UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGIONS

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 ://www

. epa . gov/regionq8



# SEP 16 2013

RE : High Wind Caused PM10 Exceedances in Pagosa Springs , Alamosa, and Grand Jun ction on May 22 and 23,2010 Dear Ms. Rudolph: This letter responds to Colorado Department ofPublic Health and Environment's (CDPHE) June 2 8 , 20 1 3, submittal for approval of a regional high wind exceptional event demonstration in sout hern Colorado. CDPHE determined that this regional hi gh wind event caused exceedances ofthe PM 10 Na tional Ambient Air Qua lity Standards (NAAQS) at the monitors in Pagosa Springs, Alamosa, and Grand Junction on May 22 and 23,2010. The EPA has reviewed the documentation provided by CDPHE to demonstrate that the se exceedances meet the criteria for an exceptional event under the Exceptiona l Events Rule (EER), 40 CFR 50. 14
. The EPA concurs, based on the weight ofevidence, that CDPHE has successfully made the demonstrations necessary to comply with 40 CFR 50.14 at the Pagosa Spr ing s and Alamosa locations on May 22, 2010. As explained in the enclosed Technical Support Document (TSD) for the May 22 and 23, 2010 Exceptiona l Events (EE), the EPA is taking no action at this time on the flagged data points at the Grand Junction Clifton and Grand Junction Powell monitors. The EPA encourages CDPHE to submit further information on the controls employed on or immediately prior to May 23, 20 10 in Grand Junction that will allow the agency to concur on th e flagged data. We are available to di scuss the issue with CDPHE s taff. Fo r the exceedances in Pagosa Springs and Alamosa, 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 staffhas entered "concurrence flags" for the May 22,2010 Pagosa Springs and A lamosa data into the EPA's Air Quality System {AQS). Based on these determinations , the EPA will exclude these data from th e following types ofcalculatio ns 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 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 ofthese 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 PM10 NAAQS. 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,

# ~\~**~LA** Shaun L. McGrath 

# W. Regional Administrator Enclosure
cc: William Allison, CDPHE Air Pollution Control Division Gordon Pierce, CDPHE Air Pollution Control Division, Technical Services Program

1 IfEPA 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 Applicable only to PM 10 and PM2
.s 2 

### @Printedon Recycled Paper