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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 


WASHINGTON, D.C. 20460

OFFICE OF


AIR AND RADIATION 

The Honorable Jeff Flake 

United States Senate 

Washington, D.C. 20510 

Dear Senator Flake: 

Thank you for your letter dated May 12, 2014, to U.S. Environmental Protection Agency Administrator 

Gina McCarthy, concerning the s current activities with respect to exceptional events. The 

Administrator has asked that I respond on her behalf. I appreciated the chance to discuss this issue with 

you in our meeting this spring and welcome a continued dialogue. 

As you know, air pollution can have damaging effects on human health, including respiratory problems, 

hospitalization for heart or lung disease, and even premature death. In addition, air pollution can have 

effects on aquatic life, vegetation, and animals. For these reasons, the Clean Air Act requires the EPA to 

set National Ambient Air Quality Standards (NAAQS) for certain air pollutants to protect human health 

and the environment. That said, sometimes "exceptional events" - e.g., high wind dust events, volcanic 

eruptions, and wildfires - may cause high pollutant concentrations for reasons outside of the control of 

states and regulated sources. In those circumstances, the Clean Air Act allows exclusion of these eventinfluenced concentrations for regulatory purposes. 

On March 22, 2007, the EPA promulgated the "Treatment of Data Influenced by Exceptional Events; 

Final Rule." The rule contains requirements and criteria for state air agency development and submittal, 

and subsequent EPA approval, of requests to exclude air quality monitoring data from regulatory 

decisions. Subsequent to issuing the final rule, the EPA received requests for clarification of certain 

provisions of the rule, suggestions to streamline implementation, and recommendations to increase 

collaboration between air agencies and the EPA during the demonstration development process. 

As a result of this feedback, the EPA released interim exceptional events guidance in May 2013. 

During the development of the interim guidance, the EPA received valuable input from a number of 

states and stakeholders. This input has also helped us better understand and expedite approval for 

demonstrations involving a number of area-specific problems. For example, last year the EPA's Region 

9 office was able to concur in a matter of months on demonstrations for over 130 high wind dust 

exceptional events in Phoenix.

Internet Address (URL) • http://www.epa.gov


Recycled/Recyclable • Printed with Vegetable Oil Based Inks on 100% Postconsumer, Process Chlorine Free Recycled Paper
Recognizing that guidance can provide only limited flexibilities within the bounds of the existing rule, 

the EPA has announced its intent to undertake a public notice and comment rulemaking effort to propose 

and finalize revisions to the 2007 rule. We anticipate proposing rule revisions in mid-2015 and 

promulgating final rule revisions in mid-2016. This schedule will allow for rule changes in advance of 

implementation activities for any potential new or revised ozone NAAQS, which the EPA is under a 

court order to complete by October 2015. It will also provide time for EPA to consult with state and 

local air agencies and other stakeholders who are interested in these issues. 

The EPA will move this rulemaking along as expeditiously as we can, given the complexity of the issues 

and our intent to work with stakeholders. In the meantime we will continue to work with state and local 

air agencies under our existing rule and guidance to process requests for exceptional event designations 

as promptly as we can. 

Again, thank you for your letter. If you have further questions, please contact me or your staff may 

contact Josh Lewis in the EPA' s Office of Congressional and Intergovernmental Relations at 

lewis.joshepa.gov or (202) 564-2095.

Sincerely, 

Janet G. McCabe 

Acting Assistant Administrator