UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

Ref: 8P-AR
Martha Rudolph Colorado Department of Public Health

and Environment 4300 Cherry Creek Drive South Denver, Colorado 80246-1530 1595 Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http :/ lwww

. epa . gov/region08 

# SEP 16 

# 2013

RE: High Wind Ca u sed PM 10 Exceedances in Pagosa Springs, Alamosa, and Durango on Apri l 28 and 29,2010 Dear Ms. Rudolph : This letter respond s to Colorado Department of Public Health and Environment 's (CDPHE) June 28, 20 13, submitta l for approval of a regional high wind exceptional event demonstration in southern Colorado. CDPHE determined that this reg i onal high w ind event caused exceedances ofthe PM10 National Ambient Air Quality S tandards (NAAQS) at the monitors in Pago sa Springs, Alamosa, and Durango on April28 and 29,2010. T he EPA has reviewed the documentation prov ided by CDPHE to demonstrate that these exceedances meet the criteria for an exceptional event under the Excep tional Events Rule (EER), 40 CFR 50.14. EPA concurs, based on the weight of evidence, that CDPHE h as successfull y made the demo nstr ations necessary to comply with 40 CFR 50.14 at the Pagosa Springs, Alamosa, and Durango locations on April 28 and 29, 2010. CDPHE has met the schedule and procedural requirements in section 50.14( c) with respect to the demonstration. A more detailed assessment ofCDPHE's demo n stration is enclo sed. My staff has entered "concurrence flags " for the April 28 and 29, 2010 Pago sa Springs , A lamosa, and Durango data into the EPA's A ir Quality System (AQS). Based on these determination s, the EPA will exclude these data from the fo ll owing types of calcul ations and activities:

• The EPA's AQS will not count these days as exceedances when generating user reports, or include them in design values estimates, unle ss the AQS user s pec ifically indicate s that they s hould be included.• The EPA will accept the exclusion ofthese data for the purposes of selecting appropriate background concentrations for New Source Review air quality analyses. 1 • The EPA will accept the exclusion ofthese data for the purposes of selecting appropriate background concentrations for transportation conformity hot spot analyses? The determinations conveyed in this letter do 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 of these areas. Final actions will take place only after the EPA complet e s 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 PM10NAAQS. If you or your staff have any questions or wish to discuss this matter further, please contact Carl Daly, Air Program Director, at (303) 312-6416. Sincerely,

# ~ \9' Regional Administrator Enclosure

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

1If EPA is the permitting authority, EPA will propose permits on this basis. If EPA is commenting on another permitting authority's proposed action, EPA's comments will be consistent with the determinations in this letter. 2 Applicabl e only to PM1 o and PM 2.s 

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# G) Printed on Recycled Paper