UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

Ref: 8P-AR

Martha Rudolph 1595 Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http://www.epa .gov/reg i on08

# NOV21~.

Colorado Department of Public Health

and Environment 4300 Cherry Creek Drive South Denver, Colorado 80246-1530

Dear Ms. Rudolph: RE: High Wind PM10 Exceedance in Pagosa Springs on March 22, 2009

T his letter responds to Colorado Department ofPublic Health and Environment's (CDPHE) March 30, 2012, submittal for approval ofa regional high wind exceptional event demonstration in southern Colorado, which was amended on September 30,2013. CDPHE determined that this regional high wind event caused an exceedance ofthe PM10 National Ambient Air Quality Standards (NAAQS) at the monitor in Pagosa Springs on March 22, 2009. The EPA has reviewed the documentation provided by CDPHE to demonstrate that this exceedance met the criteria for an exceptional event under the Exceptional Events Rule (EER), 40 CFR 50.14. EPA concurs, based on the weight ofevidence, that CDPHE has successfully made the demonstration necessary to comply with 40 CFR 50.14 at the Pagosa Springs location on March 22, 2009. In addition, CDPHE has met the schedule and procedural requirements in section 50.14(c) with respect to the demonstration. A more detailed assessment ofCDPHE's demonstration is enclosed. My staff has entered "concurrence flags" for the March 22, 2009 Pagosa Springs data into the EPA's Air Quality System (AQS). Based on this determination, the EPA will exclude these data from the following types of calculations and activities:

• The EPA's AQS will not count this day as an exceedance when generating user reports , or include them in design values estimates, unless the AQS user specifically indicates that they should be included.• The EPA will accept the exclusion ofthis data for the purposes ofselecting appropriate background concentrations for New Source Review air quality analyses. 1
• The EPA will accept the exclusion ofthis data for the purposes ofselecting appropriate background

### cl~6~ntrailons**for** transportation conformity hot spot analyses. 2 The determination conveyed in this letter does not constitute final EPA action regarding any matter on which the EPA is required to provide an opportunity for public comment. In particular, this applies to determinations regarding the attainment status or classification ofthis area. Final actions will take place only after the EPA completes notice and comment rulemaking on those determinations. As an additional clarification, - the determination conveyed in this letter is applicable only to the PM10NAAQS. If you or your staffhave any questions or wish to discuss this matter further, please contact Carl Daly, Air Program Director, at (303) 312-6416.

Enclosure Shaun L. Me rath Regional Administrator

cc: William Allison, CDPHE Air Po llution Control Division Gordon Pierce, CDPHE Air Pollution Control Division, Technical Services Program

1IfEPA i s the pennitting authority, EPA will propose pennits on this basis. IfEPA is commenting on another rennitting authority's proposed action, EPA's comments will be consistent with the detenninations in this lett er. Applicable on ly to PM 10 and PM 2.5 2 

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