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 Caused PM10 Exceedances in Pagosa Springs, 

Alamosa, and Durango on April 28 and 29,2010 

Dear Ms. Rudolph: 

This letter responds to Colorado Department of Public Health and Environment's (CDPHE) June 28, 

20 13, submittal for approval of a regional high wind exceptional event demonstration in southern 

Colorado. CDPHE determined that this regional high wind event caused exceedances of the PM10 

National Ambient Air Quality Standards (NAAQS) at the monitors in Pagosa Springs, Alamosa, and 

Durango on April28 and 29,2010. 

The EPA has reviewed the documentation provided by CDPHE to demonstrate that these exceedances 

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 successfully made the demonstrations 

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 demonstration is enclosed. My staff has 

entered "concurrence flags" for the April 28 and 29, 2010 Pagosa Springs, Alamosa, and Durango data 

into the EPA's Air Quality System (AQS). 

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

and activities: 

• The 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 specifically indicates that 

they should be included. 
• The EPA will accept the exclusion of these data for the purposes of selecting appropriate 

background concentrations for New Source Review air quality analyses. 1 

• The EPA will accept the exclusion of these 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 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 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 

1 If EPA is the permitting authority, EPA will propose perm its 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 Applicable only to PM1o and PM2.s 

2 

G) Printed on Recycled Paper