Ref: 8P-AR The Honorable Matt Mead Governor ofWyoming State Capitol UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595 Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http://www.epa.gov/region08 

### FEB 062013

Cheyenne, Wyoming 82002

Dear GovernorMead: Thank you for your recommendations dated May 24, 2011, on air quality designations for the state of Wyoming for the 2010 revision to the primaryNational Ambient Air Quality Standard for sulfur dioxide (S02 ). Reducing levels ofsulfur dioxide pollution is an important part ofthe U. S. Environmental Protection Agency's (EPA) commitmentto 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'spreliminary intentions regarding your recommended designations. On June 3, 2010, the EPA strengthened the health-based or "primary" standard for S02by establishing a standard for 1-hour average S02concentrations at a level of75 partsperbillion. The CleanAirAct requires the EPA to complete the initial designations process within two years ofpromulgating a new or revised standard. Ifthe Administratorhas insufficient informationto make these designations, theEPA has the authority to extendthe designation process by up to one year. On July 27,2012, the EPA announced that it had insufficient informationto complete the designations for the 1-hour so2standard 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 ofthe 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 ofstakeholders, EPA has developed a comprehensive implementation strategy for these future actions that focuses resources on identifying and addressing unhealthy levels ofS02. The strategy is available at: http://www.epa.gov/airquality/sulfurdioxide/implement.html. The EPA will continue to work closely with you and our otherpartners 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 Wyoming. Consequently, the EPA is not yet prepared to propose designation action in Wyoming, and is, therefore, currently deferring action to designate areas in Wyoming. The EPA expects to be able to proceed with designation action in Wyoming once additionaldata are gathered pursuantto ourcomprehensive implementation strategy. In a separate future action or actions the EPA will notify you ofour intended designations for these areas, and seekpublic comment on these actions, no later than 120 days priorto promulgating any final designations.

We look forward to a continued dialogue with you and your staffas we work together to implementthe 2010 primary S02standard. For additional information regarding initial designations on the S02 standard, please visit ourwebsite at www.epa.gov/so2designations. Should you have any questions, please do not hesitate to call me, orhave your staffcontact Crystal Ostigaard ofmy staffat (303) 312-6602 orostigaard.crystal@epa.gov. Sincerely,

# ~~~~ Regional Administrator

Enclosure

cc: Todd Parfitt, Director, DEQ Steven A. Dietrich, Administrator, AQD Gina McCarthy, Assistant Administrator for Air and Radiation Stephen D. Page, Director, Office ofAir Quality Planning and Standards