UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

Ref: 8P-AR 

The Honorable John Hickenlooper 

Office of the 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 

FEB 1 6 2aio 

Thank you for your staffs recommendations dated September 18, 2015, on air quality designations for 

the state of Colorado for the 2010 revision to the primary National Ambient Air Quality Standard 

(NAAQS) for sulfur dioxide (S02). Reducing levels of S02 pollution is an important part of the U.S. 

Environmental Protection Agency's (EPA's) commitment to a clean, healthy environment. Exposure to 

S02 can cause a range of adverse health effects, including narrowing of the airways which can cause 

difficulty breathing and increased asthma symptoms. This letter is to notify you of the EPA's 

preliminary intentions regarding your recommended 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 of 75 parts per billion. Within one year after a 

new or revised standard is established, the Clean Air Act requires the Governor of each state to submit 

to the EPA a list of all areas in the state, with recommendations for whether each area meets 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, 1 the EPA must complete the remaining S02 designations by three specific deadlines: 

July 2, 2016, December 31, 2017, and December 31, 2020. 

This current round of designations, to be completed by July 2, 2016, addresses two groups of areas: 

(1) areas that have newly monitored violations of the 2010 S02 NAAQS based on the most recent three 

calendar years of certified monitored ambient air quality data, and (2) areas that contain any stationary 

source that had not been announced as of March 2, 2015, for retirement and that according to the EPA's 

Air Markets Database emitted in 2012 either (i) more than 16,000 tons of S02 or (ii) more than 2,600 

tons of S02 with an annual average emission rate of at least 0.45 pounds of S02/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: 

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

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Intended 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 staff did not recommend 

specific boundaries but instead recommended designations for the areas around the Pawnee and Martin 

Drake power plants, 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. If your state has additional information that the EPA should consider prior 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 3 0-day period for the public to provide input on the EPA' s 

intended designation decisions. We will promulgate the designations for these areas by July 2, 2016. We 

will designate all other previously undesignated areas in the state on a schedule consistent with the 

prescribed timing of the court order, i.e., by December 31 , 2017, or December 31 , 2020. 

We look forward to a continued dialogue with you and your staff as 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 not hesitate to call me, or have your staff contact Carl Daly of my 

staff at (303) 312-6416 or daly.carl@epa.gov. 

Shaun L. 

Regional Administrator 

Enclosure 

cc: Dr. Larry Volk 

Environmental Director and Chief Medical Officer, Colorado Department of Public 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 of Air Quality Planning and Standards 

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