UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

Ref: 8P-AR 

The Honorable John Hickenlooper 

Governor of Colorado 

State Capitol 

Denver, Colorado 80203 

Dear Governor Hickenlooper: 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://www.epa.gov/region08 

FEB 0 6 2013 

Thank you for your staffs recommendations dated March 18, 2011, on air quality designations for the 

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

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

Environmental Protection Agency's (EPA) 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 ofthe 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 of75 parts per billion. The Clean Air Act 

requires the EPA to complete the initial designations process within two years of promulgating a new or 

revised standard. If the Administrator has insufficient information to make these designations, the EPA 

has the authority to extend the designation process by up to one year. On July 27,2012, the EPA 

announced that it had insufficient information to complete the designations for the 1-hour so2 standard 

within two years and extended the designations deadline to June 3, 2013. 

At this time the EPA is proceeding with designating as nonattainment most areas in locations where 

existing monitoring data from 2009-2011 indicate violations of the 1-hour S02 standard. The EPA 

intends to address the designations for all other areas in separate future actions. With input from a 

diverse group of stakeholders, EPA has developed a comprehensive implementation strategy for these 

future actions that focuses resources on identifying and addressing unhealthy levels of S02. The 

strategy is available at: http://www.epa.gov/airquality/sulfurdioxide/implement.html. The EPA will 

continue to work closely with you and our other partners at the state, tribal and local levels to ensure 

health-protective, commonsense implementation ofthe 1-hour S02 standard. 

The EPA's review ofthe most recent monitored air quality data from 2009-2011 shows no violations of 

the 2010 S02 standard in any areas in Colorado. Consequently, the EPA is not yet prepared to propose 

designation action in Colorado, and is, therefore, currently deferring action to designate areas in 

Colorado. The EPA expects to be able to proceed with designation action in Colorado once additional 
data are gathered pursuant to our comprehensive implementation strategy. In a separate future action or 

actions the EPA will notify you of our intended designations for these areas, and seek public comment 

on these actions, no later than 120 days prior to promulgating any final designations. 

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

2010 primary S02 standard. For additional information regarding initial designations on 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 Crystal Ostigaard of my staff at 

(303) 312-6602 or ostigaard.crystal@epa.gov. 

Sincerely, 

A~J~f!m~~ ~ Regional Administrator 

Enclosure 

cc: Christopher E. Urbina, Executive Director, CDPHE 

William Allison, Director, APCD 

Gina McCarthy, Assistant Administrator for Air and Radiation 

Stephen D. Page, Director, Office of Air Quality Planning and Standards