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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

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REGION IX 17 :“ L PRO1 75 Hawthorne Street

San Francisco, CA 94105-3901

OFFICE OF THE JUL u i 2013 REGIONAL ADMINISTRATOR Mr. Eric Massey

Director, Air Division

Arizona Department of Environmental Quality

1110 W. Washington St.

Phoenix. Arizona 85(07

Dear Mr. Massey:

This letter responds to Arizona Department of Environmental Quality’s (ADEQ) February 13. 2013

submittal regarding 37 exceeedanccs of the 24—hour PIV1 10 standard that occurred at several monitoring

stations within the Phoenix PM10 nonattainment area on the following days: September ii and 12, 2011.

June 16, June 27. July 11. August 11, August 14. and September 6, 2012.

ADEQ’s submittal included documentation that these exceedances were caused by high wind

exceptional events. EPA has reviewed the documentation provided by ADEQ to demonstrate that the

exceedances on these days meet the criteria for an exceptional event in the Exceptional Events Rule

(EER). EPA concurs based on the weight of the evidence that the exceedances were caused by high

wind exceptional events and finds that ADEQ has successfully made the demonstrations referred to in

40 CPR 50. 14 to EPA’s satisfaction. In addition, ADEQ has met the schedule and procedural

requirements in section 50.14(c) with respect to the same data. A more detailed assessment of ADEQ’s

demonstration is enclosed. My staff has or shortly will enter “concurrence flags” for these data into

EPA’s AQS data system.

Based on these determinations. EPA will exclude these data from the following types of calculations and

activities:

• EPA’s Air Quality Data system (AQS) will not count these days as exceedanees when

generating user reports, or include them in design values estimates, unless the AQS user

specifically indicates that they should be included.

• EPA will accept the exclusion of these data for the purposes of selecting appropriate

background concentrations for New Source Review air quality analyses.’

• EPA will accept the exclusion of these data for the purposes of selecting appropriate

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background concentrations for transportation conformity hot spot analyses. 2

data will continue to be publicly available, but EPA’s publications and public

information statements on the status of air quality in the affected area will not reflect these

data in any summary statistic of potential regulatory application, unless such inclusion is

specifically noted.

liwe are the pernlitting authority, we will propose permits on this basis. If we are commenting on another permitting

authority’s proposed action, our comments will be consistent with the determinations in this letter. 2 Applicable only to PM10 and PM2

These data may be included in statistics intended to describe trends in actual air quality in the area.

Printed on Recycled Paper
In addition. EPA will rely on calculated values that exclude these data in proposed regulatory actions.

such as a proposed designation. classification, attainment demonstration, or finding as to whether the

Phoenix PM10 nonattainment area has met the PM10 NAAQS. These regulatory actions require EPA to

provide an opportunity for public comment prior to taking a final Agency action. If EPA is pursuing one

of these actions for the Phoenix PM10 nonattainment area. EPA will open a new comment period during

which EPA may receive comments on the exceptional event submission you have made and the

determinations conveyed in this letter. If so, we must consider and respond to those comments before

taking final regulatory action. Accordingly, the determinations conveyed in this letter do not constitute

final EPA action regarding any matter on which EPA is required to provide an opportunity for public

comment. In particular. this point applies to determinations regarding the attainment status or

classification of the area. Final actions will take place only after EPA completes notice and comment

rulemaking on those determinations. As an additional clarification, the determinations conveyed in this

letter are applicable only to determinations incorporating the submitted data relative to the PM in

NAAQS.

If you have any questions or wish to discuss this matter further, please contact Deborah Jordan, Director

of the Air Division at (415) 947-8715.

Sincerely,

/ /4

1’kiared Blumenfeld

Enclosure

cc: Ms. Theresa Rigney. ADEQ