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, 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 this regional high wind event caused emission exceedances of the 

PM10 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 successfully made the 

demonstrations necessary to comply with 40 CFR 50.14 at the Pagosa Springs, Alamosa, and Durango 

locations. The EPA has added additional data for the demonstration of the exceedance in Telluride in the 

attached Technical Support Document so that the EPA can also concur on that Exceptional Event (EE). 

The EPA is taking no action on the flagged data points at the Crested Butte and Mt. Crested Butte 

monitors. 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 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, 

or shortly will, enter "concurrence flags" for the Pagosa Springs, Alamosa, Durango, and Telluride data 

into EPA's Air Quality System (AQS). 

Based on these determinations, EPA will 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 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. 1 

• EPA will accept the exclusion of these 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 classification of these areas. 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 10 NAAQS. 

If you have any questions or wish to discuss this matter further, please contact Carl Daly at 

(303) 312-6416. 

Regional Administrator 

Enclosure 

cc: William Allison, CDPHE Air Pollution Control Division 

1

Jf 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 Jetter. 2 Applicable only to PM1o and PM2$ 

2 

G) Printed on Recycled Paper