### ENVIRONMENTAL PROTECTIONAGENCY 40 CFRPart52 (EPA-R08-0AR-2007-0645); FRL- Approval and Promulgation ofStateImplementation Plans; State ofColorado; Interstate TransportofPollution Revisions for the 1997 8-hourOzone 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 ofColorado on June 18, 2009. These revisions, referred to as the Colorado Interstate Transport SIP, address the requirements ofClean Air Act section 11O(a)(2)(D)(i)(I) for the 1997 8-hour ozone National Arnbient Air Quality Standards (NAAQS). In this action EPA is approvingthe Colorado Interstate Transport SIP non-regulatory provisions that address the requirement ofsection 11O(a)(2)(D)(i)(I) that emissions from the state's sources do not "contribute significantly" to nonattainment ofthe 1997 8-hour ozone NAAQS in any other state. EPA will act at a later date onthe Colorado Interstate Transport SIP provisions that address the requirement ofsection 110(a)(2)(D)(i)(I) that emissions from the state's sources do not "interfere with maintenance" ofthe 1997 8-hour ozone NAAQS in any other state. This action is being taken under section 110 ofthe 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 notpublicly available, e.g., Confidential Business Information (CBI) orotherinformation whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is notplaced on the Internet and will be publicly available only in hard copy form. Publicly available docket materials are available eitherelectronically through www.regulations.gov, or in hard copy at the AirProgram, Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop Street, Denver, Colorado 80202-1129. EPA requests that ifat all possible, you contactthe individual listed in the FOR FURTHERINFORMATION CONTACT section to viewthe hard copy ofthe docket. You may view the hard copy ofthe docket Monday through Friday, 8:00 a.m. to 4:00 p.m., excluding Federal holidays. FORFURTHER INFORMATION CONTACT: Domenico Mastrangelo, Air Program, U.S. Environmental Protection Agency, Region 8, Mai1code 8P-AR, 1595 Wynkoop Street, Denver, Colorado 80202-1129, (303) 312-6416, mastrangelo.domenico@epa.gov. SUPPLEMENTARY INFORMATION: Definitions Forthe purpose ofthis document, we are giving meaning to certain words or initials as follows: (i) The words or initials Act or CAA mean orreferto the Clean Air Act, unless the context indicates otherwise. (ii) The words EPA, we, us or our mean orrefer to the United States Environmental Protection Agency. (iii) The initials SIP mean orrefer to State Implementation Plan. (iv) The words State orColorado mean the State ofColorado, unless the context indicates otherwise. 2Table ofContents I. Background II. Response to Comments III
. Section 110(1) IV. Final Action V. Statutory and Executive OrderReviews I. Background Section 110(a)(2)(D)(i) ofthe CAA requires that a state's SIP must contain adequate provisions prohibiting any source or othertype ofemissions activity within the state from emitting any airpollutant in amounts which will: (1) contribute significantly to nonattainment of the NAAQS in any other state; (2) interfere with maintenance ofthe NAAQS by any other state; (3) interfere with any other state'srequired measures to prevent significant deterioration ofair quality; or (4) interfere with any other state'srequired measures to protect visibility. On March 31, 2010, EPApublished a notice ofproposed rulenlaking (NPR) proposing partial approval of the State ImplementationPlan (SIP) revision "State ofColorado Implementation Plan to Meet the Requirements ofClean AirAct Section 110(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), "interferencewith maintenance." EPA'sproposed rule action reviewed and proposed approval ofthe Colorado SIP's section addressing only the "significant contribution" requirement. EPA will act at a later date onthe Colorado Interstate Transport SIP section that addresses the "interference with maintenance" requirement. To assess whether emissions from Colorado contribute significantly to downwind 3nonattainment for the 1997 8-hour ozone NAAQS, EPA's technical analysis relied on EPA's 2006 Guidance, recommending consideration ofavailable EPA modeling conducted in conjunction with CAIR,l orin the absence ofsuch EPA modeling, consideration ofother information such as the amount ofemissions, the geographic location ofviolating areas, meteorological data, orvarious other forms ofinformation that would be relevant to assessing the likelihood ofsignificant contribution to violations ofthe NAAQS in another state. Consistent withthe NOx SIP Call and CAIR, ourtechnical analysis assessed the extent ofozone transport from Colorado notjustto areas designated nonattainment, but also to areas in violation ofthe NAAQS. Because EPA did not have detailed modeling for Colorado and nearby downwind states, our approach did notrely on a quantitative determination ofColorado's contribution but on a weight-of-evidence approach using quantitative information such as Colorado's distance from areas with monitors showing violations ofthe NAAQS, modeling results outlining wind vectors for regional transport ofozone onhigh ozone days, backtrajectory analyses for the downwind nonattainment areas closest to the State, and results ofmodeling studies for the nonattainment areas specifying the range ofwind directions along which contribution ofozone transport occurred. Given thatthe assessments for each ofthese pieces of evidence are not individually definitive or outcome determinative, EPA concluded in its proposed action thatthe various factual and technical considerations supported a determination ofno significant contribution from Colorado emissions to the ozone nonattainment areas noted above. EPA did not receive comments thatpersuade the Agency that there is such significant contribution, and thus in today's final action EPA is making a final regulatory determination that

1In 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 ofFine Particulate Matterand Ozone (Clean Air Interstate Rule); Revisions to Acid Rain Program; Revisions to NOx SIP Ca11; Final Rule" (70 FR 25162). 4Colorado emissions sources do not contribute significantly to violations ofthe 1997 8-hour
ozoneNAAQS 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 ofthe portion ofthe Colorado Interstate Transport SIP that addresses the "significant contribution to nonattainmenf' requirement ofCAA Section 110(a)(2)(D)(i)(I) for the 1997 8-hourozoneNAAQS. In this section EPA responds to the significant adverse comments made by the commenter. CommentNo. 1

- The commenter asserted that EPA'sproposed approval was based on a "flawed legal standard." According to the commenter, EPA erred in the proposal by explaining that various factual ortechnical assessments indicate that it is "unlikely"that emissions from Colorado sources significantly contribute to violations ofthe 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 ofEPA's analysis and the commenter's interpretation ofthe statutory requirements. First, EPA notes that the discussion in the proposal was intended to present the various factual and technical considerations available to assess whetherthere is or is not significant contribution to nonattainment in other states as a result ofemissions 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 ofthe various 5considerations accurately. Second, EPA notes that all such technical evaluations are by their nature subject to some degree ofuncertainty. Indeed, the modeling that the commenter elsewhere contends should be the sole method for evaluating interstate transport is itselfbutone
means ofevaluating the real world impacts ofemissions in light ofmeteorological conditions, wind direction, and other such variables and produces a result that is itselfsubjectto some degree ofuncertainty. Third, EPA believes that it was also appropriate to describe the various factual and technical considerations and whetherthey indicated a "likelihood" ofsignificant contribution to nonattainment in another state becausethe proposal was seeking comment from the public upon whetherthese considerations together supported a determination ofno such significant contribution. EPA did not receive comments that persuade the Agency thatthere is such significantcontribution, and thus in today's final action EPA is making a final regulatory determination that Colorado emissions sources do not significantly contribute to violations ofthe 1997 8-hour ozone NAAQS in any other state, for the reasons explained elsewhere in this notice. In otherwords, EPA has concluded that the existing SIP for Colorado already contains adequate provisions to prevent emissions from Colorado sources from significantly contributing to violations ofthe 1997 8-hourozone NAAQS in other states and is therefore approving Colorado's submission for this purpose. CommentNo.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 ofdownwind impacts in accordance with EPA guidance and precedent. Although this is unclear from the comment, the commenterevidently 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 ofthe NOx SIP Call, the following issues need to 6be addressed in determining whether ornot an area is significantly contributing to nonattainment in downwind States: (a) The overall nature ofthe ozoneproblem; (b) the extent ofdownwind 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 ofhigh cost-effective control measures for upwind emissions. (63 FR 57356­ 57376, October 27, 1998). 

### EPA Response

- EPA disagrees withthe commenter onthis point. Section 11O(a)(2)(D) does not explicitly specify how states orEPA should evaluate the existence of, or extent of, interstate transport and whetherthat interstate transport is ofsufficient magnitude to constitute "significant contributionto 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 evaluatedthe existence of, and extent of, interstate transport. In that action, EPA developed an approach that allowed the Agency to evaluate whether there was significant contributionto ozone nonattainment across an entire region that was comprised ofmany states. That approach included regional scale modeling and othertechnical analyses that EPA deemed useful to evaluatethe issue ofinterstate transport on that geographic scale and for the facts and circumstances at issue in that rulemaking. EPA does not agree, however, thatthe approach of the NOx SIP Call is necessarily the only waythat 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 stateby state basis, and in situations where there is not evidence 0 f widespread interstate transport. 

### 7Indeed, EPA issued specific guidance making recommendations to states about how to address section 110(a)(2)(D) in SIP submissions for the 8-hour ozoneNAAQS. EPA issued this guidance document, 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" on August 15, 2006.2 This guidance document postdated theNOx 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 ofsuch a submission [are] not stipulated in the statute" and that the contents ofthe SIP submission "mayvary depending upon the facts and circumstancesrelated to the specific NAAQS.,,3 Moreover, within that guidance, EPA expressed its viewthat "the data and analytical tools available" at the time ofthe SIP submission "necessarily affect[] the content ofthe required submission.,,4 Tothat end, EPA specifically recommendedthat states located within the geographic region covered by the "CleanAir Interstate Rule" (CAIR)5comply with section 110(a)(2)(D) for the 1997 8-hour ozone NAAQS by complying with CAIR itself. For states outside the CAIRrule region, however, EPArecommended that states develop their SIP submissions for section 110(a)(2)(D) considering relevant infonnation. EPA explicitly recommended that relevant infonnation for section 11O(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 110(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 atthe regulations.gov web site as Document ID No. EPA-R08-0AR-2007-1032.0004.1. 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 andlimited to, information concerning emissions in the State, meteorological conditions in the State, the distance to the nearest nonattainment area in another State, reliance onmodeling conducted by EPA in determining that such State should not be included within the ambit ofthe CAIR, or such other infonnation as the State considers probative onthe issue ofsignificantcontribution.,,6 In addition, EPA recommended that states might electto evaluate significant contribution to nonattainment using relevant considerations comparable to those used by EPA in CAIR, including evaluating impacts as ofan appropriate year (such as 2010) and in light ofthe cost of control to mitigate emissionsthat resulted in interstate transport. The commenterdid not acknowledge ordiscuss 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 commenterwas aware ofit. In any event, EPA believes that the Colorado submission and EPA's evaluation ofit was consistent with EPA's guidance for the 1997 8-hourozone 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 ofthe nature and sources ofnonattainmentproblems in various downwind states. These are among the types ofinfonnationthat EPA recommended and that EPA considers relevant. Thus, EPA has concluded that the state's submission, and EPA's evaluation ofthat submission, meet the requirements ofsection 110(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 withthe concepts thatthe commenterenumerated from the

entitled "Rule to Reduce Interstate Transport ofFine Particulate Matter and Ozone (Clean Air Interstate Rule); Revisions to Acid Rain Program; Revisions toNOx SIP Call; Final Rule" (70 FR 25162). 6 Id. at 5. 9NOx SIP Call context: (a) the overall nature ofthe ozone problem; (b) the extent ofdownwind nonattainment problemsto which upwind State'semissions are linked; (c) the ambient impact of the emissions from upwind States' sources onthe downwind nonattainment problems; and (d) the availability ofhigh cost-effective control measures for upwind emissions. The only distinction in the case ofthe Colorado submission at issue here would be that because the available evidence indicates thatthere 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 ofcontrols for those sources is above orbelow a certain cost ofcontrol
as part ofdetermining whether the contribution constitutes "significantcontribution to nonattainment" for regulatory purposes, as was necessary in the NOx SIP Call and in CAIR. CommentNo. 3 - The commenter argued that Colorado based its claim ofno significant contribution "primarily on attainment plan modeling for the DenverMetropolitan AreaINorth Front Range (DMAINFR) nonattainment area" and noted that EPA itself"does not accept" that modeling for purposes ofassessing impacts on nonattainment in downwind States. EPA Response

- EPA disagrees with the commenter's characterization ofthe state's submission and ofEPA's evaluation ofit. This commentreflects an incomplete reading of EPA's evaluation ofhowthe results ofColorado's modeling analysis for the DMAINFR relate to
an assessment ofwhether emissions from Colorado sources contribute significantlyto downwind nonattainment ofthe 1997 8-hour ozone NAAQS in other states. Itis correctthat the Staterelied upon this information in its submission to EPA. 

### It is correct that EPA did not agree with Colorado's viewthat the modeling analysis results for the DMAfNFR attainment plan, in and ofthemselves, prove that there could be no significant contribution from Colorado sources to downwind ozone nonattainment in other states. EPA 10explicitly disagreed with the state's beliefthat: "
...these results [ofthe DMAlNFRmodeling analysis

## l demonstrate that the magnitude ofozone transport from Colorado to other States is too lowto 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 ofozone from Colorado to other states with violations ofthe NAAQS: "
.... [h]owever, as a reflection ofemission levels, the relatively (to the 1997 8-hour ozone NAAQS) moderate concentrations in eastern Colorado
...somewhatreduce the probability ofsignificant 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. CommentNo.4

- The commenterreiterated its concern that the Colorado section 110(a)(2)(D) submission was deficient because it did not strictly follow the commenter's summary ofthe structure ofthe analysis ofinterstate transport in the NOx SIP Call: (a) the overall nature ofthe ozone problem; (b) the extent ofdownwind nonattainmentproblemsto which upwind State's emissions are linked; (c) the ambient impact ofthe emissions from upwind States' sources on the downwind nonattainmentproblems; and (d) the availability ofhigh costeffective control measures for upwind emissions. EPA Response

- EPA disagrees with the commenter'sviewthat any analysis ofinterstate 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 11submissions for the 1997 8-hour ozone NAAQS. Within that guidance, EPA recommended various types ofinformation that states might wish to consider in the process ofevaluating whethertheir sources contributed significantly to nonattainment in other states. EPA has concludedthat the submission from Colorado, augmented by EPA's own analysis, sufficiently establishes that Colorado sources do not significantly contribute to violations ofthe 1997 8-hour
ozone NAAQS in other states. As noted above, EPA believes that the state's submission, and EPA's analysis ofit, address the same conceptual considerations that the commenteradvocated. CommentNo.5

- The commenter asserted that Colorado and EPA provided "no analysis" ofthe contribution from Colorado to downwind states and no "actual assessment" ofthe significance ofany such contribution. EPA Re.\ponse

- EPA disagrees with the commenter's position. The commenteragain
assumes that section 11O(a)(2)(D) explicitly requires the type ofmodeling analysis that the commenter advocates throughout its comments. Because the commenter apparently views the NOx SIP Call as the applicable guidance, the commenter contendsthat any analytical approach that is not identical to that approach is impermissible. In addition, the commenteroverlooks the fact that in otheractions based upon section 11O(a)(2)(D), EPA has also used a variety of analytical approaches, short ofmodeling, to evaluate whether specific states are significantly contributing to violations ofthe NAAQS in another state (e.g., the west coast states that EPA concluded should not be part ofthe geographic region ofthe CAIRrule based upon qualitative factors, and not by the zero out modeling EPA deemed necessary for some other States). In the proposed approval, EPA explainedthat other forms ofavailable information were sufficientto make the determinationthatthere is no significant contribution from Colorado

12sources to downwind nonattainment ofthe 1997 8-hour ozone NAAQS. As stated in the proposal:**~~EPA's** evaluation ofwhetheremissions from Colorado contribute significantly to ozone nonattainment in these areas [St. Louis and Chicago] relies on an examination ofa variety ofdata and analysis that provide insight on ozone transport from Colorado to these two areas. Because EPA does not have detailed modeling for Colorado and nearby downwind states, our approachdoes not rely on a quantitative determination of Colorado's contribution, as EPA did for other states in its CAIRrulemaking, but on a weight-of-evidence analysis based on qualitative assessments and estimates ofthe relevant factors. While conclusions reached for each ofthe factors considered in the following analysis are not in and by themselves determinative, consideration ofall 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 thatthe various forms ofinformation considered in the proposal (such as distance, orientation ofsurface and regional transport winds, back trajectory analyses, monitoring data) were not individually outcome determinative, butconcludedthat when taken together served to establish that Colorado sources do not significantly contribute to downwind nonattainment ofthe 1997 8-hour ozone NAAQS in other states. Thus, contrary to the commenter's assertion, EPAdid perform an "analysis" and an "assessment"that was a reasonable basis for its conclusionthat emissions from Colorado do not contribute significantly to downwind ozone nonattainment, using a combination ofquantitative data and qualitative

13[analYSes. EPA does not agree that onlythe type ofanalysis advocatedby the commentercould adequately evaluate the issue and support a rational determination in this instance. CommentNo.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 ofevaluating significant contributionto 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" ofthis approach. The commenter argued that this reliance onmonitor data is inconsistent with both section 1IO(a)(2)(D) and with EPA's guidance, by which the commenter evidently means theNOx SIP Call. In support ofthis assertion, the commenterquoted from the NOx SIP Call proposal in which EPA addressed the proper interpretation ofthe 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-designatednonattainment areas. Section 11O(a)(2)(D) does not refer to 'nonattainment areas,' which is a phrase that EPA interprets to refer to areas that are designated nonattainmentunder section 107(section 107(d)(l)(A)(I»" According to the commenter, this statement, and similar ones in the context ofthe final NOx SIP Call rulemaking, establish that states and EPA cannot utilize monitoring datato evaluate the existence of, and extent of, interstate transport. Furthermore, the commenterinterprets the reference to "airquality" in these statements to support its contention, amplified in later comments, that EPA must evaluate significant contribution in areas in whichthere 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 14proposal (and that EPA has subsequently made in the context ofCAIR). When EPA stated that it would evaluate impacts on air quality in downwind states, independent ofthe current formal '"designation" ofsuch downwind states, it was notreferring 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 contributionto nonattainment ofa NAAQS in another state. For example, in the case ofinitial designations, section I07(d) contemplates a process and timeline for initial designations that could well extend for two orthree years following the promulgation ofa new orrevised NAAQS. Bycontrast, section.11O(a)(l) requires states to make SIP submissions that address section 11O(a)(2)(D) and interstate transport '"within 3 years
or such shorterperiod as the Administrator may prescribe" ofEPA'spromulgation ofa new or revised NAAQS. This schedule does not support a reading ofsection 11O(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 CArRrulemaking. The commenter'smisunderstanding ofEPA's statement concerning designation status evidently caused the commenterto believe that EPA's assessment ofinterstate transport in the NOx SIP Call was not limited to evaluation ofdownwind areas with monitors. This is simply incorrect. In both the NOx SIP Call and CAIR, EPA evaluated significant contribution to nonattainment as measured orpredicted at monitors. Forexample, in the technical analysis for theNOx SIP Call, EPA specifically evaluated the impacts ofemissions from upwind states on monitors located in downwind states. The NOx SIP Call did not evaluate impacts at points 15without monitors, nor did the CAIRrulemaking. EPA believes that this approach to evaluating significant contribution is correct under section 110(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 ofsignificant contributionto downwind nonattainment must include evaluation ofimpacts on non-monitored
areas. First, neither section 110(a)(2)(D)(i)(I) provisions, nor the EPA guidance issued for the 1997 8-hour ozone NAAQS onAugust 15, 2006, support the commenter's position, as neither refers to any explicit mandatory orrecommended approach to assess air quality in non-monitored
areas. 8 The same focus onmonitored data as a means ofassessing 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 ofareas with current monitored violations ofthe ozone and/or PM1.5NAAQS. 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 ofinterstate transport under section 110(a)(2)(D) by focusing on monitoring data. Indeed, such monitoring datawas at the core ofboth ofthese efforts. In neither ofthese rulemakings did EPA evaluate significant contributionto 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 determiningthreshold despite remanding other aspects ofCAIR). 8 2006 Guidance, p. 5. 9 "Based on this approach, we predicted that in the absence ofadditional control measures, 47 countieswith air qualitymonitors [emphasis ours] would violate the 8-hourozoneNAAQS in 2010
...." From the CAIRproposed rule ofJanuary 30, 2004 (69 FR 4566, 4581). The NOx SIP call proposed rule action reads: "
...Forcurrent 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-hourNAAQS. These are the most recent 3 years offully quality assured data which were available in time for this assessment," 62 FR 60336. 16reference method monitor is the way in which EPA ascertains that there is a violation ofthe 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 mustbe a monitor with data showing a violation ofthatNAAQS. EPA has concluded that by considering data from monitored areas, its assessment ofwhether emissions from Colorado contribute significantly to
ozone nonattainment in downwind States is consistent with the 2006 Guidance, and with the approach used by boththe CAIRrule and the NOx SIP Call. CommentNo. 7 - In support ofits comments that EPA should assess significant contribution to nonattainment in nonmonitored areas, the commenter argued that existing modeling performed by another organization "indicatesthat large areas ofneighboring states will be likely to violate the ozoneNAAQS." According to the commenter, these likely "'violations" ofthe 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 ofOzone Performance in WRAP Modeling and Relevant to Future Regional Ozone Planning"). The commenter asserted that: "Slide 28 ofthis presentation displays projected 4th highest 8-hourozone reading for 2018 and indicates that air quality in areas such as northernNew Mexico, western Wyoming, southern Utah, and central Arizonawill 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 ofthe 1997 8-hour ozoneNAAQS in 2018 in non-monitored areas ofstates adjacentto 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

17significant contribution to nonattainment for the 1997 8-hourozone NAAQS by modeling ambient levels in areas where there is no monitorto provide datato establish a violation ofthe NAAQS in question. Section 110(a)(2)(D) does not require such an approach, EPA has not taken this approach in the NOx SIP Call orotherrulemakings under section 110(a)(2)(D), and EPA's prior analytical approach has not been disturbed by the courts. Second, the commenter's own description ofthe ozone concentrations predicted for the year2018 as projecting "violations" ofthe 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"
...airquality
... will exceed or violate [emphasis ours] the 1997 ozone NAAQS." By definition, a one year value ofthe 4th max above the NAAQS only constitutes an exceedance ofthe NAAQS; to constitute a violation ofthe 1997 8-hour ozone NAAQS, the standard must be exceeded for three consecutive years at the same monitor. Thus,
even ifthe WRAP presentation submittedby the commenterwere technically sound, the conclusion drawn from it by the commenter is inaccurate and does not support its claim of projected violations ofthe NAAQS in large areas (monitored or unmonitored) ofColorado's neighboring States. Finally, EPA has reviewed the WRAP presentation submittedby the commenter, and believes that there was a substantial errorin the WRAP modeling software that led to overestimation ofground 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, 18stratospheric ozone. II Environ has developed revised vertical velocity algorithms in a new version ofCAMx that eliminated the excessive downward transport ofozone from the top layers ofthe model. This revised version ofthe model is nowbeing used in a number ofapplications throughout high terrain areas in the West. In conclusion, EPA believes that this key inadequacy ofthe WRAP model, noted above, makes it inappropriate support for the commenter's concerns about large expanses of8-hour ozone nonattainment areas projected for 2018 in areas without monitors. CommentNo.8

- As additional support for its assertion that EPA should require modeling to assess ambient levels in unmonitored portions ofother states, the commenter relied
on an additional study entitled the "Uinta Basin Air Quality Study (UBAQS)." The commenter argued that UBAQS further supports its concernthat Colorado and EPA, having limited the evaluation ofdownwind impacts only to areas with monitors, failed to assess ozone nonattainment in non-monitored areas. According to the commenter, UBAQS modeling results showthat: (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 ofthe four counties in the southwest comer ofUtah 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 FourComers 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 ofWashington, Iron, Kane, and Garfield 19EPA does not agree that the 8-hour ozone nonattainment (current and projected) 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 ofthe UBAQS analysis results for counties in Utah's southwestern comer: "basedon 2005 meteorological data, portions ofWashington, 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 ofthe comment letter) is inaccurate. A close review ofthe legend in these figures indicates that the highest ozone concentrations predictedby the model for portions ofthe counties noted above are somewhere between 81.00 and 85.99 ppb, but it is not specified. Ifit is actually predicted smallerthan or equal to 84.9 ppb then the area is attaining the 1997 8-hour ozoneNAAQS, ifit is predicted as greater than 84.9 ppb then it is not attaining thoseNAAQS. 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 orboth in nonattainment, orone ofthem in attainment and the other in nonattainment, for the 1997 8-hour ozoneNAAQS. EPA does not believe that this evidence adequately establishes that one orboth areas definitely violate the NAAQS, even ifthe infonnation were taken at face value. Second, even ifthe design values predicted for these unmonitored areas were at the top of the 81.00-85.99 ppb range, theirreliability would remain questionable. The UBAQS itself identifies and illustrates major shortcomings ofits modeling analysis, only to neglect assessing the impact ofthese shortcomings on the modeling results. 13 The study deviates in at least two

Counties. 13 See UBAQS, pp. 4-27 to 4-29. 20significant ways from EPA's 2007 guidance on SIP modeling.14 One issue is the UBAQS modeling reliance on fewer thanthe five years ofdatarecommended by EPA to generate a current 8-hour ozone design value (DVC). UBAQS relaxed this requirement so that sites with as little as 1year ofdata were included as DVCs in the analysis. The otherissue is the computation ofthe relative responsive factor (RRF), which directly affects the modeling's future design value (DVF).15 Again due to unavailability ofdata satisfying EPA'srecommendation that the RRF be based on a minimum offive days ofozone concentrations above 85 ppb, UBAQS modeling uses RRFs based on one or more days ofozone 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. 

### CommentNo.9

- In support ofits arguments thatEPA should not assess significant contribution to nonattainmentthrough evaluation ofimpacts at monitors instead ofmodeling impacts where there is no such monitor, the commenter cited a past statement by EPAto the effectthat the monitor network in the western United States needs to be expanded. The quoted statements included EPA's observationthat "[v]irtually all States east ofthe Mississippi River have at least two to four non-urban 03 monitors, while many large mid-western and western States have one orno 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 ofsignificant contribution to nonattainment ofthe ozone NAAQS in other states relying on monitoring data instead ofmodeling ambient levels.

14 EPA, Guidance on the Use ofModels and otherAnalyses for Demonstrating Attainment ofAir Quality Goals for Ozone, PM2.5 and Regional Haze. Office ofAir Quality Planning and Standards, Air Modeling Group. Research Triangle Park, North Carolina (2007), available athttp://www.epa.gov/scramOOl/guidance/guide/final-03-pm-rhguidance.pdf. 15 DYC X RRF = DYF. 21EPA**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 ofwestern 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 ofcontext, because EPA was in that proposal referring to changes in state monitoring networks that it anticipates will be necessary in order to implementnot the 1997 8-hour ozone NAAQS that are the subject ofthis rulemaking, but rather the next iteration ofthe ozone NAAQS for which there are concerns that there will be a need to evaluate ambient levels in previously unmonitored areas ofthe 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 thatthey meetthe applicable requirements. Forexample, Colorado itselfsubmitsjust 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 ofthe 1997 8-hour ozone NAAQS, EPA has no reason to believe thatthe evaluation ofpossible significant contribution from Colorado sources in reliance on those monitors is incorrect. CommentNo.10

- The commenter objected to EPA'sproposed approval ofthe 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 MonitoringNetwork Plan" dated 2009-2010. Plan is available for review at the regulations.gov web site under Docket ID No. EPA-R08-0AR-2007-1032. 22assure 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 whetheremissions from Colorado contribute significantlyto downwind nonattainment is not consistent with its own preparation ofa regional model to evaluate such impacts from other states as part ofCAIR. EPA Response

- EPA disagrees with the commenter'sbeliefthat only J:11odeling can establish whether ornotthere is significant contribution from one state to another. First, as noted above, EPA does notbelievethat section 11O(a)(2)(D) requires modeling. While modeling can be useful, EPA believes that other forms ofanalysis can be sufficientto evaluate whether ornot there is significant contribution to nonattainment. Forthis reason, EPA's 2006 guidance recommended otherforms ofinformation that states might wishto evaluate as part oftheir section 110(a)(2)(D) submissions for the 1997 8-hourozone NAAQS. EPA has concluded that its qualitative approach to the assessment ofsignificant contribution to downwind ozone nonattainment is consistent with EPA's 2006 Guidance. Second, EPA notes thatthe commenter'sposition 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 widerunderstanding ofthe CAIR approach would recognize that EPA decided, based on othercriteria, 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 ofWashington, Idaho, Oregon, California, Nevada, Utah, and Arizona from further analysis due to geography, meteorology, and topography. Based on these factors we concluded that the PM2.5and 8-hour

23ozone nonattainment problems are not likely to be affected significantly by pollution transported
across these States' boundaries
...." (69 FR4581, January 30, 2004). EPA has taken a similar approach to assess whether Colorado contributes significantly to violations ofthe 1997 8-hour ozone NAAQS in downwind states. In the proposed action, EPA explained several forms ofsubstantive 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 ofSection 110(a)(2)(D). CommentNo. 11 - In further support ofits argument that EPA must use modeling to evaluate whether there is significant contribution to nonattainment under section 110(a)(2)(D), the commenter noted that EPA itselfasks 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 ofmodeling analysis to assess ozone impacts priorto 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 ofoil and gas development projects. 18 The commenterquestioned why EPA's recommendation for such an approach in its comments to other Federal Agencies, did not result in its use ofthe same approach to evaluate the impacts from Colorado emissions and to insure compliance with Section 110(a)(2)(D)(i)(I). The commenterreasoned 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 ofless magnitude and importance that the statewide emissions at issue in an evaluation under section 110(a)(2)(D).

18 WO's April 9, 2010 comment letter, pp. 9-10. Complete versions ofthe 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 orderto evaluate significantcontribution to nonattainment, whetherby section 110(a)(2)(D), by EPA guidance, orby past EPA precedent. EPA's applicable guidance made recommendations as to different approaches thatcould lead to demonstration ofthe satisfaction ofthe interstate transport requirements for significant contribution to nonattainment in other states. Even EPA's own CAIR analysis relied on a combination ofqualitative and quantitative analyses, as explained above. EPA's CAIRanalysis excluded certain western states on the basis ofa qualitative assessment oftopography, geography, and meteorology. 19 EPA believes thatthe commenter'sreferences to EPA statements commenting on the actions ofother agencies are inapposite. As the commenter is aware, those comments were made in the context ofthe evaluation ofthe impacts ofvarious federal actions pursuantto NEPA, not the Clean Air Act. As explained above, inthe contextofsection 110(a)(2)(D), EPA does not agree that modeling is always required to makethat different evaluation, and EPA itselfhas relied on other more qualitative evidence when it deemed that evidence sufficientto reach a reasoned determination. 

### CommentNo. 12

- In further support ofits argument that EPA should always require modeling to evaluate significant contributionto nonattainment, the commenterreferred to EPA regulations governing nonattainment SIPs. The commenternoted 40 CPR 51.112(a)(1), which states that: "[t]he adequacy ofa control strategy shall be demonstrated by means ofapplicable air quality models, databases, and otherrequirements specified in appendix W of[Part 51] (Guideline on Air Quality Models)." The commenter argues that this regulation appears to

19 See 69 FR4581, January 30, 2004. 25support the commenter's position that modeling is required to satisfy the significant contribution element of 11O(a)(2)(D). Response: EPA disagrees with this comment. The cited language implies thatthe need for control strategy requirements has already been demonstrated, and sets a modeling analysis requirement to demonstrate the adequacy ofthe control strategy developed to achieve the reductions necessary to prevent an area's airquality from continuing to violate the NAAQS. EPA's determinationthat emissions from Colorado do not contribute significantly to nonattainment for the 1997 8-hour ozone standard in any other state eliminatesthe need for a control strategy aimed at satisfyingthe section 11O(a)(2)(D) requirements. Moreover, EPA interprets the language at 40 CFR 51.112(a): "[e]achplan 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 ofnonattainment area SIPs under part 0 ofthe CAA. This interpretation was upheld by the Sixth Circuit Court ofAppeals. Wall v. Us. EPA, 265 F.3d 426,436 (6th Cir. 2001). Thus, the commenter's cited regulation is not relevantto EPA's technical demonstration assessing whether emissions from Colorado contribute significantlyto nonattainment in any other states under section 11O(a)(2)(D). CommentNo. 

### 13

- The commenter also objected to EPA's proposed approval ofthe Colorado submission on the groundsthat it was based upon a "weight-of-evidence analysis," and that no such weight ofevidencetest appears in the CAA generally, orin section 11O(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 orpolicy that provides for this, and failed to lend any specific 26meaningto 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 ofwhetherColorado contributes significantlyto nonattainment underminesthe agency's reliance on any 'weight-of-evidence' approach." 

### EPA Response

- The fact that neither the 

### CAA generally, nor section 11O(a)(2)(D) specifically, include the explicitphrase "weight ofevidence" does not meanthat it is inappropriate for EPAto use such an approach in this context. As explained above, section 110(a)(2)(D) does not explicitly stipulate how EPA is to assess whetherthere is a significant contributionto nonattainment in other states. Theproperconsideration, therefore, is whether EPA has a rational technical basis for its decision. Even ifthe term "weight ofevidence" does not appear in section 110(a)(2)(D) or elsewhere in the CAA, courts have recognized EPA's reliance on such an analytical approach wherereasonable.2o As described above, EPA's guidance issued for the 1997 8-hour ozoneNAAQS, the Agency specifically recommendedtypes ofinformation that states might wish to rely upon to evaluatethe presence of, and extent of, instate transport for this purpose. EPAbelieves that a weight ofevidence approach that properly considers appropriate evidence is sufficientto make a valid determination, as in this case. Specifically, EPA'stechnical 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 110(a)(2)(D)(i) recommended various methods by which states might evaluate whether ornot its emissions significantly contribute to violations ofthe 1997 ozone standards in another state. Among other methods, EPA recommended consideration ofavailable EPA modeling conducted in conjunction with CAIR, 

### or

27

### in the absence of such EPA modelin$' consideration of other information such as the amount of emissions, the geographic location of violatingareas, meteorologicaldata, or various other forms of information that wouldbe relevant to assessing the likelihoodof significant contribution to violations o/theNAAQS in anotherstate [emphasis added].,,21 On the basis ofthis guidance, Colorado and EPA choseto assess the impacts ofemissions from Colorado sources onthe closestdownwind nonattainment areas (St. Louis, Missouri, and Illinois/Wisconsin counties alongthe southwestern shore ofLake Michigan) through a weight ofevidence 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 ofozone on high
ozone days, backtrajectory analyses for the downwind nonattainment areas closestto Colorado, and results ofmodeling studies for the nonattainment areas specifying the range ofwind directions along which contributing ozone transport occurred. EPA's use ofa weightof evidence analysis is by no means unusual for the assessment ofozone 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-EvidenceDetermination ofCovered States.,,22 The differences between the specific types ofevidence used in the NOx SIP Call and in EPA's analysis for this action do not invalidatethe use ofthe 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'stechnical analysis described in the proposal did specifythe characteristics, including limitations, ofa weight ofevidence analysis: "[f]urthermore
...EPA notes that no single piece ofinformation 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 ofNOx emissions that 28itselfdispositive ofthe issue. Instead, the total weight ofall the evidence taken together supports the conclusion that emissions from Colorado s?urces are unlikely to contribute significantly to violations ofthe 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 ofevidence evaluation, EPA cannot weigh the validity ofthis commentin the absence ofan explanation ofwhat these factors might be. CommentNo. 14

- The commenter also objectedto EPA's proposed approval ofthe Colorado submission onthe grounds that EPA did not assess the potential impacts ofColorado
sources ofemissions onviolations ofthe 1997 8-hour ozone NAAQS in Arizona (Phoenix area), and Utah (Davis County area.) EPA Response

- EPA did not discuss or assess potential impacts ofColorado emissions
on Arizona orUtah in the proposal. EPA first notes that, west ofthe Continental Divide the prevailing winds generally move from south-westerly or westerly directions, as indicated by the typical movement ofweather systems. Also, EPA notes that Davis County had a monitor indicating a violation ofthe NAAQS in 2007, but has not since then. Thus, there are currently no monitors in Utah with data showing violations ofthe 1997 8-hour ozone NAAQS and, as a consequence, there are no monitors for which it would be appropriate to evaluatethe possibility ofsignificant contribution to nonattainment from Colorado sources for the 1997 8-hour ozone NAAQS. In Arizona, the Maricopa 8-hourozonenonattainment area, which includes Phoenix, does have monitors indicating a violation ofthis NAAQS. However, Phoenix lies approximately 600 miles
contribute significantly to nonattainment..
.." \998 SIP Call, 63 FR 5738\, October27, 1998. 29southwestofthe 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 orderto contribute significantlyto 8-hour ozone I10nattainment in the Phoenix area. The rarity ofnortheasterly winds in Arizona maybe gauged by images ofwind roses for Phoenix and Tucson. 23 CommentNo. 

### 15

- The commenter argued that both Colorado and EPArelied inappropriately on a flawed ozone "nonattainment" SIP for the DMA/NFRnonattainment areaas
a basis for the proposed approval. According to the commenter, EPA cannot approve Colorado's section 11O(a)(2)(d) submission because it relies heavily onthe requirements ofthe ozone nonattainment area SIP for the DMAINFRnonattainment area. The commenter argued that "many" ofthe provisions ofthe nonattainment area SIP are themselves flawed ordeficient. As examples, the commenter outlined alleged deficiencies in the Colorado Air Quality Control Commission's RegulationNo.7, RACTrequirements for NOx emissions, exemptions for certain
source categories ofNOx emissions, and otherunspecified provisions in the DMAlNFR nonattainment area SIP. EPA Response

- EPA disagrees with the commenter'spositionthat its proposed approval relied heavily onthe nonattainment area SIP for the DMAINFRarea, and that as a consequence EPA cannot approve the Colorado section 110(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 areato

23 Reproductions ofwind roses are available for review under Docket ID No. EPA-R08-0AR-2007-1032, 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 30the easternmost Colorado counties. EPA did not purportto pass upon the adequacy or approvability ofeach and every aspect ofthat nonattainment area SIP by referring to the modeling results as a source ofrelevant facts to be taken into consideration. Second, the proposal made clearthat EPA's interpretation ofthe significance ofthis information is different from Colorado's: "EPA does not acceptthe State ofColorado Interstate Transport SIP assessmentthatthese results demonstrate that 'the magnitude ofozonetransport from Colorado to other states is too lowto significantly contributeto nonattainment in
...any other state with respect to the 0.08 ppb NAAQS. ",24 EPA explained its ownviewthat the relatively moderate ozone concentrations in eastern Colorado (compared to the 1997 8-hour
ozoneNAAQS), while notexcluding a potential significant contribution from Colorado emissions to downwind nonattainment areas, reduce the probability ofits occurrence.2S This is neitherthe key piece, nor even one ofthekeypieces, ofevidence upon which EPArelies for its determination that emissions from Colorado sources do not contribute significantly to downwind nonattainment areas. Tothe contrary, EPA considered a variety oftechnical data and analyses of transport factors wholly independentofand substantively strongerthanthe modeling results connected withthe DMA/NFRnonattainment area SIP. In addition, EPA notes that the commenterdid not specify exactlyhoweach ofthe purported flaws in the Colorado nonattainment area SIP for the DMAlNFRareacould affect the reliability ofthe modeling results EPA used in the proposed rule, orthe weight-of-evidence analysis that was the basis ofthe proposed approval ofthe Colorado section 11 0(a)(2)(D)

24 See 75 FR 16034-35, and "State ofColorado Implementation Plan to Meet the Requirements ofClean AirAct Section 1JO(a)(2)(D)(i)(I)-lnterstate Transport Regarding the 1997 8-hourOzone Standard," p. 17, December 12, 2009. 25 75 FR 16035. 31submission for the significantcontribution element. Forexample, the commenterdid not explain what impact the specific alleged defects in Regulation 7 would have on emissions, and how any increases in emissions as a result ofthose defects would in tum result in significantcontribution to nonattainment in other states. Absent more data orexplanation supporting the commenter's general concerns, EPA cannotconclude that these alleged nonattainment SIP "defects,"even if EPA ultimately agrees thatthey are statutory orregulatory deficiencies, result in additional emissions that have such impacts. Given this uncertainty as to the impacts ofthe alleged defects, ifany, EPA does not agree that it isperse inappropriate to considerthe modeling results in the very limited way thatthe Agency has done so in this action. Furthermore, EPA does not agree with the commenterthat, given the alleged defects, EPA cannot approve the Colorado interstatetransport SIP for the significant contribution element ofsection 11O(a)(2)(D)(i)(I) until the alleged defects are resolved. As discussed below, the first step ofthe process to determine whetherthis element is satisfied is the factual determination ofwhether a State's emissions contribute significantly to nonattainment in downwind areas. Ifthis factual finding is in the negative, as is the case for EPA's assessment of the contribution from emissions from Colorado, then section 11O(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 ofRule 7 in the contextofthis action on the section 110(a)(2)(D) SIP submission. Coloradohas separately submitted its ozone nonattainment SIP for the DMAINFR nonattainment area to the Agency, and that submission will ultimately be the subject ofanother rulemaking in which EPA will evaluate and act upon that specific SIP submission. The commentermayresubmit its specific substantive comments on Rule 7, and any 32other comments onthe nonattainment SIP for the DMAlNFR area, in that later rulemaking. CommentNo. 16

- The commenter also objected to EPA's proposed approval because "Colorado's SIP, as written, simply does not contain any languagethatprohibits emissions that contribute significantly to nonattainment in any other state." The commenteralso notes that EPA did not assess whether the SIP does or does not contain such provisions. The commenter appears to have argued that 11O(a)(2)(D)(i) requires a state SIP to contain an explicit provision literally prohibiting emissionsthat contribute significantly to nonattainment in any other state and that, in orderto approve the Colorado interstate transport SIP, EPA mustexaminethe SIP to determine whether it contains such an explicitprohibition. EPA Response

- EPA disagrees with the commenter's interpretation ofthe statutory requirements. Section 11O(a)(2)(D)(i) has no language that requires a SIP to contain a specific provision literally prohibiting significantcontribution 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 otherprovisions that in fact ensure that sources located within the state will not produce emissions that have such an effect in other states. Therefore, EPA believesthat satisfaction ofthe "significantcontribution" requirement is not to be demonstrated through a literal requirement for a prohibition ofthe type advocated bythe commenter. EPA's past application ofsection 11O(a)(2)(D) did notrequire 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 musteliminate those amounts of emissions determined to contribute significantlyto nonattainment.
..." As a result, the first step ofthe process to determine whether this statutory requirement is satisfied is the factual 33determination ofwhether 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). Ifthis factual finding is in the negative, as is the case for EPA's assessment ofthe 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 provisionsto 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 ofwhich required theproformaliteral "prohibition" ofthe type advocated by the commenter. CommentNo. 17

- The commenternoted a provision for stationary source permitting in the Colorado SIP that the commenter argued is inadequate to ensurethat 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 ofthe 1997 8-hour ozoneNAAQS, 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 ofthe process to determine whether the "significant contribution" requirement is satisfied is the factual determination ofwhether a State's emissions contribute significantly to nonattainment in downwind areas. Ifthe factual finding is in the negative, as is the case for EPA's assessment ofthe contribution from emissions 34from Colorado, then section 110(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 110(a)(2)(D)(i) in the 2006 guidance, the CAIR Rule and the NOx SIP Call. Therefore, EPA disagrees with the commentthat EPA cannot approve the Colorado interstate transport SIP unless EPA addresses specific provisions and state guidelines for permitting stationary sources. CommentNo. 

### 18

- The commenter argued that EPA cannot approve the section 110(a)(2)(D) submission from Colorado because the state and EPA did not comply with 110(1). Evidently, the commenterbelieves that the section 110(a)(2)(D) submission is a revision to the SIP that will interfere with attainment ofthe 2006 PM25NAAQS 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 considerthe potential impact ofa proposed SIP revision on attainment and maintenance ofall NAAQS that
are in effect and impactedby a given SIP revision. However, EPA disagrees that it failed to comply with the requirements ofsection 110(1) orthat section 110(1) requires disapproval ofthe SIP submission at issue here. Section 110(1) provides in part that: "[t]he Administrator shall not approve a revision ofa plan ifthe 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 

### 35SIP submission. EPA has further concluded that preservation ofthe status quo air quality during the time newattainment 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 110(a)(2)(D)(i) for the 1997 8-hourozone. This submission does not revise orremove any existing emissions limit for any NAAQS, or any other existing substantive SIP provisionsrelevant to the 1997 8-hourozoneNAAQS. 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 ofthe submission will not interfere with attainment or maintenance ofany NAAQS. EPA'sdiscussion in the notice citedby the commenter is consistent with this interpretation. In the cited action, EPA noted that "Utahha[d] eitherremoved or altered a number ofstationary source requirements," creating the possibility ofa relaxation ofSIP requirements interfering with attainment, a possibility that is not present here. See 74 FR 62727 (Dec. 1, 2009). Thus, the action cited by the commenteris clearlydistinguishable. The commenterdid not provide any specific basis for concludingthat approval ofthis SIP submission would interfere with attainment or maintenance ofa NAAQS, or with any other applicable requirement ofthe Clean Air Act. EPA concludes that approval ofthe submission will not make the status quo air quality worse, and is in fact consistent with the development of
an overall plan capable ofmeeting the Act's attainment requirements. Accordingly, even 36assuming that section 110(1) applies to this submission, EPA finds that approval ofthe submission is consistentwith the requirements ofsection 110(1). III. Section 110(1) Section 110(1) ofthe Clean AirAct states that a SIP revision cannotbe approved ifthe revision would interfere with any applicable requirement concerning attainment and reasonable further progress towards attainment ofthe NAAQS or any other applicable requirements ofthe Act. In this action, EPA is approving portions ofthe Colorado interstate transport SIP addressing the "significant contribution" requirements ofsection 110(a)(2)(D)(i)(1) for the 1997 8-hour ozone NAAQS. As discussed above in EPA'sresponse to comments, the SIP revision that EPA is partially approving in this action does notrevise orremove 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 alterthe 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 orprocedural provisions. Therefore, the revision does not interfere with attainment ormaintenance ofthe NAAQS orother applicable requirements ofthe 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 ofthat SIP submission that address the requirement ofSection 110(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, establishthat emissions from Colorado sources do not have such an 37impact on other states for purposes ofthe 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 110(a)(2)(D)(i)(I) for these NAAQS. At a laterdate, EPA will act on those portions of the Interstate Transport SIP that address the requirement ofsection 110(a)(2)(D)(i)(I) that emissions from the state's sources do not "interfere with maintenance" ofthe 1997 8-hourozone NAAQS in any other state. 

### V. Statutory and Executive Order Review Underthe Clean Air Act, the Administrator is required to approve a SIP submissionthat complies with the provisions ofthe Act and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteriaofthe 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. Forthat reason, this action:
• Is not a "significant regulatory action" subject to reviewby the Office ofManagement and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
• Does not impose an information collection burden under the provisions ofthe Paperwork Reduction Act (44 U.S.C. 3501 

### etseq.);
• Is certified as not having a significant economic impact on a substantial number ofsmall entities under the Regulatory Flexibility Act (5 U.S.C. 601 

### 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 significantregulatory action based on health or safety risks subject to Executive Order 13045 (62 FR 19885, April 23, 1997);
• Is not a significantregulatory action subject to Executive Order 13211 (66 FR 28355, May 22,2001);
• is not subjectto requirements ofSection 12(d) ofthe National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application ofthose requirements would be inconsistent with the Clean Air Act; and
• Does not provide EPA with the discretionary authority to address, as appropriate, disproportionate human health or environmental effects, using practicable and legally permissible methods, underExecutive Order 12898 (59 FR7629, February 16, 1994). In addition, this rule does not have tribal implications as specified by Executive Order 13175 (65 FR 67249, November 9, 2000), becausethe SIP is not approved to apply in Indian country located in the state, and EPA notes that it will not impose substantial direct costs on tribal governments orpreempt tribal law. The Congressional ReviewAct, 

### 5 U.S.C. 801 

### etseq., 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 ofthe rule, to each House ofthe Congress and to the Comptroller General ofthe United States. EPA will submit areport containingthis action and other required information to the U.S. Senate, the U.S. House ofRepresentatives, and the Comptroller General ofthe United States prior to publication ofthe rule in the Federal Register. A major rule cannot take effect until 60 days after 39

### IDENTIFICATION OFDOCUMENT: Approval and Promulgation ofState Implementation Plans; State ofColorado; InterstateTransport ofPollution Revisions for the 1997 8-hourOzone NAAQS: "SignificantContribution to Nonattainment" Requirement. FinalRule. (EPA-R08-0AR-2007-0645) Page40 of41. it is published inthe Federal Register. This action is not a "n1ajorrule" as defined by 5 U.S.C. 804(2). Under section 307(b)(l) ofthe Clean Air Act, petitions forjudicialreview ofthis action must be filed in the United States Court ofAppeals for the appropriate circuit by [FEDERAL REGISTER OFFICE: insert date 60 days from date ofpublication ofthis document in the Federal Register]. Filing apetition for reconsideration bythe Administrator ofthis final rule does not affect the finality ofthis action for the purposes of judicial review nor does it extendthe time within which apetition forjudicialreview may be filed, and shall not postponethe effectiveness ofsuchrule or action. This action may not be challenged later in proceedings to enforce its requirements. (See section 307(b)(2).) 

### List ofSubjects in 40 CFRPart52 Environmental protection, Airpollution control, Carbon monoxide, Incorporation by reference, Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeepingrequirements, Sulfur oxides, Volatile organic compounds. 

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

### etseq.



# silz/ouJID Dated Carol Rushin Deputy Regional Administrator Region 8


### 4040 CFRpart 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 addedto read as follows: § 52.352 Interstate transport (a) Addition to the Colorado State Implementation Plan ofthe 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