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/region08 

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 

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

March 30, 2012, submittal for approval of a 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 of the 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 of evidence, 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 of CDPHE'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 of this data for the purposes of selecting 

appropriate background concentrations for New Source Review air quality 

analyses. 1 

• The EPA will accept the exclusion of this data for the purposes of selecting 

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 of this 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 staff have 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 Pollution Control Division 

Gordon Pierce, CDPHE Air Pollution Control Division, Technical Services Program 

1

IfEPA is the pennitting authority, EPA will propose pennits on this basis. If EPA is commenting on another 

rennitting authority's proposed action, EPA's comments will be consistent with the detenninations in this letter. 

Applicable only to PM10 and PM2.

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2 

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