UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

Ref: 8P-AR 

The Honorable Matthew H. Mead 

Office of the Governor 

State Capitol 

Cheyenne, Wyoming 82002 

Dear Governor Mead: 

1595 Wynkoop Street 

Denver, CO 80202-1129 

Phone 800-227-8917 

www.epa.gov/region08 

FEB 1 ~ 2U16 

Thank you for your recommendation dated October 27, 2015, on air quality designations for the state of 

Wyoming 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 designation. 

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. 

Based on ambient air quality data collected between 2012 and 2014 indicating a violation of the 2010 

S02 NAAQS, the EPA initially identified the area around the Sinclair Oil Corp Refinery in Sinclair, 

Wyoming, as one that would potentially create the obligation for us to designate by July 2, 2016. 

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

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However, the EPA has since discovered that the monitor reading violations near the Sinclair Refinery 

had been located within the company's fence line, and thus was not in the ambient air. Since the monitor 

was not in the ambient air it is considered a non-regulatory monitor and the air monitor data cannot be 

used for designation purposes. Therefore, the EPA has determined that the air monitor was nonregulatory during the 2012-2014 period in which the design value was above the 2010 S02 NAAQS, and 

continued to be non-regulatory for the 2013-2015 period. For this reason, the area around the Sinclair 

Refinery is not subject to the July 2, 2016, deadline for designation under the court order. We intend to 

designate the area by December 31, 2020, based on regulatory ambient monitoring near the Sinclair 

Refinery. 

We look forward to a continued dialogue with you and your staff as we work together to complete the 

2017 and 2020 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. 

Regional Administrator 

cc: Todd Parfitt 

Director, Wyoming Department of Environmental Quality 

Nancy Vehr 

Administrator, Air Quality 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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