Approval and Promulgation of Implementation Plans; Idaho, 72705-72719 [2010-29626]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 75, Number 227 (Friday, November 26, 2010)]
[Rules and Regulations]
[Pages 72705-72719]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-29626]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R10-OAR-2010-0669; FRL-9231-2]


Approval and Promulgation of Implementation Plans; Idaho

AGENCY: Environmental Protection Agency.

ACTION: Final rule.

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SUMMARY: EPA is approving a State Implementation Plan (SIP) revision 
submitted by the State for Idaho for the purpose of addressing the 
``good neighbor'' provisions of the Clean Air Act (the Act or CAA) 
section 110(a)(2)(D)(i) for the 1997 8-hour ozone National Ambient Air 
Quality Standards (NAAQS or standards) and the 1997 PM2.5 
NAAQS. This SIP revision addresses the requirement that the State of 
Idaho's SIP have adequate provisions to prohibit air emissions from 
adversely affecting another state's air quality through interstate 
transport. In this action, EPA is approving the Idaho Interstate 
Transport SIP provisions that address the requirement of section 
110(a)(2)(D)(i) that emissions from Idaho sources do not significantly 
contribute to nonattainment of the 1997 8-hour ozone NAAQS and the 1997 
PM2.5 NAAQS in any other state, interfere with maintenance 
of the 1997 8-hour ozone NAAQS and the 1997 PM2.5 NAAQS in 
any other state, and interfere with measures required in the SIP of any 
other state under part C of subchapter I of the CAA to prevent 
significant deterioration of air quality. This action is being taken 
under section 110 and part C of subchapter I of the CAA.

DATES: This action is effective on December 27, 2010.

ADDRESSES: Copies of the State's SIP revision and other information 
supporting this action are available for inspection at EPA Region 10, 
Office of Air, Waste, and Toxics (AWT-107), 1200 Sixth Avenue, Suite 
900, Seattle, Washington 98101.

FOR FURTHER INFORMATION CONTACT: Donna Deneen, EPA Region 10, Office of 
Air, Waste, and Toxics (AWT-107), 1200 Sixth Avenue, Seattle, 
Washington 98101, or at (206) 553-6706.

SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we'', 
``us'' or ``our'' are used, we mean EPA. Information is organized as 
follows:

Table of Contents

I. What action is EPA taking?
II. What is the background for this action?
III. Response to Comments
    A. Comments Relating to the ``Significant Contribution to 
Nonattainment'' Element
    B. Comments Relating to the ``Interfere With Maintenance'' 
Element
    C. Comment Relating to Section 110(l)
IV. Final Action
V. Scope of Action

I. What action is EPA taking?

    EPA is approving a portion of Idaho's Interstate Transport State 
Implementation Plan (SIP) revision for the 1997 8-hour ozone and 1997 
PM2.5 NAAQS submitted by the Idaho Department of Quality 
(IDEQ) on June 28, 2010. Specifically, we are approving the portion of 
the plan that addresses

[[Page 72706]]

the following elements of CAA section 110(a)(2)(D)(i): (1) Significant 
contribution to nonattainment of these NAAQS in any other state, (2) 
interference with maintenance of these NAAQS by any other state, and 
(3) interference with any other state's required measures to prevent 
significant deterioration (PSD) of its air quality with respect to 
these NAAQS. IDEQ addressed element (4), interference with any other 
state's required measures to protect visibility, by referring to its 
Regional Haze SIP, which will be submitted separately. EPA will take 
action on the visibility element in a separate action. None of the 
findings and conclusions in this notice, accordingly, relate to EPA's 
analysis of interference with another state's required measures to 
protect visibility. EPA will also take action on the portion of Idaho's 
SIP that addresses the 2006 PM2.5 NAAQS \1\ in a separate 
action.
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    \1\ The PM2.5 standard was revised in 2006. See 
``National Ambient Air Quality Standards for Particulate Matter,'' 
at 71 FR 61144 (October 17, 2006).
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II. What is the background for this action?

    On July 18, 1997, EPA promulgated new standards for 8-hour ozone 
and fine particulate matter (PM2.5). This action is being 
taken in response to the promulgation of the 1997 8-hour ozone NAAQS 
and 1997 PM2.5 NAAQS. This action does not address the 
requirements of the 2006 24-hour PM2.5 NAAQS or the 2008 8-
hour ozone NAAQS; those standards will be addressed in a future action.
    Section 110(a)(1) of the CAA requires states to submit SIPs to 
address a new or revised NAAQS within three years after promulgation of 
such standards, or within such shorter period as EPA may prescribe. 
Section 110(a)(2) lists the elements that such new SIPs must address, 
as applicable, including section 110(a)(2)(D)(i) which pertains to 
interstate transport of certain emissions. On August 15, 2006, EPA 
issued its ``Guidance for State Implementation Plan (SIP) Submissions 
to Meet Current Outstanding Obligations Under Section 110(a)(2)(D)(i) 
for the 8-hour ozone and PM2.5 National Ambient Air Quality 
Standards'' (2006 Guidance) for SIP submissions that states should use 
to address the requirements of section 110(a)(2)(D)(i). EPA developed 
this guidance to make recommendations to states for making submissions 
to meet the requirements of section 110(a)(2)(D) for the 1997 8-hour 
ozone standards and 1997 PM2.5 standards.
    On June 28, 2010, we received a SIP revision from the State of 
Idaho to address the requirements of section 110(a)(2)(D)(i) for both 
the 1997 8-hour ozone NAAQS and 1997 PM2.5 NAAQS. The state 
based its submittal on EPA's 2006 Guidance. As explained in the 2006 
Guidance, the ``good neighbor'' provisions in section 110(a)(2)(D)(i) 
require each state to submit a SIP that contains adequate provisions to 
prohibit emissions from sources within that state from adversely 
affecting another state in the ways contemplated in the statute. 
Section 110(a)(2)(D)(i) identifies four distinct elements related to 
the evaluation of impacts of interstate transport of air pollutants. In 
this rulemaking EPA is addressing the first three elements: (1) 
Significant contribution to nonattainment of these NAAQS in any other 
state, (2) interference with maintenance of these NAAQS by any other 
state, and (3) interference with any other state's required measures to 
prevent significant deterioration (PSD) of its air quality with respect 
to these NAAQS. Idaho asserted in its SIP submission that its current 
SIP is adequate to prevent such contribution and interference, and thus 
no additional controls or revisions are needed with respect to the 1997 
8-hour ozone NAAQS and 1997 PM2.5 NAAQS.
    On September 13, 2010, EPA published a proposal to approve the 
portion of Idaho's SIP submission that addresses the three elements of 
CAA section 110(a)(2)(D) for both the 1997 8-hour ozone NAAQS and 1997 
PM2.5 NAAQS: (1) Significant contribution to nonattainment 
of these NAAQS in any other state, (2) interference with maintenance of 
these NAAQS by any other state, and (3) interference with any other 
state's required measures to prevent significant deterioration (PSD) of 
its air quality with respect to these NAAQS (75 FR 55494). EPA finds 
that Idaho's Interstate Transport SIP provisions addressing elements 
(1), (2), and (3) of section 110(a)(2)(D)(i) are consistent with the 
requirements of the CAA.

III. Response to Comments

    EPA received one letter from WildEarth Guardians (WG) commenting on 
several aspects of EPA's proposed approval of the Idaho Interstate 
Transport SIP. These comments addressed the ``significant contribution 
to nonattainment,'' and ``interfere with maintenance,'' elements of the 
SIP for the 1997 8-hour ozone and 1997 PM2.5 NAAQS. WG also 
alleged in its comments that EPA failed to comply with the requirements 
of CAA Section 110(l) with respect to the attainment and maintenance of 
the current NAAQS. No comments were received that specifically 
addressed EPA's proposed approval of the ``interfere with any other 
state's required measures to prevent significant deterioration'' 
elements of the SIP for the 1997 8-hour ozone and 1997 PM2.5 
NAAQS. In this section EPA summarizes and responds to the significant 
adverse comments submitted by the commenter.

A. Comments Relating to the ``Significant Contribution to 
Nonattainment'' Element

    Comment No. 1--WG argued that Idaho and EPA did not appropriately 
assess impacts to nonattainment in downwind states. According to WG, 
Idaho failed to assess significance of downwind impacts in accordance 
with EPA guidance and precedent. The commenter identified statements by 
EPA in the context of the 1998 NOX SIP Call as the 
applicable guidance for this purpose. WG asserts that, based on the 
precedent of the NOX SIP Call, the following issues need to 
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 the upwind state's emissions are linked; (c) the 
ambient impact of the emissions from the upwind state's sources on the 
downwind nonattainment problems; and (d) the availability of highly 
cost-effective control measures for upwind emissions. 63 FR 57356, 
57376 (October 27, 1998).
    EPA Response--EPA disagrees with the commenter's conclusions 
regarding the relevant guidance and standards necessary to determine 
whether or not a state's emissions contribute significantly to 
nonattainment in another state. Section 110(a)(2)(D) does not 
explicitly specify how states or EPA should evaluate the existence of, 
or extent of, interstate transport and whether such transport is of 
sufficient 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 
and its application to factual situations before the Agency.
    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

[[Page 72707]]

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 used in 
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 of widespread interstate 
transport.
    The commenter failed to acknowledge that EPA issued specific 
guidance making recommendations to states about how to address section 
110(a)(2)(D) in SIP submissions for the 8-hour ozone and 
PM2.5 NAAQS. 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 (``2006 Guidance'').\2\ The 2006 
Guidance postdated the NOX SIP Call, and was developed by 
EPA specifically to address SIP submissions for the 1997 8-hour ozone 
and PM2.5 NAAQS. In EPA's proposal, this Guidance was 
identified by the Agency as applicable to the analysis before it.
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    \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 at the regulations.gov Web site as Document ID 
No. EPA-R10-OAR-2010-0669-0005.
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    In the 2006 Guidance, EPA 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 110(a)(2)(D) for the 
1997 8-hour ozone and PM2.5 NAAQS by complying with CAIR 
itself. For states outside the CAIR rule region, however, EPA 
recommended that states develop their SIP submissions for section 
110(a)(2)(D) considering relevant information.
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    \3\ 2006 Guidance at 3.
    \4\ Id.
    \5\ In this action, ``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 Call; Final Rule.'' 70 FR 25162.
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    EPA explicitly recommended that relevant information for section 
110(a)(2)(D) submissions addressing significant contribution to 
nonattainment ``might include, but is not 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 
information 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 and 
in light of the cost of control to mitigate emissions that resulted in 
significant contribution.\7\
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    \6\ 2006 Guidance at 5.
    \7\ Id.
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    WG did not acknowledge or discuss EPA's 2006 Guidance for section 
110(a)(2)(D) SIP submissions for the 1997 8-hour ozone and 
PM2.5 NAAQS, even though it was specifically identified and 
applied in EPA's proposal. EPA believes that the Idaho submission and 
EPA's evaluation of it were consistent with EPA's 2006 Guidance for the 
1997 8-hour ozone and PM2.5 NAAQS. For example, as discussed 
in the proposal notice, the state and EPA considered information such 
as monitoring data in Idaho and downwind states, geographical and 
meteorological information, and technical studies of the nature and 
sources of nonattainment problems in various downwind states. These are 
among the types of information that EPA recommended and that EPA 
considers relevant under the circumstances of this action. Thus, EPA 
has concluded that the state's submission meets the requirements of 
section 110(a)(2)(D) and that EPA's evaluation of the state's SIP is 
consistent with the applicable 2006 Guidance and the Act.
    Finally, EPA notes that the considerations in the 2006 Guidance are 
consistent with the concepts that WG identified as applicable from the 
NOX SIP Call: (a) The overall nature of the problem; (b) the 
extent of the downwind nonattainment problems to which the upwind 
state's emissions are linked; (c) the ambient impact of the emissions 
from the upwind state's sources on the downwind nonattainment problems; 
and (d) the availability of highly cost-effective control measures for 
upwind emissions. These factors were taken into account in EPA's 
analysis of the Idaho SIP with the exception of consideration of the 
costs of controls for sources. EPA did not evaluate those costs because 
the available evidence indicated that there is very little contribution 
from emissions from Idaho sources to nonattainment in other states.
    Comment No. 2 --WG objected to EPA's proposed approval on the 
grounds that Idaho and EPA failed to adequately analyze and assess the 
contribution from Idaho's emissions to downwind states, and did not 
conduct an actual assessment of the significance of any such 
contribution or impacts.
    EPA Response--EPA disagrees with WG's characterization of Idaho's 
and EPA's demonstration and analysis. WG again assumes that section 
110(a)(2)(D) explicitly demands the type of modeling analysis that the 
commenter advocates throughout its comments. WG contends that any 
analytical approach that is not identical to the approach used in the 
NOX SIP Call is impermissible. In addition, WG failed to 
acknowledge that in other actions under section 110(a)(2)(D), EPA has 
used a variety of analytical approaches, short of modeling, to evaluate 
whether a specific state is 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).
    EPA's analysis took into account meteorological conditions, 
monitoring data, distance, topography and other quantitative and 
qualitative forms of available information to evaluate and identify a 
potentially significant contribution from Idaho's emissions to 
nonattainment of the 1997 8-hour ozone and 1997 PM2.5 NAAQS 
in other states. As noted in EPA's proposal, no single piece of 
information informing this analysis is, by itself, dispositive of the 
issue. Instead, the total weight of all the evidence taken together was 
used to evaluate significant contributions to violations of the 1997 8-
hour ozone or 1997 PM2.5 NAAQS in another state. Based on 
the available information,

[[Page 72708]]

using a combination of quantitative data and qualitative analyses, we 
concluded emissions from Idaho do not contribute significantly to 
downwind ozone nonattainment. Thus, contrary to WG's assertion, EPA did 
perform an analysis and assessment that formed a reasonable basis for 
the conclusion that emissions from Idaho do not contribute 
significantly to downwind ozone and PM2.5 nonattainment, 
using a combination of quantitative data and qualitative analyses. EPA 
does not agree that the type of analysis advocated by WG is required by 
the statute and is necessary to support a rational determination in 
this instance.
    Comment No. 3--WG objected to EPA's proposed approval because EPA's 
assessment of impacts on downwind states was based upon monitoring data 
in those states, and WG alleges that this is not an adequate means of 
evaluating significant contribution to nonattainment. WG is concerned 
that the impacts of Idaho's emissions in areas without monitors were 
not assessed and that EPA only assessed ``impacts to areas that are 
designated as nonattainment or with monitors that have recorded 
violations of the ozone and PM2.5 NAAQS.'' WG argued that 
this reliance on monitoring data is inconsistent with both section 
110(a)(2)(D) and with EPA's guidance provided in the NOX SIP 
Call. In support of its objections, WG quoted statements from the 
NOX SIP Call proposal in which EPA discussed its proposed 
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 110(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)(1)(A)(I)).''

    According to WG, 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, WG 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 WG's arguments. First, WG 
misunderstands the point that EPA was making in quoted statement from 
the NOX SIP Call 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 107(d)(1), or for a redesignation to 
nonattainment for an existing NAAQS under section 107(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 107(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 110(a)(1) requires states to 
make SIP submissions that address section 110(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 110(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 CAIR rulemaking and in the matter at hand.
    WG's misunderstanding of EPA's statement concerning designation 
status evidently caused WG 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 without monitors, nor did the CAIR 
rulemaking. 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.\8\
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    \8\ Michigan v. U.S. EPA, 213 F.3d 663, 674-681 (DC 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 of CAIR).
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    Finally, EPA disagrees with WG's argument that the assessment of 
significant contribution to downwind nonattainment must include 
evaluation of impacts on non-monitored areas. First, neither section 
110(a)(2)(D)(i)(I) provisions, nor the 2006 Guidance support WG's 
position, as neither refers to any requirement or recommendation to 
assess air quality in non-monitored areas.\9\ 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 of the ozone and/or PM2.5 
NAAQS.\10\ 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, WG is simply in error that EPA has not previously 
evaluated the presence and extent of interstate transport under section 
110(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. Reliance on monitoring data is 
reasonable and appropriate, because data from a properly placed federal 
reference method monitor is the way in which EPA ascertains that there 
is a violation of the 1997 8-hour ozone or PM2.5 NAAQS in a 
particular area. Put another way, in order for there to be significant 
contribution to nonattainment for the 1997 8-hour ozone or 
PM2.5 NAAQS, there must be a monitor with data showing a 
violation of that NAAQS. EPA concludes that by considering data from 
monitored areas, its assessment of whether emissions from Idaho 
contribute significantly to ozone or PM2.5 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.
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    \9\ 2006 Guidance, p. 5.
    \10\ ``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 1-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.
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    Comment No. 4--In support of its comments that EPA should assess 
significant contribution to nonattainment in nonmonitored areas,

[[Page 72709]]

WG argued that existing modeling performed by another organization 
``indicates that large areas of neighboring states will likely violate 
the ozone NAAQS.'' According to WG, 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''). WG asserted that: 
``Slide 28 of this presentation displays projected 4th highest 8-hour 
ozone reading for 2018 and indicates that air quality in areas 
throughout Utah, Wyoming, Colorado, and Nevada will exceed and/or 
violate the 1997 ozone NAAQS. * * *'' In short, WG 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 in these western 
states.
    EPA Response--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 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 110(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 
110(a)(2)(D), and EPA's prior analytical approach has not been 
disturbed by the courts.
    Second, WG'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 [our emphasis] 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 
WG were technically sound, the conclusion drawn from it by WG is 
inaccurate and does not support its claim of projected violations of 
the NAAQS in surrounding states.
    EPA has also reviewed the WRAP presentation submitted by WG and 
believes that there was a substantial error in the WRAP modeling 
software that led to an overestimation of ground level ozone 
concentrations. A recent study conducted by Environ for the Four 
Corners Air Quality Task Force (FCAQTF; Stoeckenius et al., 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 stratospheric 
ozone.\11\ 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 WG's concerns about large expanses of 8-hour 
ozone nonattainment areas projected for 2018 in areas without monitors.
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    \11\ 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 Corners Region.'' Prepared for the New Mexico Environment 
Department, Air Quality Bureau, Santa Fe, NM, by ENVIRON 
International Corporation, Novato, CA.
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    Comment No. 5--As additional support for its assertion that EPA 
should require modeling to assess ambient levels in unmonitored 
portions of other states, WG relied on an additional study entitled the 
``Uinta Basin Air Quality Study (UBAQS).'' The commenter argued that 
the UBAQS study further supports its concern that limiting the 
evaluation of downwind impacts only to areas with monitors fails 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 corner of Utah are also currently in 
nonattainment and will be in nonattainment in 2012.\12\
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    \12\ The southwestern area referred to by the commenter includes 
portions of Washington, Iron, Kane, and Garfield Counties.
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    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 WG. Even taking the 
UBAQS modeling results at their face value, however, EPA 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 of the UBAQS analysis results for 
counties in Utah's southwestern corner: ``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, WG's interpretation of the predicted ozone concentrations 
shown in Figures 4-3a and 4-3b (pages 5 and 6 of the comment letter) is 
inaccurate. A close review of the 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 a specific concentration is not provided. If the ozone 
concentration is actually predicted to be smaller than or equal to 84.9 
ppb, then the area is attaining; if it is predicted as greater than 
84.9 ppb then it is not attaining. This means that 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 of them in attainment and the other in 
nonattainment, for the 1997 8-hour ozone NAAQS.
    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 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

[[Page 72710]]

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 comments.
---------------------------------------------------------------------------

    \13\ See ``UBAQS,'' pages 4-27 to 4-29.
    \14\ EPA. 2007. 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 (https://www.epa.gov/scram001/guidance/guide/final-03-pm-rh-guidance.pdf).
    \15\ DVC x RRF = DVF.
    \16\ See UBAQS, p. 4-28.
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    Comment No. 6--In support of its arguments that EPA should not 
limit assessment of significant contribution to nonattainment through 
evaluation of impacts at monitors, but include, through a modeling 
analysis, impacts where there are no such monitors, 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 O3 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 the 
evaluation of significant contribution to nonattainment in other states 
to a consideration of monitor data instead of modeling ambient 
pollutant levels because there are states with few or no non-urban 
monitors surrounding Idaho.
    EPA Response--EPA acknowledges that WG's observation 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, is 
factually correct. 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 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 is the subject of this rulemaking, but 
rather the 2008 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 the 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 monitoring network plans to EPA and EPA 
evaluates these to insure that they meet the applicable requirements. 
For example, Idaho itself submits just such a report on an annual 
basis, and EPA reviews it for adequacy.\17\ All other states submit 
comparable reports.
---------------------------------------------------------------------------

    \17\ EPA most recently reviewed the adequacy of the Idaho 
monitoring network on October 14, 2010. See letter dated October 14, 
2010 from Debra Suzuki, EPA Region 10, to Dave Broker, IDEQ.
---------------------------------------------------------------------------

    Comment No. 7--WG objected to EPA's proposed approval of the Idaho 
SIP submission because neither Idaho nor EPA performed a specific 
modeling analysis to assure that emissions from Idaho 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 Idaho 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 WG's proposition that only 
modeling can establish whether or not there is significant contribution 
from one state to the nonattainment of another. First, as noted above, 
EPA does not believe that section 110(a)(2)(D) requires a modeling 
analysis in all instances. 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 may rely upon as part of their section 110(a)(2)(D) submissions 
for the 1997 8-hour ozone and 1997 PM2.5 NAAQS. EPA has 
concluded that its qualitative approach to the assessment of 
significant contribution to downwind ozone and PM2.5 
nonattainment is consistent with EPA's 2006 Guidance.
    Second, EPA notes that WG's comment also reflects a 
misunderstanding of the approach EPA used in the remanded CAIR. In 
CAIR, EPA determined that several factors provided a reasonable basis 
to exclude certain western states from the ambit of that rulemaking: 
``[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 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 Idaho 
contributes significantly to violations of the 1997 8-hour ozone and 
PM2.5 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 Idaho sources do not 
contribute significantly to nonattainment, in accordance with the 
requirement of Section 110(a)(2)(D).
    Comment No. 8--In further support of its argument that EPA must use 
modeling to evaluate whether there is significant contribution to 
nonattainment under section 110(a)(2)(D), WG noted that EPA itself asks 
other agencies to perform such modeling in other contexts. As examples, 
the commenter cited four instances in which EPA commented on actions by 
other agencies and recommended the use of a 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 projects.\18\ WG 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 Idaho emissions and to insure compliance with Section 
110(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 than the statewide emissions at issue in an 
evaluation under section 110(a)(2)(D).
---------------------------------------------------------------------------

    \18\ WG's October 13, 2010, comment letter, pp. 9-10. The 
referenced letters have been included in the docket for this action.
---------------------------------------------------------------------------

    EPA Response--As explained above, EPA disagrees with WG's 
fundamental argument that modeling is required to evaluate significant 
contribution to nonattainment, whether by section 110(a)(2)(D), by EPA 
guidance, or by past EPA precedent. EPA's applicable guidance made 
recommendations as to different approaches that can satisfy 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. As indicated in our response to

[[Page 72711]]

Comment No. 7, the CAIR analysis excluded the western states based on a 
qualitative assessment of the regions topography, geography and 
meteorology.\19\
---------------------------------------------------------------------------

    \19\ 69 FR 4581, January 30, 2004.
---------------------------------------------------------------------------

    EPA believes that the commenter's references to EPA statements 
commenting on the actions of other agencies are inapposite. As WG is 
aware, those comments were made in the context of the evaluation of the 
impacts of various federal actions pursuant to the National 
Environmental Policy Act (NEPA), not the Clean Air Act. As explained 
above, section 110(a)(2)(D) governs this particular decision-making 
process, and EPA does not agree that modeling is always required to 
support the evaluation. EPA itself has relied on qualitative evidence 
for this purpose when the relevant record provides evidence sufficient 
to reach a reasoned determination.
    Comment No. 9--In further support of its argument that EPA should 
always require modeling to evaluate significant contribution to 
nonattainment, WG referred to EPA regulations governing nonattainment 
SIPs. The commenter referenced 40 CFR 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 argued that this regulation supports its 
position that modeling is required to satisfy the significant 
contribution element of 110(a)(2)(D).
    EPA Response--EPA disagrees with this comment. The cited language 
addresses the control strategy requirements when the necessity of 
controls has already been established. The cited provision requires a 
modeling analysis 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 Idaho do not contribute significantly to nonattainment 
for the 1997 8-hour ozone standard in any other states eliminates the 
need for a control strategy aimed at satisfying the section 
110(a)(2)(D) requirements. The provision cited by the commenter, 
therefore, is inapplicable in this context. 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 of the national 
standard that it implements,'' to refer to modeling for attainment 
demonstrations, an integral part of nonattainment area SIPs under 
subchapter I, part D of the CAA. This interpretation was upheld by the 
Sixth Circuit Court of Appeals. Wall v. U.S. EPA, 265 F.3d 426, 436 
(6th Cir. 2001). Thus, the commenter's cited regulation is not relevant 
to EPA's technical analysis assessing whether emissions from Idaho 
contribute significantly to nonattainment in any other states under 
section 110(a)(2)(D).
    Comment No. 10--WG referenced several modeling analyses of 
emissions in the western United States which it contends renders EPA's 
analysis inadequate. The commenter ``challenged'' EPA to prove the 
modeling results it presented are insufficient by presenting a contrary 
modeling analysis, and argued that EPA has an obligation to do so.
    Response: EPA disagrees with WG's contention that EPA is obligated 
to evaluate and disprove the modeling analyses it has submitted with a 
competing modeling analysis when other available information is 
available to dispute the modeling analysis. EPA's interpretation of 
section 110(a)(2)(D) is that the statute does not explicitly require 
modeling, and while modeling can be useful in certain circumstances, 
there is no obligation to use it to evaluate whether or not there is 
significant contribution to nonattainment. Section 110(a)(2)(D)(i) does 
not specify the forms of evidence to be used for meeting the 
requirements, and the 2006 Guidance specifically recommends other forms 
of information that states might wish to evaluate as part of their 
section 110(a)(2)(D) submissions. We evaluated whether Idaho's SIP met 
the requirement of section 110(a)(2)(D)(i) based on EPA's 2006 Guidance 
and have a reasonable basis, as discussed in the proposed approval, for 
concluding that Idaho has met the requirement of 110(a)(2)(D)(i) for 
the 1997 8-hour ozone and 1997 PM2.5 NAAQS in the absence of 
a modeling analysis.
    Comment No. 11--WG also objected to EPA's proposed approval of the 
Idaho 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 110(a)(2)(D) in particular. 
According to the commenter, there is no regulatory support for using a 
``weight-of-evidence'' approach to assessing air quality impacts. The 
commenter asserted that EPA neither cited nor quoted regulations or 
policy that provides for this, and failed to lend any specific meaning 
to the phrase through its proposed approval. Finally, the commenter 
asserted, without explaining, its belief that EPA failed to address 
``several relevant factors related to the determination of whether 
Idaho contributes significantly to nonattainment undermines the 
agency's reliance on any `weight-of-evidence' approach.''
    EPA Response--EPA agrees with WG that neither the CAA generally, 
nor section 110(a)(2)(D) specifically, include the explicit phrase 
``weight of evidence.'' It simply does not follow, however, that it is 
inappropriate for EPA to use such an approach in this context. As 
explained above, section 110(a)(2)(D) does not explicitly stipulate how 
EPA may assess whether there is a significant contribution to 
nonattainment in other states. Through past actions such as CAIR, EPA 
has used a weight of evidence approach to exclude some states from 
further consideration.\20\ As described above, in EPA's 2006 Guidance 
the Agency specifically recommended types of information that states 
might wish to rely upon to evaluate the presence of, and extent of, 
interstate 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.
---------------------------------------------------------------------------

    \20\ See: 69 FR 4581, January 30, 2004.
---------------------------------------------------------------------------

    Specifically, EPA's technical analysis in the September 13, 2010 
proposed 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 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 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 [our emphasis].'' \21\ On the basis of this 
Guidance, Idaho and EPA chose to assess the impacts of emissions from 
Idaho sources on nonattainment areas for the 1997 ozone NAAQS and 1997 
PM2.5 NAAQS in surrounding states through a weight of 
evidence approach

[[Page 72712]]

using quantitative and qualitative information such as monitoring data 
for those other states, Idaho's distance from areas with monitors 
showing violation of the NAAQS, meteorological conditions, and other 
characteristics for those areas. 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 our analysis do not invalidate the use 
of the weight of evidence approach.
---------------------------------------------------------------------------

    \21\ 75 FR 55494, September 13, 2010.
    \22\ ``As discussed above, EPA applied a multi-factor approach 
to identify the amounts of NOX emissions that contribute 
significantly to nonattainment.* * *'' 1998 SIP Call, 63 FR 57381, 
October 27, 1998.
---------------------------------------------------------------------------

    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 is by itself dispositive of the issue. Instead, the total 
weight of all the evidence taken together is used to evaluate 
significant contributions to violations of the 1997 8-hour ozone or 
1997 PM2.5 NAAQS in another state.'' (75 FR 55496).
    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. 12--WG questioned whether a regulatory provision from 
Idaho's SIP, IDAPA 58.01.013.203.02, that was identified in the 
proposed action constitutes a ``prohibition on emissions that 
significantly interfere with nonattainment.'' \23\ WG argued that this 
provision does not appear to ensure compliance with section 
110(a)(2)(D)(i)(I) because, the commenter explains, the provision 
applies only to stationary sources (actually point sources) and not to 
mobile or field burning emissions, and that all sources must be 
considered in order to meet the requirements of the statute. The 
commenter alleged that 110(a)(2)(D)(i)(II) applies to any source or 
other type of emission activity and, therefore, Idaho's SIP provision 
is inadequate if it is limited in its application to stationary 
sources. WG went on to identify emission inventory information to 
support its argument that mobile source emissions and agricultural 
burning emissions are significant sources of emissions in Idaho. The 
commenter questioned the assertion that the abovementioned regulatory 
provision provides authority to limit a source's emissions to ensure 
attainment in other states. WG also questioned how the provision would 
apply in attainment areas. Finally, the commenter concluded that the 
Idaho SIP does not appear to contain provisions that effectively 
prohibit emissions from any source from significantly contributing to 
nonattainment in any other state.
---------------------------------------------------------------------------

    \23\ EPA notes that WG appears to have incorrectly stated and 
conflated the two different standards presented in CAA section 
110(a)(2)(D)(i)(I) in this comment. EPA assumes that, due to the 
placement of this comment in a section that WG entitled ``Measures 
in the SIP do not Appear to Ensure that Idaho will not Significantly 
Contribute to Nonattainment'' and statements made later in the 
comment, that the comment applies only to EPA's proposed approval of 
the nonattainment prong of 110(a)(2)(D)(i)(I) and was not provided 
in reference to the maintenance prong.
---------------------------------------------------------------------------

    EPA Response--EPA agrees with the commenter's assertion that the 
requirements of section 110(a)(2)(D)(i)(I) are applicable to all source 
categories and not only to stationary sources. The commenter seems to 
have read EPA's proposed action to imply that the provisions cited by 
Idaho are the only consideration in evaluating whether Idaho has met 
the requirement regarding whether or not a state's emissions 
significantly contribute to violations of 1997 ozone and 1997 
PM2.5 standards in another state. In fact, these provisions, 
which provide IDEQ with the authority to require a permit if emission 
rate reductions are necessary to attain any ambient air quality 
standard, were identified by EPA in the proposed action as ``additional 
support for [EPA's] conclusion that emissions from Idaho sources do not 
significantly contribute to nonattainment in any other state * * *.'' 
As noted in EPA's proposed action, no single piece of information was 
by itself dispositive in evaluating Idaho's potential contribution to 
nonattainment in another state. EPA has taken into account the Idaho 
SIP as a whole, which includes but is not limited to the cited 
permitting provisions, and the actual contribution of emissions from 
Idaho to nonattainment receptors in other states to evaluate whether 
the significant contribution element has been met.
    EPA disagrees with the commenter's apparent view that under section 
110(a)(2)(D) SIPs must contain literal provisions 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. In conducting its analysis of 
whether or not the state's SIP is adequate, EPA evaluates the actual 
contribution of a state's emissions to nonattainment in another state 
and does not base its analysis on the written provisions of the SIP 
alone. 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 110(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 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 Idaho, then section 110(a)(2)(D)(i)(I) does not 
require any changes to a state's provisions. 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 110(a)(2)(D)(i) in the 2006 guidance, 
the CAIR Rule, and the NOX SIP call, none of which required 
the pro forma literal ``prohibition'' of the type advocated by the 
commenter.

B. Comments Relating to the ``Interfere With Maintenance'' Element

    Comment No. 1--The commenter stated that EPA inappropriately 
defined the term ``interfere with maintenance.'' It argued that EPA's 
definition appeared to be ``inappropriately conflated with the

[[Page 72713]]

definition of nonattainment.'' It argued that the definition of 
maintenance appeared to be tied to nonattainment, asserting that 
``unless an area has violated or is in violation of the NAAQS, the 
agency will not consider whether Idaho is interfering with that area's 
ability to maintain compliance with the NAAQS.'' For this reason, it 
argued EPA did not give independent meaning to the ``interfere with 
maintenance'' prong of section 110(a)(2)(D)(i)(I).
    The commenter also maintains that EPA's analysis did not consider 
Idaho's impacts on neighboring states that have not previously 
violated, but that ``may be barely attaining the NAAQS.'' To illustrate 
its contention that EPA has inappropriately defined ``interference with 
maintenance,'' the commenter pointed to information regarding Cache 
Valley, Utah, which it describes as an example of an area that has not 
violated the 1997 24-hour PM2.5 NAAQS, but that may be 
barely attaining the NAAQS and should, therefore, be classified as a 
maintenance receptor. The commenter did not provide any other concrete 
examples of areas that EPA should have identified as maintenance 
receptors.
    Response--The definition of maintenance used by EPA is consistent 
with the direction given to EPA by the Court of Appeals for the DC 
Circuit in North Carolina v. EPA, 531 F.3d 896 (DC Cir. 2008).\24\ In 
that case, the court analyzed the definition of ``interfere with 
maintenance'' used in the CAIR rule. The court found that the 
definition EPA used ``gave no independent significance to the 
`interfere with maintenance' prong of section 110(a)(2)(D)(i)(I) to 
separately identify upwind sources interfering with downwind 
maintenance.'' North Carolina at 910. It further reasoned that 
``[u]nder EPA's reading of the statute, a state can never ``interfere 
with maintenance'' unless EPA determines that at one point it 
``contribute[d] significantly to nonattainment.'' Id. Based on this 
analysis, the court found the definition unlawful holding that 
``[b]ecause EPA describes CAIR as a complete remedy to a section 
110(a)(2)(D)(i)(I) violation and does not give independent significance 
to the 'interfere with maintenance' language to identify upwind states 
that interfere with downwind maintenance, EPA unlawfully nullifies that 
aspect of the statute and provides no protection for downwind areas 
that, despite EPA's predictions, still find themselves struggling to 
meet NAAQS due to upwind interference in 2010.'' Id. at 910-911.
---------------------------------------------------------------------------

    \24\ As EPA noted in the proposal, the term ``interfere with 
maintenance'' is not defined in the CAA. As such, the term is 
ambiguous and EPA's interpretation of that term in this action is 
both reasonable and consistent with the overall goals of the CAA. By 
this approach, EPA is giving independent meaning to the term and 
supporting that interpretation with technical analysis to apply it 
to the facts of this action.
---------------------------------------------------------------------------

    The approach used by EPA to evaluate Idaho's SIP submission and to 
determine whether emissions from sources in Idaho interfere with 
maintenance in any other state directly addresses these flaws. It gives 
significant independent meaning to the term ``interfere with 
maintenance.'' It establishes a process to identify any specific 
receptors in downwind states that, even though they are projected to be 
in attainment and thus would not be nonattainment receptors, may have 
difficulty maintaining the NAAQS in question. These receptors are 
referred to as maintenance receptors.
    The methodology EPA used to identify maintenance receptors gives 
independent meaning to the term ``interfere with maintenance'' and 
establishes a process to identify projected attainment receptors that, 
based on the historic variability of air quality at that site (which 
may be due to variability in emissions and/or meteorology), may have 
difficulty maintaining the standard. As explained in greater detail 
below, the commenter's objection to EPA's approach appears to be based 
on the misconception that the methodology EPA used to identify 
maintenance sites was dependent on base year NAAQS violations.
    The commenter's statement that EPA's designation of maintenance 
receptors is ``firmly hitched to a finding that the maximum design 
value based on a single three-year period between 2003 and 2007 is in 
excess of the NAAQS'' appears to be based on a misunderstanding of the 
methodology used by EPA to identify maintenance receptors. EPA's 
methodology did not, as the commenter appears to assume, require a site 
to have a design value above the NAAQS for one of the three base 
periods (2003-2005, 2004-2006, 2005-2007) to be considered a 
maintenance site. The methodology is based on an analysis of the future 
year average and future year maximum design values. It does not depend 
on whether