contribution to nonattainment, we 

determined it was reasonable to exclude the Western U.S., including the States of Washington, 

Idaho, Oregon, California, Nevada, Utah, and Arizona from further analysis due to geography, 

meteorology, and topography. Based on these factors we concluded that the PM2.5 and 8-hour 

23
 
ozone nonattainment problems are not likely to be affected significantly by pollution transported 

across these States' boundaries...." (69 FR 4581, January 30, 2004). 

EPA has taken a similar approach to assess whether Colorado contributes significantly to 

violations of the 1997 8-hour ozone NAAQS in downwind states. In the proposed action, EPA 

explained several forms of substantive and technically valid evidence that led to the conclusion 

that emissions from the Colorado sources do not contribute significantly to nonattainment, in 

accordance with the requirement of Section 11 0(a)(2)(D). 

Comment No. 11 - In further support of its argument that EPA must use modeling to 

evaluate whether there is significant contribution to nonattainment under section 11 0(a)(2)(D), 

the commenter noted that EPA itself asks other agencies to perform such modeling in other 

contexts. As examples, the commenter cited four examples in which EPA commented on actions 

by other agencies in which EPA recommended the use of modeling analysis to assess ozone 

impacts prior to authorizing oil and gas development projects. As supporting material, the 

comment includes quotations from and references to EPA letters to Federal Agencies on 

assessing impacts of oil and gas development proj ects. 18 The commenter questioned why EPA's 

recommendation for such an approach in its comments to other Federal Agencies, did not result 

in its use of the same approach to evaluate the impacts from Colorado emissions and to insure 

compliance with Section 11 0(a)(2)(D)(i)(I). The commenter reasoned that the emissions that 

would result from the actions at issue in the other agency decisions, such as selected oil and gas 

drilling projects, would be of less magnitude and importance that the statewide emissions at issue 

in an evaluation under section 11 0(a)(2)(D). 

18 WO's April 9, 2010 comment letter, pp. 9-10. Complete versions of the EPA comment letters referenced here 

were attached to the comment as Exhibits 3 through 6, and are viewable on the Regulations.gov web site as 

Documents ID No. EPA-R08-0AR-2007-1032-0007,4 through 1032-0007.7. 

24
 
EPA ReL\ponse - As explained above, EPA disagrees with the commenter's fundamental 

argument that modeling is mandatory in all instances in order to evaluate significant contribution 

to nonattainment, whether by section 11 0(a)(2)(D), by EPA guidance, or by past EPA precedent. 

EPA's applicable guidance made recommendations as to different approaches that could lead to 

demonstration of the satisfaction of the interstate transport requirements for significant 

contribution to nonattainment in other states. Even EPA's own CAIR analysis relied on a 

combination of qualitative and quantitative analyses, as explained above. EPA's CAIR analysis 

excluded certain western states on the basis of a qualitative assessment of topography, 

geography, and meteorology. 19 

EPA believes that the commenter's references to EPA statements commenting on the 

actions of other agencies are inapposite. As the commenter is aware, those comments were made 

in the context of the evaluation of the impacts of various federal actions pursuant to NEPA, not 

the Clean Air Act. As explained above, in the context of section 110(a)(2)(D), EPA does not 

agree that modeling is always required to make that different evaluation, and EPA itself has 

relied on other more qualitative evidence when it deemed that evidence sufficient to reach a 

reasoned determination. 

Comment No. 12 - In further support of its argument that EPA should always require 

modeling to evaluate significant contribution to nonattainment, the commenter referred to EPA 

regulations governing nonattainment SIPs. The commenter noted 40 CPR 51.112(a)(1), which 

states that: "[t]he adequacy of a control strategy shall be demonstrated by means of applicable air 

quality models, data bases, and other requirements specified in appendix W of [Part 51] 

(Guideline on Air Quality Models)." The commenter argues that this regulation appears to 

19 See 69 FR 4581, January 30, 2004. 

25 
support the commenter's position that modeling is required to satisfy the significant contribution 

element of 11 O(a)(2)(D). 

Response: EPA disagrees with this comment. The cited language implies that the need 

for control strategy requirements has already been demonstrated, and sets a modeling analysis 

requirement to demonstrate the adequacy of the control strategy developed to achieve the 

reductions necessary to prevent an area's air quality from continuing to violate the NAAQS. 

EPA's determination that emissions from Colorado do not contribute significantly to 

nonattainment for the 1997 8-hour ozone standard in any other state eliminates the need for a 

control strategy aimed at satisfying the section 11 O(a)(2)(D) requirements. Moreover, EPA 

interprets the language at 40 CFR 51.112(a): "[e]ach plan must demonstrate that the measures, 

rules, and regulations contained in it are adequate to provide for the timely attainment and 

maintenance ofthe national standard that it implements," to refer to modcling for attainment 

demonstrations, an integral part of nonattainment area SIPs under part 0 of the CAA. This 

interpretation was upheld by the Sixth Circuit Court of Appeals. Wall v. Us. EPA, 265 F.3d 

426,436 (6th Cir. 2001). Thus, the commenter's cited regulation is not relevant to EPA's 

technical demonstration assessing whether emissions from Colorado contribute significantly to 

nonattainment in any other states under section 11 O(a)(2)(D). 

Comment No. 13 - The commenter also objected to EPA's proposed approval of the 

Colorado submission on the grounds that it was based upon a "weight-of-evidence analysis," and 

that no such weight of evidence test appears in the CAA generally, or in section 11 O(a)(2)(D) in 

particular. According to the commenter, there is no regulatory support for using a "weight-ofevidence" approach to assessing air quality impacts. The commenter asserted that EPA neither 

cited nor quotcd regulations or policy that provides for this, and failed to lend any specific 

26 
meaning to the phrase through its proposed approval. Finally, the commenter asserted, without 

explaining, its beliefthat EPA failed to address "several relevant factors related to the 

determination of whether Colorado contributes significantly to nonattainment undermines the 

agency's reliance on any 'weight-of-evidence' approach." 

EPA Response - The fact that neither the CAA generally, nor section 11 O(a)(2)(D) 

specifically, include the explicit phrase "weight of evidence" does not mean that it is 

inappropriate for EPA to use such an approach in this context. As explained above, section 

11 0(a)(2)(D) does not explicitly stipulate how EPA is to assess whether there is a significant 

contribution to nonattainment in other states. The proper consideration, therefore, is whether 

EPA has a rational technical basis for its decision. Even if the term "weight of evidence" does 

not appear in section 11 0(a)(2)(D) or elsewhere in the CAA, courts have recognized EPA's 

reliance on such an analytical approach where reasonable.2o As described above, EPA's 

guidance issued for the 1997 8-hour ozone NAAQS, the Agency specifically recommended types 

of information that states might wish to rely upon to evaluate the presence of, and extent of, 

instate transport for this purpose. EPA believes that a weight of evidence approach that properly 

considers appropriate evidence is sufficient to make a valid determination, as in this case. 

Specifically, EPA's technical analysis in the March 31,2010, proposed rule action 

underscores its reliance on implementation policies set in the EPA 2006 Guidance: "EPA's 

August 15, 2006, guidance to states concerning section 11 0(a)(2)(D)(i) recommended various 

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

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

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

27
 
in the absence ofsuch EPA modelin$' consideration ofother information such as the amount of 

emissions, the geographic location ofviolating areas, meteorological data, or various other 

forms ofinformation that would be relevant to assessing the likelihood ofsignificant contribution 

to violations o/the NAAQS in another state [emphasis added]. ,,21 On the basis of this guidance, 

Colorado and EPA chose to assess the impacts of emissions from Colorado sources on the 

closest downwind nonattainment areas (St. Louis, Missouri, and Illinois/Wisconsin counties 

along the southwestern shore of Lake Michigan) through a weight of evidence approach using 

quantitative information such as Colorado's distance from areas with monitors showing violating 

the NAAQS, modeling results outlining wind vectors for regional transport of ozone on high 

ozone days, back trajectory analyses for the downwind nonattainment areas closest to Colorado, 

and results of modeling studies for the nonattainment areas specifying the range of wind 

directions along which contributing ozone transport occurred. EPA's use of a weight of 

evidence analysis is by no means unusual for the assessment of ozone impacts through long 

range transport. The same analytical framework was used in the 1998 NOx SIP Call, as 

indicated under Section II.C., entitled "Weight-of-Evidence Determination of Covered States.,,22 

The differences between the specific types of evidence used in the NOx SIP Call and in EPA's 

analysis for this action do not invalidate the use of the weight-of-evidence approach. 

As for the commenter's argument that EPA "fails to lend any specific meaning to the 

phrase through its proposed approval," the Agency's technical analysis described in the proposal 

did specify the characteristics, including limitations, of a weight of evidence analysis: 

"[f]urthermore ...EPA notes that no single piece of information in the following discussion is by 

20 See, e.g., BCCA v. EPA, 355 F.3d 817 (5th Cir. 2003).
 

21 75 FR 16034, March 31, 2010.
 

22 "As discussed above, EPA applied a multi-factor approach to identitY the amounts of NOx emissions that
 

28 
itself dispositive of the issue. Instead, the total weight of all the evidence taken together supports 

the conclusion that emissions from Colorado s?urces are unlikely to contribute significantly to 

violations of the 1997 8-hour ozone standard in any other state." (75 FR 16034). 

Finally, as to the commenter's assertion that EPA failed to consider "several relevant 

factors" and thus failed to conduct an appropriate weight of evidence evaluation, EPA cannot 

weigh the validity of this comment in the absence of an explanation of what these factors might 

be. 

Comment No. 14 - The commenter also objected to EPA's proposed approval of the 

Colorado submission on the grounds that EPA did not assess the potential impacts of Colorado 

sources of emissions on violations of the 1997 8-hour ozone NAAQS in Arizona (Phoenix area), 

and Utah (Davis County area.) 

EPA Response - EPA did not discuss or assess potential impacts of Colorado emissions 

on Arizona or Utah in the proposal. EPA first notes that, west of the Continental Divide the 

prevailing winds generally move from south-westerly or westerly directions, as indicated by the 

typical movement of weather systems. 

Also, EPA notes that Davis County had a monitor indicating a violation of the NAAQS in 

2007, but has not since then. Thus, there are currently no monitors in Utah with data showing 

violations of the 1997 8-hour ozone NAAQS and, as a consequence, there are no monitors for 

which it would be appropriate to evaluate the possibility of significant contribution to 

nonattainment from Colorado sources for the 1997 8-hour ozone NAAQS. In Arizona, the 

Maricopa 8-hour ozone nonattainment area, which includes Phoenix, does have monitors 

indicating a violation of this NAAQS. However, Phoenix lies approximately 600 miles 

contribute significantly to nonattainment.. .." \998 SIP Call, 63 FR 5738 \, October 27, 1998. 

29 
southwest of the Colorado DMAlNFR area, and this area is generally upwind from Colorado 

sources. Emissions from Colorado would have to be affected by strong winds from the 

northeast, which are very infrequent, in order to contribute significantly to 8-hour ozone 

I10nattainment in the Phoenix area. The rarity of northeasterly winds in Arizona may be gauged 

by images of wind roses for Phoenix and Tucson. 23 

Comment No. 15 - The commenter argued that both Colorado and EPA relied 

inappropriately on a flawed ozone "nonattainment" SIP for the DMA/NFR nonattainment area as 

a basis for the proposed approval. According to the commenter, EPA cannot approve Colorado's 

section 11 O(a)(2)(d) submission because it relies heavily on the requirements of the ozone 

nonattainment area SIP for the DMAINFR nonattainment area. The commenter argued that 

"many" of the provisions of the nonattainment area SIP are themselves flawed or deficient. As 

examples, the commenter outlined alleged deficiencies in the Colorado Air Quality Control 

Commission's Regulation No.7, RACT requirements for NOx emissions, exemptions for certain 

source categories of NOx emissions, and other unspecified provisions in the DMAlNFR 

nonattainment area SIP. 

EPA Response - EPA disagrees with the commenter's position that its proposed approval 

relied heavily on the nonattainment area SIP for the DMAINFR area, and that as a consequence 

EPA cannot approve the Colorado section 11 0(a)(2)(D) submission for the significant 

contribution element for the 1997 8-hour ozone NAAQS. First, EPA notes that its reliance on 

material from, and related to, the "8-Hour Ozone Attainment Plan" was limited to considering 

the modeling results indicating a quick drop in ambient ozone levels from the DMAlNFR area to 

23 Reproductions of wind roses are available for review under Docket ID No. EPA-R08-0AR-2007-1 032, and 

online at: http://home.pes.com/windroses/wrgifs/ 6200.GIF; 

http://www.wrh.noaa.gov/twc/aviation/windrose TUS.php; and http://www.wrcc.dri.edu/htmlfiles/westwinddir.html 

30
 
the easternmost Colorado counties. EPA did not purport to pass upon the adequacy or 

approvability of each and every aspect ofthat nonattainment area SIP by referring to the 

modeling results as a source of relevant facts to be taken into consideration. 

Second, the proposal made clear that EPA's interpretation of the significance of this 

information is different from Colorado's: "EPA does not accept the State of Colorado Interstate 

Transport SIP assessment that these results demonstrate that 'the magnitude of ozone transport 

from Colorado to other states is too low to significantly contribute to nonattainment in... any 

other state with respect to the 0.08 ppb NAAQS. ",24 EPA explained its own view that the 

relatively moderate ozone concentrations in eastern Colorado (compared to the 1997 8-hour 

ozone NAAQS), while not excluding a potential significant contribution from Colorado 

emissions to downwind nonattainment areas, reduce the probability of its occurrence.

2S This is 

neither the key piece, nor even one ofthe key pieces, of evidence upon which EPA relies for its 

determination that emissions from Colorado sources do not contribute significantly to downwind 

nonattainment areas. To the contrary, EPA considered a variety of technical data and analyses of 

transport factors wholly independent of and substantively stronger than the modeling results 

connected with the DMA/NFR nonattainment area SIP. 

In addition, EPA notes that the commenter did not specify exactly how each ofthe 

purported flaws in the Colorado nonattainment area SIP for the DMAlNFR area could affect the 

reliability of the modeling results EPA used in the proposed rule, or the weight-of-evidence 

analysis that was the basis of the proposed approval of the Colorado section 11 0(a)(2)(D) 

24 See 75 FR 16034-35, and "State of Colorado Implementation Plan to Meet the Requirements of Clean Air Act
 

Section 1JO(a)(2)(D)(i)(I)-lnterstate Transport Regarding the 1997 8-hour Ozone Standard," p. 17, December 12,
 

2009.
 

25 75 FR 16035.
 

31 
submission for the significant contribution element. For example, the commenter did not explain 

what impact the specific alleged defects in Regulation 7 would have on emissions, and how any 

increases in emissions as a result of those defects would in tum result in significant contribution 

to nonattainment in other states. Absent more data or explanation supporting the commenter's 

general concerns, EPA cannot conclude that these alleged nonattainment SIP "defects," even if 

EPA ultimately agrees that they are statutory or regulatory deficiencies, result in additional 

emissions that have such impacts. Given this uncertainty as to the impacts of the alleged defects, 

if any, EPA does not agree that it is per se inappropriate to consider the modeling results in the 

very limited way that the Agency has done so in this action. 

Furthermore, EPA does not agree with the commenter that, given the alleged defects, 

EPA cannot approve the Colorado interstate transport SIP for the significant contribution 

element of section 11 O(a)(2)(D)(i)(I) until the alleged defects are resolved. As discussed below, 

the first step ofthe process to determine whether this element is satisfied is the factual 

determination of whether a State's emissions contribute significantly to nonattainment in 

downwind areas. If this factual finding is in the negative, as is the case for EPA's assessment of 

the contribution from emissions from Colorado, then section 11 O(a)(2)(D)(i)(I) does not require 

any changes to a state's provisions. 

Finally, EPA does not agree that it is appropriate to address the commenter's specific 

substantive comments about the merits of Rule 7 in the context of this action on the section 

110(a)(2)(D) SIP submission. Colorado has separately submitted its ozone nonattainment SIP 

for the DMAINFR nonattainment area to the Agency, and that submission will ultimately be the 

subject of another rulemaking in which EPA will evaluate and act upon that specific SIP 

submission. The commenter may resubmit its specific substantive comments on Rule 7, and any 

32
 
other comments on the nonattainment SIP for the DMAlNFR area, in that later rulemaking. 

Comment No. 16 - The commenter also objected to EPA's proposed approval because 

"Colorado's SIP, as written, simply does not contain any language that prohibits emissions that 

contribute significantly to nonattainment in any other state." The commenter also notes that 

EPA did not assess whether the SIP does or does not contain such provisions. The commenter 

appears to have argued that 11 O(a)(2)(D)(i) requires a state SIP to contain an explicit provision 

literally prohibiting emissions that contribute significantly to nonattainment in any other state 

and that, in order to approve the Colorado interstate transport SIP, EPA must examine the SIP to 

determine whether it contains such an explicit prohibition. 

EPA Response - EPA disagrees with the commenter's interpretation ofthe statutory 

requirements. Section 11 O(a)(2)(D)(i) has no language that requires a SIP to contain a specific 

provision literally prohibiting significant contribution to nonattainment in any other state, or, for 

that matter, to contain any particular words or generic prohibitions. Instead, EPA believes that 

the statute requires a state's SIP to contain substantive emission limits or other provisions that in 

fact ensure that sources located within the state will not produce emissions that have such an 

effect in other states. Therefore, EPA believes that satisfaction of the "significant contribution" 

requirement is not to be demonstrated through a literal requirement for a prohibition of the type 

advocated by the commenter. 

EPA's past application of section 11 O(a)(2)(D) did not require the literal prohibition 

advocated by the commenter. .For example, in 1998 NOx SIP call (63 FR 57356, October 27, 

1998) EPA indicated that "the term 'prohibit' means that SIPs must eliminate those amounts of 

emissions determined to contribute significantly to nonattainment. ..." As a result, the first step 

of the process to determine whether this statutory requirement is satisfied is the factual 

33
 
determination of whether a State's emissions contribute significantly to nonattainment in 

downwind areas. See 2005 CAIR Rule (70 FR 25162) and 1998 NOx SIP Call (63 FR 57356). 

If this factual finding is in the negative, as is the case for EPA's assessment of the contribution 

from emissions from Colorado, then section 1IO(a)(2)(D)(i)(I) does not require any changes to a 

state's SIP. If, however, the evaluation reveals that there is such a significant contribution to 

nonattainment in other states, then EPA requires the state to adopt substantive provisions to 

eliminate those emissions. The state could achieve these reductions through traditional 

command and control programs, or at its own election, through participation in a cap and trade 

program. Thus, EPA's approach in this action is consistent with the Agency's interpretation of 

II0(a)(2)(D)(i) in the 2006 guidance, the CAIR Rule, and the NOx SIP call, none of which 

required the proforma literal "prohibition" of the type advocated by the commenter. 

Comment No. 17 - The commenter noted a provision for stationary source permitting in 

the Colorado SIP that the commenter argued is inadequate to ensure that sources in Colorado 

will not significantly contribute to nonattainment in other states. The commenter also argued 

that Colorado does not sufficiently implement a requirement in the SIP to ensure stationary 

sources do not cause a violation of the 1997 8-hour ozone NAAQS, because Colorado guidelines 

do not unifonnly require ozone modeling for such sources. The commenter stated that EPA 

cannot approve the Colorado interstate transport SIP unless the issues commenter identifies are 

first resolved. 

EPA Response - As discussed above, the first step of the process to determine whether the 

"significant contribution" requirement is satisfied is the factual determination of whether a 

State's emissions contribute significantly to nonattainment in downwind areas. If the factual 

finding is in the negative, as is the case for EPA's assessment of the contribution from emissions 

34
 
from Colorado, then section 11 0(a)(2)(D)(i)(I) does not require any substantive changes to a 

state's SIP, nor does it require EPA to determine whether a state should require modeling in all 

permitting actions. As discussed above, EPA's approach in this action is consistent with the 

Agency's interpretation of 11 0(a)(2)(D)(i) in the 2006 guidance, the CAIR Rule and the NOx 

SIP Call. Therefore, EPA disagrees with the comment that EPA cannot approve the Colorado 

interstate transport SIP unless EPA addresses specific provisions and state guidelines for 

permitting stationary sources. 

Comment No. 18 - The commenter argued that EPA cannot approve the section 

11 0(a)(2)(D) submission from Colorado because the state and EPA did not comply with 110(1). 

Evidently, the commenter believes that the section 11 0(a)(2)(D) submission is a revision to the 

SIP that will interfere with attainment of the 2006 PM25 NAAQS and the 2008 ozone NAAQS. 

The commenter argued that a section 110(1) analysis must consider all NAAQS once they are 

promulgated, and argued that EPA took the same position in proposing to disapprove a PM10 

maintenance plan. 

EPA Response - EPA agrees that a required section 110(1) analysis must consider the 

potential impact of a proposed SIP revision on attainment and maintenance of all NAAQS that 

are in effect and impacted by a given SIP revision. However, EPA disagrees that it failed to 

comply with the requirements of section 110(1) or that section 110(1) requires disapproval of the 

SIP submission at issue here. 

Section 110(1) provides in part that: "[t]he Administrator shall not approve a revision of a 

plan if the revision would interfere with any applicable requirement concerning attainment and 

reasonable further progress ..., or any other applicable requirement ofthis chapter." EPA has 

consistently interpreted Section 110(1) as not requiring a new attainment demonstration for every 

35
 
SIP submission. EPA has further concluded that preservation of the status quo air quality during 

the time new attainment demonstrations are being prepared will prevent interference with the 

states' obligations to develop timely attainment demonstrations. 70 FR 58,199,58,134 (Oct. 5. 

2005); 70 FR 17.029, 17,033 (Apr. 4,2005); 70 FR 53, 57 (Jan. 3, 2005); 70 FR 28,429, 28,431 

(May 18, 2005). 

Colorado's submission is the initial submission by the state to address the significant 

contribution to nonattainment element of 11 0(a)(2)(D)(i) for the 1997 8-hour ozone. This 

submission does not revise or remove any existing emissions limit for any NAAQS, or any other 

existing substantive SIP provisions relevant to the 1997 8-hour ozone NAAQS. Simply put, it 

does not make any substantive revision that could result in any change in emissions. As a result, 

the submission does not relax any existing requirements or alter the status quo air quality. 

Therefore, approval of the submission will not interfere with attainment or maintenance of any 

NAAQS. 

EPA's discussion in the notice cited by the commenter is consistent with this 

interpretation. In the cited action, EPA noted that "Utah ha[d] either removed or altered a 

number of stationary source requirements," creating the possibility of a relaxation of SIP 

requirements interfering with attainment, a possibility that is not present here. See 74 FR 62727 

(Dec. 1, 2009). Thus, the action cited by the commenter is clearly distinguishable. 

The commenter did not provide any specific basis for concluding that approval of this 

SIP submission would interfere with attainment or maintenance of a NAAQS, or with any other 

applicable requirement of the Clean Air Act. EPA concludes that approval of the submission 

will not make the status quo air quality worse, and is in fact consistent with the development of 

an overall plan capable of meeting the Act's attainment requirements. Accordingly, even 

36 
assuming that section 110(1) applies to this submission, EPA finds that approval of the 

submission is consistent with the requirements of section 110(1). 

III. Section 110(1) 

Section 110(1) ofthe Clean Air Act states that a SIP revision cannot be approved if the 

revision would interfere with any applicable requirement concerning attainment and reasonable 

further progress towards attainment ofthe NAAQS or any other applicable requirements of the 

Act. In this action, EPA is approving portions of the Colorado interstate transport SIP 

addressing the "significant contribution" requirements ofsection 11 0(a)(2)(D)(i)(1) for the 1997 

8-hour ozone NAAQS. As discussed above in EPA's response to comments, the SIP revision 

that EPA is partially approving in this action does not revise or remove any existing emissions 

limit for any NAAQS, or any other existing substantive SIP provisions relevant to the 1997 8­

hour ozone NAAQS. As a result, the SIP revision does not relax any existing requirements or 

alter the status quo air quality. Furthermore, EPA has determined that the revision is consistent 

with all applicable federal requirements and will not interfere with requirements ofthe Act 

related to administrative or procedural provisions. Therefore, the revision does not interfere with 

attainment or maintenance ofthe NAAQS or other applicable requirements of the Act. 

IV. Final Action 

EPA is partially approving the Interstate Transport SIP submitted by the State of 

Colorado on June 18, 2009. Specifically, in this action EPA is approving the portions of that SIP 

submission that address the requirement of Section 11 0(a)(2)(D)(i)(I) that emissions from 

sources in that state do not "significantly contribute" to violations of the 1997 8-hour ozone 

NAAQS in any other state. EPA has concluded that the state's submission, and additional 

evidence evaluated by EPA, establish that emissions from Colorado sources do not have such an 

37
 
impact on other states for purposes of the 1997 8-hour ozone NAAQS. Therefore, the state's SIP 

does not need to include additional substantive controls to reduce emissions for purposes of 

section 11 0(a)(2)(D)(i)(I) for these NAAQS. At a later date, EPA will act on those portions of 

the Interstate Transport SIP that address the requirement of section 11 0(a)(2)(D)(i)(I) that 

emissions from the state's sources do not "interfere with maintenance" of the 1997 8-hour ozone 

NAAQS in any other state. 

V.	 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 Refonn Act of 1995 (Public Law 

104-4); 

38 
•	 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. 

The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the Small Business 

Regulatory Enforcement Fairness Act of 1996, generally provides that before a rule may take 

effect, the agency promulgating the rule must submit a rule report, which includes a copy of the 

rule, to each House of the Congress and to the Comptroller General of the United States. EPA 

will submit a report containing this action and other required information to the U.S. Senate, the 

U.S. House of Representatives, and the Comptroller General of the United States prior to 

publication of the rule in the Federal Register. A major rule cannot take effect until 60 days after 

39
 
IDENTIFICATION OF DOCUMENT: Approval and Promulgation of State
 

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

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

Requirement. Final Rule. (EPA-R08-0AR-2007-0645) Page 40 of 41.
 

it is published in the Federal Register. This action is not a "n1ajor rule" as defined by 5 U.S.C.
 

804(2).
 

Under section 307(b)(l) ofthe Clean Air Act, petitions for judicial review of this action 

must be filed in the United States Court of Appeals for the appropriate circuit by [FEDERAL 

REGISTER OFFICE: insert date 60 days from date of publication of this document in the 

Federal Register]. Filing a petition for reconsideration by the Administrator of this final rule 

does not affect the finality ofthis action for the purposes ofjudicial review nor does it extend the 

time within which a petition for judicial review may be filed, and shall not postpone the 

effectiveness of such rule or action. This action may not be challenged later in proceedings to 

enforce its requirements. (See section 307(b)(2).) 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air pollution control, Carbon monoxide, Incorporation by 

reference, Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, 

Reporting and recordkeeping requirements, Sulfur oxides, Volatile organic compounds. 

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

silz /ouJID 

Dated Carol Rushin 

Deputy Regional Administrator 

Region 8 

40
 
40 CFR part 52 is amended as follows: 

PART 52-[AMENDED] 

1. The authority citation for Part 52 continues to read as follows: 

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

Subpart G-Colorado 

2. Section 52.352, paragraph (a) is added to read as follows: 

§ 52.352 Interstate transport 

(a) Addition to the Colorado State Implementation Plan of the Colorado Interstate 

Transport SIP regarding the 1997 8-Hour Ozone Standard for the "significant contribution" 

requirement, as adopted by the Colorado Air Quality Control Commission on December 30, 

2008, State effective January 30, 2009, and submitted by the Governor's designee on June 18, 

2009. 

41