UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

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

and E nvironment 4300 Cherry Creek Drive South Denver, CO 80246-1530
Dear Ms. Rudolph: 1595 Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http ://www
. epa.gov/region08 

# AUG 212013

This letter responds to Colorado Department of Public Health and Environment's (CDPHE) June 28, 2013, submittal for approval of a regional high wind exceptional event demonstration in southern Colorado. CDPHE determined that thi s regional high wind event caused emi ssion exceedances ofthe PM 10 NAAQS at the monitors in Pagosa Springs, Alamosa, Durango, Telluride, Crested Butte , and Mt. Crested Butte on April 5, 2010. EPA has reviewed the documentation provided by CDPHE to demonstrate that these exceedances on April 5, 2010, meet the criteria for an exceptional event under the Exceptional Events Rule (EER), 40 CFR 50. 14. EPA concurs based on the weight of evidence that CDPHE has successfull y made the demonstrations necessary to comp ly with 40 CFR 50.14 at the Pagosa Springs, Alamosa, and Durango locations. The EPA has added additional data for the demonstration ofthe exceedance in Telluride in the attached Tec hni cal Support Document so that the EPA can al so concur on that Exceptiona l Event (EE). The E PA is taking no action on the flagged data points at the Crested Butte and Mt. Crested Butte monitor s. Due to the large number ofEE demonstration packages that EPA Region 8 receives, only those that occur at monitors which have a potential bearing on regulatory activities are being reviewed at this time. In addition, CDPHE has met the schedul e and procedural requirements in section 50.14( c) with respect to th e demonstration
. A more detailed assessment ofCDPHE's demonstration is enclosed. My staff has , or sh ortly will, enter "concurrence flags" for the Pagosa Spri ngs, Alamosa, Durango , and Telluride data into EPA's Air Qual ity System (AQS). Based on th ese determinations, EPA wi ll exclude these data from the following types of calculations and activities:
• EPA's AQS will not count these days as exceedances when generating user reports, or include them in design values estimates, unless the AQS user specifica lly indicates that they should be included.• EPA will accept the exclus ion ofthese data for the purposes of sel ecting appropriate background concentrations for New Source Review air quality analyses. 1 • EPA will accept the exclusion ofthese data for the purposes of selecting appropriate background concentrations for transportation conformity hot spot analyses. 2 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 applies to determinations regarding the attainment status or c lassification ofthese areas. Final actions will take p l

ace 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 10 NAAQS. If you have any questions or wish to discuss this matter further, please contact Carl Daly at (303) 312-6416.

Regional Administrator Enclos ure
cc: William Allison, CDPHE Air Pollution Control Division

1 Jf EPA is the permitting authority, EPA will propose permits on this basis
. If EPA i s commenting on another permitting authority's proposed action , EPA's comments will be consistent with the determination s in this Jetter
. 2 Applicable only to PM1 o and PM 2$ 2 

# G) Printed on Recycled Paper