UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8

Ref: 8P-AR The Honorable John Hickenlooper Office ofthe Governor 136 State Capitol Building Denver, Colorado 80203 Dear Governor Hickenlooper: 1595 Wynkoop Street Denver, CO 80202-1129

Phone 800-227-8917 www.epa.gov/region08 

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Thank you for your staffs recommendations dated September 18, 2015, on air quality designations for the state ofColorado for the 2010 revision to the primary National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (S02). Reducing levels ofS02 pollution is an important part ofthe U.S. Environmental Protection Agency's (EPA's) commitment to a clean, healthy environment. Exposure to S02 can cause a range ofadverse health effects, including narrowing ofthe airways which can cause difficulty breathing and increased asthma symptoms. This letter is to notify you ofthe EPA's preliminary intentions regarding yourrecommended designations. On June 3, 2010, the EPA strengthened the health-based or "primary" standard for S02 by establishing a standard for 1-hour average S02 concentrations at a level of75 parts perbillion. Within one year after a new or revised standard is established, the Clean Air Act requires the Governor ofeach state to submit to the EPA a list ofall areas in the state, with recommendations for whether each areameets the standard. Through an interactive process, the EPA considers the recommendations and then promulgates designations for all areas across the country. On July 25, 2013, the EPA designated 29 areas in 16 states as nonattainment, but did not at that time designate other areas. Pursuant to a March 2, 2015, courtordered schedule, 1the EPA must complete the remaining S02 designations by three specific deadlines: July 2, 2016, December 31, 2017, and December 31, 2020. This current round ofdesignations, to be completed by July 2, 2016, addresses two groups ofareas: (1) areas that have newly monitored violations ofthe 2010 S02 NAAQS based on the most recent three calendar years ofcertified monitored ambient air quality data, and (2) areas that contain any stationary source that had not been announced as ofMarch 2, 2015, for retirement and that according to the EPA's Air Markets Database emitted in 2012 either (i) more than 16,000 tons ofS02 or (ii) more than 2,600 tons ofS02 with an annual average emission rate ofat least 0.45 pounds ofS02/mmBTU. Because the EPA has insufficient information to determine whether the following areas are meeting or not meeting the S02 NAAQS, the EPA intends to designate these areas as unclassifiable:

1Sierra Club v.McCarthy, No. 3-13-cv-3953 (SI) (N.D. Cal. Mar. 2, 2015). 

### 1Intended Unclassifiable Areas Colorado Springs* Morgan County* Intended Unclassifiable Counties El Paso County Morgan County
The asterisks(*) indicate the boundaries for these intended unclassifiable areas represent modifications to the boundaries that you have recommended. In this case, because your staffdid not recommend specific boundaries but instead recommended designations for the areas around the Pawnee and Martin Drake powerplants, the EPA has proposed full-county unclassifiable boundaries for the counties in which these sources are located. The enclosed Technical Support Document provides a detailed analysis that supports our intended designation decisions
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### Ifyour state has additional information that the EPA should considerprior to finalizing these designations,please submit it to us by April 19, 2016. We also will be publishing a notice in the Federal Register announcing a 30-day period for the public to provide input onthe EPA's intended designation decisions. We will promulgate the designations for these areas by July 2, 2016. We will designate all otherpreviously undesignated areas in the state on a schedule consistent with the prescribed timing ofthe court order, i.e
., by December 31 , 2017, or December 31 , 2020. We look forward to a continued dialogue with you and your staffas we work together to complete the area designations and implement the 2010 primary S02 standard. For additional information regarding designations under the S02 standard, please visit our website at www.epa.gov/so2designations. Should you have any questions, please do nothesitate to call me, or have your staffcontact Carl Daly ofmy staffat (303) 312-6416 or daly.carl@epa.gov.

Shaun L. Regional Administrator

Enclosure

cc: Dr. Larry Volk Environmental Director and ChiefMedical Officer, Colorado Department ofPublic Health and Environment William Allison Director, Air Pollution Control Division Janet G. McCabe, Acting Assistant Administrator for Air and Radiation Stephen D
. Page, Director, Office ofAir Quality Planning and Standards
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