STATE OF IDAHO 

DEPARTMENT OF 

ENVIRONMENTAL QUALITY OFFICE OF THE EXECUTIVE 

MAY 192011 

1410 North Hilton. Boise, Idaho 83706' (208) 373-0502 C. L. "Butch" Otter, Governor 

Toni Hardesty, Director 

May 16,2011 

Dennis McLerran 

Regional Administrator 

EPA Region 10 


1200 Sixth Avenue, Suite 900 


Seattle, W A 98101 

Dear Mr. McLerran: 

On behalf of the Governor of the State of Idaho and as the Director of the Idaho Department of 

Environmental Quality (DEQ), I am submitting Idaho's recommendations for area designations 

related to the recently revised Sulfur Dioxide (S02) National Ambient Air Quality Standard 

(NAAQS). 

On June 2, 2010, the U.S. Environmental Protection Agency (EPA) revised the health-based 

primary National Ambient Air Quality Standard (NAAQS) for S02 by establishing a new I-hour 

standard at a level of 75 parts per billion (ppb). In the same action EPA revoked the two existing 

primary standards of 140 ppb evaluated over 24-hours, and 30 ppb evaluated over an entire year 

because they will not add additional public health protection given a I-hour standard at 75 ppb. 

The revised S02 standard includes a new "form." The new form is the 3-year average of the 99th 

percentile of the annual distribution of daily maximum i-hour average concentrations. 

EPA anticipates initially designating areas based on 2008-2010 monitoring data, or refined 

dispersion modeling results if provided by the state. Areas which violate the standard would be 

designated as "nonattainment'. Areas that have both monitoring data and appropriate refined 

modeling results showing no violations would be designated as "attainment." All other areas 

would be designated as "unclassifiable." 

Per your letter received by DEQ on March 24,2011 EPA does not expect states to complete 

modeling for all significant sources of S02 and assess the results in time for the designation 

recommendations due to EPA by June 3, 2011. 

DEQ has monitored S02 for a number of years in Caribou (AQS ID 160290031) and Bannock 

County (AQS ID 160050004). The 2008-2010 design values for these two monitors are 53 ppb 

and 60 ppb, respectively (please note: 2010 data is not yet certified). 
Dennis McLerran 

May 16,2011 

Page 2 

To date DEQ has not modeled significant sources of S02 to determine compliance with the new 

I-hour standard. The Clean Air Act (CAA) directs states to submit by June 3, 2013 a State 

Implementation Plan (SIP) demonstrating an adequate program to implement, maintain and 

enforce the S02 NAAQS. In light of the lack of modeling data available at this time, DEQ plans 

to include in this plan a demonstration of expeditious attainment and maintenance of the S02 

NAAQS. 

On this basis, and on behalf of the Governor of the State of Idaho, c.L. "Butch" Otter, I am 

recommending that the entire State of Idaho and all of Idaho's Air Quality Control Regions 

(AQCRs 61,62,63 and 64) be designated as unclassifiable for the one-hour SOl NAAQS. 

If EPA has any further questions or concerns, please coordinate through Martin Bauer, Air 

Quality Division Administrator of DEQ (208/373-0552). 

Sincerely, 

Toni Hardesty 

Director 

c: Governor C.L."Butch" Otter